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

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.