TRMM/PR降雨估算之驗證及其應用－台灣陸地降雨之研究

Verification of TRMM/PR Derived Rain Rate and Its Applications-The Study of Precipitation over the Taiwan Land

蔡明達(Ming-Da Tsai) ； 陳萬金(Wann-Jin Chen) ； 方錫棋(Chin-Hui Feng) ； 劉振榮(Gin-Rong Liu) ； 李慶忠(Ching-Chung Li)

《大氣科學》 34卷1期 (2006/03) Pp. 1-24

摘要

TRMM(Tropical Rainfall Measuring Mission)衛星上之降雨雷達(Precipitation Radar, PR)，是第一具星載的氣象雷達。所使用的頻率為13.8GHz、水平解析度5公里、垂直解析度250公尺、刈幅(swath)寬為220公里。本研究將針對TRMM辦公室所提供PR 2A25的標準產品，利用台灣地區地面自動雨量站的觀測資料進行驗證。此外，也利用PR三維的降雨觀測資料，針對台灣地區的降雨特徵進行研究。
在PR降雨估算驗證方面，本研究蒐整2002-2004三年內通過台灣陸地的衛星降雨資料進行研究。研究中發現，在2002年梅雨與颱風的個案，梅雨期間PR估算的降雨量與地面觀測站的降雨分佈二者較為一致，其相關係數為0.66。而颱風期間二者之問的差異較大，其相關係數為0.54。而三年平均的相關係數約為0.32-0.47。經分析比較後，發現相關性與每月累積降雨量有關，當每月累積降雨量較大時，其相關性較佳，反之，則其相關性較差：而另外一個影響PR與地面雨量站之間相關性的因素為地形效應對。
於台灣地區的降雨特徵，本研究利用PR可辨識雨區的優點，分析對流性降雨及層狀性降雨的垂直分布特徵，以瞭解其微物理過程。研究發現對流性降雨與層狀性降雨隨不同季節及地區，降水發展高度有所改變，對流性降雨普遍高於層狀性降雨，而在層狀性降雨的剖面圖則有明顯的亮帶顯現。在春、冬兩季主要降雨型態為層狀性降雨，而夏、秋季對流性降雨的雨量皆大於層狀性降雨，尤其是在南台灣地區特別明顯。對流性降雨與層狀性降雨的垂直剖面分布有明顯區別，降水垂直剖面清楚反應了降水微物理過程的垂直分布。

關鍵字

TRMM ； PR ； 自動雨量站 ； 梅雨 ； 颱風 ； 對流性 ； 層狀性

並列摘要

The Precipitation Radar (PR) of Tropical Rainfall Measuring Mission (TRMM) satellite is the first space-borne meteorological radar. And the frequency is 13.8GHz, the horizontal resolution is 5 km, the vertical resolution is 250 m and the swath is 220 km. In this study, rainfall rate of Automatic Rainfall and Meteorological Telemetry System (ARMTS) measurements of Taiwan are used as a ground truth to validate the accuracy of rainfall retrievals that TRMM office provide a standard products of 2A25 derived from Precipitation Radar. In addition, using the data of 3 dimension precipitation observed with PR to investigate the characteristic of Precipitation over the Taiwan land region.
Verification of TRMM/PR derived rain rate, this study collected all the TRMM/PR data covering the Taiwan island area from 2002 to 2004 and validated the satellite rainfall retrievals with the rain gauge data. Results show that the rain maps derive from TRMM/PR and rain gauge are comparison in the Meiyu cases, and the average correlation coefficient is 0.66. In the typhoon cases, the parts of the rain maps are difference between device from TRMM/PR and rain gauge, and the average correlation coefficient is 0.54. There are three year data sets, and the annual average correlation coefficient from 0.32 to 0.47. It is also shown that the correlation coefficient depends on the amount of rainfall, better one with huge accumulated rainfall and poor one with little accumulated rainfall. One another factor which affects the value of correlation coefficient is terrain.
About to investigate the characteristic of Precipitation over the Taiwan land region, the vertical rainfall structures for convective and stratiform were analyzed for the understanding of the microphysical rainfall processes. It is shown that in general the height of development depends on season and on location that precipitation occurs. The height of development for convective rainfall is larger that that for straitform rainfall and there is a bright band appeared on the stratiform rainfall profile. Straitfall rainfall is the primary rain type in the spring and winter seasons, while convective rainfall is significantly dominant and the amount of rainfall is usually more than that of stratiform both in summer and in fall, especially in the south of Taiwan. It is easily to distinguish convective from stratiform rainfall from the vertical rainfall profile and the understanding of their microphysical precipitation processes.

並列關鍵字

TRMM ； PR ； ARMTS ； Meiyu ； Typhoon ； Convective ； Straitform