Submission of an article about electric currents at the solar photosphere

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.

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Media pressure is growing

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

 

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Solar eclipse is coming

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

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

 

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Seminar at LESIA

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.

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Seminar at UNAM-Morelia

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.

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Submission of an article about magnetic helicity conservation

This paper is now accepted: see here

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ISSI team on Magnetic Helicity

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.

 

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