was observed on top of the old snowpack, which 
temporarily increased the albedo. 
The albedo variations shown in Fig. 23 are 
only typical values that vary from one spot to 
another, particularly during melting. During 
breakup the snow cover disintegrates into 
patches, with bare ground appearing at an early 
stage where the snow is shallow. The albedo of 
the remaining snow patches should generally be 
much higher than the values representing the 
latter part of the melting period shown in Fig. 
23. One might guess that for clean snow the 
albedo remains around 70% or so, except during 
the last stages, when the snow generally was 
coarse-grained and perhaps often consisted of 
superimposed ice. The albedo of the snow 
patches might then have been considerably 
lower. On 5 June 1973 the total snow area in 
the vicinity of the measuring site at Prudhoe Bay 
was estimated to be approximately 15% of the 
tundra surface. Away from the road system and 
the camps, etc., the snow area was estimated 
to be approximately 50% on the same day. 
It is obvious that point albedo measurements 
cannot be used for interpretations of the average 
conditions over larger areas during snowmelt. An 
illustration of this is shown in Table 9, where 
values are given of the incoming solar radiation, 
the albedo, and the absorbed radiation at two 
measuring places 8 m apart, but with a 10-20 cm 
deep trench causing slightly increased snow ac- 
cumulation under one of the sensors. The differ- 
ence in absorbed radiation between these two 
adjacent places during this 10-day melting 
period is almost 700 cal cm*?, corresponding to 
the energy required to melt about 9 g of ice per 
sq cm, or almost the entire snowpack, as far as 
the average conditions go. 
The influence of various climatic parameters 
and microtopography on the breakup is obvious- 
ly very complex. As long as the albedo is high, 
the net radiation is generally higher with over- 
cast skies than with clear skies (Liljequist 1956; 
Holmgren 1971; Ambach 1974). Later, when 
the albedo is lowered by melting, the net radia- 
tion will be higher with clear than with cloudy 
skies. 
Satellite observations show that the breakup 
on the Arctic Slope generally proceeds from the 
upper foothills into the coastal plains (Holmgren 
et al. 1975). Furthermore, the melt season 
advances faster along the major rivers when 
41 
Table 9 
Daily insolation, albedo, and difference in absorbed radi- 
ation at two adjacent observation sites at Prudhoe Bay. 
Difference in 
Day Insolation A; Ag AA absorbed radiation 
Galidays 95 19 1% cal day | 
05.26 720 68 68 0 0 
05.27 675 6567 2 14 
05.28 575 57, 66 9 52 
05.29 361 55 65 10 36 
05.30 449 48 63 15 67 
05.31 321 10) (G7/ 1N7/ 55 
06.01 273 40 61 21 57 
06.02 317 34) 56822 70 
06.03 310 Sipe on e2 68 
06.04 382 271 AG) 19 73 
06.05 434 29 bile 22: 95 
06.06 453 24 40 16 72 
06.07 511 15) 20 5 26 
06.08 590 15a 0 0 
Sum 6371 685 
meltwater, flowing down the rivers, floods the 
snow cover, reduces the albedo, and causes 
increased absorption of radiation. On the region- 
al scale there exists a north-to-south temperature 
gradient from the coast and inland toward the 
valleys in the Brooks Range in spite of an 
increase in elevations from sea level to about 
600 m over that distance (Conover 1960). At 
Prudhoe Bay temperature gradients from the 
shore to about 25 km inland were measured to 
investigate possible effects on the breakup by 
the proximity to the Arctic Ocean (Brown et al., 
this volume). Fig. 24 shows some maximum and 
minimum daily temperatures from Point 
McIntyre, 75m from the shore, and from a 
point on the Sagavanirktok River, approximate- 
ly 20 km south of the Deadhorse Airfield. The 
greatest differences are observed in the maxi- 
mum temperatures during the main summer 
period. In spring, before and during the first part 
of the snowmelt, the temperature differences are 
hardly significant for either the maximum or 
minimum temperatures. The same applies for 
the period around freezeup. The minimum tem- 
peratures are on the average only a few degrees 
above 0°C in midsummer. The surface tempera- 
ture contrast between land and sea is apparently 
small at night. 
