Estimation of air-sea heat and gas fluxes from infrared imagery and surface wave measurements during GASEX 2001

Sea surface infrared images (over a 0.3m by 0.3m patch) as well as surface wave slope data were obtained during the GASEX2001 experiment in the South Equatorial Pacific waters. Previous laboratory and field experiments suggest that at low to intermediate wind regimes the surface heat and gas fluxes are better correlated with surface wave slope rather than with wind speed or wind stress. Our observations of infrared imagery and wave slope during the GASEX2001 also indicate the same trend. Furthermore, they reveal two distinct regimes of heat flux. The surface wave slope data show the existence of sporadic steep slope events, whilst the infrared imagery demonstrates intermittent passage of strong temperature fronts with steep gradients in the heat flux estimates. They therefore suggest the coexistence of weak background turbulence and intermittent small scale breaking events. The former yields moderate heat fluxes, while the latter are associated with enhanced subsurface turbulence and much higher heat fluxes. In addition, the infrared imagery analysis reveals potentially significant effects of near surface temperature stratification on the heat and gas flux estimation and highlights ambiguity in the present definition of the “bulk temperature”. The difference in the surface boundary conditions for heat and gas may also affect the gas transfer velocity estimates based on the observed heat transfer velocity.