Performance evaluation of GPM IMERG precipitation products over the tropical oceans using Buoys

Abstract

The major fraction of the global precipitation falls in tropical oceans. Nonetheless, due to the lack of in-situ precipitation measurements, the number of studies over the tropical oceans remains limited. Similarly, the performance of IMERG products over the tropical oceans, is yet to be known. In this context, this study quantitatively evaluates the 20 years (2001 – 2020) of IMERG V06 Early, Late, and Final products against the in-situ buoys estimates using the pixel-point approach at a daily scale across the tropical oceans. Results show that IMERG represents well the mean spatial pattern and spatial variation of precipitation, though significant differences exist in the magnitude of precipitation amount. Overall, IMERG notably overestimates precipitation across the tropical ocean, with maxima over the West Pacific and Indian oceans, while it performs better over the East Pacific and Atlantic oceans. Moreover, irrespective of the region, IMERG sufficiently detects precipitation events (i.e., > 0.1 mm/day) for high-precipitation regions, though it significantly overestimates the magnitude. Despite IMERG’s detection issues of precipitation events over the regions with lower precipitation, it depicts good agreement with the buoys in total precipitation estimation. The positive hit bias and false alarm bias are the major contributions to the overall total positive bias. Furthermore, the detection capability of IMERG tends to decline with increasing precipitation rates. In terms of IMERG runs, IMERG-F shows slightly better performance than the −E, −L runs. More detailed studies over the tropical oceans are required to better characterize the biases and their sources.