Abstract:
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.