512 BELL SYSTEM TECHNICAL JOURNAL 



component having superposed on it a small amplitude, variable phase, 

 "^" component. A relatively low mean amplitude value and the 

 coincidence of scintillation conditions with conditions of convective 

 instability of the atmosphere would thus be explained. All the 

 scintillation records came on days of relatively high wind and convec- 

 tive instability. A turbulent atmospheric condition would dissipate 

 or attenuate any boundaries, especially the lower ones. The rapid 

 flutter about the mean amplitude value is the normal expectation from 

 a high, turbulent, low reflection coefBcient boundary. 



Our two polarization results are qualitatively explicable on the 

 mechanism proposed. As can be seen in Fig. 15, the change from 

 vertical to horizontal polarization results in a relative lowering of the 

 "5" curve without much change in the "^ " curve, which should 

 result in increased fading. For our circuit and a boundary at 1500 

 meters the relative "5" vs. "A " drop is 13 db. 



As Fig. 16 shows, the variations of the "^ " components with height 

 are markedly different for the two polarizations. The "Ay" compo- 

 nent falls steadily with height up to 4700 meters; the "Ah" component 

 has a deep and sharp minimum at 3000 meters after which it rises 

 again. Since most of our observations concerned boundaries at 2000 

 meters or less, this high altitude disparity between "Ah" and "Ay" 

 does not affect our explanation. The disparity between vertical and 

 horizontal fading should be much more marked for high boundaries 

 than for low boundaries. 



Further Experimental Curves and Checks 

 The curves given have illustrated the variability in the fading, a 

 variability which no short period of recording can encompass. The 

 tentative explanations proposed have been shown to be in accord with 

 several of the features characteristic of this fading. Certain other 

 experimental results will now be adduced which offer further verifica- 

 tion along somewhat different lines. 



For the forty-five mornings on which simultaneous recording was 

 carried out during the United States Weather Bureau plane flight, we 

 have calculated, from the airplane data, the values of the "A" and 

 "B" components. As stated earlier, there were twenty-four days when 

 boundaries above 400 meters altitude, and of sufficient distinctness to 

 be fairly accurately estimated (Ae ^ 10~^) were shown by the meteoro- 

 graph records. For these the "A" components have been computed. 

 By taking the dielectric constant gradient for the first half kilometer, 

 the effective earth's radius was determined and inserted in the Wwe- 

 densky formula to give the "B" component. These calculated values 



