Irreversible stratosphere-troposphere mass exchange characteristics over the Asian summer monsoon region

A particle dispersion model combined with "domain filling" technique is applied to the analyzed data from Global Forecast System of National Centers for Environmental Prediction (NCEP/GFS) to study the troposphere-to-stratosphere mass transport (TST) and the stratosphere-to-troposphere mass transport (STT) over the Asian monsoon region for the period from June to August in 2005. A residence time criterion serves to distinguish between transient (reversible) exchange and irreversible exchange, and special emphasis is paid to the later mass exchange, which has great impact on the budget of chemical constitutes in both the stratosphere and troposphere. The source and sink features in the irreversible exchange are also analyzed by trajectory-track method. The main conclusions can be summarized as follows: (1) The results show that the sensitivity of the Troposphere-Stratosphere mass Exchange (STE) distributions to the threshold residence time is pronounced at all latitudes. The major part of exchange air parcels return rapidly (within less than 1 similar to 2 days) to their "original sphere". The quantitative STT and TST mass flux estimates are strongly dependent upon whether these transient events are considered or not. (2) In general, the overall analysis of STT, TST and net mass exchange reveals that upward and downward transport of mass at the middle and high latitude accompany with each other. The meridional distribution of the net flux reveals an upward branch in the subtropics, pronounced downward exchange in the midlatitudes from 45 degrees N to 55 degrees N latitude and weak upward fluxes in high latitude region. Detailed geographical distributions show strong downward cross tropopause mass flux mainly in the north of Tibetan Plateau, which corresponds to the large scale troughs in summer. The results also show that the whole Asian monsoon region is the region of upward cross tropopause mass flux. Tibetan Plateau and its adjoint regions are the main channels of the upward mass flux into the stratosphere, which makes a fraction contribution of 46%. (3) The four days source and sink characteristics of the irreversible mass exchange also reveal that the STT mainly come from the high latitude regions of west of 100 degrees E and north of 50 degrees N, and transport to the middle latitude areas, such as the northeast of China and north Korea. But the source and sink characteristics of TST reveal that the upward mass from the troposphere into the lowermost stratosphere can be transported to the high latitude and low latitude torpocical regions respectively, which indicate that the TST of Asian monsoon have an enhanced potential for water vapor transportation into the stratosphere tropical pipe and play an important role in the global stratosphere water budget.