Plasmoids and Resulting Blobs due to the Interaction of Magnetoacoustic Waves with a 2.5D Magnetic Null Point

Abstract

We performed a numerical study for interpreting observations of plasma blobs occurring in the solar corona. Considering all of the previous studies and the presence of magnetic null points together with propagating MHD waves in the solar corona, we guessed that the interaction of fast magnetoacoustic waves with null points could give rise to blobs under coronal conditions. The outcome of these interactions contributes to coronal jets and flares which directly affects us on Earth. The propagation of magnetoacoustic waves in the vicinity of a magnetic null point contributes to the high current density accumulation at the small scale around the magnetic null point which has significant magnetic gradients. When nonlinearity gets dominant, the variation of current density could result in instabilities and thus anomalous resistivity. Moreover, it is demonstrated that plasmoids with eruption events take place in the solar corona without considering the transition region. In our numerical simulation results, it is interesting that plasma blobs manifest themselves in many parameters including current density, temperature, plasma density, flows and magnetic fields simultaneously, and consistent with the generation of plasmoids. In this work, it is found that plasmoid instability is the reason of the plasma blobs and tiny blobs are produced by the tearing instability occurring in thin current sheets.

The Independence of Oscillatory Reconnection Periodicity from the Initial Pulse

“…Using stronger pulses, or driving the null point collapse by moving the magnetic field footpoints, will potentially lead to longer current sheets with higher values of J z current density. However, as was the case with Sabri et al (2020) for a null point collapse in hot plasma due to an external pulse, we would then face the prospect of initiating the plasmoid instability in this high, overly long sheet. In Thurgood et al (2018a) it was shown that high aspect ratio current sheets can be subjected to nonlinear tearing in coronal conditions.…”

“…In Thurgood et al (2018a) it was shown that high aspect ratio current sheets can be subjected to nonlinear tearing in coronal conditions. The formation of the overly long current sheet, accompanied by an emerging O-point magnetic field configuration, and the resulting tearing of the current sheet in Sabri et al (2020) blocked the evolution of oscillatory reconnection after the first two reversals in magnetic connectivity.…”

“…Null points have also been shown to behave as resonant cavities (Santamaria & Van Doorsselaere 2018), generating waves at frequencies depending on the plasma conditions, such as highfrequency wave trains (∼80 mHz) (Santamaria et al 2016(Santamaria et al , 2017. In Sabri et al (2020), the interaction of fast magnetoacoustic waves with a 2.5D null point produced plasmoids due to the tearing mode instability, while a plethora of numerical studies have shown null points can act as sources of coronal jets, slow, fast and Alfvén waves (e.g., Lynch et al 2014;Karpen et al 2017;Thurgood et al 2017;Cranmer 2018) when subjected to various wave-based driving motions. All the above results reveal, among other things, the importance of these wave-null point interactions for coronal seismology (Uchida 1970;Roberts et al 1984).…”

Oscillatory Reconnection of a 2D X-point in a hot coronal plasma

“…Nishizuka et al 2008;He et al 2009) and compared directly with observations. The interaction of fast magnetoacoustic waves with a 2.5D null point has been shown to produce plasmoids due to the tearing mode instability in a numerical study (Sabri et al 2020). Numerical simulations have shown that 3D null points to act as sources of Alfvén waves (e.g.…”

Oscillatory reconnection as a plasma diagnostic in the solar corona

“…Oscillatory reconnection has also been studied for a realistic solar atmosphere, as a result of flux rope emergence (Murray et al 2009;McLaughlin et al 2012b), while other studies revolved around the effects of resistivity, initial perturbation amplitude, and the length of the initial current sheet on the period of the reconnection process (McLaughlin et al 2012a;Thurgood et al 2018aThurgood et al ,b, 2019. Stewart et al (2022) reported the onset of oscillatory reconnection and the generation of waves through the coalescence of two cylindrical flux ropes, while Sabri et al (2020) reported the development of the plasmoid instability in a magnetic O-point and the resulting manifestation of plasmoid-mediated quasi-oscillatory magnetic reconnection. The results of McLaughlin et al (2009) have recently been expanded for a hot coronal plasma in Karampelas et al (2022a), studying the relation between the oscillation period and the strength of the background magnetic field, while also taking into account the effects of anisotropic thermal conduction.…”