seasonality of the mesoscale sea surface variability from multi-year satellite altimetry
Event: 2022 Ocean Surface Topography Science Team Meeting
Session: Science III: Mesoscale and sub-mesoscale oceanography
Presentation type: Type Forum only
Sea surface slope (SSS) varies in response to a range of physical processes: tides, geostrophic flows, surface and internal waves, etc. We present the sea surface variation in the form of the SSS variability using 30 years of heterogeneous satellite altimetry measurements. We apply band-pass filters to the along-track SSS, and derive the mean and seasonal (annual and bi-annual) components of SSS variability in multiple wavelength sub-bands from 30 to 1000 km. We show the power spectral density of the mean and seasonal SSS variability versus wavenumber, and find that the seasonal components are small (less than 10% in amplitude) compared to the overall mean variability on a global scale. Through correlation analysis, we show evidence that SSS variability with wavelengths less than 30 km is mostly dominated by wave height noise. At longer wavelengths there are real oceanic signals. For example, there are clear signatures of unbalanced flow motions (internal tides/waves) above the mid-Atlantic Ridges and the Amazon outflow. On a global scale, there is higher mesoscale variability (30-100 km) in local wintertime. Some regions, for example the Philippine Sea and the South Equatorial Countercurrents, deviate from this hemispheric-scale pattern. The Northern Hemisphere shows stronger seasonal change than the Southern Hemisphere.