Multithermal Jet Formation Triggered by Flux Emergence

Magnetic flux emergence has been accepted to be essential for many solar activities. Unprecedented high-resolution observations have provided us with unique opportunities to investigate flux emergence and its associated dynamics in different solar atmospheric layers, such as the triggering of spicules, jets and flares. As it is hard to study all facets of magnetic flux emergence through observations, numerical magnetohydrodynamic (MHD) simulations have been employed to mimic the emergence of non-twisted or twisted flux tubes into the solar atmosphere and their corresponding eruptions. Here we present a 2.5D MHD simulation on coronal rain with emerging flux on one side of the coronal loops, to study the influence of the emerging flux on the chromospheric and coronal plasma.

As shown in the following movie, condensations form continuously in the loops, at first demonstrating a zig-zag structure due to sympathetic runaway cooling on nested loops. Starting from this coronal rain-filled arcade system at 144.6 min, we put an emerging flux at the left footpoint. As the emerging flux changes the pressure in the loops, the cool condensations move preferentially to the other side of the loop, instead of splitting into small blobs and dropping to both footpoints. After the emerging flux enters the corona, a current sheet is created on top of the emerging flux, and there is a dense loop located at the current sheet (between times 209.0 - 224.7 min), which is believed to be an arched filament. As the dipole is emerging upwards, multiple magnetic islands form in the current sheet due to the tearing instability. Each island encloses dense and cool plasma originally in the emerging loop. Soon after formation, the small islands merge into a large island, then the resulting large island is ejected horizontally out of the current sheet. At the same time, the plasma near the current sheet is heated to a high temperature. The ejection of the cool plasma forms a cold surge with a temperature of 6000 K, and the nearby corresponding heating is manifested as a hot X-ray jet, whose temperature is more than 4 MK. More details about the formation process and the evolution of the multithermal jet can be found here.