Snow wetness and icing can affect ecosystem processes at multiple spatial and temporal scales including hydrology, carbon cycling, wildlife movement, and human transportation. Snow wetness occurs when the cold content of part or all of the snowpack is less than the positive energy fluxes from radiative, sensible, or latent heat transfer. Icing events normally occur daily in the spring and summer and less predictably following wintertime rain on snow or warm weather. In the future, the frequency and extent of wet snow followed by icing events is predicted to increase, particularly in the high latitudes due to the effects of amplified temperatures on rain-to-snow transition gradients.
Snowmelt and icing processes result in marked changes to snowpack processes such as snowmelt, surface albedo, and energy balance. Changes in the surface structure of the snowpack are visible using optical remote sensing, and changes in the relative content and distribution of water, air, and ice in the snowpack are detectable using passive microwave remote sensing. This project aims to develop products showing the spatial and temporal distribution of snow wetness and icing events using satellite data products derived from both optical and passive microwave satellite records.
To detect snow wetness and icing, NPS researchers used brightness temperature measurements derived from vertical and horizontal polarizations at 19 and 37 GHz from the Advanced Microwave Scanning Radiometer (AMSER-E and AMSER-2) passive microwave satellites, which are downscaled to 6 km. Unlike optical measurements, passive microwave retrievals are not susceptible to cloud cover or the polar darkness of high latitude winters and can produce daily measurements of snow properties. Combining these products with finer resolution optical snow cover data will provide a more complete picture of snow processes in Alaska and allows us to address important management questions regarding wildlife mortality and regional transportation.
Alaska and modified climate divisions showing the greatest occurrence of rain on snow events are in the southwest and south-central regions for the 2005 water year.