EAPS

PAOC colloquium: Brian Arbic
Date Time Location
October 29th, 2018 12:00pm-1:00pm
This talk is about modeling oceanic internal gravity waves (IGWs) on a global scale.
IGWs are waves having gravity as a restoring force, with their largest displacement
signals at depth, but with a measurable sea surface height (SSH) signal. IGWs are
important for several reasons. IGW breaking controls most of the mixing in the
open-ocean beneath the mixed layer, and thus impacts the large-scale oceanic
circulation, heat transport, and carbon transport. IGWs impact the speed of sound and
are therefore important for operational oceanography. Finally, because IGWs yield a
measurable SSH signal, they are important for satellite altimetry missions, including
the upcoming Surface Water Ocean Topography (SWOT) mission that will measure
SSH in two dimensions, and at smaller scales than current altimeters do. We will
discuss three important "flavors" of IGWs, near-inertial motions (generated by the
high-frequency component of wind stress), internal tides (generated by
tidal currents impinging upon topographic features), and IGW continuum spectrum,
also called the Garrett-Munk spectrum. The IGW continuum spectrum consists of
high-frequency (supertidal) IGWs. The classical paradigm is that the IGW continuum
spectrum is generated by nonlinear interactions amongst internal waves, with
the near-inertial waves and internal tides serving as primary energy sources.
Based upon this paradigm, we expect that generating an IGW continuum
spectrum in global models will require high-frequency atmospheric forcing
(to generate near-inertial waves), tidal forcing (to generate internal tides),
and high vertical and horizontal resolution (to facilitate nonlinear wave-wave
interactions). We will describe our work with the US Navy HYbrid Coordinate
Ocean Model (HYCOM), in which we introduced high-resolution global ocean
models simultaneously forced by atmospheric fields and the astronomical
tidal potential. We will also show newer simulations performed under similar
conditions with the Massachusetts Institute of Technology general circulation
model (MITgcm) and the Nucleus for European Modeling of the Oceans (NEMO).
We summarize several papers on comparison of the modeled internal tides and
the IGW continuum spectrum to altimetry and observations from moorings. We
briefly discuss the generation of the continuum spectrum and the potential implications
for a better understanding of ocean mixing. We also briefly mention other applications
of global IGW models, including interpretation of satellite altimeter missions.