Baker, D.; (2011) Drivers of solar coronal dynamics. Doctoral thesis , UCL (University College London).

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Abstract

Multi-wavelength observations from various solar missions have revealed the dynamic nature of the solar corona. The work presented in this thesis represents a contribution towards understanding some of the physical mechanisms that drive the activity observed in the corona and out into the heliosphere. In particular, the role of reconnection in active region (AR) outflows and AR-coronal hole (CH) interactions using observations of the associated plasma flow signatures and their relationship to the underlying magnetic field topology is examined. Persistent outflows discovered by Hinode EUV Imaging Spectrometer (EIS) occur at the boundary of all ARs over monopolar magnetic regions. It is demonstrated that the outflows originate from specific locations of the magnetic topology where field lines display strong gradients of magnetic connectivity, namely quasi-separatrix layers (QSLs). Magnetic reconnection at QSLs is shown to be a viable mechanism for driving AR outflows which are likely sources of the slow solar wind. Observational signatures and consequences of interchange reconnection (IR) are identified and analyzed in a number of solar configurations. Jet light curves of several emission lines show a post-jet enhancement in cooler coronal lines which has not been previously observed. In the case of emerging flux near a CH, it is shown that closed loops forming between the AR and CH leads to the retreat of the CH and a dimming of the corona in the vicinity of the like-polarity region. A filament eruption and coronal mass ejection (CME) from an AR inside a CH are observed from the solar disk into the heliosphere. An anemone structure of the erupting AR and the passage in-situ of an interplanetary CME (ICME) with open magnetic topology are interpreted to be a direct result of IR. Plasma flows resulting from the interaction between an AR embedded in a CH observed by Hinode EIS are investigated. Velocity profiles of hotter coronal lines reveal intensification in outflow velocities prior to a CME. The AR’s plasma flows are compared with 3D magnetohydrodynamic (MHD) numerical simulations which show that expansion of AR loops drives outflows along the neighboring CH field. The intensification of outflows observed prior to the CME is likely to result from the expansion of a flux rope containing a filament further compressing the neighboring CH field.

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