Estimation of precipitation and latent heating distributions in tropical convection from a combined analysis of passive microwave and spaceborne radar observations

A new method for evaluating consistent precipitation and latent heating distributions based upon satellite passive microwave radiometer observations is presented. The method is trained using coincident passive microwave radiometer and spaceborne radar observations- a variational method is applied to the coincident radiometer/radar data to obtain optimal estimates of precipitation structure at high vertical (0.25 km) and horizontal (4.5 km) resolutions. Then, latent heating rates are assigned to these detailed precipitation profiles with the aid of tabulated, cloud-model simulated profiles of precipitation/heating to complete the training set. Coincident radar/radiometer observations over the tropics and subtropics from the TRMM Microwave Imager and Precipitation Radar are collected over periods of one month or longer, in order to create very general training sets containing ~1 million profiles.

Upwelling microwave radiances associated with the training profiles are simulated using radiative transfer calculations, such that the relationships between precipitation/latent heating and observed radiances applicable to any satellite microwave radiometer (e.g., TRMM Microwave Imager; Special Sensor Microwave/Imager, Advanced Microwave Scanning Radiometer-EOS) can be established. Given a set of observed radiances, the large set of training data is quickly searched and radiatively compatible profiles are composited to obtain best estimates of precipitation/latent heating. It is demonstrated that the new method has a better ability to resolve the depth and vertical structure of convection than earlier approaches, and retrieved latent heating profiles are generally consistent with independent radiometer/radar estimates and limited surface observations.

Three-dimensional precipitation/heating estimates at a variety of scales will be presented at the conference, ranging from instantaneous distributions in individual convective systems to monthly-mean distributions over the global tropics/subtropics. One intended application of these estimates is to produce, in combination with other observations, a more consistent picture of the earth's energy and water cycles. In this regard, an advantage of the radiometer-based estimation technique relative to spaceborne radar methods is the potential for greater temporal sampling of precipitation systems globally, given that several satellite microwave instruments are currently operating, and additional radiometer missions are planned.