Model GISS (Russell): Elaborations
Model GISS (Russell) is an entry in both the CMIP1 and CMIP2
The procedure for spinup/initialization to the simulation starting
of the coupled model is as follows (cf. Russell
et al. 1995).
- The atmospheric model was initialized from the NMC analysis for
- The ocean model was initialized from the Levitus
(1982) temperature and salinity fields. In the upper 1500 m,
the Levitus seasonal climatology was temporally interpolated to obtain
values appropriate for December 1; below 1500 m, Levitus annual-mean
were used. (The Levitus climatologies on 33 vertical levels were
integrated to the 13 layers in the ocean model.) The initial ocean
boundary condition was zero elevation everywhere (i.e., mean sea-level
conditions). All ocean currents were initially 0, but the height
field adjusted soon after the start of coupled integration to conform
that for geostrophic flow. The initial heat and salt in the
straits were calculated by using the ocean values at the two ends of
strait. The initial sea ice distribution was after Walsh
and Johnson (1979) in the Northern Hemisphere, and after Alexander
and Mobley (1976) in the Southern Hemisphere.
- The atmospheric and ocean models were coupled and integrated for
without flux adjustment, the ocean's peak heat transports becoming
stable after about 25 years. Thereafter, a slow climate drift was
evident in the (increasing) sea ice extents in the North Atlantic, the
(weakening) thermohaline circulation, the (decreasing) elevation of the
ocean's free surface, the imbalance of 3.7 W m^-2 in ocean surface
fluxes, and the 0.007 degrees K per year warming in the mass-weighted
integrated ocean temperature.
Land Surface Processes
- Soil temperature is computed by solving a heat diffusion equation
layers, where the upper layer (depth 0.1 m) simulates diurnal
and the lower layer (depth 4 m) seasonal variations. Thermal
and heat capacity vary with snow cover and soil moisture amount and
(i.e., liquid vs solid water). In vegetated regions during winter, the
thermal conductivity also reflects the insulating effects of dead grass
- Soil moisture, predicted in two layers, is expressed as a ratio
water to field capacity, which is a function of surface type and
according to Matthews (1983,
1984). Soil moisture in the upper
reflects short-term variations in hydrological variables, while that of
the lower layer functions as a reservoir. Surface evaporation is
as the product of the fractional wetness of the upper layer and the
evaporation. Moisture diffusion from the lower layer varies seasonally
to account for greater potential for depletion of this reservoir during
the growing season; otherwise, the effects of a vegetation canopy are
explicitly simulated. Runoff is represented as one-half the product of
the fractional wetness of the upper layer and the rainfall rate, with
occuring as needed to keep the fractional wetness no larger than unity.
Cf. Hansen et al.
for further details.
- Runoff is returned to the ocean by means of a river transport
et al. 1994). Runoff instantaneously increases the river and lake
of a grid box, which is also affected by the local balance of
and evaporation. For each continental grid box, a river direction file
indicates the downstream routing to one of the 8 neighboring grid
The mass flux out of a grid box is computed as a function of the river
and lake mass that lies above the local sill depth, an effective flow
that depends on the local orography gradient, and the mean distance to
the downstream neighbor. Flow speeds are globally optimized to ensure
fresh water arrives at coastal grid boxes with the proper seasonal
- Sea ice forms when the uppermost ocean layer cools below the
of salt water. Ice cover is determined both by energy exchange with the
atmosphere and by ocean heat transport and heat capacity, following Hansen
et al. (1988). Initially, the ice is 0.5 m thick; as it melts, the
ice is contracted horizontally so as to maintain a 0.5 m thickness. The
area of ice leads is calculated after the method of Hansen
et al. (1983): the minimum fraction of open ocean area in a grid
varies inversely with the ice thickness. As sea ice forms or thickens,
the salinity of the uppermost ocean layer increases.
- Snow also may accumulate on the ice, and a two-layer model
temperatures within the ice and the snow pack. When, from consideration
of surface heat balance, the temperature begins to exceed the
melt temperature of 0 deg C, it remains there as long as the ice/snow
continues. If the temperature of the uppermost ocean layer rises
above 0 deg C, the sea ice melts both vertically and laterally, thereby
keeping the ocean temperature at 0 deg C.
- Sea ice is not advected; instead, the atmospheric momentum stress
ice is passed directly to the uppermost layer of the ocean model.
In model development history, the atmospheric model is
"between" the GISS Model II (described by Hansen
et al. 1983) and AMIP model GISS
Model II Prime (4x5 L9) 1994. Cf. Russell
et al. (1995) for further details.
Chief Differences from Closest AMIP Model
The chief differences from this AMIP model include:
The momentum equation is expressed on a C-grid (not
on a B-grid as in the AMIP
model). The linear upstream scheme of Russell
and Lerner (1981) is used for the advection of heat and water vapor.
The convection scheme is after Hansen
et al. (1983), not Del Genio and Yao (1988), as in the AMIP
A diagnostic cloud formation scheme is used
the Del Genio et al. (1993) prognostic formulation in the AMIP
Precipitation is determined diagnostically, rather
prognostically as in the AMIP
The formulation of the PBL is simpler than that of
model, in that surface air quantities are linearly related to
in the first full atmospheric layer and to their vertical gradients.
A simple 2-layer
model is used instead of the Abramopoulos et al. (1988) scheme in
Abramopoulos, F., C. Rosenzweig,
and B. Choudhury, 1988: Improved ground hydrology calculations for
climate models (GCMs): Soil water movement and evapotranspiration. J.
Climate, 1, 921-941. (Abstract)
Alexander, R.C., and R.L.
1976: Monthly average sea-surface temperatures and ice-pack limits on a
1 degrees global grid. Mon. Wea. Rev., 104, 143-148.
Hansen, J., G. russell, D. Rind, P.
Stone, A. Lacis, S. Lebedeff, R. Ruedy, and L. Travis, 1983: Efficient
three-dimensional global models for climatic studies: Models I and II.
Weather Rev., 111, 609-662.
Hansen, J.; I. Fung, A. Lacis, S.
D. Rind, R. Ruedy, and G. Russell. 1988. Global climate changes
forecast by the Giss 3-D model. J.Geophys.Res., 92:
Levitus, S., 1982: Climatological atlas
the world's oceans. NOAA Professional Paper 13, 173 pp.
Matthews, E., 1983: Global vegetation
land use: New high-resolution data bases for climate studies. J.
Appl. Meteor., 22, 474-487. (Abstract)
Matthews, E., 1984: Vegetation,
and seasonal albedo data sets: Documentation of archived data tape.
Tech. Memo. 86107, National Aeronautics and Space Administration,
D.C., 20 pp.
Miller, J.R., G.L. Russell, and G.
Caliri, 1994: Continental scale river flow in climate models. J.
Russell, G.L., and J.A.
1981: A new finite differencing scheme for the tracer transport
Appl. Meteorol., 20, 1483-1498.
Russell, G.L., J.R. Miller, and D.
Rind, 1995: A coupled atmosphere-ocean model for transient climate
studies. Atmosphere-Ocean, 33, 683-730.
Walsh, J., and C. Johnson,
An analysis of Arctic sea ice fluctuations. J. Phys. Oceanogr.,
CMIP Documentation Directory
Last update 15 May, 2002. This page is maintained by Tom