Holly Gilbert

Kink-induced Catastrophe in a Coronal Eruption

We investigate the kinking motion and its role in the eruption of a filament/cavity system that occurred on 2002 October 31. The evolution of the eruptive filament consists of four distinct phases. After an initial slow upward acceleration, the filament experiences a quasi-static phase exhibiting kinking motions of the filament axis. The kinking phase is followed by a sudden jump, coincident with the onset of the unkinking of the filament. The loss of equilibrium initiates a gradual relaxation phase at the end of which the filament reattains a similar unkinked configuration as its initial state. The filament/cavity structure, evident in the white-light observations, interacts with a large-scale coronal helmet streamer to the north, and material is observed to eject outward, aligned with a preexisting, low-density, dark channel that originally separated the northern helmet streamer from the southern streamer, where the dark cavity resides. The bulk of the filament, however, remains confined in the lower corona throughout the eruption along the channel. This suggests a partial eruption of the filament/cavity structure. The observations presented here manifest a catastrophic loss of equilibrium in response to the evolution of kinking motions in the filament activation.

The Filament-Moreton Wave Interaction of 2006 December 6

We utilize chromospheric observations obtained at MLSO of the 2006 December 6 Moreton wave, which exhibits two distinct fronts, and subsequent filament activation to conduct a comprehensive analysis of the wave-filament interaction. By determining the period, amplitude, and evolution of the oscillations in the activated filament, we make certain inferences regarding the physical properties of both the wave and the filament. The large-amplitude oscillations induced in the filament by the wave passage last on the order of 180 minutes and demonstrate a complicated mixture of transverse and perpendicular motion with respect to the filament spine. These oscillations are predominantly along the filament axis, with a period of ~29 minutes and maximum line-of-sight velocity amplitude of ~41 km s−1. A careful examination of the complex oscillatory response of the filament elucidates some of the fundamental characteristics of the related Moreton wave. Specifically, we infer the maximum total kinetic energy involved in the interaction, the structure and topology of the passing wave, and discuss implications for the topology of the responding magnetic structure supporting the filament. The results of this observational study equip us with a better understanding of how filaments become activated and the nature of their responses to large propagating disturbances.

ASYMMETRIC ERUPTIVE FILAMENTS

Filaments are often observed to erupt asymmetrically, during which one leg is fixed to the photosphere (referred to as the anchored leg) while the other undertakes most of the dynamic motions (referred to as the active leg) during the eruptive process. In this paper, we present observations of a group of asymmetric eruptive filaments, in which two types of eruptions are identified: whipping-like, where the active leg whips upward, and hard X-ray sources shift toward the end of the anchored leg; and zipping-like, where the visible end of the active leg moves along the neutral line like the unfastening of a zipper as the filament arch rises and expands. During a zipping-like eruption, hard X-ray sources shift away from where the eruption initiates toward where the visible end of the active leg eventually stops moving. Both types of asymmetric eruptions can be understood in terms of how the highly sheared filament channel field, traced by filament material, responds to an external asymmetric magnetic confinement, where force imbalance occurs in the neighborhood of the visible end of the active leg. The dynamic motions of the active leg have a distinct impact on how hard X-ray sources shift, as observed by RHESSI.

Partially-erupting prominences: a comparison between observations and model-predicted observables

Aims. To investigate several partially-erupting prominences to study their relationship with other CME-associated phenomena and to compare these observations with observables predicted by a model of partially-expelled flux ropes (Gibson & Fan, 2006a, b). Methods. We have studied 6 selected events with partially-erupting prominences using multi-wavelength observations recorded by the Extremeultraviolet Imaging Telescope (EIT), Transition Region and Coronal Explorer (TRACE), Mauna Loa Solar Observatory (MLSO), Big Bear Solar Observatory (BBSO) and soft X-ray telescope (SXT). The observational features associated with partially-erupt ing prominences were then compared with the predicted observables from the model. Results. The partially-expelled-flux-rope (PEFR) model of Gibson & F an (2006a, b) can explain the partial eruption of these prominences, and in addition predicts a variety of other CME-related observables that provide evidence for internal reconnection during eruption. We find that all of the partially-erupting prominences studied in this p aper exhibit indirect evidence for internal reconnection. Moreover, all cases showed evidence of at least one observable unique to the PEFR model, e.g., dimmings external to the source region, and/or a soft X-ray cusp overlying a reformed sigmoid. Conclusions. The PEFR model provides a plausible mechanism to explain the observed evolution of partially-erupting-prominence-associated CMEs in our study.

