Measuring rain on snow followed by freezing at Alaska SNOTEL sites
Abstract
Arctic rain-on-snow events have garnered increasing interest in recent years because they have been implicated in the mass die-off of ungulate herds, such as on Banks Island in 2003 or Svalbard in 2012. The conceptual model of the cause of the die-offs is that if temperatures become warm enough during a winter storm, rainfall may occur on a winter snowpack, percolate down, and then, if it cools sufficiently, freeze within the snowpack. This creates a hard ice layer that is difficult for ungulates to penetrate as they seek winter forage. This study advances past research by examining seasonal differences in the characteristics and distribution of rain-on-snow events in Alaska using new data from recently installed SNOTEL sites. Spring has the greatest rain-on-snow frequency, and even in northern Alaska, most events are associated with large storm systems in the Pacific storm track that tap large plumes of warmth and moisture. Additionally, this study examines more closely the sensitivity of rain-on-snow event detection to common identification parameters. Past studies cataloguing rain-on-snow events typically use two parameters: 1) some measure of a snowpack and 2) some measure of precipitation. Some studies use presence/absence; others use minimum thresholds for snowpack and/or rainfall. However, percolation and freezing of the rainfall within the snowpack is typically omitted from consideration, and not all rain-on-snow events necessarily lead to ice formation. The most dangerous rain-on-snow events for ungulates may be better isolated by limiting identification to those for which the air temperature falls below freezing following the rain-on-snow event.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.A51P2449C
- Keywords:
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- 3311 Clouds and aerosols;
- ATMOSPHERIC PROCESSESDE: 3339 Ocean/atmosphere interactions;
- ATMOSPHERIC PROCESSESDE: 0738 Ice;
- CRYOSPHEREDE: 0750 Sea ice;
- CRYOSPHERE