Impacts on climate of the SST anomaly over the Indian Ocean
WU Guo-xiong, LIU Yi-min. LIU Ping
State Key Lab of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics (LASG), Institute of Atmospheric Physics (IAP), Chinese Academy of Sciences, Beijing, 100029 China
Abstract
Based on the equation of Ertel potential vorticity, a complete form of vorticity equation (CVE) and thermal adaptation theory are developed to study the impacts on the formation of subtropical anticyclone of surface sensible heating and deep convective latent heating. Based upon the CVE, the effect of spatially inhomogenous heating on the formation and variation of subtropical high is discussed. It is shown that due to the overshooting at the top of surface heating, even shallow adiabatic heating can affect the circulation of the atmosphere aloft. By using simple scale analysis, it is found that, compared with horizontal inhomogenous heating, vertical inhomogenous heating has stronger impacts on the formation of enclosed subtropical anticyclone centers. In a steady state, low level subtropical anticyclone center is forced on the western side of surface sensible heating and eastern side of deep condensation heating, whereas upper level subtropical anticyclone center appears on the eastern side of surface sensible heating and western side of deep condensation heating.
Data analysis and numerical simulation both show that in summer over the Asia and Northwestern Pacific area, it is the latent heat release of deep convective condensation associated with Asian monsoon that contributes basically to the formation of the 500hPa subtropical anticyclone over the Northwestern Pacific, and of the 200hPa subtropical anticyclone over South Asia. However, surface sensible heating and orography also affect such configuration to some extent. 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.
