High-wavenumber variability of sea surface height: Evaluating sub-100-km scales with altimetry, ADCP, and model output
- (University Of California, San Diego)
The TOPEX/Poseidon and Jason series of altimeters provided pioneering observations of mesoscale sea surface height variability in the ocean. A new class of altimeters, including CryoSat-2, AltiKa, Sentinel-3, and Jason-CS will further refine our understanding of oceanic variability by providing a means to study submesoscale variability in sea surface height. Theoretical predictions of submesoscale variability originally hypothesized largely geostrophic motions on scales smaller than 50 to 60 km in most parts of the ocean. However, preliminary assessments suggest that when tides and internal wave generation mechanisms are enabled, submesoscale sea surface height has a signature of internal waves rather than geostrophic motions, at least on scales ranging from 10 to 100 km. We have carried out preliminary exploration of these issues in the Drake Passage, using altimetry from AltiKa, Acoustic Doppler Current Profiler (ADCP) data from the L. M. Gould, and numerical model results from the JPL 1/48 degree version of the MITgcm with tidal forcing and internal wave generation. The data products agree in showing high wavenumber spectral slopes that are more consistent with internal wave generated variability rather than geostrophically balanced motions. However, Drake Passage is a highly energetic regime with significant wind forcing and large internal tide generation. In the proposed research, we intend to extend our initial work from Drake Passage to a range of additional environments that we have selected both because of the availability of high-quality data from in situ and satellite sources, as well as model output, and also because they span a range of dynamical regimes.
We have targeted the following regions:
For each of these targeted regions, our objectives are to use spectral methods to identify the dominant physical properties governing oceanic variability at the submesoscale and to ask how these submesoscale motions contribute to oceanic transport of heat and freshwater and to the interactions of eddies and submesoscale structures with larger scale mean flow. Theoretical developments that articulate relationships between velocity spectra and potential energy spectra can be tested in locations where ADCP measurements and buoyancy observations are both available (for example, from thermosalinograph data).