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SUMMARY:Eddies and circulation: lessons from oceans\, atmospheres and the 
 GFD lab - Rhines\, P (Washington)
DTSTART:20081208T093000Z
DTEND:20081208T100000Z
UID:TALK15630@talks.cam.ac.uk
CONTACT:Mustapha Amrani
DESCRIPTION:Planetary fluids inherit the angular momentum of their planets
 . Concentrated and diluted\, and fragmented into potential vorticity (PV)\
 , angular momentum controls the circulation under a limited budget of ener
 gy. In particular\, wherever energy decays\, planetary PV takes control of
  the dynamics. This so-called β-control is manifested in the stiffness an
 d scale-dependent PV elasticity of rotating fluids which leads to many kin
 ds of wave motion\, and to limitation of turbulent mixing. The fluid finds
  ways\, for example PV staircases and their attendant jets\, of dealing wi
 th limited energy and PV control. Momentum rearrangement that follows stir
 ring of the PV field by eddies is a key process. We see numerous zonal jet
 s on the rapidly rotating\, gas giants (strong β-control)\, and a weaker 
 β-control over Earths subpolar atmospheric jet streams\, where the kineti
 c energy density averages 10^6 J m^-2. The Earths oceans\, operating at lo
 wer kinetic energy levels (10^4 J m^-2). have selected jets of much finer 
 scale\, and a dominant energy-containing eddy mode manifested as dimples o
 n the sea surface\, simply marching westward. These are strongly nonlinear
  baroclinic Rossby waves which do not obey the simple rules of geostrophic
  turbulence\, namely\, expansion of scale laterally and vertically toward 
 a barotropic state\, and coalescence into sparsely distributed hard-core v
 ortices. A second mode of oceanic eddy that is widespread is the (equivale
 nt-) barotropic mode of geostrophic flow\, tall eddies which are highly co
 ordinated with bottom topography.\n\nHere we describe field observations a
 nd simulations from the GFD laboratory. These demonstrate Rossby wave prop
 agation\, induction of zonal circulation and inhibition of mixing which le
 ads to the ozone hole in the terrestrial southern stratosphere\; also tran
 sition between Rossby waves and solitary eddies which transport fluid (as 
 in the worlds oceans)\, topographic production of eddies and waves\, with 
 steering by PV waveguides (formed by topography and circulation). Using a 
 new laboratory technique known as optical altimetry we now can see the int
 eraction of unbalanced flows (downslope winds\, gravity- and inertial wave
 s) with the energy-containing geostrophic eddies\, as seen in the upward r
 adiation of gravity waves as storms encounter the Greenlands icy topograph
 y.
LOCATION:Seminar Room 1\, Newton Institute
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