Third Meeting, February 1, 2006

Implications of Reconnection

Nathan Schwadron

NESSC Purpose:

• To facilitate interaction among colleagues in space science in the New England Area (UNH, CfA, BU, MIT, Hanscom/AFRL, Haystack, Dartmouth)
• To leverage these interactions for initiating new, cross-disciplinary and far-reaching projects

Meetings:

• Monthly meetings (first Wednesday each month)
• Workshop?

Brief Talks:

• Terry Forbes
  • Transient Coronal Holes and CME Models (ppt)
• Trish Jibben
  • TRACE coronal hole observations (pdf) (ps)
• Hui Zhang
  • High Latitude Magnetopause Current Sheet (ppt)
• John Belcher
  • Collisionless reconnection in the solar wind and at MIT’s Plasma Science Fusion Center (ppt)
• George Siscoe
  • Comparative reconnection (ppt)
• Jun Lin  
• 2003 November 18 Flare (ppt) (pdf)

NOTE:  The powerpoint files won't work properly unless downloaded along with their appropriate movie files from here.  In addition the QuickTime movies (.mov) will probably not work on Windows machines.

Ideas (from last month’s discussion)

• Where are the transitions (on open field lines as they move across the coronal hole boundary)?
• Do we see them with TRACE?
• Source Surface Models .. Which field lines have opened during CMEs?
• What is the connection between a region with open field and a region that appears dark in a particular band?

What is the right question (reconnection)?

• Is the Axford conjecture correct?
  • Micro-physics vs. a driven system

• 3-Dimensionality is critical

• Examples:
  • Transpolar potential example (substorm)
  • Solar problem?

• CMEs, plasmoids in the downtail
  • Lifetime of the flare ribbons, relaxation process
  • Sequence of events in substorms (Cluster)
  • Find the method to distinguish paradigms (e.g., test the Axford conjecture)

• Intermittency of Reconnection
  

Summary:

• Magnetic Reconnection plays a critical role in the evolution of large-scale magnetic topologies, the rapid heating of plasmas and possibly the acceleration of high energy particles. The microphysics of reconnection is certainly complex and remains an area of active research. Despite this complexity, the "Axford Conjecture" puts forth a relatively simple condition that reconnection takes place at an average rate determined by external boundary conditions. In other words, the microphysics may adjust to the macrophysical constraints imposed on the system. If so, the quantitative effects of reconnection may be relatively straightforward to predict in diverse astrophysical environments. Comparing the effects of reconnection in disparate plasmas may provides a means to test the Axford Conjecture. A good example is found in the plasmoids released in the magnetotail during substorms. Is this phenomenon a direct parallel to coronal mass ejections, in which magnetic buoyancy plays the central in the release of a disturbance (plasmoid or CME)? If so, this comparative example would provide support for the Axford conjecture.

• Magnetic reconnection also appears to be intermittent. Is this a result of the external boundary conditions? In the case of CMEs, when does the system become unstable, and what makes it erupt. This same question may be asked of plasmoids in the magnetotail. Intermittency also appears in the laboratory experiments that achieve magnetic reconnection. At first glance, intermittency seems to be a result of the creation of thin current sheets, suggesting the release of energy of very small spatial and temporal scales. In this respect, it may be natural that the dissipation of thin current sheets channels significant quantities of energy into a minority of plasma particles that participate in the dissipation of thin current sheet.