Author(s):
Thomas H. Painter - National Snow and Ice Data Center
Chris Landry - Center for Snow and Avalanche Studies
Jason Neff - Department of Geological Sciences, University of Colorado
Andrew P. Barrett - National Snow and Ice Data Center
Abstract:
Red dust entrained from the desert regions of the Colorado Plateau in winter and spring is frequently deposited on snow cover in the San Juan Mountains of southwest Colorado. Dust layers reduce the albedo of snow and increase energy available to reduce snow cold content and generate snowmelt. Extensive use of grasslands of the desert southwest has enhanced soil loss/dust emission by disturbing biological soil crusts and decreasing vegetation cover. Indeed, regions in the Colorado Plateau subject to grazing have two to three orders of magnitude greater dust emission.
Our observations in the San Juan Mountains in 2003 and 2004 showed multiple dust-deposition events in each year that resulted in significantly reduced snow albedo and enhanced surface melt. Atmospheric back trajectory analyses with the NOAA/ARL Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) Model for seven observed dust deposition events in the San Juan and Elk Mountains indicate dust emission from northeast Arizona for six of the seven events. The remaining dust event had its source in southeast Utah. Dust chemistry and mineralogy of analyzed samples from snowcover likewise suggests origins in the western US and the influence of combustion related pollutants to the dust prior to or during transport. The reflectance of dust-covered snow, measured with a field spectrometer in spring 2004, was approximately 25% lower than of snow scraped free of the surface dust layer. This albedo decrease results in a near doubling of absorbed shortwave radiation, already the dominant component of the energy balance contributing to snowmelt.
