Snow Temperature Changes within a Seasonal Snowpack and Their Relationship to Turbulent Fluxes of Sensible and Latent Heat

Sean P. Burns, Noah P. Molotch, Mark W. Williams, John F. Knowles, Brian Seok, Russell K. Monson, Andrew A. Turnipseed, and Peter D. Blanken

Snowpack in alpine regions is a critical reservoir for water storage. The warming climate is affecting the amount of snow in these areas and the timing for when that snow melts. High elevation areas are particularly vulnerable to changes in the climate. In order to better understand how specific changes in the climate will affect snowpack a better understanding of how energy moves through the snowpack is required. Snowpack’s within forested areas add and an additional level of complexity when investigating heat transfer. The tree canopy blocks incoming shortwave radiation from the sun and shades the snow pack. Trees enhance longwave radiation cooling during the night when shortwave radiation diminishes. Trees also shelter the snowpack from the wind, which decreases changes in temperature at the surface of the snow. Heat is transferred through a snowpack primarily by conduction through the ice crystals. The ice crystals are in contact with one another, allowing heat to transfer from one crystal to another. Changes in snow temperature in a snow pack equate to changes in snow crystal structure. Rapid fluctuations in temperatures can alter the snow grains and affect snowpack cohesion.

This article investigated the changes to internal snowpack temperatures and possible triggers for intensified snowpack warming prior to spring melt. The researchers used ratio data in the form of acts, behaviors, and events collected primarily at the Niwot Ridge Subalpine Forest AmeriFlux site in Colorado. Reports of acts, behaviors, and events in the form of meteorological data from the National Oceanic and Atmospheric Administration was collected as well as data from corresponding studies. Quantitative analysis using equations was used to compare a wide range of variables from snow and soil temperatures to snowpack properties, energy fluxes, wind, and aspect. These were graphed and the information that was collected to describe environmental conditions that could create the conditions required for a warm u event.

One of the conclusions that were made was that “If air with a dewpoint temperature near the snow surface temperature is present, water vapor can condense on the snow surface releasing latent heat and causing the snowpack temperature to rapidly warm.” This article was strong in its evaluation of its own practices and its understanding of the limitations of its conclusions. However, describing the environmental conditions that could create scenarios with similar warm up potential demonstrated the scope the research had and the accuracy of its results.

A connection that I found from this research to my own topic was that the high winds triggering dust events could increase turbulent fluxes at the surface of the snow. If fewer trees are present as a consequence of drought and pine beetle (positive feedback loop kills more trees) then snowpack is less sheltered increasing risk of rapid temperature changes. Changes to internal snowpack temperature modify snow crystal structure, which could produce weaker layers increasing the risk of avalanche and increasing melting rate.

 Burns, S. P., Molotch, N. P., Williams, M. W., Knowles, J. F., Seok, B., Monson, R. K., . . . Blanken, P. D. (2014). Snow Temperature Changes within a Seasonal Snowpack and Their Relationship to Turbulent Fluxes of Sensible and Latent Heat. Journal of Hydrometeorology, 15(1), 117-142. doi:10.1175/jhm-d-13-026.1