The dark side of penumbral microjets: Observations in Hα
arXiv:1905.01245 · doi:10.3847/1538-4357/ab125b
Abstract
We present data of 10 penumbral microjets (PMJs) observed in Hα, Ca II 8542 Å, and Fe I 6302 Åline pair with the Swedish 1 m Solar Telescope (SST) with CRISP and Ca II K with SST/CHROMIS in active region NOAA 12599 on the 12th October 2016 at μ=0.68. All four Stokes parameters of the Ca II 8542 Åand Fe I 6302 Ålines were observed and a series of test pixels was inverted using the Stockholm inversion code. Our analysis revealed for the first time that PMJs are visible in Hα, where they appear as dark features with average line-of-sight (LOS) upflows of 1.1\pm0.6 km/s, matching the LOS velocities from the inversions. Based on the Hαobservations we extend the previous average length and lifetime of PMJs to 2815\pm530 km and 163\pm25 s, respectively. The plane-of-sky (POS) velocities of our PMJs of up to 17 km/s tend to give increased velocities with distance travelled. Furthermore, two of our PMJs with significant Stokes V signal indicate that the PMJs possess an increased LOS magnetic field of up to 100 G compared to the local pre-/post- PMJ magnetic field, which propagates as quickly as the PMJs' POS velocities. Finally, we present evidence that PMJs display an on average 1 minute gradual precursory brightening that only manifests itself in the cores of the Ca II lines. We conclude that PMJs are not ordinary jets but likely are manifestations of heat fronts that propagate at the local Alfven velocity.
References in corpus (15)
- CRISP Spectropolarimetric Imaging of Penumbral Fine Structure
- Prevalence of Small-scale Jets from the Networks of the Solar Transition Region and Chromosphere
- Dynamic Fibrils are driven by Magnetoacoustic Shocks
- High Resolution Observations and Modeling of Dynamic Fibrils
- CRISPRED: A data pipeline for the CRISP imaging spectropolarimeter
- On the generation of solar spicules and Alfvénic waves
- Non-LTE inversions of the Mg II h&k and UV triplet lines
- Statistical properties of the Disk Counterparts of Type II Spicules from simultaneous observations of RBEs in Ca II 8542 and Hα
- Stokes imaging polarimetry using image restoration at the Swedish 1-m Solar Telescope
- Heating signatures in the disk counterparts of solar spicules in IRIS observations
- Evidence of convective rolls in a sunspot penumbra
- What causes the high apparent speeds in chromospheric and transition region spicules on the Sun?
- The properties of penumbral microjets inclination
- Dynamics of subarcsecond bright dots in the transition region above sunspot and their relation to penumbral micro-jets
- Three-dimensional magnetic structure of a sunspot: comparison of the photosphere and upper chromosphere