74 A WORLD ATLAS OF ATMOSPHERIC RADIO REFRACTIVITY 



180 150 



801 



90 60 



60 



70 

 180 150 



A. 



— TO 

 120 90 60 30 30 60 90 120 150 180 



Figure C-21. Percent of time gradient < —157 (N /km): February. 



Figure C-22. Percent of ducting layers thicker than 100 m: February. 



