Determination of high-frequency wind variability from observations and application to North Atlantic wave modeling

The influence of quasi-realistic high-frequency wind variability for the pr obability distribution of surface waves and for the skill of the prediction s with the wave model WAM is investigated. So far, the sensitivity of the s urface wave field to high-frequency wind variability has been demonstrated only for idealized wave conditions or particular events using rather simpli fied high-frequency wind forcings. In this study the problem is addressed m ore generally by estimating the high-frequency wind variability (for period s shorter than 6 hours) and by assessing its relevance for a particular Nor th Atlantic winter. Wind observations with 20 min time resolution are used to build a statistical wind generator that reconstructs (in a statistical s ense) that fraction of the wind variability that is missing in the analyzed model wind fields. These quasi-realistic wind fluctuations, superimposed o n analyzed 6 hourly wind fields, produced an increase of the air-sea moment um flux and resulted in a moderate but systematic increase of the average w ave heights and in their short-term variability. While the results are qual itatively consistent with the findings of earlier studies under simplified conditions, they differ quantitatively. The change of the distribution of t he wave data is found to be less pronounced for young sea states in the sto rm track region than for older sea states in the low latitudes. The respons e yields everywhere a significant amplification of the spectral variance fo r periods below 12 hours and an increase of the probability of extreme wave heights. Thus the increased air-sea momentum flux is seen to be effective for predictions of the probability distribution of wave data and may also i nfluence predictions of the ocean circulation.