Physics – Plasma Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsh42b..06w&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #SH42B-06
Physics
Plasma Physics
[2164] Interplanetary Physics / Solar Wind Plasma, [7509] Solar Physics, Astrophysics, And Astronomy / Corona, [7863] Space Plasma Physics / Turbulence, [7867] Space Plasma Physics / Wave/Particle Interactions
Scientific paper
The heating and acceleration of ions in the solar corona and the solar wind is a longstanding topic in solar-terrestrial physics. SOHO observations show that minor heavy ions have higher perpendicular temperature anisotropy and their outflow velocities are significantly higher than that of protons in the solar corona. It is also known that heavy ions, with mass-proportional temperatures, flow faster than the protons by approximately the local Alfven speed in the fast solar wind. The present work addresses the stochastic heating of minor ions by obliquely-propagating low-frequency Alfven waves. An important characteristic of the stochastic heating is unearthed by means of test particle simulation. That is, when the wave amplitude exceeds some threshold condition for stochasticity, the quasi-asymptotic kinetic temperature associated with the minor ions becomes independent of the wave amplitude and proportional to the ion mass, and it always approaches the value dictated by the Alfven speed, to wit, Tkin≈mivA2/2. During the course of the heating process the minor ions gain a net average parallel speed, v||˜vA in the laboratory frame. The physical mechanism for the asymptotically independent heating is the pickup process that involves the formation of spherical shell velocity distribution function via the pitch-angle scattering. These results are generally consistent with observational properties of minor ions. In the corona, minor ions may be not fully picked up and just a partial shell velocity distribution is formed. Thus, the minor ion temperature is highly anisotropic, and flow faster than protons by a fraction of the local Alfven speed. On the other hand, in the interplanetary space, the fully spherical shell velocity distribution may have been nearly formed, so the minor ion temperature is proportional to their mass, and flow faster than protons by about the local Alfven speed.
Wang Binghong
Wang Chenjie
Wu Shang-Chen
Yoon Peter H.
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