RAINFALL ATTENUATION CLIMATOLOGY 297 



Table 7.10 Correction factor {multiplicative) for rainfall attenuation 



(Burrows-Attwood) 



7.9. Rainfall Attenuation Climatology 



The above paragraphs have been concerned with a descriptive presen- 

 tation of the theoretical and technical background of the problem of 

 power loss due to attenuation by rain and atmospheric gases. In an 

 attempt to circumvent the difficulties of the above methods of attenua- 

 tion prediction it was considered important to try a climatological ap- 

 proach to this problem. However, the results of such a study were 

 disappointing due to the fact that the problems of a systematic climato- 

 logical estimation of rainfall attenuation are many and varied. Answers 

 are needed for such questions as; how often do various rainfall rates and 

 drop sizes occur in geographical areas and over how large an area do 

 these rate and drop size statistics apply? Furthermore, to what height 

 in the atmosphere do these data apply [1]? 



Unfortunately, the present state of meteorological knowledge concern- 

 ing these problems in such that no conclusions can be drawn on a syste- 

 matic and climatological basis. In view of these facts, it appears 

 prudent at this time to provide only engineering estimates of the com- 

 bined gaseous and rain absorption. 



In this regard, Bussey [1] has shown that the absorption due to rainfall 

 exceeds that of gaseous constituents about 5 percent of the time for 

 frequencies around 6,000 Mc/s. The 5 percent figure was obtained by a 

 study of the rainfall rate distribution for various locations in the United 

 States. Figure 7.21 shows the combined rain and gaseous absorption 

 to be exceeded 1 per cent of the time. 



