CLIMATIC CHARACTERICS 129 



4.3.5. Delineation of Climatic Characteristics 



Since climate is really a synthesis of weather elements taken over a 

 period of time, it is apparent that no fixed climatic boundaries exist in 

 nature. These boundaries shift from year to year with changing weather 

 and with the addition of new data into the climatic averages. Climatic 

 borders, then, represent transition zones between so-called "core climates" 

 of one type or another. A "core climate" presumably maintains its 

 climatic personality consistently over a period of time. The coniferous 

 forest regions of the far north of Canada, for example, maintain a con- 

 tinuously frigid climate under the arctic inversion during the heart of the 

 winter season. Since a simple system is required for effective classifica- 

 tion, the congeries of minute climatic areas arising from extensive climatic 

 division are, for practical purposes, coordinated into areas having broad 

 similarity of climatic character. Thus we shall only attempt here to look 

 for general patterns in our limited data sample. 



The A^'o data for the station elevation of figures 4.16 to 4.25 contain 

 information about the radio refractive index climate of the respective 

 stations that may be converted to a pair of indices, one seasonal, one 

 diurnal, useful in classifying climate. The diurnal index is the ratio 

 obtained by dividing the difference between the highest and lowest hourly 

 means for August by a similar difference for February. This ratio is then 

 plotted versus a ratio of the maximum difference for the 12 mean A'^o 

 values at 0200 divided by the maxmium differences for the 1400 means. 



The results of this analysis can be seen on figure 4.33, where the largest 

 pair of ratios are observed for Denver and Bismarck, a consequence of 

 the strong continentality effects at these inland stations. Denver, it is 

 to be noted, displays a large seasonal ratio whereas Bismarck represents 

 the extreme in diurnal ratios. Brownsville, Washington, and Columbia 

 show sizable seasonal ratios coupled with slightly greater than normal 

 diurnal ratios. Summer-to-winter climate changes are considerable at 

 these three locations. 



The remainder of the stations display the near-unity value of both 

 ratios that would be expected of maritime-dominated climates. 



A comprehensive, though simple, index of climatic variation of the 

 vertical distribution of A'' is particularly difficult to envisage. One such 

 index is the ratio, R{AN), of the summer to winter value of AA^ versus the 

 mean value of AA^ (the absolute difference in A^ at the earth's surface and 

 at 1 km above the earth's surface). The gradient, AA'', has received wide 

 engineering application and is currently being mapped on a worldwide 

 basis by the International Consultative Committee for Radio [30]. When 

 this ratio is plotted versus the yearly mean value of AA^, as on figure 4.34, 

 one again obtains about the same climatic demarcation as above. For 

 example, the maritime-dominated climates generally have values of 

 RiAN) of 1.2 or less. 



