A Study of Photospheric Vector Magnetic Field Changes During Solar Flares

Abstract. Large amounts of energy are released when magnetic field lines reconnect in the corona during solar flares. Observations have found both transient and irreversible changes in the photospheric magnetic fields during flares, but their origins and mechanisms are yet unclear. To investigate the properties of magnetic field changes during flares, e.g. their size, area, and timing, we performed a statistical analysis of 75 solar flares. We analyzed the line-of-sight (LOS) and vector magnetic field measurements obtained by the Solar Dynamics Observatory. We derived the locations of permanent magnetic field changes of these flares that were selected based on a wide energy range from small to extreme flares (18 X-class, 37 M-class, 19 C-class and 1 B-class flares), and a wide range of heliographic longitudes (disk center to limb). We identified kernels of permanent magnetic field changes in 80% of the flares. 36 events showed more positive changes, while during 23 flares more negative irreversible variations were observed. We found two decreasing exponential relations for: (i) the observed step-size values, (ii) the number of the permanent changes found with respect to the distance measured from the polarity inversion line (PIL). An enhancement in white-light (WL) emission was observed in 74% of the events. The WL emission and the permanent changes do not have a one-to-one spatial relationship, but they are near each other and often overlap. The energy emitted during each event in the soft X-ray band correlates with the total photospheric area where permanent changes are located following a power-law. We also studied the evolution of the three components of the magnetic field in the same places where permanent changes in the LOS component were found, as well as a region of few arcsecs width measured from the PIL. We concluded that the flares that show irreversible changes in azimuth and inclination do not vary with the location of the flare, although the correlation with the field strength decreases for flares that were located near the limb. Permanent changes in the field strength, and inclination are found more often than changes in azimuth with ~19% difference. The strength field irreversibly increased near the PIL in 29 flares. We observed that the field becomes tilted after 20 flares. This agrees with the implosion model (Hudson et al. 2000) that predicts the field becoming more horizontal after the flare. However, during 13 flares, the radial field showed positive and larger changes than the horizontal field. This implies another scenario when the flare-loop is untwisted after flares (Kleint 2016)

• Autores: Castellanos Durán, Juan Sebastián
• Fecha de publicación: 2016
• Institución: Universidad Nacional de Colombia
• Repositorio: Universidad Nacional de Colombia
• Idioma: spa
• OAI Identifier: oai:repositorio.unal.edu.co:unal/58310
• Acceso en línea: https://repositorio.unal.edu.co/handle/unal/58310; http://bdigital.unal.edu.co/55042/
• Palabra clave: 52 Astronomía y ciencias afines / Astronomy; El Sol; Fulguraciones Solares; Campos Magnéticos Fotosféricos; The Sun; Solar flares; Photospheric Magnetic fields
• Rights: openAccess
• License: Atribución-NoComercial 4.0 Internacional