turbulent fluxes over snow. In general,
100
however, due to the great variability of
alpine winds with respect to type,
80
space, and time, the type of analysis
seems to be impractical for operation-
al purposes, and hydrologists have usu-
60
ally resorted to the use of standard
aerodynamic formulas in dealing with
alpine snow fields and glaciers subject-
40
ed to appropriate stability correlations.
Male and Granger (1981) graphical-
20
ly showed the relative contributions of
radiative and turbulent energy trans-
fers over a snow surface as functions
0
Mar
Apr
May
Jun
Jul
Aug
Sep
of season and elevation. Figure 16
shows a large scatter in the relative
Figure 16. Relative contributions of the radiative (dashed
contributions of the radiative and tur-
line) and turbulent (solid line) energy transfer over snow
bulent fluxes because melting of the
as function of season (after Male and Granger 1981).
low-level, shallow snowpacks, which
melt quite early in the spring, depends
largely on the energy content of the air mass present. On the other hand, deeper snowpacks that
melt later in the year masked the effect of perturbations of the air masses and displayed the long-
term trend of increased relative contribution of radiant energy. Figure 17 shows the effect of
elevation on the relative contribution of energy
fluxes. It can be seen that below 2000 m there is
4000
no correlation between elevation and the rela-
tive contribution of radiant and turbulent ener-
gy fluxes, indicating the influence of other fac-
tors such as topography or air mass. For
3000
elevations above 2000 m, there is an apparent
decrease in turbulent flux contribution as the
elevation increases. However, this trend seems
to be valid only when the effect of other factors
2000
is negligible. In conclusion, it seems that there
is not enough data to distinguish the influence
of altitude and season on the relative contribu-
tions of radiant and turbulent energy transfers.
1000
The influence of the air mass on the turbu-
lent energy transfer was first reported by Sver-
drup (1936) in his paper dealing with turbulent
exchange with snow. He broadly classified his
0
20
40
60
80
100
results in terms of the prevailing general weath-
Relative Contribution (%)
er conditions, i.e., a cold dry period is associat-
ed with a negative sensible heat transfer (heat Figure 17. Influence of elevation on the relative
leaving the surface) accompanied by evapora- contributions of radiative (open circles) and turbu-
lent (solid circles) energy transfers over snow. Sol-
tion from the snow surface; and warm, dry and
id lines represent a range of values from a single
wet periods are connected with a positive sensi- location and dashed lines show the relationship be-
ble heat transfer with evaporation from and con- tween elevation (above 2000 m) and the relative con-
densation to the snow surface, respectively.
tribution (after Male and Granger 1981).
37
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