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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 27, issue 3
Ann. Geophys., 27, 1067–1078, 2009
https://doi.org/10.5194/angeo-27-1067-2009
© Author(s) 2009. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue: Ninth International Conference on Substorms (ICS9)

Ann. Geophys., 27, 1067–1078, 2009
https://doi.org/10.5194/angeo-27-1067-2009
© Author(s) 2009. This work is distributed under
the Creative Commons Attribution 3.0 License.

  04 Mar 2009

04 Mar 2009


Reconnection in substorms and solar flares: analogies and differences

J. Birn1 and M. Hesse2 J. Birn and M. Hesse
  • 1Los Alamos National Laboratory, Los Alamos, NM, USA
  • 2NASA Goddard Space Flight Center, Greenbelt, MD, USA

Abstract. Magnetic reconnection is the crucial process in the release of magnetic energy associated with magnetospheric substorms and with solar flares. On the basis of three-dimensional resistive MHD simulations we investigate similarities and differences between the two scenarios. We address in particular mechanisms that lead to the onset of reconnection and energy release, transport, and conversion mechanisms. Analogous processes might exist in the motion of field line footpoints on the sun and in magnetic flux addition to the magnetotail. In both cases such processes might lead to a loss of neighboring equilibrium, characterized by the formation of a very thin embedded current sheet, which acts as trigger for reconnection. We find that Joule (or ohmic) dissipation plays only a minor role in the overall energy transfer associated with reconnection. The dominant transfer of released magnetic energy occurs to electromagnetic energy (Poynting) flux and to thermal energy transport as enthalpy flux. The former dominates in low-beta, specifically initially force-free current sheets expected for the solar corona, while the latter dominates in high-beta current sheets, such as the magnetotail. In both cases the outflow from the reconnection site becomes bursty, i.e. spatially and temporally localized, yet carrying most of the outflow energy. Hence an analogy might exist between bursty bulk flows (BBFs) in the magnetotail and pulses of Poynting flux in solar flares. Further similarities might exist in the role of collapsing magnetic flux tubes, as a consequence of reconnection, in the heating and acceleration of charged particles.

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