Go to SUNYA References
Dr. Wei-Chyung Wang and Dr. Xin-Zhong Liang, Atmospheric Sciences Research Center, State University of New York at Albany, 100 Fuller Road, Albany, NewYork 12205; Phone: +1-518-442-3816; Fax: +1-518-442-3360; e-mail: wang@climate.asrc.albany.edu (Wang) and liang@climate.asrc.albany.edu (Liang); World Wide Web URL: http://www.atmos.albany.edu/das.html
SUNYA CCM1-TG (R15 L12) 1990
The SUNYA model is identical to the standard version 1 of the NCAR Community Climate Model (CCM1), except for the addition of radiatively active trace gases other than carbon dioxide. The resulting modified CCM1 is designated as CCM1-TG (see Model Designation).
Key documents for the standard CCM1 model are Williamson et al. (1987) [1], Kiehl et al. (1987) [2], and Bath et al. (1987a [3], b [4]) Wang et al. (1991a [5], b [6]) describe the treatment of radiative effects of trace gases that are added to CCM1.
Spectral (spherical harmonic basis functions) with transformation to a Gaussian grid for calculation of nonlinear quantities and some physics.
Spectral rhomboidal 15 (R15), roughly equivalent to 4.5 x 7.5 degrees latitude-longitude.
Surface to 9 hPa; for a surface pressure of 1000 hPa, the lowest atmospheric level is at 991 hPa.
Sigma coordinates, with energy-conserving vertical finite-difference approximations (cf. Williamson 1983 [8], 1988 [9]).
There are 12 unevenly spaced sigma levels. For a surface pressure of 1000 hPa, 3 levels are below 800 hPa and 5 levels are above 200 hPa.
The AMIP simulation was run on a Cray 2 computer using a single processor in a UNICOS environment.
For the AMIP experiment, about 1.2 minutes Cray 2 computer time per simulated day.
For the AMIP experiment, initial conditions for the atmospheric state, soil moisture, and snow cover/depth were specified from the NCAR CCM1 model's standard January initial dataset (cf. Bath et al. 1987a [3]). The model then was "spun up" for 210 days in a perpetual January mode. The resulting climate state was then taken as the 1 January 1979 starting point for the AMIP simulation.
Time integration is by a semi-implicit Hoskins and Simmons (1975) [27] scheme with an Asselin (1972) [7] frequency filter. The time step is 30 minutes for dynamics and physics, except for full (at all Gaussian grid points and vertical levels) radiation calculations which are done once every 12 hours (see Solar Constant/Cycles.
Orography is smoothed (see Orography). Negative values of atmospheric specific humidity (which arise because of numerical truncation errors in the discretized moisture equation) are filled by horizontal borrowing of moisture in a globally conserving manner. See also Convection.
For the AMIP simulation, the model history is written once every 12 hours.
Primitive-equation dynamics are expressed in terms of vorticity, divergence, potential temperature, specific humidity, and surface pressure.
Gravity-wave drag is not modeled.
The solar constant is the AMIP-prescribed value of 1365 W/(m^2). A seasonal, but not a diurnal cycle, in solar forcing is simulated.
The carbon dioxide concentration is the AMIP-prescribed value of 345 ppm. The vertical distribution of zonal-mean mixing ratios of ozone is specified from monthly data of Dütsch (1978) [11], updated by linear interpolation every 12 hours. The radiative effects of water vapor and oxygen, as well as methane, nitrous oxide, and chlorofluorocarbon compounds CFC-11 and CFC-12 also are included, but not those associated with aerosols (see Radiation).
Moist convective adjustment after the method of Manabe et al. (1965) [19] performs several functions: removal of negative atmospheric moisture values (operating with a scheme for horizontal borrowing of moisture--see Smoothing/Filling); dry convective adjustment of unsaturated, unstable layers in the model stratosphere, with vertical mixing of moisture; and moist static adjustment of saturated unstable layers and of supersaturated stable layers.
Cloud forms in layers where the relative humidity exceeds 100 percent. If the vertical lapse rate of the layer also exceeds the moist adiabatic value, convective cloud forms (see Convection); otherwise, the cloud is nonconvective, and the fractional cloud cover is set to 0.95 in the layer. Convective cloud cover depends on the depth of the vertical instability, with the cloud amount in each layer adjusted so that the total fractional area is at most 0.30. If there is no associated precipitation (see Precipitation), a minimum convective cloud fraction of 0.01 is specified in each layer. Cloud is not allowed to form in the lowest model layer or in the top 3 layers, but clouds form together in the second and third layers above the surface if either of these layers is supersaturated. Cf. Kiehl et al. 1987 [2] for further details. See also Radiation for treatment of cloud-radiative interactions.
Precipitation results from application of convective adjustment (see Convection), if the vertical column is supersaturated with a lapse rate exceeding moist adiabatic. Precipitation also results if the column is supersaturated but with a stable lapse rate. There is no subsequent evaporation of precipitation before it falls to the surface.
The height of the PBL top is assumed to be that of the first level above the surface (sigma = 0.991), except for the calculation of a bulk Richardson number (see Surface Fluxes). In that case, the PBL top is computed from the temperature at the first sigma level but is constrained to be at least 500 m.
After interpolation of 1 x 1-degree Scripps Institution surface height data (cf. Gates and Nelson 1975 [20]) to the model grid, the data are smoothed using a Gaussian filter with 1.5-degree radius. The resulting heights are transformed into spectral space and truncated at the R15 model resolution. Cf. Pitcher et al. (1983) [21] for further details.
AMIP monthly sea surface temperature fields are prescribed, with daily values determined by linear interpolation.
Monthly AMIP sea ice extents are prescribed. The ice thickness is assumed to be a uniform 2 m, and the sub-ice ocean temperature is specified as a fixed 271.2 K. The surface temperature of the sea ice is computed prognostically by determining heat conduction from the underlying ocean through the ice, following the method of Holloway and Manabe (1971) [22]. Sea-ice surface temperature is constrained to be always < 0 degrees C (ice melting is not treated), and snow is not allowed to accumulate on the ice (see Snow Cover).
Precipitation falls as snow if the temperatures of the surface and the first two atmospheric levels above it are all < 0 degrees C. Snow cover is determined from a combination of a monthly latitude-dependent climatology (cf. Bath et al. 1987a [3]) and prognostic snow accumulation (on land only) that is determined from a budget equation. A surface temperature > 0 degrees C triggers snowmelt, which augments soil moisture (see Land Surface Processes). Snow cover is also depleted by sublimation, which is calculated as part of the surface evaporative flux (see Surface Fluxes).
Go to SUNYA References
Return to SUNYA Table of Contents
Return to Main Document Directory
UCRL-ID-116384