DRY AND WET TERM SCALE HEIGHTS 



315 



for both winter (February) and summer (August). The immediate con- 

 clusion that one reaches from these maps, figures 8.5 and 8.8, is that H^ 

 has a year round, country-wide average value of perhaps 2.5 km while 

 H d has an average value of about 9 km. 



Since the scale height is the height at which the value of an atmos- 

 pheric property has decreased to \/e of its surface value it reflects the 

 degree of stratification of the property. For example, cold arctic air is 

 very stratified with very little vertical motion, with the result that its 

 density scale height would be expected to be low. By contrast, tropical 

 maritime air that has moved over land is characteristically unstable with 

 convective activity thoroughly mixing the original moist surface air 



N 



1,000 

 700 

 500 



300 

 200 



100 

 70 

 50 



30 

 20 



10 

 7 

 5 



3 

 2 



2 4 6 8 10 12 14 



ALTITUDE ABOVE M.S.L. IN km 



Figure 8.3. N distribution for Bismarck, N.Dak. 



Note that altitude rather than geopotential height is used here to facilitate the eventual calculation of radio- 

 ray bending through actual atmospheric layers. 



