The Hydromagnetic Nature of Solar Coronal Mass Ejections

Zhang, Mei; Low, B. C.

doi:10.1146/annurev.astro.43.072103.150602

Cited by 174 publications

(110 citation statements)

References 136 publications

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“…In that case the accumulation of magnetic helicity and energy in the corona leads to an instability of closed field structures that erupt as coronal mass ejections (CMEs), eliminating the excess of helicity (Zhang & Low 2005;Zhang et al 2006). In the present model, in addition to the CME mechanism, the interaction between the coronal field and the planetary magnetosphere takes part in the helicity dissipation process.…”

Section: Discussionmentioning

confidence: 89%

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Stellar coronal magnetic fields and star-planet interaction

Lanza¹

2009

A&A

123

151

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Context. Evidence of magnetic interaction between late-type stars and close-in giant planets is provided by the observations of stellar hot spots rotating synchronously with the planets and showing an enhancement of chromospheric and X-ray fluxes. Possible photospheric signatures of such an interaction have also been reported. Aims. We investigate star-planet interaction in the framework of a magnetic field model of a stellar corona, considering the interaction between the coronal field and that of a planetary magnetosphere moving through the corona. This is motivated, among other reasons, by the difficulty of accounting for the energy budgets of the interaction phenomena with previous models. Methods. A linear force-free model is applied to describe the coronal field and study the evolution of its total magnetic energy and relative helicity according to the boundary conditions at the stellar surface and the effects related to the planetary motion through the corona.Results. The energy budget of the star-planet interaction is discussed, assuming that the planet may trigger a release of the energy of the coronal field by decreasing its relative helicity. The observed intermittent character of the star-planet interaction is explained by a topological change in the stellar coronal field, induced by a variation in its relative helicity. The model predicts the formation of many prominence-like structures in the case of highly active stars owing to the accumulation of matter evaporated from the planet inside an azimuthal flux rope in the outer corona. Moreover, the model can explain why stars accompanied by close-in planets have a higher X-ray luminosity than those with distant planets. It predicts that the best conditions for detecting radio emission from the exoplanets and their host stars are achieved when the field topology is characterized by field lines connected to the surface of the star, leading to a chromospheric hot spot rotating synchronously with the planet. Conclusions. The main predictions of the model can be verified with current observational techniques, by a simultaneous monitoring of the chromospheric flux and X-ray (or radio) emission, and spectropolarimetric observations of the photospheric magnetic fields.

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Section: Discussionmentioning

confidence: 89%

“…In the same limit, the relative magnetic helicity grows without bounds because q 0 → 0 in Eq. (6), but the helicity density (i.e., the magnetic helicity per unit volume) tends to zero (see Berger 1985;Zhang & Low 2005, for a further description of this limit state).…”

Section: Coronal Field Modelmentioning

confidence: 99%

Stellar coronal magnetic fields and star-planet interaction

Lanza¹

2009

A&A

123

151

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“…The expansion of the cavity is clearly associated with the rise of the prominence plasma. One possible explanation for the expansion is that the loss of free magnetic energy from the active region by flares and CMEs (Zhang & Low 2005) resulted in a contraction of the active region field, the Hudson effect (Hudson 2000;Zhang & Low 2003;Janse & Low 2007). Subsequently, the surrounding fields, including the cavity field, expanded to fill the vacated space.…”

Section: Discussionmentioning

confidence: 99%

A solar tornado triggered by flares?

Panesar

Innes

Tiwari

et al. 2013

A&A

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Context. Solar tornados are dynamical, conspicuously helical magnetic structures that are mainly observed as a prominence activity. Aims. We investigate and propose a triggering mechanism for the solar tornado observed in a prominence cavity by SDO/AIA on September 25, 2011. Methods. High-cadence EUV images from the SDO/AIA and the Ahead spacecraft of STEREO/EUVI are used to correlate three flares in the neighbouring active-region (NOAA 11303) and their EUV waves with the dynamical developments of the tornado. The timings of the flares and EUV waves observed on-disk in 195 Å are analysed in relation to the tornado activities observed at the limb in 171 Å. Results. Each of the three flares and its related EUV wave occurred within ten hours of the onset of the tornado. They have an observed causal relationship with the commencement of activity in the prominence where the tornado develops. Tornado-like rotations along the side of the prominence start after the second flare. The prominence cavity expands with the accelerating tornado motion after the third flare. Conclusions. Flares in the neighbouring active region may have affected the cavity prominence system and triggered the solar tornado. A plausible mechanism is that the active-region coronal field contracted by the "Hudson effect" through the loss of magnetic energy as flares. Subsequently, the cavity expanded by its magnetic pressure to fill the surrounding low corona. We suggest that the tornado is the dynamical response of the helical prominence field to the cavity expansion.

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“…For the magnetograms that are not at the central area of the Sun's disk, the projection effect and the 180°ambiguity in the SP magnetic field data also need to be resolved more carefully and accurately [Georgoulis, 2005;Metcalf et al, 2006;Wiegelmann et al, 2008;Martin et al, 2008;Leka et al, 2009]. Besides the comparison between the extrapolated field lines and the coronal loop images, and the preliminary physical analyses used in this paper, topological techniques and more physical measures should be introduced to quantitatively analyze the topological and physical properties of the extrapolated fields [Longcope, 2005;Zhao et al, 2005;DeVore and Antiochos, 2000;Bleybel et al, 2002;Zhang and Low, 2005;Régnier and Canfield, 2006;Démoulin, 2007;Thalmann et al, 2008;Schrijver et al, 2008;DeRosa et al, 2009] and their relationships to the solar eruptive events.…”

Section: Discussionmentioning

confidence: 99%

Nonlinear force-free field extrapolation of the coronal magnetic field using the data obtained by the Hinode satellite

Wang

Yan

2011

J. Geophys. Res.

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[1] The Hinode satellite can obtain high-quality photospheric vector magnetograms of solar active regions and the simultaneous coronal loop images in soft X-ray and extreme ultraviolet (EUV) bands. In this paper, we continue the work of and apply the newly developed upward boundary integration computational scheme for the nonlinear force-free field (NLFFF) extrapolation of the coronal magnetic field to the

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The Hydromagnetic Nature of Solar Coronal Mass Ejections

Cited by 174 publications

References 136 publications

Stellar coronal magnetic fields and star-planet interaction

Stellar coronal magnetic fields and star-planet interaction

A solar tornado triggered by flares?

Nonlinear force-free field extrapolation of the coronal magnetic field using the data obtained by the Hinode satellite

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