These suggest that Asian monsoon rainfall is not just passively influenced by subtropical anticyclone as was thought traditionally, but can also actively affect the formation of the subtropical anticyclones in the monsoon area.
Comparison experiments based upon the Global Ocean- Atmosphere- Land System model developed at LASG (LASG/IAP GOALS) are designed to study the impacts of the SST anomaly over the Indian Ocean on the mean July climate. In a numerical experiment in which latent heating associated with precipitation is not allowed to heat the atmosphere, the response of the atmospheric circulation is confined to the neighboring region, appearing as a first- stage thermal response to the associated surface sensible heating alone. After such restriction is removed in another experiment, remarkable different results are obtained. Torrential rain appears in the East Asian monsoon region, and strong anomalies in the subtropical anticyclone over the Western Pacific are formed. It is shown that this is due to the second-stage thermal response of the atmospheric circulation to the latent heating released by condensation heating of the torrential rain. A theory of two-stage thermal adaptation is then established to explain the response of the atmospheric circulation to the SST anomaly over the Indian Ocean.
Although the vertical inhomogenous heating dominates the generation of vorticity within the heating region, it does not mean that horizontal inhomogenous heating is negligible. Outside the heating region, such kind of heating becomes extremely important. Both theoretical study and numerical experiment show that it forms an additional vorticity source to the north of the heating region within the mid-latitude westerlies, resulting in a quasi-barotropic wavetrain in geopotential height via energy dispersion, and affecting the climate over the northern hemisphere.
