Florian Feppon has received the Wunsch Foundation Silent Hoist and Crane Award for Outstanding Graduate Research. The honor was presented at the Mechanical Engineering Student Awards Luncheon on Friday, May 13, 2016. An honor well-deserved. Congratulations Florian!

Abstract The impact of horizontal resolution (1/12 to 1/50 degree) on Gulf Stream separation and penetration is analyzed in a series of identical North Atlantic HYCOM configurations. The specific questions that will be addressed are as follows: When does a solution converge or is “good enough”? Are the mesoscale and sub-mesoscale eddy activity representative of interior quasigeostrophic (QG) or surface quasigeostrophic (SQG) turbulence? How well do the simulations compare to observations? We will show that the increase in resolution (1/50 degree) does lead to a substantial improvement in the Gulf Stream representation (surface and interior) when compared to observations and the results will be discussed in terms of ageostrophic contributions and power spectra.

Regional ocean models are capable of forecasting conditions for usefully long intervals of time (days) provided that initial and ongoing conditions can be measured. In resource-limited circumstances, the placement of sensors in optimal locations is essential. Here, a nonlinear optimization approach to determine optimal adaptive sampling that uses the Genetic Algorithm (GA) method is presented. The method determines sampling strategies that minimize a user-defined physics-based cost function. The method is evaluated using identical twin experiments, comparing hindcasts from an ensemble of simulations that assimilate data selected using the GA adaptive sampling and other methods. For skill metrics, we employ the reduction of the ensemble root-mean-square-error (RMSE) between the “true” data-assimilative ocean simulation and the different ensembles of data-assimilative hindcasts. A 5-glider optimal sampling study is set up for a 400 km x 400 km domain in the Middle Atlantic Bight region, along the New Jersey shelf-break. Results are compared for several ocean and atmospheric forcing conditions.

Congratulations to LT Matthew Swezey for being awarded the First Prize for his poster on “Ocean Acoustic Uncertainty – For Submarine Applications” at the ASNE Day 2016 Student Poster Competition. ASNE Day is an annual meeting of the American Society of Naval Engineers, which features keynote speakers, panel presentations, technical papers presented by subject matter experts and various student specific programs. Keynote speakers this year included Secretary Stackley the Assistant Secretary of the Navy for Research, Development and Acquisition.

Abstract: Far from boundaries, oceanic motion is primarily a mix of two modes: nearly-balanced and slowly-evolving eddies and currents, and more rapidly oscillating internal waves with near-inertial and tidal frequency. Here, we present a three-component asymptotic model which isolates the coupled evolution of near-inertial waves and quasi-geostrophic flow from the Boussinesq equations. A principal implication of our “NIW-QG” model is that near-inertial waves — which may be externally forced by winds, tides, or flow-topography interaction — can extract energy from mesoscale or submesoscale quasi-geostrophic flows. A second and separate implication of the model is that this wave-flow interaction catalyzes a loss of near-inertial energy to freely propagating near-inertial second harmonic waves with twice the inertial frequency. The newly-produced harmonic waves both propagate rapidly to depth and transfer energy back to the near-inertial wavefield at very small vertical scales. The upshot of second harmonic generation is a two-step mechanism whereby quasi-geostrophic flow catalyzes a nonlinear transfer of near-inertial energy to the small scales of wave breaking and mixing.

Biography: Greg is working with William R. Young on theories for the interaction between oceanic near-inertial waves and nearly-balanced currents. Originally from Massachusetts, he obtained his Bachelor’s and Master’s degrees in Aerospace Engineering from the University of Michigan before making his way to the Mechanical and Aerospace Engineering Department at UCSD. In addition to his current focus on geophysical fluid dynamics, topics of former research include land-based locomotion, mixing, and low Reynolds number fluid dynamics.

Host: Prof. Tom Peacock