EVIDENCE FOR SHEET-LIKE ELEMENTARY STRUCTURES IN THE SUN'S ATMOSPHERE?

Abstract

Narrow, thread-like structures in the Sun's chromosphere are currently understood to be plasma guided along narrow tubes of magnetic flux. We report on 1 s cadence imaging spectroscopic measurements of the Hα line with the IBIS Fabry-Perot instrument at the Dunn Solar Telescope, obtained +0.11 nm from line center. Rapid changes grossly exceeding the Alfven speed are commonly seen along the full extent of many chromospheric threads. We argue that only an optical superposition effect can reasonably explain the data, analogous to striations of curtains blowing in the wind. Other explanations appear to require significant contrivances to avoid contradicting various aspects of the data. We infer that the absorbing plasma exists in two-dimensional sheet-like structures within the three-dimensional magnetofluid, related perhaps to magnetic tangential discontinuities. This interpretation demands a re-evaluation of basic assumptions about low-β solar plasmas, as advocated by Parker, with broader implications in astrophysics and plasma physics. Diverse, high-cadence observations are needed to further define the relationship between magnetic field and thermal fine structure.