Abstract
Abstract Oscillatory reconnection (a relaxation mechanism with periodic changes in connectivity) has been proposed as a potential physical mechanism underpinning several periodic phenomena in the solar atmosphere, including, but not limited to, quasi-periodic pulsations (QPPs). Despite its importance, however, the mechanism has never been studied within a hot, coronal plasma. We investigate oscillatory reconnection in a one million Kelvin plasma by solving the fully-compressive, resistive MHD equations for a 2D magnetic X-point under coronal conditions using the PLUTO code. We report on the resulting oscillatory reconnection including its periodicity and decay rate. We observe a more complicated oscillating profile for the current density compared to that found for a cold plasma, due to mode-conversion at the equipartition layer. We also consider, for the first time, the effect of adding anisotropic thermal conduction to the oscillatory reconnection mechanism, and we find this simplifies the spectrum of the oscillation profile and increases the decay rate. Crucially, the addition of thermal conduction does not prevent the oscillatory reconnection mechanism from manifesting. Finally, we reveal a relationship between the equilibrium magnetic field strength, decay rate, and period of oscillatory reconnection, which opens the tantalising possibility of utilizing oscillatory reconnection as a seismological tool.
Highlights
Null points are magnetic field singularities at which the magnetic field strength and Alfven speed are zero
Our first goal in this study is to explore oscillatory reconnection in the case of a hot coronal plasma; we will first focus on the setup with a resolution of 24012 grid points for an initial hot plasma of 1 MK and in the absence of thermal conduction
This paper presents an investigation of the phenomenon of oscillatory reconnection in the neighborhood of a 2D magnetic X-point for hot coronal plasma
Summary
Null points are magnetic field singularities at which the magnetic field strength and Alfven speed are zero. Numerical simulations have shown that 3D null points to act as sources of Alfven waves (e.g. Lynch et al 2014; Cranmer 2018), coronal jets in the form of propagating nonlinear Alfven waves (Karpen et al 2017) as well as other sources of fast and slow (and Alfven) waves (Thurgood et al 2017), when these 3D null points are subjected to various wavebased driving motions Apart from their interaction with the ubiquitous waves in the solar atmosphere (e.g. Nakariakov & Verwichte 2005; De Pontieu et al 2007; Okamoto et al 2007; Tomczyk et al 2007; McIntosh et al 2011), null points play a key role in highly energetic phenomena such as solar flares (e.g. Shibata & Magara 2011). An initially cold (β = 0) plasma setup was considered, but the solution included the full compressible resistive MHD equations and allowed for plasma heating to take place This mechanism has been studied for a 3D null point in Thurgood et al (2017), where the by-product of oscillatory reconnection was the generation of freely propagating MHD waves, escaping the vicinity of the null point.
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