104 



METEOROLOGICAL EQUIPMENT FOR SHORT WAVE 



.2 



ABC D 



Figure 3. Sounding tecliniques for use at the wind speed ranges indicated. ^^ 



Teinpeiufuie and Iiumidity elements mounted within the radiation shield .S' are connected through the 3-conductor cable C with slip rings on 

 the cable reel R. The meter box (not shown) is connected to the brushes of i?. B: 300-g Neoprene balloon. L: light fishline. F: fishline reel. SK: Sey- 

 fang 7-ft kite. .V: nylon kite line. Tl': kite winch. HK: Hoffman single cell box kite. Arrangement (D) is suitable for sounding from mo^-ing ships; 

 its ceiling is limited to about 400 ft by the small lift of this kite. 



ings the pull of this kite is excessive aud launching cor- 

 respondingly difficult. 



Sounding techniques are shown schematically in 

 Figure 3. For the kite a braided, waterproof nylon 

 line, breaking strength 150 lb. is recommended. For 

 ship-based soundings or conditions where sudden high 

 stresses are likely, a 300-lb test nylon line may be used. 



There seems to be no difficulty in measuring the 

 altitude of the captive balloon or kite.^'' The length 

 of line paid out is determined either by counting the 

 turns of the reel or by means of markers attached to 

 the cable at regular intervals; if the line is off the 

 vertical, its mean inclination can be measured with 

 sufficient accuracy by a simple hand inclinometer. 



7-2 AUTOMATIC RECORDING OF 



METEOROLOGICAL SOUNDINGS" 



A means has been developed for making automatic 

 recordings on a Leeds and Northrup Speedomax or 

 Friez Cyeloray recorder of low-level meteorological 

 soundings of temperature and humidity. The design 

 of the equipment has been restricted in the sense that 

 the standard Weather Bureau-Army-Navy electrolytic 

 hygrometer and negative resistance temperature units 

 must be utilized ; all recordings must be made on the 

 existing automatic radiosonde recorders just named. 



''By E. Dillon Smith, U. S, Weather Bureau, Washington, 

 D. C. 



Gexeiul Design Considerations 



The existing standardized electrolytic hygrometer 

 strip polarizes when direct current is placed on its 

 terminals. However, if a reversed direct current is 

 placed on tlie terminals of the strip, this polarization 

 tendency is neutralized. This would seem to indicate 

 the desirability of placing a low-frequency alternating 

 current on its terminals in lieu of the direct current 

 commutation principle which generally has been used 

 in existing low-level meteorological sounding equip- 

 ment. 



The frequency of the alternating current to be 

 placed on the strip will in general be controlled by the 

 reactance of the low-level sounding cable. In view of 

 this limitation a frequency of approximately 10 c has 

 been used. 



The temperature resistor operates equally well on 

 either direct or alternating current; therefore, it re- 

 quires no equipment design considerations. 



Electrical Characteristics of Elements 



Present practice makes the "lock-in" for the tem- 

 perature and humidity elements through a resistor in 

 series with the elements. However, this technique in- 

 troduces errors in the readings both al)ove and below 

 that for the lock-in point. Effectively, the slopes of 

 the calibration curves are altered, affecting the read- 

 ings on the indicators. In view of this situation, it is 

 fundamental that voltages should be measured across 



