An observational investigation of coronal rain in the quiescent and flaring solar corona

Sahin, Seray (2023) An observational investigation of coronal rain in the quiescent and flaring solar corona. Doctoral thesis, Northumbria University.

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Abstract

The corona is the outer layer of the solar atmosphere and has a puzzling temperature hundreds of times higher than the underlying surface, which is a major unsolved astrophysics problem. The corona also contains a substantial quantity of cool material called coronal rain, hundreds of times colder and denser plasma grouped in showers, and is mainly observed in quiescent and flaringactive regions (AR). The properties of rain are known to be deeply linked to the way the corona is heated, but its dynamics, origin, and morphology are yet poorly understood. In particular, the rain’s spatial and temporal occurrence in an AR is unknown. Rain formation is driven by thermal instability (TI) in coronal loops that are in thermal non-equilibrium (TNE). In this thesis, using the IRIS and SDO instruments, I conducted the first high-resolution imaging statistical study of coronal rain (and showers) to investigate its origin, dynamics, morphology, energetics, and its link to coronal heating and solar flare mechanisms. In particular, I find that the volume under TNETI conditions can be over half the AR volume, indicating a prevalence of strongly stratified and high-frequency coronal heating. Overall, plasma downflows in the form of rain showers can be as energetic or more than the upward flare-driven chromospheric evaporation, placing coronal rain as a major player in the mass and energy circulation in the quiescent and flaring solar corona.

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