The magnetic topology of solar coronal structures following mass ejections

Abstract

The bright radial structures observed in the solar corona for 1–2 days following a coronal mass ejection (CME) have traditionally been interpreted as unidirectional magnetic fields, commonly known as “legs,” at the sides of the ejections. We examine in detail the bright structures following 16 CMEs observed with the coronagraph on the Solar Maximum Mission (SMM) spacecraft and find that these structures can form anywhere within the lateral span of a CME, not only at the sides. We suggest that a more plausible interpretation is that the bright radial structures are the tops of coronal streamers containing magnetic neutral sheets across which the magnetic fields reverse direction. The observational support for this view is that: (1) the bright features left behind at CME sides, when a CME has left the field of view of this instrument, last <10 hours; (2) some bright radial structures form at the sites of preexisting streamers; (3) some such structures have the broad bases characteristic of helmet streamers; and (4) in several cases, narrow radial structures form over H α prominences. A reexamination of the structures observed in the Skylab era, including the well‐studied CME of August 10, 1973, reveals that they are also consistent with the streamer interpretation. This interpretation avoids several difficulties encountered with the “leg” interpretation: (1) the systematic brightening of legs −1 day after the CME; (2) the origin of the energetic electrons characteristic of stationary type IV bursts if they are associated with high‐density, unidirectional‐field structures unfavorable for particle acceleration; and (3) the lack of strong evidence of magnetic reconnection in the coronagraph data following CMEs.