Above-the-Loop-Top Oscillation and Quasi-Periodic Coronal Wave Generation in Solar Flares

Abstract

Unlike all previous models for QPFs, our model includes essential physics for solar flares, such as magnetic reconnection, heat conduction, and chromospheric evaporation. We revealed that QPFs can be spontaneously excited by the abovethe-loop-top oscillation. It was found that this oscillation is controlled by the backflow of the reconnection outflow. The new model revealed that flare loops and the above-the-loop-top region are full of shocks and waves, which is different from the previous expectations based on a standard flare model and previous simulations. In this paper, we will show the QPF generation process based on our new picture of flare loops and will briefly discuss a possible relationship between QPFs and QPPs. Our findings will change the current view of solar flares to a new view in which they are a very dynamic phenomenon with full of shocks and waves.

Stellar flare oscillations: evidence for oscillatory reconnection and evolution of MHD modes

“…Therefore, these waves are found to be the fast waves of which the period is determined by the Alfvén speed profile around the X-point forming the resonator, generating the multiperiodic QPP around the peak of the flare (Craig & McClymont 1991). This is similar to the work by Takasao & Shibata (2016), who showed QPPs could be spontaneously excited by above-the-loop-top oscillations controlled by the back-flow of the reconnection outflow. As a variation to the above, the detected periodicities in the flares may be best described as due to an avalanche of periodic bursts that occur at time intervals that correspond to the detected periods.…”

A Quasi-periodic Fast-propagating Magnetosonic Wave Associated with the Eruption of a Magnetic Flux Rope

“…Previous studies have revealed that there are several nonlinear processes in magnetic reconnection that can cause quasiperiodic pulsation in flares. For example, the periodic interaction of the outward moving plasmoids in the current sheet with the ambient magnetic fields (e.g., Kliem et al 2000;Ni et al 2012;Yang et al 2015;Takasao & Shibata 2016), the presence of shear flows in the current layer (Ofman & Sui 2006), and the mechanism of oscillatory magnetic reconnection (e.g., McLaughlin et al 2012a,b;Thurgood et al 2017). In the present event, the periodic radio bursts during the rising phase of the flare could be regarded as the evidence of the periodic releasing of magnetic energy that are possibly caused by the periodic processes in the magnetic reconnection.…”

“…For example, Yang et al (2015) showed that QFP wave fronts can be excited by the collision of outward moving plasmoids in reconnection current sheet with the ambient magnetic fields. Takasao & Shibata (2016) found that QFP waves can be spontaneously excited by the backflow of reconnection outflow above the region of flaring loops. In addition, oscillatory magnetic reconnection can also naturally produces quasi-periodic pulsations (QPPs) and QFP wave (e.g., McLaughlin et al 2012a,b;Thurgood et al 2017).…”

Observations of the Formation, Development, and Structure of a Current Sheet in an Eruptive Solar Flare

“…One question we investigated was whether there was any evidence of a thermal halo surrounding the sheet, which has been predicted by several authors (Yokoyama & Shibata 1997, 2001Seaton & Forbes 2009;Takasao & Shibata 2016) to form as a result of thermal conduction out of the current sheet and into the surrounding plasma. In simulations that include strong thermal conduction, the conduction substantially increases the density in the current sheet, because it cools the plasma substantially.…”