8 A WORLD ATLAS OF ATMOSPHERIC RADIO REFRACTIVITY 



four dissimilar stations : Dakar (low-level sub- 

 sidence), Antofagasta (intermediate subsid- 

 ence-trade wind ducting) , Hilo (trade wind in- 

 version), and Balboa (steep exponential gra- 

 dient) . A check of figure A-30 reveals that the 



first three of these stations are located in areas 

 where, because the rms of the wet-term error 

 exceeds 5 iV-units for at least 1 month, the three- 

 part exponential model is not recommended. 



OS U> 1.5 2.0 !S 



HEIGHT ABOVE SURFACE IN KILOMETERS 



Figure 3. Five-year mean wet refractivity term: February. 



