Spectral characteristics of sea level variability along the west coast of North America during the 1982-83 and 1997-98 El Nino events

We use hourly sea level records from southern California to the Aleutian Is lands to examine low-frequency variability in the northeast Pacific during the 1982-83 and 1997-98 El Nino events. Comparison between events is facili tated by long-term records for Yakutat, Tofino, Neah Bay, and San Francisco which appear to be representative of distinct coastal oceanic regimes. Res idual (tide-removed) time series reveal that the anomalously high sea level s of the 1997-98 El Nino persisted from the spring of 1997 to the spring of 1998, and this event was more protracted than the 1982-83 El Nino. During both major events, the annual (Sa), semiannual (Ssa), and synoptic-scale se a level constituents were amplified relative to non El Nino years, with syn optic fluctuations in sea level height and sea level pressure for mid-latit ude sites Tofino and Neah Bay strongly correlated through the inverted baro meter response. The spectral anomaly coefficient, S-R(j)(omega)=[R-j(omega) +1]/[R-j(omega)+1] (where R-j(omega)+1]=S-j/(S) over bar (j) is the spectra l ratio between the El Nino spectrum, S-j(omega), and the time-averaged non -El Nino spectrum, <(S(<omega>)(j))over bar>, for tide gauge site "j'') ind icates that both events gave rise to enhanced sea level variability at peri ods of days to weeks because of passing atmospheric systems. However, the 1 982-83 El Nino generated greater signal variance at seasonal-scales (period s of months) while the 1997-98 El Nino generated greater variance at synopt ic scales (periods of days). Findings further indicate that poleward oceani c propagation of the 1982-83 and 1997-98 events terminated near central Cal ifornia, and that much of the enhanced sea level variability observed at mi d to high latitudes was associated with atmospheric teleconnection response s that gave rise to amplified variations in coastal sea level pressure and/ or surface wind stress. Crown Copyright (C) 2001 Published by Elsevier Scie nce Ltd. All rights reserved.