Use of drifting buoys for wave observation: Effect of current on wave data

Drifting buoys can measure wave data even in areas far from land and with strong currents, such as the western boundary current. We evaluated the dependence of the difference between ERA5 wave data and buoy data on the Lagrangian surface current speeds derived from the drifting buoy positions. The ERA5 wave data does not consider the effects of ocean currents. The difference between the ERA5 wave heights and the buoy wave heights increases as the surface current speed increases. The ERA5 wave height is notably underestimated in the case of the opposing current to the mean wave direction, and the wave height is overestimated in the case of the following current to the mean wave direction. The magnitude of them is up to 20%. The wave periods from ERA5 data and the drifting buoy also have differences in the case of opposing and following currents, mainly due to the Doppler shift. Marked over-and underestimation of the ERA5 wave heights can be observed at higher surface current speeds in the Kuroshio extension area, where currents are influenced by mesoscale eddies. Overestimation and underestimation of the ERA5 wave heights are also frequent in the Kuroshio area.

Automated summary

Drifting buoys are effective in measuring wave data in remote areas with strong currents, such as the western boundary current. The difference between ERA5 wave data and buoy data depends on the surface current speed derived from the drifting buoy positions. ERA5 wave data does not account for ocean currents, resulting in underestimation or overestimation of wave heights, especially when there is opposing or following current to the mean wave direction. These differences can reach up to 20%. The Kuroshio extension area, influenced by mesoscale eddies, shows significant over- and underestimation of ERA5 wave heights at higher surface current speeds.