evaluation of trmm precipitation radar for estimates of surface rainfall rate

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


WSR-88D Ground-Based Radar


Earth Coordinate System

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


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


Radar Measurements (3/9/1998)


PR vs. WSR-88D in Melborne


Radar Reflectivity (3/9/1998) h

= 1

.5 k

mh

= 3

km


Radar Reflectivity at h=7.5 (1998-2007)


Radar Reflectivity at h=1.5 (1998-2007)


Scatter Plots of Mean Reflectivity (h=3 km)


Scatter Plots of Rain (1998-2007)


Scatter Plots of Mean Rain (1998-2007)


Area-Averaged Rain

WSR-88DTRMM PR


Area-Averaged Rain (1998-2007)


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


Scatter Plots of Mean Rain (2008-2009)

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


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%


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


evaluation of trmm precipitation radar for estimates of surface rainfall rate

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