Most of the fiercest eruptions on the Sun originate in active regions. Understanding how the field reshapes in this process is therefore key in unraveling what sets the stage for flares and coronal mass ejections. A post written by Dr. Gregal Vissers, from the Institute for Solar Physics (Stockholm, Sweden).
Magnetic field emergence in an active region leading to several Ellerman bomb and microflare-like brightenings. The observations were taken at the Swedish 1-m Solar Telescope on La Palma by Drs. Jaime de la Cruz Rodríguez and Jorrit Leenaarts (ISP/SU).
Most of the fiercest eruptions on the Sun originate in active regions. They are ultimately driven by the release of stresses that have been building up in the local magnetic field as the regions emerge and evolve. Understanding how the field reshapes in this process is therefore key in unraveling what sets the stage for flares and coronal mass ejections.
While rising through the lower atmosphere, the active region magnetic field interacts with the ambient field. This leads to bursty energy releases and vigorous heating that can be observed in the near-infrared and ultraviolet parts of the solar spectrum as small-scale, elongated brightenings sparkling throughout the active region. The most prominent examples of such intense brightenings were discovered already over one hundred years ago by Ferdinand Ellerman at Mt. Wilson Observatory (California, USA). He called them ‘hydrogen bombs on the Sun’. Later, they were renamed ‘Ellerman bombs’ in his honour.
The movie shows a partial view of an active region on 19 September 2019 during magnetic field emergence leading to several Ellerman bombs and microflare-like brightenings. They present a high level of fine structure, at the limit of what the Swedish 1-m Solar Telescope (SST) on La Palma (Spain) can resolve.
Indeed, over the last decade SST observations like this one have revealed flame- and blob-like fine structure at the scale of 100-150 km in such Ellerman bombs, providing important insights on the physical mechanism that drives them and how it operates. In addition, with the help from space-based instruments, such as NASA’s Interface Region Imaging Spectrograph (IRIS) that observes in the ultraviolet, as well as numerical simulations, we now know that they are part of a family of similarly-driven, but height-dependent energy releases during magnetic field evolution, with so-called UV bursts and microflares as increasingly higher-energy siblings.
With the European Solar Telescope we will gain an unprecedented high-resolution view of these phenomena, both morphologically and in terms of their magnetic field environment. This will help deepen our understanding of their role in active regions, in particular their impact on the magnetic field evolution and the heating of the atmosphere on large scales.