In a study dealing with differences between air and snow surface temperatures during snow
from the air stream to the snow surface under stable conditions (based on a total measurement of 14
data points from 1030 to 1930 hr), which is about 7 W/m2 higher than the value reported by Hicks
and Martin (1972) and approximately 9 W/m2 less than the value obtained from this study. Bernier
and Edwards concluded that the sensible heat flux from air to snow is the essential source of the
energy escaping from the snowpack surface through the latent heat flux. They concluded that snow
surface temperatures are generally lower than the air temperature and therefore, based on their
theoretical analysis, if the air and snow temperatures are equal and air temperatures are below 273
K, the heat flux will be overestimated. It should be noted, however, that the snow surface is rather
ill-defined because of its dynamic nature, so it is hard to measure its temperature.
Bates and Gerard (1989) discussed the various alternative means to predict snow surface
temperature. With the assumption that a measurement by an infrared radiometer was the snow
surface temperature, they compared the temperature measured by thermistor/ thermocouple, the air
temperature at 2 m, and the dew point temperature against the infrared temperature and concluded
that the radiometer would provide the most accurate estimate of the snow surface temperature,
followed in order by thermistor/thermocouple, the air temperature, and the dew point temperature.
De La Casiniere (1974) conducted studies on heat exchange over a melting snow cover with
reported means of diurnal and nocturnal balance of sensible heat flux of 0.2 MJ/m2 and 0.23 MJ/
m2, respectively, which are equivalent to 4.6 and 5.3 W/m2, respectively (without a description of
the test conditions, it is hard to compare these reported values with others).
In a comprehensive study of snow surface energy exchange, Male and Granger (1981) discussed
extensively the numerous factors affecting the turbulent energy exchange over a snow surface.
They made the following observations: a) there have been many studies involving energy transfer,
covering all areas of the world and various sites, i.e., open, forested, mountain snowpacks, isolated
snowpacks, etc.; b) most of the studies dealt with melting snow, especially on glacier snowpacks,
and virtually all were area point studies; c) very few direct measurements of turbulent energy fluxes
are available (estimates based on aerodynamic formulas do not constitute direct measurement); d)
although a number of absolute values (measured or calculated) are reported, the general trend is to
present results regarding the relative contributions of the various forms of energy transfers; and e)
only a few investigations attempted to note any diurnal or seasonal trends and to describe similari-
ties between their findings or those of others. They concluded that the majority of investigators
estimate the turbulent sensible heat flux from the use of aerodynamic formulas derived with the
assumption of steady turbulent flow of a viscous fluid over an infinite, uniform, and hydrodynami-
cally rough surface, implying that the transfer is only in the vertical direction and is time-indepen-
dent (inferring the vertical flux is constant with height). However, the extent to which the turbulent
fluxes vary with height has been the subject of several investigations. Dyer (1968) reported a 16.8%
departure from the surface value for the turbulent sensible and latent heat fluxes at the 16-m level.
Haugen et al. (1971) reported that turbulent heat flux and shear stress are constant only to within
20% up to a height of 23 m.
The variation of heat flux with height may be more pronounced over snow and melting snow
because of their high albedo and the limiting upper-bound temperature of 0C. De La Casiniere
(1974), Granger (1977), and Halberstam and Schieldge (1981) conducted measurements over
melting snow and showed that temperature anomalies are introduced by radiative heating of the air
above the snow surface. Because the upper-bound temperature is 0C, the air over snow will be
heated above the snow temperature, resulting in a stable profile, but if the air mass is cool, a
temperature maximum is observed in the air layer 2050 cm above the surface. In this situation, not
only is the heat flux not constant with height, but it undergoes a reversal in direction at the level of
the raised maximum.
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