Dynamics of granules and intergranular lanes at the base of Hα jets

¹ Shandong Key Laboratory of Space Environment and Exploration Technology, Institute of Space Sciences, Shandong University, Shandong, China
² National Key Laboratory of Deep Space Exploration, School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China
³ CAS Center for Excellence in Comparative Planetology/CAS Key Laboratory of Geospace Environment/Mengcheng National Geophysical Observatory, University of Science and Technology of China, Hefei 230026, China
⁴ Yunnan Observatories, Chinese Academy of Sciences, 396 Yangfangwang, Guandu District, Kunming 650216, PR China
⁵ Yunnan Key Laboratory of Solar Physics and Space Science, Kunming 650216, PR China
⁶ Center for Integrated Research on Space Science, Astronomy, and Physics, Institute of Frontier and Interdisciplinary Science, Shandong University, Qingdao 266237, China

^⋆⋆ Corresponding author: xld@sdu.edu.cn

Received: 4 July 2025
Accepted: 26 September 2025

Abstract

Aims. Using observations taken by the New Vacuum Solar Telescope at the Hα ±0.8 Å passbands and TiO 7058 Å passband, we investigate the photospheric dynamics at the bases of 85 Hα jets.

Methods. By applying the Fourier local correlation tracking algorithm on the TiO data, we find that the horizontal velocities increase significantly at the bases of an Hα jet during its appearance, and the statistics for these Hα jets at their bases gives an average of 1.50 km s⁻¹ with a sigma of 0.64 km s⁻¹, which is about 25% greater than the typical value of the granules. We find that the intergranular lanes at the bases of Hα jets are expanding, with an expansion rate up to 300%. With the automated swirl detection algorithm, we find that the occurrence rate of photospheric swirls in the region abundant in Hα jets is 2.0 × 10⁻⁵ Mm⁻² s⁻¹, significantly larger than 1.4 × 10⁻⁵ Mm⁻² s⁻¹ obtained in the rest of the studied field of view.

Results. In the region abundant in Hα jets, 61.2% of swirls are expanding. By contrast, in the rest of the field of view, only 52.3% of swirls are expanding. Although a definitive one-to-one relationship among Hα jets, dynamics of granules and intergranules, and swirls remains challenging, a case study shows that the appearance of an Hα jet is apparently associated with the occurrence and rotation of a swirl and the expansion of the intergranular lane, while the disappearance of the jet is accompanied by the contraction of the intergranular lane.

Conclusions. Based on our statistical analyses, we suggest that higher horizontal velocity sweeps more small magnetic elements into network lanes, leading to stronger magnetic activity and consequently the expansion of intergranular lanes and swirls, which in turn further drives Hα jets in the chromosphere.