Multiple Time- and Space-Scale Comparisons of ATLAS Buoy Rain Gauge Measurements with TRMM Satellite Precipitation Measurements

Yolande L. Serra Joint Institute for the Study of the Atmosphere and Ocean, University of Washington, Seattle, Washington

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Michael J. McPhaden NOAA/Pacific Marine Environmental Laboratory, Seattle, Washington

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Abstract

This study compares the Tropical Rainfall Measuring Mission (TRMM) microwave imager (TMI) and precipitation radar (PR) rainfall measurements to self-siphoning rain gauge data from 14 open-ocean buoys located in heavy-rain areas of the tropical Pacific and Atlantic Oceans. These 14 buoys are part of the Tropical Atmosphere–Ocean (TAO) array and Pilot Research Moored Array in the Tropical Atlantic (PIRATA). Differences between buoy and TRMM monthly and seasonal rainfall accumulations are calculated from satellite data within 0.1° × 0.1°–5.0° × 5.0° square areas centered on the buoys. Taking into account current best estimates of sampling and instrumental errors, mean differences between the buoy and TMI rainfall are not significant at the 95% confidence level, assuming no wind-induced undercatch by the buoy gauges. Mean differences between the buoy and PR monthly and seasonal accumulations for these spatial scales suggest that the PR underestimates these accumulations by about 30% in comparison with the buoys. If the buoy rain rates are corrected for wind-induced undercatch, TMI accumulations fall systematically and significantly below buoy values, with underestimates of up to 22% for both monthly and seasonal data. Also the PR underestimates, relative to wind-corrected buoy values, increase to up to 40% for both monthly and seasonal data. Regional and rain-rate dependencies of these comparisons are also investigated.

Corresponding author address: Dr. Yolande Serra, Joint Institute for the Study of Atmosphere and Ocean, Box 357941, University of Washington, Seattle, WA 98195-7941. yolande.serra@noaa.gov

Abstract

This study compares the Tropical Rainfall Measuring Mission (TRMM) microwave imager (TMI) and precipitation radar (PR) rainfall measurements to self-siphoning rain gauge data from 14 open-ocean buoys located in heavy-rain areas of the tropical Pacific and Atlantic Oceans. These 14 buoys are part of the Tropical Atmosphere–Ocean (TAO) array and Pilot Research Moored Array in the Tropical Atlantic (PIRATA). Differences between buoy and TRMM monthly and seasonal rainfall accumulations are calculated from satellite data within 0.1° × 0.1°–5.0° × 5.0° square areas centered on the buoys. Taking into account current best estimates of sampling and instrumental errors, mean differences between the buoy and TMI rainfall are not significant at the 95% confidence level, assuming no wind-induced undercatch by the buoy gauges. Mean differences between the buoy and PR monthly and seasonal accumulations for these spatial scales suggest that the PR underestimates these accumulations by about 30% in comparison with the buoys. If the buoy rain rates are corrected for wind-induced undercatch, TMI accumulations fall systematically and significantly below buoy values, with underestimates of up to 22% for both monthly and seasonal data. Also the PR underestimates, relative to wind-corrected buoy values, increase to up to 40% for both monthly and seasonal data. Regional and rain-rate dependencies of these comparisons are also investigated.

Corresponding author address: Dr. Yolande Serra, Joint Institute for the Study of Atmosphere and Ocean, Box 357941, University of Washington, Seattle, WA 98195-7941. yolande.serra@noaa.gov

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