Observations of Instability-driven Nanojets in Coronal Loops

Abstract

The recent discovery of nanojets by Antolin et al. represents magnetic reconnection in a braided field, thus clearly identifying reconnection-driven nanoflares. Due to their small scale (500 km in width, 1500 km in length) and short timescales (<15 s), it is unclear how pervasive nanojets are in the solar corona. In this paper, we present Interface Region Imaging Spectrograph and Solar Dynamics Observatory 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, KHI and Rayleigh–Taylor instability (RTI) are likely to be the drivers. However, we find that 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.

Solar coronal heating from small-scale magnetic braids

“…In these cases, energy release is likely at smaller spatial scales, which then leads to the formation of blob-like features and rapidly evolving EUV emission from these loops. All these features are also consistent with the interpretation of the recently discovered nanojets (Antolin et al 2021;Sukarmadji et al 2022). While providing evidence for intermittent coronal heating from the relaxation of braided loops, our study identified the operation of both gentle and impulsive modes of energy release through reconnection in the solar corona.…”

“…The authors suggested that nanojets are produced as a result of magnetic reconnection and subsequent relaxation of braided coronal loops. Furthermore, Sukarmadji et al (2022), who observed additional cases of nanojets in magnetic features hosting cooler plasma including coronal rain, suggested that nanojets are a general result of magnetic reconnection and that not only braiding, but also Kelvin-Helmholtz and Rayleigh-Taylor instabilities can cause them. An open question in nanojets is whether they occur in coronal loops that do not show a signature of cool plasma or coronal rain.…”

Hi-C 2.1 Observations of Reconnection Nanojets

“…From the plots in the left and middle panels it can be seen that these parameters are positively correlated for the outward jets, but negatively correlated for inward jets. We found a similar negative correlation of 45% and 49% was found for speed-length and speed-lifetime for the inward jets listed by Sukarmadji et al (2022). It can be seen in the right panel of the Figure 6 that there is a good correlation of ≈75% between the length and widths of the outward jets.…”

“…However, for the observed sample of inward jets, a negligible correlation was found between the two parameters. A similar, however unreported, strong correlation of ≈82% was found for such jets listed by Sukarmadji et al (2022).…”

“…Their analysis explained that the inward moving jets are more frequent and energetic than those moving outwards (away from the curvature of coronal loops). In a recent study it was found that the Kelvin-Helmholtz and Rayleigh-Taylor instabilities are the drivers for the reconnection in coronal loops leading to nanojets (Sukarmadji et al 2022). In this paper, we present the observational study of outward and inward nanojets using Hi-C data complemented by the multiwavelength observations from the AIA.…”