1. The front acts as a quasi-stationary frontal system bounding 

 the polar high, sometimes advancing as a cold front or retreating 

 as a warm front, and usually as boundaries of a wedge moving 

 eastward. The weather along these fronts follows that of normal 

 frontal systems, except on a less well developed scale. 



2. The cold front has a line or zone of snow showers or squalls 

 along which, if air mass showers are also present, become very 

 dense. There is a wind shift across it varying from a few degrees 

 when weak, to over 90° when well formed. A temperature drop 

 of 5° to 7° F. has been observed across this front, though 2° to 

 3° is more common, and a definite change in air mass character- 

 istics occurs. 



3. As a warm front, the cloud shield is well defined, but omits 

 the cirrus and cirrostratus forms of an ordinary system. When 

 advancing, a well ordered layer of alto-cumulus at 8,000 to 10,000 

 feet is the leading edge of the shield, changing into an alto- 

 stratus — alto-cumulus system as it lowers. Air mass weather, 

 in the form of snow showers, usually begins before the snow 

 shield is reached. Cirrus and cirro-stratus clouds can frequently 

 be seen above this cloud shield, but they belong to the low pressure 

 system that usually lies to the northwest in such cases. 



4. As a quasi-stationary front, it may combine the characteris- 

 tics of both a warm and a cold front, depending on the trajectory 

 of the westerlies to the north. With over-running occurring, a 

 narrow band of alto-cumulus clouds and a sparse line of weak 

 snow showers exists. 



5. The average location of this front is from 50 to 150 miles 

 north of the ice pack, varying from 300 to 400 miles north as a 

 maximum, and retreating to near the coastline as a minimum. 

 It may retreat on to the continental plateau itself, under the in- 

 fluence of an extremely strong northerly circulation — but such 

 cases are rare. 



AIR MASSES 



The following description of antarctic air masses was extracted 

 from reports of naval units which operated in that area: 



"The average depth of the polar air mass between the Antarctic 

 Front and the continent varies inversely as the distance of the 

 front from the continent increases. When the front is less than 

 150 miles from the continent this depth is about 8,000 to 10,000 

 feet, and when the front is 200 to 300 miles distant the depth is 

 near 4,000 to 6,000 feet. This results from the seepage of the 



205 



