The Topology of Magnetic Reconnection in Solar Flares

1CHAPTER 1INTRODUCTIONMotivationThe first solar flare was observed independently by R. C. Carrington and R. Hodgson on1 September 1859. Both Carrington and Hodgson were observing sun spots in white lightwhen they saw an intense brightening near a complex spot group. We now know that onlythe most energetic solar flares produce the type of white light emission they observed thatday. Solar flares result from rapid release of energy in the solar corona and are typicallyobserved as enhancements in the emission of a wide range of wavelengths including radio,Balmer-α emission of neutral hydrogen – called Hα, ultra violet (UV), extreme ultra violet(EUV), soft X-rays (SXR) and hard X-rays (HXR). Since we are unable to view the Sunfrom Earth in many of these wavelengths, our knowledge of solar flares was limited until theadvent of spacecraft in the 1960’s. While our observational and theoretical understandingof flares has advanced greatly since 1859, there are still several scientific questions aboutflares, including how a vast amount of energy is stored over tens of hours and how it isreleased in tens of minutes.The intensity and energy output of solar flares varies greatly. The strength of a solarflare is commonly given by its flux in 1-8 Å soft X-rays at 1 AU, where a C flare has a fluxon the order of 10 −3 erg cm −2 s −1 . Some flares are so weak that they are on the edge ofdetection by current soft X-ray telescopes. Others are so powerful that their soft X-ray fluxis one (M flares), two (X flares), or even more orders of magnitude higher than C flares. Thetotal amount of energy released during a solar flare in the form of thermal and nonthermalcharged particles, kinetic energy and shock waves can exceed 10 32 ergs.