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SUMMARY:Scale selection and feedback loops for formation and sustainment o
 f a mesoscopic staircase structure in drift wave-zonal flow turbulence - W
 eixin  Guo (Huazhong University of Science and Technology)
DTSTART:20240118T141500Z
DTEND:20240118T150000Z
UID:TALK208510@talks.cam.ac.uk
DESCRIPTION:The scale selection and feedback loops for the formation and s
 ustainment of a mesoscopic staircase profile structure are investigated fo
 r drift wave-zonal flow turbulence. A mean field model derived from the Ha
 segawa-Wakatani system and including the evolution of mean density\, mean 
 vorticity and perturbed potential enstrophy (PE)\, is used. It is found th
 at a quasi-periodic zonal staircase forms from self-sharpening of modulati
 on. The principle feedback loop is through the nonlinear dependence of mix
 ing length on electron density gradient\, which enters by way of the poten
 tial vorticity (PV) gradient. Counterintuitively\, ExB shearing is not eff
 ective. Moreover\, the number of steps in the staircase is sensitive to bo
 th the drive (production rate of PE and initial density gradient) and damp
 ing (flow viscosity and collisional diffusivity) factors. The minimal step
  scale is selected by competition between the initial density gradient and
  diffusive dissipation. Finite turbulence spreading is necessary to form t
 he staircase\, but moderate enhancement of turbulence spreading tends to w
 ash out the pattern. The staircase retains a memory of its initial state. 
 Both the mean ExB &nbsp\;shear and zonal shear affect the staircase evolut
 ion. A strong mean shear quenches the pattern by suppressing the drift wav
 e turbulence. The implications of these findings are also discussed.&nbsp\
 ;
LOCATION:Seminar Room 1\, Newton Institute
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