H217-02
A TRMM/GPM Composite Climatology and its Use in the New Version of GPCP

Wednesday, 16 December 2020: 20:34
Virtual
Robert F Adler1, Jian-Jian Wang1, George John Huffman2, Ali Behrangi3 and David T Bolvin4, (1)University of Maryland College Park, College Park, MD, United States, (2)NASA Goddard Space Flight Center, Greenbelt, MD, United States, (3)University of Arizona, Department of Hydrology and Atmospheric Sciences, Tucson, AZ, United States, (4)Science Systems and Applications, Inc., Lanham, MD, United States
Recorded Presentation
Abstract:
A Tropical Composite Climatology (TCC) is described using 22 years (1998-2019) of TRMM and GPM-based surface precipitation estimates from the three main algorithms, i.e., from passive microwave (PMW), radar (RDR) and combined passive microwave and radar (COMB) observations. The final TCC estimate is a simple mean over the 22 years of the three estimates for each month-of-the-year at a resolution of 0.5º latitude-longitude over the latitude band 36º N to 36º S. The standard deviation of the three mean estimates provides a measure of dispersion and therefore of the consistency of the final estimate.

Over ocean, in the deep tropics (25º N to 25º S), the mean annual TCC value of 3.37 mm/d is about 6% higher than the GPCP V2.3. Of the three component inputs to the TCC the PMW estimate is the largest (3.44 mm/d). Poleward of the sub-tropical minima the TCC becomes slightly lower than the GPCP V2.3, especially in the southern hemisphere. There are larger deviations evident for various seasons and also for regions. Some of these factors will be discussed.

Over land in the tropics the TCC mean annual value is more than 20% lower than that of the GPCP V2.3 (which contains rain gauge information over land), with the PMW estimate about 10% lower, but with the two estimates involving the radar data very much lower.

For the new monthly GPCP V3 the TCC over tropical oceans is meant to provide a ‘best” estimate of month-of-the-year climatological means on a regional basis. The TCC month-of-the-year climatologies are used to derive grid-based adjustments by comparing to the near-final V3 satellite mean estimates (driven by SSMI and SSMIS data) over ocean for the same 1998-2018 period. These bias adjustment ratios are then applied to each individual month and region (with some smoothing) to provide the final monthly estimates for the entire GPCP V3 record (1983-near present). This procedure in the deep tropics (25º N to 25º S) is linked to similar adjustments at higher latitudes based mainly on CloudSat. Thus, the final monthly GPCP V3 should have mean values over ocean based on TRMM/GPM in the tropics, about 6% larger in the deep tropics as compared to V2.3.

More specific details from V3 in the tropics will also be described, including regional and seasonal differences and amplitude of inter-annual (ENSO) variations.

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