Heating the solar corona: Enhanced phase mixing and current loop coalescence
arxiv: Astrophysics::Solar and Stellar Astrophysics | Physics::Space Physics
It has been known since the 1930s that the solar corona is hundreds of times hotter than \ud the solar photosphere. Numerous theoretical models have since been proposed to explain \ud what has become known as the coronal heating problem. These models are broadly cate- \ud gorised as either wave heating (AC) or magnetic reconnection (DC). In this thesis aspects \ud of both AC and DC heating models are investigated using analytical and numerical tech- \ud niques.\ud The dominant AC heating model, known as phase mixing, proposes that magnetic \ud Alfven waves, generated at the photosphere, dissipate in the corona due to inhomoge- \ud neous coronal structures. In this work corrected analytical solutions are presented for the \ud enhanced phase mixing of linear Alfven waves in divergent and stratified coronal struc- \ud tures. Numerical simulations are used to confirm the validity of these analytical solutions. \ud Further numerical simulations investigate the magnitude and location of the wave dissi- \ud pation. It is found that the enhanced phase mixing of 0.1 Hz Alfven waves can fulfil the \ud coronal heating energy requirement.\ud The DC heating models propose that eruptions of photospheric plasma, known as so- \ud lar flares, are initiated by the reconnection of magnetic fields. These frequently observed \ud flares release significant quantities of stored magnetic energy over a wide range of spa- \ud tial scales, heating the surrounding plasma. In this work the magnetic reconnection of \ud coalescing chromospheric current loops is investigated using two-fluid numerical simula- \ud tions. It is found that the rate of the magnetic reconnection, and hence energy release, is \ud strongly affected by the initial local plasma conditions.\ud Finally, a model is proposed to explain the recently discovered penumbral micro-jets, \ud based on the interaction of coalescing current loops with background magnetic flux tubes. \ud Bidirectional jets and significant proton heating are observed in numerical simulations of \ud the proposed model.