Microwave Radiative Transfer in the Mixed-Phase Regions of Tropical Rainfall

Here airborne observations of the mixed-phase regions of tropical oceanic rainfall are reported as part of the Kwajalein Experiment. The University of Washington Convair-580 aircraft carrying upward-viewing 21- and 37-GHz microwave radiometers spiraled down through stratiform rain. It was observed that the microwave absorption coefficient in the bright band (melting layer) in the stratiform rainfall was roughly twice or thrice that of the rain below. Radiative transfer models of the melting layer have a similar range of uncertainties. In addition to the potential bias from modeling uncertainties, comparison with previous observations suggests that there is a natural variability of about the same magnitude. The aircraft also made penetrations of a convective line at altitudes of 2.6, 3.4, and 4.5 km. From the microwave observations, it can be concluded that the effect of supercooled water above the freezing level was extremely small, on the order of 2% or less of the total rain signal for this case.