Clouds are observed in great quantities in the Palmer Peninsula 

 region, averaging eight-tenths. In the Ross Sea area the mean 

 is seven-tenths, though cloudless skies over Marie Byrd Land are 

 rare. Observations indicate a maximum cloud condition during 

 the equinoctial months, with minima during the summer and 

 w^inter months. 



The low summer temperatures, particularly the maximum tem- 

 peratures, are distinctive of Antarctica. The warmest month 

 isotherm of 32° F. lies roughly along the Antarctic Circle except 

 in the South Atlantic Ocean where it reaches the 60th parallel. On 

 the western coast of Palmer Peninsula, due to the oceanic influence, 

 average summer temperatures above the freezing point have been 

 recorded. Winter temperatures vary in different areas, somewhat 

 dependent upon latitude, but principally upon the frequency of 

 southern blizzards and the presence of open water in the vicinity 

 of the base. 



The Bay of Whales region is believed to have the lowest annual 

 temperatures (minus 10° F. to minus 15° F.) with minimum 

 temperatures in the minus 70's being observed by each of the 

 expeditions basing in that locality. The minimum temperature 

 so far recorded there was minus 75° F. on 5 September 1940. 



A winter sledge party camped on the Ross shelf ice near Cape 

 McKay, Ross Island, recorded low temperatures. On 6 July 1911, 

 the minimum of minus 77° F. was observed. 



Very little is known of winter temperatures in the interior of the 

 continent, but absence of the moderating effect of the sea is sug- 

 gested by the winter temperatures recorded by Byrd at a station 

 occupied from late March to mid-October 1934. This station was 

 94 miles south of the main base located at the Bay of Whales. A 

 minimum temperature of minus 83° F. was recorded at the interior 

 station on 21 July 1934, and the thermometer reached the lower 

 70's several times during the months of May, July, August, and 

 September; temperatures were from 10° to 20° lower than those 

 existent simultaneously at the main base at the Bay of Whales. 



The outer boundary which separates the polar continental high 

 lying over Antarctica from the polar maritime air masses of the 

 prevailing westerlies is termed the Antarctic Front. This front 

 varies from a maximum intensity where polar easterlies meet 

 the westerlies, to non-existence in the vicinity of major low pres- 

 sure areas where convergence destroys it. That this front exists 

 has been well established in some cases of large wind sheer. Some 

 characteristics are: 



204 



