Kiyoshi Ichimoto

We performed a spectroscopic observation of an erupting prominence occurred on the solar limb on 2015 May 8 in He i 7065 Å, O i 7772 Å triplet and Ca ii 8498 Å lines to investigate differences in the Doppler velocity between ions and neutrals in a plasma strongly accelerated by the Lorentz force. We found that the ion–neutral velocity difference between Ca ii and He i reached an order of 15 km s–1. On the other hand, the velocity difference between Ca ii and O i was significantly smaller than that between Ca ii and He i. This result can be interpreted as the formation of O i 7772 Å lines in the erupting prominence is mainly contributed by the recombination from O ii ions through charge transfer with hydrogen atoms, resulting in a behavior close to ions. According to an order estimate of the collisional friction among He i atoms and protons, the observed velocity difference between Ca ii and He i implies the acceleration of the eruption reaches about 150 times the solar gravity. We propose a new method to evaluate the ionization degree of hydrogen from the velocity differences observed in Ca ii, He i, and O i lines.

On 2022 September 26, we observed a quiescent solar prominence with H α imaging spectroscopy using the Solar Dynamics Doppler Imager (SDDI) on board the Solar Magnetic Activity Research Telescope (SMART). Unlike earlier works that detected 4 and 15 minute oscillations through long-slit, 1D wavelet methods, we adapt the wavelet analysis to 3D data to explore the full prominence structure. Complementary data from Solar Dynamics Observatory/Atmospheric Imaging Assembly (304, 171 Å) STEREO-A Extreme Ultraviolet Imager (EUVI; 304 Å), and Solar Orbiter Extreme Ultraviolet Imager/Full Sun Imager (304, 174 Å) enable a multiview, multithermal investigation of wave periodicity across the prominence. Our aim is to characterize how oscillatory periods are distributed in plasma at different temperatures and viewing angles, thereby assessing wave propagation and variability throughout the prominence body. We analyze time series of Doppler signal from SMART/SDDI H α observations alongside extreme-ultraviolet intensity variations from space-based instruments. We detect oscillatory plasma motions with periods spanning 3–74 minutes. Strong periodicity at 20, 31, and 53 minutes dominates in neutral plasma (H α ), while 13 and 74 minute oscillations are pronounced in the 304 Å passband, concentrated mainly in the central prominence. Additional short-period fluctuations include weaker 3–6 minute oscillations and rapid 30 s transverse waves in Doppler signals near the solar surface. These findings highlight the richness of wave periodicity in quiescent prominences, revealing a dynamic superposition of long- and short-period oscillations and kink-like disturbances. This multi-instrument, 3D perspective advances our understanding of how prominence plasma supports and modulates diverse wave modes.

Context. Solar filament eruptions usually appear to occur in association with the sudden explosive release of magnetic energy accumulated in long-lived arched magnetic structures. The released energy occasionally drives fast-filament eruptions that can be the source regions of coronal mass ejections. A quantitative analysis of high-speed filament eruptions is thus essential to help elucidate the formation and early acceleration of coronal mass ejections. Aims. The goal of this paper is to investigate the dynamic processes of a fast-filament eruption by using unprecedented high-resolution full-disk Hα imaging spectroscopy observations. Methods. The whole process of the eruption was captured in a wide spectral window of the Hα line (±9.0 Å), which allowed for the detection of highly Doppler-shifted plasma. By applying the “cloud model” and obtaining two-dimensional optical thickness spectra, we derived the Doppler velocity; the true eruption profiles (height, velocity, and acceleration); and the trajectory of the filament eruption in 3D space. Results. The Doppler velocity maps show that the filament was predominantly blueshifted. During the main and final process of the eruption, strongly blueshifted materials manifest, traveling with velocities exceeding 250 km s⁻¹. The spectral analysis further revealed that the erupting filament is made of multiple components, some of which were Doppler-shifted approximately to −300 km s⁻¹. We found that the filament eruption attains a maximum true velocity and acceleration of about 600 km s⁻¹ and 2.5 km s⁻², respectively, and its propagation direction deviates from the radial direction. On the other hand, downflows manifested as redshifted plasma close to the footpoints of the erupting filament move with velocities of 45–125 km s⁻¹. We interpret these redshifted signatures as draining material and therefore as mass loss of the filament, which has implications for the dynamic and the acceleration process of the eruption. Furthermore, we have estimated the total mass of the Hα filament, resulting in ∼5.4 × 10¹⁵ g.

Spectropolarimetric observation of a quiescent prominence was performed in He i 1083 nm. With the slit of the spectrograph fixed on the prominence, we obtained a time series of Stokes profiles for a duration of 108 minutes with a cadence of 8 s. Also using imaging spectroscopic data in Hα and extreme-ultraviolet images at 193 Å, we obtained the following results: (1) The prominence harbors persistent waves propagating across its body. (2) The waves are conspicuous in the line-of-sight (LOS) velocity with an amplitude of about 2 km s⁻¹ but not detectable in the intensity of emission lines or magnetic field. (3) Noticeable periods are about 4 minutes (220 and 260 s) and 15 minutes (910 s), and they propagate with phase speeds of 140 ∼ 200 and ∼24 km s⁻¹ preferentially in horizontal and vertical directions, respectively. (4) Magnetic field strength was estimated to be about 2.5 G with its LOS component of 0 ± 1 G on average. We interpret the 4 minute oscillation as Alfvénic waves propagating in the corona containing the prominence threads, and it is not a resonant wave trapped in the prominence body but excited by an external source. On the other hand, a 15 minute oscillation is interpreted as Alfvénic waves propagating upward in the prominence body. The prominence was evolving in its height during our observation, and there is a hint that the 15 minute period gradually gets longer during the observation. These waves are thought to be taking place in layers with different field directions and strength superposed in the LOS.

Whitepaper #020 in the Decadal Survey for Solar and Space Physics (Heliophysics) 2024-2033. Main topics: space weather applications; basic research. Additional topics: space weather research/applications/operations pipeline; ground-based missions/projects; solar physics.

We often find spectral signatures of chromospheric cold plasma ejections accompanied by flares in a wide range of spatial scales in the solar and stellar atmospheres. However, the relationship between physical quantities (such as mass, kinetic energy, and velocity) of cold ejecta and flare energy has not been investigated in a unified manner for the entire range of flare energies to date. This study analyzed the spectra of cold plasma ejections associated with small-scale flares and solar flares (energy 10²⁵–10²⁹ erg) to supply smaller energy samples. We performed Hα imaging spectroscopy observation by the Solar Dynamics Doppler Imager on the Solar Magnetic Activity Research Telescope. We determined the physical quantities of the ejecta by cloud model fitting to the Hα spectrum. We determined the flare energy by differential emission measure analysis using the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory for small-scale flares and by estimating the bolometric energy for large-scale flares. As a result, we found that the ejection mass M and the total flare energy E _tot follow a relation of M ∝ E tot 2 / 3 . We show that the scaling law derived from a simple physical model explains the solar and stellar observations with a coronal magnetic field strength as a free parameter. We also found that the kinetic energy and velocity of the ejecta correlate with the flare energy. These results suggest a common mechanism driven by magnetic fields to cause cold plasma ejections with flares on the Sun and stars.