NO A A PROFESSIONAL PAPER 11 



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Constancy 



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1955 1960 1965 



Years 



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1975 



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FIGURE 3-9. — Average wind constancy and number of extratropical cyclone centers crossing New York Bight, February-June 1949-76. 



sultant winds from 24r-270° occurred about three times 

 or slightly over 10 percent in the northern marine areas, 

 one time from 2ir-240° (less than 5% of the time) in the 

 southwest area, and three times (a little over 10%) in the 

 southeast area. These figures indicate that the surface 

 wind flow during February-March was somewhat more 

 anomalous over the Southern Bight. April had a more 

 even distribution from all sectors, consistent with the low 

 wind constancies in figure 3-7. Wind patterns during May 

 and June were close to the climatological norm. The most 

 unusual character of the wind field during these months 

 is its above-normal persistence. 



The relative absence of cyclonic activity between Feb- 

 ruary and June 1976 should be retlectd in low wind var- 

 iability as expressed by a higher constancy ratio. The high- 

 est average constancy over this period coincided with the 

 two minima in cyclonic activity over the Bight (in 1969 

 and 1976) during the 27-year period of record (fig. 3-9). 

 Although constancy is a measure of the vector variance 

 of wind and hence of its directional persistence, scalar 

 variance gives a better measure of turbulence associated 

 with wind. The choice of the 27-year (1949-75) record at 



John F. Kennedy International Airport (fig. 3-10) as an 

 indicator of the larger scale behavior of the wind field 

 offshore is a reasonable one, since, as may be seen in 

 figure 3-7, changes in wind constancy during 1976 were 

 mirrored by similar changes over the Bight. The wind 

 variance in February and March 1976 was considerably 

 below the long-term mean, as expected. During May, 

 however, the variance was the highest since 1955. showing 

 a substantial increase over 1975. April and June did not 

 have marked differences from their respective means. 



Regardless of the particular response time of a water 

 body to changes in atmospheric forcing, it might be ex- 

 pected that in the New York Bight area major features 

 in the wind field, such as its constancy, averaged over a 

 month's time would in turn be reflected in the mean Bight 

 circulation features. The wind data in figure 3-10 correlate 

 well with current meter measurements (see chapter 7), 

 which show a higher total current variance in the Bight 

 during May 1976 than during 1975. The currents also have 

 periods of northeastward flow in accordance with the 

 higher wind constancies (sustained southwesterly winds) 

 in May (fig. 3-7). 



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