48 



S. L. Dingman et al. 



24j— I— I — I I I I I I — p — I — p— 1 — [— r— 1 — p— I — I I I I I I — [— 1 I — p~i p-p-T 



o 



c 

 o 



o 



z 



FIGURE 2-11. MecTAi (—), maximum (k.) and minimum (y) net radiation 

 for five-day intervals over the coastal tundra at Barrow. The data are 

 based on 1962 and 1964-66 from Kelley et al. (1964), Lieske and Stros- 

 chein (1968), Weaver (1969, 1970), Maykut and Church (1973), and 

 LeDrew and Weller (1978). 



as the snow melts from the land surface. Over lakes the ice cover extends 

 this transition to two or three weeks. During the snow-free period, the 

 average albedo generally varies between 10 and 20^q, with large spatial 

 variations. During freeze-up, the albedo fluctuates between 18% and 60% 

 as snow falls and melts; the permanent snow cover forms by early October. 

 Maykut and Church (1973) found that incoming longwave radiation 

 for three years averaged 7440 MJ m"^ yr'', which is more than twice the 

 annual receipt of incoming shortwave solar radiation (Table 2-3). The 

 longwave input exceeds the shortwave in every month except April and 

 May (Lieske and Stroschein 1968). The longwave radiation balance is at 

 a minimum during the coldest part of the year when cloud cover is at a 

 minimum (February and March), and maximum values are reached dur- 

 ing the summer months when cloud cover increases and cloud tempera- 

 tures are highest. 



