12. Appendix C. World Maps and Cumulative Distribution Charts 

 of Gradients of Ground-Based Atmospheric Layers 



Initial gradient data, obtained (see sec. 5) for 99 of the 112 stations listed in table 

 A-l, are presented in groups of seasonal world maps which illustrate various aspects of 

 the percentage distribution of gradients in ground-based layers. The specific map groups 

 are given below. 



Figures C-l through C-4: Percent of time gradient ^ (N/kva) . 



Figures C-5 through C-12 : Gradient exceeded 10 and 2 percent of the time for 100-m 

 layer. 



Figures C-13 through C-20 : Percent of time gradient ^ -100 (TV/km) and percent 

 of superrefractive layers > 100 m thick. 



Figures C-21 through C-28: Percent of time gradient ^ -157 (iV/km) and percent 

 of ducting layers > 100 m thick. 



Figures C-29 through C-40: Percentage of time trapping frequency is below 3000 

 Mc/s, below 1000 Mc/s, and below 300 Mc/s. 



Figures C-41 through C-56: Lapse rate of refractivity (N/km) exceeded 25, 10, 5, 

 and 2 percent of the time for 100-m layer. 



Cumulative probability distribution charts were prepared for 22 climatically diverse 

 locations for the months of February, May, August, and November (figs. C-57 through 

 C-78) . The alphabetical listing of these stations in table C-l includes seasonal median and 

 minimum trapping frequency values when these were available. Distribution data for two 

 separate times of day at Aden and Nicosia are shown in figures C-57 and C-71. The nega- 

 tive gradient of 50 iV-units/km, which is generally considered to be a good normal value 

 for ground-based layers, has been indicated on each of the distributions by a dashed line to 

 provide a common reference for the vertical scale. The circled value on the distribution 

 line represents the mean ground-based gradient (of any layer thickness greater than 

 20 m) for each month. 



63 



