Satellite precipitation retrieval has so far been almost exclusively focused on rainfall. Scattering signature from solid precipitations (mostly snowfall), while weak, is detectable at high microwave frequencies. In this paper we will present both observational data of snowfall at high microwave frequencies (89 and 150 GHz) and results of radiative transfer modeling studies to show the feasibility of retrieving snowfall over ocean from current and future satellite sensors.

We have studied the snowfall signatures using both surface based observations and satellite data. The surface based observation was conducted over the Sea of Japan using both ground-based radar and airborne microwave radiometers. The clouds are shallow convections (~ 2 km deep) with snowfall rate around 2 mm/h (liquid water equivalent). While brightness temperature at 37 GHz did not respond, 89 GHz channel showed a decrease in brightness temperature of ~15 K. Radiative transfer simulations show that brightness temperature at 150 GHz could decrease ~30 K for the same snow cloud. Satellite data at 150 GHz from SSM/T-2 are used to study the snowfall signatures over N. Atlantic during winter months. It is found that the retrieved snowfall index is higher along the east coast of Canada and Greenland, a pattern corresponded well with snowfall frequency observed by ship observers (COADS data). Radiative transfer modeling studies are focused on how the following factors affect snowfall retrievals: atmospheric (particularly water vapor) profiles, snow profiles, liquid water in the cloud, snow density.