Differences between Doppler velocities of ions and neutral atoms in a solar prominence

Abstract

Context. In astrophysical systems with partially ionized plasma the motion of ions is governed by the magnetic field while the neutral particles can only feel the magnetic field's Lorentz force indirectly through collisions with ions. The drift in the velocity between ionized and neutral species plays a key role in modifying important physical processes like magnetic reconnection, damping of magnetohydrodynamic waves, transport of angular momentum in plasma through the magnetic field, and heating. Aims. This paper investigates the differences between Doppler velocities of calcium ions and neutral hydrogen in a solar prominence to look for velocity differences between the neutral and ionized species. Methods. We simultaneously observed spectra of a prominence over an active region in H I 397 nm, H I 434 nm, Ca II 397 nm, and Ca II 854 nm using a high dispersion spectrograph of the Domeless Solar Telescope at Hida observatory, and compared the Doppler velocities, derived from the shift of the peak of the spectral lines presumably emitted from optically-thin plasma.Results. There are instances when the difference in velocities between neutral atoms and ions is significant, e.g. 1433 events (∼ 3 % of sets of compared profiles) with a difference in velocity between neutral hydrogen atoms and calcium ions greater than 3σ of the measurement error. However, we also found significant differences between the Doppler velocities of two spectral lines emitted from the same species, and the probability density functions of velocity difference between the same species is not significantly different from those between neutral atoms and ions. Conclusions. We interpreted the difference of Doppler velocities as a result of motions of different components in the prominence along the line of sight, rather than the decoupling of neutral atoms from plasma.

A New View of the Solar Interface Region from the Interface Region Imaging Spectrograph (IRIS)

“…The existence of such velocity drifts carries large importance due to its effect on physical quantities such as wave damping and the magnetic-reconnection rate. While recent results provide support for such multi-fluid physics, more observations are needed to understand such plasma dynamics (Anan, Ichimoto, and Hillier, 2017;Wiehr, Stellmacher, and Bianda, 2019).…”

Two-fluid simulations of Rayleigh-Taylor instability in a magnetized solar prominence thread

“…the development of the RTI. Some observational studies show hints in support of the decoupling in the velocity of ions and neutrals in prominences (Gilbert et al 2007;Khomenko et al 2016;Anan et al 2017;Wiehr et al 2019), however, these observations are at the edge of the observational capabilities of the Sun. In Earth's ionosphere, plasma is also partially ionized, and many phenomena related to the uncoupled behavior of ions and neutrals are similar in the solar atmosphere and in the ionosphere (see e.g., the review in Leake et al 2014).…”

Critical Science Plan for the Daniel K. Inouye Solar Telescope (DKIST)

“…Zweibel, 1989;Chiueh, 1998;Zweibel et al, 2011;Leake et al, 2012;Mei et al, 2012;Murphy et al, 2012;Zweibel, 2015;Ni et al, 2020). These in turn have important implications for solar phenomena, likely being responsible for increased damping of MHD waves (De Pontieu, Martens, and Hudson, 2001), increased current dissipation and heating of the solar chromosphere (Khomenko and Collados, 2012;Martínez-Sykora, De Pontieu, and Hansteen, 2012), increased flux emergence rates into the corona, reduced Alfvén wave flux from photospheric foot-point motion, and changes in the structure of MHD shocks, prominences, and quiet-Sun magnetic features (see Anan, Ichimoto, and Hillier, 2017, and the references therein). Observational verification of the reconnection implications of partial ionization is more readily achieved in these solar contexts than in more distant astrophysical settings.…”