Measurements Of Snowpack Temperature In A Colorado Subalpine Forest

It is well documented that strong winds force air into snowpacks and result in the mixing of atmospheric air with air trapped in the interstitial snowpack space (Colbeck 1989; Clarke and Waddington 1991; Albert and Hardy 1995; Massman et~al. 1997). In this study, three years (2004-2006) of snow temperature data from the Niwot Ridge Ameriflux site were examined with respect to atmospheric temperature, humidity, wind speed, radiation, and turbulent fluxes of heat and water vapor. (Atmospheric measurements were provided by the 26-meter University of Colorado Ameriflux tower that is within 30~m of the study site.) Snow temperature probes consisted of polycarbonate rods embedded with thermistors every 10cm (model TP101 probes, Measurement Research Corporation (MRC), Gig Harbor, WA, 98335). Continuous measurements of soil temperature (by thermocouple and platinum resistance thermometer (PRT) sensors) and soil moisture complete the data set. Snow density profiles were determined weekly by manual snow pits. The MRC snow temperature probes were arranged in a transect across a forest clearing approximately 8~m wide allowing for an assessment of atmospheric drivers of snow temperature oscillations in the context of proximity to vegetation. Ventilation events typically occurred at time scales ranging from minutes to hours but the effect on snowpack temperatures can last for several days. During the early winter (when the snowpack is shallow and snow density is low), snowpack temperature oscillations were on the order of 5°C. These oscillations continue until snowpack density increased and the snowpack became isothermal as the phase transition of snow crystals into water began. These multi-year, season-long observations provide new insight into the atmospheric and ecological controls on snowpack microstructure and temperature during the winter and winter-spring transition periods.