The following abstracts are for PhD and Master's theses written using global NCAR climate models since the release of CSM1 in 1996. The list is current through June 2005.
Title: Quantitative paleoclimatic reconstructions for the Late
Quaternary of southern South America based on calibration
of modern pollen and climate relationships
Pub No: 9827679
Author: Anderson, Lysanna
Degree: PhD
School: UNIVERSITY OF COLORADO AT BOULDER
Date: 1998
Pages: 219
Adviser: Markgraf, Vera
ISBN: 0-591-80013-6
Source: DAI-B 59/03, p. 1017, Sep 1998
Subject: GEOLOGY (0372); PALEOECOLOGY (0426); PALYNOLOGY (0427)
Abstract: Three approaches to deriving quantitative estimates of
past temperature and precipitation (multiple regression,
response surfaces, and the method of modern analog) were
evaluated using a modern pollen and climate data set from
southern South America. The results of this analysis show
that, under conditions of sparse climate data, response
surfaces are the most robust approach. The three
calibrated data sets were then applied to four pollen
records, covering the last glacial - interglacial
transition, to derive quantitative estimates of changes
in temperature and precipitation for the South American
mid-latitudes (41$/sp/circ$). Although there are
variations among the records, there is generally good
agreement, indicating largely consistent regional scale
change. Comparisons of the quantitative climate
reconstructions with qualitative records of
paleoenvironmental conditions in the region show good
agreement.
Data from the Lake District of Chile and Argentina were
then integrated with quantitative paleotemperature
records from the equatorial region of South America, and
with temperature estimates from the Byrd (Antarctica)
$/delta/sp[18]$O record. This paleoenvironmental data set
was compared to general circulation model (GCM) scenarios
of climate change. Three different sets of model output
from the GIST-NESS GCM for the LGM, each with different a
different set of sea surface temperature (SST) values
were compared. The model run using calculated values for
SST based on an ocean heat convergence (OHC) and ocean
heat transport (OHT) model reproduced the most accurate
surface temperature values for the equatorial and polar
regions. However, this model did not perform well in the
mid-latitudes $(30/sp/circ$-60$/sp/circ$S). Model output
from the NCAR community climate model (CCM1) for time
slices spanning from the LGM to 6000 years ago were then
compared to the paleoenvironmental data set. This
comparison shows that the model's linear response to
changing boundary conditions is not an accurate
reconstruction of the pattern of climate change that has
occurred since the LGM. The paleoenvironmental data show
that the onset of warming occurred first at the high and
mid-latitudes, preceding equatorial warming by as much as
7000 years. The paleoenvironmental data also show that
the continuous warming shown in the model output is
inaccurate. Warming occurred abruptly, and reversals are
recorded at all latitudes. In the polar region,
temperatures jumped 5$/sp/circ$C from 21 Ka to 16 Ka, and
had reached modern conditions by 14 Ka. At the mid-
latitudes, temperatures transitioned from the full
glacial minimum to warmer than today between 21 Ka and 16
Ka, while at the equator, temperatures did not start to
warm until ca. 14 Ka.
------------------------------------------------------------
Title: Role of atmosphere-ocean interaction in the midlatitude
North Atlantic on interannual climate variability
Pub No: 9611415
Author: Bhatt, Uma Suren
Degree: PhD
School: THE UNIVERSITY OF WISCONSIN - MADISON
Date: 1996
Pages: 174
Adviser: Houghton, David D.; Battisti, David S.
Source: DAI-B 57/01, p. 397, Jul 1996
Subject: PHYSICS, ATMOSPHERIC SCIENCE (0608)
Abstract: The primary mode of observed interannual variability in
the North Atlantic is characterized by a north-south
oriented dipole pattern in anomalies of surface air
temperature and sea surface temperature (SST). The
atmospheric circulation associated with the dipole mode
of variability is consistent with the notion of the
atmosphere forcing the ocean. The impact of air-sea
interaction on the dipole-like mode of variability is
examined using a mixed layer model (MLM) of the upper
ocean in the North Atlantic between 20-60$/sp/circ$N
coupled to the NCAR Community Climate Model (CCM1). The
climatology of the MLM ocean temperature is adjusted to
be consistent with the SSTs that form the lower boundary
conditions for CCM1 by including heat flux corrections in
the net forcing of the ocean. Heat and salt flux
corrections are calculated in a series of uncoupled
simulations where the MLM is forced with CCM1 surface
fluxes.
The natural variability in a 31-year integration of the
MLM in the North Atlantic coupled to CCM1 is compared to
a CCM1 control simulation of similar length with SSTs
specified to have the same climatological annual cycle as
in the coupled integration. The mean December to February
(DJF) climatology is essentially unchanged with the
inclusion of midlatitude air-sea interaction. However,
air-sea interaction leads to significant increases in the
persistence of air temperature anomalies on interannual
as well as monthly time scales.
In the model subpolar North Atlantic, air and ocean
temperature anomalies are significantly autocorrelated
(0.4 to 0.6) from one winter to the following winter.
These autocorrelations are consistent with the 'Re-
emergence' mechanism (Namias and Born, 1970). Deep ocean
temperature anomalies, present at the end of one winter,
remained sequestered below the shallow summer mixed
layer. As the mixed layer deepens during the following
fall, ocean temperature anomalies from the previous
winter are reincorporated into the surface layer.
February mixed layer ocean temperatures are strongly
correlated with submixed layer ocean temperatures during
the following summer and surface ocean temperature
anomalies the following winter. An uncoupled sensitivity
experiment is performed, in which the MLM is forced with
heat, momentum, and freshwater fluxes from the coupled
simulation, and anomalies are supressed in mixed layer
depth and entrainment heating. The sensitivity experiment
finds that the autocorrelations from one winter to the
next in ocean temperature are weak when anomalies in
entrainment heating or mixed layer depths are supressed.
The 'Re-emergence' mechanism does not play an important
role in the subtropical model domain. Observed air and
ocean temperature autocorrelations from one winter to the
next are strong (weak) in the northern (southern) part of
the North Atlantic basin, in agreement with model
results.
Air temperature anomalies decay more slowly as a result
of air-sea interaction. Short-term autocorrelations of
air temperature are statistically significant up to 1-2
and 3-4 months in the control and coupled simulations,
respectively. When air temperatures are not affected by
SST anomalies as in the control simulation, the turbulent
heat fluxes act to strongly damp air temperature
anomalies (Frankignoul, 1985). With the inclusion of
variable ocean temperatures, the 'thermal damping' of
atmospheric temperature anomalies is weaker. Consistent
with these findings, the variance of air temperature
increases and of total heat flux decreases as a result of
coupling. (Abstract shortened by UMI.)
------------------------------------------------------------
Title: Global optimization of numerical models by simulated
annealing (Weather prediction)
Pub No: 9957125
Author: Campbell, William Francis
Degree: PhD
School: UNIVERSITY OF MARYLAND, COLLEGE PARK
Date: 1999
Pages: 212
Adviser: Baer, Ferdinand
ISBN: 0-599-60324-0
Source: DAI-B 60/12, p. 6156, Jun 2000
Subject: PHYSICS, ATMOSPHERIC SCIENCE (0608); GEOPHYSICS (0373)
Abstract: The problems of vertical level placement and three-
dimensional truncation of numerical models are
investigated. Because the atmosphere is inhomogeneous,
anisotropic, and unbounded above, there are no natural
basis functions in the vertical upon which to base
spectral methods for numerical prediction. A finite
difference formulation in the vertical, with levels
typically chosen to match observational levels, is used
by most forecast and climate models. Our method computes
the number of vertical levels as a function of horizontal
scaling, and selects their location as a function of
vertical coordinate system and atmospheric data.
The central premise of our research is that the optimal
grid for computation is the grid that yields the best
linear spline fit to the meteorological fields of
interest. A continuous “ground truth” for
each field was constructed from analyzed wind and
temperature data, via cubic splines. The best linear
spline fit was then found by minimizing the integral of
the squared difference between arbitrary linear splines
and ground truth, via simulated annealing. Using NCAR's
Community Climate Model (CCM3), grids produced with
seasonal mean data for summer and winter were tested
against each other and against the standard grid at the
same average resolution.
Allowing resolution to change dynamically between the
horizontal and the vertical enables the direct prediction
of the optimum truncation ratio. Because the energy of
the grid is affected only by the <italic>distribution
</italic> of curvature in each dimension, simulated
annealing, meteorological data, and the linear spline
hypothesis suffice to solve the level placement and
relative truncation problems with no additional
assumptions.
The applicability of this procedure is quite general:
given the characteristic structures of any set of PDE's,
the optimal predictive grid can be constructed. In
addition, a global optimization method that is heretofore
absent from the meteorological literature, but of general
utility, is employed. Most importantly, a specific,
testable prediction of truncation ratio is produced.
------------------------------------------------------------
Title: Climate variability in the North Atlantic on decadal and
multi-decadal time scales: A numerical study
Pub No: 3001162
Author: Cheng, Wei
Degree: PhD
School: UNIVERSITY OF MIAMI
Date: 2000
Pages: 154
Adviser: Bleck, Ranier; Rooth, Claes G. H.
ISBN: 0-493-09584-5
Source: DAI-B 62/01, p. 133, Jul 2001
Subject: PHYSICAL OCEANOGRAPHY (0415); PHYSICS, ATMOSPHERIC
SCIENCE (0608)
Abstract: The goal of this work is to understand the mechanisms
that drive the decadal and multi-decadal climate
variability in the North Atlantic. Natural climate
variability on these particular time scales occupies a
central position in discussions of anthropogenic climate
changes, but many aspects related, to this issue are
still poorly understood.
The major tool used in this study is a coupled general
circulation model consisting of the NCAR CCM3 and the
Miami Isopycnic Coordinate Ocean Model. The simulated
decadal variability in the North Atlantic is dominated by
a tri-pole pattern in sea surface temperature and a North
Atlantic Oscillation (NAO) pattern in sea level pressure.
The associated oceanic fluctuations are characterized by
a delayed subtropical gyre response to anomalou's NAO
surface wind stress forcing and advection of SST
anomalies originating near the western boundary into the
interior ocean. Separate ocean-alone experiments suggest
that the SST variability can not be attributed solely to
passive response of the ocean to atmospheric thermal
forcing.
It is also found that a quasi-oscillatory fluctuation of
the thermohaline circulation (THC) in the North Atlantic
ocean with an approximate time scale of 30 years is
present in the coupled but not in uncoupled simulations.
The latter were forced with either Newtonian relaxation
boundary conditions (based on a monthly climatology of
the atmospheric state variables such as the surface air
temperature and surface specific humidity) or with
imposed monthly varying heat and fresh water flux
conditions.
These results suggest that the variability of the THC in
this model is neither an ocean internal phenomenon nor a
passive response of the ocean to atmospheric forcing.
Rather, it is a coupled process involving both the ocean
and the atmosphere. The THC oscillation appears to be
driven by surface heat flux forcings while the effects of
surface fresh water fluxes are secondary. Two delay
effects are crucial for maintaining this oscillation. One
is the delay of the North Atlantic overturning strength
relative to the deep water formation rate in the deep
water production region; the other is the delay of the
associated SST and surface heat flux anomalies in the
sinking region relative to the overturning amplitude
itself.
The sea surface temperature signal associated with the
THC oscillation bears some resemblance to an SST
interdecadal pattern extracted from observational data
(Kushnir, 1993). Accompanying anomalies of northern
hemispheric surface air temperature have positive values
over the Pacific and Atlantic Oceans and negative values
over the Eurasian and North American continents. In
addition to anomalies in sea surface temperature and
surface air temperature, there are also variations in
atmospheric flow pattern over the North Atlantic, namely,
an anomalous northerly flow over the Labrador Sea when
the THC circulation is strong.
------------------------------------------------------------
Title: Modeling the direct and indirect climatic effects of
tropospheric sulfate aerosols
Pub No: 9967719
Author: Cox, Stephen J.
Degree: PhD
School: STATE UNIVERSITY OF NEW YORK AT ALBANY
Date: 2000
Pages: 103
Adviser: Wang, Wei-Chyung
ISBN: 0-599-72439-0
Source: DAI-B 61/04, p. 1996, Oct 2000
Subject: PHYSICS, ATMOSPHERIC SCIENCE (0608); ENVIRONMENTAL
SCIENCES (0768)
Abstract: Modeling studies of the climatic effects of tropospheric
sulfate aerosols are presented. Both the direct
scattering by the aerosols and the indirect effect of
enhanced cloud albedo from increased aerosol numbers are
addressed, in separate studies. The direct effect study
uses aerosol mass concentrations from the MOGUNTIA
chemical transport model. A parameterization is developed
to model the radiative forcing due to direct shortwave
scattering by the aerosols in the NCAR Community Climate
Model, an atmospheric general circulation model. Aerosol
layer optical properties are folded into the direct and
diffuse surface albedo. The aerosol forcing is similar in
magnitude, but opposite in sign, to the longwave forcing
by anthropogenic greenhouse gases such as CO<sub>
2</sub>, CH<sub>4</sub>, N<sub>2</sub>O,
CF<sub>2</sub>CL<sub>2</sub>, and CFCL<sub>3</sub>. CCM1
is run for thirty-five years with equal and opposite
global annual mean aerosol and greenhouse forcings, and
the results compared to a control run with no forcing. It
is determined that the global mean temperate responds to
the forcings equally, with a global sensitivity of 1.25
K/(W m<super> −2</super>), but the regional
temperature response shows marked variation, which could
not be predicted simply from the forcing pattern. The
aerosol forcing is concentrated in the industrial
continental areas of the Northern Hemisphere
midlatitudes, yet a strong cooling response is noted in
regions thousands of kilometers away (for instance,
western Canada) from centers of aerosol concentration.
The indirect effect is studied with more recent sulfate
estimates, from the Oslo Chemical Transport Model. Field
studies are used to relate sulfate mass concentration to
cloud droplet number concentration, and subsequently to
cloud droplet effective radius. The indirect
parameterization is incorporated into NCAR CCM3, along
with a new shortwave parameterization which allows the
full vertical distribution of the aerosols to be
accounted for. The indirect radiative forcing is found to
be a cooling of 0.47 W m<super>−2</super>, smaller
than the direct forcing of 1.15 W
m<super>−2</super>, though still significant. The
direct forcing is strongest over the Northern Hemisphere
land, whereas the indirect forcing occurs more strongly
over the Northern Hemisphere ocean, likely due to greater
susceptibility of the more pristine marine air to
condensation nuclei enhancement.
