Physical Validation of Microwave Properties of Winter Precipitation Over the Sea of Japan

In order to evaluate variations in the physical properties of winter precipitation over the Sea of Japan, we analyzed the Wakasa Bay Experiment 2003 datasets. The results show that synoptic scale differences in freezing-level height (FLH) were observed between extra-tropical low cases and winter monsoon and upper cold low cases, and that, frozen-particle density and cloud liquid water content (CLWC) observed at the surface showed great variation independent of the precipitation rate, although positive correlation may exist between these two properties. The radiative transfer model (RTM) simulation and the validation using the advanced microwave scanning radiometer on EOS (AMSR-E) and millimeter-wave imaging radiometer brightness temperatures (TBs) indicate that sensitivity to frozen precipitation rate (0-5 mm ldr h^-1) was found in 89-GHz polarization-corrected temperature (PCT89), 89-GHz polarization difference (PD89), and 150-GHz TBs and that this sensitivity decreased with FLH due to emission from mixed- and liquid-phase particles. The RTM simulation, however, overestimated the AMSR-E PCT89 depressions for nonzero FLH cases. This indicates that microwave retrieval for winter precipitation requires a priori information about FLH and an efficient mixed-phase-particle model for RTM. The relationship between surface precipitation rate and TBs was also influenced by the observed variation of CLWC. The relationship between PCT89 and PD89 is greatly altered in terms of CLWC. Relationship between AMSR-E PCT89 precipitation sensitivity and CLWC estimated from PCT89 and PD89 was qualitatively consistent with those of the RTM simulations. This suggests that CLWC, another important retrieval parameter, can be estimated from PCT89 and PD89.