The influence of changing soil moisture and surface albedo on climate is studied with an atmospheric general circulation model (MRI•GCM-I). In a control run (C run), a standard bucket model with a spatially uniform water holding capacity of 15g cm^-2 is used for the ground hydrology. The surface albedo over bare land is specified as 0.14 and that over snow-covered land varies from 0.7 to 0.85 depending on the height of the ground surface. In the second run (AW run), the surface albedo and ground wetness are specified as the climate values. In the AW run, there is no snow-albedo feedback and the ground wetness is not predicted. Two additional runs are performed for separating the effect of albedo from that of ground wetness and for examining the effect of snow albedo.
The results show that the atmospheric circulation in the Northern Hemisphere is very sensitive to the surface albedo specification in winter. In the C run, the Siberian high is stronger and extended southeastward compared with that in the AW run due to snow-albedo feedback in C. The Aleutian low in the C run is deeper and shifts eastward. On the other hand, the Icelandic low is deeper in the AW run than in the C run.
It is found that snow albedo is an important factor which controls the northern summer climate. When snow albedo is low, snow melts earlier in spring and land becomes dry and warm in summer over the Eurasian arid region. Thus the summer precipitation is reduced there. Over the southeast Asia summer monsoon region in the model, however, moisture flux convergence is enhanced and the summer precipitation is increased. The increased precipitation makes soil wet, which in turn increases precipitation. In short, snow albedo affects summer climate significantly through the interaction of atmosphere and ground hydrological processes.
Albedo of snow-free land also has a significant effect on climate particularly in low latitudes. High/low albedo produces less/much precipitation.