Observations of instability-driven nanojets

TL;DR

This study presents IRIS and SDO observations of nanojets in the solar corona, revealing their association with magnetic reconnection driven by instabilities like KHI and RTI, and highlighting their widespread occurrence.

Contribution

It provides the first detailed observational evidence of nanojets across different coronal structures and identifies the dynamic instabilities responsible for their formation.

Findings

Nanojets are accompanied by nanoflare-like intensity bursts.

Nanojets have velocities of 150-250 km/s and occur transversely to magnetic field lines.

Kelvin-Helmholtz and Rayleigh-Taylor instabilities are identified as drivers.

Abstract

The recent discovery of nanojets by Antolin et al. (2021) represents magnetic reconnection in a braided field, thus clearly identifying the reconnection-driven nanoflares. Due to their small scale (500 km in widths, 1500 km in lengths) and short timescales ($<$ 15 s), it is unclear how pervasive nanojets are in the solar corona. In this paper, we present IRIS and SDO observations of nanojets found in multiple coronal structures, namely in a coronal loop powered by a blowout jet, and in two other coronal loops with coronal rain. In agreement with previous findings, we observe that nanojets are accompanied by small nanoflare-like intensity bursts in the (E)UV, have velocities of 150-250 km s$^{-1}$ and occur transversely to the field line of origin, which is sometimes observed to split. However, we find a variety of nanojet directions in the plane transverse to the loop axis. These nanojets are found to have kinetic and thermal energies within the nanoflare range, and often occur in clusters. In the blowout jet case study, the Kelvin-Helmholtz instability (KHI) is directly identified as the reconnection driver. For the other two loops, we find that both, the KHI and the Rayleigh-Taylor instability (RTI) are likely to be the drivers. However, we find that the KHI and RTI are each more likely in one of the other two cases. These observations of nanojets in a variety of structures and environments support nanojets being a general result of reconnection, that are driven here by dynamic instabilities.