Study On The Microphysical Characteristics Of Precipitation In M(?)dog, South-eastern Tibetan Plateau

Mêdog,located at the entrance of the water vapor channel of the Yarlung Zangbo Grand Canyon（YGC）,has the largest rainfall totals over the Tibetan Plateau（TP）,a comprehensive cloud and precipitation observation test base was established at the Mêdog National Climate Observatory at the end of 2018,supported by“the Second Tibetan Plateau Scientific Expedition and Research（STEP）”.The monthly and diurnal variation characteristics of precipitation in Mêdog were analyzed with the automatic rain gauge data collected from 2019 to 2021.And then,the seasonal variation of the drop size distribution（DSD）of rainfall in Mêdog was studied based on the data collected from the precipitation phenomenometer from July 1,2019,to June 30,2020.Based on the observations from precipitation phenomenometer and X–band dual polarization phased array radar,the evolution process of two heavy precipitation events occurred in Mêdog were explored.Additionally,the microphysical characteristics of precipitation under the influence of four weather types（WTs）were analyzed by applying the T–PCA objective typing method.The results revealed that:（1）From the statistical results,precipitation frequently occurs in Mêdog with a predominating light rain less than 5 mm h^-1.The occurrence frequency of light rain with daily rainfall less than 10 mm is the highest,while moderate rain with daily rainfall between 10 mm and 25 mm has the largest contributor to rainfall amount.Mêdog precipitation has obvious monthly and daily variations.The highest occurrence frequency of rainfall occurred in monsoon season from June to September,which is attributed to the warm and humid airflow from the Indian Ocean.Furthermore,rainfall frequently occurs at night due to mountain-valley wind,which is probably related with the valley terrain of Mêdog.（2）The DSDs exhibits distinct seasonal characteristics.Overall,the concentration of large raindrops is highest during the pre-monsoon,while the concentration of small raindrops is highest during the monsoon period.The concentration of small raindrops is lowest during the winter.The pre-monsoon periodis characterized by prevailing westerly winds and precipitation dominated by cold rain processes,leading to the formation of more large raindrops via the melting of ice particles.Convective precipitation during the pre-monsoon period has the highest D_m（1.67 mm）and lowest log₁₀（N_w）（3.70）,is classified as between the maritime-and continental-like convective precipitation.During the monsoon period,precipitation is dominated by warm rain processes due to the influx of warm and moist air masses from the Indian Ocean.A large number of small raindrops are formed by the collision and coalescence process of water droplets.Convective rainfall during the monsoon period could be classified as maritime-like.During the winter,precipitation is dominated by cold rain processes,with the melting of ice particles resulting in a certain number of large raindrops.The relatively dry air and higher wind speeds lead to a decreased amount of small raindrops during the winter.The humid and weak wind conditions during the post-monsoon favor the production of small raindrops.（3）According to the objective classification results,the precipitation above medium in Mêdog was predominantly influenced by four weather types:WT1,featuring precipitation influenced by the southwest wind;WT2,marked by precipitation influenced by the southern branch trough;WT3,characterized by precipitation controlled by slanted atmospheric pressure;and WT4,featuring locally induced convective precipitation.Across the different weather conditions,the concentration of small raindrops was highest in WT1,while the concentration of medium to large raindrops was highest in WT4.Meanwhile,WT2 and WT3 exhibited similar DSD patterns,with relatively low concentrations of both small and large raindrops.The mean D_m values of the four WTs with stratiform precipitation were not significantly different,and the convective precipitation in WT1,WT2,and WT4 was classified as maritime-like,while the convective precipitation in WT3 was considered to be continental-like.