Dry Precipitation on the Greenland Ice Sheet: A Study of Properties and Characteristics

We have developed a method of identifying dry ice clouds and precipitation over the Greenland Ice Sheet (GIS).  We define these "dry" ice clouds as those contating little to no cloud liquid water.  Using differences in the spectral variation of the absorption and scattering properties of the cloud liquid water and ice in the microwave, we are able to isolate the occurrence of such clouds.  This is achieved using microwave radiometer (MWR) observations from the Integrated Characterization of Energy, Clouds, Atmospheric State, and Precipitation at Summit (ICECAPS) in Greenland.  Once identified, we use six years of co-located, multi-instrument data from ICECAPS to examine properties and characteristics of these clouds: When do they occur; do they have a seasonality?  What are the physical properties of these clouds; are they deep or shallow; calm or turbulent?  Where do these clouds come from? It is difficult to advect air over the GIS, so where do air masses that form ice clouds tend to originate?  Though these dry ice cloud events are a small percentage of the overall cloud and precipitation at Summit, they contribute a disproportionally large amount to the mass deposited on the ice sheet.  Additionally, better understanding of the physics of these ice clouds will help to improve current retrievals of atmospheric properties.  These ice clouds are excellent test cases for radiative transfer studies as well.  We intend to take advantage of the unique environment at Summit and the ICECAPS instrument suite to study these clouds.