雨滴分篩現象(Hydrometeor size sorting)是一個受到雨滴終端落速不同產生的雲微物理現象。當強水平風存在時雨滴會受到水平應力而向下風處移動，大雨滴受到其質量大終端落速快的特性，會落在小雨滴水平風方向的相對上游處。這樣的現象在強風場如颱風、龍捲風下會更為顯著。本研究旨在使用雷達觀察颱風眼牆區域中的雨滴粒徑分類過程，分為使用地面雷達與衛星雷達。其中，差異反射率(Z_DR)與質量權重粒徑(D_m)對於雨滴大小較敏感，而回波(Z_H/Z_e)則對雨滴數量更為敏感。本次研究利用四個地面雷達的個案，分別是凱米颱風(2024)、丹娜絲颱風(2025)、山陀兒颱風(2024)以及燦樹颱風(2021)。藉由分析颱風眼牆中回波與差異反射率之間的差異，結果顯示在逆時針旋轉的颱風眼牆中，高Z_DR偏向落在風場上游(順時針)處，而高Z_H則更偏向往下游(逆時針)延伸，。除此之外，本研究利用數值方法量化水平雨滴分篩現象的程度。利用相關係數權重值代表Z_H與Z_DR之間的差異性。結果說明在絕大部分時間下，相關係數權重值都偏向正值，表示高Z_DR偏重在高Z_H上游處。但當75百分位Z_DR數值大於0.7時，權重值的大小會有更顯著的結果。將此方法套用至衛星雷達觀測結果時，發現權重值同樣為正值居多，但偏折數值相對減少許多，可能的因素為衛星雷達(GPM)解析度影響。未來也可繼續針對此方面問題作探討。;Hydrometeor size sorting is a microphysical phenomenon driven by differences in raindrop terminal velocity. With strong horizontal wind， hydrometeors can be transported downstream as they fall. While big drops descent faster and tend to fall in the upstream area， small drops which fall slower， tend to propagate further downstream. Such a result can be more prominent in the presence of enhanced horizontal winds such as those in a Tropical Cyclone (TC) or tornado. This research aims to discover such a phenomenon within TC’s eyewall region using both ground-based and space borne radar. With differential reflectivity (Z_DR) / mass weighted mean diameter (D_m) being more sensitive to bigger size of droplets and reflectivity (Z_H) being more sensitive to the concentration of drops， this research analyze the behavior of those polarimetric variables and discover the signature of size sorting within the eyewall region of TC. Four ground based cases were investigated in this study， including Gaemi (2024)， Krathon (2024)， Chanthu(2021) and Danas (2025). The result indicate that high Z_DR region is primarily located where it originated. At the same time， high reflectivity often seen in the downstream area， which rotates counterclockwise. Such a signature is more prominent at a lower altitude， where droplets have had sufficient time to be separated by the eyewall’s tangential wind. Furthermore， an algorithm is developed to quantify the sorting effect using both Z_H and Z_DR. By comparing the signal distribution between Z_H and Z_DR. Results show that， most of the time， the TC yields a positive sorting signal， with higher shifting signal accompanied by more intense wind and larger Z_DR， especially for Z_DR larger than 0.7 dB. However， result from space borne radar showed different result as shifting magnitude being reduced due to data resolution. Which needs further investigation in the future.
