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SUMMARY:Application of Open Quantum System Concepts to Internal Wave / Pla
 netary Wave Coupling and consequences for Earth System Behaviour - Kurt Po
 lzin\, Woods Hole Oceanographic Institution
DTSTART:20251010T150000Z
DTEND:20251010T160000Z
UID:TALK237958@talks.cam.ac.uk
CONTACT:Duncan Hewitt
DESCRIPTION:We assess a prognostic formulation of triple coherence relatin
 g to energy exchange between mesoscale eddies and the internal wavefield a
 nd compare with observations from the Sargasso Sea. \n \nWe break new grou
 nd in the following ways:  \n(1) We utilize concepts from Open Quantum Sys
 tems to arrive at the essential results presented in Muller 1976\, JFM\, w
 here eddy induced internal wave-stress perturbations are damped using a no
 nlinear relaxation time scale approximation. The broad brush take on Open 
 Quantum Systems is that there is a system (ray tracing)\, a bath (the back
 ground internal wavefield) and a system bath interaction (nonlinear relaxa
 tion).  We avoid the asymptotic expansion involving small perturbations to
  wave phase speed that is the basis of Muller.  \n \n(2) We define the bac
 kground internal wave spectrum based upon a regional characterization of t
 he wavefield in the Sargasso Sea.  This differs from the canonical descrip
 tion referred to as GM76 in crucial respects.  \n \n(3) We use recent theo
 retical work on both extreme scale separated interactions and the internal
  wave kinetic equation to properly define nonlinear relaxation time scales
 .  \n \nAgreement of the prognostic formulation with data is remarkable an
 d is consistent with eddy-wave coupling dominating the regional internal w
 ave energy budget\, as in the diagnostic study of Polzin 2010\, JPO\, usin
 g data from the Local Dynamics Experiment of PolyMode III\, circa 1978-197
 9.  Extraction of eddy energy happens at the horizontal and vertical scale
 s that characterize baroclinic instability and potential vorticity fluxes.
   The goodness of this effort reinforces a prior hypothesis (Polzin and Lv
 ov 2011\, RoG) that the character of the internal wavefield in the Sargass
 o Sea is set by this interaction\, which\, in turn\, serves as an amplifie
 r of tertiary energy inputs from larger vertical scales that characterize 
 internal swell.   With this knowledge and confidence\, we then speculate o
 n the role that this coupling plays in mesoscale eddy dynamics in the Sout
 hern Recirculation Gyre of the Gulf Stream.  In this instance our interest
  is the potential enstrophy budget\, in which enstrophy is the square of t
 he perturbation potential vorticity and\, as is energy\, an inviscid invar
 iant.  \n \nWe argue that this nonlinear relaxation effectively provides a
  local eddy enstrophy damping consistent with potential vorticity flux obs
 ervations from the Local Dynamics Experiment.  This happens at spatial sca
 les somewhat smaller than the energy extraction scale and locates the end 
 of the potential enstrophy cascade in the spectral domain as the energy co
 ntaining scale of the internal wavefield.  We offer insight into how such 
 speculation might acquire firmer ground by ​ describing how to incorpora
 te modulations of the lower bound of internal wave frequency by potential 
 vorticity perturbations into the existing formulation.  In the context of 
 a formal WKB approximation\, the current formulation stands as a 'geometri
 c optics' approximation controlling system behavior whereas modulations of
  the waveguide are a 'physical optics' correction.  \n \nRegardless\, the 
 dynamical consequence is that wave-eddy coupling is responsible for the ma
 intenance of gyre scale potential vorticity gradients that are crucial to 
 Rossby wave propagation and Earth system behavior.\n
LOCATION:MR2
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