Interannual Baroclinic Rossby Waves in the Midlatitude North Atlantic

Abstract

Twenty-six year time sequences of upper thermocline temperature block-averaged in 5-degree latitude and longitude squares reveal strong, in-phase vertical coherence and low to moderate horizontal coherence over 550 km. Least-squares fitting theoretical cross spectra from a stochastic, first baroclinic mode Rossby wave model to cross spectra of the temperature?time sequences yields several best-fit wavenumber vectors that conform to the dispersion relation of first baroclinic mode Rossby waves in a flat bottom ocean with no mean current. The slope of the midocean ridge, which is as important as midlatitude beta, and the mean circulation were ignored. About 25%?55% of the cross-spectral energy can be attributed to the best-fit waves. A composite spectrum of the baroclinic potential energy of all the demonstrated Rossby waves is qualitatively similar to the spectrum of North Pacific first baroclinic mode Rossby waves, showing a peak around 6?7 years, but is 30 times larger in magnitude. The geographic distribution of wave energy is curiously congruent with the shape of the midocean ridge.