Exploratory Description of Low Frequency Ocean Temperature Variability and Its Global Structure

Abstract

An exploratory description is made of nearly global potential temperature variability from to months to 20 years using the field derived from the ECCOv4 state estimate. Relative to higher frequencies, longer periods do not exhibit simplification in the space-time structures. Frequency spectra at individual points are usefully described by a reduced form of a previously proposed analytic model. In contrast, the vertical structure of the variability at low frequencies--periods beyond 1 year---has a very complex form, with only a few global generalizations apparent. Meridional wavenumber spectra, reflecting the dominant zonality of oceanic low frequencies, are spatially comparatively simple, while the zonal wavenumber spectra are spatially complex and not very meaningful. The emergence of strong spatial structures at longer periods is consistent with the presence of complex time-mean (0 frequency) structures in bottom topography, sidewalls, and meteorological forcing.