76 A WORLD ATLAS OF ATMOSPHERIC RADIO REFRACTIVITY 



180 150 



90 60 



30 60 



90 120 150 180 



180 150 120 90 



60 30 



60 90 120 150 



Figure C-25. Percent of time gradient < —157 (N/ifcm): August. 



180 150 



120 90 



30 60 



90 120 150 180 



180 150 120 90 



90 120 150 180 



Figure C-26. Percent of ducting layers thicker than 100 m: August. 



