A new study has investigated the formation mechanism of spicules in the solar chromosphere and found that these spicules are triggered by microfilament eruptions.

Led by PhD candidate DONG Qifan and Prof. YAN Xiaoli from the Fuxian Lake Solar Observatory of the Yunnan Observatories (YNAO) of the Chinese Academy of Sciences (CAS), the study was published in The Astrophysical Journal Letters on July 6.

Solar spicules are ubiquitous, dynamic, small-scale jets in the chromosphere, appearing as plasma protrusions ejected from the magnetic network. Understanding their formation mechanism is important for clarifying how mass and energy are transported from the lower solar atmosphere into the corona.

Using high-resolution observational data from the 4 m Daniel K. Inouye Solar Telescope (DKIST) — specifically, high spatio-temporal resolution Hα observations of the quiet-Sun disk center obtained on August 29, 2023 by the Visible Broadband Imager on board DKIST — the researchers analyzed 30 spicule events associated with microfilament eruptions.

They detected that microfilaments had an average length of only 0.93 ± 0.46 Mm, with the minimum length being a mere 0.17 Mm. This scale is notably smaller than the minifilaments reported in previous study.

The team also identified two distinct spicule morphologies: individual spicules associated with smaller microfilaments, and enhanced spicular activities associated with larger microfilaments. Furthermore, some spicules exhibit apparent twisting motions, which are similar to the kinematic characteristics of coronal jets. The total energy released by a single microfilament eruption is estimated at approximately 0.15 × 10²⁴ erg. Extrapolated to the entire solar chromosphere, the number of such eruptions occurring at any given moment is about 2.4 × 10⁴.

According to the researchers, the findings provide empirical support for the model in which spicules are driven by microfilament eruptions. The study reveals a correlation between the spatial scale of microfilaments and the morphology of the resulting spicules, and further confirms that solar eruptive activities across different spatial scales are governed by common physical mechanisms.

They added that the results also validate the high-resolution capabilities of DKIST in observing fine chromospheric structures, and lay a reliable foundation for defining the scientific objectives of China's Giant Solar Telescope.

Evolution of five microfilament eruptions. The locations of the microfilaments are marked by purple ellipses, and the spicules produced by the eruptions are denoted by cyan dotted lines. In panel (a2), the red contour represents +12 G and the green contour represents −12 G. (Image by DONG Qifan)