Analysis of 15 years of ocean surface momentum and heat fluxes from remotely sensed observations

The key surface parameters involved in the exchange of energy between the atmosphere and oceans are: radiative fluxes, momentum, and turbulent heat fluxes. This study aims at using and investigating the quality of the newly-estimated long time series of remotely sensed surface wind vector, specific air humidity, surface wind stress, and latent and sensible heat fluxes. For the period 1992 – 2006, measurements from scatterometers onboard ERS-1,ERS-2, ADEOS-1, and QuikScat, and from radiometers onboard several Defense Meteorological Satellite Program (DMSP) satellites (Special Sensor Microwave/Imager [SSM/I] F10 – F15), are matched in combination with daily sea surface temperature estimates. The fluxes are estimated and weekly-averages calculated over global ocean with a spatial resolution of 1° in longitude and latitude. The quality of all satellite observations has been inspected to remove suspect data. The calculations of air-sea fluxes from satellite observations are accomplished using bulk formulas that take atmospheric stability into consideration. The quality of the retrieved satellite fluxes is determined through comprehensive comparisons with moored buoy estimated at various oceanic sites. The in-situ fluxes are calculated from basic measured variables (wind speed, seas surface temperature, air temperature, and relative humidity) using COARE3.0 model. At global as well as at local scales, the new flux estimates are compared to fluxes calculated from satellite observations such as HOAPS and GSSTF, or provided by ECMWF, ERA-2, and NCEP. The paper will present the main results characterizing the accuracy of surface fluxes and their spatial and temporal features. For instance, the comparison analysis indicates that in general the remotely sensed fluxes are underestimated with respect to the buoy observations, while numerical model data overestimate the fluxes. The difference bias with IFREMER and ECMWF latent heat fluxes are about 7 W/m² and -33 W/m², respectively. The corresponding rms values are about 29 W/m² and 40 W/m². Depending upon the region, season, and flux source, the statistical parameters characterizing the differences between buoy, satellite and numerical flux estimates, vary significantly. They are related to the bulk parameterization used to estimate the fluxes, and to the bias in surface variables.