Observations and a Theory of Temperature Profiles in a Surface Layer of Snow Cooling through Nocturnal Radiation

Soma, Seiji; Nemoto, Shigeru; Miyata, Yasumitsu; Tokitue, H.; Kudo, T.

doi:10.5331/seppyo.18.43

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“…In an effort to better understand the meteorological conditions that affect snowmelt, energy budgets of snowpacks have been studied for nearly 80 yr. Many studies use slow-response meteorological instruments with empirical bulk aerodynamic formulas to estimate the turbulent energy fluxes (e.g., Niederdorfer 1933;Sverdrup 1936;Takahashi et al 1956;Schlatter 1972;Male and Granger 1981;Marks and Dozier 1992;Marsh and Pomeroy 1996;Cline 1997;Hood et al 1999;Hawkins and Walton 2007), whereas more recent studies use fast-response instrumentation with the eddy covariance technique to calculate turbulent energy exchange (Hicks and Martin 1972;McKay and Thurtell 1978;Yen 1995;Mahrt and Vickers 2005;Hayashi et al 2005;Molotch et al 2007;Marks et al 2008;Reba et al 2009;Mott et al 2011). Marks et al (2008) showed that, for a snowpack under a pine canopy, the mean differences calculated over several weeks between the eddy covariance and bulkmethod fluxes were within 1-4 W m 22 (with better agreement during the day than at night); hourly differences, however, were significantly larger than the longterm mean difference.…”

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

Burns

Molotch

Williams

et al. 2014

Journal of Hydrometeorology

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Snowpack temperatures from a subalpine forest below Niwot Ridge, Colorado, are examined with respect to atmospheric conditions and the 30-min above-canopy and subcanopy eddy covariance fluxes of sensible Q h and latent Q e heat. In the lower snowpack, daily snow temperature changes greater than 18C day 21 occurred about 1-2 times in late winter and early spring, which resulted in transitions to and from an isothermal snowpack. Though air temperature was a primary control on snowpack temperature, rapid snowpack warm-up events were sometimes preceded by strong downslope winds that kept the nighttime air (and canopy) temperature above freezing, thus increasing sensible heat and longwave radiative transfer from the canopy to the snowpack. There was an indication that water vapor condensation on the snow surface intensified the snowpack warm-up. In late winter, subcanopy Q h was typically between 210 and 10 W m 22 and rarely had a magnitude larger than 20 W m 22 . The direction of subcanopy Q h was closely related to the canopy temperature and only weakly dependent on the time of day. The daytime subcanopy Q h monthly frequency distribution was near normal, whereas the nighttime distribution was more peaked near zero with a large positive skewness. In contrast, above-canopy Q h was larger in magnitude (100-400 W m 22 ) and primarily warmed the forest-surface at night and cooled it during the day. Around midday, decoupling of subcanopy and above-canopy air led to an apparent cooling of the snow surface by sensible heat. Sources of uncertainty in the subcanopy eddy covariance flux measurements are suggested. Implications of the observed snowpack temperature changes for future climates are discussed.

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