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UID:20261030T164213EDT-9795IAl5U6@132.216.98.100
DTSTAMP:20261030T204213Z
DESCRIPTION:Dr. Nicolas Grisouard joins us from the University of Toronto f
 or his seminar 'Damping of Geostrophic Motions by Oceanic Internal Waves\,
  Critically Reflecting off the Sea Surface”. Refreshments will be served\n
 \n\nAbstract\n\nNowadays\, physical oceanographers view density fronts as 
 hotspots for oceanic kinetic energy dissipation. Within oceanic fronts\, d
 ue to the sloping isopycnals and associated thermal wind shear\, the possi
 ble directions of the group velocity of inertia-gravity waves (IGWs) depar
 t from the classical St Andrew's cross. However\, waves oscillating at the
  Coriolis frequency\, f\, keep one of these directions horizontal\, while 
 the other direction allows for vertical propagation of energy. This implie
 s the existence of critical reflections of such inertial waves off the sea
  surface\, after which incident wave energy cannot escape. This is analogo
 us to the classical critical reflection of IGWs in a quiescent medium off 
 a sloping bottom. We present a series of numerical experiments exploring p
 arameter space that highlight properties of critical (ω=f)\, forward (ω>f)
 \, and backward (ω<f) reflections. In particular\, we report on irreversib
 le energy exchanges between IGWs and geostrophically-balanced frontal flow
 s that are enabled by friction and the modification of IGW-physics at fron
 ts. We also show analytically that this is exacerbated during critical ref
 lections where intense frictional effects under the surface induce a net t
 ransfer of energy from the balanced flow to ageostrophic motions\, which a
 re subsequently dissipated. Forward reflections are also favorable to tria
 dic resonant interactions and therefore to turbulence which is weak in our
  simulations\, but likely to be fully developed under oceanic conditions. 
 The existence of this non-linear flow activity further increases the extra
 ction of geostrophic energy from the front. On the other hand\, backward r
 eflections inhibit triadic interactions and\, consequently\, such “spectac
 ular” energy exchanges.\n\n \n
DTSTART:20151005T193000Z
DTEND:20151005T203000Z
LOCATION:Room 934\, Burnside Hall\, CA\, QC\, Montreal\, H3A 0B9\, 805 rue 
 Sherbrooke Ouest
SUMMARY:Seminar: Dr. Nicolas Grisouard
URL:https://www.mcgill.ca/meteo/channels/event/seminar-dr-nicolas-grisouard
 -255825
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