| Due to the high altitude,the Tibetan Plateau receives the strong solar radiation and the atmosphere at high level is very unstable,so it can be very easy to produce convection activities over the Tibetan Plateau.The severe ascending movement caused by strong convection will transport atmospheric components such as water vapor,carbon monoxide to the upper troposphere-lower stratosphere,and these atmospheric components will have a significant impact on the global climate.Therefore,the Tibetan Plateau has become an important channel of tropospheric water vapor and other trace gases into the stratosphere.However,the topography of the Tibetan Plateau is very complex and the observational data are scarce.In particular,the study of the lower stratosphere in the upper troposphere requires more observational data and numerical model data.The latest generation of Global Precipitation Missions(GPM)with Dual-frequency Precipitation Radar(DPR)and Microwave Limb Sounder on Aura satellite provide valuable observations for detailed study on convection and atmospheric composition over the Tibetan Plateau.Based on the satellite data of GPM DPR from 2014 to 2016 and the Microwave Limb Sounder(MLS)satellite data from 2005 to 2016,combined with the reanalysis data and IPSL(Institute Pierre Simon Laplace)model data,this study researched the distribution and the vertical structure of convective activities in summer over the Tibetan Plateau and its surrounding areas.The horizontal distributions of water vapor(WV),ozone and carbon monoxide at several typical altitudes(215h Pa,147 h Pa,100 h Pa),and the correlations between three atmospheric compositions in the upper troposphere-lower stratosphere were analyzed.Then a case of strong convection activity was selected to study and the correlation between atmospheric composition and vertical motion was analyzed based on the model data.The main conclusions are as follows:(1)Overall,the number of samples of precipitation with rain top altitude greater than10 km increase from June to August,and the total number diminishes with the increase of altitude.That is,the higher the storm top altitude,the less the number of precipitation times.The number of precipitation samples with the storm top altitude greater than 10 km over the surrounding regions is always larger than that over the plateau.The frequency of deep convection over the Tibetan Plateau and the surrounding areas is less than 0.8%.The frequency of overshooting convection is obviously less than that of deep convection,not exceeding 0.2%.Whether it is deep convection or overshooting convection,the distribution of frequency decreases gradually from low latitudes to high latitudes.With the increase of rain top altitude,the proportion of corresponding deep convection decreases exponentially.The contribution of convective precipitation to total rain and the contribution to total rain frequency are consistent,and both of the area fraction decrease rapidly with the increase of the contribution of convection.(2)The storm top altitude and surface rain rate of convective precipitation are the lowest in June and the highest in August.The mean summer profile is consistent with the precipitation profile in July.Furthermore,the storm top altitude over the main body of the TP rises slowly from west to east,and the rain rate shows a significant gradient change with the increase of storm top height.(3)A high WV content is more apparent in the UTLS over the southern part of the Tibetan Plateau than in the northern area of the plateau in JJA,due to the monsoon-induced strong upward motions.During the winter and spring,the distribution differences between the north and south in the lower stratosphere showed opposite trends.In MAM,the WV in the UTLS diminished rapidly with an increase of altitude,and was similar to that in DJF,which shows a “V”structure.The lower position of the UTLS may lead to a higher WV content over the northern Tibetan Plateau than in ambient regions of the same latitude.The temporal variations of WV show a weak increasing trend at 100 h Pa over the past12 years,while trends in MAM and DJF remained essentially constant.Downtrends occurred at 147 and 215 h Pa,and the WV in summer is much greater than in other seasons,with autumn next,then the minimum in winter.Moreover,WV shows a rough wave structure in MAM and SON at 215 h Pa.(4)At 215 h Pa,the O3 mixing ratio is lower in the south and higher in the north,and a low O3 content generally existed over the main body of Tibetan Plateau.At147 h Pa and 100 h Pa,this distribution characteristic was more obvious.The distribution characteristics of CO in 2014-2016 were very similar,indicating that there is not much change in annual.The vertical characteristics of CO were the same as WV,and the content decreases as the increases of height.At 215 h Pa,the mixing ratio of CO was higher in the south and lower in the north,but the change in the southern Tibetan Plateau was more obvious.At 147 h Pa and 100 h Pa,the large CO content shifted westward,and it was more consistent with the anti-cyclonic closed circulation region.In the UTLS region,there was obviousintraseasonal oscillations of WV and CO,showing a heterogeneous phase variation.The correlations between water vapor and CO at 215 h Pa and 147 h Pa were good,and the correlation coefficients were 0.73 and 0.69,respectively.The correlation at 100 h Pa was not very good.At these three pressure levels,the CO and O3 concentrations showed a variation of anti-phase characteristics.At 147 h Pa,the abnormal changes of CO and O3 concentrations were similar.(5)During the strong convection,the mixing ratio of O3 and CO changed obviously,and the CO mixing ratio in the troposphere appeared high and extended upward.Meanwhile,the strong ascending movement could transport the lower air to the upper layer and downgrade the O3 concentration in the upper layer.The WV of the troposphere increased obviously,and mainly concentrated between 150 h Pa and 215 h Pa.Approximately the drier tropopause,the WV changed little.The content of IWC changed most significantly,an increase of two times.O3 and WV fluxes crossing the tropopause were positive during the convection,and air moves upward into the stratosphere from the troposphere,whereas air movement gradually shifted from downward to upward during the period of convection.(6)At 200 h Pa,the CO and vertical velocities showed a weak negative correlation in the middle and northeastern parts of the Tibetan Plateau.The negative correlation at 150 h Pa further weakened.On the contrary,the weakening positive correlation began to appear in the southwest region.At 100 h Pa,the area of the positive correlation expanded and the correlation was further strengthened in the completely southern plateau.The correlation coefficient between O3 and vertical velocity was positive in the northern plateau and negative in the south,and the correlation decreased with increasing altitude.At 200 h Pa,O3 had the strongest positive(negative)correlation with vertical velocity.At 150 h Pa,the area of positive correlation decreased and the correlation diminished.At the height of100 h Pa,the positive correlation between O3 and vertical velocity did not exist,and the negative correlation started to dominate the plateau. |
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