Dacie, SC;
(2017)
Evolution of the Magnetic Field Distribution of Solar Active Regions.
Masters thesis , UCL (University College London).
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Abstract
Magnetic flux emergence through the solar photosphere in the form of an active region (AR) and the subsequent evolution of this flux are crucial processes in the solar cycle for their role in converting toroidal magnetic field to poloidal magnetic field. Although the temporal evolution of ARs is relatively well understood, the processes involved continue to be the subject of investigation. To better characterise how ARs emerge and disperse, the distribution of the vertical component of the photospheric magnetic field (flux density) of a series of ARs has been studied. A kernel density estimation plot of the magnetic field distribution was created on a log-log scale for each AR at each time step. The central portion of the distribution was found to be approximately linear and its slope was used to characterise the evolution of the magnetic field. The slopes were seen to evolve with time, becoming less steep as the fragmented emerging flux coalesces. The slopes reached a maximum value of -1.5 just before the time of maximum flux before becoming steeper during the decay phase towards the quiet Sun value of -3. This behaviour differs significantly from a classical diffusion model, which produces a slope of -1, suggesting that simple classical diffusion is not responsible for the observed changes in field distribution. Other processes must play a significant role in flux dispersion, one of which may be magnetic flux reprocessing by (super)granular convective cells. Moreover, comparisons of the observed distributions to those produced by data from simulations of AR emergence with and without convection suggest that convective processes also play an important role in magnetic flux emergence.
| Type: | Thesis (Masters) |
|---|---|
| Title: | Evolution of the Magnetic Field Distribution of Solar Active Regions |
| Event: | University College London |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| UCL classification: | UCL > Provost and Vice Provost Offices UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics |
| URI: | https://discovery.ucl.ac.uk/id/eprint/1541191 |
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