Kernels and Ribbons

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Nugget
Number:	129
1st Author:	Jiong QIU
2nd Author:
Published:	2010 June 14
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Introduction

A solar flare has a complicated three-dimensional structure involving all layers of the solar atmosphere. Many of the models that we use to explain them, though, are inherently two-dimensional and indeed often involve the concept of the current sheet, geometrically a manifold with only two dimensions. On the other hand, modern theories of magnetic reconnection require three-dimensionality to make the plasma physics work.

Many of the observations also seem to point to intrinsic two-dimensionality. Chief among these are the [flare ribbons], the magnetic footpoints of an arcade of loops that looks entirely consistent with the presence of a large-scale current sheet in the solar corona. One observation that generally does not agree with this picture is the hard X-ray picture (e.g. RHESSI's), and this one is fundamentally important to understand because the hard X-rays show us where the flare energy appears. Instead of ribbons, the hard X-rays usually show a much simpler structure, often two bright compact sources termed "footpoints" on the reasonable assumption that they show the two ends of a thin coronal magnetic loop. This nugget studies the fine structure of footpoints and ribbons in a search for an answer to the simple geometrical (2D vs 3D?) question.