Quality Control Of Phased Array Radar And Analysis Of Macro Characteristics Of Precipitation In Motuo,Tibet

In order to analyze the influence of monsoon,topography,snow on both sides,glacier and valley wind on the precipitation in Motuo,the characteristics of cloud precipitation in Motuo were studied.This study is scientific and practical in assessing the changes of water resources in Asian water towers.In order to make up for the research blank of cloud precipitation in the valley area of southeast Qinghai Tibet Plateau,an X-band phased array polarization radar was set up in the second comprehensive scientific investigation and research project of Qinghai Tibet Plateau,which realized the continuous observation of cloud and precipitation in Motuo for the first time.The main purpose of using X-band phased array weather radar to observe is to improve the stability and reliability of the radar,and realize the unattended continuous observation.However,the performance parameters of phased array radar array antenna deteriorate with the elevation deviation from the normal angle of the array,which makes the quantitative measurement difficult.In this paper,the observation data reliability of the X-band phased array polarization radar was firstly tested.Due to the lack of contrast radar which can be used as"standard"in Motuo,three X-band phased array polarization radars with the same model as Motuo were selected for data verification.The S-band dual polarization radar in Guangzhou was regarded as the“standard”.Based on different longitude and latitude radar data matching method,the systematic deviation of echo intensity,differential reflectivity and differential phase shift rate of three phased array radars from March to April in 2019 in Guangzhou were analyzed.The comparison results show that the error of echo intensity is small,about0.82 d B,while the error of differential reflectivity factor is as high as 1.04 d B,and the fluctuation between different elevation and different time is also found.The variation range of Z_H bias with time is 1～3 d B,and the variation range of Z_H bias with elevation is 1～2 d B.The variation of Z_DR bias with time is 1～2 d B,and the fluctuation range is0.5 d B at different elevation angles.Through the above comparative study,the reliability of the radar data is preliminarily verified,and the X-band phased array dual polarization radar data can be used for cloud and precipitation statistical analysis.The observation data of X-band phased array polarization radar at Motuo station from November 2019 to October 2020 are subsequently used to analyze the monthly,daily and altitude variations of echo intensity and echo top height of cloud precipitation in Motuo,and compared with Doppler radar observation data during summer monsoon in Naqu area.The results show that:（1）The echo peak height,echo area,the proportion of strong echo and echo distribution range in April to October are greater than those in November to march in Motuo area,which indicates that the precipitation frequency is high and convective precipitation is more in April to October,especially in June.However,the increase of the number of weak echoes in April leads to the fact that the echo intensity from April to October is less than that from November to March.According to the monthly variation characteristics of cloud precipitation in Motuo and the plateau monsoon index,the year is divided into dry season（November to March）and rainy season（April to October）.（2）The echo frequency,top height and area of precipitation in rainy season are larger than those in dry season,which indicates that the precipitation frequency in rainy season is higher and the convective activity is more vigorous.The diurnal variation of precipitation echo frequency,top height and area showed that the daily precipitation mainly occurred in the afternoon and the first half of the night in the dry season,and in the second half of the night in the rainy season.（3）The echo intensity of precipitation in Motuo is mostly less than 30dbz.The echo frequency is higher in dry season when the altitude is more than 3km,and higher in rainy season when the altitude is less than 3km.（4）During the summer monsoon,the echo peak height of Motuo is lower than that of Naqu,and the diurnal variation trend of its peak height and area is different from that of Naqu.During the summer monsoon,the daily precipitation in Naqu is mainly concentrated in the afternoon and the first half of the night,while the precipitation in Motuo is mainly concentrated in the second half of the night.The characteristics of cloud precipitation in dry season of Motuo are similar to those in summer monsoon period of Naqu.