Characteristics Of Temperature,Water Vapor And Convective Overshooting Over The Tibetan Plateau From Multi-Source Data

It has long been realized that temperature and water vapor profiles are important basic data,which are used to study convection,the release of latent heat and the energy budget over the Tibetan Plateau.As the important parameters of the Earth’s energy budget,the temperature and humidity and tropopause characteristics have always been a scientific problem of concern over the Tibetan Plateau.However,systematic studies of temperature and water vapor profiles over the plateau are difficult and progress has been slowed by the short history of meteorological observations and the sparse distribution of observational stations in this harsh environment.It has long been understood that convective overshooting strongly affects the thermal structure,moisture distribution and chemical constituents of the tropopause and lower stratosphere.To date,what we have known about the thermal and moisture structure of overshooting convection in Tibetan Plateau is incomprehensive due to the lack of temperature and water vapor profiles with high vertical resolution over the Plateau.Using IGRA2 as a benchmark,the applicability of Multi-Source Data(COSMIC,ERA5,JRA55 and MERRA2)for studying the temperature and water vapor profiles over the Tibetan Plateau is verified for the first time.Besides,we compared temperature and humidity profiles from SBDART model with that from sounding stations.Then,we put these data of profiles into SBDART model and calculated the effects of temperature and humidity profiles on radiation fluxes.And we analyse the characteristics of the mean temperature and water vapor profiles,and the temperature and absolute humidity profiles in cloudy and clear sky condition,along with the diurnal variation of the temperature and absolute humidity profiles over the Tibetan Plateau.Last,the characteristics of convective overshooting and its impact on the temperature and water vapor structure over the Plateau are studied.The research period over the Tibetan Plateau selected in this paper is the summer from 2006 to 2014.The main conclusions are as follows.1.Difference analysis of multi-source temperature and water vapor data and its impact on radiation budgetThe mean temperature profiles of COSMIC,ERA5,JRA55,MERRA2 and IGRA2 are generally consistent,and the differences between them mainly occur in the low to middle layer of the troposphere(3-8.5 km)and close to the tropopause(16-18 km).The differences in the water vapor content between the COSMIC,ERA5 and IGRA2 datasets were largest near the surface and decreased with increasing altitude.The water vapor in the COSMIC dataset was clearly higher than that in the ERA5 dataset and the largest difference was 1-1.5 g/m3 at the surface.There are obvious differences between temperature and humidity profiles from SBDART model with that from sounding stations,which can influence the radiation budget obviously.There are significant differences between total downward fluxes which are calculated from model and from sounding stations at the surface,the differences reach to 20-35 W/m2 and the relative errors are from 2.01%to 2.95%.The differences between total upward fluxes which are calculated from the two kinds of profiles reach to 10-22 W/m2 at the top of atmosphere.And the relative errors are from 1.82%to 8.94%.The differences of radiative heating rate between that from model and that from sounding stations are from 0.03 to 0.29 K/d.2.The characteristics of temperature and water vapor structure over the Tibetan Plateau in summerThe atmosphere over the CTP(Central Tibetan Plateau)is warmest and wettest in the lower to midtroposphere,whereas the WTP(Western Tibetan Plateau)is warmest and driest in the mid to high troposphere.The coldest and wettest air near the tropopause is over the ETP(Eastern Tibetan Plateau).The height of the tropopause decreases gradually from west to east over the plateau,although the difference in height is≤0.5 km.Relative to clear sky conditions,cloudy conditions are characterized by warming and wetting anomalies in the lower to midtroposphere and cooling and wetting anomalies in the tropopause and lower stratosphere.The largest vertical diurnal differences in temperature are at the surface and the difference decreases with increasing altitude from the surface to～12 km.The difference between the six time periods of early morning,morning,noon,afternoon,evening and midnight are within-0.5 to 0.5 K above 12 km.The difference in water vapor between the six time periods is≤0.2 g/m3.The lowest tropopause is at early morning.The height of the tropopause then increases followed by a decrease,with a sharp peak at noon.This establishment of a set of atmospheric standard profiles over Tibetan Plateau provides more accurate inputs for climate models.3.The characteristics of convective overshooting and its impact on the temperature and water vapor structure over the Tibetan PlateauIt was found that convective overshooting mainly occurs in the central and eastern part of the Tibetan Plateau,and its frequency varies from 0.1 × 10-5 to 9.1 ×10-5.The characteristics of temperature and water vapor structure of the convective overshooting were emphatically studied and the results show that the convective overshooting warms the low middle tropopause and cools the tropopause nearby significantly,which can also make air get wetter.The tropopause of the convective overshooting is substantially lower than the mean tropopause.Statistical results calculated from the five datasets are generally consistent;however,each dataset has its own strengths and weaknesses.The high spatiotemporal resolution temperature profiles from ERA5 along with the high vertical resolution temperature profiles from COSMIC can be combined to accurately study convective overshooting in the Tibetan Plateau.