ENERGY RELEASE FROM IMPACTING PROMINENCE MATERIAL FOLLOWING THE 2011 JUNE 7 ERUPTION

Solar filaments exhibit a range of eruptive-like dynamic activity, ranging from the full or partial eruption of the filament mass and surrounding magnetic structure as a coronal mass ejection to a fully confined or failed eruption. On 2011 June 7, a dramatic partial eruption of a filament was observed by multiple instruments on board the Solar Dynamics Observatory (SDO) and Solar-Terrestrial Relations Observatory. One of the interesting aspects of this event is the response of the solar atmosphere as non-escaping material falls inward under the influence of gravity. The impact sites show clear evidence of brightening in the observed extreme ultraviolet wavelengths due to energy release. Two plausible physical mechanisms for explaining the brightening are considered: heating of the plasma due to the kinetic energy of impacting material compressing the plasma, or reconnection between the magnetic field of low-lying loops and the field carried by the impacting material. By analyzing the emission of the brightenings in several SDO/Atmospheric Imaging Assembly wavelengths, and comparing the kinetic energy of the impacting material (7.6 ? 1026-5.8 ? 1027 erg) to the radiative energy (1.9 ? 1025-2.5 ? 1026 erg), we find the dominant mechanism of energy release involved in the observed brightening is plasma compression.

Observational Evidence Supporting Cross-Field Diffusion of Neutral Material in Solar Filaments

We investigate the temporal and spatial variation of the relative abundance of He to H in a sample of solar filaments by comparing cotemporal observations of Hα and He I λ10830 obtained at MLSO. Motivated by indications that cross-field diffusion of neutral filament material is an important mechanism in mass loss, the present study offers results that provide a convincing test of the mechanisms proposed in Gilbert and coworkers. Specifically, when observed across an entire disk passage, we find a majority of stable, quiescent filaments show a relative helium deficit in the upper portions of their structure coupled with a relative helium surplus in the lower regions, a consequence of the large loss timescale for neutral helium compared to neutral hydrogen. Moreover, we find that the variation of the relative He/H ratio is uniform across filament barbs and footpoints on both short and long timescales.

Observations and Implications of Large-amplitude Longitudinal Oscillations in a Solar Filament

On 2010 August 20, an energetic disturbance triggered large-amplitude longitudinal oscillations in a nearby filament. The triggering mechanism appears to be episodic jets connecting the energetic event with the filament threads. In the present work, we analyze this periodic motion in a large fraction of the filament to characterize the underlying physics of the oscillation as well as the filament properties. The results support our previous theoretical conclusions that the restoring force of large-amplitude longitudinal oscillations is solar gravity, and the damping mechanism is the ongoing accumulation of mass onto the oscillating threads. Based on our previous work, we used the fitted parameters to determine the magnitude and radius of curvature of the dipped magnetic field along the filament, as well as the mass accretion rate onto the filament threads. These derived properties are nearly uniform along the filament, indicating a remarkable degree of cohesiveness throughout the filament channel. Moreover, the estimated mass accretion rate implies that the footpoint heating responsible for the thread formation, according to the thermal nonequilibrium model, agrees with previous coronal heating estimates. We estimate the magnitude of the energy released in the nearby event by studying the dynamic response of the filament threads, and discuss the implications of our study for filament structure and heating.

Ionized Plasma and Neutral Gas Coupling in the Sun's Chromosphere and Earth's Ionosphere/Thermosphere

We review physical processes of ionized plasma and neutral gas coupling in the weakly ionized, stratified, electromagnetically-permeated regions of the Sun’s chromosphere and Earth’s ionosphere/thermosphere. Using representative models for each environment we derive fundamental descriptions of the coupling of the constituent parts to each other and to the electric and magnetic fields, and we examine the variation in magnetization of the components. Using these descriptions we compare related phenomena in the two environments, and discuss electric currents, energy transfer and dissipation. We present examples of physical processes that occur in both atmospheres, the descriptions of which have previously been conducted in contrasting paradigms, that serve as examples of how the chromospheric and ionospheric communities can further collaborate. We also suggest future collaborative studies that will help improve our understanding of these two different atmospheres, which while sharing many similarities, also exhibit large disparities in key quantities.

Partially Ionized Plasmas in Astrophysics

Partially ionized plasmas are found across the Universe in many different astrophysical environments. They constitute an essential ingredient of the solar atmosphere, molecular clouds, planetary ionospheres and protoplanetary disks, among other environments, and display a richness of physical effects which are not present in fully ionized plasmas. This review provides an overview of the physics of partially ionized plasmas, including recent advances in different astrophysical areas in which partial ionization plays a fundamental role. We outline outstanding observational and theoretical questions and discuss possible directions for future progress.

GONG Catalog of Solar Filament Oscillations Near Solar Maximum

We have catalogued 196 filament oscillations from the GONG