Variability in the wave climate of the North Pacific: links to interannual and interdecadal variability

Variability in the wave climate of the North Pacific is of interest from many perspectives including coastal management, near-shore engineering, sediment transport and beach erosion, and maritime safety. Recent results document variability in North Pacific winter wave heights (both averages and extremes) over the past 40-50 years as seen in hindcasts produced with wave models driven with winds from the National Centers for Environmental Prediction (NCEP) reanalysis. This variability is marked by changes at a variety of time scales ranging from inter-annual to multi-decadal, the latter dominated by an upward trend in wave heights over much of the eastern North Pacific. It is of interest to link these changes to the dominant modes of circulation variability over the North Pacific, most notably El Nin/spl tilde/o-Southern Oscillation (ENSO) and Pacific inter-decadal variability (often referred to as the Pacific Decadal Oscillation or PDO). During El Nin/spl tilde/o episodes, and during periods when the PDO index is high, North Pacific winter cyclones tend to be stronger and tend to track farther to the south and east. Such changes in cyclone behavior have important effects on wave climate. This note examines how ENSO and PDO variability are reflected in hindcast North Pacific winter wave climate [as seen in a 50-year hindcast with the WAVEWATCH III model]. To give an example how changes in the large-scale wave climate are expressed in regional coastal waters, results are also shown from a derivative data set created by transforming 3-hourly hindcast deep-water wave spectra from a point just off Point Conception into the Southern California Bight. Other results, most relevant to multi-decadal changes, come from a statistically derived hindcast for the winter North Pacific from 1899-2000 using techniques similar to those applied in the wave trends study in the North Atlantic.