Statistical Analysis Of Summer Precipitation Characteristics In Motuo Based On X-Band Dual Polarization Phased Array Radar

The variation in precipitation in Motuo is closely associated with the transport of water vapor from the India Ocean and the Bay of Bengal to inland China,the Asia summer monsoon,and the progression of the rain band in eastern China,and is of great importance to the research of the variation of water resource in the Tibet Plateau.An X-band dual-polarization phased array weather radar(XPAR)is installed during the Second Tibetan Plateau Scientific Expedition and Research Program.The advanced dual-polarization phased array radar is used to continuously observe the precipitation in Motuo,overcoming the difficulties posed by the peculiar topography,insufficient electricity,and inadequate traffic conditions.For X-band weather radar,attenuation of the electromagnetic beam caused by raindrops is a significant issue.Before using XPAR data,it is necessary to conduct quality control procedures to correct the impact of attenuation,eliminate ground clutter,and remove random jitter caused by electromagnetic interference.XPAR data is not directly related to precipitation,before using XPAR data for statistical analysis of precipitation characteristics,it is necessary to obtain Quantitative Precipitation Estimation(QPE)formulas that is consistent with the characteristics of precipitation.Using DSD data from Motuo in 2019,the localized QPE formulas were obtained.We then selected three processes of precipitation with different cumulative precipitation,duration,and average rain rate from July to August 2020.We estimated precipitation piecewise utilizing reflectivity factor and differential propagation phase shift rate.We analyzed the distribution of radar parameters at typical moments,the variation of radar parameters and true value of precipitation with time.We evaluated the QPE effect of XPAR data using per-minute precipitation data from China surface station as the true value of precipitation.The result shows that the Piecewise Estimation Method(PEM)outperformed the QPE methods using reflectivity factor or differential propagation phase shift rate separately,with a NB of only 0.59%,a CC of 0.87,and RMSE and NE were performed well.Precipitation in Motuo may occur and grow as a result of the lifting of the southwest air flow by northern slopes of the XPAR,the precipitation is mostly composed of small and medium drops,and the diameter of raindrops is not closely related to the rain rate.We then used XPAR data from June to August 2020 to calculate and analyze the frequency of convective precipitation in Motuo,the probability distribution of rain rate and Liquid Water Content(LWC)of stratiformis and convective precipitation,as well as their distribution from June to August 2020,ten-day variation,and diurnal variation;the contribution of rain rate and LWC of stratiformis and convective precipitation to different hourly precipitation.The results show that:(1)The convective precipitation in Motuo mainly occur in the valley entrance area in the southwest of XPAR,and the valley in front of the slopes in the northeast of the XPAR.The frequency of convective precipitation gradually decreases from June to August 2020,the convective precipitation mostly occurring in mid-June to early July and late July to mid-August.Convective precipitation occurs more frequently after 16:00 and before 04:00(UTC).(2)Due to the noticeably lower average rain rate in late July of the summer of 2020,the average rain rate in Motuo is lowest in the summer of 2020.When convective precipitation is less frequent at 04:00 to 11:00,the rain rate is also relatively small.(3)The LWC of summer precipitation in Motuo exhibits a bimodal distribution.Similar to the distribution of rain rate,the first peak of the distribution probability of LWC is slightly shifts to the left,with the maximum probability increasing slightly.The overall LWC is relatively small in July,especially in late July.During the period of frequent occurrence of convective precipitation,the second peak of LWC in convective precipitation significantly increases,while from 04:00 to 07:00,the first peak of stratiformis precipitation increases significantly.(4)With the increasing of the hourly precipitation,the rain rate that mainly contributes to precipitation also gradually increases.Stratiformis precipitation is always dominated by precipitation less than10mm/h,while convective precipitation has a more pronounced increase in rain rate.The two peaks of LWC in both stratiformis and convective precipitation shift to the right.The rightward shift of convective precipitation is greater and gradually increases,while the second peak is dominant when the hourly precipitation is greater than 3mm.However,the first peak always dominants in stratiformis precipitation.