Energy consistent climate modelling crucially depends on the spatial distribution of internal wave energy flux and dissipation. The shape of the internal wave energy spectrum forms the basis for existing parameterizations like IDEMIX. And, while there is a growing data base for this shape in the vertical wavenumber direction thanks to finescale observations using the ARGO fleet and standard CTD/LADCP measurements, observations of the shape in the horizontal wavenumber direction are very sparse and mostly confined to the more readily accessible ocean surface layer.
In this project, we will employ a new hybrid pelagic glider using an innovative approach of combining advanced numerical model informed sampling techniques in real-time to observe internal wave spectra and turbulence in the ocean interior. As a key sensor, a pressure rated microstructure probe will be integrated into the pelagic glider system; this use of a new technology combined with new sampling algorithms potentially offers unprecedented insights into deep ocean mixing and internal wave climate. The objective is to simultaneously observe the oceanic energy spectrum below the submesoscale range and the spatial distribution of energy dissipation, using adaptive/reactive sampling to guide the observations.
The development of an on-board adaptive/reactive sampling algorithm for the glider will be informed by output from high-resolution ocean circulation models. Fieldwork will consist of glider tests at a base on the Canary Islands (PLOCAN), and participation in the CRC SONETT expeditions to the eastern south Atlantic (Walvis Ridge region). The glider system will be responsible for the pelagic dissipation measurements for the local energy budget in the Walvis Ridge region during the SONETT cruises. Operator guided reactive sampling techniques will be used to focus on regions of interest (e.g. gradients, fronts), where the internal wavefield interacts and/or is modified by mesoscale flow. Horizontal wavenumber spectra from interior ocean motions will be obtained for selected regimes.
The observational data will be contextualized by idealized and regional numerical modelling studies carried out in L3 and L2. The results of this project will complement the observations carried out in L3 and T2, that will be jointly used to construct the upper- and pelagic oceanic energy spectrum ("Nastrom-Gage for the ocean") within L3, and the observations towards obtaining a local energy budget carried out in T2, T4, L3 and synthesized in W2.
Löb, J., Köhler, J., Walter, M., Mertens, C., & Rhein, M. (2021). Time Series of Near-Inertial Gravity Wave Energy Fluxes: The Effect of a Strong Wind Event. J. Geophys. Res.-Oceans, doi: https://doi.org/10.1029/2021JC017472.