. Ecological investigations of the tundra biome in the Prudhoe Bay region, Alaska . d. 13 June 1972 (S view). 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 condi
. Ecological investigations of the tundra biome in the Prudhoe Bay region, Alaska . d. 13 June 1972 (S view). 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 0°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 The daily Prudhoe Bay temperature data are from the unpublished BP radio station data obtained in the vicinity of the Mukiuk Camp (Brown et al., this volume) about 8 km from the coast.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
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