A Preliminary Study On The Distribution Of Deep Convection Over The Tibetan Plateau And The Mechanism Of Stratosphere-troposphere Exchange

The dynamic and thermal effects generated by the large topography of the Tibetan Plateau make the region a frequent area of deep convection.The near-surface atmospheric components can be transported to the Upper Troposphere and Lower Stratosphere(UTLS)region by deep convection,which can affect the global energy cycle and climate change.The spatial distribution,seasonal variation and annual variation of the deep convection over the Tibetan Plateau are analysed,using the Ku-band data of the GPM satellite from 2014 to 2019(Including plateau area with terrain height greater than 3km in the range of 70°E-105°E,28°N-40°N,and the surrounding area of the plateau with terrain height less than 3 km in the range of 70°E-105°E,25°N-35°N).Then a deep convection in the southeast of the Tibetan Plateau was simulated by WRF-Chem model.The characteristics and its influence mechanisms of the Stratosphere-Troposphere Exchange(STE)in the deep convection were analyzed by adding a no-convection test.(1)The distribution characteristics of deep convection in the Tibetan Plateau are analyzed by using GPM satellite data from 2014 to 2019.The results show that the deep convection at 16 km and above account for 13.3%,and the Himalayas and the southeast of the plateau are the dense distribution areas of deep convection,where the strong deep convection is mostly distributed,while the weak deep convection is mainly on the plateau.The deep convection is concentrated in the Ganges delta and the southeast of the plateau in spring;it basically covers the entire Tibetan Plateau except the western part of the plateau in summer;it is scattered and weak in autumn;it is not detected in winter.Deep convection accounts for the largest proportion in August of the year,followed by July.(2)Based on the WRF-Chem model,the characteristics and mechanisms of STE are analyzed in a deep convection that occurred in the southeastern part of the Tibetan Plateau on August 12,2010.The results show that the convection has the characteristics of penetrating convection,and the strong updraft in the deep convection could directly transport the air with high concentration of CO and low concentration of O₃near the ground into the lower stratosphere within an hour,and increased the concentration of CO and decreased the concentration of O₃in the lower stratosphere.The water vapor increased significantly in the upper troposphere while decreased firstly and then increased in the lower stratosphere because of the condensation and dehydration.(3)The deep convection induced a strong turbulent mixing process,which caused the continuous STE in the UTLS region within 3-4 hours after the deep convection,transporting the ice crystals,CO and O₃in the troposphere to the lower stratosphere.The water vapor that entered the lower stratosphere through turbulent mixing process reduced because of the condensation and dehydration.