Ellerman Bombs at high resolution: II. Visibility, triggering and effect on upper atmosphere

TL;DR

This study uses high-resolution imaging spectroscopy to analyze Ellerman bombs, revealing their occurrence in the photosphere, their magnetic triggers, and their limited impact on the upper atmosphere, thus confirming their photospheric reconnection nature.

Contribution

First detailed high-resolution multi-wavelength analysis of Ellerman bombs, linking their occurrence to magnetic flux cancelation and confirming their photospheric origin.

Findings

Ellerman bombs occur at sites of magnetic flux cancelation.

They are visible in multiple spectral lines with differing morphologies.

No clear impact on the overlying transition region and corona.

Abstract

We use high-resolution imaging spectroscopy with the Swedish 1-m Solar Telescope (SST) to study the transient brightenings of the wings of the Balmer Halpha line in emerging active regions that are called Ellerman bombs. Simultaneous sampling of Ca II 854.2 nm with the SST confirms that most Ellerman bombs occur also in the wings of this line, but with markedly different morphology. Simultaneous images from the Solar Dynamics Observatory (SDO) show that Ellerman bombs are also detectable in the photospheric 170 nm continuum, again with differing morphology. They are also observable in 160 nm SDO images, but with much contamination from C IV emission in transition-region features. Simultaneous SST spectropolarimetry in Fe I 630.1 nm shows that Ellerman bombs occur at sites of strong-field magnetic flux cancelation between small bipolar strong-field patches that rapidly move together over the solar surface. Simultaneous SDO images in He II 30.4 nm, Fe IX 17.1 nm, and Fe XIV 21.1 nm show no clear effect of the Ellerman bombs on the overlying transition region and corona. These results strengthen our earlier suggestion, based on Halpha morphology alone, that the Ellerman bomb phenomenon is a purely photospheric reconnection phenomenon.