Simulation of the summer Indian monsoon beginning during the experiments with the atmosphere general circulation model of Hydrometcenter of Russia

The influence of the Earth’s gravitational field on the simulation of the time of the beginning of monsoon circulation in Asia by the model is analyzed. The results of numerical experiments carried out with the circulation model of the Hydrometcenter of Russia during ten years (1979–1988) following the AMIP protocol are considered. Two standards were used during the analysis of results. The data of NCEP/NCAR (the United States) reanalysis were used for the comparison of circulation characteristics and the data of GPCP (Global Precipitation Climatology Project), for the precipitation analysis. Four different criteria of the monsoon beginning are analyzed: the occurrence of the negative divergence in the area under study, the beginning of heavy precipitation fall, the marked kinetic energy increase in the lower troposphere, and the origination of anticyclonic vorticity. The comparison of the data obtained during the numerical experiments with the chosen standards demonstrated that, in all cases, taking account of gravitation field variations results in the improvement of the simulation of the time of monsoon circulation beginning by the model.