HR: 1340h
AN: SH23A-1139 [Abstracts]
TI: Whistler Turbulence: Particle-in-Cell Simulations
AU: * Gary, S P
EM: pgary@lanl.gov
AF: Los Alamos National Laboratory, Mail Stop D466, Los Alamos, NM 87545, United States
AU: Saito, S
EM: ssaito@lanl.gov
AF: Los Alamos National Laboratory, Mail Stop D466, Los Alamos, NM 87545, United States
AU: Li, H
EM: hli@lanl.gov
AF: Los Alamos National Laboratory, Mail Stop D466, Los Alamos, NM 87545, United States
AB:
The broadband, incoherent magnetic fluctuations in the solar wind
measured by in situ spacecraft instrumentation typically show two
distinct frequency ranges: The inertial range at
observed frequencies f less than the proton cyclotron frequency
with power spectra which scale as ~ f-5/3 and the so-called
"dissipation range" at higher frequencies with steeper power-law
dependences.
There are two competing hypotheses as to which basic mode
populates the latter, short wavelength turbulence domain:
whistler fluctuations which propagate approximately parallel
to the background magnetic field and at frequencies
above the proton cyclotron frequency, Ømegap,
and kinetic Alfvén fluctuations which propagate
at steeply oblique angles to the background field and at frequencies
below Ømegap.
We have carried out one-dimensional particle-in-cell (PIC) simulations
in which enhanced narrowband whistler spectra are introduced;
the computations show no evidence of fluctuation energy migration
in wavenumber.
We have also done PIC simulations in two spatial dimensions.
The whistler anisotropy instability driven by an electron anisotropy
produces enhanced fluctuations near kc/ωpe ~ 1; the
simulations show a clear cascade of fluctuation energy to much
longer wavelengths.
Furthermore, our PIC simulations in which a
two-dimensional spectrum of enhanced whistlers is initially introduced at
kc/ωpe < 0.4 show evidence of a cascade
of magnetic fluctutaion energy to kc/ωpe ~eq 1.
Implications for solar wind observations will be discussed.
DE: 2159 Plasma waves and turbulence
DE: 7829 Kinetic waves and instabilities
DE: 7839 Nonlinear phenomena (4400, 6944)
DE: 7863 Turbulence (4490)
SC: SPA-Solar and Heliospheric Physics [SH]
MN: 2007 Fall Meeting