Wednesday, 12 February 2003
High resolution satellite-derived surface turbulent fluxes over the global ocean
A method is presented for determining estimates of sea surface winds and latent heat flux from several satellite measurements. The methodology for obtaining the surface turbulent fluxes uses physical properties of radar and radiometer measurements, empirical and inverse models relating satellite observations to surface parameters, and objective analysis merging various satellite estimates. A high resolution dataset is prepared for the global ocean, using the same inverse algorithms, geophysical model functions, and the same objective method. The satellite data come from the European Remote Sensing satellite scatterometer (ERS-2), NASA scatterometers NSCAT onboard ADEOS-1 and Seawinds onboard QuikScat, and several Defense Meteorological Satellite Program (DMSP) radiometers (Special Sensor Microwave/Imager [SSM/I] F10 - F14). A long time series of surface wind fields (daily, weekly and monthly) and heat fluxes (weekly and monthly ) is computed over global oceans during 1991-2002, using a single sensor and/or merging the measurements from various sensors. Two regular longitude and latitude grids are available, 1°(1° and 0.5°(0.5°, depending on each sensor resolution.
The reliability of the derived surface winds and heat fluxes is examined and validated through comprehensive comparisons with available in-situ data. On average, the rms error for wind speed and direction do not exceed 2m/s and 20°, respectively. The resulting satellite wind and latent heat flux fields are also compared with other published flux fields estimated from satellite observations. At global scale, the agreement between different sources is good. The main discrepancies are related to the methods used to calculate the gridded fields from polar satellite data. Using the validated remotely sensed wind and heat fluxes, spatial and seasonal characteristics of both fluxes are investigated in several oceanic areas. The derived results are compared to those determined from the ECMWF data , and NCEP re-analysis. On average, the numerical models and satellite turbulent flux estimates are in good agreement. However, both numerical model fields show noticeably weaker surface wind fields in the tropics than satellite estimates. Furthermore, a significant seasonal and regional biases (difference between satellite and atmospheric models) are depicted and discussed.