- 期刊
第五版IMERG Early、Late及Final runs衛星資料對2014-2017年期間臺灣暖季降雨特性的表現能力比對
Comparison of the Warm Season Rainfall Estimations in Taiwan during 2014-2017 from IMERG Version 5 Early, Late and Final run Satellite Products
摘要
本研究評估第五版Integrated Multi-satellite Retrieval for Global Precipitation Measurement（簡稱IMERG）Early run，Late run及Final run衛星降水產品對2014-2017年臺灣暖季（5-10月）降雨特性的表現能力。其中Final run產品的發布時間較實際觀測時間延遲2.5個月，而 Early run（延遲4小時）、Late run（延遲12小時）產品的發布時間則較即時。研究重點在了解上述三組產品對（1）降雨的平均狀態，（2）不同降雨強度的發生頻率比例，及（3）極端降雨指數的表現能力差異。結果發現，以降雨的平均狀態來說，Final run的表現能力比Early run及Late run好。就降雨事件的發生頻率來看，Final run在強度為20 mm/day以上的降雨發生頻率比例幾乎與地面觀測一致，Early run和Late run則為低估的情況。此外，三組衛星資料都對於越強降雨的掌握能力越低，但Final run對於定量降雨掌握能力優於Early run及Late run。最後我們參考世界氣象組織氣候變化檢測和指標專家小組提出的4種極端降雨指數來檢驗衛星資料對臺灣極端降雨的掌握情況。結果顯示，Final run較Early run及Late run能夠掌握臺灣暖季極端降雨的空間分布特徵。而對於即時資料的使用者，我們提醒若僅就降雨的空間分布來看，Late run相較於Early run更能掌握臺灣降雨的分布特徵。但需注意到Early run、Late run對於較強的降雨量都有明顯低估的情形，並以Late run低估的程度較多。以上成果有助於未來應用IMERG產品進行臺灣降雨相關議題分析之參考。
並列摘要
This study evaluates the performance of IMERG (Integrated Multi-satellite Retrieval for Global Precipitation Measurement) version 5 Early run, Late run, and Final run satellite products in identifying the characteristics of warm season (May to October) rainfall in Taiwan during 2014-2017. The update time of Final run product is delayed about 2.5 months from the observed time, while the update time of Early run (delayed about 4 hours) and Late run (delayed about 12 hours) products is closer to real-time. The analyses of this study focus on the assessment of satellite products in depicting (1) the mean status of rainfall, (2) the occurrence frequency of rainfall in various criteria of intensity and (3) the extreme rainfall indices. Analytical results show that the Final run performs better than Early and Late runs for measuring the mean status of rainfall. In addition, the Final run estimation of the occurrence frequency of rainfall ≥ 20 mm/day is almost the same as the surface observation result, while the Early and Late runs underestimate the percentage. The Final run also performs better than Early and Late runs for quantitative precipitation estimation, even though all three satellite products show a similar feature that the performance skill usually declines with increasing thresholds of rainfall intensity. Finally, the performance of satellite products in depicting the extreme rainfall in Taiwan is assessed using four extreme rainfall indices suggested by the WMO (World Meteorological Organization) ETCCDI (Expert Team on Climate Change Detection and Indices). Analytical results reveal that the Final run performs better than the Early and Late runs in depicting the four extreme rainfall indices. However, researchers who wish to use more real-time data (e.g., Early and Late runs) should note that Late run (Early run) performs better than Early run (Late run) in qualitatively (quantitatively) depicting the spatial-temporal variations of warm season rainfall in Taiwan. These analytical results provide valuable information for future application of IMERG products in studying the related issues of warm season rainfall in Taiwan.
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