Melting layer model evaluation using fall velocity spectra at Ku-band

A melting layer model used for the rainfall retrievals from spaceborne weather radars is examined using Doppler radar measurements at 13.8 GHz, taken in the zenith-pointing mode. From the pulse-to-pulse variation of the phase measurements, the fall velocity spectra were obtained for each of the range gates from 1 to 5 km, including the melting layer. The spectra show a narrow distribution in the snow region with a mean velocity of 1.5 ms^-1, getting wider as the melting progresses. The results indicate that the BB thickness is intensity dependent, which is consistent with previous studies in mid-latitude regions but not reflected in the predictions from the model considered in the paper. Measurements made at lower frequency, i.e. at L-band, also indicate the deficiency of the model in terms of the bright-band thickness. However, because the model has been shown to be consistent with measurements in the tropics, it is suggested that any modification and/or enhancement to the model be applied to mid-latitudes only. Implications for propagation prediction methods are also discussed.