METEOROLOGY OF TRANSMISSION EXPERIMENTS 



69 



10 20 



WIND SPEED AT 1000 FT IN MPH 



Figure 4. Ratio of heiglit of M inversion to 3/ deficit. 

 For positive temperature excess the over-water trajec- 

 tory is 10 to 30 miles. 



water trajectory this diagram gives tlie height of the 

 j\[ inversion as a function of temperature excess, wind 

 speed, and M deficit. A complete analysis of the ob- 

 servations will yield similar diagrams both more ac- 

 curate and more detailed. These should prove of 

 definite use in forecasting 31 curves. 



In conclusion, it should be made clear that the work 

 summarized in this report is a group undertaking. 

 A large number of persons, some of them members 

 of Eadiation Laboratory Group 43 and other mem- 

 bers of the U. S. Army Air Forces, took part in the 

 development and construction of the instruments and 

 in the observing. 



6* METEOROLOGY OF THE SAN DIEGO 

 TRANSMISSION EXPERIMENTS" 



During the summer of 1944 a rather intensive ex- 

 perimental propagation program was carried on in 

 San Diego area. The main purpose was to determine 

 the distribution of radiated radio energy in the lower 

 troposphere under the wide range of weather condi- 

 tions prevailing during this season. A temperature 

 inversion was present from around the first of June 

 through October; the base of the inversion varying 

 from the surface, on a few occasions, up to an alti- 

 tude of some 4,000 ft. This inversion is characterized 

 by dry superior air subsiding over moist maritime 

 polar air. 



6.4.1 Methods of Observation 



The field strength data were taken in two ways. A 

 fixed one-way link between San Pedro and San Diego 



■^By Lt. A. P. Stokes, U. S. Navy Radio and Sound Laboratory. 



gave continuous records on frequencies of 52, 100, 

 and 547 megacycles, and vertical airplane sections 

 taken at several different distances west of San Diego 

 gave almost instantaneous records of the energy dis- 

 tribution for the same range of frequencies. 



The meteorological data were obtained by the use 

 of an airplane and wired sonde; the technique of the 

 hitter was described in detail in a previous report." 

 The captive balloon or Avired sonde is a modified ver- 

 sion of the "Washington State College equipment." 

 Daily soundings were taken at the Scripps Pier at 

 La Jolla, 11 miles north of the laboratory. Two 1-week 

 periods of continuous shipboard soundings were made 

 from a YP ship operating in the middle of the San 

 Pedro to San Diego link. 



The principal use of the airplane has been in tak- 

 ing vertical field strength sections seaward from the 

 laboratory. During these flights meteorological sound- 

 ings were made as frequently as possible. The labora- 

 tory was fortunate in obtaining from the Washington 

 State College group one of their original sonde units 

 and has adapted this equipment for use in the air- 

 plane soundings. The temperature and humidity ele- 

 ments were mounted iii an unobstructed aluminum 

 housing approximately 11/2 ft above the nose of the 

 PBY-5A airplane. 



Since the airplane served the dual purpose of ob- 

 taining both meteorological and field strength meas- 

 urements, all the data were ol>taiued on a fixed course. 

 Field strength sections were made in rapid descents 

 and the meteorological data were obtained in ascents. 

 Navigational difficulties prohibited spiraling for the 

 meteorological data and therefore these soundings 

 covered considerable horizontal distance. Due con- 

 sideration of this was made in plotting the cross 

 sections. 



6.1.2 The San Diego High Inversion 



In the summer season San Diego lies within the 

 belt of the subtropical anticyclones, and, with the 

 absence of surface frontal activity, a stagnant circula- 

 tion exists. Because of the persistence of high-level 

 auticyclonic circulation aloft, pronounced subsidence 

 is maintained throughout this season; 1944, in par- 

 ticular, was characterized l)y very low humidity above 

 the 2-km level. By subsidence aloft a thermal inver- 

 sion exists o\'er a large maritime area and thus forms 

 the boundary between the lower maritime polar and 

 the continental tropical or superior air aloft. Varia- 

 tion in height and magnitude of the inversion is the 



