INTERANNUAL AND INTERDECADAL OSCILLATION PATTERNS IN SEA-LEVEL

Relative sea-level height (RSLH) data at 213 tide-gauge stations have been analyzed on a monthly and an annual basis to study interannual, a nd interdecadal oscillations, respectively. The main tools of the stud y are singular spectrum analysis (SSA) and multichannel SSA (M-SSA). V ery-low-frequency variability of RSLH was filtered by SSA to estimate the linear trend at each station. Global sea-level rise, after postgla cial rebound corrections, has been found to equal 1.62 +/- 0.38 mm/y, by averaging over 175 stations which have a trend consistent with the neighboring ones. We have identified two dominant time scales of El Ni no-Southern;Oscillation (ENSO) variability, quasi-biennial and low-fre quency, in the RSLH data at almost all stations. However, the amplitud es of both ENSO signals are higher in the equatorial Pacific and along the west coast of North America. RSLH data were interpolated along oc ean coasts by latitudinal intervals of 5 or 10 degrees, depending on s tation density. Interannual variability was then examined by M-SSA in five regions: eastern Pacific (25 degrees S-55 degrees N at 10 degrees resolution), western Pacific (35 degrees S-45 degrees N at 10 degrees ), equatorial Pacific (123 degrees E-169 degrees W, 6 stations), easte rn Atlantic (30 degrees S, 0 degrees, and 30 degrees N-70 degrees N at 5 degrees) and western Atlantic (50 degrees S-50 degrees N at 10 degr ees). Throughout the Pacific, we have found three dominant spatio-temp oral oscillatory patterns, associated with time scales of ENSO variabi lity; their periods are 2, 2.5-3 and 4-6 y. In the eastern Pacific, th e biennial mode and the 6-y low-frequency mode propagate poleward. The re is a southward propagation of low-frequency modes in the western Pa cific RSLH, between 35 degrees N and 5 degrees S, but no clear propaga tion in the latitudes further south. However, equatorward propagation of the biennial signal is very clear in the Southern Hemisphere. In th e equatorial Pacific, both the quasi-quadrennial and quasi-biennial mo des at 10 degrees N propagate westward. Strong and weak El Nino years are evident in the sea-level time series reconstructed from the quasi- biennial and low-frequency modes. Interannual variability with periods of 3 and 4-8 y is detected in the Atlantic RSLH data. In the eastern Atlantic region, we have found slow propagation of both modes northwar d and southward, away from 40-45 degrees N. Interdecadal oscillations were studied using 81 stations with sufficiently long and continuous r ecords. Most of these have variability at 9-13 and some at 18 y. Two s ignificant eigenmode pairs, corresponding to periods of 11.6 and 12.8 y, are found in the eastern and western Atlantic ocean at latitudes 40 degrees N-70 degrees N and 10 degrees N-50 degrees N, respectively.