Numerical Simulation of Solar Microflares in a Canopy-Type Magnetic Configuration

TL;DR

This study uses 2.5D MHD simulations to explore how magnetic reconnection in a canopy-type magnetic field configuration causes solar microflares, revealing differences based on their coronal or chromospheric origins and key parameters influencing their features.

Contribution

It introduces a novel simulation approach for microflares in a canopy magnetic configuration, highlighting the impact of flux emergence and reconnection location on microflare characteristics.

Findings

Coronal microflares are larger and hotter than chromospheric ones.

Coronal microflares produce hot and cold jets similar to observed phenomena.

Emerging flux strength influences reconnection height and microflare features.

Abstract

Microflares are small activities in solar low atmosphere, some are in the low corona, and others in the chromosphere. Observations show that some of the microflares are triggered by magnetic reconnection between emerging flux and a pre-existing background magnetic field. We perform 2.5D compressible resistive MHD simulations of magnetic reconnection with gravity considered. The background magnetic field is a canopy-type configuration which is rooted at the boundary of the solar supergranule. By changing the bottom boundary conditions in the simulation, new magnetic flux emerges up at the center of the supergranule and reconnects with the canopy-type magnetic field. We successfully simulate the coronal and chromospheric microflares, whose current sheets are located at the corona and the chromosphere, respectively. The microflare of coronal origin has a bigger size and a higher temperature enhancement than that of chromospheric origin. In the microflares of coronal origin, we also found a hot jet ($\sim$$1.8 \times 10^6$ K), which is probably related to the observational EUV/SXR jets, and a cold jet ($\sim$$10^4$ K), which is similar to the observational H$\alpha$/Ca surges, whereas there is only an H$\alpha$/Ca bright point in the microflares of chromospheric origin. The study of parameter dependence shows that the size and strength of the emerging magnetic flux are the key parameters which determine the height of the reconnection location, and further determine the different observational features of the microflares.