Ground-based Remote Sensing Of The Atmospheric Boundary Layer Height And Its Distribution And Trend In China

Atmospheric boundary layer is the lowest atmosphere directly affected by the surface,and the bridge between surface and upper atmosphere to transporting momentum,water vapor,greenhouse gases and various atmospheric pollutants.The occurrence and development of weather system,global climate change and the impact of human activities on the earth system are all closely linked to the atmospheric movement within the boundary layer.Atmospheric boundary layer height(BLH)is a key parameter to describe the structural characteristics of the atmospheric boundary layer.The study of it is helpful to understand the process and structure of the boundary layer,and is of great significance to local atmospheric pollution monitoring and prediction.So in this article,The atmospheric boundary layer height was determined based on the data measured by micro pulse lidar(MPL-4B)and microwave radiometer(TP/WVP-3000)at the Semi-Arid Climate and Environment Observatory of Lanzhou University(SACOL).The results of the two data were compared and analyzed,and then the BLH climate characteristics in China were analyzed using the ERA-Interim reanalysis data and radiosonde data(1)When determining BLH based on lidar,strong echoes caused by clouds and residual layer at night will affect the accuracy and stability of the algorithm.Cloud identification algorithm was used to remove the influence of clouds,and the daytime convection boundary layer top was used as the upper limit of night BLH retrieval,and then the Haar wavelet covariance method was used to determine BLH.More reliable results were obtained,and the method was simpler and more suitable for automatic processing of large amounts of data.For the detection of microwave radiometer,the height of boundary layer was defined as the top of the surface inversion layer when it exists;otherwise,it was defined as the height with the maximum potential temperature gradient.The height of the boundary layer determined by the lidar was higher than that of the microwave radiometer,and it has a larger daily amplitude.The result of the boundary layer height obtained by the lidar inversion was generally larger than that of microwave radiometer,and the daily variation amplitude was also larger,up to 500 m.The variation amplitude of the microwave radiometer is about 300 m.Since the aerosol layer dropped later than the atmospheric stratification state change,BLH obtained by microwave radiometer began to fall at 17:00,while BLH obtained by lidar began to decrease after 18:00.(2)To understand the climate characteristics of China's BLH,the the ERA-Interim reanalysis data and radiosonde data(download from university of Wyoming meteorological website)form January 1979 to December 2017 were used to determine the BLH bulk Richardson number method,and the climate distribution characteristics and change trend of BLH in China were analyzed.Firstly,the reliability of BLH determined by standard isobaric surface and characteristic layer sounding data were analyzed by compared to the second level sounding data of Beijing(54511)and Yuzhong railway(52983).The correlation coefficients of BLH obtained from the two kinds of data were 0.96 and 0.94 in Beijing at 08:00 and 20:00 BJT,and it was 0.75 and 0.85 in Yuzhong,both of which pass the significance test.Therefore,the vertical resolution of the characteristic layer data can meet the need of determining BLH by the bulk Richardson number.This paper used the characteristic layer data from 1979 to 2017 to study the climate characteristics of BLH in China.Secondly,the correlation coefficient of BLH obtained from the ERA-Interim reanalysis data and radiosonde data was 0.35-0.73,and passed the significance test.Therefore,the BLH obtained from the ERA-Interim reanalysis data can reveal the characteristics of BLH in China.Based on the 1979-2017 average BLH obtained from the ERA-Interim reanalysis data,it can be seen that there were BLH high-value regions about 400 m in Gobi Desert regions such as Taklimakan Desert,Tibet Plateau and eastern Inner Mongolia;There were BLH low-value about 150 m in Tianshan Mountains,Qilian Mountains,southeast of Yunnan-guizhou Plateau and the Sichuan Basin.Both the high and low value centers of BLH have high or low value of sensible heat flux on the ground.BLH high value area had highest standard deviation(250-300 m),The standard deviation of the low value area of BLH was the lowest,which is 100-150 m.According to the characteristics of seasonal changes,In northwest China,BLH is the highest in summer,followed by spring,and the lowest in winter.In Tibet Plateau,BLH in spring and winter is higher than summer and autumn.In northeast China,BLH is the highest in spring,followed by summer,and the lowest in winter compares the monthly and seasonal changes of BLH in radiosondeFrom the trend of BLH obtained from the 1979-2017 ERA-Iinterim reanalysis data,it can be seen that BLH in Qilian Mountains,the southeast of Tibet Plateau plateau,north Xinjiang,central Inner Mongolia,Northeast Plain,Shandong Peninsula,southeast of Yunnan-guizhou Plateau and South China has a significant downward trend,with 14:00 BJT being the most obvious,and the largest decrease is up to-2 m/year.The BLH of east of Loess plateau,the surrounding mountains of Taklamakan Desert,southeast of the Tibet Plateau and the Beijing-Tianjin region increase significantly,with 14:00 BJT being the most obvious,up to 0.9 m/year,the area of increase is the largest at 2:00 BJT.Using radiosonde data to verify trends,there are also some sites trend does not agree.In general,the BLH has obvious trend and regional differences in China.