Air-Sea Turbulent Fluxes From a Wave-Following Platform During Six Experiments at Sea

Denis Bourras (1) , Rémi Cambra (2) , Louis Marié (3) , Marie-Noëlle Bouin (4) , Lucio Baggio (5) , Hubert Branger (6) , Houda Beghoura (3) , Gilles Reverdin (7) , Boris Dewitte (8, 9, 10, 11) , Aurélien Paulmier (8) , Christophe Maes (3) , Fabrice Ardhuin (3) , Ivane Pairaud (3) , Philippe Fraunié (1) , Christophe Luneau (12) , Danièle Hauser (13)

1 MIO - Institut méditerranéen d'océanologie
2 France Energies Marines [Brest]
3 LOPS - Laboratoire d'Océanographie Physique et Spatiale
4 CNRM - Centre national de recherches météorologiques
5 LATMOS - Laboratoire Atmosphères, Milieux, Observations Spatiales
6 IRPHE - Institut de Recherche sur les Phénomènes Hors Equilibre
7 PROTEO - Processus et interactions de fine échelle océanique
8 LEGOS - Laboratoire d'études en Géophysique et océanographie spatiales
9 CEAZA - Centro de Estudios Avanzados en Zonas Aridas
10 Departamento de Biología Marina [Coquimbo]
11 ESMOI - Millennium Nucleus Center for Ecology and Sustainable Management of Oceanic Island
12 OSU PYTHEAS - Institut Pythéas
13 SPACE - LATMOS

Turbulent fluxes at the air‐sea interface are estimated with data collected in 2011 to 2017 with a low‐profile platform during six experiments in four regions. The observations were carried out with moderate winds (2–10 m/s) and averaged wave heights of 1.5 m. Most of the time, there was a swell, with an averaged wave age (the ratio between wave phase speed and wind speed) being equal to 2.8 ± 1.6. Three flux calculation methods are used, namely, the eddy covariance (EC), the inertial dissipation (ID), and the bulk methods. For the EC method, a spectral technique is proposed to correct wind data from platform motion. A mean bias affecting the friction velocity (u*) is then evaluated. The comparison between EC u* and ID u* estimates suggests that a constant imbalance term (ϕimb) equal to 0.4 is required in the ID method, possibly due to wave influence on our data. Overall, the confidence in the calculated u* estimates is found to be on the order of 10%. The values of the drag coefficient (CD) are in good agreement with the parameterizations of Smith (1988, https://doi.org/10.1029/JC093iC12p15467) in medium‐range winds and of Edson et al. (2013, https://doi.org/10.1175/JPO‐D‐12‐0173.1) in light winds. According to our data, the inverse wave age varies linearly with wind speed, as in Edson et al. (2013, https://doi.org/10.1175/JPO‐D‐12‐0173.1), but our estimates of the Charnock coefficient do not increase with wind speed, which is possibly related to sampling swell‐dominated seas. We find that the Stanton number is independent from wind speed.

Domaines: Physique Atmosphérique et Océanique [physics.ao-ph]; Océan, Atmosphère; Océanographie

Denis Bourras, Rémi Cambra, Louis Marié, Marie-Noëlle Bouin, Lucio Baggio, et al.. Air-Sea Turbulent Fluxes From a Wave-Following Platform During Six Experiments at Sea. Journal of Geophysical Research. Oceans, 2019, 124 (6), pp.4290-4321. ⟨10.1029/2018JC014803⟩. ⟨insu-02160613⟩