Model GISS (Miller): Elaborations
Model GISS (Miller) is an entry in the CMIP1 intercomparison only.
The procedure for spinup/initialization to the simulation starting
of the coupled model is as follows (cf. Miller
and Jiang 1996):
- The atmospheric model was integrated for a decade with AMIP
- The computed surface winds then were used to force the ocean
restoring the SST and SSS to Levitus (1982) annual-mean values. The
model was integrated for 6000 x 365 ocean-tracer time steps (equivalent
to 6000 years of the tracer field, with time step length of 1 day).
- Seasonally varying values of SST and SSS then were used to force
model for an additional 500 years, with the tracer time step reduced
1 day to 4 hours.
- At this point, the globally integrated surface energy flux
to the difference between the Levitus temperature and the first model
temperature) was < 0.001 W m-2, and the ocean and atmosphere models
- The coupled model was integrated for 110 years without flux
Land Surface Processes
- Soil temperature is computed by solving a heat diffusion equation
layers. The thickness of the top layer varies, but is approximately 0.1
m. The thicknesses of deeper layers increase geometrically, with the
boundary of the soil column at a nominal bedrock depth of 3.444 m. The
upper boundary condition is the balance of surface energy fluxes; at
bottom boundary, zero net heat flux is specified. The thermal
and heat capacity of the ground vary with snow cover, as well as soil
amount and phase.
- Land-surface hydrology is treated after the
model of Abramopoulos et al.
The scheme includes a vegetation canopy, a composite over each grid box
from the vegetation types of Matthews
that intercepts precipitation and dew. Evaporation from the wet canopy
and from bare soil is treated, as well as soil-moisture loss from
according to moisture availability and variable vegetation resistance
root density. Diffusion of moisture is predicted in the six soil
accounting for spatially variable composite conductivities and matric
that depend on soil type and moisture content. Infiltration of
and snowmelt is explicitly calculated, with surface runoff occurring
the uppermost soil layer is saturated; underground runoff that depends
on topographic slope also is included.
- Sea ice is represented by the two-layer model of Hansen
et al. (1983), where the top layer simulates accumulating snow up
a depth of 0.1 m. When this threshold depth is exceeded, 0.01m of
the snow is added to the lower layer as ice, thereby keeping the upper
layer thin enough to simulate diurnal temperature changes. A fraction
an ocean grid square may be covered by ice at a thickness that is a
of the fractional coverage.
- The snow-free albedo of sea ice is 0.55 in the visible
0.7micrometers) and 0.3 in the near-infrared, resulting in a spectrally
weighted ice albedo of 0.45.
- Sea ice dynamics and rheology are neglected.
Chief Differences from Closest
The atmospheric component of the GISS (Miller) coupled model (internal
designation: Model B122AM9) differs from AMIP model GISS
Model II Prime (4x5, L9) 1994 (internal designation: Model B150AM9)
mainly in the following respects:
A linear upstream scheme is used for the advection of tracers,
than the AMIP
model's more accurate quadratic advection scheme.
The model lacks the improved
used in the AMIP
Rather than calculating radiative fluxes at every horizontal grid
as in the AMIP
model, these fluxes are computed only at every other horizontal
point, using interpolation to obtain values at intermediate grid
The land surface hydrology
is somewhat less sophisticated than that of the AMIP
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)
Hansen, J., G. Russell, D. Rind, P. Stone,
A, Lacis, S. Lebedeff, R. Ruedy, and L. Travis, 1983: Efficient
global models for climate studies: Models I and II. Mon. Wea. Rev.,
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, R.L., and X. Jiang,
Surface energy fluxes and coupled variability in the Tropics of a
General Circulation Model. J. Climate, 9,
CMIP Documentation Directory
Last update 15 May, 2002. This page is maintained by Tom