ANNUAL VARIATION. 



85 



iatitudc in the north can be found from the values given by Mohn * for each 5° of latitude 

 between 60" N. and the North Pole. Interpolating from these values we find the following as 

 the mean monthly temperatures for 78^ N. 



Table 46. 

 Mean Monthh/ Temperature at 78" N. ^F.) 



Annual Variation of Insolation. — Angot has calculated the total heat received durin" each 

 month at all ten degrees of latitude from the equator to each pole.f In his calculations he 

 takes as unity ' the quantity of heat which falls on unit horizontal surface at the equator 

 during an equinoxial day, supposing the sun to be at its mean distance from the earth 

 and neglecting atmospheric absorption.' He then calculates the heat received assuming difierent 

 values of atmospheric absorption, from which we choose the results obtained by taking the 

 coefficient of transmission to be 0-7. 



The following table shows the total insolation received in each month at 78° N. and 78" S. 



Table 47. 

 Total Insolation Received at 78° N. and 78° S. 



Comparison of Temperature with Insolation in the North and South Polar Begions.—The 

 curves on figure 29 represent the following : — 



The mean monthly temperature at 78° N. 



The mean monthly temperature on the north of the Barrier. 



The total monthly insolation at 78° S. 



The difference between the insolation for 78° N. and 78° S. is too small to affect the 

 following discussion ; therefore only the curve for 78° S. has been shown. For convenience of 

 reference the curves for the north have been plotted against the corresponding months for 

 the south, .i.e., the value of January in the north has been plotted against July in the south 

 and so on. 



The curves for the Barrier and 78° N. show several most important dift'erences : 



(a) Whereas the temperature curve for the Barrier follows that of the insolation very 



closely, the curve for 78° N. has a lag of a month. 



(b) During the months of no insolation the temperature on the Barrier undergoes very 



little change, while in the north the temperature continues to fall after the 

 insolation ceases in April nearly as rapidly as it had fallen previously. 



* Norwegian Nortli Pole Expedition, 1893-1896, page 575. 



+ Ansot. Annales du Bureau Cent. Met. de France, 1883, page B 121. 



