Paper on topology of solar flares accepted

Posted on 17 June 2015 by Etienne Pariat

The first paper of a serie of 2 (for the moment) has been accepted by the Astrophysical Journal. It’s a work done in collaboration with Antonia Savcheva from the Center for Astrophysics in Harvard that we started 3 years ago following our 2012 paper. This new paper can be found in ArXiv for the moment

“The Relation between Solar Eruption Topologies and Observed Flare Features I: Flare Ribbons”

A. Savcheva, E. Pariat, S. McKillop, P. McCauley, E. Hanson, Y. Su, E. Werner, E. E. DeLuca

Abstract:

In this paper we present a topological magnetic field investigation of seven two-ribbon flares in sigmoidal active regions observed with Hinode, STEREO, and SDO. We first derive the 3D coronal magnetic field structure of all regions using marginally unstable 3D coronal magnetic field models created with the flux rope insertion method. The unstable models have been shown to be a good model of the flaring magnetic field configurations. Regions are selected based on their pre-flare configurations along with the appearance and observational coverage of flare ribbons, and the model is constrained using pre-flare features observed in extreme ultraviolet and X-ray passbands. We perform a topology analysis of the models by computing the squashing factor, Q, in order to determine the locations of prominent quasi-separatrix layers (QSLs). QSLs from these maps are compared to flare ribbons at their full extents. We show that in all cases the straight segments of the two J-shaped ribbons are matched very well by the flux-rope-related QSLs, and the matches to the hooked segments are less consistent but still good for most cases. In addition, we show that these QSLs overlay ridges in the electric current density maps. This study is the largest sample of regions with QSLs derived from 3D coronal magnetic field models, and it shows that the magnetofrictional modeling technique that we employ gives a very good representation of flaring regions, with the power to predict flare ribbon locations in the event of a flare following the time of the model.

Posted in Article, Flares, Topology | Comments Off on Paper on topology of solar flares accepted

Submission of an article about electric currents at the solar photosphere

Posted on 6 June 2015 by Etienne Pariat

My former PhD student, Kevin Dalmasse, recently submitted an extensive article dealing with the formation of electruc currents flowing through the solar photosphere.

“The origin of net electric currents in solar active regions” (pdf)

K. Dalmasse, G. Aulanier; P. Démoulin; B. Kliem, T. Török, E. Pariat

Abstract:

There is a recurring question in solar physics about whether or not electric currents are neutralized in active regions (ARs). This question was recently revisited using three-dimensional (3D) magnetohydrodynamic (MHD) numerical simulations of magnetic flux emergence into the solar atmosphere. Such simulations showed that flux emergence can generate a substantial net current in ARs. Another source of AR currents are photospheric horizontal flows. Our aim is to determine the conditions for the occurrence of net vs. neutralized currents with this second mechanism. Using 3D MHD simulations, we systematically impose line-tied, quasi-static, photospheric twisting and shearing motions to a bipolar potential magnetic field. We find that such flows: (1) produce both direct and return currents, (2) induce very weak compression currents — not observed in 2.5D —  in the ambient field present in the close vicinity of the current-carrying field, and (3) can generate force-free magnetic fields with a net current. We demonstrate that neutralized currents are in general produced only in the absence of magnetic shear at the photospheric polarity inversion line — a special condition rarely observed. We conclude that, as magnetic flux emergence, photospheric flows can build up net currents in the solar atmosphere, in agreement with recent observations. These results thus provide support for eruption models based on pre-eruption magnetic fields possessing a net coronal current.

Posted in Article | Comments Off on Submission of an article about electric currents at the solar photosphere

Media pressure is growing

Posted on 19 March 2015 by Etienne Pariat

More and more journalist are asking for interviews.

Matinale de LCI (en direct)

France 3 TV journal 19h

TFI 13h TV journal (at 23’20)

Insu website

Le Journal du CNRS

Some videos made by the Public outreach department of the Paris Observatory:

What to observe in France that day

Scientific discovery

 

Posted in Eclipse, Public Outreach | Comments Off on Media pressure is growing

Solar eclipse is coming

Posted on 17 March 2015 by Etienne Pariat

A partial solar eclipse will occur on March 20th 2015 at the Paris/Meudon Observatory. The solar physics group is getting ready to welcome public and news media.

