Effects of Inertial Current on the Oceanic Surface Waves: HF Observed Current -Wave Buoy Measurements Matched Data, and Wave-Current Coupled Model

Currents can significantly modulate surface waves: (i) the development of wind-generated waves, where the effective wind is relative to the surface current, (ii) wave propagation is dependent on the spatial variation of the currents, and (iii) Doppler shift. Regions with persistent strong tidal currents, such as the North Sea can have wave-height modulations up to 50%. In the open ocean, inertial currents can reach speeds of up to 0.5 m/s. Although ambient currents can change the amplitudes, directions, and frequencies of surface waves on various time scales, their interactions with waves have not previously been reported, except by Gemmrich and Garrett (2012, JPO), using long records of surface wave heights from buoy data. They show that wave heights can be modulated by up to 20% by local inertial currents. However, their analysis is based data from a relatively small number of buoys (8), without any surface current data. Here, we analyze surface currents observed by HF radar, from the Coastal Observing Research and Development Center, and NDBC wave data. We matched all the HF radar current data from 1st Jan 2011 to late 2014 with all co-located NDBC buoys (more over 50). Moreover, in order to explore the spatial distributions and features of the impacts of inertial currents on surface waves, a fully coupled wave-current model (COAWST) was upgraded, adapted and implemented for the Northeast Pacific and Northwest Atlantic. We find: (1) the effects of inertial currents on surface waves are dependent on local weather, bathymetry, and latitude, (2) the effects of inertial currents on surface waves are more significant in high latitudes, and weaker in mid- and low latitudes, (2) data analysis of co-located matched HF radar current and buoy data suggests that the effects of inertial currents on surface waves are over 10%, and (3) the fully coupled wave-current model suggests that surface currents can strongly influence waves, up to 10~30% for the wave heights.