The role of mesoscale strain in the near-surface decay and propagation of high-mode near-inertial wave energy
Abstract
It is not well understood how high-mode near-inertial waves (NIWs) decay in the upper ocean, since vertical radiation of wave energy, the dominant damping mechanism for NIWs, is thoughtto be weak for these modes. While this is true for NIWs with a large lateral wavelength that does not change in time, if the wavelength is compressed, the radiation can be amplified. In thisproposal I will investigate a new mechanism???the interaction of NIWs with mesoscale strain and fronts ??? that is particularly effective at compressing the lateral scales of high-mode NIWs.Mesoscale strain acting on a front generates a vertical circulation. When the vertical circulation and strain interact with a NIW, they tilt and compress the wave???s phase lines (i.e. its crests and troughs), generating small lateral scales in the wave field and triggering radiation. The process is particularly rapid for high-mode NIWs and damps their energy within a few inertial periods. Idealized preliminary numerical simulations illustrate this mechanism and suggest that it could be important for not only damping NIWs but also mesoscale eddies through wave-mean flow energy transfers. However, several open questions remain and these guide the proposed research. Namely, how does the wave radiation triggered by the interaction vary with thevertical wavenumber of the NIWs? And, how does the net amount of wave energy that is radiated in the process vary with the properties of the front, eddies, and wind-forcing thatgenerates the NIWs? Numerical experiments of increasing levels of complexity will be performed to address these questions and study the NIW-front-eddy interaction in a morerealistic setting representative of the conditions that will be observed during the NISKINE field campaigns. In addition, I plan to collaborate with the observationalists involved in this DRI totest these theoretical ideas in the field and to assist in pre-cruise planning of the field campaigns, on-board decision making and preliminary analyses during the cruise, and postcruiseinterpretation and analysis of the observations. The research should enhance our understanding of the energetics of both the internal wave and mesoscale eddy fields in theocean and thus will ultimately contribute to the improvement of circulation models, such asthose used by the Navy.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Sep 04, 2018
- Source ID
- N000141812798
Entities
People
- Leif Thomas
Organizations
- Office of Naval Research
- Stanford University
- United States Navy