Impacts Of Spatially Non-uniform Diabatic Heating On The Formation Of Subtropical Anticyclone In Boreal Summer

Based upon a systematic review on the study of subtropical anticyclone, in this study, the mechanism linking the formation of subtropical anticyclone in boreal summer to zonally asymmetric diabatic heating is investigated via data diagnosis, theoretical study, and numerical experiment. The complete form of the tendency equation for vertical vorticity development, the NCEP/NCAR reanalysis data, and the IAP/LASG GOALS climate model are employed for the study. The main results obtained from this study can be summarized as follows.1. Limitation of classical theory.Either in zonal mean sense or in three dimensional sense, the classical theory that subtropical anticyclone is forced by air sinking is proved to be inappropriate in explaining the formation of the system. By virtue of spectral expansion, this study shows that, the appearance of asymmetric subtropical anticyclone requires either asymmetric initial field or asymmetric external forcing. The formal is a nonlinear process that involves wave-mean flow interaction or wave-wave interaction; whereas the later is a linear process. Based on this conclusion, a symmetric July circulation is simulated.2. Impacts of negative orography on the simulation of subtropical anticyclone.The original version of the IAP/LASG GOALS climate model does not provide satisfied simulation of the western Pacific subtropical anticyclone. This is found to result from the existence of negative orography in this low-resolution model. It is shown that, over the grid-points where orography height is negative, there exists false sensible heat source that leads to warmer temperature and higher geopotential height. A new orography scheme is then developed and introduced into the model, and helps the improvement of simulation of the subtropical systems over the Asian and western Pacific region.3. Thermal adaptation and overshooting.Based upon the complete form of the tendency equation for vertical vorticity development and the concept of potential vorticity, a theory of thermal adaptation is developed to study the response of the atmosphere to diabatic heating in short- time scales. A new concept of "overshooting" is proposed: beyond the top of heating layer, even there is no diabatic heating there still exist rising, anticyclone circulation, and cold center. This overshooting is proved to be necessary for maintaining vorticity balance. It can be used to explain why a surface heating can affect the upper tropospheric circulation even within a period shorter than one day, and provides a theory for understanding the dynamics of subtropical anticyclone.4. Vorticity advection, β- effect, and heating profile.