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 t ransition 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 con siderable degree and has a profound influence on climate in North China. Th e experiment results in this paper indicate whether in the dry case or in t he wet case of the large-scale climatological background field, the surface air temperature in a wide range of the transition zone migration and its s urrounding decreases as the transition zone migrates northward. Moreover, t he net upward fluxes of the surface long wave radiation and the sensible he at decrease, and the evaporation to the atmosphere increases. As the transi tion zone migrates southward, the results are opposite. This kind of signif icant thermal forcing between the land and the atmosphere can excite second ary cell circulation or circulation cells, which interact with the large-sc ale circulation systems, changing the atmospheric motion, affecting the wat er vapor transportation and consequently having an effect on the precipitat ion.