沙尘暴过程中沙尘对流层-平流层输送的数值模拟初步分析

A preliminary numerical analysis of the troposphere-stratosphere transportation of dust aerosol in a dust storm event

中文关键词:  沙尘暴, 沙尘气溶胶, 对流层 平流层输送, 数值模拟

英文关键词:Dust storm, Dust aerosol, Troposphere-stratosphere transportation, Numerical simulation

中文摘要:

      在初步明确东亚沙尘气溶胶对流层-平流层输送监测事实的基础上，利用观测资料、NCEP再分析资料以及基于中尺度天气模式MM5的数值模拟方法，对一次蒙古气旋沙尘暴过程中沙尘对流层 平流层输送问题进行了初步分析。结果表明：斜压不稳定是本次蒙古气旋发展的主要强迫要素，伴随气旋发展成熟，高空切断低涡的形成引导高空急流下落并诱发对流层顶折叠和高空位涡下传。对流层顶折叠区呈漏斗状，底部达500 hPa左右。高空急流产生近似垂直的下落，并在高空切断低涡的南侧和东侧达到最强。在对流层顶折叠区周边的300—500 hPa，上升气流与低涡区偏西、偏南、偏东气流叠加，或水平横穿折叠的对流层顶，或斜升并准垂直地穿过下落的对流层顶到达平流层，且随时间的推移，空气质点能够进一步抵达平流层中部（100 hPa）。轨迹分析表明，沙尘天气区对流层低层的空气质点在气旋涡旋上升气流的驱动下呈气旋式盘旋上升，并在对流层高层形成分支，一支穿过对流层顶到达平流层，并在平流层向下游进行反气旋式螺旋运动，另一支则留在对流层高层并向下游进行准水平的气旋式螺旋运动。在高空位涡下传过程中，主要产生平流层到对流层的净输送；高空位涡停止下传之后则出现对流层到平流层的净输送，且强度随时间呈指数型增长。这一特征有利于形成更强的沙尘对流层 平流层输送。

英文摘要:

      Based on a confirmation of the troposphere-stratosphere transportation (TST) of dust aerosol in East Asia from the observational data, the TST of dust aerosol in a Mongolia cyclongenesis induced super dust storm process was analyzed by using the observational data and the NCEP reanalysis data and through the numerical simulation method. The results show that: the baroclinic instability is the dominant forcing causing the Mongolia cyclongenesis. Following the maturation of cyclone, the formation of upper level cut low led the subsiding of upper level jetstream, which induced the tropopause fold and the downward transportation of upper level potential vorticity. The folded tropopause was funnel shaped with its bottom approaching near 500 hPa. The upper level jet stream underwent quasi vertical subsiding with its core locating at the south and east sides of the cut low. Around the tropopause fold region between 300 hPa and 500 hPa, the resultant wind between the ascending motion and the western, southern and eastern wind, passed through the folded tropopause into the stratosphere horizontally or aslant upwards (through the bottom of the folded tropopause). As time goes by it approached the deep part of the stratosphere (100 hPa). The trajectory analysis shows that the air particles at the lower troposphere in the areas with dust weather occurred were raised upward driven by the spiral ascending motion over the cyclonic area. The dust aerosol transportation belt split into two branches when it got to the upper level of the troposphere. One passed through the folded tropopause into the stratosphere and then conducted an anticyclonic movement downwards within it. The other retained in the troposphere and maintained the cyclonic movement downwards. A net Stratosphere Troposphere Transportation occurred accompanying with the process of downward transportation of upper level potential vorticity. After that, a net Troposphere Stratosphere Transportation took place and its strength exhibits an exponential growth. This characteristic is favorable for the Troposphere Stratosphere Transportation of dust aerosol.