The Influence Of The Temporal And Spatial Distribution Of The Tropopause Of The Qinghai-Tibet Plateau On The Atmospheric Composition Of The UTLS Region

The Tibetan Plateau is a key start-up area affecting climate change in East Asia and even the Northern Hemisphere.The changes in atmospheric composition in the UTLS(Upper Troposphere and Lower Stratosphere)region will also have an important impact on the global climate.Therefore,in order to study the characteristics of the atmospheric components of the tropopause and UTLS over the Tibetan Plateau,based on the COSMIC(Constellation Observing System for Meteorology Ionosphere and Climate)data,MLS(Microwave Limb Sounder)satellite data and ERA-Interim reanalysis data from 2008 to 2016,the paper obtains LRT1(the first lapse-rate tropopause),LRT2(the second lapse-rate tropopause)and CPT(cold point tropopause)according to the definition of WMO.Then we discuss the temporal and spatial evolution characteristics of various tropopauses,the correlation between LRT2 and CPT height and temperature field is analyzed.In addition,the horizontal and vertical distribution characteristics and time evolution characteristics of water vapor,CO and O3 are also analyzed by 215 h Pa,147 h Pa and100 h Pa for UTLS region.According to the abnormality of the tropopause height of LRT2,four abnormal periods are selected,and the changes of atmospheric composition in UTLS are discussed.Finally,the physical mechanism is explored by combining temperature field,circulation field and vertical velocity field.The main conclusions are as follows:(1)The frequency of LRT1 in summer is less than 5%,and LPT2 accounts for over90% in LPT from July to September;the height of LRT1,LRT2 and CPT presents the bimodal type,single-peak type and single peak-valley type respectively during the year;LPT1 is higher in spring and autumn but lowest in summer;LPT2 is highest in summer with the distinct latitudinal distribution in space;CPT is relatively higher in spring and winter.(2)When there is a warming trend in the upper part of the troposphere,the height of LRT2 will also increase,while the height of CPT will decrease.When the temperature change in the lower part of the stratosphere shows an increase,the height of LRT2 will show a downward trend,but the height of CPT will increase.(3)The water vapor in the UTLS region decreased during the winter half year,showing zonal distribution at 215 h Pa and 147 h Pa,and the northern part of the plateau was low and the south was high;but the water vapor distribution during the winter half year of 100 h Pa showed a decrease from north to south.On the contrary,the water vapor mixing ratio shows a relatively obvious upward trend.The water vapor content in the summer half year is the highest in the whole year,especially in the south of the plateau from June to August.From the vertical distribution,the summer water vapor mixing ratio is the fastest between 215 h Pa and 100 h Pa,and the summer-autumn water-vapor mixing ratio is not significantly higher than the minimum value.The winter water vapor profile is roughly.The distribution characteristics of the "<" type are exhibited,and the water vapor content rises from the vicinity of the minimum value as the height increases.(4)In terms of time,the CO mixing ratio has the characteristics of low summer and low winter.The CO mixing ratio of 215 h Pa and 147 h Pa in summer has obvious fluctuation characteristics with time,and the CO mixing ratio in winter shows an upward trend;in spatial distribution,The CO mixing ratios in summer and early autumn are all obvious zonal distributions in the south and north;the CO mixing ratio is the highest on the west and south sides of the summer plateau.The high value of O3 mixing ratio is mainly concentrated in January-March and October-December,and the O3 content in spring,summer and winter all show a certain increasing trend;in space,the O3 mixing ratio has a distribution of north high and low south.Characteristics,above 215 h Pa to 50 h Pa,the O3 concentration always increases with height;the O3 concentration increases rapidly above100 h Pa.(5)When the LRT2 is higher in summer,the temperature in the upper part of the plateau troposphere increases,the height of the potential increases obviously,and there is a relatively active ascending motion.The easterly anomaly in the upper part of the troposphere corresponds to the enhancement of the Indian summer monsoon of 850 h Pa,which is beneficial to water vapor.The mixing ratio with CO is increased in the UTLS region,but the higher tropopause top and upward airflow movement is not conducive to the downward transport of O3 in the stratosphere,so the O3 content in the lower layer of UTLS is significantly reduced.On the contrary,LRT2 is low,the temperature in the upper part of the plateau troposphere is lowered,the potential height is lowered,and the sinking movement occupies the main body of the plateau,which weakens the process of water vapor and CO upward transport in the lower troposphere,but is conducive to the downward diffusion of O3,and thus in the UTLS region.The water vapor content decreased compared with the season average.The CO content in the middle of the plateau decreased most obviously,and the lower layer of UTLS had a significant increase in O3.(6)When the LRT2 is higher in winter,the upper part of the plateau UTLS region is significantly warmer,the 300 h Pa potential height is significantly reduced,and it is increased at 100 h Pa.The plateau is mainly uplifting,and the downward transport of O3 in the stratosphere is Negative influence,the westerly wind in the middle and upper troposphere is weak,which is not conducive to the water vapor transport to the plateau.Therefore,the water vapor content and O3 content in the UTLS region are lower,but the CO content is higher than the seasonal average.On the other hand,when LRT2 is low,the temperature in the upper part of the troposphere is lowered,and the height of the northern part of the plateau is increased.However,the height of the southern part of the 100 h Pa plateau is decreasing,and the submerged movement is mainly on the plateau.However,there is still some ascending motion in the southern part of the plateau.The westerly wind is stronger,which is conducive to the transport of water vapor to the plateau.Therefore,the water vapor and O3 content in the UTLS region are higher,and the CO content is higher in the upper layer of the troposphere,but less in the lower stratosphere.