A new approach to the old subject of monsoon - A comparison between numerical simulations of forced local Hadley (anti-Hadley) circulation in east Asian and Indian monsoon regions

Two numerical simulations of forced local Hadley circulation are carried ou t based on a linear diagnostic equation to provide an insight into the mech anisms of monsoon evolution in different monsoon regions. One simulation is for the zonal mean Hadley circulation over East Asia (from 95 degrees E to 122.5 degrees E), another over India (from 70 degrees E to 85 degrees E). With the NCEP/NCAR re-analysis data re-processed by Chinese Academy of Scie nce in Beijing, the former simulation displays a dominant anti-Hadley circu lation pattern over East Asia at 1200 UTC May 1, 1994. The simulated circul ation pattern is consistent well enough with the circulation pattern plotte d directly from the data for lack of the radiation information at each leve l 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 ana lysis shows that the defective simulation over India is due to the presence of statically unstable condition at some grid points in the lower troposph ere. This circumstance slightly violates the hydrodynamic stability criteri on 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 in ternal processes, the horizontal temperature advections account obviously f or 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 rele asing. The calculation of latent heat energy is a little bit unreliable due to the unclear cloud physics in the convection processes and the less accu rate humidity data. These preliminary results are consistent with the resul ts of previous studies which show that the feature of the seasonal warming in the upper troposphere and the corresponding processes are part of key pr ocesses closely related to the evolution of the summer monsoon over East As ia and India.