Abrupt Longitudinal Magnetic Field Changes and Ultraviolet Emissions Accompanying Solar Flares

Abstract

We have used Transition Region and Coronal Explorer (TRACE) 1600 Åimages and Global Oscillation Network Group (GONG) magnetograms to compare ultraviolet (UV) emissions from the chromosphere to longitudinal magnetic field changes in the photosphere during four X-class solar flares. An abrupt, significant, and persistent change in the magnetic field occurred across more than ten pixels in the GONG magnetograms for each flare. These magnetic changes lagged the GOES flare start times in all cases, showing that they were consequences and not causes of the flares. Ultraviolet emissions were spatially coincident with the field changes. The UV emissions tended to lag the GOES start times for the flares, and led the changes in the magnetic field in all pixels except one. The UV emissions led the photospheric field changes by 4 minutes on average with the longest lead being 9 minutes, however, the UV emissions continued for tens of minutes, and more than an hour in some cases, after the field changes were complete. The observations are consistent with the picture in which an Alfvén wave from the field reconnection site in the corona propagates field changes outward in all directions near the onset of the impulsive phase, including downwards through the chromosphere and into the photosphere, causing the photospheric field changes, whereas the chromosphere emits in the UV in the form of flare kernels, ribbons and sequential chromospheric brightenings during all phases of the flare.

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Cited by in corpus (10)

• Flare-productive active regions
• Investigating the Magnetic Imprints of Major Solar Eruptions with SDO/HMI High-Cadence Vector Magnetograms
• First Detection of Chromospheric Magnetic Field Changes During an X1-Flare
• Structure and Evolution of Magnetic Fields Associated with Solar Eruptions (Invited Review)
• A unified view of coronal loop contraction and oscillation in flares
• A Statistical Study of Photospheric Magnetic Field Changes During 75 Solar Flares
• Sunquake Generation by Coronal Magnetic Restructuring
• A statistical Analysis of Magnetic Field Changes in the Photosphere During Solar Flares Using High-cadence Vector Magnetograms and Their Association with Flare Ribbons
• A Survey of Changes in Magnetic Helicity Flux on the Photosphere During Relatively Low Class Flares
• Alfvén Waves in Solar Flares