Chapter 3 

 TRANSMISSION EXPERIMENTS IN ARIZONA 



3 1 ATMOSPHERIC REFRACTION UNDER 

 CONDITIONS OF A RADIATION 

 INVERSION" 



AN INVESTIGATION of propagation of high-freqviency 

 - radio waves under conditions of a nocturnal tem- 

 perature inversion was made in Arizona over a sliort 

 period in December 1944. Climatic conditions in this 

 region permitted testing the dependency of refractive 

 index in the lower troposphere on the temperature 

 lapse rate, since the water vapor content was expected 

 to remain relatively constant. 



During the day in this area the soil heats rapidly, 

 producing vertical instability and convection mixing 

 near the ground and hence a temperature lapse rate 

 in the lower atmosphere approaching the dry adia- 



•By J. B. Smyth, U. S. Na 



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batic rate. After sunset the soil temperature drops 

 rapidly, cooling the layer of air adjacent to the sur- 

 face and producing a low-level radiation inversion 

 during the night. 



It was thought that the progression of this low- 

 level inversion would at times cause the lapse rate of 

 refractive index to vary between slightly positive and 

 zero, which would be the case of greatest interest. If 

 during such a variation of lapse rate field strength 

 observations are made with a receiving antenna which 

 under standard conditions is in the earth shadow re- 

 gion, a test can be made of Hoyle's hypothesis^ that 

 temperature lapse rate is of greater significance than 

 is now believed. If, for exaniple, the field strength 

 during one-way transmission reaches the value cal- 

 culated for a flat earth while the modified refractive 

 index lapse rate is still positive, then something must 

 be wrong with eitlier the modified index concept or 



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S 9 



6 8 10 12 14 16 18 20 22 24 2 4 6 8 10 ' 12 14 16 18 20 22 24 2 



Figure 1. Surface air temperatures at Ajo, Gila Bend, and Phoenix, December 16 to 17, 1944. 



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