The distribution of cross\|tropopause mass flux over the Tibetan Plateau and its surrounding regions

Based on ECMWF data sets from 1958 to 2001, the cross-tropopause mass flux (CTF) over the Tibetan Plateau and its surrounding regions was calculated by Wei formula, and its spatial-temporal distribution and long-term trend was analyzed. Analysis results show that: (1) the CTF has a zonal distribution structure, and shows two distinct features on both sides of the subtropical jet. In the steep tropopause belt to the north of the jet, the CTF varies in a zonal wave-like pattern from TST (troposphere to stratosphere transport) to STT (stratosphere to troposphere transport) to TST, and so on, which is mainly caused by the horizontal CTF; and the CTF distribution on the south side is dominated by the vertical transport term. (2) In the longitude range (80°E-105°E), southern Tibetan Plateau and its southward regions are covered by TST, and the northern part by STT in winter-spring; however, the whole region from 20°N to 40°N is almost controlled by TST in summer-autumn. In all seasons, CTF is dominated by the vertical term to the south of the jet, and by the horizontal term in the steep tropopause belt, and by both terms to the further north. (3) The statistically regional averaged monthly CTF over the Tibetan Plateau and the Gulf of Bengal is controlled by TST in all seasons, with two maxima in February and July, which are caused by two different mechanisms, the vertical transport for July while the horizontal term for February. (4) The regional mean annual CTF undergoes a transition from a decreasing trend before 1982 to a relatively stronger increasing trend afterwards.