Interpretation of Polarization Features in Ground-Based Microwave Observations as Caused by Horizontally Aligned Oblate Raindrops

Abstract

Based on comparision of ground-based radiometer measurements with microwave radiative transfer calculations it is shown that raindropswith oblate shape and preferred horizontal orientation have a significant effect on microwave polarization signals when compared with spherical perticle shape. Measurements with dual-polarized 19-GHz radiometer reveal a polarization difference of as much as -18K in the downwelling microwave radiation at 30 degree elevation angle. Averaging of all rain observations within 19 months leads to a polarization difference of -6K. The averaged model results for oblate raindrops lead to a polarization difference of -8K, which is in reasonable agreement with long-term averaged observations.