BACKGROUND 



179 



mass type and the climatic controls of season and latitude, as is substan- 

 tiated by mean A^ profiles for 34 weather observing sites located in or near 

 four distinct air mass source regions about the world. These data show 

 that a definite difference does exist in the profiles of various air masses. 

 Refraction effects were found to be largest in tropical maritime air, inter- 

 mediate in polar continental and polar maritime, and least in tropical 

 continental. Fannin and Jehn also published graphs showing day-to-day 

 variations in profiles representing the effects of air mass changes over a 

 given observing station and graphs of diurnal profile variations. 



In other studies along these lines, Bean, Horn, and Riggs [23], demon- 

 strated that radio ray refraction within the lower layers of an air mass is 

 mirrored by the difference between the observed refractive index structure 

 and that of a standard atmosphere. Figure 5.5 shows a graph of bending, 

 T, plotted together with a modified refractive index profile for an example 

 of summertime tropical maritime air. It is apparent that near the ground 

 bending departures reflect refractive index profile departures from stand- 

 ard. Figure 3.16 presents a series of graphs of departures of refractive 







^ 









3.1 



1.9 



1.7 



1.5 



1.3 



0.9 



0.7 



0.5 



.Cold front 



4 posses Rtcttfnond 



I Squoll line 



I crosses pothlCold front posses Wash. 

 I230 1650 20SO 0030 



July 19, 1947 



8. 

 10- 



12 Cold front passes 



y*tos^lngtool830 



— July 19- 



+7 Squ oil lino crosses 

 potti 1330 JolyO 



-3 



Cold fron t posses RKJimond 

 15" _4 2130 July 19 

 -2 



Points 6, 1 3, a 14 missinij 



320 330 340 350 360 370 380 390 



Hourly Mean Surface Refracfivify 



Figure 5.4. Field strength and N changes during frontal passage. 



Scatter diagram showing passage of a cold front system over the Washington-Richmond path and graph 

 indicating the fluctuation of hourly median field strength with time. 



