Buoy data in principle are available every hour. Only a fraction of these data are used in the date data assimilation phase of NCEP's Global atmospheric forecast system (GDAS), and in the GDAS, these data presents only a small fraction of all data used. The buoy data can therefore be considered as independent data for GDAS.

The abundance of buoy data allows for an analysis per region. Considered are Japan (21004 and 22001), Hawaii (51000 series), Gulf of Mexico (42000 series), NE Pacific (46000 series), NW Atlantic (41000 and 44000 series) and NE Atlantic (62000 through 64000 series). For the GDAS winds, it makes sense to address wind speed error as a function of wind speed. This is done by performing an error-corrected bin-averaged (BA) analysis (Tolman 1998a) as in a previous wind analysis for the experimental version of NWW3 (Tolman 1998b). For forecast winds such an analysis is irrelevant, as the unavoidable random errors in a forecast will result in an apparent decrease of the slope of the regression lines of the modeled on the observed wind speeds. This would erroneously suggest systematic biases (see, e.g., Tolman 1998a). Alternatively, distributions, which are less sensitive to random errors, can be compared.

Remarks on the Wind Validation Figures:

• The observed wind speed distributions for in particular the NE Atlantic include noise due to the fact the data is archived at a resolution close to that at which the pdf is estimated
• The winds driving the wave model at the Japanese buoy locations are of rather poor quality both in terms of rms error and in terms of scatter indices, particularly in the northern hemisphere summer. This appears to be related at least in part to the representation of Typhoons. In the northern hemisphere winter, the corresponding wind field errors more closely follow the composite data set
• For the buoys around Hawaii, the GDAS wind fields show a systematic low bias of approximately 0.5 m/s, and small rms errors and scatter indices. The negative bias appears to disappear in the 48h forecast, and the bias becomes slightly positive in the 72h forecast
• In the Gulf of Mexico , biases and rms wind speed errors are generally small. Due to the low mean wind speeds, in particular in the summer, scatter indices nevertheless may become rather large
• In the NE Atlantic and Pacific Oceans, small biases, rms error and scatter indices are generally found. Whereas the rms errors show a moderate seasonal cycle, scatter indices stay fairly constant throughout the year
• In contrast, rms error for the NW Atlantic Ocean are somewhat larger and fairly constant throughout the season, resulting in a clear seasonal cycle in the scatter indices, with the largest values in the northern hemisphere summer. In this area, wind speeds appear biased high by up to 0.5 m/s
• In particular in the NW Atlantic Ocean in the summer, extremely stable atmospheric conditions occur in particular around buoys 44004, 44008, and 44011. In such conditions the surface winds become separated from the higher atmosphere, and the (already low) winds are systematically overestimated by the model. This is particularly obvious in corresponding wind distribution functions above
• For the period of the middle of June 1998 through the beginning of October, 1998 the winds were generated by the T70 resolution GDAS and AVN. This model had serious problems with generating tropical systems, which translates into larger rms error and scatter indices for this period. With the subsequent reduction in resolution errors have been reduced again