32 A WORLD ATLAS OF ATMOSPHERIC RADIO REFRACTIVITY 



180 150 



90 60 



30 60 



90 120 150 ISO 





180 150 120 90 



60 30 



60 90 



150 180 



Figure A-l. Location of N(z) data stations. 



(3) If these values are substituted in (A-2), N (z) is found to be 20.7 A7-units at 

 20 km above the surface. 



Figures A-26 through A-29 are seasonal maps of the standard prediction error of 

 the exponential fits to the mean wet-term profiles used in the N (z) parameter maps. An 

 rms error in the wet term of more than 5 iV-units was considered to be a reasonable 

 limiting criterion for locations where the N (z) model should be used with caution, if at 

 all. Figure A-30 delineates these areas ; the cross-hatched areas indicate that the error 

 was in excess of 5 A r -units for 2 or more of the seasonal months (February, May, August, 

 and November) and the single-hatching depicts areas where only 1 of the 4 months 

 showed such large errors. Further discussion of the uncertainty in these areas can be 

 found in section 3.4. 



