Study On Tropopause Structure And Its Temporal-spatial Variation Using Atmospheric Refractivity Profiles

The Upper Troposphere and Lower Stratosphere(UTLS)is the transition region of atmospheric structural properties from troposphere to stratosphere,and the tropopause exists in UTLS region,which is considered as the boundary layer between troposphere and stratosphere in the study,the tropopause obstructs the vertical exchange of water vapor,ozone and aerosol in the atmosphere,and has high sensitivity to atmospheric movement processes and climate changes.The structural distribution and interannual changes of the tropopause are closely related to surface temperature,near-surface weather and climate change,and the accurate determination of global and regional tropopause is helpful to improve the accuracy of GNSS meteorological model.In this paper,based on the atmospheric refractivity profile to accurately detect the position of the tropopause as the main research goal,the theory and method of using the atmospheric refractivity to obtain the tropopause height are studied.The problems in estimating tropopause height based on common methods,such as the limitation of using area,over dependence on atmospheric temperature,and the requirement of using data types,are mainly studied and improved,that is,it does not have strong generality.Based on the data of tropopause determined in this paper,the spatial distribution,seasonal change and interannual trend change of tropopause structure in global and Chinese land areas are analyzed in depth.Some meaningful conclusions are obtained by combining the data of surface morphology,surface temperature,near surface weather change and atmospheric convection movement.The main contents of this paper are as follows:(1)The reason why the atmospheric refractivity is used to determine the tropopause is analyzed,and the method of obtaining the atmospheric refractivity profile from radiosonde and occultation data is introduced.On this basis,the specific process of determining the tropopause using the refractivity covariance transform method of the atmospheric refractivity profile is described in detail.(2)In-depth study on the method of determining the tropopause by using the covariance transformation of atmospheric refractivity.Using different data sources,a statistical comparison of the refractivity tropopause with LRT,CPT,BAT proves that the refractivity covariance transform method is a method with higher stability and wider application range to determine the tropopause.(3)The tropopause structure based on the global and Chinese land areas changes seasonally,focusing on the areas with abnormal performance.In the subtropical region of the northern and southern hemispheres,there is a tropopause fault zone,and it changes significantly with the seasons.This region is prone to produce atmospheric jets,which is conducive to the exchange of material energy between the upper troposphere and the lower stratosphere.The Antarctic region during the summer and autumn in the northern hemisphere has an abnormally high value at the height of the tropopause,and an abnormally low value at the temperature and air pressure.It is considered that the area has a special geographical location and surface morphology,which makes it affected by local high and low-level exogenous forcing forces;because of the less thermal effect of the earth's surface on the atmosphere,the tropopause of the Tibetan Plateau region in summer in the northern hemisphere is slightly lower than that of other regions in the same latitude;due to the special surface reflectance and the response of soil to solar radiation in desert area,the tropopause in Taklimakan desert area is higher than other areas in the same latitude in summer.The tropopause height of the northeast region in winter in the northern hemisphere is slightly lower than that in the same latitude,mainly because the region is close to the origin of the winter wind.(4)According to the occultation refractivity from May 2001 to December 2018,it is found that the tropopause height of global and China's land area has been on the rise in the past 18 years,and the global tropopause height has risen 175 m in the study period,and its change is closely related to the surface temperature and climate change;The tropopause height of China's land area has risen 276 m in the study period,and the rising speed is slightly faster than that of the global scale,which is mainly caused by the small regional scale,the large population in China and the great influence of human activities.