Coronal magnetic reconnection driven by CME expansion -- the 2011 June 7 event

Coronal mass ejections (CMEs) erupt and expand in a magnetically structured solar corona. Various indirect observational pieces of evidence have shown that the magnetic field of CMEs reconnects with surrounding magnetic fields, forming, e.g., dimming regions distant from the CME source regions. Analyzing Solar Dynamics Observatory (SDO) observations of the eruption from AR 11226 on 2011 June 7, we present the first direct evidence of coronal magnetic reconnection between the fields of two adjacent ARs during a CME. The observations are presented jointly with a data-constrained numerical simulation, demonstrating the formation/intensification of current sheets along a hyperbolic flux tube (HFT) at the interface between the CME and the neighbouring AR 11227. Reconnection resulted in the formation of new magnetic connections between the erupting magnetic structure from AR 11226 and the neighboring active region AR 11227 about 200 Mm from the eruption site. The onset of reconnection first becomes apparent in the SDO/AIA images when filament plasma, originally contained within the erupting flux rope, is re-directed towards remote areas in AR 11227, tracing the change of large-scale magnetic connectivity. The location of the coronal reconnection region becomes bright and directly observable at SDO/AIA wavelengths, owing to the presence of down-flowing cool, dense (10^{10} cm^{-3}) filament plasma in its vicinity. The high-density plasma around the reconnection region is heated to coronal temperatures, presumably by slow-mode shocks and Coulomb collisions. These results provide the first direct observational evidence that CMEs reconnect with surrounding magnetic structures, leading to a large-scale re-configuration of the coronal magnetic field.Comment: 12 pages, 12 figure

Observation of An Evolving Magnetic Flux Rope Prior To and During A Solar Eruption

Explosive energy release is a common phenomenon occurring in magnetized plasma systems ranging from laboratories, Earth's magnetosphere, the solar corona and astrophysical environments. Its physical explanation is usually attributed to magnetic reconnection in a thin current sheet. Here we report the important role of magnetic flux rope structure, a volumetric current channel, in producing explosive events. The flux rope is observed as a hot channel prior to and during a solar eruption from the Atmospheric Imaging Assembly (AIA) telescope on board the Solar Dynamic Observatory (SDO). It initially appears as a twisted and writhed sigmoidal structure with a temperature as high as 10 MK and then transforms toward a semi-circular shape during a slow rise phase, which is followed by fast acceleration and onset of a flare. The observations suggest that the instability of the magnetic flux rope trigger the eruption, thus making a major addition to the traditional magnetic-reconnection paradigm.Comment: 13 pages, 3 figure

Temporal Correlation of Hard X-rays and Meter/Decimeter Radio Structures in Solar Flares

We investigate the relative timing between hard X-ray (HXR) peaks and structures in metric and decimetric radio emissions of solar flares using data from the RHESSI and Phoenix-2 instruments. The radio events under consideration are predominantly classified as type III bursts, decimetric pulsations and patches. The RHESSI data are demodulated using special techniques appropriate for a Phoenix-2 temporal resolution of 0.1s. The absolute timing accuracy of the two instruments is found to be about 170 ms, and much better on the average. It is found that type III radio groups often coincide with enhanced HXR emission, but only a relatively small fraction ($\sim$ 20%) of the groups show close correlation on time scales $<$ 1s. If structures correlate, the HXRs precede the type III emissions in a majority of cases, and by 0.69$\pm$0.19 s on the average. Reversed drift type III bursts are also delayed, but high-frequency and harmonic emission is retarded less. The decimetric pulsations and patches (DCIM) have a larger scatter of delays, but do not have a statistically significant sign or an average different from zero. The time delay does not show a center-to-limb variation excluding simple propagation effects. The delay by scattering near the source region is suggested to be the most efficient process on the average for delaying type III radio emission

Decoding the Pre-Eruptive Magnetic Field Configurations of Coronal Mass Ejections

