Dear loops aficionados,
I hope this email finds you well in these challenging times. You may be interested in these two recently-published papers.
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Non-thermal line broadening due to braiding-induced turbulence in solar coronal loops (A&A, 639, A21, 2020. D. I. Pontin, H. Peter, and L. P. Chitta) https://arxiv.org/abs/2008.11915https://www.aanda.org/articles/aa/abs/2020/07/aa37582-20/aa37582-20.html
ABSTRACT:
Aims: Emission line profiles from solar coronal loops exhibit properties that are unexplained by current models. We investigate the non-thermal broadening associated with plasma heating in coronal loops that is induced by magnetic field line braiding. Methods: We describe the coronal loop by a 3D magnetohydrodynamic model of the turbulent decay of an initially-braided magnetic field. From this we synthesize the Fe XII line at 193 Angstroms that forms around 1.5 MK. Results: Key features of current observations of extreme UV lines from the corona are reproduced in the synthesised spectra: (i) Typical non-thermal widths range from 15 to 20 km/s. (ii) The widths are approximately independent of the size of the field of view. (iii) There is a correlation between line intensity and the non-thermal broadening. (iv) Spectra are found to be non-Gaussian, with enhanced power in the wings of order 10-20%. Conclusions: Our model provides an explanation that self-consistently connects the heating process to the observed non-thermal line broadening. The non-Gaussian nature of the spectra is a consequence of the non-Gaussian nature of the underlying velocity fluctuations, interpreted as a signature of intermittency in the turbulence.
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The Parker problem: existence of smooth force-free fields and coronal heating (Living Reviews in Solar Physics, 17, 5, 2020. D. I Pontin and G. Hornig) https://link.springer.com/article/10.1007%2Fs41116-020-00026-5<https://link.springer.com/article/10.1007/s41116-020-00026-5>
ABSTRACT:
Parker (Astrophys J 174:499, 1972) put forward a hypothesis regarding the fundamental nature of equilibrium magnetic fields in astrophysical plasmas. He proposed that if an equilibrium magnetic field is subjected to an arbitrary, small perturbation, then—under ideal plasma dynamics—the resulting magnetic field will in general not relax towards a smooth equilibrium, but rather, towards a state containing tangential magnetic field discontinuities. Even at astrophysical plasma parameters, as the singular state is approached dissipation must eventually become important, leading to the onset of rapid magnetic reconnection and energy dissipation. This topological dissipation mechanism remains a matter of debate, and is a key ingredient in the nanoflare model for coronal heating. We review the various theoretical and computational approaches that have sought to prove or disprove Parker’s hypothesis. We describe the hypothesis in the context of coronal heating, and discuss different approaches that have been taken to investigating whether braiding of magnetic field lines is responsible for maintaining the observed coronal temperatures. We discuss the many advances that have been made, and highlight outstanding open questions.
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Best wishes,
David
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David I. Pontin | Assoc Prof Physics
School of Mathematical and Physics Sciences
T: +61 2 4055 3261
E: david.pontin(a)newcastle.edu.au<mailto:david.pontin@newcastle.edu.au>
W: newcastle.edu.au/profile/david-pontin<http://newcastle.edu.au/profile/david-pontin>
The University of Newcastle
University Drive, Callaghan NSW 2308 Australia
Hello all,
Thank you very much to everyone who nominated colleagues, and submitted
self-nominations, to the Loops Workshops Steering Committee. The votes are
in and I am very pleased to announce the following new committee members:
Clara Froment (Center National De La Recherche Scientifique)
Boris Gudiksen (Rosseland Center for Solar Physics, University of Oslo)
Amy Winebarger (NASA Marshall Space Flight Center)
Congratulations to all!
The full Steering Committee is:
David Brooks (US Naval Research Laboratory)
Philippa Browning (University of Manchester)
Ineke De Moortel (University of St. Andrews)
Giulio Del Zanna (University of Cambridge)
Clara Froment (Center National De La Recherche Scientifique)
Boris Gudiksen (Rosseland Center for Solar Physics, University of Oslo)
Fabio Reale (University of Palermo)
Durgesh Tripathi (Inter-University Centre for Astronomy and Astrophysics)
Amy Winebarger (NASA Marshall Space Flight Center)
I would like to thank Paola Testa and Viggo Hansteen, who are rotating off
with me and have both served full six year terms, for their time and
contributions to the Steering Committee, and to the workshops they have been
involved in organizing.
The first order of business for the new committee will be to elect a new
Chairperson, who will be announced in due course.
Best wishes,
Steve
From: Stephen Bradshaw <stephen.bradshaw(a)rice.edu>
Sent: Sunday, May 24, 2020 11:25 PM
To: 'loops(a)solar.physics.montana.edu' <loops(a)solar.physics.montana.edu>
Subject: Call for Nominations to the Coronal Loops Workshops Steering
Committee
Dear Colleagues,
The Coronal Loops Workshop series, inaugurated in Paris (2002) with the most
recent Workshop in St. Andrews (2019), has been tremendously successful in
bringing together researchers from all over the world to discuss current
problems related to the physics of closed magnetic structures in the solar
corona, and to present their progress toward solving them. The Workshops
have also provided an excellent venue for young researchers to participate
in discussions and to showcase their work.
The Steering Committee for the Coronal Loops Workshops is responsible for
soliciting and selecting Workshop proposals, and assisting / advising each
Scientific Organizing Committee in choosing a topical, over-arching theme
and setting an agenda and goals for their Workshop.
The current members of the Steering Committee are: Steve Bradshaw [Chair];
David Brooks; Philippa Browning; Ineke De Moortel; Giulio Del Zanna; Viggo
Hansteen; Fabio Reale; Paola Testa; Durgesh Tripathi.
Three members of the Steering Committee (Steve Bradshaw, Viggo Hansteen, and
Paola Testa) have reached the end of their 6 year terms. Since they were
elected in 2014 they have been involved in the organization of 3 Loops
Workshops (Loops VII - IX).
It is now time to elect 3 new members of the Steering Committee. We are
soliciting nominations and self-nominations of scientists who are active in
the physics of closed magnetic structures in the solar corona, to serve on
the Coronal Loops Workshops Steering Committee for a 6 year term.
Self-nominations are particularly encouraged to help ensure a diverse pool
of candidates to represent the interests of our community.
Please submit your nominations and self-nominations to Steve Bradshaw
(Steering Committee Chair: <mailto:stephen.bradshaw@rice.edu>
stephen.bradshaw(a)rice.edu) no later than Monday June 8th. The current
members of the Steering Committee will vote per the Bylaws and the
newly-elected members will be duly contacted and announced directly
thereafter.
With best wishes,
Steve Bradshaw
(on behalf of the Coronal Loops Workshops Steering Committee)
Dr. Stephen J. Bradshaw
(Associate Professor of Physics and Astronomy / Chair of the Undergraduate
Program)
Department of Physics and Astronomy (MS 108)
Rice University,
6100 Main Street,
Houston,
TX 77005,
USA.
Tel: +1 713 348 4045
Email: <mailto:stephen.bradshaw@rice.edu> stephen.bradshaw(a)rice.edu
Web: solar.rice.edu