Adrian Matei edited observations.tex  about 10 years ago

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Usually, a purely geostrophic horizontal wind at sea surface cannot inject enough turbulence to generate wave breaking. Therefore, a downward ageostrophic component or a shift from the purley geostrophy in the wind at sea surface should be present. The wave-driven supergeostrophic jet subdues the downward ageostrophic component (and enhances the upward ageostrophic component or the upward momentum flux), thus it reduces turbulent injection from atmosphere to ocean. The surface value of this wave-driven jet or stress can be described by integrating the wave-induced stress going into each wave component:  \begin{equation}  \tau_{w}\left(0 \right) = \int_{0}^{\infty}\rho_{w}\omega\beta\phi(\omega)d\omega,   \end{equation} where $\omega$ is the wave angular frequency, $\phi(\omega)$ is the frequency spectrum, and $\beta$ is the dimensionless wave growth parameter. \par  \section{Observational mechanisms}  We observed the sea state and fluxes in a high winds regime, during the HIWINGS experiment project. Our region of interest was the North Atlantic ocean, south of Greenland, in the path of strong and frequent cyclones. There was an acute positive NAO (North Atlantic Oscillation) index during that period, namely from the beginning of October to middle November, 2013. Because of this phenomenon, a powerfull jet stream and intense horizontal pressure gradients were present, hence the repetitive cyclones. We succeeded to perform the measurements during winds of over 20 m/s, which makes the data and the future results more valuable, because it is something that probably hasn't been realized in the past. A notable variety of instruments that measured the sea state and fluxes were used during this field experiment. \par  The scientific crew was partitioned in different teams having specific goals regarding their interest for the data, but a unique goal when it comes to understand the big picture of the air-sea coupled system dynamics. Our specific scientifc goal is to understand the mechanisms of primary source for aerosol production, and hence aerosol turbulent fluxes. We already made the consideration that aerosol turbulent fluxes occur via bubble, whitecap, and bubble plume dynamics. Our main focus is on bubble plume and whitecap physics, but on individual bubble physics as well. In order to have a deep understanding of this natural process in a high winds regime, we need to harmonize and correlate the measurements performed using this rich variety of instruments. We used a foam camera to detect whitecap fractions, a submerged bubble camera to explore the optical properties of bubbles within bubble plumes, two resonators to assess the acoustical properties of bubbles within bubble plumes, and a sonar to detect the bubble plumes dynamics. All instruments were set in place along a 11 meters spar buoy. Just under the foame camera, we had wires that could measure the sea state. More detailed informations on the sea state can be generated by the Wave Rider, which was separated from the spar buoy. Other instruments took measurements from the ship's board, including measurements of aerosol and gas fluxes. \par  \section{Research approaches and further study}