Some interesting websites:

On the March 20th solar eclipse

La page de l’IMCCE sur l’éclipse du 20 mars 2015

La page Wikipedia de l’éclipse du 20 mars 2015

Questions-réponses autour de l’éclipse du 20 mars 2015

On our activities that day:

L’Observatoire de Paris vous informe sur l’éclipse de Soleil du 20 mars 2015

A Meudon, observation de l’éclipse sur la terrasse publique de l’Observatoire

 More generally on solar eclipses:

Un cours sur les éclipses de l’IMCCE

 

Posted in Eclipse, Public Outreach | Comments Off on Solar eclipse is coming

Seminar at LESIA

Posted on 12 March 2015 by Etienne Pariat

Today a seminar for the Solar Physic Group of LESIA, my home group.

Magnetic helicity and its conservation: a future proxy for solar eruption predictions?

PDF version of the seminar
Abstract:

Nowadays, no quantity has been discovered that can be satisfactorily used as an efficient proxy to predict solar flares and eruptions. Solar eruptivity forecast are still mainly based empirical methods based on multiple criterions about the properties of actives regions. In this talk, I’ll present potentially good deterministic predictor of eruption: magnetic helicity.

Magnetic helicity quantifies the geometric properties of the magnetic field such as its level of twisting and braiding. The amount of helicity present in a domain constrains the final stage that a magnetic system can reach by resistive relaxation. It is therefore a key quantity for models of coronal heating and solar/stellar flares. Unlike most quantities, magnetic helicity is one of the few invariant of ideal magnetohydrodynamics, the physical paradigm that governs the evolution of eruptions.

About forty years ago, Taylor hypothesized that helicity is quasi- conserved even when magnetic reconnection develops. Because of the difficulty to properly compute magnetic helicity, this prediction has not yet been satisfactorily demonstrated. Using a state-of-the-art methods to correctly estimate magnetic helicity in a numerical domain I will show the very high-level of conservation of magnetic helicity in a numerical simulation of a solar active event, even though most of the free magnetic energy is dissipated. This pave the way for further studies of a innovative and effective proxy for space weather.

Posted in Magnetic Helicity, Seminars | Comments Off on Seminar at LESIA

Seminar at UNAM-Morelia

Posted on 20 February 2015 by Etienne Pariat

I’m giving a seminar today in Morelia at the Instituto de Geofísica, Unidad Michoacan, Universidad Nacional Autonomía de Mexico. This seminar is about:

Magnetic helicity and its conservation: a future proxy for solar eruption predictions?

Abstract:

Nowadays, no quantity has been discovered that can be satisfactorily used as an efficient proxy to predict solar flares and eruptions. Solar eruptivity forecast are still mainly based empirical methods based on multiple criterions about the properties of actives regions. In this talk, I’ll present potentially good deterministic predictor of eruption: magnetic helicity.

Magnetic helicity quantifies the geometric properties of the magnetic field such as its level of twisting and braiding. The amount of helicity present in a domain constrains the final stage that a magnetic system can reach by resistive relaxation. It is therefore a key quantity for models of coronal heating and solar/stellar flares. Unlike most quantities, magnetic helicity is one of the few invariant of ideal magnetohydrodynamics, the physical paradigm that governs the evolution of eruptions.

About forty years ago, Taylor hypothesized that helicity is quasi- conserved even when magnetic reconnection develops. Because of the difficulty to properly compute magnetic helicity, this prediction has not yet been satisfactorily demonstrated. Using a state-of-the-art methods to correctly estimate magnetic helicity in a numerical domain I will show the very high-level of conservation of magnetic helicity in a numerical simulation of a solar active event, even though most of the free magnetic energy is dissipated. This pave the way for further studies of a innovative and effective proxy for space weather.

Posted in Magnetic Helicity, Seminars | Comments Off on Seminar at UNAM-Morelia

Submission of an article about magnetic helicity conservation

Posted on 6 February 2015 by Etienne Pariat

This paper is now accepted: see here

Posted in Article, Magnetic Helicity | Leave a comment

ISSI team on Magnetic Helicity

Posted on 21 December 2014 by Etienne Pariat

With my dear colleague Gherardo Valori from MSSL, we are organising a focused team on the estimation of magnetic helicity. This team is meeting under the patronage of the International Space Science Institue (ISSI) in Bern, Switzerland.

The name of the team is: Magnetic Helicity estimations in models and observations of the solar magnetic field

You can visit the team website to check our activities. The first meeting of the team took place on the first week of december.

 

Posted in Article, Magnetic Helicity | Comments Off on ISSI team on Magnetic Helicity