Analysis of the melting layer by using 400 MHz wind profiler and 35 GHz Doppler radar

To understand the microphysical properties in the melting layer is important to improve the rain retrieval algorithms for both active and passive spaceborne microwave sensors. Several melting layer models have been proposed to explain the reflectivity factor (Z) profile of the bright band. In this study, the detail structure of the melting layer is analyzed by using a 400 MHz wind profiler (WPR) owned by National institute of Information and Communications Technology (NICT) and a 35 GHz Doppler radar (MP-Ka) owned by National Research Institute for Earth Science and Disaster Prevention (NIED) in order to examine and improve the melting layer models proposed by Nishitsuji et al. (1983) and Yokoyama and Tanaka (1984) which are planned to be introduced to the Global Satellite Mapping of Precipitation (GSMaP) rain retrieval algorithm. First of all, both radar are calibrated each other; the drop size distribution (DSD) profile is calculated from the WPR with (un-calibrated) spectrum data, then the attenuation coefficient and the vertical gradient of effective reflectivity factor (Ze) of Ka-band radar are calculated by using the DSD data. Since the gradient of the Ze profile is free from the calibration, the calculated gradient of Ze is utilized to calculate the attenuation coefficient with the observation data of the MP-Ka. The ratio of the two attenuation coefficients will be the calibration factor for WPR. Then the Ze of Ka-band is re-calculated with the calibrated DSD data for the calibration of the MP-Ka. The melting layer models are examined in terms of fall velocity and DSD profile. The characteristics of the fall velocity in the melting layer models are compared with the Doppler velocity profiles of both radars. The comparison of two models indicates that fully melted smaller drops may have higher fall velocity than larger size un-melted or partially melted particles. The DSD properties are examined by using the spectrum information of the WPR assuming that the several characteristics such as fall velocity, volume water fraction and backscattering cross section of each particle are the same in the melting layer model. The estimated DSD profile changes largely with height indicating active break-up/coalescence process in the melting layer.