A probabilistic approach for SeaWinds data assimilation

Abstract

AbstractScatterometer sea surface wind observations are being successfully assimilated into numerical weather prediction models. The quality of the winds retrieved from the new SeaWinds scatterometer (onboard the QuikSCAT satellite) depends on the subsatellite cross‐track location. In particular, the poor azimuth separation or diversity between views in the nadir region results in poor quality winds. In the QuikSCAT nadir region, where the local cost‐function minima are broad, the use of the standard procedure results in arbitrary and inaccurate winds. A new scheme, which accounts for broad cost‐function minima by allowing more ambiguous wind solutions, i.e. a multiple solution scheme (MSS), is proposed as an alternative to the standard procedure. The probability of every ambiguous solution being the ‘true’ wind is empirically derived, and used in the ambiguity‐removal procedure to make the scheme flexible enough to accept many wind solutions.A comparison between the standard wind retrieval and the MSS procedures at 100 km resolution is then performed, using independent model winds for validation. The MSS turns out to be more in agreement with the model reference than the standard procedure, especially at nadir. Moreover, it shows more spatially consistent and realistic winds by more effectively exploiting the information content of the observations. Copyright © 2004 Royal Meteorological Society