128 



METEOROLOGY— FORECASTING 



130 



LEGEND 

 HEAVY LINES SEPARATE THE OCEANIC REGIONS. 



MONTHS (DECEMBER, JANUARY AND FEBRUARY). J 



RANGE OF DUCT WIDTH IN FEET (5 TO 30 FEET). 3 



PERCENTAGE OF TIME DUCTS OF WIDTH GREATER THAN 40 " 

 FEET OCCUR (0 PER CENT). 



PERCENTAGE OF TIME DUCTS OF WIDTH 20 TO 40 FEET OCCUR " 

 (30 PER CENT); PREVAILING WIND DIRECTION WITH DUCTS OF 

 THESE WIDTHS (NORTH), WIND VELOCITY NECESSARY TO CAUSE 

 DUCTS OF THESE WIDTHS (GREATER THAN 20 MPH). 

 PERCENTAGE OF TIME DUCTS OF WIDTH LESS THAN 20 FEET- 

 OCCUR ( 70 PER CENT). 



JFMAMJ 

 JASOND 



0-15 









 100 



N D 

 J F 



5-40 



5iNW,>50 



50iNW,>20 



45 



M 



5-30 







50,N,>25 



50 



M J 

 J A 



0-25 







10.— ,>40 



90 



10-40 



5,NE,>50 



55iNE,>IO 



40 



J F M 



5-40 



5,NW,>50 



60iNW,>20 



25 



A M J 

 J A 



15-30 







70i-,>5 



30 



S 



20-45 



10,— ,>40 



65, — ,>5 



25 



N D 



10-50 



I5^NW,>30 



55i— ,>I0 



30 



5-40 



5iNW,>50 



45,NW,>20 



50 



A M J 

 J A 



15-30 







70,—, >I0 



30 



25-40 



5i — ,>40 



85,—,— 



10 



N 



10-50 

 IOiNW,>30 

 50^N, >I0 

 40 



Figure 20. Summarized results of climntological duet with calculations. 



of the time in wliieli X-baiid radars would be needed 

 to benefit from surface duct conditions ; the percentage 

 of time that no duets (or exceedingly small ducts) 

 occur points out limitations in the utilization of 

 simple surface trapping. Inasmuch as the transmitter 

 should be located within the duct (if the maximum 

 benefit is to be received from trapping conditions), 

 these factors indicate preferable elevations of the 



transmitter. lu general, tlie information given in Fig- 

 ure 20 can be helpful in relatively long-range plan- 

 ning procedures, in deciding on the most effective 

 type of radar set, the opitinium frequency to rise, and 

 the most advantageous elevations at which to estab- 

 lish sites, etc., for operations to be conducted during 

 a particular season of the year and in a jDarticular 

 recfion. 



