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A compelling and growing body of observational data, supported by results from climate models and other theoretical considerations, shows that the high latitudes of the Northern Hemisphere are a particularly sensitive component of Earth’s climate system [e.g., Serreze et al., 2000].

Rain on snow affects both Reindeer (ungulates) and permafrost temperatures

Rain on snow  

Severe wintertime rain-on-snow (ROS) events create a strong ice layer (or layers) in the snow on arctic tundra that act as a barrier to ungulate grazing. They are linked with large-scale ungulate (reindeer, caribou, elk, and musk-ox) herd declines via starvation and reduced calf production rate when the animals are unable to penetrate the resulting subsnowpack ice layer. ROS events also produce considerable perturbation in the mean wintertime soil temperature under the snowpack. ROS is a sporadic but well-known and significant phenomenon that is currently very poorly documented. Characterization of the distribution and occurrence of severe ROS events is based only on anecdotal evidence, indirect observations of carcasses found adjacent to iced snowpacks, and irregular detection by a sparse observational weather network. We have analyzed in detail a particular ROS event that took place on Banks Island in early October 2003 that resulted in the death of 20,000 musk oxen. We make use of multifrequency passive microwave imagery from the Special Sensor Microwave Imager satellite sensor suite in conjunction with a strong-fluctuation-theory (SFT) emissivity model. We show that a combination of time series analysis and cluster analysis based on microwave spectral gradients and polarization ratios provides a means to detect the stages of the ROS event resulting from the modification of the vertical structure of the snowpack, specifically wetting the snow, the accumulation of liquid water at the base of the snow during the rain event, and the subsequent modification of the snowpack after refreezing. SFT model analysis provides quantitative confirmation of our interpretation of the evolution of the microwave properties of the snowpack as a result of the ROS event. In addition to the grain coarsening owing to destructive metamorphism, we detect the presence of the internal water and ice layers, directly identifying the physical properties producing the hazardous conditions. This analysis offers the potential to characterize both the frequency and global distribution of ROS using multifrequency satellite passive microwave imagery.



The precence of permafrost at a given location is dictated by the external drivers (climate) and the local conditions (snow, aspect, vegetation, et.c). We found that in Spitsbergen at our study site the general existence of permafrost is dictated by the long and cold winter and short and cool summer. However, the snow depth and timing of the deep snow pack establishment were important in dictating the annual variations in soil temperature. The most important effect on soil temperatures was a midwinter rain on snow events. During those events the rain water penetrated the snow pack and pooled at the base of the snow/on top of soil. There the water slowly froze sometimes over a period of several weeks. This essentially kept the soil surface temperature a 0 deg celsius (freezing point of water) and significantly warmed the soil underneath. The water/ice bath kept the soil surface temperature several degrees Celsius warmer than it would have been in the absence of the rain on snow event.

Field site in Spitsbergen where permafrost and sorted circles have been studied since early 1980’s