Le Néant

Romano, Claude

doi:10.3917/puf.laure.2011.01.0525

Cited by 4 publications

(5 citation statements)

References 3 publications

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“…Nevertheless, examples of inconsistency between the chirality of the source active region and the one of the associated filament have been observed and interpreted as due to local phenomena of helicity injections in active regions prior and during the eruption (Chandra et al 2010;Romano et al 2011;Zuccarello et al 2011).…”

Section: Magnetic Parametersmentioning

confidence: 99%

Observation-based modelling of magnetised coronal mass ejections with EUHFORIA

Scolini

Rodriguez

Mierla

et al. 2019

A&A

135

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Context. Coronal Mass Ejections (CMEs) are the primary source of strong space weather disturbances at Earth. Their geoeffectiveness is largely determined by their dynamic pressure and internal magnetic fields, for which reliable predictions at Earth are not possible with traditional cone CME models. Aims. We study two well-observed Earth-directed CMEs using the EUropean Heliospheric FORecasting Information Asset (EUH-FORIA) model, testing for the first time the predictive capabilities of a linear force-free spheromak CME model initialised using parameters derived from remote-sensing observations. Methods. Using observation-based CME input parameters, we perform magnetohydrodynamic simulations of the events with EUH-FORIA, using the cone and spheromak CME models.Results. Simulations show that spheromak CMEs propagate faster than cone CMEs when initialised with the same kinematic parameters. We interpret these differences as result of different Lorentz forces acting within cone and spheromak CMEs, which lead to different CME expansions in the heliosphere. Such discrepancies can be mitigated by initialising spheromak CMEs with a reduced speed corresponding to the radial speed only. Results at Earth evidence that the spheromak model improves the predictions of B (B z ) up to 12-60 (22-40) percentage points compared to a cone model. Considering virtual spacecraft located within ±10 • around Earth, B (B z ) predictions reach 45-70% (58-78%) of the observed peak values. The spheromak model shows inaccurate predictions of the magnetic field parameters at Earth for CMEs propagating away from the Sun-Earth line.Conclusions. The spheromak model successfully predicts the CME properties and arrival time in the case of strictly Earth-directed events, while modelling CMEs propagating away from the Sun-Earth line requires extra care due to limitations related to the assumed spherical shape. The spatial variability of modelling results and the typical uncertainties in the reconstructed CME direction advocate the need to consider predictions at Earth and at virtual spacecraft located around it.

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Section: Magnetic Parametersmentioning

confidence: 99%

Observation-based modelling of magnetised coronal mass ejections with EUHFORIA

Scolini

Rodriguez

Mierla

et al. 2019

A&A

135

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“…Inferred from the evolution of the photospheric magnetic field, magnetic helicity transported across the photosphere is often used to diagnose the helicity that is instantaneously injected into the higher solar atmosphere. Some investigates showed that the local injection of helicity with opposite signs played a role in triggering the eruptions of the studied filaments (Romano et al 2011;Dhara et al 2014). Romano et al (2005) found the impulsive input of helicity at the beginning of the eruption of a kinked filament.…”

Section: Introductionmentioning

confidence: 99%

Partial Eruption of a Filament With Twisting Non-Uniform Fields

Jiang

Yang

et al. 2015

ApJ

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The eruption of the filament with the kink fashion is often regarded as a signature of the kink instability. However, the kink instability threshold for the filament magnetic structure has been not widely understood. Using the Hα observation from the New Vacuum Solar Telescope (NVST), we present a partial eruptive filament. In the eruption, a filament thread appeared to split from the middle portion of the filament and to break out in a kinklike fashion. During this period, the left filament material remained below, which erupted without the kinking motion later on. The coronal magnetic field lines associated with the filament are obtained from the nonlinear force-free field (NLFFF) extrapolations using the 12 minutes cadence vector magnetograms of the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamic Observatory (SDO). We studied the extrapolated field lines passing through the magnetic dips that are in good agreement with the observed filament. The field lines are non-uniformly twisted and appear to be made up by two twisted flux ropes winding about each other. One of them has higher twist than the other, and the highly twisted one has its dips aligned with the kinking eruptive thread at the beginning of its eruption. Before the eruption, moreover, the highly twisted flux rope was found to expand with the approximately constant field twist. In addition, the helicity flux maps deduced from the HMI magnetograms show that some helicity is injected into the overlying magnetic arcade, but no significant helicity is injected into the flux ropes. Accordingly, we suggest that the highly twisted flux rope became kink unstable when the instability threshold declined with the expansion of the flux rope.

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“…Few studies claim that the monotonous accumulation of helicity in the corona comes from magnetic domains with uniform signed distribution of helicity flux and therefore are prone to launch coronal mass ejections (Pariat et al 2006;Vemareddy et al 2012a,b). On the other hand, domains with opposite signed distribution of helicity flux were speculated to be related to more energetic events as they can liberate more free energy since the system can relax to a more potential field (Chandra et al 2010;Romano et al 2011;Vemareddy et al 2012b).…”

Section: Introductionmentioning

confidence: 99%

Successive injection of opposite magnetic helicity in solar active region NOAA 11928

Vemareddy

Démoulin

2017

A&A

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Aims. Understanding the nature and evolution of the photospheric helicity flux transfer is a key to reveal the role of magnetic helicity in coronal dynamics of solar active regions. Methods. Using SDO/HMI photospheric vector magnetograms and the derived flow velocity field, we computed boundary driven helicity flux with a 12 minute cadence during the emergence of AR 11928. Accounting the foot point connectivity defined by nonlinear force-free magnetic extrapolations, we derived and analyzed the corrected distribution of helicity flux maps. Results. The photospheric helicity flux injection is found to changes sign during the steady emergence of the AR. This reversal is confirmed with the evolution of the photospheric electric currents and with the coronal connectivity as observed in EUV wavelengths with SDO/AIA. During about the three first days of emergence the AR coronal helicity is positive while later on the field configuration is close to a potential field. As theoretically expected, the magnetic helicity cancelation is associated to enhanced coronal activity. Conclusions. The study suggests a boundary driven transformation of the chirality in the global AR magnetic structure. This may be the result of the emergence of a flux rope with positive twist around its apex while it has negative twist in its legs. The origin of such mixed helicity flux rope in the convective zone is challenging for models.

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Le Néant

Cited by 4 publications

References 3 publications

Observation-based modelling of magnetised coronal mass ejections with EUHFORIA

Observation-based modelling of magnetised coronal mass ejections with EUHFORIA

Partial Eruption of a Filament With Twisting Non-Uniform Fields

Successive injection of opposite magnetic helicity in solar active region NOAA 11928

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