112 



METEOROLOGY— FORECASTING 



than attenij^tiug to forecast a hypothetical representa- 

 tive M curve, a series of correlations was made relat- 

 ing the general synoptic situation directly to the radar 

 performance. Using this method, the actual over- 

 land forecasting results showed that, while approxi- 

 mately 80 to 85 per cent of the total operating hours 

 could be correctly forecast as either standard or non- 

 standard propogation periods, only some 50 per cent 

 of the nonstandard hours could be forecast correctly. 

 This is only a little better than climatology, and 

 more work remains to be done on the over-land fore- 

 casts of propagation variations. 



In addition to the ground clutter verification of 

 superrefraction, several low-level coverage flights were 

 made from Leesburg to Crystal Eiver and some 80 

 miles out into the Gulf at an altitude of 100 ft, ret- 

 turning at 1,000 ft to check coverage above duct levels. 

 Only a very few flights were made during periods of 

 extended propagation, but during these periods, while 

 interference from extended ground clutter prevented 

 detection of the plane over laud, extended ranges were 

 recorded for the YHF (very high frequency) air-to- 

 ground communication contact. 



In a further attempt to investigate some of the 

 operational possibilities of trapping conditions at low 

 and intermediate altitudes, measurements were taken 

 of maximum ranges on the airl^orne X-band APQ/13 

 radar during routine flights. However, as the ranges 

 observed were very erratic, no conclusions could be 

 drawn. In this respect it should be stated that while 

 excellent cooperation was olitained in getting various 

 radar and aircraft observations, the project had a 

 low priority and as a consequence could not fully in- 

 vestigate many of the more important operational 

 IDOssibilities which would have required extensive use 

 of radar and aircraft facilities. 



The over-water forecasting program at Tarpon 

 Springs was set up to compare the results of fore- 

 casts made under field conditions of limited meteoro- 

 logical data with those made using all available mete- 

 orological information given in the forecasting sys- 

 tem presented in reference 3. This system was based 

 primarily on the over-water modification studies 

 presented at the last conference, where duct height d 

 was related to the wind speed at 1,000 ft, the distance 

 of over-water travel, and tlie M deficit, which is the 

 difference between the .1/ value at some reference level, 

 in this case the sea surface, and the M value of the 

 unmodified air reduced to sea level. In general, no 

 attempt was made to forecast the specific lapse rates 



Figure 3A. Typical Class 1 pattern, P-band SCR-271, 

 Crystal River. Grid squares are approximately .5 miles 

 on a side. 



Figure 3B. Typical Class 2 pattern, P-band SCR-271, 

 Ciystal River. 



and M curves corresponding to the current meteoro- 

 logical situation. With uniform weather conditions 

 existing over water, there was assumed a 100 per cent 

 correlation betwen the M curve and the corresponding 

 radar performance, so that it was merely necessary 

 to determine the representative d and Ail/ of the air 

 mass to obtain the complete propagation forecast. 



