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SUMMARY:The structure and lifecycle of stratified mixing in forced shear f
 lows - Adrien Lefauve (DAMTP\, University of Cambridge)
DTSTART:20250210T130000Z
DTEND:20250210T140000Z
UID:TALK226687@talks.cam.ac.uk
CONTACT:Kasia Warburton
DESCRIPTION:Our environment is shaped by stably stratified air and water m
 asses and the turbulent mixing of heat and chemicals within them. This tal
 k addresses the challenge of understanding and predicting the density-stra
 tified turbulent mixing driven by shear instabilities at high Reynolds num
 bers (Re > 10^5). These shear instabilities are a key process in the turbu
 lent energy cascade in the ocean\, spanning a great range of scales\, from
  coherent instabilities at kilometre scales to the smallest eddies at micr
 ometre scales. We present observational data taken by collaborators from t
 he Woods Hole Oceanographic Institution at the mouth of the Connecticut Ri
 ver\, a shallow salt-wedge estuary. Multi-beam echo-sounding imagery provi
 des access to the spatial structure and temporal evolution of the intense 
 interfacial mixing with unprecedented detail. The data demonstrate that mi
 xing occurs primarily by turbulence in the 'braids' connecting the 'cores'
  of Kelvin-Helmholtz billows\, rather than within the cores themselves. Th
 is secondary braid turbulence appears to be continuously forced by the bar
 oclinic generation of shear in the tilted braid. This finding challenges t
 he prevailing paradigm built upon direct numerical simulations (DNS) at lo
 wer Reynolds and Prandtl numbers\, where mixing tends to occur primarily b
 y overturning in the billow cores. This distinction may represent a shift 
 in our understanding of mixing in highly dissipative hotspots driven by la
 rge-scale shear — not only in estuaries but also in wind-driven surface 
 currents and deep oceanic overflows.
LOCATION:MR3\, CMS
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