Polarization intermittency in Alfvenic turbulence.

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Polarization intermittency in Alfvenic turbulence.
Andrey Beresnyak, Alex Lazarian, Univ. of
Wisconsin-Madison
?tz(VA?)z(w?)z-?P
v
B
?tw-(VA?)w(z?)w-?P

• Perpendicular-polarized alfvenic waves cascade
  (shear) each other faster than parallel
  polarized. Therefore there is a dynamic alignment
  of otherwise independent elsasser vectors w and
  z. This is purely nonlinear effect possible only
  in strong turbulence.
• First noticed in MaronGoldreich 01.
• Must have a local character, if turbulence is
  local.

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• Results
• 5123 incompressible MHD simulations with
  Alfvenic Mach of 0.5, 1.0 and 2.0 were conducted
• Alignment of Alfvenic parts of w and z exists in
  a large range of wavevectors, starting with
  driving scale.
• There is very slow dependence of weakening of
  interaction with scale. Alignment have an
  intermittent nature, being stronger in regions
  with large wave amplitude.

MA0.5, k7. Distribution of angles between w and
z
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Interaction weakening with scale
k-0.158
Interaction is weakened, in comparison with GS95
by a factor of ltwzsin?gt/ltwzgt
Conclusion Goldreich-Sridhar 95 picture of
strong Alfvenic turbulence could be amended by
including of scale-dependent weakening of
interaction.
k