Zonostrophic Instability Drive by Discrete Particle Noise
Authors: D.A. St-Onge, J.A. Krommes
Abstract: The consequences of discrete particle noise for
a system possessing a possibly unstable collective mode are
discussed. It is argued that a zonostrophic instability (of
homogeneous turbulence to the formation of zonal flows) occurs
just below the threshold for linear instability. The scenario
provides a new interpretation of the random forcing that is
ubiquitously invoked in stochastic models such as the second-order
cumulant expansion (CE2) or stochastic structural instability
theory (SSST); neither intrinsic turbulence nor coupling to
extrinsic turbulence is required. A representative calculation of
the zonostrophic neutral curve is made for a simple two-field
model of toroidal ion-temperature-gradient-driven modes. To the
extent that the damping of zonal flows is controlled by the
ion-ion collision rate, the point of zonostrophic instability is
independent of that rate.
Submitted to: Physics of Plasmas
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