116 



METEOROLOGY— FORECASTING 



S('E-588 (duft lic'iglit dO I't above the autemia), while 

 from midnight to 0300 an elevated duct of the order 

 of 380 ft traps both sets (duct height some 250 ft 

 above the SCE-588 antenna). By 0400 the winds 

 became strong enough to wipe out the stratified layers 

 and mix the air, giving standard conditions. At O.'iOO 

 a trace of a transitional condition aloft appears in the 

 sounding but is not sutBcieut to extend the range. 



During the months of January and February data 

 were collected on S-band V beam at Tomato Hill 

 during 47 days. Of these days' observations 37 per cent 

 showed nonstandard conditions. During the same pe- 

 riod the SCE--271 at Crystal River showed at least 

 slight increases in langes on 73 per cent of the days' 

 observations which were rccoi'ded. although cmly 17 

 jicr cent attained the strength of class 3. 



The longest ground range observed on the S-band 

 set at Tomato Hill was 200 miles on the morning of 

 January 25, while the longest ground range observed 

 on the SCR-271 at Crystal Eiver was 140 miles on the 

 morning of February 17. Both these ranges were the 

 maximum permitted by the radar presentation. 



During the month of April at Tarpon Springs, 65 

 per cent of 24 days' observations showed nonstandard 

 conditions, with 46 per cent giving surface return at 

 greater than 80 miles, indicating strong superrefrac- 

 tion. The longest range recorded was the eoast-liiic 

 ellect out to 220 miles. 



To determine suitable low-level airborne sounding 

 equipment, the psyclirometer equipment ML-313/AM, 

 the WSC wired sonde, and sling psyclirometer ML- 

 24A were mounted in aircraft L-4 (cruising speed 55 

 mph) and compared with the MIT psychrograph car- 

 ried by a barrage balloon. 



From considerations of the forecasting method an 

 accui-acy of ±0.2 C in wet and dry Inilb temperatures 

 and a lag coefficient less than 45 sec are desirable. The 

 accuracy of the MIT psychrograph is ±0.2 C in tem- 

 peratures, with a lag coefficient of the order of 15 sec. 



These data w-ere gathered during hours of daylight 

 and are spread rather evenly between 0000 and 1700. 

 The MIT psychrograph was held at a fixed point in 

 space where a conservative estimate of the fluctuations 

 of temperature was 0.3 C. The airborne instrtiments 

 integrate the measurements for a given level, hence a 

 s|jread in the data is reasonably indicated and the 

 statistical value of sigma may be considered represen- 

 tative of the accuracy of the test instrument. 



The procedure for each test instrument involved 

 making five to ten regular low-level soundings supple- 



mented by a series of pas.ses at a fixed le\cl. Necessary 

 ground checks w'erc carefully made using forced ven- 

 tilation, and standard corrections for airborne instru- 

 ments were applied. 



Psychrometer equipment ML-313/AM, consisting 

 of a wet and ili'v ))ulb thermometer in a streamline 

 housing, was mounted as far back in the cabin of the 

 L-4 as was practical. Since the L-4 is a single engine 

 plane it was expected that the engine heat and propel- 

 ler blast would influence the readings. The data are 

 as follows : 



Dry bulb 



Number of ])airs of readings: 174 



Average difference: — 0.06 C 



Oy^c of the ])(iints agree to within 0.20 C 



Wet bulb 



Number of pairs of readings: 156 



Average difference: -|- 0.08 C 



67% of the points agree to within 0.14 C 



The ML-313 was, in addition, mounted on aircraft 

 L-5 (singie-engined, cruising speed 100 mph). The 

 data are similar to those given above. The data indicate 

 that, despite the expected influences of propeller blast 

 and engine heat, the equipment is suitable for low- 

 level soundings for ]3ropagation work. 



-0.6 "2 



-0.5 1 



-0.4 ' T 



-0.3 

 -0.2 

 -0.1 

 

 + 0.1 

 +0.2 

 +0.3 

 + 0.4 

 + 0.5 

 + 0.6 



DRY BULB TEMPERATURE 

 DIFFERENCE DISTRIBUTION 



^ 



10 



20 



NUMBER OF POINTS 174 



WERAGE DIFFERENCE 0.06C 



MEDIAN 0.1 



MODE 0.0' 

 a = 0.20 



40 



I 



FREQUENCY OF OCCURRENCE 



111 



-0.5 



-0.4 

 <n -0.3 

 y -0.2 



-0.1 

 



z + 0.1 

 UJ +0.2 

 3 +0.3 

 !; +0.4 

 ffi +0.5 



1 +0.6 

 y +0.7 



~71 . 



WET BULB TEMPERATURE 

 DIFFERENCE DISTRIBUTION 



•' 10 



NUMBER OF POINTS 156 

 AVERAGE DIFFERENCE +0.08 C 

 MEDIAN +0.1 



MODE +0.1 



a =:0.I4 



20 



30 



_l 



40 



50 



_J 



FREQUENCY OF OCCURRENCE 



DIFFERENCE EQUALS MIT PSYCHROGRAPH LESS 

 ML3I3 IN DEGREES CENTIGRADE 



Figure S. In^^tniiueut cumpariscm. .\HT p.sj'chrograph 

 and psychrometer JML 313/AiM on Aircraft L-4. 



