Estimates of the power spectrums for fully developed seas for wind speeds of 20 to 40 knots

Abstract

Various criteria pertaining to the synoptic situation are presented in order to determine when a fully developed wind-generated sea might be found in the North Atlantic Ocean. Four hundred and sixty wave records, corresponding to various synoptic situations, were digitized and analyzed spectrally as a first step in the preparation of a climatology of ocean wave spectrums. The wave records were taken by the ocean weather ships of the United Kingdom by means of a Tucker shipborne wave recorder. Selected subsets from the available spectrums based on these synoptic criteria were averaged in order to produce spectrums for various wind speeds. These selected subsets were examined to see if they came from the same population by means of the Kolmogorov-Smirnov test, and the results show that, within the accuracy expected, the samples chosen represent fully developed seas. A second subset chosen at random without using these criteria was tested, and the results showed that wind speed alone does not properly characterize the sea state. A nested family of spectrums was obtained for wind speeds of 20, 25, 30, 35, and 40 knots in which the frequency of the maximum appeared to be inversely proportional to the wind speed and the significant height was proportional to the square of the wind speed. The spectrums and the results deducible from them yield results that appear to be a compromise among the various published theoretical forms for the spectrums and the equations for the significant height of a fully developed sea.