Solar Xray Flare X 20, April 2, 2001 / ESA/NASA/SOHO
Our active Sun Our Sun is our nearest star and the only star we can study at close range. From Earth, we can detect visible light from the photosphere at about 6000 K and radio waves. Solar eclipses reveal the corona, the million-degree region which is the source of the solar wind. The material is hot enough to be a ‘plasma’ – the fourth state of matter beyond solid, liquid and gas. A million tonnes per second of solar wind escapes the Sun, carrying the solar magnetic field into the heliosphere. We study how the solar wind is produced and escapes, why the corona is hotter than the photosphere, and impulsive events on the Sun such as flares and coronal mass ejections (CMEs). One of the key processes is magnetic reconnection, where oppositely directed magnetic fields explosively join, unleashing accelerated particles, flares and CMEs. High in the Sun’s atmosphere, filaments of slightly cooler plasma may arch away from the Sun. In space, we study energetic radiation from active events, such as X-rays and far ultraviolet wavelengths. We work on magnetic topologies and their evolution and propagation, with a goal of forecasting solar wind conditions away from the Sun. Energetic radiation tells us about solar flares and CMEs. We study the active Sun using spacecraft such as Hinode, STEREO (Solar TErrestrial RElations Observatory) and SOHO (Solar & Heliospheric Observatory), and from 2018, Solar Orbiter . One key aspect is the north-south polarity of the emerging magnetic field, as well as shocks and variations in the solar wind. The polarity is critical to how damaging a solar event may be when it arrives at Earth. If there is a southward polarity, reconnection can be triggered upstream and downstream of Earth, allowing solar wind in.
What is the relationship between coronal mass ejections and the heliosphere, including the magnetic field polarity? What are the mechanisms for energetic proton release from solar flares, and the relation to sun- quakes?
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