A clear understanding of the nature of the pre-eruptive magnetic field configurations of Coronal Mass Ejections (CMEs) is required for understanding and eventually predicting solar eruptions. Only two, but seemingly disparate, magnetic configurations are considered viable; namely, sheared magnetic arcades (SMA) and magnetic flux ropes (MFR). They can form via three physical mechanisms (flux emergence, flux cancellation, helicity condensation) . Whether the CME culprit is an SMA or an MFR, however, has been strongly debated for thirty years. We formed an International Space Science Institute (ISSI) team to address and resolve this issue and report the outcome here. We review the status of the field across modeling and observations, identify the open and closed issues, compile lists of SMA and MFR observables to be tested against observations and outline research activities to close the gaps in our current understanding. We propose that the combination of multi-viewpoint multi-thermal coronal observations and multi-height vector magnetic field measurements is the optimal approach for resolving the issue conclusively. We demonstrate the approach using MHD simulations and synthetic coronal images. Our key conclusion is that the differentiation of pre-eruptive configurations in terms of SMAs and MFRs seems artificial. Both observations and modeling can be made consistent if the pre-eruptive configuration exists in a hybrid state that is continuously evolving from an SMA to an MFR. Thus, the 'dominant' nature of a given configuration will largely depend on its evolutionary stage (SMA-like early-on, MFR-like near the eruption).Comment: Space Science Reviews, accepted for publicatio

Review article: MHD wave propagation near coronal null points of magnetic fields

We present a comprehensive review of MHD wave behaviour in the neighbourhood of coronal null points: locations where the magnetic field, and hence the local Alfven speed, is zero. The behaviour of all three MHD wave modes, i.e. the Alfven wave and the fast and slow magnetoacoustic waves, has been investigated in the neighbourhood of 2D, 2.5D and (to a certain extent) 3D magnetic null points, for a variety of assumptions, configurations and geometries. In general, it is found that the fast magnetoacoustic wave behaviour is dictated by the Alfven-speed profile. In a $\beta=0$ plasma, the fast wave is focused towards the null point by a refraction effect and all the wave energy, and thus current density, accumulates close to the null point. Thus, null points will be locations for preferential heating by fast waves. Independently, the Alfven wave is found to propagate along magnetic fieldlines and is confined to the fieldlines it is generated on. As the wave approaches the null point, it spreads out due to the diverging fieldlines. Eventually, the Alfven wave accumulates along the separatrices (in 2D) or along the spine or fan-plane (in 3D). Hence, Alfven wave energy will be preferentially dissipated at these locations. It is clear that the magnetic field plays a fundamental role in the propagation and properties of MHD waves in the neighbourhood of coronal null points. This topic is a fundamental plasma process and results so far have also lead to critical insights into reconnection, mode-coupling, quasi-periodic pulsations and phase-mixing.Comment: 34 pages, 5 figures, invited review in Space Science Reviews => Note this is a 2011 paper, not a 2010 pape

Could Public Restrooms Be an Environment for Bacterial Resistomes?

PMCID: PMC3547874This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited

The evolution of writhe in kink-unstable flux ropes and erupting filaments

Copyright © 2014 IOP Publishing Ltd. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence (http://creativecommons.org/licenses/by/3.0/). Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.The helical kink instability of a twisted magnetic flux tube has been suggested as a trigger mechanism for solar filament eruptions and coronal mass ejections (CMEs). In order to investigate if estimations of the pre-emptive twist can be obtained from observations of writhe in such events, we quantitatively analyze the conversion of twist into writhe in the course of the instability, using numerical simulations. We consider the line tied, cylindrically symmetric Gold–Hoyle flux rope model and measure the writhe using the formulae by Berger and Prior which express the quantity as a single integral in space. We find that the amount of twist converted into writhe does not simply scale with the initial flux rope twist, but depends mainly on the growth rates of the instability eigenmodes of higher longitudinal order than the basic mode. The saturation levels of the writhe, as well as the shapes of the kinked flux ropes, are very similar for considerable ranges of initial flux rope twists, which essentially precludes estimations of pre-eruptive twist from measurements of writhe. However, our simulations suggest an upper twist limit of ~6π for the majority of filaments prior to their eruption.European Commission’s Seventh Framework ProgrammeScience & Technology Facilities Council (STFC)Hungarian Researc