Other
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufmsh33b..04b&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #SH33B-04
Other
2104 Cosmic Rays, 2134 Interplanetary Magnetic Fields, 2149 Mhd Waves And Turbulence (2752, 6050, 7836), 2159 Plasma Waves And Turbulence, 2164 Solar Wind Plasma
Scientific paper
In numerical modulation models low-energy cosmic-ray nuclei experience the adiabatic limit, where their intensity becomes proportional to their kinetic energy per nucleon, independent of the properties of the diffusion tensor and interstellar spectrum. Electrons, on the other hand, remain sensitive to changes in the diffusion tensor and associated turbulence quantities down to very low energies. In principle, electron modulation can therefore be used as an indirect probe of the properties of turbulence at small scales, notably the wavenumber kD where the dissipation range occurs, and the latter's spectral index. We consider two relationships for kD suggested by Leamon et al. (2000 ApJ, 537), based on observational results. In one case, the proton gyrofrequency is used as predictor for the steepening wavenumber kD where the dissipation range occurs, and in the second case, the ion inertial scale is used. We use a steady-state three-dimensional modulation model for this study, with the parallel mean free path (MFP) given by an analytical expression based on results of Teufel and Schlickeiser (2002, A&A, 393), and the perpendicular MFP an approximation derived by Shalchi et al. (2004, ApJ, 604) for the nonlinear guiding center model (NLGC) of Matthaeus et al. (2003, ApJ, 590). The drift coefficient is from Burger et al. (2000, JGR, 105). We show that different combinations of models for kD, the spectral index in the dissipation range, and the strength of dynamical turbulence lead to orders of magnitude differences in the predicted intensity of electrons at Earth. Our preliminary results suggest that a model for kD based on the ion inertial scale is possibly the more appropriate choice.
Burger R. A.
Engelbrecht N. E.
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