Fan-shaped jets above the light bridge of a sunspot driven by reconnection

Abstract

We report on a fan-shaped set of high-speed jets above a strongly magnetized light bridge (LB) of a sunspot observed in the H$\alpha$ line. We study the origin, dynamics and thermal properties of the jets using high-resolution imaging spectroscopy in H$\alpha$ from the Swedish 1-m Solar Telescope and data from the Solar Dynamics Observatory and Hinode. The H$\alpha$ jets have lengths of 7-38 Mm, are impulsively accelerated to a speed of $\sim 100$ km/s close to photospheric footpoints in the LB, and exhibit a constant deceleration consistent with solar effective gravity. They are predominantly launched from one edge of the light bridge, and their footpoints appear bright in the H$\alpha$ wings. AIA data indicates elongated brightenings that are nearly co-spatial with the H$\alpha$ jets. We interpret them as jets of at least transition region temperatures. The magnetic field in the light bridge has a strength of $0.8-2$ kG and it is nearly horizontal. All jet properties are consistent with magnetic reconnection as the driver.