178 



SYNOPTIC RADIO METEOROLOGY 





;| i 

 is M 



It 



is 



15 



13 



09 



0.5 



320 



330 



340 



580 



39C 



Hour// Mean Surface Refracfivity 



Figure 5.3. Field strength versus refractivity. 

 Scatter diagram of select hourly median field strength vs. hourly mean refractivity July 17 to Aug. 8, 1947. 



In another article Gray [19] considered radio propagation and related 

 meteorological conditions over the Caribbean Sea. Utilizing the effective 

 earth's radius factor as a representative index, Gray presented an em- 

 pirical curve of annual median scatter loss versus effective propagation 

 distance designed to fit both Caribbean and temperate regions. Effective 

 distance as defined by Gray is the angular distance in radians multiplied 

 by the radius of the earth modified for normal refraction. Gray reports 

 that the refractive gradient in the first 100 m is in general the determining 

 factor in median scatter loss for transhorizon telecommunications, as one 

 would expect from earlier refraction studies [20]. 



Other studies on refraction problems during the 1950's have led to 

 systematic computation of refraction effects and to significant applica- 

 tions such as the evaluation of radar elevation angle errors in differing air 

 masses and climates [21 , 23]. Schulkin [21] advanced a practical and very 

 fundamental method for numerical calculation of atmospheric refraction 

 (radio ray bending) from radiosonde data. Figure 4.55 [after Schulkin] 

 gives mean angular bendings for radio rays passing completely through 

 the earth's atmosphere for two extremes of air mass type. Fannin and 

 Jehn concluded that a particular refractive index profile depends on air 



