Hot protons in the inner corona and their effect on the flow properties of the solar wind

Nonlin. Processes Geophys.

Hollweg

2004

Abstract. Recently, we suggested that the source of ion heating in solar coronal holes is small-scale reconnection events (microflares) at the coronal base. The microflares launch intermittent heat flux up into the corona exciting ion cyclotron waves through a plasma microinstability. The ions are heated by these waves during the microflare bursts and then evolve with no energy input between the bursts. The overall coronal heating by this mechanism is a summed effect of all microflare bursts during the expansion time of the solar wind and adiabatic cooling between the microflares. The intermittent heat flux produced by the microflares was modeled as electron beams with constant speed and temperature for simplicity. In this paper, we consider a more sophisticated model of the heat flux taking into account the action of the mirror force and the charge separation electric field on the beam particles. We show that the radial evolution of the heat flux is determined mainly by the beam expansion along the magnetic field roughly at the root mean square velocity of the beam particles, while the variation of the beam bulk speed and thermal energy is less important.

Section: Solution Of the Fluid Equationssupporting

confidence: 49%

“…The momentum addition can be incorporated into a fluid model (e.g. Esser et al, 1997). From a mathematical standpoint, it appears as a source or sink term in the momentum equation.…”

Section: Solution Of the Fluid Equationsmentioning

confidence: 99%

Radial evolution of intermittent heat flux in solar coronal holes

Nonlin. Processes Geophys.

Hollweg

2004

“…is almost 3 orders of magnitude higher than the rate successfully producing the solar wind acceleration in a fluid model (see, e.g., Esser et al 1997). Equation (5) shows that the heating by the fast waves in this model is, in fact, too strong.…”

Section: Plasma Heatingmentioning

confidence: 88%

Perpendicular Proton Heating Due to Energy Cascade of Fast Magnetosonic Waves in the Solar Corona

Vasquez

Chandran

2010

ApJ

Observational data and theoretical models suggest that the wave spectrum in the solar wind and corona may contain a fast magnetosonic mode component. This paper presents two-dimensional hybrid simulations of the energy cascade among the fast waves in the vicinity of the proton inertial scale. The initial spectrum consists of modes propagating in the positive direction, defined by the mean magnetic field, and is allowed to evolve freely in time. The plasma beta is set to low values typical of the solar corona. The cascade proceeds from lower to higher wavenumbers and mostly in the direction across the magnetic field. The highly oblique fast waves are strongly dissipated on the protons. The resulting proton heating is preferentially perpendicular to the magnetic field. If the wave intensity is constrained by the observed density spectra in the corona, the heating is fast enough to generate the solar wind.

“…In our case, the momentum added by the instability is negative because this velocity is directed to the Sun. The momentum addition can be incorporated into a fluid model (e.g., Esser et al 1997). From a mathematical standpoint, it appears as a source or sink term in the momentum equation.…”

Section: Heating Function and Momentum Additionmentioning

confidence: 99%

Intermittent Heating of the Solar Corona by Heat Flux–generated Ion Cyclotron Waves

Hollweg

2004

ApJ

Self Cite

Recently, we suggested that the source of ion heating in solar coronal holes is small-scale reconnection events (microflares) at the coronal base. The microflares launch intermittent heat flux up into the corona exciting ion cyclotron waves through a plasma microinstability. The ions are heated by these waves during the microflare bursts and then evolve with no energy input between the bursts. In this paper, we show that the structure of the proton distribution in the relatively long time periods between the microflares is determined by collisions at small heliocentric distances. At greater distances, the collisional processes can be replaced by similar processes due to secondary instabilities. These are excited by the distortion of the distribution under the action of the mirror force. At the same time, the heating during the microflare bursts is not affected by either the collisions or the secondary instabilities because of the short duration of the bursts. We demonstrate that in each intermittent heating event the protons diffuse approximately along one-dimensional curves in the phase space and can develop a quasi-plateau. The corresponding temperature increase can then be calculated without solving the diffusion equations. The overall coronal heating by this mechanism is a summed effect of all microflare bursts during the expansion time of the solar wind and adiabatic cooling between the microflares. The calculations for the collision-dominated region suggest that the overall heating is efficient enough to account for the acceleration of the fast solar wind in this region.