Change of wind forcing from the NCEP/NCAR data to the QuikSCAT

We have changed the wind forcing of the JCOPE model from the NCEP/NCAR realanysis data to the QuikSCAT data. The QuikSCAT data is introduced into the calculation of the wind stress (Large and Pond, 1981) and the heat flux (Rodati and Miyakoda, 1989) from 19 February 2003. The QuikSCAT wind fileds are derived from the observations by the scatterometer SeaWinds on space mission QuikSCAT, of the National Aeronautics and Space Administration (NASA). The QuikSCAT Near-Realtime (NRT) data product is used for the JCOPE operation because this product effectively removes aliasing of the satellite ground track using the objective interpolation. The product has a 0.5 degree laltitude by 0.5 degree longitude and 12-hourly resolution.

The scatterometers provide more realistic wind forcing with better spatial resolution for the ocean modeling than the numerical weather prediction(Liu, 2002); the horizontal resolution of the NCEP/NCAR reanalysis is about 2.5 degree. In particular, the QuikSCAT wind data is more suitable for the coastal application than the NCEP/NCAR data because the wind forcing significantly affects coastal currents. The NSCAT, old version of the QuikSCAT, wind fields detect the sharp gradient caused by land mass and change of the Coriolis force at the equater (Liu et al., 1998). The QuikSCAT wind also captures more detailed structure of the wind stress than the NCEP/NCAR wind as shown in Fig.1 (snapshot) and Fig. 2 (the monthly mean wind stress curl). In addition, the difference of wind data causes a considerable change of the heat flux. Stronger cooling is represented in the monthly mean heat in January flux calculated from both QuikSCAT and NCEP/NCAR data than that calculated from only the NCEP/NCAR data (Fig.3).

In spite of the difference of small scale signals, large scale structures of the QuikSCAT and the NCEP/NCAR wind fields are almost similar as indicated by Fig.2. Compasrison of the Sverdrup transport, which is related to volume transport of the Kuroshio south of Japan, also shows much correspondence between both data (Fig.4).

Acknowledgement

The QuikSCAT data is obtained from the NASA/NOAA sponsored data system Seaflux, at JPL through the courtesy of W. Timothy Liu and Wenqing Tang.

References

Large, W. G., and S. Pond, 1981: Open ocean momentum flux measurements in moderate and strong winds, J. Phys. Oceanogr., 11, 324-336.

Liu, W. T., W. Tang, and P. S. Polito, 1998: NASA scatterometer global ocean-surface wind fields with more structures than numerical weather prediction, Geophys. Res. Lett., 25, 761-764.

Liu, W. T., 2002: Progress in scatterometer application, J. Oceanogr., 58, 121-136.

Rosati, A. and K. Miyakoda, 1988: A general circulation model for upper ocean simulation, J. Phys. Oceanogr., 18, 1601-1626.

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