Observation of First and Second Baroclinic Mode Yanai Waves in the Ocean
NAVAL RESEARCH LAB STENNIS DETACHMENT STENNIS SPACE CENTER MS OCEANOGRAPHY DIV
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The structure and propagation of oceanic Yanai waves also known as mixed Rossby -gravity waves are investigated by analysis of satellite-derived sea-surface-height SSH data. Significant spectral peaks along the dispersion curves of first and second baroclinic mode Yanai waves are identified by the wavenumber -frequency spectral analysis of SSH for the period 10 -17 days. The spatial structure and propagation of these modes are described by an analysis of SSH time series filtered in the frequency -wavenumber domain that includes strong signals along the dispersion curves but excludes those of 17-day tropical instability waves. The difference in meridional structure between the first and second baroclinic modes, which is consistent with theory, is evident. The slow eastward propagation of first and second baroclinic mode Yanai wave packets, which is consistent with the group velocity derived from theory, is also isolated from the SSH data. Year-to-year variability of Yanai wave activity is compared with that of the El Nino -Southern Oscillation ENSO, showing a moderate correlation with ENSO Modoki.
- Physical and Dynamic Oceanography