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  • Author or Editor: Michael McPhaden x
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Yolande L. Serra
and
Michael J. McPhaden

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.

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Mark L. Morrissey
,
Witold F. Krajewski
, and
Michael J. McPhaden

Abstract

The relationship between the fractional time raining and tropical rainfall amount is investigated using raingage data and a point process model of tropical rainfall. Both the strength and the nature of the relationship are dependent upon the resolution of the data used to estimate the fractional time raining. It is found that highly accurate estimates of rainfall amounts over periods of one month or greater can be obtained from the fractional time raining so long as high-time-resolution data are used. It is demonstrated that the relationship between the fractional time raining and monthly atoll rainfall is quasi-homogeneous within the monsoon trough region of the equatorial western Pacific.

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Jeffrey A. Nystuen
,
Michael J. McPhaden
, and
H. Paul Freitag

Abstract

Surface measurements of precipitation in oceanic environments have proven especially difficult to obtain because traditional technologies such as tipping-bucket rain gauges are unsuitable for deployment from oceanic platforms such as ships and moorings. Recently, the Pacific Marine Environmental Laboratory of the National Oceanic and Atmospheric Administration has modified a collection gauge, the R. M. Young Company rain gauge, for long-term deployment on deep ocean moorings. This instrumentation package was deployed during part of the South China Sea Monsoon Experiment. Also deployed on the same mooring were two acoustic rain gauges (ARGs) that monitor precipitation through the interpretation of the high-frequency, from 500 to 50 000 Hz, underwater sound field. The mooring was located at 20°22.2′N, 116°31.2′E and was in place from 7 April–5 June 1998. Unfortunately, pirates stole the surface instrumentation on 6 May 1998, limiting data from the R. M. Young rain gauge to satellite transmissions prior to the attack. The ARGs survived the attack and reported data throughout the deployment. The acoustic data are interpreted to provide quantification of wind speed; detection, classification, and quantification of rainfall; and the detection and quantification of near-surface bubble layers. Percentage-of-time-raining data from the two rainfall measurements are in excellent agreement. Based on comparison with the R. M. Young rain gauge data, modified acoustic rainfall algorithms are proposed. The acoustic detection of several instances of high near-surface bubble injections during extremely heavy rainfall is described.

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