A Model for Estimation of Rain Rate on Tropical Land from TRMM Microwave Imager Radiometer Observations

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概要

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• Over the tropical land regions scatter plots of the rain rate (R_<PR>), deduced from the TRMM Precipitation Radar (PR) versus the observed 85GHz brightness temperature (T_<85v>) made by the TRMM Microwave Imager (TMI) radiometer, for a period of a season over a given geographic region of 3°×5°(lat×lon), indicate that there are two maxima in rain rate. One strong maximum occurs when T_<85v> has a value of about 220K, and the other weaker one when T_<85v> is much colder 〜150K. Also these two maxima are vividly revealed in plots of R_<PR> vs. (T_<19v>-T_<37v>). The strong maximum occurs when (T_<19v>-T_<37v>) is 〜20K and the weaker maximum when it is greater than 〜40K. Together with the help of a) earlier investigations based on airborne Doppler Radar observations and b) radiative transfer theoretical simulations, we infer the strong maximum is a result of relatively weak scattering due to super cooled rain drops and water coated ice hydrometeors associated with a developing thunderstorm (Cb) that has a strong updraft. The other maximum is associated with strong scattering due to ice particles that are formed when the updraft collapses and the rain from the Cb is transitioning from convective type to stratiform type. Incorporating these ideas with a view to improve the estimation of rain rate from existing operational method applicable to the tropical land areas, we have developed a rain retrieval model. This model utilizes two parameters, that have a horizontal scale of 〜20km, deduced from the TMI measurements at 10, 19, 21 and 37GHz (T_<10v>, T_<19v>, T_<21v>, T_<37v>). The third parameter in the model, namely the mean horizontal gradient <dT_<85v>/dr>(K km^<-1>) within the 20km scale, is deduced from TMI measurements at 85GHz that have the scale of 〜5km. Utilizing these parameters our retrieval model is formulated to yield instantaneous rain rate on a scale of 20km. This retrieval model is initially tuned with the help of a limited amount of PR rain rate. After initial tuning, the model is applied to widely different tropical land areas, and for different seasons. Our estimates of instantaneous rain rate, on a scale of 20km, and seasonal averages on a scale of 3°×5°(lat×lon) agree better with PR than that given by the operational TMI rain retrievals.

• 社団法人日本気象学会の論文
• 2005-08-25

著者

• Iacovazzi R.

  Center For Research On The Changing Earth System

• Prabhakara C.

  Nasa Goddard Space Flight Center

• YOO J.

  EWHA Womans University

• KIM K.

  Science Systems and Applications, Inc.

• Kim K.

  Science Systems And Applications Inc.

• Iacovazzi Jr.

  Center for Research on the Changing Earth System

関連論文

• 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
• A Model for Estimation of Rain Rate on Tropical Land from TRMM Microwave Imager Radiometer Observations

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