Diurnal Variation in the Vertical Profile of the Raindrop Size Distribution for Stratiform Rain as Inferred from Micro Rain Radar Observations in Sumatra

Abstract

The diurnal variation in the vertical structure of the raindrop size distribution (RSD) associated with stratiform rain at Kototabang, West Sumatra (0.20°S, 100.32°E), was investigated using micro rain radar (MRR) observations from January 2012 to August 2016. Along with the MRR data, the RSD from an optical disdrometer and vertical profile of precipitation from the Tropical Rainfall Measuring Mission were used to establish the microphysical characteristics of diurnal rainfall. Rainfall during 0000–0600 LST and 1800–2400 LST had a lower concentration of small drops and a higher concentration of large drops when compared to rainfall during the daytime (0600–1800 LST). The RSD stratified on the basis of rain rate (R) showed a lower total concentration of drops and higher mass-weighted mean diameter in 0000–0600 LST and 1800–2400 LST than in the daytime. During the daytime, the RSD is likely governed by a riming process that can be seen from a weak bright band (BB). On the other hand, during 0000–0600 LST and 1800–2400 LST, the BB was stronger and the rainfall was associated with a higher concentration of midsize and large drops, which could be attributed to more active aggregation right above the melting layer with minimal breakup. Diurnal variation in the vertical profile of RSD led to a different radar reflectivity (Z)-R relationship in the rain column, in which Z during the periods 0000–0600 LST and 1800–2400 LST was larger than at the other times, for the same R.

摘要

本文利用2012年1月至2016年8月的微降水雷达 (MRR) 观测资料, 研究了西苏门答腊Kototabang (0.20°S, 100.32°E) 层状云降水过程的雨滴谱 (RSD)垂直结构日变化.

除微降水雷达数据外, 文中同时采用激光雨滴谱仪观测的雨滴谱分布和热带降水测量卫星 (TRMM) 探测的降水垂直结构以建立日降水–微物理特征关系.

与白天 (0600–1800 LST) 相比, 0000–0600 LST 和 1800–2400 LST 期间降水小雨滴数浓度较低, 大雨滴数浓度较高. 由雨强 (R) 对雨滴谱的分档研究表明, 0000–0600 LST 和 1800–2400 LST 期间, 雨滴总浓度比白天低, 质量加权平均直径比白天大. 白天雨滴谱分布很可能受弱亮带 (BB) 上呈现出的凇附过程影响. 另一方面, 0000–0600 LST 和 1800–2400 LST 期间, 亮带更强, 降水与较高的大中雨滴浓度相关, 这可归因于融化层上方更活跃的聚合以及影响极小的破碎过程. 雨滴谱垂直廓线日变化导致了降水垂直方向上不同的雷达反射率–雨强关系, 对于相同的雨强, 在 0000–0600 LST 和 1800–2400 LST 期间, 其反射率比其他时间大.