A New Mechanism of Coronal Heating

Abstract

The interaction between network magnetic fields and emerging intranetwork fields may lead to magnetic reconnection and microflares, which generate fast shocks with an Alfven Mach number MA<2. Protons and less abundant ions in the solar corona are then heated and accelerated by fast shocks. Our study of shock heating shows that (a) the nearly nondeflection of ion motion across the shock ramp leads to a large perpendicular thermal velocity (vth⊥), which is an increasing function of the mass/charge ratio; (b) the heating by subcritical shocks with 1.1 ≤ MA ≤ 1.5 leads to a large temperature anisotropy with T⊥/T∥ ≈ 50 for O5+ ions and a mild anisotropy with T⊥/T∥ ≈ 1.2 for protons; (c) the large perpendicular thermal velocity of He++ and O5+ ions can be converted to the radial outflow velocity (u) in the divergent coronal field lines; and (d) the heating and acceleration by shocks with 1.1 ≤ MA ≤ 1.5 can lead to u(O5+) ≈vth⊥(O5+) ≈ 460 km s−1 for O5+ ions, u(He++) ≈vth⊥(He++) ≈ 360 km s−1 for He++ ions, and u(H+) ≈vth⊥(H+) ≈ 240 km s−1 for protons at r=3–4 R⊙. Our results can explain recent SOHO observations of the heating and acceleration of protons and heavier ions in the solar corona.