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Vertical Structure Characteristics of Precipitation in Mêdog Area of Southeastern Tibet During the Monsoon Period
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摘要: 以2021年6—9月（季风期）藏东南水汽输送通道入口关键区墨脱布设的微雨雷达、降水现象仪和雨量计的观测数据为基础，对比不同仪器测量结果的一致性。将降水划分为对流云降水、层状云降水、浅层云降水3种类型，研究不同类型降水的雨滴谱分布、下落速度、降水率、液态水含量和雷达反射率因子的平均垂直分布特征。结果表明：微雨雷达、降水现象仪和雨量计测量结果一致性较好，微雨雷达和雨量计日降水量相关系数最高达到0.96，各相关系数的显著性水平较高；对流云降水的各微物理量特征值较大，雨滴在下落过程中碰并增长过程显著，雨滴数浓度迅速增加，在1~2 km高度处存在明显的上升气流；层状云降水回波强度较弱，反射率因子、降水率和液态水含量随高度降低有所增加，雨滴下落速度在垂直方向基本保持均匀，中等大小的雨滴浓度随高度不变，蒸发、破碎和碰并过程处于相对平衡状态；浅层云降水各微物理量较小，但随高度变化明显，垂直方向上为明显的负梯度变化，以雨滴的碰并过程为主。Abstract: Precipitation is particularly important for the earth's climate system. Understanding the structural characteristics, microphysical processes and drop size distribution (DSD) of precipitation is very important for quantitative precipitation estimation with radar and improving microphysical parameter schemes of numerical weather prediction models. With the launch of the Second Tibet Plateau Scientific Expedition and Research(STEPS), Chinese Academy of Meteorological Sciences has deployed Ka-band cloud radar (KaCR), X-band dual polarization phased array radar (X-PAR), disdrometer, micro rain radar (MRR) and other detection equipment in Mêdog, filling the gap of cloud and precipitation observation in this area and provides data basis for studying the physical characteristics of clouds and precipitation. Mêdog is located at Yarlung Zangbo Grand Canyon, the entrance of the water vapor channel in southeastern Tibet. Influenced by the warm and humid airflow brought by the Indian Ocean monsoon, the precipitation of Mêdog during the monsoon period exceeds 60% of the annual precipitation. MRR is a low-cost, miniaturized vertical directional Doppler rain radar that can more accurately analyze the vertical structural changes of precipitation. Based on observation of the rain gauge, MRR and disdrometer set up at Mêdog National Climate Observatory from 1 June to 30 September in 2021, the consistency of different instruments is studied. The observed rainfall is classified into convective, stratiform and shallow precipitation types, and the average vertical distribution characteristics of different precipitation types are studied from the aspects of raindrop size distribution, falling speed, rain rate, liquid water content and radar reflectivity. The results show that the measurement of rain gauge, MRR and distrometer are highly consistent. The correlation coefficient of daily rainfall is above 0.89, and the highest correlation coefficient between MRR and rain gauge is 0.96. However, MRR overestimates weak precipitation and underestimate strong precipitation. There are significant differences in the vertical structure of different precipitation types during the monsoon period of Mêdog. Values of each microphysical quantity of convective precipitation are larger. The collision and growth process of raindrop is significant during the falling process below 3 km height, and the raindrop number concentration increases rapidly. There is significant updraft at a height of 1-2 km. The echo intensity of stratiform cloud precipitation is weak below the height of the melting layer. The radar reflectivity, rain rate and liquid water content increase with altitude decrease, the falling speed of raindrops remains basically stable in the vertical direction. The concentration of medium-sized raindrops remains constant with height, and the evaporation, fragmentation, and coalescence processes are in a relatively balance. Values of each microphysical quantity of shallow precipitation are relatively small but vary significantly with height and show negative slops in the vertical direction. The shallow precipitation is dominated by the collision process of raindrops.
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图 1 墨脱国家气候观象台位置(红色实心圆点)及青藏高原地形(填色)
(叠加2021年季风期平均垂直积分水汽通量(黑色箭头))
Fig. 1 Location of Mêdog National Climate Observatory(the red solid dot) and topography(the shaded) of Tibetan Plateau
(which is superimposed with mean vertical integral of water vapor flux(black arrows) in monsoon period of 2021)
图 2 2021年6月1日—9月30日雨滴数浓度随直径和下落速度的分布
(黑色实线为Altas经验曲线，黑色虚线为经验关系±60%的范围)
Fig. 2 Distribution of raindrop number concentration with diameter and fall speed from 1 Jun to 30 Sep in 2021
(the solid black line denotes Altas experience curve, dashed black lines denote ±60% range of the experience relationship)
图 3 2021年9月29日微雨雷达、雨量计、降水现象仪观测对比
(a)日降水量, (b)03:00—07:00 6 min降水率随时间变化
Fig. 3 Rainfall Observed by micro rain radar, rain gauge and disdrometer on 29 Sep 2021
(a)daily rainfall, (b)6-minute average rain rate from 0300 BT to 0700 BT
图 4 2021年9月29日03:00—07:00雷达反射率因子(a)、下落速度(b)和地面雨滴谱(c)
Fig. 4 Radar reflectivity(a),falling speed(b) and ground raindrop size distributions(c) from 0300 BT to 0700 BT on 29 Sep 2021
图 5 2021年6月1日—9月30日墨脱3种类型降水的雷达反射率因子、下落速度、降水率和液态水含量的归一化高度-频率分布
(黑色实线为不同高度微物理特征量最大值连线，填色为发生频率)
Fig. 5 Normalized height-frequency of radar reflectivity, falling speed, rain rate and liquid water content for 3 rain types at Mêdog from 1 Jun to 30 Sep in 2021
(the solid black line connects points of the maximum at different altitude frequencies, the shaded denotes frequency)
图 6 2021年6月1日—9月30日墨脱3种类型降水微物理特征量的平均垂直廓线
(a)雷达反射率因子, (b)下落速度, (c)降水率, (d)液态水含量
Fig. 6 Average vertical profiles of the micro-physics for 3 rain types at Mêdog from 1 Jun to 30 Sep in 2021
(a)radar reflectivity, (b)falling speed, (c)rain rate, (d)liquid water content
图 7 2021年6月1日—9月30日墨脱3种类型降水的雨滴谱分布
(a)对流云降水，(b)层状云降水，(c)浅层云降水
Fig. 7 Raindrop spectrum distribution for 3 rain types at Mêdog from 1 Jun to 30 Sep in 2021
(a)convective, (b)stratiform, (c)shallow
表 1 微雨雷达主要性能参数
Table 1 Main performance parameters of micro rain radar
性能参数 取值 发射频率 24.230 GHz 操作模式 FMCW 发射功率 50 mW(+17 dBm) 波束宽度 1.5° 时间分辨率 10 s(最低1 s) 高度分辨率 10~200 m(可调节) 距离库数 128(可调节) 
下载: 导出CSV
表 2 降水类型分类
Table 2 Classification of rain types
降水类型 样本 降水量 降水率/(mm·h-1) 数量 占比/% 数值/mm 占比/% 对流云降水 1933 6.7 363.32 32.03 11.27 层状云降水 25485 88.4 747.53 65.90 1.74 浅层云降水 1417 4.9 23.55 2.07 0.99
下载: 导出CSV
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