Acceleration of Type 2 Spicules in the Solar Chromosphere - 2: Viscous Braking and Upper Bounds on Coronal Energy Input

Abstract

A magnetohydrodynamic model is used to determine conditions under which the Lorentz force accelerates plasma to type 2 spicule speeds in the chromosphere. The model generalizes a previous model to include a more realistic pre-spicule state, and the vertical viscous force. Two cases of acceleration under upper chromospheric conditions are considered. The magnetic field strength for these cases is <= 12.5 and 25 G. Plasma is accelerated to terminal vertical speeds of 66 and 78 km/s in 100 s, compared with 124 and 397 km/s for the case of zero viscosity. The flows are localized within horizontal diameters ~ 80 and 50 km. The total thermal energy generated by viscous dissipation is ~ 10 times larger than that due to Joule dissipation, but the magnitude of the total cooling due to rarefaction is >~ this energy. Compressive heating dominates during the early phase of acceleration. The maximum energy injected into the corona by type 2 spicules, defined as the energy flux in the upper chromosphere, may largely balance total coronal energy losses in quiet regions, possibly also in coronal holes, but not in active regions. It is proposed that magnetic flux emergence in inter-granular regions drives type 2 spicules.

20 pages, 3 figures. Accepted for publication in The Astrophysical Journal

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