------------------------------------------------------------
Title: Longwave radiative transfer in the atmosphere: Model
development and applications
Pub No: 3092290
Author: Delamere, Jennifer Simmons
Degree: PhD
School: UNIVERSITY OF ALASKA FAIRBANKS
Date: 2003
Pages: 153
Adviser: Stamnes, Knut H.
ISBN: 0-496-39997-9
Source: DAI-B 64/05, p. 2231, Nov 2003
Subject: PHYSICS, ATMOSPHERIC SCIENCE (0608); GEOPHYSICS (0373)
Abstract: A FLexible Radiative Transfer Tool (FLRTT) has been
developed to facilitate the construction of longwave,
correlated <italic>k</italic>-distribution, radiative
transfer models. The correlated <italic>k</italic>-
distribution method is a technique which accelerates
calculations of radiances, fluxes, and cooling rates in
inhomogeneous atmospheres; therefore, correlated <italic>
k</italic>-distribution models are appropriate for
simulations of satellite radiances and inclusion into
general circulation models. FLRTT was used to build two
new rapid radiative transfer models, RRTM_HIRS and
RRTM_v3.0, which maintain accuracy comparable to the
line-by-line radiative transfer model LBLRTM.
<italic>Iacono et al</italic>. [2003] evaluated upper
tropospheric water vapor (UTWV) simulated by the National
Center for Atmospheric Research Community Climate Model,
CCM3, by comparing modeled, clear-sky brightness-
temperatures to those observed from space by the High-
resolution Radiation Sounder (HIRS). CCM3 was modified to
utilize the rapid radiative transfer model RRTM and the
separate satellite-radiance module, RRTM_HIRS, which
calculates brightness temperatures in two HIRS channels.
By incorporating these accurate radiative transfer models
into CCM3, the longwave radiative transfer calculations
have been removed as a significant source of error in the
simulations. An important result of this study is that
CCM3 exhibits moist and dry discrepancies in UTWV of 50%
in particular climatic regions, which may be attributed
to errors in the CCM3 dynamical schemes.
RRTM_v3.0, an update of RRTM, is a rapid longwave
radiative transfer appropriate for use in general
circulation models. Fluxes calculated by RRTM_v3.0 agree
with those computed by the LBLRTM to within 1.0
W/m<super>2</super> at all levels, and the computed
cooling rates agree to within 0.1 K/day and 0.3 K/day in
the troposphere and stratosphere, respectively.
This thesis also assessed and improved the modeling of
clear-sky, longwave radiative fluxes at the Atmospheric
Radiation Measurement Program North Slope of Alaska site
by simultaneously addressing the specification of the
atmosphere, radiometric measurements, and radiative
transfer modeling. Consistent with findings from other
field sites, the specification of the atmospheric water
vapor is found to be a large source of uncertainty in
modeled radiances and fluxes. Improvements in the
specification of carbon dioxide optical depths within
LBLRTM resulted, in part, from this analysis.
------------------------------------------------------------
Title: Speciated local aerosol characteristics and radiative
forcing at a rural midwestern site
Pub No: 9971067
Author: Dillner, Ann Marie
Degree: PhD
School: UNIVERSITY OF ILLINOIS AT URBANA-CHAMPAIGN
Date: 2000
Pages: 162
Adviser: Larson, Susan M.
ISBN: 0-599-76207-1
Source: DAI-B 61/05, p. 2697, Nov 2000
Subject: ENGINEERING, ENVIRONMENTAL (0775); PHYSICS, ATMOSPHERIC
SCIENCE (0608)
Abstract: In this research, physical and chemical properties of
ambient aerosols were measured at a rural perturbed mid-
latitude site (Bondville, IL) and used to calculate the
aerosol optical properties and the resulting direct
radiative forcing. Size-segregated aerosol samples were
collected during the summer of 1997 using three parallel
MOUDIs operating at ambient relative humidity. Two sample
sets were used to obtain sulfate, organic carbon (OC),
elemental carbon (EC), carbonate and total aerosol mass.
The third sample set was used to obtain the size-specific
and wavelength-dependent extinction efficiency of EC.
The measured submicrometer mass concentration was 11.4
± 4.0 μg m<super>−3</super>. Ammonium
sulfate comprised nearly half of the submicrometer
aerosol and OC plus EC comprised 25%.
Water content for ammonium sulfate and OC was estimated
using both Köhler theory and parameterized water
uptake curves from the literature. Water content for
internally mixed aerosols was determined using a ZSR
method. Aerosol optical properties (extinction
efficiency, asymmetry parameter, single scatter albedo)
were calculated from measured size distributions and
wavelength dependent refractive indexes for each species
and for internal and external mixtures using Mie theory.
A technique, utilizing transmission measurements through
extracts of size segregated ambient aerosol samples, was
developed to obtain the extinction efficiency of EC.
Measured EC extinction efficiencies ranged from 7.3 to
1.7 m<super>2</super> g<super>−1</super> at 550 nm,
depending on particle diameter. Normalized direct aerosol
radiative forcing (W g<super>−1 </super>) was
calculated using the Column Radiation Module (CRM) of the
National Center for Atmospheric Research (NCAR) Community
Climate Model (CCM3). Aerosol optical properties, used in
the model, were assumed to be uniform throughout the
lowest one kilometer of the atmosphere. The normalized
forcing due to ammonium sulfate was −340 ±
10 W g<super>−1</super>. OC was 1/3 larger and
residue was 1/3 smaller. EC within an internally mixed
aerosol was shown to suppress forcing.
This research supports the view that species other than
ammonium sulfate, namely EC, OC and dust-like aerosol,
have significant radiative effects. Although the mass
percentage of EC may be low at rural sites, ignoring the
presence of EC aerosol leads to an over estimation of the
aerosol forcing.
------------------------------------------------------------
Title: Short-range ensemble forecasting of an explosive
cyclogenesis with a limited-area model
Pub No: 9626568
Author: Du, Jun
Degree: PhD
School: THE UNIVERSITY OF ARIZONA
Date: 1996
Pages: 146
Adviser: Mullen, Steven L.; Sanders, Frederick
Source: DAI-B 57/04, p. 2623, Oct 1996
Subject: PHYSICS, ATMOSPHERIC SCIENCE (0608); HYDROLOGY (0388)
Abstract: Since the atmosphere is a chaotic system, small errors in
the initial condition of any numerical weather prediction
(NWP) model amplify as the forecast evolves. To estimate
and possibly reduce the uncertainty of NWP associated
with initial-condition uncertainty (ICU), ensemble
forecasting has been proposed which is a method of,
differently from the traditional deterministic
forecasting, running several model forecasts starting
from slightly different; initial states.
In this dissertation, the impact of ICU and short-range
ensemble forecasting (SREF) on quantitative precipitation
forecasts (QPFs), as well as on sea-level cyclone
position and central pressure, is examined for a case of
explosive cyclogenesis that occurred over the contiguous
United States. A limited-area model (the PSU/NCAR NM4) is
run at 80-km horizontal resolution and 15 layers to
produce a 25-member, 36-h forecast ensemble. Lateral
boundary conditions for the MM4 model are provided by
ensemble forecasts from a global spectral model (the NCAR
CCM1). The initial perturbations of the ensemble members
possess a magnitude and spatial decomposition which
closely match estimates of global analysis error, but
they were not dynamically-conditioned. Results for 80-km
ensemble forecast are compared to forecasts from the then
operational Nested Grid Model (NGM), a single 40-km MM4
forecast, and a second 25-member MM4 ensemble based on a
different cumulus parameterization and slightly different
initial conditions.
Acute sensitivity to ICU marks ensemble QPF and the
forecasts of cyclone position and central pressure.
Ensemble averaging always reduces the rms error for QPF.
Nearly 90% of the improvement is obtainable using
ensemble sizes as small as 8-10. However, ensemble
averaging can adversely affect the forecasts related to
precipitation areal coverage because of its smoothing
nature. Probabilistic forecasts for five mutually
exclusive, completely exhaustive categories are found to
be skillful relative to a climatological forecast.
Ensemble sizes of $/sim$10 can account for 90% of
improvement in probability density function.
Our results indicate that SREF techniques can now provide
useful QPF guidance and increase the accuracy of
precipitation, cyclone position, and cyclone's central
pressure forecasts. With current analysis/forecast
systems, the benefit from simple ensemble averaging is
comparable to or exceed that obtainable from improvement
in the analysis/forecast system.
------------------------------------------------------------
Title: Regional simulation of North American interannual climate
variability
Pub No: 9998321
Author: Dutton, Jan Frederik
Degree: PhD
School: THE PENNSYLVANIA STATE UNIVERSITY
Date: 2000
Pages: 134
Adviser: Barron, Eric
ISBN: 0-493-06588-1
Source: DAI-B 61/12, p. 6518, Jun 2001
Subject: PHYSICS, ATMOSPHERIC SCIENCE (0608); APPLIED MECHANICS
(0346)
Abstract: The interannual variability of the RegCM2 regional
climate model, with a U.S. centered domain, forced by the
NCAR CCM3 global climate is the main focus of this study.
A 6 member 10 year CCM3 ensemble, from January 1, 1968 to
December 31, 1978, forced globally by reconstructed
observed sea surface temperatures, provides RegCM2
boundary conditions.
An understanding of how RegCM2 responds to CCM3
interannual variability is developed using an anomaly
pattern correlation (APC) analysis of the CCM3 and RegCM2
monthly averaged 500 mb heights, surface temperature, and
precipitation. All three variables show a distinct APC
annual cycle.
The effect of regional climate modeling on simulated
climate reproducibility compared using the modeled
ensemble run variances. In certain regions RegCM2 surface
temperature normalized ensemble run variance is
significantly lower than CCM3, suggesting higher
reproducibility in these regions. RegCM2 precipitation
reproducibility is found to be lower than CCM3 in all
regions, indicating higher resolution simulations have
lower reproducibility.
A empirical orthogonal function (EOF) analysis of the
dominant precipitation and surface temperature modes of
variability is also presented. The EOF analyses use 60
years (6 ensemble members x 10 years) of RegCM2, CCM3,
and a gridded observed data. RegCM2 does not
significantly alter the primary modes of CCM3 surface
temperature variability. Furthermore, the observed
primary modes of surface temperature variability are
similar to those modeled. Neither model captures the
primary mode of winter precipitation variability. The
modeled primary mode of precipitation variability,
focused on the west U.S. coast, is similar to the
observed second mode. The RegCM2 increases the amplitude
of the CCM3 mode, improving the simulation of winter
precipitation variability relative to the observations.
The analysis of summer surface temperature and
precipitation variability reveals that regional scale
forcing, such as the low-level jet, plays an important
role in modifying the locations of the primary modes of
variability. The RegCM2 significantly improves the jet
simulation, shifting the precipitation variability to
midwestern and eastern U.S. Despite these changes, the
results show the CCM3 interannual variability signal is
present in the RegCM2 signal throughout the year.
------------------------------------------------------------
Title: Tropical climate stability, Hadley circulation, and deep
cumulus convection: Vital synergism on a wet planet
Pub No: 9975794
Author: Fleischfresser, Luciano
Degree: PhD
School: THE UNIVERSITY OF OKLAHOMA
Date: 2000
Pages: 129
Adviser: Fiedler, Brian
ISBN: 0-599-81465-9
Source: DAI-B 61/06, p. 3095, Dec 2000
Subject: PHYSICS, ATMOSPHERIC SCIENCE (0608); ENVIRONMENTAL
SCIENCES (0768); APPLIED MECHANICS (0346)
Abstract: This research is about developing a more internally
consistent formulation of cumulus convection and the
atmospheric branch of the hydrological cycle in a newly
developed Hadley circulation model. The ultimate goal is
to analyze the climate equilibrium of a symmetric
tropical hydrostatic atmosphere, particularly studying
cause and effect relations determining the magnitude of
water vapor-related feedbacks in climate sensitivity
experiments.
Important features of the proposed formulation for
precipitating deep turbulent clouds include the ability
to calculate precipitation efficiencies, a new
postulation relating cumulus buoyancy to solar radiation,
and the implicit account of latent heat release that
manifest itself by scaling cumulus drafts to observed
magnitudes. The Hadley model is based on primitive
equations, and it incorporates the NCAR column radiation
scheme as well as the atmospheric branch of the
hydrological cycle. To calculate climatic feedbacks, the
inverse simulation approach is used. An interrelationship
technique is applied to diagnose feedback factors
associated with changes of water vapor amount and
distribution, of lapse-rate, and of deep cumulus cloud
cover. The aim is to contrast the novel model for deep
clouds with a mass flux deep cumulus parameterization
when a thermally direct circulation (Hadley cell) is
present.
When only a lapse-rate adjustment is used to crudely
represent tropical convection, the calculated climate
sensitivity lies in the typical range of equatorial
sensitivities given by global circulation models (GGMs).
This result suggests that the Hadley model is capturing
the essential physics of these models as far as these
sensitivities are concerned. In the comparison analyses,
the climate equilibrium is stable and effected by net
positive feedback when the new cumulus model is used.
Moreover, the calculated tropical climate sensitivities
are consistently lower than the aforementioned typical
range, bringing them closer to sensitivities suggested by
observed data. Interestingly, the tropical climate
equilibrium is unstable with the mass flux scheme. It is
shown quantitatively that relative humidity changes in
the model upper-troposphere determine the sign of the
water vapor feedback. Recommendations to narrow humidity
uncertainties in climate change simulations are
presented.
------------------------------------------------------------
Title: The development of a three-dimensional general
circulation model with coupled chemistry
Pub No: 9805287
Author: Gross, Gerhard Wayne
Degree: PhD
School: PORTLAND STATE UNIVERSITY
Date: 1997
Pages: 382
Adviser: Khalil, M. Aslam K.
