Non-WKB Alfven Wave Reflection from the Solar Photosphere to the Distant Heliosphere

Details Non-WKB Alfven Wave Reflection from the Solar Photosphere to the Distant Heliosphere Non-WKB Alfven Wave Reflection from the Solar Photosphere to the Distant Heliosphere

Dec 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufmsh21b0115c&link_type=abstract

American Geophysical Union, Fall Meeting 2003, abstract #SH21B-0115

Other

2149 Mhd Waves And Turbulence, 2164 Solar Wind Plasma, 7507 Chromosphere, 7511 Coronal Holes, 7863 Turbulence

Scientific paper

Magnetohydrodynamic (MHD) turbulence has been considered for several decades as a possibly substantial heat source for the solar chromosphere, corona, and heliosphere. However, it is still not well understood how the turbulent fluctuations are generated and how they evolve in frequency and wavenumber. Although the dominant population of Alfvén waves near the Sun must be propagating outwards, one also needs waves propagating inwards in order to ``seed'' a turbulent cascade. As a part of an ongoing study of various aspects of solar MHD turbulence, we present a model of linear, non-WKB reflection of Alfvén waves that propagate in both directions along an open magnetic flux tube. Our work differs from previous models in the following ways. (1) The background plasma density, magnetic field, and flow velocity are constrained empirically from below the photosphere to distances past 1 AU. The successive merging of flux tubes on granular and supergranular scales is described using a two-dimensional magnetostatic model of a magnetic network element in the stratified solar atmosphere. (2) The amplitudes of horizontal wave motions are specified only at the photosphere, based on previous analyses of G-band bright point motions. Everywhere else in the model the amplitudes of outward and inward propagating waves are computed self-consistently. We compare the resulting wave properties with observed nonthermal motions in the chromosphere and corona, radio scintillation measurements, and in-situ fluctuation spectra. Quantities such as the MHD turbulent heating rate and the non-WKB wave pressure are computed, and the need for other sources of inward waves (e.g., nonlinear reflection or scattering off density inhomogeneities) will also be discussed. This work is supported by the National Aeronautics and Space Administration under grants NAG5-11913 and NAG5-12865 to the Smithsonian Astrophysical Observatory, by Agenzia Spaziale Italiana, and by the Swiss contribution to the ESA PRODEX program.

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