polar air from the continental plateau, downwards and outwards 

 from its edge toward the sea. Hence, the further the front from 

 the continent the more shallow the air mass, and, therefore, the 

 frontal surface slopp is less. The result is that for a given amount 

 of over-running of the westerlies, the precipitation and cloud 

 shields are wider, the further the front is from the continent, and 

 vice versa. 



"It was assumed that polar continental air (cP) on the plateau 

 region has the ideal vertical structure of that type of air, i. e., a 

 surface inversion (shallow during summer) with an approximately 

 isothermal layer above the surface to a depth of 3,000 to 4,000 feet 

 and a normal lapse rate above this layer. This air was then modi- 

 fied by subsidence as it sank from the plateau to sea level and by 

 heating from below as the mean temperature of the underlying 

 surface increased downward and outward. Thus, the air had an 

 almost neutrally stable vertical structure at the coastline. Further 

 travel northward over solid pack ice was accompanied by heating 

 from below, resulting in a dry adiabatic lapse in the lower levels. 

 The depth of this layer varied from 1,000 to 2,000 feet as a mini- 

 mum, to 4,000 to 5,000 feet as a maximum, depending on the width 

 of the pack. Immediately above this layer an inversion of 2° to 

 5° C. existed, formed as a result of mixing and heating from 

 below and subsidence as the air moved northward. From this 

 inversion to the frontal surface a slightly stable lapse rate pre- 

 vailed. The strength of the inversion and the character of the 

 lapse rate above also varied, depending on convergence or diver- 

 gence due to the flow pattern. With cyclonic flow, the inversion 

 is small and nearly isothermal and a moist adiabatic lapse rate 

 lies above. With anticyclonic flow, the inversion is larger and 

 deeper, with a definitely stable lapse rate above. 



"The cP air of the plateau was assumed to have a low moisture 

 content throughout, which decreased with elevation. As this air 

 flowed downward and outward, a slight amount of moisture was 

 added in the surface layers but it was insufficient to raise the rela- 

 tive humidity to more than 50 or 60 percent. The dryness aloft 

 was accentuated by subsidence so that a sharp decrease of moisture 

 occurred at the base of the inversion. This dryness was also ac- 

 centuated by divergence when the flow pattern was anticyclonic; 

 it was decreased by convergence when the flow was cyclonic. 



"The above assumptions led to the concept of two different types 

 of cP air ; that on the continental plateau and that along the 

 coastal area and ice pack. Since each type had different struc- 



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