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

Tetsu Anan   Submitted: 2017-03-08 17:14

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. 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. 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. 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 3sigma 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. 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.

Authors: Tetsu Anan, Kiyoshi Ichimoto, Andrew Hillier
Projects: None

Publication Status: 13 pages, 10 figures, accepted for publication in A&A
Last Modified: 2017-03-08 17:24
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Diagnosis of Magnetic and Electric Fields of Chromospheric Jets through Spectropolarimetric Observations of HI Paschen Lines  

Tetsu Anan   Submitted: 2014-02-20 21:43

Magnetic fields govern the plasma dynamics in the outer layers of the solar atmosphere, and electric fields acting on neutral atoms that move across the magnetic field enable us to study the dynamical coupling between neutrals and ions in the plasma. In order to measure the magnetic and electric fields of chromospheric jets, the full Stokes spectra of the Paschen series of neutral hydrogen in a surge and in some active region jets that took place at the solar limb were observed on May 5, 2012, using the spectropolarimeter of the Domeless Solar Telescope at Hida observatory, Japan. First, we inverted the Stokes spectra taking into account only the effect of magnetic fields on the energy structure and polarization of the hydrogen levels. Having found no definitive evidence of the effects of electric fields in the observed Stokes profiles, we then estimated an upper bound for these fields by calculating the polarization degree under the magnetic field configuration derived in the first step, with the additional presence of a perpendicular (Lorentz type) electric field of varying strength. The inferred direction of the magnetic field on the plane of the sky (POS) approximately aligns to the active region jets and the surge, with magnetic field strengths in the range 10 G < B < 640 G for the surge. Using magnetic field strengths of 70, 200, and 600 G, we obtained upper limits for possible electric fields of 0.04, 0.3, and 0.8 V/cm, respectively. This upper bound is conservative, since in our modeling we neglected the possible contribution of collisional depolarization. Because the velocity of neutral atoms of hydrogen moving across the magnetic field derived from these upper limits of the Lorentz electric field is far below the bulk velocity of the plasma perpendicular to the magnetic field as measured by the Doppler shift, we conclude that the neutral atoms must be highly frozen to the magnetic field in the surge.

Authors: Tetsu Anan, Roberto Casini, Kiyoshi Ichimoto
Projects: Other

Publication Status: Accepted
Last Modified: 2014-02-24 13:04
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Spicule Dynamics over Plage Region  

Tetsu Anan   Submitted: 2010-02-11 01:36

We studied spicular jets over a plage area and derived their dynamic characteristics using Hinode Solar Optical Telescope (SOT) high-resolution images. The target plage region was near the west limb of the solar disk. This location permitted us to study the dynamics of spicular jets without the overlapping effect of spicular structures along the line of sight. In this work, to increase the ease with which we can identify spicules on the disk, we applied the image processing method `MadMax' developed by Koutchmy et al. (1989). It enhances fine, slender structures (like jets), over a diffuse background. We identified 169 spicules over the target plage. This sample permits us to derive statistically reliable results regarding spicular dynamics. The properties of plage spicules can be summarized as follows: (1) In a plage area, we clearly identified spicular jet features. (2) They were shorter in length than the quiet region limb spicules, and followed ballistic motion under constant deceleration. (3) The majority (80%) of the plage spicules showed the cycle of rise and retreat, while 10% of them faded out without a complete retreat phase. (4) The deceleration of the spicule was proportional to the velocity of ejection ( i.e. the initial velocity ).

Authors: Tetsu Anan, Reizaburo Kitai, Tomoko Kawate, Takuma Matsumoto, Kiyoshi Ichimoto, Kazunari Shibata, Andrew Hillier, Kenichi Otsuji, Hiroko Watanabe, Satoru UeNo, Shin'ichi Nagata, Takako T.Ishii, Hiroyuki Komori, Keisuke Nishida, Tahei Nakamura, Hiroaki Isobe, Masaoki Hagino
Projects: Hinode/SOT

Publication Status: PASJ (accepted)
Last Modified: 2010-02-11 13:34
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Abstracts by Author
Differences between Doppler velocities of ions and neutral atoms in a solar prominence
Diagnosis of Magnetic and Electric Fields of Chromospheric Jets through Spectropolarimetric Observations of HI Paschen Lines
Spicule Dynamics over Plage Region

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