Passive Microwave Signatures and Retrieval of High-latitude Snowfall over Open Oceans and Sea Ice: Insights from Coincidences of GPM and CloudSat Satellites

This paper studies changes in microwave signals of oceanic snowfall in response to formation of snow-covered sea ice using active and passive coincident data from the radar and radiometer onboard the CloudSat and the Global Precipitation Measurement satellites. Using reanalysis data of liquid and ice water path as well as satellite retrievals of sea ice snow-cover depth, spectral regions are determined over which the snowfall signatures are likely to be obscured or falsely detected. Relying on an a-priori database populated with the active-passive coincidences, a Bayesian snowfall retrieval algorithm is presented that links a k-nearest neighbor matching with the inverse Gaussian estimator used in the Goddard Profiling algorithm. Without relying on any ancillary data of air temperature, the results demonstrate that over open oceans (sea ice), we can passively retrieve the CloudSat active snowfalls with true positive rate of 91 (87%) and the root mean squared error of 0.25 (0.14) mm/hr.