A Comparison between Numerical Simulations of Forced Local Hadley (Anti-Hadley) Circulation in East Asian and Indian Monsoon Regions

摘要

Two numerical simulations of forced local Hadley circulation are carried out based on a linear diagnostic equation to provide an insight into the mechanisms of monsoon evolution in different monsoon regions. One simulation is for the zonal mean Hadley circulation over East Asia (from 95°E to 122.5°E), another over India (from 70°E to 85°E). With the NCEP / NCAR re-analysis data re-processed by Chinese Academy of Science in Beijing. the former simulation displays a dominant anti-Hadley circulation pattern over East Asia at 1200 UTC May 1. l994. The simulated circulation pattern is consistent well enough with the circulation pattern plotted directly from the data for lack of the radiation information at each level. Although the simulation over India is not as good as that over East Asia. a dominant Hadley circulation pattern is obvious as data show. Further analysis shows that the defective simulation over India is due to foe presence of slatically unstable condition at some grid points in the lower troposphere. This circumstance slightly violates the hydrodynamic stability criterion required by the elliptic diagnostic equation for the forced circulation. Since the simulations are reliable enough compared with the given data, the linear equation facilitates a systematic assessment of relative importance of each internally forcing process. The assessment shows that among the internal processes, the horizontal temperature advections account obviously for the Hadley (anti-Hadley) circulation over India (East Asia) at 1200 UTC May 1. 1994 in addition to the process associated with the latent heat releasing. The calculation of latent heat energy is a little bit unreliable due to the unclear cloud physics in the convection processes and the less accurate humidity data. These preliminary results are consistent with the results of previons studies which show that the feature of the seasonal warming in the upper troposphere and the corresponding processes are part of key processes closely related to the evolution of the summer monsoon over East Asia and India.