A Method to Estimate Rain Rate over Tropical Oceans with the TRMM Microwave Imager Radiometer

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概要

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• In this preliminary study, we have developed a method to retrieve rain rate on a scale of 20 km from the brightness temperatures measured by the TRMM microwave imaging radiometer (TMI) over the tropical oceans, using the estimates of rain rate R_<PR> made by the TRMM Precipitation Radar (PR) as a benchmark. The purpose of this study is to demonstrate with a limited amount of PR and TMI data the feasibility of improving the TRMM operational rain retrieval method V6 over the tropical oceans. This study utilizes the TMI-measured brightness temperatures T_<19H>, T_<37H>, and T_<85H> of horizontally polarized microwave radiances at 19, 37 and 85 GHz, respectively, to deduce a salient non-linear parameter ξ, that is highly correlated with R_<PR> over the oceans. Two additional parameters generated from TMI data, ω and Г, add significant amounts of rain information to our retrieval method. The parameter ω is based on T_<19V> and T_<21V>, the brightness temperatures measured by TMI for vertically polarized microwave radiances at 19 and 21 GHz respectively. This parameter takes advantage of the independent information contained in T_<21V>. The parameter Г depends on the average horizontal gradient of the TMI-measured T_<85V> (vertically-polarized 85 GHz radiance) in a 20 km footprint. Initially our TMI rain retrieval algorithm is tuned with the help of R_<PR> for seven cases of 2°x 3° area over tropical oceans. Then it is applied to 13 other independent tropical ocean cases. For these independent cases, the rain rate R^* estimated from our method correlates better with R_<PR> than the rain rate R_<V6> retrieved from the present TMI V6 operational retrieval method. On a 20 km scale, the correlation between R_<PR> and R^* is better by about 6% compared to that between R_<PR> and R_<V6>. The slope of the regression line between the rain rates R_<PR> and R_<V6> is about 0.5. With respect to R_<PR>, the rain rate R_<V6> retrieved from operational V6 method tends to underestimate high rain rates and overestimate low rain rates. The slope of the regression line between R_<PR> and the rain rate R^* retrieved with our method is about 0.8, another indication of the improvement of R^* over R_<V6>. In addition, the area average rain rate on a scale of 2°x 3° deduced from our method agrees better with that of PR by about 7%.

• 社団法人日本気象学会の論文
• 2008-02-25

著者

• Iacovazzi Jr.

  Earth Resources Technology Inc

• Prabhakara C

  Nasa Goddard Space Flight Center

• Prabhakara C.

  Nasa Goddard Space Flight Center

• Yoo J‐m

  Ewha Womans University

• YOO J.-M.

  EWHA Womans University

• KIM K.-M.

  University of Maryland Baltimore County

• BELL T.

  NASA Goddard Space Flight Center

• YOO J.

  EWHA Womans University

• Prabhakara C.

  Nasa/goddard Space Flight Center Greenbelt

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• Surface Emissivity and Hydrometeors Derived from Microwave Satellite Observations and Model Reanalyses
• A Method to Estimate Rain Rate over Tropical Oceans with the TRMM Microwave Imager Radiometer
• TRMM Precipitation Radar and Microwave Imager Observations of Convective and Stratiform Rain over Land and their Theoretical Implications
• A Model for Estimation of Rain Rate on Tropical Land from TRMM Microwave Imager Radiometer Observations
• 対流雲と層雲の判別に基づくTRMMマイクロ波放射計降雨強度推定法

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