Chromospheric Bubbles in Solar Flares

TL;DR

This study uses radiative hydrodynamic simulations to investigate chromospheric bubbles in solar flares, revealing their formation, spectral signatures, and driving mechanisms in the solar atmosphere.

Contribution

It is the first detailed simulation-based analysis of chromospheric bubbles, identifying their spectral features and formation conditions in solar flare models.

Findings

Chromospheric bubbles appear as high-velocity components in Balmer lines.

Bubbles are visible in Ca II 8542A line wings.

Bubbles are driven upward by shock-induced wave fronts.

Abstract

We analyze a grid of radiative hydrodynamic simulations of solar flares to study the energy balance and response of the atmosphere to nonthermal electron beam heating. The appearance of chromospheric bubbles is one of the most notable features that we find in the simulations. These pockets of chromospheric plasma get trapped between the transition region and the lower atmosphere as it is superheated by the particle beam. The chromospheric bubbles are seen in the synthetic spectra, appearing as an additional component to Balmer line profiles with high Doppler velocities as high as 200 km/s. Their signatures are also visible in the wings of Ca II 8542A line profiles. These bubbles of chromospheric plasma are driven upward by a wave front that is induced by the shock of energy deposition, and require a specific heating rate and atmospheric location to manifest.