CONTINENTAL CROSS SECTIONS 



123 



FEBRUARY 



^ >25 



335 





I AUGUST I 



PWM 

 



OCA HAT 



COF PWM 

 2 



DISTANCE (KmxIO') 



Figure 4.27. North-soxdh No cross section along the eastern coast of the United States. 



The cross section for the eastern seaboard of the United States, figure 

 4.27, presents a considerably different picture of refractive index chmate 

 than the Pacific coast. On the winter cross section the area between 

 Portland and Washington falls within a low produced by frequent occur- 

 rence of polar air masses during this season of the year. Southward to- 

 ward Cocoa, Fla. (COF) there is a significant A'' increase that corresponds 

 to the considerable latitudinal temperature gradient that exists on the 

 east coast of the continent during the winter months. On the summer- 

 time cross section the temperature gradient difference between the two 

 coasts is even more pronounced and is reflected in the strong east-coast A^'o 

 difference of about 40 N units as compared to the Tatoosh-San Diego 

 difference of about 10 A'' units. The vertical gradients are also seen to 

 increase in a systematic fashion from north to south, reflecting the in- 

 creased vapor pressure gradients in the warmer southern regions. 



The extensive continental cross section from Isachsen (IC) to Balboa 

 (BLB), figure 4.28, discloses several interesting features. On the winter- 

 time chart the relatively high A^o values between Isachsen and Churchill 

 (YQ) indicate the presence of very cold, dense, dry air. To the south over 

 Bismarck, N.Dak. (BIS), and the Great Plains, relatively warm, dry air of 



