Field‐aligned potential drops in the solar corona

Abstract

A field‐aligned potential drop of Φ∥ ≤ 100 kV can be produced in the corona due to the loss cone constriction effect on a 0.25 A/m² field‐aligned current driven by the dynamo process in the photosphere under the condition that Nm ≥ 2×104 cm−3 and Bm ≥ 60 G near the top region of a coronal loop. This condition probably can be satisfied during coronal mass ejections when the coronal loop rises to a height greater than one solar radius. Since coronal mass ejection events are often observed to precede solar flares, the proposed model of field‐aligned potential drop can be related to solar flares through coronal mass ejection events. The resulting 100 kV field‐aligned potential drop in the corona can accelerate an electron beam to produce nonthermal hard X‐ray bursts. The magnetic field produced by the field‐aligned current is estimated to be δB(0) ≈ 0.3 T at the foot of an erupting coronal loop. The ratio δB(0)/Bo = 1, which is on the high side, but is probably acceptable for coronal mass ejection events of very large spatial scales.