ISBN: 0-591-55236-1
Source: DAI-B 58/08, p. 4282, Feb 1998
Subject: PHYSICS, ATMOSPHERIC SCIENCE (0608)
Abstract: A coupled climate-chemistry model for the troposphere and
lower stratosphere has been developed that includes on-
line local actinic flux calculation. The coupling of
chemistry with a climate model and the internal
calculation of actinic flux allows the model to simulate
a variety of interactions and feedbacks between
atmospheric processes that are ordinarily excluded from
general circulation models.
The climate model is an altered version of the CCM3
(Community Climate Model Version 3) from NCAR (National
Center for Atmospheric Research). The spectral resolution
of the radiation code of the model has been increased 8-
fold in the region 200-700 nm, with highest resolution
between 245-350 nm. Actinic flux is calculated by the
radiation code for each spectral interval and each model
grid cell at a user defined frequency set to 1 hour in
this work. The coupled tropospheric chemistry component
uses climatological data from the climate model including
temperature, pressure, water vapor concentration, actinic
flux, and atmospheric transport.
The OH distributions generated by a 3 year simulation of
the coupled model in the partially coupled mode show a
zonal maximum over the tropics as expected. Seasonal
variations displace the zonal maximum towards the summer
pole by about 5$/sp/circ$ in the southern hemisphere and
about 15$/sp/circ$ in the northern hemisphere. The
distributions show somewhat more structure compared to
results from other model studies. During the solstice
months the OH concentration is greatest at the surface
and during the equinox months the maximum is slightly
elevated to approximately 1.5 km. The concentration of
the equatorial maximum decreases with altitude and then
increases above about 400 mb (7 km).
The model calculated, global, tropospheric, average is
1.1 $molecules/cm/sp3$ and is slightly higher than
results from other studies. The global average at the
surface is 1.2 $molecules/cm/sp3$ and agrees with
measurements and model studies. The globally averaged
amount of $CH/sb4$ destroyed by oxidation with OH is
calculated to be 461 $Tg/yr$ and also agrees with
independent estimates from other researchers. The
distribution of formaldehyde is consistent with
measurements made by other groups.
------------------------------------------------------------
Title: I. Variability of the outgoing thermal IR spectra and its
application in GCM validation. II. The detection of
cloud/aerosol in the outgoing thermal IR spectra
Pub No: 3151366
Author: Huang, Xianglei
Degree: PhD
School: CALIFORNIA INSTITUTE OF TECHNOLOGY
Date: 2004
Pages: 182
Adviser: Yung, Yuk L.
ISBN: 0-496-11390-9
Source: DAI-B 65/10, p. 5193, Apr 2005
Subject: PHYSICS, ATMOSPHERIC SCIENCE (0608); PHYSICS, ASTRONOMY
AND ASTROPHYSICS (0606)
Abstract: The theme of this thesis is studying the outgoing
infrared spectra of Earth and Mars. In Chapter 1, the
importance and the feasibility of using the outgoing
thermal IR spectra in testing model's variability are
discussed. Chapter 2 investigates the temporal
variability over the tropical and midlatitude Pacific
seen from Infrared Interferometer Spectrometer (IRIS)
observations and corresponding synthetic spectra based on
simulations from two general circulation models (GCMs),
UCLA GCM and NCAR CAM2. The discrepancies between modeled
and observed variability are substantial. Further
examination shows that these discrepancies are most
likely due to deficiencies in simulating the seasonal and
intraseasonal variations of the Walker Circulation in the
tropical Pacific and the seasonal variations of low
cloud, boundary-layer temperature, and stratospheric
temperature in the midlatitude Pacific. Chapter 3
presents a survey of the spatial variability seen from
Atmospheric Infrared Sounder (AIRS) spectra and
corresponding synthetic spectra based on NCAR CAM2
simulation. To a large extent, the simulated variability
agrees well with the observed counterpart. The major
discrepancies can be attributed to the incorrect location
of ITCZ in the western Pacific, the underrepresented dust
aerosol over the Arabian Sea and off the Atlantic Coast
of North Africa, and the overestimated spatial variation
of stratospheric temperature in the model. Chapter 4
presents a comparative study of the variability seen in
the Martian outgoing infrared spectra collected by MGS-
TES (Thermal Emission Spectrometer). The negative
correlation between dust and water ice spectral features
seen in this analysis suggests that, to some extent, dust
and water ice cloud are mutually exclusive of each other
in the Martian atmosphere. Chapter 5 presents a
sensitivity study of identifying optically thin cirrus
from high-resolution infrared spectra based on the line
shapes in the residual spectra. This cirrus-detection
approach is original in the sense of making use of
information content contained in such measurements.
Chapter 6 presents a tri-spectral algorithm to detect
water ice cloud, dust, and surface anisothermality from
low-resolution Martian outgoing thermal IR spectra. This
algorithm can be used to screen large amounts of data to
get a quick overview.
------------------------------------------------------------
Title: Adaptive grids in weather and climate modeling
Pub No: 3121951
Author: Jablonowski, Christiane
Degree: PhD
School: UNIVERSITY OF MICHIGAN
Date: 2004
Pages: 266
Adviser: Penner, Joyce E.
ISBN: 0-496-69302-7
Source: DAI-B 65/02, p. 792, Aug 2004
Subject: PHYSICS, ATMOSPHERIC SCIENCE (0608)
Abstract: Adaptive Mesh Refinement (AMR) provides an attractive
framework for atmospheric flows since it allows improved
horizontal resolution in a limited region without
requiring a fine grid resolution throughout the entire
model domain. In this thesis, the adaptive grid technique
has been applied to a revised version of NCAR/NASA's next
generation dynamical core for climate and weather
research. This hydrostatic so-called Lin-Rood dynamics
package with a conservative finite volume discretization
in flux form provides highly efficient algorithms for
high performance computing.
The adaptive model design utilizes a spherical adaptive-
grid library which is based on a cache-efficient block-
structured data layout. This AMR communication library
for parallel processors has been newly developed in the
Computer Science Department at the University of
Michigan. All blocks are self-similar and split into four
in the event of refinement requests. The resolution of
neighboring blocks can only differ by a factor of two
which leads to cascading refinement regions.
The adaptive dynamical core is run in two configurations:
the full 3D hydrostatic dynamical core on the sphere and
the corresponding 2D shallow water model that has been
extracted out of the 3D version. This shallow water setup
serves as an ideal testbed for the horizontal
discretization and the 2D adaptive-mesh strategy. It
further allows the efficient testing of interpolation
routines at fine-coarse grid interfaces.
The static and dynamic adaptations are tested using the
standard shallow water test suite and a newly-developed
idealized 3D baroclinic wave test case. Static
adaptations are used to vary the resolution in pre-
defined regions of interest. This includes static
refinements near mountain ranges or static coarsenings in
the longitudinal direction for the implementation of a
so-called reduced grid in polar regions. Dynamic
adaptations are based on flow characteristics and guided
by refinement criteria that detect user-defined features
of interest during a simulation. In particular, flow-
based refinement criteria, such as vorticity or gradient
indicators, are suggested. Refinements and coarsenings
occur according to pre-defined threshold values.
This research project is characterized by an
interdisciplinary approach involving atmospheric science,
computer science and applied mathematics.
------------------------------------------------------------
Title: A physically-based snow model coupled to a general
circulation model for hydro-climatological studies
Pub No: 3050315
Author: Jin, Jiming
Degree: PhD
School: THE UNIVERSITY OF ARIZONA
Date: 2002
Pages: 162
Adviser: Sorooshian, Soroosh
ISBN: 0-493-64911-5
Source: DAI-B 63/04, p. 1761, Oct 2002
Subject: HYDROLOGY (0388); PHYSICS, ATMOSPHERIC SCIENCE (0608)
Abstract: A Snow-Atmosphere-Soil Transfer (SAST) model has been
developed to extend the point snowmelt model to vegetated
areas using the parameterization concepts of the
Biosphere-Atmosphere Transfer Scheme (Dickinson et al.
1993). The model applications for short-grass and forest
fields show that the simulated surface temperature,
albedo, and snow depth have close agreement with
observations. In addition, because of biases in simulated
runoff in the high-latitudes, a Shuffled Complex
Evolution (Sorooshian et al. 1993) scheme for automatic
calibration has been connected with the SAST model to
determine the realistic distribution of runoff components
from different soil layers and search the optimized
parameter set. The calibrated runoff closely matches
observations.
Because the Community Climate Model version 3 (CCM3)
coupled with the SAST model overestimates snow depth and
precipitation and underestimates surface temperature over
the Rocky Mountains, remotely sensed snow depth data have
been assimilated in the model to alleviate model
discrepancies based on energy and mass balances. The
improved surface temperature simulations result from the
decreased snowmelt and albedo in winter and spring and
from the weakened evaporation in summer due to drier
soil. Meanwhile, modeled summer precipitation over the
Rocky Mountains has a minor improvement.
The relationship between the variations of tropical
Pacific SST and snowpack anomalies in the western United
States (U.S.) has been studied by comparing observations
and CCM3 output. The results indicate that in the
northwestern U.S., the warm tropical Pacific phase of the
El Niño-Southern Oscillation (ENSO) is associated
with diminished snowpack while its cool phase is related
to enhanced snowpack. This relationship is largely
determined by winter precipitation variability for the
observations; however, it relies heavily on the
variations of temperature due to the biases in
atmospheric patterns for the model output. In the
southwestern U.S., positive snowpack anomalies for both
observations and simulations result from the strong warm
phase of the ENSO and negative ones are connected with
exaggerated local precipitation in fall.
------------------------------------------------------------
Title: Interpolation of surface radiative temperature measured
from polar orbiting satellites to a diurnal cycle
Pub No: 9923351
Author: Jin, Menglin
Degree: PhD
School: THE UNIVERSITY OF ARIZONA
Date: 1999
Pages: 152
Adviser: Dickinson, Robert E.
ISBN: 0-599-22782-6
Source: DAI-B 60/03, p. 1128, Sep 1999
Subject: PHYSICS, ATMOSPHERIC SCIENCE (0608); REMOTE SENSING
(0799); ENVIRONMENTAL SCIENCES (0768)
Abstract: The land surface skin temperature diurnal cycle (LSTD) is
very important for the understanding of surface climate
and for evaluating climate models. This variable,
however, cannot be obtained globally from polar-orbiting
satellites because the satellites usually pass a given
area twice per day and because their infrared channels
cannot observe the surface when the sky is cloudy.
In order to more optimally use the satellite data, this
research is designed, for the first time, to solve the
above two problems by advance use of remote sensing
techniques and climate modeling. Specifically, this work
is divided into two parts. Part one deals with obtaining
the skin temperature diurnal cycle for cloud-free cases.
We have developed a “cloud-free algorithm” to
combine model results with satellite and surface-based
observations, thus interpolating satellite twice-daily
observations to the diurnal cycle. Part two studies the
cloudy cases. The “cloudy-pixel treatment”
presented here is a hybrid technique of
“neighboring-pixel” and “surface air
temperature” approaches. The whole algorithm has
been tested against field experiments and climate model
CCM3/BATS in global and single column mode simulations.
It shows that this proposed algorithm can obtain skin
temperature diurnal cycles with an accuracy of 1–2
K at the monthly pixel level.
------------------------------------------------------------
Title: The onset of convection in the Madden-Julian oscillation
Pub No: 9948702
Author: Kemball-Cook, Susan Rives
Degree: PhD
School: UNIVERSITY OF CALIFORNIA, DAVIS
Date: 1999
Pages: 109
Adviser: Weare, Bryan
ISBN: 0-599-51118-4
Source: DAI-B 60/10, p. 5117, Apr 2000
Subject: PHYSICS, ATMOSPHERIC SCIENCE (0608)
Abstract: An observational study of the onset of convection in the
Madden-Julian Oscillation (MJO) was performed. Composites
of radiosonde data from the Comprehensive Aerological
Reference Data Set were constructed for an ensemble of
tropical stations in the Indian Ocean, Maritime
Continent, and western Pacific Ocean. Outgoing longwave
radiation from NOAA polar orbiting satellites was used as
a proxy for deep convection associated with the MJO, and
NCEP-NCAR Reanalysis data was used to diagnose low-level
convergence.
The composites suggest that for the off-equatorial
stations used in this study, the MJO period may be set by
the buildup and discharge of the low-level moist static
energy (h). This result supports the discharge-recharge
hypothesis of Blade and Hartmann (1993). MJO events are
most likely to occur when the off-equatorial atmosphere
has been destabilized through a combination of low level
h buildup and concurrent drying of the middle troposphere
by subsidence in the wake of the previous cycle of MJO
convection. The low-level h buildup is controlled by a
corresponding increase in low-level moisture. Following
an episode of MJO convection, a period of approximately
35 days is required to increase the low-level moisture to
the point where the atmosphere again becomes unstable to
deep convection. The convective event lasts about 20 days
and stabilizes the atmosphere by drying and cooling the
boundary layer and moistening and heating the middle and
upper troposphere. By drying and cooling the boundary
layer, convection discharges the low level h.
The increase in low-level moisture is not caused by the
1000 mb convergence, as suggested by frictional wave-CISK
theories. For the stations examined here, the convergence
lags the moist static energy buildup, and is instead in
phase with the convection. A possible mechanism for the
relatively slow moisture buildup lasting approximately 35
days is competition between surface fluxes of moisture
and the drying effect of entrainment of low h air into
the boundary layer. Evidence is found for the
preconditioning of the atmosphere to deep convection
through upward transport of moisture by shallow
convection.
------------------------------------------------------------
Title: Tropical dynamics near the stratopause: The two-day wave
and its relatives
Pub No: 9836209
Author: Limpasuvan, Varavut
Degree: PhD
School: UNIVERSITY OF WASHINGTON
Date: 1998
Pages: 209
Adviser: Leovy, Conway B.
ISBN: 0-591-89715-6
Source: DAI-B 59/06, p. 2808, Dec 1998
Subject: PHYSICS, ATMOSPHERIC SCIENCE (0608); ENVIRONMENTAL
SCIENCES (0768)
Abstract: The two-day wave is observed in the Upper Atmosphere
Research Satellite (UARS) Microwave Limb Sounder (MLS)
temperature and water vapor data. During a 3-year period
(Dec. 1991-Sep. 1994), the wave signature is prominent
semiannually after each solstice and is comprised of a
zonal wavenumber 3 component with $[/sim]2.0$-day period
and a wavenumber 4 component with $[/sim]1.8$-day period.
