Relationship between an El Nino event and the interannual variability of significant wave heights in the North Pacific

A new global 1 degrees X 1 degrees gridded monthly significant wave heights (SWHs) dataset was produced by applying an optimum interpolation method (OIM) to the TOPEX/Poseidon (TP) SWH data obtained from 1993 to 2000. We ascertain the high accuracy of this dataset by comparing it with SWH data obtained from the National Data Buoy Center (NDBC). We then investigate the interannual variability of SWH by using the empirical orthogonal function (EOF) analysis and the relationship of interannual variability between SWH and marine surface winds by using linear regression analysis. When an El Nino event occurs, significant changes can be observed in the SWH east of the Philippines (120 degrees E-135 degrees E, 10 degrees N-25 degrees N) and off the US West Coast (140 degrees W-120 degrees W, 35 degrees N-45 degrees N). The SWH variability east of the Philippines in winter (January-March) depends strongly on the northerly winds in relation to the appearance of the Pacific-North American (PNA) pattern. Off the US West Coast, both the appearance of the PNA pattern and the westerly wind associated with the Aleutian low are very important to wintertime SW11 variability. On the other hand, SWH in summer (July-September) is not related to the PNA pattern either east oj'the Philippines or off the US West Coast. It is interesting to note that summer SWH off the US West Coast is very low compared with the winter SWH, although the wind speed in summer is almost the same as that in winter. This result suggests that the winter westerlies would lead to higher SWH because of the longer fetch.