Stochastic Coupling of Solar Photosphere and Corona

Abstract

The observed solar activity is believed to be driven by the dissipation of nonpotential magnetic energy injected into the corona by dynamic processes in the photosphere. The enormous range of scales involved in the interaction makes it difficult to track down the photospheric origin of each coronal dissipation event, especially in the presence of complex magnetic topologies. In this paper, we propose an ensemble-based approach for testing the photosphere-corona coupling in a quiet solar region as represented by intermittent activity in Solar and Heliospheric Observatory Michelson Doppler Imager and Solar TErrestrial RElations Observatory Extreme Ultraviolet Imager image sets. For properly adjusted detection thresholds corresponding to the same degree of intermittency in the photosphere and corona, the dynamics of the two solar regions is described by the same occurrence probability distributions of energy release events but significantly different geometric properties. We derive a set of scaling relations reconciling the two groups of results and enabling statistical description of coronal dynamics based on photospheric observations. Our analysis suggests that multiscale intermittent dissipation in the corona at spatial scales >3 Mm is controlled by turbulent photospheric convection. Complex topology of the photospheric network makes this coupling essentially nonlocal and non-deterministic. Our results are in an agreement with the Parker's coupling scenario in which random photospheric shuffling generates marginally stable magnetic discontinuities at the coronal level, but they are also consistent with an impulsive wave heating involving multiscale Alfvénic wave packets and/or magnetohydrodynamic turbulent cascade. A back-reaction on the photosphere due to coronal magnetic reconfiguration can be a contributing factor.

Power-law Statistics of Driven Reconnection in the Magnetically Closed Corona

“…This behavior unfolds over transverse spatial scales of the order of several adjacent flux tubes and represents reconnection events on the misaligned field lines of these tubes. Our model shows results consistent with other models coupling the photospheric motions to coronal flaring statistics (e.g., Nigro et al 2004;Uritsky et al 2013;Mendoza et al 2014), but the key difference with these works is the drastically different scenario in which a complex turbulent flow is not required for multiscale flaring activity. Instead, the boundary flow applied here is quite simple, yet the resulting flaring is quite complex and multiscale, in agreement with coronal observations of power-law probability distributions.…”

Dynamic Flaring Non-Potential Fields on Quiet Sun Network Scales

“…This causes a rapid dissipation of the stored magnetic energy and initiates fast reconnection (Klimchuk 2006;Uritsky et al 2010;Pouquet et al 2011;Aschwanden 2014). This type of build-up and release is an inherent characteristic of SOC in the photospheric network (Uritsky et al 2013) and other solar atmospheric events (Uritsky et al 2007;Aschwanden & Freeland 2012;Aschwanden 2014). It is even plausable to extend the notion of self-similar non-potentiality as a possible driving force behind nanoflares.…”

“…Stochastic photospheric motions provide the asymmetric processes and helicity injections necessary to generate non-potential magnetic fields (Woodard & Chae 1999;Chesny et al 2013;Uritsky et al 2013;Wiegelmann et al 2013). Tziotziou et al (2014) subsequently determined that the free magnetic energy and helicity budgets of the QS network are sufficient to sustain finescale network structuring.…”

“…The basic photospheric dynamics leading to the formation of non-potential fields (Woodard & Chae 1999;Uritsky & Davila 2012;Uritsky et al 2013) causes the built-up helical and vortical stresses in the local turbulent environment to exceed the local threshold for instability. This causes a rapid dissipation of the stored magnetic energy and initiates fast reconnection (Klimchuk 2006;Uritsky et al 2010;Pouquet et al 2011;Aschwanden 2014).…”

“…It is known that the QS photospheric network can supply the necessary free magnetic energy for producing low-energy nonpotential magnetic fields (Woodard & Chae 1999;Zhao et al 2009;Uritsky et al 2013). The recent identification of "S-shaped" loop arcades in the supergranular network shows that the QS is able to sustain tenuous non-potential sigmoidlike structuring on small-scales (Chesny et al 2013).…”