64 A WORLD ATLAS OF ATMOSPHERIC RADIO REFRACTIVITY 



60 



-60 



70 



A. 



—170 

 180 



180 150 120 90 



60 30 



30 



60 90 120 150 



Figure C-l. Percent of time gradient > (N/km): February. 



180 150 120 90 



60 30 



90 120 150 180 



Figure C-2. Percent of time gradient > (N/tm): May. 



