Wind Field Generation

The hindcast model wind field data sets were derived from the U.S. National Center for Environmental Prediction (NCEP) Re-Analysis (NRA) database. The NRA is a 50+ year numerical simulation of global atmospheric conditions available at 6-hourly temporal resolution. The U (east-west) and V (north-south) wind fields at 10 m elevation above ground were extracted from the global database for a grid network that covered the entire Pacific Ocean region. The NRA wind database has a spatial resolution of approximately 1.9°.

The NRA winds, as with any global atmospheric model, will tend to under-represent peak wind speeds in storm events, due to limited grid resolution. As well, the NRA winds underestimate wind speeds in tropical regions.

To address these limitations, a comprehensive comparison was carried out, on a global basis, with 6 years of measured ocean winds by means of the QuikSCAT satellite scatterometer data. The Figure below shows an example of wind speed bias between the NRA and QuikSCAT winds.

A significant bias low may be noted in the tropics, while NRA over-estimates wind speeds offshore of northern Chile and Peru .

QuikSCAT Comparisons to NCEP Wind Data [1999-2004]

 

Spatially varying non-linear corrections (as a function of wind speed) were developed for the NRA winds through grid point by grid point comparisons to the QuikSCAT winds. These corrections removed any effective bias in the NRA winds and significantly improved correlation to the measured data.

The final corrected wind fields were used as input to the WAVEWATCH III model.