Rising of a magnetic null point in the wake of an erupting flux rope

Abstract

Arcades of flare loops rise, slowing down in the wake of eruptive prominences. They lag significantly from the top of prominences and do not reach too great heights in the corona. It is widely accepted that their evolution is governed by the limited reconnection rate in the current sheet developed below the eruptive prominence. We suggest that the shape of eruptive prominences may be the determining factor in the ascension of the arcade. Arcade deceleration and their limited heights are analysed in the frame of a simple rectangular circuit model representing prominence eruption. A null point that appears below the rising electric current does not follow it to a great height but is detained by the influence of the field created by currents flowing along the vertical segments,'legs', of the rectangular contour. As a result, the flare loops are able to reach only limited heights even with fast reconnection in a small current sheet.