2009年和2010年夏季我国及周边地区STE模拟与对比分析

夏季是深对流多发的季节,深对流在STE(Stratosphere Troposphere Exchange,对流层-平流层交换)过程中起着重要作用。对2005-2012年夏季我国及周边地区的深对流统计发现,2009年深对流发生的次数较少,2010年深对流发生的次数较多。通过拉格朗日输送模式对2009年和2010年夏季的大气运动状态进行模拟并统计分析,发现30°N以南和以北的地区具有明显不同的平流层-对流层交换特征,30°N以北我国及周边地区TST(Troposphere to Stratosphere Transport,对流层向平流层输送)和STT(Stratosphere to Troposphere Transport,平流层向对流层输送)较为活跃,30°N以南远没有30°N以北地区活跃,但其净输送量却大致相当。在30°N以南,6-8月净输送是对流层向平流层输送。在30°N以北,6月净输送是平流层向对流层输送,7-8月净输送是对流层向平流层输送。比较深对流出现较少的2009年夏季和深对流出现较多的2010年夏季的TST和TST-STT,发现2010年6-8月这3个月的TST和TST-STT总量都超过2009年,表明2010年夏季我国及周边地区对流层向平流层的输送和净输送都强于2009年,与深对流活动的多少可能表现出正相关。

Simulation and comparative analysis of stratosphere-troposphere exchange in the summers of 2009 and 2010 in China and surrounding areas

Stratosphere-troposphere exchange(STE) is a process not only involving transport from the troposphere to stratosphere,but also from the stratosphere to troposphere.STE is very important to the variation of water vapor and atmospheric chemical compositions.Correspondingly,it also plays an important role in the radiation balance and climate changes in the global climate system.Deep convection occurs frequently in summer.The strong upward flow in deep convective cloud can transport the atmosphere of the lower troposphere quickly to the upper troposphere,and even to the lower stratosphere.Thus,it is very important in the process of STE.To date,this conclusion has been reached largely with the help of aircraft observations.STE is a process that includes complex physical,chemical and dynamic processes.The time scale of STE can be climatological,synoptic,meso,and turbulent,while the spatial scale varies from local to global.Therefore,STE is a highly complex process,and to study such a complex process,using models to quantitatively simulate the transport processes is a good method.FLEXPART is a Lagrangian diffusion model.It is widely used in the transport of air pollution,the mesoscale transport of smoke from forest fires,as well as global STE.In this study,firstly,data on deep convection in China and surrounding areas for the period 2005-2012 were collected.The source of the data-collected 24 times a day and at a spatial resolution of 0.1°-was the FY-2 satellite.Through statistical analysis,the interannual variation of the deep convection was determined.One year of minimum convection and one year of maximum convection were selected from the overall study period.Then,the domain(15-30°N,75-135°E)was selected to represent China and its surrounding areas.In order to understand the bidirectional exchange characteristics of troposphere-to-stratosphere transport(TST)and stratosphere-to-troposphere transport(STT)in summer in this region,the atmospheric circulation status of the two selected years from June to August was simulated using FLEXPART.The statistical and model results were analyzed,revealing the following:In the summer season of 2009,deep convection occurred least frequently;while in the summer season of 2010,it occurred most frequently.The atmospheric circulation from June to August 2009 and 2010 was simulated using FLEXPART,and it was found that the area south of 30°N and the area north of 30°N possessed different characteristics of STE.In the area north of 30°N,TST and STT were active;whereas,in the area south of 30°N they were far less active than the area north of 30°N.However,the net transport (TST minus STT)was roughly equal.From June to August,in the area south of 30°N,the net transport was from the troposphere to stratosphere;while in June,in the area north of 30°N,the net transport was from the stratosphere to troposphere.In July and August,the net transport was from the troposphere to stratosphere.Comparing the TST and TST-minus-STT of summer 2009 and 2010,it was found that the total amount of TST and TST-minus-STT from June to August 2010 was more than that in 2009.This means that the transportation from the troposphere to stratosphere was larger in 2010 than in 2009.The TST and TST-minus-STT might be positively correlated with the deep convection activity,and this will be investigated in future work.