36 POLAR PROBLEMS 



result. My own researches'^ indicate that the cause of the abnormal 

 distribution of pressure arises from a change in the amount of solar 

 radiation as shown by the measurements of the Astrophysical Ob- 

 servatory of the Smithsonian Institution. Figure 8 shows the dis- 

 tribution of pressure departures from normal in July, 1910, when the 

 solar radiation averaged two per cent below normal, and Figure 9 

 shows the distribution in July, 1917, when the solar radiation was 

 two per cent above normal. The conditions in Figure 8 correspond 

 to those found by Wiese when ice was unusually abundant in late 

 summer in Barents Sea, and the conditions in Figure 9 correspond 

 to those found by Wiese when there was a scarcity of ice in late 

 summer. 



Cause of Condensation of Water Vapor in the 

 Polar Regions 



Another problem to be determined by polar research is the ques- 

 tion as to how the water vapor is condensed over the polar areas to 

 produce the dense snow and ice covers observed. The air movements 

 tend outward from these areas, and it is difficult to understand how 

 condensation can occur in the descending currents of air which would 

 prevail under such conditions. Some writers have surmised that 

 the growth of the ice and snow caps over the polar regions comes from 

 deposit of frost. To the writer it seems more probable that it comes 

 from light snows falling from upper currents approaching the pole 

 which under certain pressure conditions have an upward component 

 of motion. The amount of precipitation in the polar regions is very 

 small, and were it not for the very low rate of evaporation both re- 

 gions would be deserts. A recent estimate by C. S. Wright in Nature^^ 

 is that on the floating Ross Barrier in the Antarctic the annual precip- 

 itation is less than eight inches of solid ice, and it is probably a good 

 deal less than this over the Antarctic Continent. The source of this 

 additional moisture has not yet been satisfactorily determined. There 

 are frequent blizzards in this region which lift up the surface snow 

 into the air, but it has not yet been shown that these blizzards yield 

 an additional snowfall. 



Need for World-Wide Observations 



It is becoming more evident each year that the meteorological 

 problem cannot be solved by observations in any one part of the 



" H. H. Clayton: World Weather, Including a Discussion of the Influence of Variations of 

 Solar Radiation on the Weather and of the Meteorology of the Sun, New York, 1923, Chapters 10 

 and 12; idem: Solar Radiation and Weather, or Forecasting Weather from Observations of the Sun, 

 Smithsonian Misc. Colls., Vol. 77, No. 6, Washington, 1925. 



" C. S. W[right]: Antarctic Weather, Nature, Vol. 118, 1926, pp. 488-490; reference on p. 489. 



