Characterizing wavenumber spectra in altimetry: An ADCP perspective
Event: 2022 Ocean Surface Topography Science Team Meeting
Session: Science III: Mesoscale and sub-mesoscale oceanography
Presentation type: Type Poster
Contribution: PDF file
New satellite altimeters bring new capabilities to resolve small-scale variability and near-surface signatures of surface eddies and inertia-gravity waves (IGWs). We use underway Acoustic Doppler Current Profiler (ADCP) velocity measurements in combination with altimetry to probe the dynamics of this high-wavenumber ocean variability and to explore the interactions between geostrophic eddies and unbalanced IGWs. ADCP data allow us to diagnose the ratio of rotational (geostrophic) to divergent (unbalanced) submesoscale energy. We examine distinctions between tropics and mid-latitudes, and evaluate seasonal variations in high-wavenumber variability of the upper ocean, and we examine the role of eddies compared with IGWs. Results from ADCP data show that submesoscale rotational energy decreases with increasing depth nearly everywhere, while submesoscale divergence energy shows weak vertical dependence, but tends to peak near the stratification maximum. In the regions where IGWs appear to dominate the submesoscale, the rotational-to-divergence ratio more often is higher than predicted by the Garrett-Munk spectrum, except around the thermocline in the southeast tropical Pacific. Under the isotropy assumption, the rotational energy levels at wavelengths of 15-100 km imply O(10-1) or less eddy Rossby numbers almost everywhere and at all depths and seasons. These findings provide a framework for interpreting altimeter small-scale altimeter observations.