[an error occurred while processing this directive] [an error occurred while processing this directive] Report of the CCSM Paleoclimate Working Group

Report of the CCSM Paleoclimate Working Group

 

Fifth Annual Community Climate System Model Workshop

Co-Chairs: B. Otto-Bliesner, L. Sloan, and J. Kutzbach

The Village at Breckenridge, 29 June 2000

 

 

The CCSM Paleoclimate Working Group (PWG) met on Thursday, 29 June 2000, in Breckenridge, Colorado, as part of the Fifth Annual CCSM Workshop. The working group meeting was preceded by a presentation by B. Otto-Bliesner in the CCSM plenary session on Tuesday. These presentations brought the community up to date on the capabilities of the CCSM and studies by members of the PWG using the coupled CSM and its component models individually to understand past climates.

 

1. Plenary Talk

 

Bette Otto-Bliesner ("Spatial and Temporal Tropical Pacific Variability in the CCSM") described a simulation with a new version of the CSM that gives significantly better simulation of the tropical Pacific variability, both its magnitude and spatial pattern. Temporal evolution of warm events, which are approximately phase-locked with the seasonal cycle, are consistent with observed ENSO events. The primary model changes were to the ocean component with the inclusion of anisotropic viscosity and a background vertical diffusivity of 0.15 cm2/sec.

 

2. Working Group Talks

 

Caspar Ammann ("Explosive Volcanic Eruptions in the CSM") spoke on including the effects of volcanic aerosols on both long and short wave radiation. The initial study with the CCM examined the response to the Pinatubo eruption in 1991, an eruption well-documented in terms of both the amount of aerosols ejected into the atmosphere and the response of the climate. He will extend his study to include the other major eruptions from 1870 to present using the fully-coupled CSM.

 

Mikie Smith's talk ("Sensitivity of the Climate System to Sea Ice Extents During the Holocene and LGM Based on GCM Modeling"), given by Bette Otto-Bliesner, described simulations with the CCM with prescribed SSTs and sea ice to test the sensitivity of the climate system to changes in sea ice extents in the Northern Hemisphere. She concluded that sea ice reconstructions are critical for paleoclimate studies.

 

Sang-Ik Shin ("CSM Simulations for the LGM") showed results from his CCM and CSM simulations for the Last Glacial Maximum (LGM). His coupled simulation finds a tropical cooling of about 2-3 deg C, or about 1 deg C cooler than CLIMAP, and a North Atlantic thermohaline circulation that is shallower but of similar intensity as in the present-day simulation.

 

Bette Otto-Bliesner ("The Effect of Atmospheric CO2 Levels on Cretaceous Ocean Climate") presented results from fully-coupled CSM simulations for 80 Ma (Million years ago) when the Earth's geography and bathymetry were significantly different than today (no North Atlantic, narrow South Atlantic, large Pacific). The CSM suggests large overturning cells in both hemispheres with sinking at ~60 latitude. The northern branch is located in the Pacific and the southern branch in the southern Atlantic and Indian Oceans.

 

Zav Kothavala ("PaleoCSM Slab Model Sensitivity Simulations with Cretaceous and Present-day Boundary Conditions") compared the sensitivity of Cretaceous and present climate to atmospheric CO2 levels. Both temperature and precipitation increase nonlinearly with higher atmospheric CO2 concentrations. The amount of warming is dependent on the geography.

 

Matt Huber ("Spinup of NCOM: Effects of `Degraded' Boundary Conditions") discussed a technique of spinning up the atmosphere/land and ocean/sea ice models asynchronously for paleoclimate work. He found that the initialization of sea ice is of critical importance.

 

3. Discussion and Recommendations

 

The CSM is being widely used by university users to investigate past climates. A number of simulations have either been completed or are currently integrating that take advantage of the fully-coupled nature of the CSM to understand past climates, including Mid-Cretaceous, Early Eocene, Last Glacial Maximum, mid-Holocene, Pre-Industrial, and CSENT (Climate of the 17th-18th-19th-20th Centuries). The working group members were especially excited about the new capabilities of the CSM in simulating ENSO variability.

 

The PWG members discussed several issues concerning the future of the CCSM that are relevant to their work. A river runoff scheme that is compatible with our understanding of paleotopography and paleocoastlines should be an option in future versions of the CCSM. The group also strongly supported the work of the Biogeochemisry Working Group to include parameterizations for carbon cycling and oxygen isotopes. Concern was expressed on whether work now being done on the land model and the dynamical core of the atmospheric model would be disadvantageous for running the CCSM at more efficient lower grid resolutions. Finally, the PWG members strongly urged the porting of the PaleoCSM codes to computer platforms like the IBM and Compaq as these are the computers available to the community, both at NCAR and elsewhere.


Participants:

 

First Name

Last Name

Email

Joyce

Almaguer-Reisdorf

joycee@alumni.rice.edu

Caspar

Ammann

ammann@ucar.edu

Johanna

Balle

johanna@atmos.berkeley.edu

Jason

Bell

jbell@es.ucsc.edu

John

Bergman

jwb@cdc.noaa.gov

Esther

Brady

brady@ucar.edu

Francis

Bretherton

fbretherton@ssec.wisc.edu

William

Collins

wcollins@ucar.edu

Robert

DeConto

deconto@geo.umass.edu

Mark

Eakin

mark.eakin@noaa.gov

Jay

Fein

jfein@nsf.gov

Rong

Fu

fu@eas.gatech.edu

Andrea

Hahmann

hahmann@atmo.arizona.edu

Marika

Holland

mholland@ucar.edu

Matthew

Huber

mhuber@es.ucsc.edu

Jeffrey

Kiehl

jtkon@ucar.edu

Zavareh

Kothavala

zav@ucar.edu

Chung-Chieng

Lai

cal@lanl.gov

Kira

Lawrence

klawrence@es.ucsc.edu

Samuel

Levis

slevis@ucar.edu

Zhengyu

Liu

zliu3@facstaff.wisc.edu

Natalie

Mahowald

natalie@bren.ucsb.edu

Susan

Marshall

susanm@uncc.edu

Robert

Oglesby

roglesby@purdue.edu

Keith

Oleson

oleson@ucar.edu

Bette

Otto-Bliesner

ottobli@ucar.edu

Elisabetta

Pierazzo

betty@lpl.arizona.edu

Edwin

Schneider

schneide@cola.iges.org

Christine

Shields

shields@ucar.edu

Sang-Ik

Shin

shin@ocean.meteor.wisc.edu

Lisa

Sloan

lcsloan@emerald.ucsc.edu

Mark

Snyder

msnyder@es.ucsc.edu

Bjorn

Stevens

bstevens@atmos.ucla.edu

Dezheng

Sun

ds@cdc.noaa.gov

Michael

Toy

toy@atmos.colostate.edu