4.3. On the average atmospheric radio refractive index structure over 



North America 109 



4.3.1. Introduction 109 



4.3.2. Meteorological data and reduction techniques 109 



4.3.3. Average A'^o structure 111 



4.3.4. Continental cross sections 122 



4.3.5. Delineation of climatic characteristics 129 



4.4. The climatology of ground-based radio ducts 132 



4.4.1. Introduction 132 



4.4.2. Meteorological conditions associated with radio 

 refractive index profiles 132 



4.4.3. Refractive conditions due to local meteorological 

 phenomena 134 



4.4.4. Background 135 



4.4.5. Description of observed ground-based atmospheric 



ducts 140 



4.5. A study of fading regions within the horizon caused by a surface 



duct below a transmitter 146 



4.5.1. Introduction 146 



4.5.2. Regions and extent of fading within the horizon in 



the presence of superref raction 147 



4.5.3. Theory and results 149 



4.5.4. Sample computations 157 



4.6. Air mass refractive properties 163 



4.6.1. Introduction 163 



4.6.2. Refraction of radio rays 164 



4.6.3. Conclusions 170 



4.7. References 170 



Chapter 5. Synoptic radio meteorology 173 



5.1. Introduction 173 



5.2. Background 173 



5.3. Refractive index parameters 185 



5.4. A synoptic illustration 195 



5.5. Surface analysis in terms of A''o 197 



5.6. Constant pressure chart analysis 205 



5.7. Vertical distribution of the refractive index using A units 211 



5.8. Summary 223 



5.9. References 224 



Chapter 6. Transhorizon radio-meteorological parameters 229 



6.1. Existing radio-meteorological parameters 229 



6.1.1. Introduction 229 



6.1.2. Parameters derived from the A'^ profile 233 



6.1.3. Parameters involving thermal stability 238 



6.1.4. Composite parameter 238 



6.1.5. Potential refractive index (or modulus), K 239 



6.1.6. Vertical motion of the atmosphere 240 



6.1.7. Discussion of the parameters 241 



6.1.8. Comparison of some parameters 243 



6.1.9. Some exceptions and anomalies 243 



6.1.10. Conclusions 246 



