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

## TL;DR

This study investigates the dynamics of subarcsecond bright dots in the transition region above sunspots and their connection to penumbral micro-jets, revealing two types of BDs with different properties and suggesting a reconnection-based formation mechanism.

## Contribution

It provides the first detailed analysis of the relationship between bright dots and penumbral micro-jets using simultaneous IRIS and Hinode observations, proposing a new formation mechanism involving reconnection at lower coronal heights.

## Key findings

- BDs related to PMJs appear at the top of PMJs and show inward motion.
- Most BDs related to PMJs originate before the PMJs.
- Reconnection likely occurs at lower coronal/TR height, initiating PMJs.

## 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.