Estimate of precipitation from the dual-beam airborne radars in TOGA COARE. Part 1: The K-Z relationships derived from stereo and quad-beam analysis

The recent development of dual-beam airborne Doppler weather radar offers t he possibility to perform high-resolution observations of the three-dimensi onal air motion and precipitation fields associated with severe weather sys tems. However, the limited size of the onboard antennas imposes the use of high radar frequencies (e.g., X band) in order to achieve satisfactory beam resolutions. Therefore, the sampled radar reflectivity is attenuated when intercepting intense rain cells. This paper aims at developing algorithms f or correcting the observed radar reflectivity for attenuation that fully ex ploit the dual-beam sampling strategy and the multiple aircraft operations conducted in Tropical Ocean and Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE). Its specific contribution is twofold. Algorithm development. On the one hand, the former stereoradar analysis hel ps to retrieve independently the "true" (nonattenuated) radar reflectivity Z and specific attenuation K when using two radar beams from one aircraft. The algorithm is reformulated in Cartesian coordinates, which greatly impro ves its flexibility. And on the other hand, a new approach is developed, th e quad-beam analysis, which is particularly powerful when processing the da ta of a two dual-beam aircraft operation focused on the same rain cells. Data analysis. An application of the stereoradar and quad-beam analysis to a TOGA COARE weather system is presented. The corrected Z and K fields are cross validated using different algorithms or datasets for the same event. The radar derived K-Z relationships are also compared with that deduced fro m in situ microphysical probes sampling using a scattering model. The full three-dimensional description of the Z and K fields is then used to appreci ate to what extent the observed heavy rain reached the "equilibrium" descri bed by previous authors in response to droplet coalescence and breakup.