Intra-annually, the wavenumber 3 amplitude during the
austral summer is nearly twice as strong as during the
boreal summer. The wavenumber 4 component however can be
equally strong in both summers. The wave-number 3 signal
tends to be dominant during the austral summer while the
wave 4 component is dominant during the boreal summer.
The derived zonal wind structure suggests that the
Charney-Stern inflection instability mechanism is
responsible for generating the two-day wave whose
amplitude resides mainly on the equatorward flank of the
summer easterly jet.
In some seasons, momentum redistribution by inertial
instability appears to destabilize the easterly jet from
which the barotropically unstable two-day wave grows. In
these instances, an independent study using the UARS
Cryogenic Limb Array Etalon Spectrometer (CLAES)
temperature (Hayashi et al., 1998) coincidently
identifies 'pancake' structures associated with inertial
instability. A possible connection between inertial
instability and the two-day wave has been discussed by
Hitchman (1985) and Orsolini et al. (1997).
The National Center for Atmospheric Research (NCAR)
Community Climate Model version 2 (CCM2) mechanistic
model is used to simulate this connection. Model
experiments show that, for a prescribed initial wind
condition with strong horizontal wind shear in the
tropics, inertial instability can trigger the two-day
wave. An increase in easterly wind curvature fostered by
inertial instability circulation destabilizes the jet in
low summer latitudes and allows first the growth of the
wavenumber 4 then the wavenumber 3 component of the two-
day wave. Near the stratopause, the two-day wave energy
propagation is directed equatorward away from the wave's
critical line source and westerly momentum is fluxed into
the easterly jet core by the wave. While much of the
wavenumber 4 activity is confined near the stratopause,
the wavenumber 3 energy can propagate upward well into
the mesosphere where strong Rayleigh damping is imposed.
The simulated waves' spatial and spectral characteristics
are fairly realistic.
------------------------------------------------------------
Title: On the relationship between tropical convection and clear
sky upper troposphere moisture
Pub No: 3088067
Author: Lin, Wuyin
Degree: PhD
School: STATE UNIVERSITY OF NEW YORK AT STONY BROOK
Date: 2002
Pages: 103
Adviser: Zhang, Minghua
ISBN: 0-496-35829-7
Source: DAI-B 64/04, p. 1770, Oct 2003
Subject: PHYSICS, ATMOSPHERIC SCIENCE (0608); GEOPHYSICS (0373)
Abstract: Upper troposphere water vapor is a crucial factor in the
climate system. The moisture abundance in the clear sky
upper troposphere is strongly influenced by tropical deep
convection. TOVS upper troposphere water vapor
measurements and ISCCP deep convective clouds are used to
investigate the relationship between upper troposphere
humidity (UTH) and frequency and area coverage of
tropical deep convection. The study shows that a more
diffused distribution of convection in the tropics is
associated with a higher UTH in the free troposphere,
while a more concentrated convection distribution is
associated with a drier free upper troposphere. It is
also shown that increased convective area coverage is
accompanied with an increased area coverage of less
frequent convection and a decreased area coverage of
highly frequent convection, and vice versa. The
identification of the geographical distribution of
convection perturbation associated with a potential
climate change is therefore important to the upper
troposphere water vapor feedback.
The mechanism behind the observed relationship is
interpreted using trajectory analysis. The results show
that a more diffused distribution of convection gives
rise to a shorter average horizontal distance and a less
vertical displacement between convection and clear
regions, and hence a moister clear sky condition.
Similarly, when deep convection is more concentrated, the
average traveling distance is longer, and the clear sky
upper troposphere is drier.
This process is verified using a simple heating driven
circulation model with prescribed distributions of
convective latent heating. The NCAR CCM is then used to
examine the relationship between UTH and convection. The
model is found to capture the relationship between water
vapor concentration and total convective area reasonably,
but it fails to reproduce the respective contributions
from highly and less frequent convections. The deficiency
lies in the fact that convection frequency is broadly
overestimated in the model. The area coverages of
different convective regimes are not simulated correctly.
The increase of total spatial coverage of deep convection
in the model is mainly reflected in the increased area
coverage of highly frequent convection, leading to an
opposite relationship between UTH and highly frequent
convection compared with the observations.
------------------------------------------------------------
Title: Improvement in runoff parameterization for global climate
modelling
Pub No: NQ58635
Author: Liu, Jinliang
Degree: PhD
School: UNIVERSITY OF TORONTO (CANADA)
Date: 2001
Pages: 168
Adviser: Cho, Han-Ru
ISBN: 0-612-58635-9
Source: DAI-B 62/04, p. 1906, Oct 2001
Subject: PHYSICS, ATMOSPHERIC SCIENCE (0608)
Abstract: Diagnosed runoff was estimated from NCEP/NCAR reanalysis
data for an 8-year period from 1987 to 1994. Bonan's land
surface model (LSM) was run for the same period coupled
to NCAR's CCM3. Comparisons between the diagnosed and
simulated runoff indicate that, the runoff
parameterization in the original LSM cannot produce a
reasonable diagnosed horizontal distribution of runoff,
which is important to the model climate. One of the
possible reasons is the exclusion of topographic effects
in the original runoff parameterization. Therefore, based
on previous research results on river re-distribution
models, a modification on the original runoff
parameterization was proposed and implemented in the
original LSM. This modification has two aspects: firstly,
the topographic slopes cause outflows from higher
topography and inflows into the lower topography points;
secondly, topographic slopes also cause decrease of
infiltration at higher topography and increases of
infiltration at lower topography. Then changes in
infiltration result in changes in soil-moisture, surface
fluxes and then in surface temperature. This mechanism is
very clearly demonstrated in the point budgets analysis
at the Andes Mountains vicinities. Analysis from a re
gional scale perspective in the Canadian GEWEX basin, the
Mackenzie River basin, shows that the modified runoff
parameterization can generate an expected horizontal
distribution of total runoff which is much closer to the
horizontal distribution of the observed and diagnosed
runoff, and which is much more consistent with topography
and thus very easy to explain physically. This represents
a significant improvement over the original LSM. More
importantly, very detailed analysis from a global
perspective shows many very encouraging improvements
introduced by the modified model over the original model
in simulating basic atmospheric climate properties such
as thermodynamic features, precipitable water, net water
exchange, and precipitation. The modified model somehow
corrected some deficiencies evident in the AGCM. All of
these improvements in the atmospheric climate simulation
illustrate that the inclusion of topographic effects in
the LSM can force the AGCM to produce a more realistic
model climate. Analysis also shows that the modified
model may improve the atmospheric <italic>CO
</italic><sub>2</sub> simulation which is very important
to global environmental studies.
------------------------------------------------------------
Title: Sea ice climatology, variations and teleconnections:
Observational and modeling studies
Pub No: 3080822
Author: Liu, Jiping
Degree: PhD
School: COLUMBIA UNIVERSITY
Date: 2003
Pages: 140
Adviser: Martinson, Douglas G.; Rind, David H.
ISBN: 0-496-28696-6
Source: DAI-B 64/02, p. 768, Aug 2003
Subject: PHYSICS, ATMOSPHERIC SCIENCE (0608); PHYSICAL
OCEANOGRAPHY (0415); GEOPHYSICS (0373)
Abstract: Hypotheses, models and observations suggest that sea ice
plays an important role in the local, regional and global
climate through a variety of processes across a full
range of scales. However, our documentation and
understanding of the nature of the polar-extrapolar
climate teleconnections and their underlying causal and
mechanistic links are still rudimentary, and the largest
disagreements among model simulations of present and
future climate are in the polar regions.
In an effort to address these issues, we evaluated the
simulated Antarctic sea ice variability and its climate
teleconnections in three coupled global climate models
(GISS, NCAR and GFDL) as compared to the observations.
All the models capture the El Niño-Southern
Oscillation (ENSO)-like phenomenon to some degree,
although almost all the models miss some observed
linkages. The GISS and NCAR models also capture the
observed Antarctic Dipole and meridional banding
structure through the Pacific. The Antarctic sea ice
regions showing the strongest sensitivity to global
teleconnections differ among the models and between the
models and observations. We then proposed that the
changes of the regional mean meridional atmospheric
circulation (the regional Ferrel Cell) are one such
mechanism leading to the covariability of the ENSO and
Antarctic Dipole by modulating the mean meridional heat
flux using the observational data.
To more accurately represent sea ice simulations and
associated feedbacks with the atmosphere and the ocean,
the GISS coupled model was used to investigate the
sensitivity of sea ice to the following physical
parameterizations: (a) two sea ice dynamics
(cavitating fluid and viscous-plastic), (b) the
specification of oceanic isopyncal mixing coefficients in
the Gent and McWillams isopyncal mixing, (c) the
Wajsowicz viscosity diffusion, (d) surface albedo,
(e) the penetration of solar radiation in sea ice,
(f) effects of including a sea ice salinity budget,
and (g) the ice-ocean boundary interactions. The
atmospheric responses associated with sea ice changes
were discussed. Based on these experiments, a series of
composite experiments with the aforementioned
parameterizations were also investigated. While
improvements are seen overall, there are some unrealistic
aspects that will require further improvements to the sea
ice and ocean components. Finally, the GISS coupled
model's ability to represent observed Antarctic sea ice
variability and its global teleconnections was re-
evaluated in a composite run with the improved sea ice
and ocean processes.
------------------------------------------------------------
Title: Parameter estimation for locally coupled land surface-
atmosphere models
Pub No: 3108924
Author: Liu, Yuqiong
Degree: PhD
School: THE UNIVERSITY OF ARIZONA
Date: 2003
Pages: 239
Adviser: Sorooshian, Soroosh
ISBN: 0-496-56469-8
Source: DAI-B 64/10, p. 4833, Apr 2004
Subject: HYDROLOGY (0388)
Abstract: As land-surface modeling moves from the off-line mode to
the coupled mode, it is also highly desirable to extend
the off-line calibration of land-surface models to
coupled applications. Using the NCAR SCCM as an example,
this study proposed and implemented some effective
schemes for the application of automatic parameter
estimation procedures in a locally coupled environment,
where other relevant issues such as parameterization
tests, sensitivity analyses, and off-line calibrations
were also involved.
A parameterization deficiency having serious negative
impacts on the performance of the NCAR SCCM was
identified and rectified in this work, which led to
significantly improved model performances and formed the
basis for the subsequent sensitivity analysis and
calibration experiments. To facilitate the calibration
studies, an independent sensitivity analysis was
conducted to identify some sensitive model parameters,
followed by a multi-objective sensitivity analysis using
the MOGSA algorithm to obtain better understanding of the
model. Some off-line calibrations using the NCAR LSM were
also conducted for comparison purposes.
In the locally coupled environment, both land-surface and
atmospheric variables/parameters were involved in the
calibration processes of 14 different pre-designed
calibration cases. In brief, the results show that
atmospheric parameters are of critical importance for the
calibration of a coupled land surface-atmosphere model,
and atmospheric forcing variables generally contain more
useful information for calibration than land-surface
fluxes/variables. In the coupled environment, step-wise
calibration schemes, with land-surface and atmospheric
parameters optimized successively in the off-line and
coupled modes, respectively, appear to be superior to the
single-step calibration schemes which optimize land-
surface and atmospheric parameters simultaneously in the
coupled environment, in that the former can provide
better converged optimal solutions with less
uncertainties. In addition, the results also show that
better optimization effects can be achieved in the
partially decoupled environment by replacing the model-
generated precipitation and net radiation with the
corresponding observations to drive the land-surface part
of the model, indicating the dominant importance of
precipitation and radiation in a coupled land surface-
atmosphere model.
------------------------------------------------------------
Title: Applications of tree-structured regression for regional
precipitation prediction
Pub No: 9987703
Author: Li, Xiangshang
Degree: PhD
School: TULANE UNIVERSITY
Date: 2000
Pages: 212
Adviser: Sailor, D. J.
ISBN: 0-599-94468-4
Source: DAI-B 61/09, p. 4779, Mar 2001
Subject: ENGINEERING, MECHANICAL (0548); PHYSICS, ATMOSPHERIC
SCIENCE (0608); ENGINEERING, ENVIRONMENTAL (0775)
Abstract: This thesis presents a Tree-Structured Regression (TSR)
method to relate daily precipitation with a variety of
free atmosphere variables. Historical data were used to
identify distinct weather patterns associated with
differing types of precipitation events. Models were
developed using 67% of the data for training and the
remaining data for model validation. Seasonal models were
built for each of four U.S. sites; New Orleans Louisiana,
San Antonio and Amarillo of Texas as well as San
Francisco California. The average correlation by site
between observed and simulated daily precipitation data
series range from 0.69 to 0.79 for the training set, and
0.64 to 0.79 for the validation set. Relative humidity
related variables were found to be the dominant variables
in these TSR models. Output from an NCAR Climate System
Model (CSM) transient simulation of climate change were
then used to drive the TSR models for predicting
precipitation characteristics under climate change. A
preliminary screening of the GCM output variables for
current climate, however, revealed significant problems
for the New Orleans, San Antonio and Amarillo sites.
Specifically, the CSM missed the annual trends in
humidity for the grid cells containing these sites. CSM
output for the San Francisco site was found to be much
more reliable. Therefore, we present future precipitation
estimates only for the San Francisco site. While both GCM
and TSR predict very small change in overall annual
precipitation, they differ significantly from season to
season.
------------------------------------------------------------
Title: Effects of cloud-radiative forcing on atmospheric
response to tropical SST anomaly: Observation and
simulation
Pub No: 9712812
Author: Lu, Xiaodan
Degree: PhD
School: STATE UNIVERSITY OF NEW YORK AT STONY BROOK
Date: 1996
Pages: 134
ISBN: 0-591-20372-3
Source: DAI-B 57/11, p. 6827, May 1997
Subject: PHYSICAL OCEANOGRAPHY (0415); PHYSICS, ATMOSPHERIC
SCIENCE (0608); ENVIRONMENTAL SCIENCES (0768)
Abstract: Cloud-climate interannual variations associated with the
anomalous SST over the tropical region are investigated
by using five-year monthly mean SST, ERBE data and
CCM2/AMIP simulation. Cloud effects, in terms of cloud-
radiative forcing (CRF), on the atmospheric responses to
the tropical SST anomaly, associated with El Nino and the
Southern Oscillation (ENSO) event, have been studied by
using the NCAR CCM2.
