Abstract
Abstract. Dispersive properties of linear and nonlinear MHD waves, including shear, kinetic, electron inertial Alfvén, and slow and fast magnetosonic waves are analyzed using both analytical expansions and a novel technique of dispersion diagrams. The analysis is extended to explicitly include space charge effects in non-neutral plasmas. Nonlinear soliton solutions, here called alfvenons, are found to represent either convergent or divergent electric field structures with electric potentials and spatial dimensions similar to those observed by satellites in auroral regions. Similar solitary structures are postulated to be created in the solar corona, where fast alfvenons can provide acceleration of electrons to hundreds of keV during flares. Slow alfvenons driven by chromospheric convection produce positive potentials that can account for the acceleration of solar wind ions to 300–800 km/s. New results are discussed in the context of observations and other theoretical models for nonlinear Alfvén waves in space plasmas.
Highlights
In a recent review, Paschmann et al (2002) provide a long list of problems in auroral physics that still remain unsolved
Where k =k cos α, D= sin2 α/(cos2 α−γβ/2). This is the equation for dispersive Alfven waves (DAW) that include electron inertial Alfven waves (EIAW), kinetic Alfven waves (KAW), and shear Alfven waves for arbitrary β and propagation angle α
By analyzing the two-fluid equations, we have found that nonlinear solutions, here called alfvenons, can provide explanations to several unsolved problems related to acceleration of plasma in the magnetosphere and the solar corona
Summary
In a recent review, Paschmann et al (2002) provide a long list of problems in auroral physics that still remain unsolved. The creation of large amplitude electric field structures implies that space charge effects may play important role in particle acceleration and should be explicitly included in the governing equations. This issue has been recently highlighted by a controversy between Verheest (2007a,b) and McKenzie et al (2007) on the existence of solitary waves in charge neutral plasmas.
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