A Global Distributed Observing Program for Shear, Energy Flux, and Mixing by Internal Waves

Mixing rates in the ocean of the future will be determined to a large extent by the distribution of internal waves. Changes in the forcing of these waves by winds and tides, and modifications of the currents and density stratification that modulate internal wave propagation, evolution, and eventual dissipation into turbulence, are likely to be simulated with some skill by numerical coupled climate models.

But the waves themselves and their impacts on the climate system through diffusive transport of heat, chemicals, and other tracers are a more difficult challenge. This project starts a global sampling program for internal waves using profiling floats- measuring temperature, salinity, velocity, and turbulence—that will yield new insights into internal wave regimes and parameterizations, and that will provide direct and derived data products tailored for use by modeling groups for comparison and validation.

Velocity profiling floats paired with microstructure sensors are an ideal, proven platform for globally- distributed measurements of internal waves and their mixing impacts. Much of the energy in the internal wave field enters at large vertical scales (particularly true for internal tides), yet energy dissipation happens through shear and strain at small scales.

Velocity profiles resolve this full range of vertical scales, and bursts of profiles provide the direction and magnitude of energy flux in dominant frequency bands. Deployment of profiling floats in all dynamical regimes around the globe will provide data sets resolving both the waves and their impact on mixing. This project will also create data practices for sharing direct and derived products (metrics) with numerical modelers.

The improved insight into internal wave forcing, propagation, and dissipation will lead to improved forecasts of processes that are influenced by internal wave mixing and transport. These include centennial-scale forecasts of heat and carbon penetration into the deep ocean, seasonal forecasts of coastal ecosystem nutrient supply through upwelling and shelf-slope exchange, and decadal and longer evolution of upper-ocean stratification and the meridional overturning circulation.

Once developed, the sampling methodologies and data tools can be applied to future velocity and turbulence profiling float data sets. In addition, this work will permit maintenance of instrument development and seagoing field work expertise and will support ongoing education and outreach efforts.

Principal activities Include (1) deployment of 50 velocity and microstructure profiling floats from 6 cruises of opportunity, over 3-years, in diverse locations around the globe spanning the range of the dominant parameters that determine the internal wave environment. (2) derivation of internal wave products for use in (a) estimating internal wave impacts on mixing and the kinetic energy budget of the ocean, (b) projecting surface signatures of internal waves seen by satellite sensors into subsurface vertical structure and frequency bands, (c) validation of internal wave resolving models, and (d) internal wave resolving data assimilation. (3) Development of operational data pathways from velocity and microstructure profile collection to operational modeling and archiving centers. (4) Using the merged and augmented profiling float measurement database to assess the relative roles of wind, tides, topography, and mesoscale variability in generating and dissipating the energy seen in the oceanic internal wave field.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.