Why the Melting Layer Reflectivity is not Bright at 94-GHz?

The melting of snowflakes in stratiform precipitation causes changes in the scattering properties, density, size, and fall velocity of precipitating particles. These changes result in the appearance of a shallow horizontal layer of enhanced radar reflectivity (radar bright band), at microwave frequencies. However, at 94-GHz, the highest radar frequency used for cloud research, no bright band is observed. In this study, simulations of a vertical profile of melting particles and their scattering properties for a variety of melting particle models are used to capture the basic features of the radar reflectivity structure at 94-GHz in the melting layer. Observations of stratiform precipitation from vertically pointing 3-GHz and 94-GHz radars are used for comparison with the model results. The simulations show great agreement with the observations. The melting of precipitating particles results to an abrupt increase in the radar reflectivity without a following decrease at the base of the melting layer. The simulations also captured a small decrease in the radar reflectivity often observed at the top of the melting layer at 94-GHz. The 94-GHz attenuation profile in the melting layer is estimated. The sensitivity of the simulations for a variety of melting particles models is investigated. Accurate modeling of the melting layer at 94-GHz is critical for the development of new precipitation retrieval techniques from ground or space using cloud radars.