View source for Creation and Propagation of CMEs and Plasmoids: Loss of Equilibrium and Subsequent Evolution

'''Organizers: Kathy Reeves - Harvard (SHINE) and Joachim Birn - LANL (GEM)'''

Analogies between substorm features in the Earth’s magnetic tail and CME/flare releases have been invoked for some time: In both cases, there is a slow energy build-up leading into a rapid release of primarily magnetic energy which is then converted to kinetic energy in the form of bulk flow, and thermal and non-thermal particle energy. This process is associated with the ejection of a magnetic bubble, plasmoid, or flux rope from closed magnetic field lines into open space.

In this session we focussed on similarities and differences between the two scenarios, particularly on large scales, including release mechanisms, loss of equilibrium or large-scale instability, formation, topology, evolution, momentum gain, and energy partitioning. The session consisted of four invited presentations stimulating very lively discussions.

Mark Linton compared the formation and evolution of flux ropes in CMEs and magnetotail plasmoids.   He reviewed several mechanisms proposed for forming flux ropes  and initiating eruptions in the corona, including flux cancellation, breakout reconnection and the helical kink instability.  He pointed out that in the magnetotail, the flux rope forms when the current sheet thins (although during the discussion period, it was mentioned that the situation in the magnetotail is actually somewhat more complicated).  Once formed, flux ropes can deform upon interaction with other structures (i.e. each other, surrounding media), making it difficult to reconstruct their geometry from 1D spacecraft measurements.

Michael Hesse presented results from 3D resistive MHD simulations of reconnection and plasmoid formation in the geomagnetic tail. The initial state included a guide magnetic field (across the tail in the direction of the main current) of a few percent of the the main field, as is typical for the tail. The main results can be summarized as follows. The plasmoid formation and ejection is a continuous process that involves a changing mix of field lines with different toplogy (connected with or disconnected from Earth at one or both ends). The accumulation of mass, momentum, and energy is primarily due to the continuous addition of newly reconnected flux to the plasmoid.

Nancy Crooker presented work lead by George Siscoe, attempting to find a universal framework that covers the processes of coronal mass ejections as well as plasmoid ejection in the Earth's magnetic tail. Applying the commonly accepted CME/flare eruption scenario to the geomagnetic tail, she pointed out the potential relevance of plasma flow generated by force imbalance prior to the onset of reconnection.

Jun Lin examined the consequences of magnetic reconnection in the two different environments of the solar corona and the Earth's magnetosphere.  He presented several examples of similar post-reconnection behavior in the two environments, including dipolarizing (shrinking) reconnected loops, reconnection inflows and evidence for multiple X-points.