Diabatic Heating over the Tibetan Plateau and the Seasonal Variations of the Asian Circulation and Summer Monsoon Onset
青藏高原加热与亚洲环流季节变化和夏季风爆发

The relationship between the evolutions of the Asian monsoon circulation and the diabatic heating over the Tibetan Plateau during spring is investigated by using the daily NCEP/NCAR reanalysis data. The result shows that there is distinct seasonal variation of diabatic heating over the Tibetan Plateau. During early transition season (before mid-May) over the Tibetan Plateau, the temporal variation of total diabatic heating is in phase with sensible heating. The features of the variation of total diabatic heating and sensible heating over the Tibetan Plateau show that the sensible heating is important to the seasonal variation of the Northern Hemispheric circulation. Of the particular importance, the temporal variation of diabatic heating over the Tibetan Plateau is closely coupled to the Asian summer monsoon onset and the seasonal transition from winter to summer of the atmospheric circulation of the Northern Hemisphere. In the transition season, the change of the diabatic heating over the Tibetan Plateau leads to the changes in land-sea thermal contrast, which builds up a favorable background for the Asian summer monsoon onset. It is also shown that, due to the large domain used, the Webster-Yang monsoon index cannot present the regional characteristics of the seasonal transition in the Asian monsoon area. More over the spatial difference in seasonal transition in the area can be depicted reasonably well by using the local zonal wind difference between 850 hPa and 200 hPa.