A Study On Climate Characteristics Of The Atmospheric Heat Source Over The Tibetan Plateau And Its Impact On Atmospheric Circulation And Precipitation In Surrounding Regions

The atmospheric heat source(AHS)over the Tibetan Plateau(TP)not only plays an important role in the generation,maintenance and development of the weather system in the surrounding region but also has an important influence on the monsoon and circulation of the Northern Hemisphere and even the global climate system.The quantitative estimation of plateau AHS is of great significance to the study of global weather and climate.Many scholars have made quantitative estimations of the AHS on the plateau and reached useful conclusions.However,due to the different methods and data used in the research,there are still some differences in the conclusions.To date,there is still a lack of a quantitative comparison between the forward algorithm and the reverse algorithm.Based on the above content,this paper will carry out research from three aspects:evaluation of heat source data,quantitative estimation of AHS and influence of thermal anomalies.This paper evaluates the applicability of multisource reanalysis datasets(ERA5,JRA55,MWEEA2,NCEP2)on the TP by using the measured sounding data from six stations on the TP(Dingri Station,Gaize Station,Hongyuan Station,Linzhi Station,Naqu Station and Lhass Station).The results show that the quality of ERA5 relative humidity data is the best,the RMSE between ERA5 data and measured relative humidity data is the smallest(10.60%),the correlation coefficient is the highest(0.92),and the trend of change in the vertical direction is the most consistent.At Linzhi Station,Lhasa Station and Dingri Station,the relative humidity profile was approximately presented as "S" type.At Gaize station and Hongyuan station,the relative humidity profiles were approximately inverted "C" type.At Naqu station,the vertical profile of relative humidity is approximately "E" type.On this basis,ERA5 data and high precision precipitation and radiation data are used to compare the differences between the AHS calculated by the forward and reverse algorithms.The temporal and spatial characteristics and driving factors of AHS over the TP from 2001 to 2020 were analysed.The results show that(1)the AHS over the TP calculated by the forward and reverse algorithms showed an annual growth trend from 2001 to 2020,but the AHS calculated by the reverse algorithm was approximately 4 W/m2 higher than that calculated by the forward algorithm.(2)The AHS over the TP calculated by the forward algorithm shows that the atmosphere over the TP is a strong heat source in summer,and the dominant factor is the release of latent heat caused by precipitation.The heat source intensity reaches its maximum in July(123 W/m2).The plateau atmosphere is a cold source in winter,mainly contributed by radiative cooling,and the intensity reaches its maximum(-45 W/m2)in December.During the 20 years from 2001 to 2020,the sensible heat flux near the surface was basically stable at 40 W/m2,while the AHS,latent heat of condensation and net radiation showed an obvious increasing trend,with an annual growth rate of 0.38 W/m2,0.17 W/m2 and 0.15 W/m2,respectively.(3)In the vertical direction,the AHS of the TP calculated by the reverse algorithm shows that the atmosphere of 150-200 hPa can be regarded as a dividing line.In this vertical range,the AHS over the TP is an obvious low-value area,which only shows a weak heat source with an intensity of 5 W/m2 in summer.In the atmosphere above 150 hPa and from the surface to 200 hPa,the intensity of the AHS and the duration of the strong heat source are significantly higher than those in the atmosphere between 150 and 200 hPa.Finally,the influence of the thermal anomaly on atmospheric circulation and precipitation over the TP is studied.The atmospheric thermal index of the TP has a strong positive correlation with the atmospheric circulation and precipitation over central and eastern China,the Tibetan Plateau,the Mongolia Plateau,the Northeast Plain and the Pamir Plateau.When the plateau heat is abnormally high,on the one hand,the surface heating effect of the plateau makes the local vertical upwards motion more intense,resulting in strong positive vorticity cyclonic circulation at the low level and strong negative vorticity anticyclonic circulation at the high level,strengthening the South Asian High.Moreover,the abnormal heating effect of the plateau has also strengthened the thermal contrast between land and sea,strengthening the Western Pacific subtropical high and the East Asian summer monsoon.On the other hand,the strong thermal anomaly of the plateau will cause the temperature increase of the plateau to be much stronger than that of surrounding areas.Under the action of the wind field,the warm advection in the eastern part of the plateau is enhanced,resulting in upwards movement.At the same time,the "sensible heat pump" of the plateau makes the lower level air converge to the plateau,bringing much water vapour from the South China Sea and the Western Pacific.As a result,precipitation in the eastern part of the plateau increased significantly.However,when the plateau thermal anomaly is weak,the situation is the opposite.