Two ‘faces’ of ENSO-induced surface waves during the tropical cyclone season

The response of the wave climate to tropical cyclones (TCs) is investigated using the significant wave height (SWH) observed from satellites and the WAVEWATCH III (WW3) model. Tropical cyclone wind generates local waves (wind seas) under the TC and longer-period waves (swells) that propagate long distances. The genesis location, intensity, and frequency of tropical cyclones over the global ocean are strongly affected by the phases of the El Niño Southern Oscillation (ENSO). It is shown that the interannual variation of global ocean surface waves in the subtropics during summer is dominated by ENSO-related TC activity. In particular, in the subtropical western North Pacific, the wind power is stronger in the TC season before an El Niño and weaker before a La Niña. These ENSO-related TC variations are shown, through composite and empirical orthogonal function analyses, as well as modeling, to dominate the spatial distribution and temporal variation of the SWH over the western North Pacific. The model confirms that longer-period waves (swells) are driven into northern South China Sea, toward Japan in mid latitudes and toward the central Pacific along the equator due to ENSO-related TC activities. The wind power and SWH over the subtropical western North Pacific lead and regress well with the ENSO index, suggesting that they may potentially serve as useful ENSO predictors.