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Magnetic Origins of Cool Plasma in the Sun’s Corona

Published onJun 01, 2020
Magnetic Origins of Cool Plasma in the Sun’s Corona

Much of solar physics research focuses on two questions: how the corona's temperature becomes hundreds of times hotter than the surface, and how the slow solar wind forms. Among the most fascinating phenomena produced by coronal heating is coronal rain, in which plasma undergoes rapid cooling (from roughly 106 to 103 K), condenses, and falls to the surface. One proposed rain origin theory, thermal nonequilibrium (TNE), posits a height restriction in coronal heating. By studying condensations, physicists hope to better understand coronal heating. Solar wind is often subdivided into fast and slow wind. The former originates in coronal hole regions; slow wind's source, however, is still under debate. One leading theory postulates that it comes from coronal hole boundaries, where magnetic field lines frequently reconnect. This research investigates the origins and dynamics of coronal rain via study of recently-discovered structures called raining null-point topologies, or RNPTs. RNPTs — the first identification and characterization of which comprise part of this work — are decaying active regions situated near coronal hole boundaries, between 50-150 Mm in height. They are host to long periods of continuous coronal rain formation, and provide insight into coronal heating, slow solar wind origins, and coronal dynamics. We focus on identifying and analyzing RNPTs' observational characteristics. We process and analyze RNPT data using both the Solar Dynamics Observatory Atmospheric Imaging Assembly and the Helioseismic and Magnetic Imager. Potential field source-surface extrapolations that model the magnetic field in the corona aid in the interpretation of the structures' topology. Results indicate that RNPTs experience two rain-forming mechanisms, TNE and interchange reconnection. The interchange reconnection is posited to power much of the early bursts of coronal rain, which constitutes a new rain-formation mechanism and allows for plasma from closed loops to escape into the slow solar wind. Observations also show evidence of partial condensations, which condense but do not fully cool.

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