Surges and Si IV bursts in the solar atmosphere. Understanding IRIS and SST observations through RMHD experiments

TL;DR

This study investigates the relationship between solar surges and Si IV emission lines using coordinated IRIS and SST observations, supported by RMHD simulations, revealing new insights into plasma dynamics during magnetic flux emergence.

Contribution

It provides the first observational evidence of Si IV emission within surges and explains these features through advanced RMHD modeling of magnetic flux emergence.

Findings

Si IV emission is brighter and broader within surges.

Brightest Si IV patches are near surge footpoints.

RMHD simulations reproduce observed spectral features.

Abstract

Surges often appear as a result of the emergence of magnetized plasma from the solar interior. Traditionally, they are observed in chromospheric lines such as H$\alpha$ 6563 \AA and Ca II 8542 \AA. However, whether there is a response to the surge appearance and evolution in the Si IV lines or, in fact, in many other transition region lines has not been studied. In this paper we analyze a simultaneous episode of an H$\alpha$ surge and a Si IV burst that occurred on 2016 September 03 in active region AR12585. To that end, we use coordinated observations from the Interface Region Imaging Spectrograph (IRIS) and the Swedish 1-m Solar Telescope (SST). For the first time, we report emission of Si IV within the surge, finding profiles that are brighter and broader than the average. Furthermore, the brightest Si IV patches within the domain of the surge are located mainly near its footpoints. To understand the relation between the surges and the emission in transition region lines like Si IV, we have carried out 2.5D radiative MHD (RMHD) experiments of magnetic flux emergence episodes using the Bifrost code and including the non-equilibrium ionization of silicon. Through spectral synthesis we explain several features of the observations. We show that the presence of Si IV emission patches within the surge, their location near the surge footpoints and various observed spectral features are a natural consequence of the emergence of magnetized plasma from the interior to the atmosphere and the ensuing reconnection processes.