5-day average wind over north-west Atlantic from ERS1 using a variational analysis

A variational method is developed to produce 5-day gridded wind fields from the first European Remote Sensing (ERS1) scatterometer wind data only. The study focuses on the northwest Atlantic during a 3-month period from August to October of 1992. ERS1 wind data, processed by the Jet Propulsion Laboratory, are binned first on a 1 degree grid for 5-day periods, each period shifted by one day. The analysis method is based upon minimizing a cost function. This function is a set of constraints expressing proximity of resulting wind vector components and wind speed to ERS1 values, a smoothing term and a kinematic constraint on the curl of the resulting wind field. Relative weights for each of the constraints are adjusted by means of statistical comparisons of analysed winds with independent buoy data, and tests of sensitivity. Salient characteristics of the resultant ERS1 5-day wind and wind-curl fields are analyzed and compared with those in surface wind products from ECMWF and buoy winds, They show a general good agreement and highlight the new information provided by ERS1 data on the space and time variability of the wind over the ocean.