Item

Abstract

Light bridges (LBs) are bright lanes that divide an umbra into multiple parts in some sunspots. Persistent oscillatory bright fronts at a temperature of similar to 10(5) K are commonly observed above LBs in the 1400/1330 A passbands of the Interface Region Imaging Spectrograph (IRIS). Based on IRIS observations, we report small-scale bright blobs ejected from the oscillating bright front above a light bridge. Some of these blobs reveal a clear acceleration, whereas the others do not. The average speed of these blobs projected onto the plane of sky is 71.7 14.7 km s(-1), with an initial acceleration of 1.9 1.3 km s(-2). These blobs normally reach a projected distance of 3-7 Mm from their origin sites. They have an average projected area of 0.57 0.37 Mm(2). The blobs were also detected in multiple extreme-ultraviolet passbands of the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory, but not in the H alpha images taken by the New Vacuum Solar Telescope. The typical temperature and electron density of these blobs are around cm(-3), respectively. The estimated kinetic and thermal energies are on the order of10(22.8) erg and 10(23.3) erg, respectively. These small-scale blobs appear to show three different types of formation processes. They are possibly triggered by induced reconnection or release of enhanced magnetic tension due to interaction of adjacent shocks, local magnetic reconnection between emerging magnetic bipoles on the light bridge and surrounding unipolar umbral fields, and plasma acceleration or instability caused by upward shocks, respectively.