The energy cycle of wind waves on the sea surface |
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| Authors: | G S Golitsyn |
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| Institution: | (1) Nansen International Environmental and Remote Sensing Center (NIERSC), Saint-Petersburg, Russia;(2) Nansen Environmental and Remote Sensing Center (NERSC), Bergen, Norway;(3) Royal Netherlands Meteorological Institute (KNMI), 3730AE De Bilt, The Netherlands; |
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| Abstract: | The problems of wind-induced waves on the sea surface are considered. To this end, the empirical fetch laws that determine
variations in the basic periods and heights of waves in relation to their fetch are used. The relation between the fetch and
the physical time is found, as are the dependences of the basic characteristics of waves on the time of wind forcing. It is
found that about 5% of wind energy dissipated in the near-water air layer contributes to the growth of wave heights, i.e.
wave energy, although this quantity depends on the age of waves and the exponent in the fetch laws. With consideration for
estimates of the probability distribution functions for the wind over the world ocean 11], it is found that the rate of wind-energy
dissipation in the near-water air layer is on the order of 1 W/m2. The calculations of wind waves 19] for the world ocean for 2007 have made it possible to assess the mean characteristics
of the cycle of wave development and their seasonal variations. An analysis of these calculations 19] shows that about 20%
of wind energy is transferred to the water surface. The remaining amount (80%) of wind energy is spent on the generation of
turbulence in the near-water air layer. About 2%, i.e., one tenth of the energy transferred to water, is spent on turbulence
generation due to the instability of the vertical velocity profile of the Stokes drift current and on energy dissipation in
the surf zones. Of the remaining 18%, 5% is spent directly on wave growth and 13% is spent on the generation of turbulence
during wave breaking and on a small-scale spectral region. These annually and globally mean estimates have a seasonal cycle
with an amplitude on the order of 20% in absolute values but with a smaller amplitude in relative values. According to 19]
and to the results of this study, the annually mean height of waves is estimated as 2.7 m and their age is estimated as 1.17. |
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