NCAR CSM Pacific Basin Model, version 3.e -- User's Guide
Table of Contents
The NCAR Pacific basin model is based on the upper equatorial ocean
model of Gent and Cane (1989). It has been updated and improved by
the addition of the K-profile parameterization (KPP) boundary layer
scheme of Large et al. (1994). It is a primitive equation model
based on the reduced gravity assumption, so that the constant density
deep ocean is at rest below the active upper ocean. The depth of the
active ocean varies in time and space, but the mean depth is
independent of time and is usually chosen to be 400m.
The model domain is the tropical Pacific Ocean from 30°S to 30°N.
The model consists of a fixed depth upper layer and
the remainder of the active ocean is divided into an arbitrary number
of numerical layers by means of a sigma coordinate. Only temperature
is predicted in the model, so that the ocean salinity is taken to be
constant. Horizonal mixing is achieved by Shapiro filtering and the
vertical viscosity and diffusivity are functions of the local vertical
Richardson number. The time--stepping scheme is that due to Lorenz.
Full details of the continuous equations and numerical algorithms can
be found in Gent and Cane (1989) and Gent (1991). Details of the KPP
scheme and its numerical implementation can be found in Large
et al. (1994) and the NCAR Technical Note on the NCAR CSM ocean model.
The wind stress and heat flux to force the model are determined as follows.
Input required to determine these forcings are the atmospheric surface wind velocity,
u, and the fractional cloud cover, C.
The model has mostly been forced using the monthly pseudostress climatology from
Florida State University and the fractional cloud cover from the ISCCP C1 data set.
The wind stress and heat flux are given by
aa CDu|u| ,
|| = Qsol - Qlat - Qsen - Qlgw ,
|| = (1-A) (1-aCLD * C + aALPHA* ) Qo ,
|| = a
LCE|u| [q(SST) - RH*q(Tatm)] ,
|| = a
Cp CH |u| (SST - Tatm) ,
[SST4 [0.39 - 0.05 exp(½)] (1 -
bCLD*C²) + 4 * SST³ (SST-Tatm)] ,
|| = 6.4 * 108 exp [ -5105 / T ] ,
|| = [5*SST (°C) + 22]/ 6.
is the solar altitude, Qo is the clear sky flux, A is
albedo and RH is relative humidity. The formulae for Qlat, Qlgw and q
require the temperatures to be in degrees Kelvin. Default values for
coefficients are A=0.06, aCLD=0.75, aALPHA=0.002, RH=0.75 and
bCLD=0.6. The solar flux, Qsol, is distributed in the upper three
layers of the model according to Jevlov water type Ib with 33% of the
flux being absorbed exponentially with depth with an e-folding scale
of 17m. Finally, a minimum wind speed, WNDmin, can be set in the
formulae for Qlat and Qsen, and for monthly wind forcing this has
mostly been set to 4m/s.
Gent, P. R., and M. A. Cane, 1989: A reduced gravity, primitive
equation model of the upper equatorial ocean.
. Comp. Phys., 81, 444-480.
Gent, P. R., 1991: The heat budget of the TOGA--COARE domain in
an ocean model. J. Geophys. Res., 96, 3323-3330.
Large, W. G., J. C. McWilliams and S. C. Doney, 1994: Oceanic vertical
mixing: A review and a model with a nonlocal boundary layer
parameterization. Rev. of Geophys., 32, 363-403.