NAM 07: Plasmoids and sheaths mean success or failure for solar eruptions
Our Sun experiences regular eruptions of material into space, but solar physicists still have difficulty in explaining why these dramatic events take place. Now a group of scientists from the University of St Andrews think they have the answer: clouds of ionized gas (plasma) constrained by magnetic fields and known as 'plasmoids' that struggle to break free of the Sun's magnetic field. Dr Vasilis Archontis will present their work on Monday 18 April at the National Astronomy Meeting in Llandudno, Wales.
Active regions on the solar surface are often the site of eruptions. These are associated with magnetic fields from the solar interior rising to the surface and gradually expanding into the Sun's outer atmosphere, the corona, in a process known as magnetic flux emergence.
The St Andrews team developed 3D computer models of these phenomena, revealing that the emergence of magnetic flux naturally leads to the formation and expulsion of plasmoids that adopt a twisted tube configuration.
The formation of the plasmoids is due to the motion of plasma in the lower atmosphere of the Sun. These motions bring magnetic fieldlines closer together to reconnect and build a new magnetic flux system (i.e. the plasmoid). Whether the plasmoids are 'failed' or 'successful' (i.e. they erupt into space) depends on the level of interaction between the new emerging field and the old, pre-existing magnetic field in the solar corona.
When the new emerging field expands into the corona, it forms a 'magnetic sheath' with a fan-like shape. The sheath magnetic field consists of loop-like fieldlines, which are anchored to the solar surface and enclose the plasmoids.
A striking result from the simulations is that the plasmoids remain trapped in the solar atmosphere if the magnetic sheath is not removed by some other external mechanism. In this case, the sheath fieldlines manage to stop the plasmoids erupting.
But if the sheath magnetic field breaks and connects with the other magnetic fields in the surrounding solar corona, the researchers believe that this opens the way for the plasmoids to erupt at speeds of up to at least 500 km per second. During the faster part of this eruption the plasmoids are pushed up, transfer heavy plasma to the solar corona, expand without constraint and accelerate out into space.
Dr Vasilis Archontis (at NAM Monday – Wednesday)
Prof. Alan W. Hood
NAM 2011 Press Office (0900 – 1730 BST, 18-21 April only)
Dr Robert Massey
A series of movies showing the results of the new experiment can be downloaded from http://www-solar.mcs.st-and.ac.uk/~vasilis/nam2011
The whole evolution (i.e. from the initial emergence of flux until plasmoids reach the upper atmosphere of the Sun) in the numerical experiments occurs within 2 hours. The physical size of the simulation box is 24,000 x 24,000 x 27,000 kilometres. In the movies, the size of the area shown is 24,000 x 27,000 kilometres. The time period in the simulation corresponds to 90 minutes of real time.
Movie 1: A simulation of the evolution of plasma density in an experiment where the eruption of the plasmoid is 'failed'. The dense material rises but it does not manage to break through the sheath magnetic field. Credit: Vasilis Archontis
Movie 2: A simulation of the evolution of plasma temperature in the same experiment, where the eruption of the plasmoid is 'failed'. Cool material is transported into the solar corona, where the plasmoid relaxes to an equilibrium. Credit: Vasilis Archontis
Movie 3: A simulation of the evolution of plasma density in an experiment where the eruption of the plasmoid is 'successful'. The dense material rises slowly first, but eventually it accelerates to experience a rapid ejection out through the solar corona (at the top). Credit: Vasilis Archontis
Movie 4: A simulation of the evolution of plasma temperature during the 'successful' eruption of the plasmoid. A lot of heating is produced underneath the erupting plasmoid, due to the emission of jets from reconnection of magnetic fields. Credit: Vasilis Archontis
Notes for editors
Bringing together around 500 astronomers and space scientists, the RAS National Astronomy Meeting 2011 (NAM 2011: http://www.ras.org.uk/nam-2011) will take place from 17-21 April in Venue Cymru (http://www.venuecymru.co.uk), Llandudno, Wales. The conference is held in conjunction with the UK Solar Physics (UKSP: http://www.uksolphys.org) and Magnetosphere Ionosphere and Solar-Terrestrial Physics (MIST: http://www.mist.ac.uk) meetings. NAM 2011 is principally sponsored by the RAS and the Science and Technology Facilities Council (STFC: http://www.stfc.ac.uk).
The Royal Astronomical Society
The Royal Astronomical Society (RAS: http://www.ras.org.uk), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organizes scientific meetings, publishes international research and review journals, recognizes outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 3500 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others.
The Science and Technology Facilities Council
The Science and Technology Facilities Council (STFC: http://www.stfc.ac.uk) ensures the UK retains its leading place on the world stage by delivering world-class science; accessing and hosting international facilities; developing innovative technologies; and increasing the socio-economic impact of its research through effective knowledge exchange. The Council has a broad science portfolio including Astronomy, Particle Astrophysics and Space Science. In the area of astronomy it funds the UK membership of international bodies such as the European Southern Observatory.
Venue Cymru (http://www.venuecymru.co.uk) is a purpose built conference centre and theatre with modern facilities for up to 2000 delegates. Located on the Llandudno promenade with stunning sea and mountain views; Venue Cymru comprises a stunning location, outstanding quality and exceptional value: the perfect conference package.