THE ACCURACY AND POTENTIAL USES OF COMPUTER BASED 

 WAVE FORECASTS AND HINDCASTS FOR THE NORTH ATLANTIC 



by 



Willard J. Pierson, Jr. and Leo J. Tick 

 New York University, Bronx, New York 10453 



ABSTRACT 



The work to be described was a part of a much larger project. The aim 

 of the project was to predict the changes in airframe design that would be 

 needed to optimize performance of the automatic landing control system 

 (AN/SPN-10) to be used on aircraft carriers. To do this, carrier motions 

 have to be described, and to describe the carrier motions the wave con- 

 ditions have to be determined. 



Computer based hindcasts for fifteen months of historical data have been 

 made that describe the directional spectra of the wind generated waves and 

 swell on the North Atlantic. The months were December 1955, November 

 1956, and December 1958 through December 1959- The computed frequency 

 spectra agree well with the spectra obtained by an analysis of wave records 

 obtained by British weather ships. Verification statistics show that the bias 

 is negligible. About 40% of the hindcasts are within three feet of the ob- 

 served significant wave height. About 60% are within six feet. 



The wind field proved to be the most difficult part of the problem of 

 hindcasting the waves. Errors in the wind field due in part to inadequate 

 data coverage were responsible for the largest errors in the hindcasts. 

 Ways to improve the determination of the wind field by a finer grid and by 

 further calibration of ship reports are available. 



The climatological wave data so obtained have many potential uses in 

 military oceanography besides their original purpose. The usefulness of 

 any naval vessel, or of any floating structure in the deep sea can be studied 

 by means of the same input wave data. Instead of specifying that a certain 

 military device should function in some particular sea state, a more mean- 

 ful statement would be that the device should have assigned characteristics 

 whenever the wave spectrum, no matter what its features, as hindcasted 

 every twelve hours for a particular year of data yields a significant wave 

 height less than 20 feet and whenever the wind is under 33 knots. as an ex- 

 ample. 



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