| 摘要: | 雲物理過程為水象粒子在空氣中的變化，然而並沒有直接的觀測能量測到雲物理過程，因此要以觀測的角度來了解雲物理過程是一個具挑戰性的課題。然而2008年西南氣流實驗擁有足夠的觀測資料(美國National Center for Atmospheric Research S-band Polarimetric radar system, NCAR S-POL雷達及11部雨滴譜儀Disdrometer )，可以透過這些觀測資料來了解雲物理過程。
本研究首先利用雙偏極化雷達資料的垂直統計特性，分析西南氣流實驗中七個強降雨個案(5/26, 6/2, 6/4, 6/5, 6/13, 6/14, 6/16)的雲物理特徵，再進一步根據地面DSD (drop size distribution)的結果，透過雙偏極化雷達資料的垂直特性，找到不同地面DSD所對應的上方雲物理過程差異。從七個個案的分析結果發現有明顯的兩個群組特徵，(1) 5/26及6/13為深對流獨立降水系統其垂直發展較高、地面有較大的雨滴、明顯的碰撞結合過程及高層較多的軟雹，但卻有較低的液態水含量，(2) 6/5及6/16為有組織性的中尺度對流系統(mesoscale convective system)從南中國海向北移入台灣，其垂直發展較低、地面有較小的雨滴、碰撞結合過程較不明顯，卻有較高的液態水含量。
第二部分統計了西南氣流實驗期間近兩個月的資料，將地面雨滴譜儀資料劃分成48個特性組，針對每個特性組所對應的正上方雷達資料做平均，找到不同特性組中雷達資料的差異。其結果顯示雨滴越大且數量越多的DSD特徵組，其1公里高度的ZHH與KDP值越大，對流發展越高，有越明顯的碰撞結合過程，此外ZDR此變數與雨滴大小較有關，此結果與第一部份結果相符。本研究結果顯示可透過雙偏極化雷達及雨滴譜儀兩種觀測資料來了解降水雲物理過程。
;Studying the microphysical processes of precipitation systems from the perspective of observations is important and challenging. During the 2008 Southwest Monsoon Experiment /Terrain-influenced Monsoon Rainfall Experiment (SoWMEX/TiMREX), huge amount of observational data were collected, which allowed us to study microphysical processes using the observations of a dual-polarimetric radar (NCAR S-POL) and disdrometers.
In the first part of this research, we use vertical profiles of dual-polarimetric measurements to investigate the microphysics characteristics of seven heavy rainfall events. In the second part, we further investigate the differences of vertical structure and microphysics characteristics from different DSD results near the ground observed by disdrometers. Two distinct types of precipitating characteristics can be found in the analyses of seven heavy events. They are: (1) Deep convection (5/26 and 6/13) containing large rain drops, low liquid water content, high graupel water content and pronounced collision coalescence process. (2) Organized convection (6/5 and 6/16) with small rain drops, high liquid water content and less pronounced coalescence process.
In the second part, two months of disdrometer data near the ground during the 2008 SoWMEX are classified into 48 groups. The averages of the vertical profiles of dual-polarimetric measurements above the disdrometer are used to analyze the differences of microphysical processes based on these 48 groups. The results indicate that large and high concentration raindrops are associated with large ZHH, KDP at Z = 1.0 km, deep convection, as well as pronounced collision coalescence process. In addition, the value of ZDR is proportional to the size of raindrops. The results are consistent with those from the first part.
Overall, this study successfully demonstrates the application of combining dual-polarimetric and disdrometer data to investigate the microphysical processes in heavy rainfall events. |
