Effects of modes of climate variability on wave power during boreal summer in the western North Pacific

This study investigates extremes of wave climate in the western North Pacific (WNP) as significant responses to modes of climate variability: the El Nino-Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO). Few studies have explicitly investigated significant wave height in this context, and hence, the aim of the present study is to investigate and quantify the responses to a simulated wave data set over the WNP from 1979-2009 by focusing on the combined influences of the ENSO and PDO during the boreal summer. We conducted a composite analysis of sea surface temperatures, sea-level pressure, and extreme anomalies of wave power density (Pw) on different phase combinations of the ENSO and the PDO, and also analyzed the effects of a latitudinal shift of the ITCZ for composite samples with respect to simulated tropical storm (TS) activities. The results demonstrate that the ENSO played a primarily positive role in intensifying anomalous wave climate, while the PDO had the opposite effect. The responses of the peak wave-period were linked to a strengthened anomalous low-pressure and a cooling of sea surface temperature anomalies. The PDO played a significant role in strengthening or weakening of the effects of the ENSO on Pw, thus confirming the findings of previous studies. We found that responses were dependent on whether ENSO and PDO were in or out of phase. These responses can be described by a strengthening of the southeast trade winds that blow across the equator with respect to a latitudinal shift of the Intertropical Convergence Zone (ITCZ). Our findings contribute to the understanding of a relationship between modes of climate variability and TS activities with respect to the status of the ITCZ over the WNP, which can be relevant factors in the lifetime of wave power and related wave parameters in the WNP during the boreal summer.