Assimilation of SeaWinds scatterometer data in the GEOS data assimilation system

The first SeaWinds scatterometer was launched into space aboard the Quikscat satellite on June 19, 1999 at 7:15 pm PDT. Flying in a near polar orbit 800 km above the earth’s surface, SeaWinds uses an advanced scatterometer design to measure surface wind velocity over 90 per cent of the ice free oceans every 24 hours. This first SeaWinds mission is designed to replace the NASA Scatterometer (NSCAT) which ceased providing wind velocity data when the ADEOS I satellite failed. A second SeaWinds is scheduled to be launched late in 2000 aboard ADEOS II. Previous scatterometer assimilation experiments conducted by the NASA Data Assimilation Office, using both ERS and NSCAT wind observations, have demonstrated considerable potential for this type of data to improve both atmospheric analyses and forecasts, however much of the smaller scale information content of the scatterometer data could not be taken into account in the early coarse resolution versions of the Goddard EOS (GEOS) Data Assimilation System (DAS) or in operational data assimilation systems. In this paper, we will describe data assimilation experiments in which the new higher resolution versions of the GEOS DAS are used to assimilate SeaWinds scatterometer winds. Following a brief discussion of the SeaWinds design and the methodology used to assimilate scatterometer data in the GEOS DAS, the quality of the SeaWinds data and the impact of SeaWinds on GEOS analyses and forecasts at different resolutions will be presented.