RAINFALL ATTENUATION CLIMATOLOGY 



299 



In approaching the problem of predicting the outage time due to rain- 

 fall, it has been assumed that the annual distribution of one-hour point 

 rainfall rates is indicative of the instantaneous values over 30-mi radio 

 paths [1] and that the frequency of severe rainfall of the type measured 

 in the Mobile area will be reduced in other parts of the country in propor- 

 tion to the distribution of annual point rates of 1 in. or more rainfall 

 per hour. 



Figure 7.22 indicates the expected outage time due to rainfall for 

 various path lengths in different rain areas of the United States. The 

 curves A through H correspond to the areas contoured in figure 7.23 

 which illustrates contours of constant path length for fixed outage times 

 for different areas of the United States. The longer paths have been 

 somewhat weighted to take into account the less severe rainfall covering 

 larger geographical areas than the intense storms typical of the Gulf 

 region. 



In a complete 11-Gc/s Bell System point-to-point relay system, the 

 rain outages of the individual hops must be added to obtain the perform- 

 ance of the system. It is desirable that the individual hops meet the 

 same objective, but this is not always possible. Sometimes one or more 



15 20 26 



PATH LENGTH IN MILES 



35 40 45 50 



Figure 7.22. Expected outage time in hours per year versus path length in miles for 



various areas of the United States. 



(After Hathaway and Evans, 1959). 



The curves A through H correspond to the areas contoured in figure 7.23. 