The convection anomalies in terms of anomalous CRF appear
to be in east-west anti-phase dipole patterns with
ascending (descending) vertical motion over the central
Pacific Ocean and descending (ascending) vertical motion
over the maritime continent-South Pacific Convergence
Zone (SPCZ) and Brazil for the positive (negative)
anomalous SST presented over the central-eastern Pacific
Ocean. It is suggested that the opposite type of strong
anomalous SST may produce a reverse Walker circulation in
the anomalous sense, which could be interpreted as a
teleconnection.
In our simulation, cloud effects intensify the model
Southern Oscillation response to the SST anomaly with a
negative SLP anomaly in the central-eastern Pacific Ocean
and a positive anomaly in the western Pacific-Indian
Ocean. Cloud effects produce a warming (cooling)
throughout the troposphere and a cooling (warming) at the
tropopause in the central-eastern Pacific (western
Pacific-Indian Ocean). The zonal wind change associated
with the temperature change shows a enhanced model
Southern Oscillation with an westerly (easterly) anomaly
at low levels and a easterly (westerly) anomaly at high
levels in the central-eastern Pacific (western Pacific-
Indian Ocean). The cloud effect weakens the intensity of
the normal Walker circulation for both the east and west
branches.
The longwave heating rate change due to cloud amount
change, which is associated with the SST anomaly,
presents a warming (cooling) at low levels and a cooling
(warming) at high levels in the east (west). This change
destabilizes (stabilizes) the troposphere and enhances
(suppresses) deep convection and latent heat release in
the east (west). The shortwave heating rate change is
opposite to the longwave heating rate change and plays an
opposite role to the cloud longwave heating as it
interacts with deep convection and latent heat release.
Cloud has a large impact on the latent heating response
to the SST anomaly with a strong warming (cooling)
presented in the middle-upper troposphere in the east
(west), i.e., cloud effects enhance (suppress) the deep
convection in the east (west) with the ENSO type SST
anomaly over the central-eastern Pacific.
------------------------------------------------------------
Title: Frictional convergence and the Madden-Julian oscillation
Pub No: 9983516
Author: Maloney, Eric Daniel
Degree: PhD
School: UNIVERSITY OF WASHINGTON
Date: 2000
Pages: 138
Adviser: Hartmann, Dennis L.
ISBN: 0-599-89556-X
Source: DAI-B 61/08, p. 4213, Feb 2001
Subject: PHYSICS, ATMOSPHERIC SCIENCE (0608); APPLIED MECHANICS
(0346)
Abstract: Frictional surface convergence is shown to be important
to the Madden-Julian oscillation (MJO) of the tropical
troposphere using both observations and an atmospheric
general circulation model (GCM). An observed composite
MJO lifecycle is created using the first two empirical
orthogonal functions of the NCEP 850 mb equatorial zonal
wind as an index. Lower tropospheric water vapor over the
Indian and western Pacific Oceans is significantly
correlated with 1000 mb convergence during an MJO
lifecycle. Frictional convergence may help to
precondition the atmosphere for strong MJO convection by
moistening the lower troposphere.
Several convection schemes were substituted into the NCAR
CCM3 GCM to improve model intraseasonal variability. The
McRAS convection scheme, that includes a parameterization
of unsaturated convective downdrafts and a relative
humidity threshold for convective initiation, produces
much improved intraseasonal variability over the default
CCM3 convection scheme of Zhang and McFarlane.
Intraseasonal variability is decreased for higher
relative humidity thresholds with McRAS, contrary to the
results of Wang and Schlesinger (1999). Removal of the
unsaturated convective downdraft and rain evaporation
parameterization greatly diminishes intraseasonal
variability in zonal winds and precipitation. An
excessively dry tropical troposphere is most likely
responsible for the degradation of intraseasonal
variability.
Low-level MJO specific humidity anomalies in the model
are strongly correlated with surface convergence. This
strong coupling with surface convergence causes model MJO
convection anomalies to be associated with 850 mb
easterly perturbations. Where the eastward propagating
model MJO signal is strong, low-level specific humidity
anomalies precede those at middle and upper levels.
Surface convergence affects model convection by
moistening the lower troposphere, suggesting that surface
convergence during an MJO lifecycle may help to
precondition the atmosphere for intense MJO convection.
Meridional convergence onto the equator contributes most
of the anomalous convergence during an MJO lifecycle in
both the model and observations. The wind-induced surface
heat exchange (WISHE) mechanism of Emanuel (1987) and
Neelin and Yu (1994) does not significantly contribute to
the MJO-like mode in the CCM3 with McRAS.
------------------------------------------------------------
Title: Sensitivity studies for incorporating the direct effect
of sulfate aerosols into climate models
Pub No: 9965865
Author: Miller, Mary Rawlings Lamberton
Degree: PhD
School: THE UNIVERSITY OF ARIZONA
Date: 2000
Pages: 271
Adviser: Dickinson, Robert E.
ISBN: 0-599-70484-5
Source: DAI-B 61/03, p. 1455, Sep 2000
Subject: PHYSICS, ATMOSPHERIC SCIENCE (0608); APPLIED MECHANICS
(0346)
Abstract: Aerosols have been identified as a major element of the
climate system known to scatter and absorb solar and
infrared radiation, but the development of procedures for
representing them is still rudimentary. This study
addresses the need to improve the treatment of sulfate
aerosols in climate models by investigating how sensitive
radiative particles are to varying specific sulfate
aerosol properties. The degree to which sulfate particles
absorb or scatter radiation, termed the direct effect,
varies with the size distribution of particles, the
aerosol mass density, the aerosol refractive indices, the
relative humidity and the concentration of the aerosol.
This study develops 504 case studies of altering sulfate
aerosol chemistry, size distributions, refractive indices
and densities at various ambient relative humidity
conditions. Ammonium sulfate and sulfuric acid aerosols
are studied with seven distinct size distributions at a
given mode radius with three corresponding standard
deviations implemented from field measurements. These
test cases are evaluated for increasing relative
humidity. As the relative humidity increases, the complex
index of refraction and the mode radius for each
distribution correspondingly change. Mie theory is
employed to obtain the radiative properties for each case
study. The case studies are then incorporated into a box
model, the National Center of Atmospheric Research's
(NCAR) column radiation model (CRM), and NCAR's community
climate model version 3 (CCM3) to determine how sensitive
the radiative properties and potential climatic effects
are to altering sulfate properties.
This study found the spatial variability of the sulfate
aerosol leads to regional areas of intense aerosol
forcing (W/m<super>2</super>). These areas are
particularly sensitive to altering sulfate properties.
Changes in the sulfate lognormal distribution standard
deviation can lead to substantial regional differences in
the annual aerosol forcing greater than 2 W/m<super>
2</super>. Changes in the aerosol chemical composition
can lead to regional changes in the aerosol forcing
greater than 0.5 W/m<super>2</super>. The relative
humidity is shown to greatly influence the aerosol
optical properties. Given the differences in aerosol
forcing found due to varying sulfate properties, this
study does not encourage the use of a single aerosol
distribution to represent sulfate particles of all air
masses.
------------------------------------------------------------
Title: Estimate of the climate impact of biomass burning
aerosols in the Amazon by using NCAR-CCM3
Pub No: 9927482
Author: Montero Martinez, Martin Jose
Degree: PhD
School: THE UNIVERSITY OF ARIZONA
Date: 1999
Pages: 148
Adviser: Dickinson, Robert E.
ISBN: 0-599-27189-2
Source: DAI-B 60/04, p. 1656, Oct 1999
Subject: PHYSICS, ATMOSPHERIC SCIENCE (0608); BIOLOGY, ECOLOGY
(0329)
Abstract: It has been recognized that pollution (sulfate aerosols),
and biomass burning (smoke aerosols), are the two
principal anthropogenic sources that are now influencing
the global climate. Researchers are currently trying to
provide better estimates of the climate impact due to
anthropogenic aerosols and to lower the range of
uncertainty in their calculations. Estimations suggest a
global-mean direct radiative forcing in the range from
–0.3 to –1.0 W/m<super>2</super> for biomass
burning aerosols, with a similar value for the indirect
effect. The primary goal of this work is to estimate the
global climate impact due to smoke aerosols from biomass
burning using the National Center for Atmospheric
Research (NCAR)-Community Climate Model, Version 3
(CCM3). Analysis of data from the AERONET project was
used to define a more realistic average of the
optical/radiative properties of smoke particles from
biomass burning in the Amazon, and also, to provide
relevant information about the cloud-aerosol
interactions. This information was put into the context
of the NCAR-CCM3 BATS, and then the cloud/radiative
scheme of the standard model was modified to include both
the direct and indirect effects of the aerosols. Our
results suggest an annual global mean “total”
(direct+indirect) radiative forcing of about –0.08
W/m<super>2</super>. This value is in good agreement with
recent estimations considering that we are only including
the biomass burning aerosols in the Amazon region. In
addition, our model simulations provide a
“total” radiative forcing of about –10
W/m<super>2</super> for the Amazon region during the dry-
season, where the indirect effect is responsible for
about 80% of this value. This research hopefully will
contribute to the aerosol climate modeling area by
providing a scheme in which both the direct and indirect
effects of the aerosol can be explicitly represented in a
GCM.
------------------------------------------------------------
Title: Jet formation and equatorial superrotation in Jupiter's
atmosphere: Numerical modelling using a new efficient
parallel code
Pub No: 3037750
Author: Rivier, Leonard Gilles
Degree: PhD
School: COLUMBIA UNIVERSITY
Date: 2001
Pages: 103
Adviser: Polvani, Lorenzo M.
ISBN: 0-493-50951-8
Source: DAI-B 62/12, p. 5770, Jun 2002
Subject: PHYSICS, ATMOSPHERIC SCIENCE (0608); PHYSICS, ASTRONOMY
AND ASTROPHYSICS (0606)
Abstract: Using an efficient parallel code solving the primitive
equations of atmospheric dynamics, the jet structure of a
Jupiter like atmosphere is modeled.
In the first part of this thesis, a parallel spectral
code solving both the shallow water equations and the
multi-level primitive equations of atmospheric dynamics
is built. The implementation of this code called BOB is
done so that it runs effectively on an inexpensive
cluster of workstations. A one dimensional decomposition
and transposition method insuring load balancing among
processes is used. The Legendre transform is cache-
blocked. A “compute on the fly” of the
Legendre polynomials used in the spectral method produces
a lower memory footprint and enables high resolution runs
on relatively small memory machines. Performance studies
are done using a cluster of workstations located at the
National Center for Atmospheric Research (NCAR). BOB
performances are compared to the parallel benchmark code
PSTSWM and the dynamical core of NCAR's CCM3.6.6. In both
cases, the comparison favors BOB.
In the second part of this thesis, the primitive equation
version of the code described in part I is used to study
the formation of organized zonal jets and equatorial
superrotation in a planetary atmosphere where the
parameters are chosen to best model the upper atmosphere
of Jupiter. Two levels are used in the vertical and only
large scale forcing is present. The model is forced
towards a baroclinically unstable flow, so that eddies
are generated by baroclinic instability. We consider
several types of forcing, acting on either the
temperature or the momentum field. We show that only
under very specific parametric conditions, zonally
elongated structures form and persist resembling the jet
structure observed near the cloud level top (1 bar) on
Jupiter. We also study the effect of an equatorial heat
source, meant to be a crude representation of the effect
of the deep convective planetary interior onto the outer
atmospheric layer. We show that such heat forcing is able
to produce strong equatorial superrotating winds, one of
the most striking feature of the Jovian circulation.
------------------------------------------------------------
Title: Precipitation simulation in global climate models: Impact
of horizontal resolution and improved land surface scheme
Pub No: 9626486
Author: Shaikh, Muhammad Javed
Degree: PhD
School: THE UNIVERSITY OF ARIZONA
Date: 1996
Pages: 246
Adviser: Dickinson, Robert E.
Source: DAI-B 57/04, p. 2438, Oct 1996
Subject: HYDROLOGY (0388); PHYSICS, ATMOSPHERIC SCIENCE (0608)
Abstract: This dissertation examines the improvement in the
simulation of precipitation by using a high resolution
model and a highly physically-based land surface scheme.
To investigate the impact of the horizontal resolution on
the simulated fields, six versions of NCAR's latest
Community Climate Model (CCM2) are analyzed. The
simulations were conducted for periods of 4-20 years. To
study the effects of the improved land surface scheme in
the model, the coupling of BATS to the standard model and
a revised version of CCM2 with modified optical
properties for clouds are compared.
It is evident that the refinement of the model resolution
adds further accuracy to the simulation. The increased
resolution of the model improves the definition of the
major mountain ranges and the average surface topography
of lands and oceans. The taller mountains in a high
resolution model play an important role in modifying the
vapor flux over the land surface. They obstruct more
water flow and reduce the specific humidity and the total
precipitable water over land. The vapor transport to the
land surface is also partly influenced by the changes in
the large scale circulation. The adjusted surface
pressures over the sea surface levels simulate more
closely the position and magnitude of the observed
pressure systems.
A major problem in CCM2 is the excessive surface
radiation, which is up to 50-100 Wm$/sp[-2]$ higher than
the Surface Radiation Budget (SRB) dataset over vast
areas in the summer hemisphere. At a high resolution, the
lower land clouds reduce the planetary albedo and allow
more solar radiation to reach the surface. But in spite
of this, the high resolution model improves the amount
and distribution of the land precipitation. The RCCM2-
BATS model, which increases the optical thickness of the
summer clouds, substantially reduces the overestimate of
the surface radiation. This helps reduce the large
discrepancies obtained in summer precipitation. The land
surface scheme predicts the regional climate more
accurately than the standard model, but its performance
is restricted by the inputs and does not show any major
improvement in precipitation predictions which are mainly
controlled by various processes in the atmospheric model.
------------------------------------------------------------
Title: Snow fractional cover in land surface schemes (Alaska)
Pub No: 3113143
Author: Slater, Andrew G.
Degree: PhD
School: UNIVERSITY OF COLORADO AT BOULDER
Date: 2003
Pages: 186
Adviser: Lynch, Amanda H.
