The relationship between supergranulation flows, magnetic field evolution and network flares

Attie, Raphael GND

The quiet Sun may be the biggest laboratory to study physical elementary processes of fundamental importance to space plasma. The advantage is the continuous availability of small-scale events, carrying the hidden microphysics that is responsible for larger-scale phenomena. By small-scale events, we mean spatial dimensions of a few Mm at most, and durations of less than an hour. This thesis is an attempt to describe and understand the coupling between the photospheric flows, the photospheric magnetic flux, and small-scale energetic transient events. We adapted a highly efficient numerical method, called Balltracking, to derive the photospheric flows from images of the granulation. For studying the dynamics of magnetic flux, and more precisely, its cancellation at relevant sites, we developed a new tool called "Magnetic Balltracking", to track photospheric magnetic elements present in high-resolution magnetograms. In a multi-instrument study using observations of the low corona in soft X-rays, we analyse the triggering mechanism of small-scale network flares. Balltracking directly relates the flows with cancelling magnetic flux, while the latter is tracked with Magnetic Balltracking. We identify two patterns of horizontal flows that act as catalysts for efficient magnetic reconnection: Funnel-shaped streamlines in which the magnetic flux is carried, and large-scale vortices (>15 Mm) at the network intersections, in which distant magnetic features of opposite polarities are sucked in and ultimately cancel. The excess energy stored in the stressed magnetic field of the vortices is sufficient to power network flares.

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Attie, Raphael: The relationship between supergranulation flows, magnetic field evolution and network flares. Göttingen 2015. Max-Planck-Insitut für Sonnensystemforschung.

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