Statistics – Computation
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufmsh23a1139g&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #SH23A-1139
Statistics
Computation
2159 Plasma Waves And Turbulence, 7829 Kinetic Waves And Instabilities, 7839 Nonlinear Phenomena (4400, 6944), 7863 Turbulence (4490)
Scientific paper
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.
Gary Peter S.
Li Handong
Saito Shuji
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