Profiling of latent heating through spaceborne Doppler radar and the Hydrometeor Heating algorithm

Estimates of latent heating are currently produced by active and passive spaceborne instruments with good accuracy in the horizontal distribution, but larger uncertainties affect the estimation of the vertical distribution of latent heat. Several algorithms have been implemented and applied to large datasets (e.g., TRMM): a recent inter-comparison study summarizes the strengths and weaknesses of each (Tao et al. 2006, BAMS). We will focus here on the strengths and weaknesses of one of them (the Hydrometeor Heating algorithm, HH) from the new perspective of a hypothetical spaceborne Doppler radar platform. When applied to global passive or non-Doppler radar datasets, HH must use vertical profiles of vertical velocity inferred from models or statistics of in-situ measurements. On the other hand, Doppler measurements provide a more direct and co-located means to estimate the vertical profile of vertical velocity, therefore, in principle, they improve the quality of the estimates of vertical profiles of latent heating. In practice, however, Doppler measurements from space pose a challenge mainly because of the high velocity of the platform. Recent studies have proven that the average vertical velocity can be measured to acceptable accuracy levels by appropriate selection of radar parameters. Furthermore, methods to correct for specific errors arising from Non-Uniform Beam Filling effects and pointing uncertainties have recently been developed. In this paper we analyze the impact that a spaceborne Doppler radar would have in Latent Heating profiling, through the HH algorithm, depending on its configuration. The results of simulations obtained with the WRF cloud resolving model and a 3D Doppler radar simulator show that, while the availability of Doppler measurements contributes positively to the retrievals of vertical profiles of latent heat, a multi-frequency system is necessary to reduce the uncertainty in the estimation of the vertical profiles of hydrometeors.

The research described in this paper was performed at the Jet Propulsion Laboratory, California Institute of Technology, for the GPM and NIP Programs under contract with the National Aeronautics and Space Administration.