Some calculations bearing on the heating and cooling of quiescent prominences

Abstract

We discuss the evolution of pulses of heat both along and perpendicular to magnetic fields threading quiescent prominences. We show that while heating of prominence material can take place on a time scale of the order 103 s (of the same order as the observed ‘winking’ of Hα light from prominences and also of the same order as the dynamical Alfven time scale across a prominence sheet) individual flux tubes are effectively thermally insulated from neighboring tubes, since the transverse (to the ambient supporting magnetic field) heat conduction time scale is of order 104 yr. The exact solution to the one-dimensional parallel heat conduction problem is shown to differ significantly from the approximate solution reported by Ioshpa (1965). We also suggest that uneven heating of a quiescent prominence by the surrounding solar corona may be a contributory mechanism for surges and/or the observed ‘winking’ phenomenon - both of which are recorded in many quiescent prominences. The signature of such a temperature pulse would be a sharp (≲103 s) brightening of continuum radiation with a correlated decrease in the free-bound emission, followed by a slow (∼104 s) recovery of both to their pre-heat pulse levels.