Numerical Experiments for the influence of the Transition Zone Migration on Summer Climate in North China

As the position of the transition zone changes obviously, that is, as the transition zone migrates to the north or the south from present position, it affects water or heat balance between the land and the atmosphere in a considerable degree and has a profound influence on climate in North China. The experiment re-sults in this paper indicate whether in the dry case or in the wet case of the large-scale climatological back-ground field, the surface air temperature in a wide range of the transition zone migration and its sur-rounding decreases as the transition zone migrates northward. Moreover, the net upward fluxes of the sur-face long wave radiation and the sensible heat decrease, and the evaporation to the atmosphere increases. As the transition zone migrates southward, the results are opposite. This kind of significant thermal forcing between the land and the atmosphere can excite secondary circulation or circulation cells, which interact with the large-scale circulation systems, changing the atmospheric motion, affecting the water vapor transporta-tion and consequently having an effect on the precipitation.