| As the main source of tropospheric air across into stratosphere,the tropical tropopause layer?TTL?is a key area of the global stratosphere and troposphere exchange?STE?process.The study of the physical process in the TTL is of great scientific significance to understand STE.Using the Met Office LEM,the National Center for Atmospheric Research WRF model,various sounding data,reanalysis data and the satellite data,this thesis analyzes the physical process triggered by deep convection in the TTL,the physical mechanism of deep convection affecting low stratospheric water vapor,the quantitative results of several environmental factor impact on stratospheric water vapor,the effect of the vertical wind shear on the water vapor in the lower stratosphere,and the causes of the supersaturation in the TTL.The main conclusions are as follow:1.The high-resolution large-eddy model can well simulate the small-scale physical process triggered by the tropical overshooting convection in the TTL.The deep convection firstly transfers the ice crystal particles of the lower troposphere to the tropopause.A part of the ice crystal particles can be transferred directly into the low stratosphere through 390 K isentropic surface,and a part of the ice crystal particles can enter the low stratosphere through the turbulent mixing action around the tropopause.The sinking and warming effect of the air mass caused by the convection gravity wave near the top of the troposphere causes the sublimation of the ice crystals to be water vapor,and when the gravity wave is broken,the isentropic surface starts to recover.Finally,this part of the water vapor enters into the low stratosphere completely with the recovery of the isentropic surface,which plays a significant role to in the humidification of the low stratosphere.The low stratospheric water vapor mixing ratio in the whole simulation time period is characterized by a continuous increase.In this case,the water vapor in the low stratosphere is increased by about 0.13 ppmv caused by the deep convection.The increased water vapor is divided into two parts:the former part is from sublimation of ice crystal transferred directly into the low stratosphere by the deep convection,and the latter part is from sublimation of ice crystal generated by the turbulent mixing.2.The height of the ice cloud top shows two peak structures in the sensitivity tests of changing the convection intensity:the first peak is formed by the first time the cloud top of the deep convection reaches the tropopause;The second peak is caused by the upward transfer of ice crystals and water vapor to the plume cloud formed in the low stratosphere during the gravity wave broken process.The greater the convective strength,the more ice crystals transported from deep convection to the lower stratosphere,the more the low stratospheric water vapor that is caused by deep convection.The change of the vertical wind shear of the tropopause has a significant effect on the upward transport of water vapor and ice crystals.In the larger vertical tropopause wind shear sensitivity tests,the ice crystals and the water vapor in the low stratosphere are less,while in the smaller vertical wind shear tests,there are more ice crystals and more water vapor in the lower stratosphere.The change of the tropopause temperature has a significant effect on the upward transport of water vapor and ice crystals.When a large amount of ice crystal particles are transported to the tropopause,the sublimation of the ice crystal particles is enhanced by the increased temperature of the tropopause,so that the water vapor entering into the low stratosphere is increased.The effect of change in the turbulence activity caused by the temperature change can be ignored.3.There was a well anti-correlation between the 100 hPa water vapor anomaly and the tropopause wind shear anomaly in the tropic?30°S—30°N?from 1979 to 2016.The correlation coefficient from annual mean data of time series between the tropopause vertical wind shear and the low stratospheric water vapor anomaly is-0.72,and the correlation coefficient from month mean data of time series is-0.61.Under different convection conditions,the 100 hPa water vapor anomaly,the 100 hPa temperature anomaly and the 150hPa vertical velocity anomaly are respectively synthesized according to the strong and weak tropopause vertical wind shear:Under the weak convection condition,the anomalies of the tropopause temperature anomalies of the weak vertical wind shear synthesis are consistent with that of the water vapor,while the anomaly of the tropopause temperature of the strong vertical wind shear synthesis is not exactly the same as that of the water vapor.The vertical velocity of 150 hPa under the strong vertical wind shear is less than that of the weak vertical wind shear.The vertical wind shear at 150 hPa is weak under the strong tropopause vertical wind shear,and the vertical wind shear of the tropopause can influence the water vapor in the low stratosphere by affecting the vertical transport near the tropopause;While under the condition of strong convection,the vertical wind shear has a significant effect on the vertical velocity near the top of the troposphere,and the vertical wind shear has a significant effect on the vertical velocity near the tropopause.The effect of the vertical wind shear on the 150 hPa vertical velocity of the upper troposphere under the strong convection is higher than that under the weak convection.4.Numerical simulation of the ice supersaturation near the tropopause in Kunming area is found by the triple nested mesoscale weather WRF model.Four different microphysical parametrization schemes can well simulate the phenomenon of ice supersaturation,and the relative humidity of the ice simulated by the Thompson aersaol-aware scheme is the closest to the actual observation.The temperature of the ice supersaturated region and the temperature of the ice supersaturated region in the same height have not been shown to be significantly different.The temperature is not the cause of the ice supersaturation in this region.The concentration of the aerosol in the ice supersaturated area is analyzed.It is found that when the concentration of the aerosol is as low as 5.8×107 kg-1,the ice supersaturation phenomenon can occur.When the concentration of the aerosol exceeds this critical value,the relative humidity of the ice surface is less than 100%at this height?110 hPa?.The model shows that the moisture-absorbing is the most important aerosol type near the tropopause in this case.The low concentration of the hygroscopic aerosol is the main cause of the ice supersaturation of the upper troposphere in this case. |
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