Plasma heating and thermal transport in the solar wind near 1 AU

Details Plasma heating and thermal transport in the solar wind near 1 AU Plasma heating and thermal transport in the solar wind near 1 AU

Aug 2000

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000phdt.........5n&link_type=abstract

Thesis (PhD). UNIVERSITY OF CALIFORNIA, LOS ANGELES, Source DAI-B 61/02, p. 747, Aug 2000, 383 pages.

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Scientific paper

Despite the fact that it is a thermally driven plasma, the thermal properties of the expanding solar wind are not well understood. In particular, the electron and proton components are generally hotter than expectations based upon free expansion of the solar wind. In this dissertation, we examine processes which contribute to this solar wind heating and are also observable with in- situ spacecraft in the vicinity of the Earth's orbit. First, we examine the state of electrons at 1 AU. The thermal properties of electrons are generally independent from other concurrent solar wind properties, and on average the total electron temperature at 1 AU is a constant 141,000 K. However, we find a lower bound on electron temperature which is a function of proton temperature. Although the source of this bound remains unknown, the bounded observations correspond to turbulent or compressed plasma, and are coincident with enhanced whistler waves. We further examine heating at compressions associated with colliding streams of solar wind plasma to test the applicability of the polytropic law. At the macroscopic scale, we show that the compressions are heated adiabatically according to the polytropic relation. Microscopically, such fluid relations cannot describe the detailed features of particle distributions. Comparing the threshold conditions of the whistler heat flux and whistler temperature anisotropy instabilities with observations of solar wind plasma and enhanced whistler waves, we find that electron temperature anisotropy observations are bounded by the instability threshold and that there are enhanced whistler fluctuations along the bound. We see no evidence for the whistler heat flux instability, however. Finally, we examine the collisionless shock, a very efficient plasma heating mechanism that dominates the thermal profile of the solar wind at large heliocentric distances. We take advantage of the detailed observations of the Earth's bow shock to study the detailed electric and magnetic fields. In the supercritical shock, the presence of substructure appears to be an important component of the shock layer in order to maintain stability, to reduce ion reflection, and to increase cross-shock potential.

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