C. 
d. 
73 June 1972 (S view). 
39 
are layer clouds, their optical properties are not 
very homogeneous. The cloud forms are often a 
transitional form between stratus and _ strato- 
cumulus. Frequently, the sun becomes visible 
through the cloud layers. The variations of the 
incoming solar radiation often suggested waves 
within the cloud layers inducing regular varia- 
tions of the radiation intensity. Also the emis- 
sivity of the thin stratus clouds appeared to be 
highly variable. 
The albedo and the surface and weather 
conditions 
The changes of the albedo in connection 
with snowmelt and onset of the snow cover 
cause a Startling increase of the net radiation and 
of the turbulent, sensible, and latent heat trans- 
fers at the surface (Weller et al. 1972). The most 
obvious climatic parameter affecting 
the snow melting is the air temperature. Daily 
values of the albedo and air temperature at 
screen height are shown in Fig. 23 (see also Fig. 
8 and Table 1). As the air temperature increases 
and melting starts, the albedo decreases. At low 
air temperatures, the positive net radiation dur- 
ing the daytime is either used for heat conduc- 
tion into the snowpack, or for transport of 
sensible or latent heat into the atmosphere. As 
the air temperature increases toward or above 
O°C, the positive net radiation also increases, 
and this excess energy is used to melt and 
evaporate snow and to heat the air and soil in 
the relative proportions shown by the energy 
balance (Weller et al. 1974). 
The daily Prudhoe Bay temperature data are 
from the unpublished BP radio station data 
obtained in the vicinity of the Mukluk Camp 
(Brown et al., this volume) about 8 km from the 
coast. 
One may note that in the Prudhoe Bay area, 
the albedo in 1972 appears to decrease in con- 
nection with relatively low daily air tempera- 
tures. This is probably due to dust contamina- 
tion of the snow. In May 1973 the albedo values 
are for a short time above 80%, even with air 
temperatures above freezing, but then they drop 
suddenly. The observation site in 1973 was not 
the same as in 1972, and the influence from dust 
may have been slightly less in 1973. Further- 
more, on 24 May 1973 a thin layer of new snow 
