PROPAGATION IN S AND X BANDS IN LOW-LEVEL OCEAN DUCTS 



41 



Carei'ul independent measurements were made nsing 

 a number of locations and techniques. All these tests 

 confirmed the failure of the sea surface values to fit 

 to the smooth curve. It appeared possible that propa- 

 gation results might be more dependent on the il/ 

 deficit as computed using the 1-ft value than ou that 

 computed from the sea temperature. The terms "effec- 

 tive surface values" of temperature, mixing ratio, and 

 M were therefore established, these being defined as 

 the values of these quantities at 1 ft above the water 

 surface. Correspondingly, the effective value of M 

 deficit is the difference between the value of M at 1 ft 

 above the sea surface and the lowest value of M for a 

 given sounding, and this effective value should not be 



100 



80 



20 



B 



340 



350 



380 



390 



360 370 

 MODIFIED INDEX »- 



Figure 10. Mean sounding during high winds, April 

 10, 11, 12, 13. 



confused with the total M deficit, which may be con- 

 siderably different. This concept will be employed 

 later in the paper. 



Another significant feature of the normal sounding 

 is the fact that, although the minimum value of M 

 is at a height of about 40 ft, the curve does not quite 

 reach the slope corresponding to mixed air in the first 

 100 ft. Due to the roughness of the few higher sound- 

 ings obtained, it has been impossible to determine the 

 exact height at which the air becomes mixed. It appears 

 to be between 100 and 200 ft. 



The next four soundings show what happened to the 

 duct under abnormal synoptic conditions. The major 

 variations were (a) relatively low winds, (b) rela- 

 tively high winds, (c) relatively dry air, and (d) rela- 

 tively moist air. 



The figures which follow are mean or representative 

 sample soundings made dirring each of the conditions 

 described above. All were made on the tower and are 

 chosen as liest illustrating the effect on the M curve. 



Figure 9 is a mean cur\e for low winds. It shows a 

 lowering of the top of the duct and a change in slope 

 of that portion of the curve lying between 1 ft and 

 the top of the duct. No marked change is found in the 

 total M deficit. 



With wind speeds greater than normal, the duct 

 thickness increased, tlie effective il/ deficit decreased, 



Figure 11. Mean soundings during an influx of dry 

 air, March 27, 28, 29. 



and the total -V deficit also decreased slightly. The 

 average of 4 days' soundings during a windy j)eriod 

 is shown in Figure 10. 



At one time there was an influx of exceptionally 

 dry air with winds of normal speed. Figure 11 shows 

 the effect on the M curve. The major change is an in- 

 crease in the total M deficit. 



Figure 12 is a sample sounding made during a pe- 

 riod when the air was relatively moist. The significant 

 deviation from the normal Sdimdino-s is tlie decrease in 



330 340 350 360 370 380 390 400 

 MODIFIED INDEX ^ 



Figure 12. Mean soundings during an influx of moist 

 air, March 27, 28, 29. 



the total 31 deficit and the lack of any change in the 

 effective M deficit or in the duct height. 



In addition to the shore soundings made at the 

 water's edge, a few soundings were obtained inland, 

 in an effort to determine how far in over the land the 

 duct extended. Unfortunately, most of the data are 



