Abstract
The heating of ‘post’-flare loops in the Kopp-Pneuman (1976) model is here reconsidered. In that kinematic model the loops are heated by gas-dynamic shocks to at most 3–4 × 106 K. However, in a full dynamic model they would be replaced by slow magnetohydrodynamic shocks, which may provide more heating due to the additional release of magnetic energy. It is shown from a local compressible analysis that such shock waves can account for the observed temperatures of 5 × 106–107 K and also for the observed upward loop speeds of 1–50 km s-1. The above values are obtained when the ambient plasma beta is 0.01 and the shocks propagate at highly sub-Alfvénic velocities. However, if the velocity of shock propagation approaches the Alfvén speed, then temperatures of 108 K are produced. This may explain the extremely high temperatures that have been observed with the Solar Maximum Mission, when it is realised that the ‘post’-flare loop phenomenon may well be occurring very early on in the flare.
A full dynamic model would require a sophisticated numerical computation, and so a simple global analytic model is developed here instead. It is incompressible and includes a strong solar-wind inflow along the reconnecting field lines. As the upflow increases, the loops become more compressed and the Alfvén waves approach one another.
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Cargill, P.J., Priest, E.R. Slow-shock heating and the Kopp-Pneuman model for ‘post’-flare loops. Sol Phys 76, 357–375 (1982). https://doi.org/10.1007/BF00170991
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DOI: https://doi.org/10.1007/BF00170991