Neutral hydrogen in the solar wind acceleration region

Details Neutral hydrogen in the solar wind acceleration region Neutral hydrogen in the solar wind acceleration region

Jan 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apj...420..913o&link_type=abstract

The Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 420, no. 2, p. 913-925

Astronomy and Astrophysics

Astrophysics

30

Hydrogen, Magnetohydrodynamic Waves, Particle Acceleration, Solar Corona, Solar Wind, Charge Exchange, Flow Velocity, Lyman Alpha Radiation, Protons, Recombination Reactions, Velocity Distribution

Scientific paper

Observation of solar Ly alpha radiation scattered by coronal neutral hydrogen atoms can be used to investigate the acceleration region of the solar wind. In this paper we focus on the use of these observations to study Alfven waves, which can accelerate the solar wind plasma to flow speeds observed in high-speed streams if their amplitude at the coronal base is 20 km/s or larger. The wave amplitude is then larger than the proton thermal speed in the outer corona, so that the mean proton speed (averaged over a wave period) is significantly larger than the proton thermal speed. For low-frequency wave the hydrogen atoms follow the proton motion in the waves, while for higher frequencies the protons move relative to the neutrals. Nevertheless, in the higher frequency case, the rates for charge exchange and recombination are high enough to broaden the velocity distribution function of neutral hydrogen. Both the wave motion of the hydrogen atoms in low-frequency Alfven waves and the 'heating' by higher frequency waves lead to a broadening of the scattered solar Ly alpha line. For coronal base amplitudes of 20 km/s, the line broadening increases with heliocentric distance beyond 4-5 solar radii.

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