RADIOSONDE PROFILE ANALYSIS 



43 



Table 2.L Comparison of ground-based ducting statistics derived from various sensor 



time lag corrections 



which, for normal conditions of 15 °C, 1013 mbar, and 60 percent RH, is 

 approximated by 



AAT ^ -1.27 AT + 4.50 Ae + 0.27 AP. 



(2.14) 



Since, for ducting, a large negative gradient of A^ is required, the effect 

 of temperature sensor lag correction is to make temperate and arctic 

 temperature increases wath height more pronounced with a resultant 

 larger contribution to a negative A^ gradient. Humidity lag corrections 

 under all conditions lead to a larger decrease of RH with height than 

 indicated and concomitant more rapid decrease of N with height. Such 

 an explanation does not seem so evident for tropical conditions, however, 

 where both temperature and relative humidity decrease with height. 

 This apparent paradox is explained by the relatively great change in 

 saturation vapor pressure of water associated with a small change of 

 temperature near 25 °C which then produces the required large decrease 

 of e and A'' with height. It is seen, then, that the temperature sensor lag 

 correction produces an added humidity correction. Thus one must cor- 

 rect both sensing elements for the purpose of preparing A^ profiles. Even 

 in the case of the arctic inversion the interplay of the temperature and 

 humidity lag corrections is very important, as has been noted by Yerg 

 [48]. 



Thus, the correction for humidity sensor lag alone tends to overestimate 

 ducting incidence since the corrected relative humidity decrease, coupled 

 with the indicated temperature increase, produces a greater decrease in 

 water vapor pressure than is actually present. 



2.5.4. Conclusion 



It appears from the present study that if studies of refractive index 

 profile characteristics are to include sensor lag correction, then allowance 

 should be made for both temperature humidity sensor time lags, regard- 

 less of climate. Any systematic application of these conclusions to large 



