Verification of wind prediction in the upper troposphere in the north Pacific via flight observation

The observation of wind over oceans remains challenging. This results in difficulty in predicting the wind speed and direction. In this study, we examined the accuracy of upper-tropospheric wind speed forecasts along the flights between Tokyo International Airport and Los Angeles International Airport. We compared the Global Spectral Model data from the Japan Meteorological Agency (as forecast data) with the observation data from the aircraft's Quick Access Recorder (as true values). The forecast errors are highest over the North Pacific Ocean, not at the end of flight when the elapsed hours are longest, with meridional winds having a larger forecast error than zonal winds. Analysis of the meteorological field where a large meridional wind forecast error occurred using ERA5 indicates that the convergence-divergence of the jet stream or the blocking of westerly winds by the upper trough may have affected the large forecast error.