ISBN: 0-496-60639-9
Source: DAI-B 64/11, p. 5569, May 2004
Subject: PHYSICS, ATMOSPHERIC SCIENCE (0608)
Abstract: Land surface scheme forcing data sets are constructed
using observations from the Seward Peninsula in Alaska.
Non-parametric statistical techniques are successfully
applied to fill data gaps in precipitation.
An extensive validation of the NCAR models, LSM and CLM,
is undertaken using a variety of independent data such as
turbulent fluxes measured via eddy correlation
techniques. The models perform consistently compared to
pervious studies, that is, CLM is a warmer dryer model
than LSM. Several weaknesses regarding parameter
assignment in the summer albedo, snow density and the
lack of organic soil layers are identified in CLM. The
additional physics in CLM are shown to perform better
than the simpler LSM if the appropriate parameters are
assigned.
Using synthetic data generated from observations, a
spatially implicit comparison between the models and
remotely sensed products is made. The aim is to assess
the ability of the models to capture the albedo and
fractional snow cover over a larger area than a point.
The models cannot emulate the observed variability of the
region, even that within vegetation classes. Part of this
stems from the uniform view of vegetation as well as the
ever problematic snow albedo parameterization. The MODIS
and AVHRR albedo products are compared against each other
and can demonstrate consistent performance suggesting
they may provide a key to the fractional cover issue.
The implicit inclusion of a partial snow cover in the
models is compared to explicit simulation of snow covered
and snow free areas. Some differences are evident in the
resulting mean surface temperature. The impact of non-
linear behaviour in surface temperature with fractional
cover was investigated through an upscaling exercise.
Results suggest the models are largely scale invariant in
off-line simulations.
------------------------------------------------------------
Title: Carbonate diagenesis and paleoclimate of the Desmoinesian
Lower Ismay zone, Paradox Basin, southeast Utah
Pub No: 3113055
Author: Smith, Linda Sue Susanna
Degree: PhD
School: THE UNIVERSITY OF TEXAS AT DALLAS
Date: 2003
Pages: 251
Adviser: Mitterer, Richard M.
ISBN: 0-496-60551-1
Source: DAI-B 65/06, p. 2821, Dec 2004
Subject: GEOLOGY (0372); PALEOECOLOGY (0426); PHYSICAL
OCEANOGRAPHY (0415)
Abstract: The Paradox Basin is located in present day four corner
area of SE Utah, USA. However, during the Desmoinesian
the basin migrated from the equator to 5°N.
Carbonates developed on topographic highs during late
transgressive system tracts (TST) and highstand system
tracts (HST). Lowstand system tracts (LST) are
characterized by more than 33 evaporite cycles. Platform
carbonates and basin evaporite sequences are tied by
cyclic regional dolomudstones that blanket both carbonate
and evaporite sediments in the early TST. Detail analyses
of the Lower Ismay Zone reveals rapid sea level falls
within system tracts and climate fluctuations from
extreme aridity to monsoon periods.
Paleoclimate interpretation was enhanced by applying
geochemical and petrographic analyses of all three
depositional systems carbonate, evaporite and
dolomudstone) of the Lower Ismay and Evaporite Cycle 3.
Paragenetic sequences were constructed from four
different horizons within the Lower Ismay Zone. These
sequences identified three rapid sea level falls within
the Lower Ismay. Meteoric cements in the lowest horizon
indicate wetter periods in contrast to the more arid
upper horizons that show well-developed sabkha fabrics
and evaporite cements.
To better understand the effect climate change played on
sea level fluctuations and diagenesis, climate models
were run in the NCAR CSM3 program. The Late Carboniferous
Earth plate configuration is the geographic base to test
two obliquity extremes (21.5° and 24.5°). Results
from these simulations suggest a significant shift in the
Inter-tropical Convergence Zone (ITCZ) for 21.5° and
24.5° obliquities. This shift indicates that wet
sediment cycles in the Desmoinesian of Wyoming are out of
phase with those in the Paradox Basin. A strong seasonal
shift in wind direction with cyclonic movement occurs in
both models in the Paleo-Tethys, suggesting the strong
monsoon climate in this region is not driven by
obliquity. The maximum solar insolation latitudinal band
is expanded in the January/July 24.5° obliquity
model. Also, the tropical sea surface temperatures show a
broader warm band at the equator in high obliquity
models.
------------------------------------------------------------
Title: Examining vegetation and climate interactions: A
comparative study of different vegetation types and their
impacts on atmospheric energetics and dynamics at the
regional and global scales
Pub No: 3128110
Author: Snyder, Peter K.
Degree: PhD
School: THE UNIVERSITY OF WISCONSIN - MADISON
Date: 2004
Pages: 205
Adviser: Foley, Jonathan A.
ISBN: 0-496-75373-1
Source: DAI-B 65/04, p. 1914, Oct 2004
Subject: PHYSICS, ATMOSPHERIC SCIENCE (0608); ENVIRONMENTAL
SCIENCES (0768)
Abstract: It is widely recognized that terrestrial ecosystems play
an important role in maintaining the climate system.
Vegetation influences the climate through complex
biophysical exchanges of energy, water, and momentum, and
changes to these fluxes can have a significant impact on
the climate. As a result, natural and anthropogenic land
use and land cover change can have a substantial impact
on climate.
Using a coupled atmosphere-biosphere model (CCM3-IBIS),
the influence of vegetation on climate at the regional,
continental, and global scales is evaluated. Comparison
of the vegetation removal and control simulations
illustrates the climatic influence of particular
vegetation types. The mechanisms responsible for
influencing the climate away from the surface, into the
atmosphere, and to remote regions not directly coupled to
the surface forcing are investigated.
It was found that vegetation biomes from around the globe
have a significant influence on the climate system with
the response dictated by the vegetation type, the
geographic location, and the physical processes important
for that biome. For instance, the climate response to
tropical deforestation is a surface warming due to a
large reduction in latent cooling. In contrast, boreal
deforestation causes a large surface temperature cooling
due to a higher surface albedo.
It was also shown that changes in the land surface
resulting from land cover change affect the transport of
energy throughout the three-dimensional atmosphere and
can change the climate in adjacent regions or locations
far removed from the surface forcing through modification
of deep moist convection.
Finally, the results indicate that tropical deforestation
can have a significant influence on the northern
hemisphere climate through changes to the atmospheric
thermodynamics and general circulation. Tropical
deforestation was found to influence the northern
hemisphere climate through changes to the high-level
tropical outflow, the strength and structure of the East
Asian Jet, the poleward shift in the high-latitude jet,
and changes to the Eurasian climate through amplification
of the positive phase of the North Atlantic Oscillation.
------------------------------------------------------------
Title: A numerical modeling study of the coupled variability of
Lake Victoria in eastern Africa and the regional climate
Pub No: 3033715
Author: Song, Yi
Degree: PhD
School: NORTH CAROLINA STATE UNIVERSITY
Date: 2000
Pages: 184
Adviser: Xie, Lian; Semazzi, Fredrick H. M.
ISBN: 0-493-46685-1
Source: DAI-B 62/12, p. 5770, Jun 2002
Subject: PHYSICS, ATMOSPHERIC SCIENCE (0608); GEOPHYSICS (0373)
Abstract: The objective of this investigation was to investigate
and study the coupled atmosphere-lake climate system over
the Lake Victoria basin, and determine the corresponding
physical mechanisms that are involved. The primary
research vehicle for the investigation is a fully coupled
model of the regional climate of Eastern Africa and Lake
Victoria which has been developed and applied in this
study. The atmospheric component of the model is the NCAR
Regional Climate Model (RegCM2).
The results show that the bythemetry and geometry of the
lake play a fundamental role in determining the
climatology of Lake Victoria. There exists Kelvin-like
waves in the thermocline trapped along the coast and they
propagate clockwise around Lake Victoria with periodicity
of about 30 days. Preliminary comparison of the coupled
RegCM2-POM model simulation results with the observations
indicates that the model produces more realistic lake
surface temperatures (LST) and rainfall over and around
the lake than the standard version of RegCM2 in which a
simple one dimensional thermal diffusion lake model is
used.
Over Eastern Africa, the regional climate variability is
significantly influenced by the circulation over the Lake
Victoria basin. The interaction between the lake-land
breeze and the prevailing northeasterly flow accounts for
the asymmetry in the distribution of the diurnal rainfall
variations and the southwestward movement of the dominant
bands of divergence/convergence.
During the 1982 El Nino when the averaged LST over the
lake was higher than that during the normal year, the LST
gradient was weakened along the SW-NE axis over the lake
by the strong lake circulation. The hydrodynamics of the
lake play an important role in determining the coupled
variability of the lake circulation and the lake basin-
wide climatic conditions.
The potential climate change resulting from total
clearing of the tropical rain forests in Africa was also
investigated by the standard version of the NCAR CCM3
global climate model. Over Eastern and Western Africa the
impact of deforestation is primarily characterized by
reduction in rainfall, however the CCM3 resolution of T42
which we have adopted may not be adequate to resolve the
large contrasts in terrain and vegetation types. A
striking result is that the strong remote response of the
Southern Africa region to deforestation over Central
Africa. (Abstract shortened by UMI.)
------------------------------------------------------------
Title: The influence of atmospheric chemistry and climate on
atmosphere-biosphere interactions
Pub No: 3095758
Author: Steiner, Allison L.
Degree: PhD
School: GEORGIA INSTITUTE OF TECHNOLOGY
Date: 2003
Pages: 133
Adviser: Chameides, William L.
ISBN: 0-496-43383-0
Source: DAI-B 64/06, p. 2718, Dec 2003
Subject: PHYSICS, ATMOSPHERIC SCIENCE (0608)
Abstract: A modeling tool is developed to investigate the feedbacks
between the terrestrial biosphere and the atmosphere, two
major components of the Earth system. Changes in
environmental variables such as solar radiation,
temperature, and atmospheric water vapor can influence
the water and energy balances at the land surface. These
changes can, in turn, strongly impact vegetation
processes, including transpiration, photosynthesis, and
the emission of biogenic volatile organic compounds
(VOCs). These processes are part of the complex
mechanisms within the Earth system that can feedback upon
each other and create unexpected responses.
A biogenic VOC emissions algorithm is developed for use
within the modeling system. Biogenic VOC emissions,
including isoprene, monoterpenes and ORVOCs, account for
over half of the total amount of VOCs emitted in East
Asia. Additionally, the emissions can be significantly
affected by both land cover changes and rising
CO<sub>2</sub> concentrations. Because of their
importance in predicting ground-level ozone, these
terrestrial biosphere-atmosphere feedbacks could have an
important influence on air quality prediction and
compliance.
As part of the coupled climate-land surface model
development, a new land surface model, the Common Land
Model (CLM0) is integrated into a regional climate model
(RegCM2). For a yearlong simulation over East Asia, the
RegCM2/CLM0 slightly improves the winter cold bias that
is present in the former RegCM2 simulation and reproduces
the seasonal cycle of climate in the region.
Three-dimensional fields of anthropogenic aerosols are
added to the RegCM2/CLM0 to investigate biosphere-
atmosphere feedbacks. The presence of aerosols reduces
leaf temperatures crucial for photosynthesis and biogenic
VOC emissions. In a five-day summertime simulation that
includes the so-called direct effect of aerosols, there
is a 5–8 degree reduction in leaf temperatures
within the canopy. In the absence of aerosols, leaf
temperatures are beyond the optimum leaf temperature,
which slows the photosynthetic rate. The presence of
aerosols reduces these temperatures below the optimum,
leading to an increase in photosynthesis and
transpiration. This result indicates a previously
undiscovered mechanism between aerosols and the
terrestrial biosphere, and this could have significant
implications for future studies in aerosol-climate
interactions and the terrestrial carbon balance.
------------------------------------------------------------
Title: A one-dimensional mixed-layer ocean model for use in
three-dimensional climate simulations
Pub No: 9830538
Author: Stephens, Monica Yvette
Degree: PhD
School: BROWN UNIVERSITY
Date: 1998
Pages: 196
Adviser: Maxey, Martin
ISBN: 0-591-83340-9
Source: DAI-B 59/04, p. 1689, Oct 1998
Subject: MATHEMATICS (0405); PHYSICS, ATMOSPHERIC SCIENCE (0608);
PHYSICAL OCEANOGRAPHY (0415)
Abstract: A study has been made of the dynamic interactions between
the surface layer of the oceans and the atmosphere as it
relates to global climate variations. The atmospheric
conditions are simulated numerically with the NCAR
Atmospheric General Circulation Model (AGCM), CCM3. A
one-dimensional mixed layer ocean model (MLOM) for the
upper ocean has been developed and coupled to the AGCM.
The mixed-layer model simulates vertical ocean dynamics
and demonstrates the effect of mixed-layer depth and
convective instability on the sea surface temperature and
on the formation of sea-ice. The purpose of the coupling
was to make direct calculations of mixed-layer depth
convection in a climate simulation using CCM3. The
current mixed-layer model that is used in CCM3, known as
the slab ocean model, contains seasonally and spatially
specified depths. It also uses a prescribed horizontal
heat flux (QFLUX) that determines the vertical heat
transport and models the large scale heat transport by
ocean currents. The MLOM allows the coupled simulation to
capture the physics of sea-ice and mixed-layer
interaction, and the effects of the seasonal variation of
mixed-layer depth and entrainment on the sea surface
temperature. This model has also been run in stand-alone
simulations with data derived from the AGCM, CCM1. These
simulations show that the MLOM is able to simulate SSTs
and depths that closely approximate the observed climate.
The addition of the variable-depth mixed-layer model to
CCM3 provides several potentially interesting features to
the climate simulation. The mixed-layer model deals
explicitly with vertical heat transport--one of the
phenomena parameterized by QFLUX in current slab ocean
models, calculates mixed-layer depth which is currently
seasonally and spatially specified in CCM3, and
introduces a negative feedback for sea-ice growth from
the interaction between the mixed layer and sea ice. An
explicit calculation of mixed-layer depth and vertical
heat flux will make CCM3 better able to make physically
accurate predictions of sea surface temperature and sea
ice for past and future climate scenarios since these
quantities will no longer be tuned to meet present-day
conditions. Currently, CCM3 coupled to the slab ocean
model only includes the ice-albedo feedback mechanism
which is a positive feedback for sea-ice growth.
