18 



METEOROLOGY FORECASTING 



site, and suinilfinciitary aii'bome soiuidiiigs are re- 

 quired. 



5. rsyclironieter ('(juipnient ML-313/AM mounted 

 on a slow, siugle-engiiied aircraft is suitable for low- 

 level airborne soundings for propagation forecasting 

 work. 



83 APPLICATION OF FORECASTING 

 TECHNIQUES AND CLIMATOLOGY' 



"■^■^ Introduction 



Puiil'OSES OF THE EePOET 



1. To make available, primarily' to radar and mete- 

 orological officers, information on the principal mete- 

 orological factors wliicli have an important effect on 

 radio and radar performance. 



3. To indicate how suitable utilization of certain 

 of these meteorological factors can lead to improved 

 efficiency and increased exploitation of radio and 

 radar devices : 



a. With respect to variable adjustments applied 

 to daily routine operations (such as the sup- 

 plementary use of scouting planes when the 

 coverage of early warning radars is anticipated 

 to be poor, etc.). 



b. With respect to longer-range planning in es- 

 tablishing radio and radar stations (optimum 

 choice of sites, most desirable frecpiencics to 

 use, etc.). 



Material Coveked ix the Eei'Odt 



nadio-Mcfeorologjj. Since most of the basic infor- 

 mation which has been obtained by various research 

 groups and in military and naval operations involving 

 radar is familiar to the reader or is adequately covered 

 in other reports, ■*'' the essential points with reference 

 to the effect of meteorological factors have been ex- 

 tracted and are here presented in condensed form. The 

 primary emphasis is on the plienomcna associated with 

 nonstandard propagation, i.e., on the conditions under 

 wliich radar ranges are unusually large or unusually 

 suialK Eclated elements — temperature, humidity, the 

 variation of each of these with height, J/ curves, 

 ducts, etc. — are defined, and the role they play in the 

 effectiveness of radar performance is discussed briefly. 



Specific Relationsltips hclween Meteorological Ele- 

 ments and Radar Performance. Of the several investi- 



'By A. T. Waterman, Jr., and C. Harrison Dwight, Colum- 

 bia University Wave Propagation Group. 



gations carried out on this suijject, mostly in connec- 

 tion with the prediction of trapping effects and conse- 

 quently of radar ranges, one which has met with as 

 much success as any and is fairly similar in essence 

 to some of the others is presented here. It was devel- 

 oped in a study of the modification that air undergoes 

 in passing over water and is designed to predict the 

 formation and subsequent structure of surface ducts 

 which are formed along coast lines and over oceanic 

 areas. 



From observations of the representative surface 

 tempierature and humidity of the air, the sea tempera- 

 ture, and the wind direction and velocity, this method 

 indicates whether a surface duct is to be expected and 

 the height to which it is likely to extend. Practical 

 application of the method can therefore be of direct 

 assistance in anticipating radar performance for short 

 periods in advance or for regions where detailed mete- 

 orological observations may be limited. Enough par- 

 ticulars, together with charts and nomograms, are 

 given to enable one with meteorological training to 

 apply these prediction techniques and thus facilitate 

 daily or hourly adjustments to make optimum use of 

 radar equipment. 



Computed Climalological Inforinaiion on Surface 

 Ducts. To obtain a broad picture of the variation in 

 radio and radar ranges likely to be encountered in the 

 western Pacific region, average duct widths (height 

 from the base to the top of the duct) have been com- 

 puted. These computations are based on the relation- 

 ships between meteorological elements and radar per- 

 formance mentioned above and utilize climatological 

 data consisting of monthly averages of air tempera- 

 ture, humidity and sea temperature, and monthly 

 frequencies of winds with specified direction and 

 speed. 



The area covered includes the Japanese islands, the 

 coasts of Korea, Manchuria, and China, the northern 

 Philippines, the Marianas, the Bonins, and the Eyukyu 

 Islands— approximately 10°to50°N latitude ancl 120° 

 to 150° E longitude. The computations indicate the 

 ]>ercentage of time surface ducts of various widths may 

 be exj^ceted at different times of the year and at dif- 

 ferent locations within the region. This information is 

 summarized in tabular form. The results are not in- 

 tended to represent an accurately detailed picture but 

 do give a sufficiently close approximation of average 

 conditions influencing certain aspects of radio and 

 radar performance so that they may be used as a 

 guide in long-term operational planning. 



