| Popis: |
A Lagrangian particle dispersion model combined with “domain filling” technique is applied to study the upward troposphere-to-stratosphere mass transport (TST) and the downward stratosphere-to-troposphere mass transport (STT) over the Asian monsoon region for the period from June to August in 2005 using the data from Global Forecast System of National Centers for Environmental Prediction (NCEP/GFS) analysis. A residence time criterion is used to distinguish between transient (reversible) exchange and irreversible exchange, and special emphasis is paid to the latter, which has great impact on the budget of chemical constituents on both the stratosphere and troposphere. The source and sink features in the irreversible two-way mass exchange are also analyzed by the forward/backward trajectory-track method. The results summarized as follows: (1) The Stratosphere-Troposphere mass Exchange (STE) is sensitive to the selected threshold value of residence time. Most air parcels can return rapidly (within 1~2 days) to their “original sphere”. The quantitative STT and TST mass flux estimates are strongly dependent upon whether these transient exchange events are considered or not, especially in mid-latitude storm track regions. (2) From the zonal distribution of the net STT and TST mass flux in the Asian monsoon region, TST dominates the areas south of 45°N with a most strong upward branch in the subtropics, while pronounced downward STT from 45°N to 55°N and weak upward fluxes in high-latitude regions. Detailed geographical distributions show the strong downward cross-tropopause STT flux is mainly in the north of Tibetan plateau, which corresponds to the large-scale troughs in the Asian summer monsoon region. The results also show that the Asian monsoon region is dominated by upward cross-tropopause TST flux. The Tibetan plateau and its adjacent regions are the main channels of the upward mass flux into the stratosphere, which makes a fraction contribution of 46%. (3) The four-day source and sink characteristics of the irreversible mass exchange also reveal that the source of STT mainly comes from the high-latitude regions west of 100°E and north of 50°N, and is transported to the middle-latitude areas, such as the northeast of China and North Korea. And the source of upward TST mainly originates from mid-latitude and subtropical regions, moves across the tropopause, and turns towards above polar and tropical regions, respectively, which indicates that the TST of Asian monsoon has an enhanced potential for water vapor transportation into the stratosphere tropical pipe and plays an important role in the global stratosphere water budget. |
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