Including the negative feedback from mixed-layer and sea-
ice interaction provides a means for studying the
competing effects of both negative and positive feedbacks
on sea-ice growth.
------------------------------------------------------------
Title: Tropospheric constituent variability associated with
baroclinic waves
Pub No: 9814700
Author: Stone, Elizabeth Mary
Degree: PhD
School: IOWA STATE UNIVERSITY
Date: 1997
Pages: 111
Adviser: Stanford, John L.
ISBN: 0-591-65736-8
Source: DAI-B 58/11, p. 6018, May 1998
Subject: PHYSICS, ATMOSPHERIC SCIENCE (0608)
Abstract: Baroclinic waves are fundamental to tropospheric
dynamics, and therefore it is of interest to understand
their impact on atmospheric constituents. Here we examine
the dynamics of the troposphere during baroclinic wave
life cycles and study in detail their influence on
constituent transport. We incorporate two methods of
studying the atmosphere. The first is the study of
observations made by remote sensing of the atmosphere by
satellites. The second is the examination of the
atmosphere through the use of an atmospheric general
circulation model.
In an observational case study, we used upper
tropospheric water vapor measurements from the Upper
Atmosphere Research Satellite Microwave Limb Sounder to
investigate the structure and evolution of eastward
traveling medium-scale wave features in Southern
Hemisphere summertime and found that the water vapor
field is well correlated with meteorological fields and
derived potential vorticity fields. These results are
consistent with model paradigms for the structure and
evolution of baroclinic disturbances.
In order to study the details of transport associated
with baroclinic waves, we build upon the successes of
other studies which use general circulation models to
simulate baroclinic wave life cycles. These nonlinear
simulations have shown that the wave evolution consists
of baroclinic growth, maturity and barotropic decay. In
our study, two life cycles are simulated with the
National Center for Atmospheric Research (NCAR) community
climate model (CCM2), starting with baroclinically
unstable initial conditions similar to those used by
Thorncroft et al. (1993). The two life cycles differ in
the strength and sense of the horizontal shear of the
zonal wind. This strongly influences the behavior which
ensues. In terms of potential vorticity-potential
temperature diagnostics, the basic case is characterized
by thinning troughs which are advected anti-cyclonically
and equatorward, while the anomalous case has broadening
troughs which wrap up cyclonically and poleward. In order
to investigate transport during these two life cycles,
four passive tracers are included in the simulation to be
advected by the semi-Lagrangian transport scheme of CCM2.
The resulting tracer budgets are analyzed in terms of the
transformed Eulerian mean constituent transport
formalism. Results show a net upward and poleward
transport and a strong influence of the eddy flux term on
the time tendency of the tracer. The largest transport
occurs during the nonlinear growth stage of the life
cycle. We also find that the transport varies little with
the initial tracer distributions.
------------------------------------------------------------
Title: Diurnal variation of deep convection over the tropical
western Pacific
Pub No: 3115874
Author: Sun, Moguo
Degree: PhD
School: STATE UNIVERSITY OF NEW YORK AT STONY BROOK
Date: 2003
Pages: 123
Adviser: Cess, Robert D.
ISBN: 0-496-63311-9
Source: DAI-B 64/12, p. 5987, Jun 2004
Subject: PHYSICAL OCEANOGRAPHY (0415)
Abstract: An integration of observational and modeling studies of
the diurnal variation of deep convection is presented in
this thesis. The thesis consists of three parts:
(1) an observational study on the diurnal variation
of deep convection, (2) Adequacy of the National
Center for Atmospheric Research (NCAR) Community Climate
Model version 2 (CCM2) radiation scheme used in the
modeling study and the sensitivity of outgoing longwave
radiation (OLR) to atmospheric variables, (3) a
modeling study on the mechanisms of the diurnal variation
of deep convection.
The observational study concentrates on the tropical
western Pacific (TWP) during the Tropical Ocean Global
Atmosphere-Coupled Ocean Atmosphere Response Experiment
(TOGA-COARE) intensive observation period (IOP). Four
months of Geostationary Meterorological Satellite (GMS)
infrared (IR) temperature data are analyzed using IR
temperature threshold and cloud cluster techniques. Both
techniques reveal the same results, that deep convective
cloudiness reaches a maximum in the early morning
(03–06 local standard time (LST)). The feature is
very different from lower level cloudiness that reaches a
maximum in the late afternoon. A cross-plot of IR
temperature versus time shows that the phase of the
diurnal variation has an abrupt change around 220K and
propagates downward. Spectral analysis is used to
establish the robustness of the diurnal signal of deep
convection.
Unlike previous studies using idealized simulations, this
study employs a three-dimensional regional model, the
NCAR Mesoscale Model Version 5 (MM5), to realistically
simulate the diurnal variation. Before this, however, the
study focuses on the radiation code of MM5, since
radiation is particularly important in the modeling
study. Comparisons between CCM2 radiation code used in
MM5 and its updated CCM3 version are to show the adequacy
of CCM2 radiation code in the current study. The
comparisons show that both solar and longwave radiation
produced by the CCM2 code are close to the later CCM3
version under the clear sky condition. (Abstract
shortened by UMI.)
------------------------------------------------------------
Title: Ensemble forecasting with the ensemble transform Kalman
filter
Pub No: 3147696
Author: Wang, Xuguang
Degree: PhD
School: THE PENNSYLVANIA STATE UNIVERSITY
Date: 2004
Pages: 75
Adviser: Young, George S.
ISBN: 0-496-06817-2
Source: DAI-B 65/09, p. 4626, Mar 2005
Subject: PHYSICS, ATMOSPHERIC SCIENCE (0608)
Abstract: A new initial perturbation generation method, the
ensemble transform Kalman filter (ETKF), is introduced
and compared with the breeding scheme. The ETKF generates
initial perturbations by postmultiplying forecast
perturbations by a transformation matrix. This matrix is
chosen to solve the error covariance update equation for
an optimal data assimilation scheme within the ensemble
perturbation subspace. Version 3 of the community climate
model (CCM3) developed at National Center for Atmospheric
Research is used to test and compare the ETKF and
breeding schemes. It is found that with only a little
more computational expense, the ETKF samples initial
condition uncertainties significantly better than the
breeding. The ETKF ensemble mean and ensemble covariance
are considerably more accurate than those of the
breeding.
A new method to center initial ensemble perturbations on
the initial analysis is introduced and compared with the
commonly used centering method of positive-negative
paired perturbations. In the new method, called spherical
simplex centering, one linearly dependent perturbation is
added to a set of linearly independent initial
perturbations to ensure that the sum of the new initial
perturbations equals zero; the covariance calculated from
the new initial perturbations is equal to the analysis
error covariance estimated by the independent initial
perturbations; and all the new initial perturbations are
equally likely. 16-member CCM3 ETKF ensemble initially
centered by the new method is found to be more skillful
than that centered by the positive-negative paired
method.
A new ensemble postprocessing method that reduces
seasonally averaged second moment errors of the ensemble
forecasts is introduced. The method involves adding
(“dressing”) independent sets of statistical
perturbations to each member of a dynamical ensemble
forecast. The new dressing method mathematically
constrains the stochastic process used to generate the
statistical perturbations so that it entirely removes
seasonally averaged errors in the second moment measures.
ETKF ensembles dressed with this new method are found to
be more skillful than the undressed ETKF ensembles. It is
shown that the previously proposed “best
member” dressing method fails to reliably predict
the second moment of the distribution of forecast errors
whereas the new dressing method reliably predicts this
second moment.
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Title: Spatial and temporal scales of precipitating tropical
cloud systems
Pub No: 3071048
Author: Wilcox, Eric Martin
Degree: PhD
School: UNIVERSITY OF CALIFORNIA, SAN DIEGO
Date: 2002
Pages: 131
Adviser: Ramanathan, V.
ISBN: 0-493-90927-3
Source: DAI-B 63/11, p. 5293, May 2003
Subject: PHYSICS, ATMOSPHERIC SCIENCE (0608); GEOPHYSICS (0373);
REMOTE SENSING (0799)
Abstract: Precipitation, radiative forcing, and aerosol scavenging
in tropical cloud systems over the wintertime Indian
Ocean are examined in satellite observations and global
atmospheric simulations. Measurements of surface rain
rate and top-of-atmosphere radiative fluxes from the TRMM
satellite, as well as brightness temperature measurements
from the METEOSAT-3 satellite, are used to identify the
boundaries of cloud systems, track their evolution, and
determine the spatial and temporal scales of cloud
thermodynamic forcing. The resulting quantitative,
statistical description of monsoonal cloud systems is
compared with simulated cloud systems in the NCAR CCM3
model.
Monsoonal clouds span a spectrum of spatial scales from
smaller than 25 km<super>2</super> to greater than
10<super>7</super> km<super>2</super>. Atmospheric
heating owing to precipitation and the cloud greenhouse
effect, as well as surface cooling owing to cloud albedo,
increases with the spatial scale of cloud systems. As a
result, thermodynamic forcing of the monsoonal
environment is dominated by the contribution from giant
semi-permanent decks of overcast cloud that persist for
days to weeks. Embedded within such cloud decks are
numerous rain cells reaching up to 1 million square-
kilometers because deep convection organizes into
clusters of narrow overturning cells attached to a broad
stratiform region of precipitation. A relatively few such
mesoscale convective systems are greater than
10<super>5</super> km<super>2</super>, yet are
responsible for up to 70% of monsoonal precipitation. In
contrast, simulated cloud systems in the model gently
precipitate throughout their duration and everywhere
within their boundaries. The model lacks a process that
acts to organize convection into mesoscale episodic
structures.
Precipitation is the principal means by which particulate
pollution is removed from the atmosphere. The effect of
model biases in the distribution of precipitation is
tested by integrating satellite precipitation
measurements into the MATCH chemical transport model.
Mesoscale convective systems in the equatorial Indian
Ocean are a substantial barrier to the transport of
aerosols from South Asia to the Southern Hemisphere.
Using observations of the spatial coverage of
precipitation in the model reduces the amount of South
Asian aerosol transported to the remote Northern
Hemisphere by more than a factor of 2 compared to a
simulation using model derived precipitation.
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Title: Biome-scale vegetation dynamics in North America since
the last glacial maximum: Maps and reconstructions from
fossil pollen data and the testing of biogeography models
Pub No: 9987861
Author: Williams, John Warren
Degree: PhD
School: BROWN UNIVERSITY
Date: 2000
Pages: 266
Adviser: Webb, Thompson III
ISBN: 0-599-94261-4
Source: DAI-B 61/09, p. 4630, Mar 2001
Subject: PALEOECOLOGY (0426); PALYNOLOGY (0427)
Abstract: The changing biome distributions reconstructed from
fossil pollen data illustrate the dynamic nature of the
vegetation in boreal and eastern North America since the
last glacial maximum, 21,000 years ago. Biomes, defined
as mixtures of plant functional types, emphasize
structural changes in the vegetation in response to
climate change. A primary use of these data-based biome
maps is to test simulations produced by atmospheric
general circulation models (AGCM's) and vegetation
models.
Biome maps for 6000 and 18,000 radiocarbon years B.P.
were created as part of an international effort to
assemble global paleovegetation maps for model testing.
The biome reconstructions for 6000 years B.P. serve as a
benchmark for a series of detailed evaluations of the
biogeography models BIOME1 and BIOME3. A 2 x 2 factorial
set of biome simulations was performed in which climate
simulations for 6 rka from CCM1 and CCM3 each were used
to run BIOME1 and BIOME3. Only the biome simulation
produced by CCM1 and BIOME3 matched the data well.
Sensitivity analyses revealed the poor performance of the
CCM3/BIOME3 simulation primarily was caused by BIOME3
being overly sensitive to secondary influences such as
cloud cover and soil characteristics. This sensitivity
builds a greater uncertainty into the BIOME3 simulations,
particularly because cloudiness may not be accurately
simulated by AGCM's.
Biome distributions and individual pollen taxon
abundances were mapped at 1000-year intervals to explore
vegetation dynamics in eastern North America. Pollen
assemblages without any close modern analog prevailed
adjacent to the Laurentide Ice Sheet between 17,000 and
12,000 kcal. These “no-analog” pollen samples
indicate that late-glacial plant associations were unlike
any today. Distinguished by the intermixing of boreal
taxa with temperate taxa and herbs, these no-analog
communities were likely a mixed parkland. CCM1
simulations suggest that the no-analog vegetation grew
under highly seasonal and dry climates. The temporal and
spatial distribution of the no-analog vegetation strongly
corresponds to the distribution of no-analog climatic
conditions simulated by CCM1. The fastest rates of
climatic and vegetation change occurred after the peak
periods of no-analogs. Together, these lines of evidence
support the hypothesis that vegetation is in equilibrium
with climate at millennial timescales.
------------------------------------------------------------
Title: Optimal climate change signal detection using space-time
empirical orthogonal functions
Pub No: 9969031
Author: Wu, Qigang
Degree: PhD
School: TEXAS A&M UNIVERSITY
Date: 2000
Pages: 116
Adviser: North, Gerald R.; Kim, Kwang-Yul
ISBN: 0-599-73836-7
Source: DAI-B 61/04, p. 1998, Oct 2000
Subject: PHYSICS, ATMOSPHERIC SCIENCE (0608); APPLIED MECHANICS
(0346)
Abstract: Space-time optimal filtering is used to estimate the
response of the Earth's surface temperature to both
natural and anthropogenic climate forcings over the past
century. In this study, a variety of site/record-length
configurations is used to represent the climate change
signals, natural variability and observational data
streams. The hypothesized space-time patterns of the
response to the climate forcings are generated from an
energy balance climate model (EBCM) and four coupled
ocean/atmosphere general circulation models (GCMs). The
natural variability statistics are estimated from 1000-
year control runs from four coupled GCMs and then such
natural variability is represented precisely in terms of
the space-time empirical orthogonal functions (EOFs),
obtained directly from the lagged space-time covariance
matrix on the approximate time interval. Optimal filters
are constructed using the hypothesized space-time
patterns along with the EOF-represented natural
variability. The constructed filters are then applied to
the observational surface temperature data. With a
proposed orthogonalization process, signals ‘not-
of-interest’ are optimally removed from the data
stream in the estimation process.
