PRECIPITATION 



There are few, if any, reliable statistics of the amount of pre- 

 cipitation, but it is known to be scanty, equivalent probably to not 

 more than 5 to 10 inches of rain ; it all falls as snow, mostly fine 

 crystals, dry and powdery. The difficulty in measuring it is due 

 to the strong winds which almost always accompany it, for the 

 snow is whirled about and cannot settle in a gauge. Moreover, 

 it is impossible to say how much of the snow is newly fallen from 

 the cloudg and how much has been swept up from the ice cap. 



A perplexing problem is the cause of the precipitation in view 

 of the anticyclonic conditions which prevail. That precipitation 

 exceeds evaporation — and evaporation is certainly considerable — 

 seems to be proved by the great glaciers that move down from 

 the plateau and by the calving from the edge of the ice sheet of 

 the numerous icebergs that beset the surrounding oceans. There 

 must be considerable precipitation in the interior to feed this 

 dispersal from the long periphery. The depressions of the 

 westerlies provide considerable snowfall on the coasts that come 

 within their influence, but their influence does not appear to extend 

 far inland. 



Antarctica enjoys very clear skies and long sunshine in the 

 summer months, the sunshine traces being sometimes continuous 

 for the whole 24 hours. In December, 1903, the Discovery station 

 at McMurdo Sound recorded 490 hours, 66 percent of the possible 

 duration, and in a year there were 1,725 hours, which is more than 

 we have in the sunniest parts of England, though the sun in 

 Antarctica was above the horizon for only 246 days. (See tables 

 VIII and IX.) 



FORECASTING AIDS 



The Norwegian theory of air mass analysis and the forecasting 

 rules and techniques derived therefrom may be applied in the 

 antarctic areas by use of certain modifications based mainly on 

 results of topographical influences. The observations of changes 

 in certain weather elements were found to be of major aid in fore- 

 casting. Hence, the following paragraphs are headed according 

 to these indicative elements. 



WINDS 



Due to the absence of any topographical interference over ocean 

 areas to the gradient air flow, wind speed and direction were the 

 most important factors in determining the positions and intensity 



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