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Dynamics of the marine atmospheric boundary layer at high wind conditions

Vladimir Kudryavtsev and Vladimir Makin

The impact of ocean spray on the dynamics of the marine atmospheric boundary layer (MABL) in conditions of very high (hurricane) wind speeds is investigated. To that end a model of the MABL in presence of sea spume spray is constructed. The model is based on the classical theory of the motion of suspended particles in a turbulent flow, where the mass concentration of droplets is not mandatory small. A description of the spume droplets generation in the model assumes that they being torn off from breaking waves are injected in the form of a jet of spray into the airflow at the altitude of breaking rests. The distribution of droplets inside the jet is proportional to the radius to the power 2; the total production of droplets is proportional to the length of wave breaking fronts. Droplets affect the MABL dynamics in two ways: via redistribution of the momentum between droplets and air forming the so-called spray stress, and via the impact of droplets on the turbulent mixing through stratification. The latter is parameterized through the extension of the MoninObukhov similarity theory. At high wind speeds the tearing off shortest breaking wave rests results in the appearance of the near surface sheet of spray with the mixture density exceeding the air density in few times. The spray stress mechanism per se leads to the increase of the momentum flux in the MABL. The dominant impact of droplets on the MABL dynamics appears through stratification. That leads to the suppression of the turbulent mixing and the momentum flux in the MABL and, as a consequence, to the acceleration of the wind velocity and the suppression of the sea surface drag. Model results are consistent with observations.

Bibliografische gegevens

Vladimir Kudryavtsev and Vladimir Makin. Dynamics of the marine atmospheric boundary layer at high wind conditions
KNMI number: WR-10-01, Year: 2010, Pages: 23

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