Model MRI1: Elaborations
Model MRI1 is an entry in the CMIP1 intercomparison only.
The procedure for spinup/initialization to the simulation starting point
of the MRI coupled model is as follows (reference: Tokioka
et al. 1996):
The atmospheric model was integrated for 2.5 years with observed AMIP SST/sea
The ocean model was integrated by the acceleration method of Bryan (1984)
for 1000 years from an initial rest state with uniform potential temperature
(1.5 deg C) and salinity (34.65 ppt). The surface momentum, energy,
and freshwater (P-E) fluxes obtained from the atmospheric model integration
were used as forcing at the ocean's upper boundary. In addition,
the temperatures and salinities of the uppermost ocean layer were relaxed
toward the SSTs used in the atmospheric run and towards the seasonally
varying Levitus (1982) SSS data.
In order to obtain more realistic sea ice extents, the integration of the
ocean model was extended an additional 500 years using the same atmospheric
forcing, but with relaxation of the temperature and salinity of the upper
ocean (upper 130 m southward of 70 N and upper 30 m northward of 70 N)
to modified climatological Levitus (1982) SST
and SSS data. The modification involved resetting the ocean mixed-layer
temperature in the regions of sea ice to the freezing temperature
calculated from salinity.
The atmosphere and ocean models then were coupled and integrated for 30
years with sea ice initial conditions obtained from the 1973-1990 Joint
Ice Center sea-ice concentration data. (The initial sea ice thicknesses
were estimated as linear functions of the concentration, with maximum of
3 m in the Northern Hemisphere and 0.5 m in the Southern Hemisphere.)
During this coupled integration, the temperature and salinity of the uppermost
ocean layer were relaxed to the modified Levitus
(1982) climatological SST and SSS data described above. The monthly
means of the relaxation terms over the last 10 years of the coupled integration
were stored as heat and freshwater flux adjustment terms for subsequent
The coupled model was integrated for an additional 70 years with these
flux adjustments which mostly kept the annual mean SST close to Levitus
(1982) values. The greatest deficiency was a weak thermohaline
circulation in the Northern Hemisphere ocean, related to the different
ocean depths used for the relaxations above. (The positive heat flux
adjustments required to maintain the observed SST in the North Atlantic
may excessively stabilize the very thin ocean surface layer in the final
stage of ocean spinup, resulting in weak overturning.)
Land Surface Processes
Land surface parameterizations follow Katayama
(1978), with subsequent modifications in the treatment of soil moisture
described by Kitoh et al. (1988). Soil
heat and moisture move along the gradients of temperature and wetness,
respectively. The thermodynamic and hydrologic effects of a vegetation
canopy are not explicitly modeled, however.
The temperature of bare and snow-covered land is predicted in four layers,
and that of glacial ice in a single-layer. The upper boundary condition
is the net balance of surface energy fluxes, while there is zero heat transfer
at the lower boundary. Heat exchange associated with the freezing or melting
of soil moisture and interstitial ice is taken into account. Snow cover
and soil moisture/ice also affect the heat capacity/conductivity of the
surface, but the heat capacity of snow is assumed to be independent of
Soil moisture (in both liquid and frozen form) is predicted in four layers
(with bottom boundaries at 0.10, 0.50, 1.50, and 10.0 m below the surface);
it is augmented by precipitation and snow/ice melt, and is depleted by
surface evaporation and runoff. The evapotranspiration efficiency beta
is set to unity if the fractional soil moisture (the ratio of soil moisture
to the field capacity, assumed to be 20 percent of the volume of a soil
column) is at least 0.5; beta is set to twice the fractional soil moisture
otherwise. When all of the moisture in a soil layer is completely frozen
(freezing begins when the layer temperature falls below 0 degrees C), no
deeper penetration of moisture is allowed. Runoff occurs in any layer that
is either saturated or completely frozen.
Runoff from the land is distributed to the ocean by means of a simple river
routing model. Surface runoff is assumed to instantaneously reach the outlet
of each river basin, which are determined at 4x5-degree resolution from
the drainage basin map of Walter (1957).
Prognostic variables include ice thickness, concentration, velocity, and
internal energy (cf. Mellor and Kantha
1989 ). The salt content of the ice is concentrated in brine
pockets, with the average salinity prescribed as a vertical constant.
The treatment of thermodynamics is similar to that of Semtner
(1976), but with inclusion of an ice concentration parameter A
in each grid box. Surface energy fluxes are calculated separately
for ice and leads, weighted according to their respective fractional areas.
Snow is represented by a top layer and ice by a bottom layer. Snow acts
as a heat insulator and an absorber of incoming radiation during melting;
its sensible heat capacity is neglected. Temperatures are predicted at
the snow surface, the snow-ice interface, the interior ice interface, and
the ice bottom. Melting and freezing rates are calculated at the
ice-atmosphere, ice-ocean, and atmosphere-ocean interfaces.
The ice is advected via reduced (by a constant fraction) surface ocean
Katayama, A., 1978: Parameterization of the
planetary boundary layer in atmospheric general circulation models. Kisyo
Kenkyu Note No. 134, Meteorological Society of Japan, 153-200 (in Japanese).
Kitoh, A., K. Yamazaki, and T. Tokioka,
1988: Influence of soil moisture and surface albedo changes over the African
tropical rain forest on summer climate investigated with the MRI GCM-I.
Meteor. Soc. Japan, 66, 65-86.
Levitus, S., 1982: Climatological atlas of
the world's oceans. NOAA Professional Paper 13, 173 pp.
Mellor, G.L. and L. Kantha, 1989:
An ice-ocean coupled model. J. Geophys. Res., 94, 10,937-10,954.
Semtner, A.J., 1976: A model for the thermodynamic
growth of sea ice in numerical investigations of climate. J. Phys.
Oceanogr., 6, 379-389.
Tokioka, T., A. Noda, A. Kitoh, Y.
Nikaidou, S. Nakagawa, T. Motoi, S. Yukimoto, and K. Takata, 1996: A transient
CO2 experiment with the MRI CGCM: Annual Mean Response.
CGER Supercomputer Monograph Report Vol. 2, CGER-I022-'96, Center for Global
Environmental Research, National Institute for Environmental Studies, Environment
Agency of Japan, ISSN 1341-4356, 86 pp.
Walter, Y. (ed.), 1957: Encyclopedia Britanica
World Atlas. Encyclopedia Britanica, Inc.
CMIP Documentation Directory
Last update 15 May, 2002. This page is maintained by Tom Phillips