Dynamics of subarcsecond bright dots in the transition region above sunspot and their relation to penumbral micro-jets

Abstract

Recent high-resolution observations reveal that subarcsecond bright dots (BDs) with sub-minute lifetimes appears ubiquitously in the transition region (TR) above sunspot penumbra. The presence of penumbral micro-jets (PMJs) in the chromosphere have also been reported earlier. It was proposed that both the PMJs and BDs are formed due to magnetic reconnection process and may play an important role in heating of the penumbra. Using simultaneous observation of the chromosphere from the Solar Optical Telescope (SOT) aboard Hinode and the TR from the Interface Region Imaging Spectrograph (IRIS), we study the dynamics of BDs and their relation with PMJs. We find two types of BDs, one which is related to PMJs and the others which do not show any visible dynamics in the SOT Ca II H images. From a statistical analysis we show that these two types have different properties. The BDs which are related to PMJs always appear at the top of the PMJs, the vast majority of which show inward motion and originate before the generation of the PMJs. These results may indicate that the reconnection occurs at the lower coronal/TR height and initiates PMJs at the chromosphere. This formation mechanism is in contrast with the currently believed formation of PMJs by reconnection in the (upper) photosphere between differently inclined fields.

6 pages, 5 Figures, 6 movies. The Astrophysical Journal Letters (accepted). Movies will be available online in the ApJL

References in corpus (4)

• The Solar Optical Telescope for the Hinode Mission: An Overview
• Observations of Subarcsecond Bright Dots in the Transition Region above Sunspots with the Interface Region Imaging Spectrograph
• Detection of supersonic downflows and associated heating events in the transition region above sunspots
• Multi-wavelength Study of Transition Region Penumbral Subarcsecond Bright Dots Using IRIS and NST

Cited by in corpus (7)

• The formation of small-scale umbral brightenings in sunspot atmospheres
• Signatures of ubiquitous magnetic reconnection in the deep atmosphere of sunspot penumbrae
• Sunspot penumbral filaments intruding into a light bridge and the resultant reconnection jets
• Penumbral micro-jets at high spatial and temporal resolution
• The dark side of penumbral microjets: Observations in Hα
• A multi-diagnostic spectral analysis of penumbral microjets
• SolO/EUI Observations of Ubiquitous Fine-scale Bright Dots in an Emerging Flux Region: Comparison with a Bifrost MHD Simulation