Aspects of melting layer and fall streaks in stratiform cloud system over the Western Ghats, India from Ka-band polarimetric radar observations

Abstract

During the Indian summer monsoon, high temporal and spatial resolution observations from Ka-band dual-polarization radar deployed in the Western Ghats (WG), India are utilized to investigate the vertical structure of the stratiform precipitating system. First, the radar reflectivity (Z) measurements are corrected for rain attenuation, based on the relationship between specific attenuation (A) and Z. The disdrometer dataset is used to calculate the expected value of A at Ka-band for a given Z using microwave scattering simulation. The radar data are also corrected for wet radome transmission loss, gaseous, and melting layer (ML) attenuation. Within the ML, a change in Z and other radar polarimetric variables suggest hydrometeors phase change. In addition to Z, polarimetric measurements such as differential reflectivity (ZDR), linear depolarization ratio (LDR), and copolar correlation coefficient between horizontal and vertical channel (ρHV) are used to determine the ML height. Ka-band polarimetric radar signatures near the ML are characterized by a low ρHV (∼0.93), high Z (∼25–30 dBZ), ZDR (∼3 dB), and LDR (∼ −15 dB) values. In the stratiform precipitation region, well-defined fall streaks are observed above ML, which descends through 0 °C isotherm into the rain region. When the fall streaks are present above the ML, Z increases below the ML, indicating a seeder-feeder mechanism. Because there is little observational evidence concerning the vertical distribution of stratiform clouds over the Indian subcontinent, the current study may help to understand stratiform clouds and the ice processes that occur within them.