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Decay of the coronal magnetic field can release sufficient energy to power a solar flare

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Science  17 Jan 2020:
Vol. 367, Issue 6475, pp. 278-280
DOI: 10.1126/science.aax6874

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Magnetic energy release in a solar flare

Solar flares are bright flashes and associated eruptions of plasma from the Sun that are thought to be powered by violent rearrangement of the magnetic fields near sunspots. Fleishman et al. observed a bright solar flare with a microwave interferometer, allowing them to map the magnetic field in the solar corona and monitor how it changed during the flare. They found a large drop in the local field strength over 2 minutes, releasing enough magnetic energy to power the entire solar flare. Determining the origin of this energy will help to predict how strong future solar flares may be and their potential space weather impacts on Earth.

Science, this issue p. 278

Abstract

Solar flares are powered by a rapid release of energy in the solar corona, thought to be produced by the decay of the coronal magnetic field strength. Direct quantitative measurements of the evolving magnetic field strength are required to test this. We report microwave observations of a solar flare, showing spatial and temporal changes in the coronal magnetic field. The field decays at a rate of ~5 Gauss per second for 2 minutes, as measured within a flare subvolume of ~1028 cubic centimeters. This fast rate of decay implies a sufficiently strong electric field to account for the particle acceleration that produces the microwave emission. The decrease in stored magnetic energy is enough to power the solar flare, including the associated eruption, particle acceleration, and plasma heating.

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