Comparisons show that the responses to the anthropogenic
climate forcings generated from the EBCM and four GCMs
are very similar to each other. A robust greenhouse-gas
signal is detected in the observational surface
temperature data, but with a weak amplitude only about
60–70% of that expected from the hypothesized
signal patterns. An anthropogenic aerosol signal is very
weak and not statistically significant. The estimated
amplitude of aerosol indicates that four GCMs in this
study might overpredict the response to greenhouse gas-
plus-aerosol forcing by a factor of two to five. A
volcanic signal is also robust but with about 65%
expected amplitude. A solar-cycle signal is significant
at a level of 90% and somewhat stronger than the
amplitude of the EBCM-predicted response to the 11-year
component of the solar luminosity variations.
A simplified version of NCAR Community Climate Model
(CCM2) is used to generate natural variability and an
artificial solar signal for the optimal filtering scheme.
A theoretical examination of whether detection
performance could be enhanced by the addition of
vertically distributed spatial information rather than
information only on the surface is presented.
------------------------------------------------------------
Title: Single-column modeling: Methodology and application to
the evaluation of cumulus convection schemes in GCMs
Pub No: 9927551
Author: Xie, Shaocheng
Degree: PhD
School: STATE UNIVERSITY OF NEW YORK AT STONY BROOK
Date: 1998
Pages: 126
Adviser: Zhang, Minghua
ISBN: 0-599-27273-2
Source: DAI-B 60/04, p. 1657, Oct 1999
Subject: PHYSICS, ATMOSPHERIC SCIENCE (0608)
Abstract: I have studied two subjects on single-column modeling in
this thesis: One is related with interfacing single-
column models (SCMs) with observations. The other is
related to the causes of large errors in SCM simulations.
Problems with the discrepancy in the time resolution
between observations and SCMs were studied through
modeling sensitivity tests. These include study of the
model sensitivity to time steps and to the time-averaged
large-scale forcing. Experiments show that most of the
simulation results are sensitive to time steps but
insensitive to the use of time-averaged large-scale
forcing within the 3-hour time period (the typical
sampling frequency of observations). The SCM, along with
a 3-hour time step, produces serious errors and causes
computational instability. Therefore, a time step, that
is the same as used in GCMs, is the most optimal time
step for SCMs.
Causes of large errors in SCM simulations were
investigated by focusing on deficiencies in the model
cumulus parameterizations. Three cumulus convection
schemes were implemented in the NCAR CCM3 Single-Column
Model and were evaluated by the ARM 1995 summer Intensive
Observing Period (IOP) data. They are the CCM3 deep
convection scheme, the moist convective adjustment (MCA)
scheme, and the KUO scheme. The simulation results show
that the SCM with the CCM3 deep convection scheme
produces large warm and dry biases, while the SCMs with
the other two convection schemes produce large cold and
wet biases.
The triggering conditions of convection in these three
schemes have been found to account for a significant part
of these biases. Based on the observations, a
modification is made to the triggering condition of the
CCM3 deep convection scheme to account for the dynamical
influences of circulation on the initiation of
convection. The modified scheme is tested using the ARM
data. Improved simulation results were obtained.
Modifications of triggering conditions were also made to
the MCA and KUO schemes to illustrate possible
improvements to SCM simulations.
Additional tests were made to the CCM3 deep convection
scheme by using the ARM 1997 summer IOP and the GATE
phase III data. These tests confirm the results obtained
from the ARM 1995 experiments.
------------------------------------------------------------
Title: Intraseasonal oscillation in an idealized general
circulation model
Pub No: 9634876
Author: Yi, Yuhong
Degree: PhD
School: TEXAS A&M UNIVERSITY
Date: 1996
Pages: 94
Adviser: North, Gerald R.
Source: DAI-B 57/06, p. 3796, Dec 1996
Subject: PHYSICS, ATMOSPHERIC SCIENCE (0608); GEOPHYSICS (0373)
Abstract: The intraseasonal oscillations (ISOs) that appear in the
perpetual equinox simulation of a spectral general
circulation model (GCM) have been systematically studied.
The NCAR Community Climate Model (CCM2, R15) has been
implemented on an idealized planet with no ocean and no
topography and with uniform boundary conditions, such as
constant vegetation and surface albedo, and also has been
integrated for 15 years.
The wave-frequency distributions at different latitudes,
obtained from space-time spectral analysis, show that
well-defined spectral peaks occur in the eastward
propagating wave components of the zonal and meridional
winds, especially in the wavenumber one component which
has a period of about 40 days. Wavenumber 2 travels at a
slightly slower phase speed and takes about 50-54 days to
encircle the globe once.
A phase-shifting composite procedure has been used to
further demonstrate the three-dimensional spatial
structure of the model's ISO. The horizontal structure of
the simulated oscillation is dominated by the eastward-
moving wavenumber 1; wavenumber 2, however, is also
important and its amplitude is about half that of
wavenumber 1. ISOs exhibit a baroclinic structure in the
tropics but a barotropical structure in the extratropics.
These results suggest that ISOs are internally generated
and maintained by the model dynamics and physics.
A newly-developed time-varying spectral analysis has been
used to study the characteristics of the temporal
evolution of the intraseasonal oscillation, and thus to
explore the mechanism of ISO maintenance. The most
interesting and striking result is that the internally
generated intraseasonal oscillation exhibits an episodic
feature, referred to as intermittency of ISO. Large- and
small-amplitude oscillations occur intermittently.
Although intermittency is a frequently observed feature
in nonlinear and turbulent flows, it appears to be the
first time that such intermittency has heen documented in
such model studies of the intraseasonal oscillation.
The relationship between the zonal-mean flow and low-
frequency waves has been investigated by using the EOF
analysis. The results show that intense ISOs are
associated with weak, broad and poleward-shifted
subtropical jets as well as intense westerlies in the
upper tropics; less intense ISOs are associated with
strong, narrow and equatorward-shifted subtropical jets.
This finding suggests that nonlinear interactions between
the zonal-mean flow and low-frequency waves may be
important for maintaining the episodic feature of the
intraseasonal oscillations.
------------------------------------------------------------
Title: Validation of the coupled NCEP mesoscale spectral model
and an advanced land surface model over the Hawaiian
Islands
Pub No: 3151140
Author: Zhang, Yongxin
Degree: PhD
School: UNIVERSITY OF HAWAI'I
Date: 2004
Pages: 207
Adviser: Cheng, Yi-Leng
ISBN: 0-496-11098-5
Source: DAI-B 65/10, p. 5195, Apr 2005
Subject: PHYSICS, ATMOSPHERIC SCIENCE (0608); ENVIRONMENTAL
SCIENCES (0768)
Abstract: The National Centers for Environmental Prediction (NCEP)
Mesoscale Spectral Model (MSM) coupled with an advanced
Land Surface Model (LSM) is used in assessing the impact
of the improved representation of island terrain and
surface boundary conditions on simulating orographic
effects and local circulations under various large-scale
settings.
The surface variables predicted by the operational 10-km
Regional Spectral Model (RSM) during a one-month period
of 20 May through 20 June 2002 agree well with
observations over the buoy stations in the Hawaiian
waters. Over land with adequate representation of the
terrain, the 1.5-km MSM provides better forecasts of
surface variables than the 10-km RSM. Further
improvements are achieved by coupling the MSM with the
LSM. In particular, over-estimation of the surface wind
speed and daytime cold biases in the MSM are largely
corrected in the coupled MSM/LSM. The observed composite
diurnal cycles of surface variables are also better
forecasted by the MSM/LSM than the MSM.
Evaluations of the 3-km MSM/LSM simulations are performed
for sea breeze cases during 23 June to 28 June 1978 over
northwest Hawaii. Except for 27 June, the model predicted
onset time, duration and vertical extent of the sea
breezes agree with observations. Sensitivity tests using
the MSM/LSM demonstrate the non-trivial effects of
surface properties and initialization processes on sea
breeze behavior.
Heavy rainfall and high wind events over the Hawaiian
Islands display a large variability in rainfall and wind
distribution related to complex terrain and local winds.
The 10-km RSM/LSM reasonably resolves regional-scale
weather features associated with significant synoptic
systems but fails to accurately reproduce rainfall
distribution and rate, and orographically amplified
strong winds. The MSM/LSM, with its higher resolution
(≤3 km), has better capability in simulating localized
rainfall distributions and airflows associated with these
heavy rainfall and high wind events.
Major model bias is that the MSM/LSM produces excessive
rainfall on the windward side of steep mountains with
little rainfall downstream of the mountain ranges.
------------------------------------------------------------
Title: An algorithm for retrieving surface downwelling longwave
radiation: A study of interactive physical mechanisms
Pub No: 9958706
Author: Zhou, Yaping
Degree: PhD
School: STATE UNIVERSITY OF NEW YORK AT STONY BROOK
Date: 1999
Pages: 131
Adviser: Cess, Robert D.
ISBN: 0-599-62066-8
Source: DAI-B 61/01, p. 348, Jul 2000
Subject: PHYSICS, RADIATION (0756); PHYSICS, ATMOSPHERIC SCIENCE
(0608)
Abstract: In this thesis, a new algorithm for retrieving the
surface downwelling longwave flux is developed based on a
detailed study of radiation models and observational
data. The radiation models used in this study, the Column
Radiation Models (CRM) from the National Center for
Atmospheric Research (NCAR) community climate model (CCM)
version2 and version3 and the Moderate Resolution
Transmittance (MODTRAN3) Code, are validated with the
CAGEX (CERES/ARM/GEWEX) project version 1.1.2 data taken
at the Atmospheric Radiation Measurement (ARM) Program
Oklahoma Central Facility. Results show that the accuracy
of the radiation model is quite consistent with the
models' level of complexity for clear skies. For cloudy
skies, the cloud input parameters from various
instruments need careful examination and preprocessing.
The discrepancy between model calculations and
observations can be significantly reduced by choice of
input parameters and by tuning the optical properties
within the models.
Detailed sensitivity tests are conducted on the CCM3CRM
to study the effect of atmospheric temperature and water
vapor profiles upon the clear sky surface and top of
atmosphere outgoing longwave fluxes. The study shows that
the surface downwelling longwave flux can be largely
determined from only two parameters: the surface
upwelling longwave flux and the total precipitable water
vapor. Cloudy sky sensitivities are conducted with both
CCM3CRM and Modtran3. Both models find the cloud base
height to be the most important factor determining the
surface downwelling longwave, especially for low clouds.
However, when considering partial cloud cases in the real
world, column cloud liquid water seems to be a better
parameter for the cloudy sky algorithm.
The ARM observations at the Oklahoma Central Facility and
the Tropical Western Pacific (TWP) Manus Island are used
in deriving and validating the algorithm. The
observations show similar relations found in the
sensitivity tests for both clear skies and all skies. An
algorithm is derived based on 6 Intensive Observational
Period (IOP) data set at the Oklahoma Central Facility
The rms error of this algorithm ranges from 5.8% for the
data taken at the same location and 2.5% for the TWP data
set.
The generality of this algorithm is further demonstrated
with CCM3 simulation data. A single algorithm can be
applied to six geographically different areas, with rms
errors ranging from 1.4% to 5.5%. However, the algorithm
has not been tested with data from polar regions where
clouds are mainly in the form of ice. Large errors are
possible for such regions and modifications may be
necessary.
This algorithm only requires three input parameters: the
surface upwelling longwave radiation, the total
precipitable water vapor and column cloud liquid water.
The column cloud liquid water used in this study is
measured by surface microwave radiometer. It would be
beneficial if cloud liquid water were more accurately
measured by satellite in the future.
------------------------------------------------------------
Title: An analysis of observation and GCM simulations of
seasonal cycle of monsoon climate in Southeast Asia and
Tibet Plateau
Pub No: 9967726
Author: Zhu, Li
Degree: PhD
School: STATE UNIVERSITY OF NEW YORK AT ALBANY
Date: 2000
Pages: 185
Adviser: Bakhru, Hass
ISBN: 0-599-72446-3
Source: DAI-B 61/04, p. 1998, Oct 2000
Subject: PHYSICS, ATMOSPHERIC SCIENCE (0608)
Abstract: Atmospheric general circulation models have been used for
climate study. Evaluation of the GCM ability to simulate
the observed climate features can identify the models'
inadequacy so that further improvement can be made. The
research diagnoses GCM simulation of East Asian Climate,
and is a part of a subproject in the Atmospheric Model
Intercomparison Program and Coupled Model Intercomparison
Program. We used three AMIP models and two CMIP models.
Four land and oceanic regions in East Asia are chosen for
the diagnostic study. In addition, the Tibetan Plateau is
included due to its importance to the monsoon system.
Monthly observational data and GCM simulations for the
AMIP period 1979–1993 are used. The work focuses on
seasonal cycles of surface temperature and precipitation,
although other climate parameters such as outgoing
longwave radiation, wind and surface energy balance
components are also examined.
ECHAM4 seasonal cycles fit observation the best, with
correlation coefficients above 0.9 for precipitation and
almost 1.0 for surface temperature. Other model
performances are fair. NTU-GCM can simulate particular
detailed seasonal cycles: the precipitation summer
retreats in the South China Sea and the Indo-China
Peninsula. But at the same time its precipitation cycle
is 78% larger in the Bay of Bengal, showing its
inconsistency for different domains. NCAR-CCM3
systematically underestimates the seasonal cycle strength
in the oceanic domains. Particularly, it underestimates
the precipitation seasonal cycle 75% in the South China
Sea and the Tropical Western Pacific.
NCAR-CSM simulates SST seasonal cycles well compared with
observation, within 5% discrepancy and improves
substantially the summer precipitation of CCM3.
Especially in the South China Sea and the Tropical
Western Pacific, CSM has summer precipitation of 11.6 and
12.2 mm/day, compared with observation 11.1 and 9.4
mm/dcy (CCM3 has 5.37 and 5.49 mm/day respectively). The
improvement in summer precipitation is mainly due to
improved surface wind (from 2.6 ms<super>
−1</super> in CCM3 to 10.4
ms<super>−1</super> in CSM, which enhances the
latent heat flux). Therefore the effect of air-sea
interaction plays an important role in NCAR GCM.
However, the comparison of MPI GCMs does not show the
similar improvement for including the air-sea
interaction.
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