Electron heat flow in the solar corona: Implications of non-Maxwellian velocity distributions, the solar gravitational field, and Coulomb collisions

Details Electron heat flow in the solar corona: Implications of non-Maxwellian velocity distributions, the solar gravitational field, and Coulomb collisions Electron heat flow in the solar corona: Implications of non-Maxwellian velocity distributions, the solar gravitational field, and Coulomb collisions

Jul 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003jgra..108.1294d&link_type=abstract

Journal of Geophysical Research Space Physics, Volume 108, Issue A7, pp. SSH 7-1, CiteID 1294, DOI 10.1029/2002JA009484

Physics

Plasma Physics

9

Solar Physics, Astrophysics, And Astronomy: Corona, Space Plasma Physics: Transport Processes, Space Plasma Physics: Numerical Simulation Studies, Space Plasma Physics: Nonlinear Phenomena

Scientific paper

It has long been known that weak electron temperature gradients in fully ionized plamas (satisfying λ |∇Te|/Te <~ 10-4, where λe is the electron mean free path and Te is the electron temperature) can lead to the development of significant non-Maxwellian suprathermal tails on electron velocity distributions, invalidating the Spitzer and Härm [1953] perturbation theory [ Gray and Kilkenny, 1980; Bell et al., 1981; Scudder and Olbert, 1983]. In this paper we work out the implications of such nonlocal heat flow for electrons in the solar corona, comparing a new analytical theory to numerical solutions of the Fokker-Planck equation. While electron-electron Coulomb collisions are strong enough at coronal densities to influence the local temperature, the electron heat flux is determined by the essentially collisionless high-energy tail. The deceleration of suprathermal electrons in the polarization electric field allows electron heat to flow radially outward against the local temperature gradient, in contrast to the local thermodynamic equilibrium picture, in which heat is constrained to flow down the local temperature gradient. We discuss the implications of this effect for empirical constraints of coronal heating mechanisms.

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