Experiments on the Seasonal Variation of the General Circulation in a Statistical-Dynamical Model

Abstract

A study of the seasonal change of a climaticc state of the atmosphere is made through the investigation of a response of a statistical-dynamical model to insolation having seasonal variation. Numerical experiments are performed for the two hypothetical cases: the land-covered earth (LCE) and the ocean-covered earth (OCE). The two cases differ in the thermal and aerodynamical conditions at the surface, and a hydrologic cycle is incorporated only in the model for OCE. Numerical integrations are carried out until the same climatic state as one year before reappears. Then, annual marches of the zonal mean field, the eddy statistics, and the energetics are analyzed. Baroclinicity at the middle latitudes is noticeable, in summertime, only for the OCE. Strong upper level easterly flow evolved at low latitudes for the LCE. The mean meridional circulation at low latitudes for both LCE and OCE is characterized by one big Hadley cell extending from the summer into the winter hemisphere. In the OCE, the water vapor is exported from the subtropics equatorward by the mean meridional circulation and poleward by large-scale eddies. The effect of ocean is to moderate the seasonal change of eddy activity so that the eddy transport of heat for the OCE is smaller in winter and larger in summer than that for the LCE. The additional experiments show the dependency of the eddy statistics of the model an the internal viscosity. It is also shown that the after-effect of a sudden shock lasts about five months in the atmosphere for the OCE.