Liang LiaoGoddard Earth Sciences & Technology Research

Morgan State UniversityGreenbelt, MD 20771

Robert MeneghiniNASA/Goddard Space Flight Center

Greenbelt, MD 20771

Evaluation of TRMM Precipitation Radar for Estimates of Surface Rainfall Rate

Objectives

IGARSS 2011 Vancouver

• Validating TRMM PR Measurements– Compare with the well-calibrated non-

attenuated ground-based radar measurements.

• Examining TRMM PR Algorithms– Rain attenuation correction

– Rain rate estimation

– Version-7 vs. Version-6

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WSR-88D Ground-Based Radar

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Earth Coordinate System

Schematic diagram of the earth coordinate system in which the latitude, , and longitude, , are defined.

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Geometry for correction of PR offsets (x and y) in x and y axes at a height of h.

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Radar Measurements (3/9/1998)

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PR vs. WSR-88D in Melborne

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Radar Reflectivity (3/9/1998) h

= 1

.5 k

mh

= 3

km

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Radar Reflectivity at h=7.5 (1998-2007)

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Radar Reflectivity at h=1.5 (1998-2007)

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Scatter Plots of Mean Reflectivity (h=3 km)

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Scatter Plots of Rain (1998-2007)

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Scatter Plots of Mean Rain (1998-2007)

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Area-Averaged Rain

WSR-88DTRMM PR

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Area-Averaged Rain (1998-2007)

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Scatter Plots of Mean Reflectivity (2008-2009)

PR (v6) vs. WSR-88D at a height of 3.0 km in MELB PR (v7) vs. WSR-88D at a height of 3.0 km in MELB

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Scatter Plots of Mean Rain (2008-2009)

PR (v6) vs. WSR-88D in MELB PR (v7) vs. WSR-88D in MELB

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Relative Biases (2008-2009)

)(

)()(

WSRR

WSRRPRRR

Storm Type

(Surface) R6(PR) R7(PR)

Stratiform -5.5% -3.8%

Convective -27.8% -18.8%

Ocean -22.0% -12.8%

Land -22.3% -16.6%

Coast -18.2% -14.0%

All Cases -20.9% -14.1%

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Relative Bias (2008-2009)

• Comparisons of the PR-derived reflectivities and rain rates with the same quantities derived from near-simultaneous measurements by the WSR-88D ground-based Melbourne radar are presented for more than 230 overpasses during 1998-2007.

• The reflectivity fields derived from the PR data after attenuation correction, and the conditional mean and area-averaged rain rates from the PR agree well with those obtained from the WSR-88D.

• Improvement of rain estimates is found from PR version-6 to version-7 standard products.

• Further comparisons will be conducted in the future as more data become available and these procedures will be extended to the other climatological sites.

Summary

IGARSS 2011 Vancouver