The Turbulent Cascade and Proton Heating in the Solar Wind at 1 AU with Emphasis on High Cross Helicity States (Invited)

Details The Turbulent Cascade and Proton Heating in the Solar Wind at 1 AU with Emphasis on High Cross Helicity States (Invited) The Turbulent Cascade and Proton Heating in the Solar Wind at 1 AU with Emphasis on High Cross Helicity States (Invited)

Dec 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmsm42b..02s&link_type=abstract

American Geophysical Union, Fall Meeting 2009, abstract #SM42B-02

Physics

Geophysics

[2134] Interplanetary Physics / Interplanetary Magnetic Fields, [2149] Interplanetary Physics / Mhd Waves And Turbulence, [2752] Magnetospheric Physics / Mhd Waves And Instabilities, [4490] Nonlinear Geophysics / Turbulence

Scientific paper

The spectrum of interplanetary magnetic field fluctuations has been widely studied for 40 years. The spectrum of velocity fluctuations has been studied for as long, but perhaps with less intensity. The observations seem so simple and easily characterized: power law forms with spectral indices consistent with predictions of MHD turbulence theory. Granted, magnetic and velocity fluctuations have different spectral forms at 1 AU, but Roberts et al. [2007] claim this ends by 5 AU. Hidden beneath the seemingly simple power spectral forms are a broad range of different dynamics operating throughout the spectrum but dominating at different spatial scales. We see the geometry of the large-scale fluctuations ordered by wind speed [Dasso et al., 2005] while the small scales show no such ordering [Hamilton et al., 2008]. MacBride et al. [2008] uses third-moment assessments of the energy cascade rate to show there is a strong cascade away from field-aligned wave vectors at the large scales in fast winds, although the slow winds show a more nearly isotropic cascade. Third-moment analyses of high cross-helicity states [Stawarz et al., 2009 and this meeting] show a remarkable backtransfer of energy associated with the dominant outwardly propagating component that works to reinforce the existing high cross helicity. All the while anisotropies such as those predicted by Goldreich and Sridhar [1995] are subtle and at best existing at the smallest scales of the inertial range where geometry analysis support the underlying assumptions [Hamilton et al., 2008]. What is most remarkable throughout these studies is the broad range of dynamics that are operating to modify the 3D spectrum while the measured power spectrum remains largely unperturbed and highly reproducible. References: Dasso et al., Astrophys. J. Lett., 635, L181--L184, 2005. Goldreich and Sridhar, Astrophys. J., 438, 763--775, 1995. Hamilton et al., J. Geophys. Res., 113, A01106, doi:10.1029/2007JA012559 2008. MacBride et al., Astrophys. J., 679, 1644--1660 2008. Roberts et al., Fall AGU, paper SH31B-06, 2007. Stawarz et al, Astrophys. J., 697, 1119--1127, 2009.

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