Statistical Characteristics of Mesoscale Convective Systems over the Tibetan Plateau in Warm Season and Their Large-scale Atmospheric Background Fields

Using the data sets of the FY-2C and FY-2E hourly equivalent temperature of black body (TBB) from 2005 to 2010, the mesoscale convective systems (MCSs) in warm season (March-September) over the Tibetan Plateau are investigated. Then, the large-scale environmental characteristics during the MCSs' life cycle are analyzed using the NCEP FNL data. The results are as follows. The hinterland of the Tibetan Plateau is the high-frequency occurrence area of MCSs. There is noticeable inter-monthly and diurnal variation in the distribution of MCSs over the Tibetan Plateau. The MCSs precipitation occurs more frequently in the summer season and from sunset to midnight. Most of the MCSs over the Tibetan Plateau are eastward, low-speed, short-life-cycle MβCS. With respect to the large-scale atmospheric condition, the results show that in the upper troposphere there is a wind divergence center and in the low troposphere there is a moisture convergence center associated with strong upward vertical motion that is beneficial to the occurrence of strong convection. Also, in the lower troposphere (500 hPa) there exists an eastward positive vorticity advection, which might be a reason for the MCSs moving toward the east. The large-scale atmospheric condition in spring is different from that in summer. The wind shear is the main factor for the MCSs to occur in spring, and the unstable atmosphere structure is the reason for the MCSs to occur in summer.