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Abstract

A lake parameterization is developed for climatic models. The scheme is
especially designed to simulate the skin temperature of a lake grid at various stages,
such as the stages of an evolution of a thermocline, potential ice formation/destruction,
and snowfall/snowmelt on the ice. It is basically an one column model with a good
vertical resolution. It can deal with salt and fresh water. The only forcing on the lake
model comes from the atmosphere model. For great lake, e.q. the Caspian Sea, also
some horizontal exchange between neighboring grid point is in the model.
In order to develop a general lake model for a climatic model, we have to
consider the characteristics of all the large lakes in the world. The most important
lakes include the Caspian Sea and the Great Lakes. The Caspian Sea occupies six
connected grids points in T42 resolution, and the Great Lakes two-separated grid
points (DKRZ, 1994). The Caspian Sea is a terminal saline lake. It covers 393,000
km2 with depths varying from few meters in the north and 1000 m in the south. The
Volga River supplies the largest river discharge of 7260 m3 s‘1 to the lake (0.77 m yr'1
in increase of sea level of the Caspian Sea). The North Caspian freezes over every
year and a greater part of it is covered with pack ice during the winter (Kosarev and
Yablonskaya, 1994). Skin temperature is a key variable to couple with an atmospheric
model. In order to simulate the skin temperature of a lake such as the Caspian Sea,
temperature of water, ice and snow, salinity, current as well as turbulent kinetic energy
are simulated in the model. The ice forms when the water skin temperature reaches
the freezing point, and the time of ice melt and snowmelt occurs when their skin
temperatures raise to the freezing point, respectively. A theory presented here is to
simulate the skin temperature including periods of snow cover, ice cover and open
water. Different to ocean models, the lake model is very sensitive to the water level.
The model presented here pays special attention to water level calculation.