Context . Eruptions from coronal bright points (CBPs) are investigated in a two-part study.Aims . The present study aims to explore in full detail the morphological and dynamical evolution of these eruptions in the context of the full lifetime evolution of CBPs. A follow-up study employs data-driven modelling based on a relaxation code to reproduce the time evolution of the magnetic field of these eruptive CBPs, and provide insight into the possible causes for destabilisation and eruption.Methods . Observations of the full lifetime of CBPs in data taken with the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory in four passbands, He II 304 A, Fe IX/X 171 A, Fe XII 193 A, and Fe XVIII 94 A are investigated for the occurrence of plasma ejections, micro-flaring, mini-filament eruptions, and mini coronal-mass ejections (mini-CMEs). Data from the Helioseismic and Magnetic Imager are analysed to study the longitudinal photospheric magnetic field evolution associated with the CBPs and related eruptions.Results . First and foremost, our study shows that the majority (76%) of quiet Sun CBPs (31 out of 42 CBPs) produce at least one eruption during their lifetime. From 21 eruptions in 11 CBPs, 18 of them occur, on average, ∼17 h after the CBP formation. The average lifetime of the CBPs in AIA 193 A is ∼21 h. The time delay in the eruption occurrence coincides in each CBP with the convergence and cancellation phase of the CBP bipole evolution during which the CBPs become smaller until they fully disappear. The remaining three eruptions happen 4–6 h after the CBP formation. In 16 out of the 21 eruptions, the magnetic convergence and cancellation involve the CBP main bipoles, while in three eruptions, one of the BP magnetic fragments and a pre-existing fragment of opposite polarity converge and cancel. In one BP with two eruptions, cancellation was not observed. The CBP eruptions involve in most cases the expulsion of chromospheric material either as an elongated filamentary structure (mini-filament, MF) or a volume of cool material (cool plasma cloud, CPC), together with the CBP or higher overlying hot loops. Coronal waves were identified during three eruptions. A micro-flaring is observed beneath all erupting MFs/CPCs. Whether the destabilised MF causes the micro-flaring or the destabilisation and eruption of the MF is triggered by reconnection beneath the filament remains uncertain. In most eruptions, the cool erupting plasma either partially or fully obscures the micro-flare until the erupting material moves away from the CBP. From 21 eruptions, 11 are found to produce mini-CMEs. The dimming regions associated with the CMEs are found to be occupied by both the “dark” cool plasma and areas of weakened coronal emission caused by the depleted plasma density.Conclusions . The present study demonstrates that the small-scale loop structures in the quiet Sun, the evolution of which is determined by their magnetic footpoint motions and/or ambient field topology, evolve into an eruptive phase that triggers the ejection of cool and hot plasma in the corona.

/pdf/eruptions-from-quiet-sun-coronal-bright-points-i-1qvt28xgeu.pdf

Eruptions from quiet Sun coronal bright points - I. Observations

We report on early results from a suite of instruments for imaging and spectra we deployed to Salem, Oregon, for two minutes of totality at the August 21, 2017, total solar eclipse. Our instruments included refracting telescopes and telephoto lenses for use with CCD detectors and DSLR cameras, narrow-band filters at the wavelengths of coronal emission lines ([Fe XIV] 530.3 nm and [Fe X] 637.4 nm), and spectrographs. We also monitored the effect of the eclipse penumbra and umbra on the terrestrial atmosphere.

/pdf/images-and-spectra-of-the-2017-total-solar-eclipse-corona-16pl2bnnio.pdf

Images and Spectra of the 2017 Total Solar Eclipse Corona from our Oregon Site

Science at the Great American Eclipse

/pdf/nonthermal-motions-in-a-polar-coronal-hole-measured-with-3cayy6r1r0.pdf

Nonthermal Motions in a Polar Coronal Hole Measured with Hinode/EIS during an on-Orbit Partial Solar Eclipse on 2017 August 21

Observations of the full lifetime of CBPs in data taken with the AIA on board SDO in four passbands, He II 304 A, Fe IX/X 171 A, Fe XII 193 A, and Fe XVIII 94 A are investigated for the occurrence of plasma ejections, micro-flaring, mini-filament eruptions and mini coronal mass ejections (mini-CMEs). First and foremost, our study shows that the majority (76%) of quiet Sun CBPs (31 out of 42 CBPs) produce at least one eruption during their lifetime. From 21 eruptions in 11 CBPs, 18 occur in average ~17 hrs after the CBP formation for an average lifetime of the CBPs in AIA 193 A of ~21 hrs. This time delay in the eruption occurrence coincides in each BP with the convergence and cancellation phase of the CBP bipole evolution during which the CBPs become smaller until they fully disappear. The remaining three happen 4 - 6 hrs after the CBP formation. In sixteen out of 21 eruptions the magnetic convergence and cancellation involve the CBP main bipoles, while in three eruptions one of the BP magnetic fragments and a pre-existing fragment of opposite polarity converge and cancel. In one BP with two eruptions cancellation was not observed. The CBP eruptions involve in most cases the expulsion of chromospheric material either as elongated filamentary structure (mini-filament, MF) or a volume of cool material (cool plasma cloud, CPC), together with the CBP or higher overlying hot loops. Coronal waves were identified during three eruptions. A micro-flaring is observed beneath all erupting MFs/CPCs. It remains uncertain whether the destabilised MF causes the micro-flaring or the destabilisation and eruption of the MF is triggered by reconnection beneath the filament. In most eruptions, the cool erupting plasma obscures partially or fully the micro-flare until the erupting material moves away from the CBP. From 21 eruptions 11 are found to produce mini-CMEs.

/pdf/eruptions-from-quiet-sun-coronal-bright-points-i-38vyd5trxn.pdf

Eruptions from quiet Sun coronal bright points. I. Observations

Coronal jets, which extend from the solar surface to beyond 2 R ⊙, were observed in the polar coronal hole regions during the total solar eclipse on 2017 August 21. In a time-series of white-light images of the corona spanning 70 minutes taken with our multi-site observations of this eclipse, six jets were found as narrow structures upwardly ejected with an apparent speed of about 450 km s−1 in polar plumes. On the other hand, extreme-ultraviolet (EUV) images taken with the Atmospheric Image Assembly of the Solar Dynamics Observatory show that all of the eclipse jets were preceded by EUV jets. Conversely, all the EUV jets whose brightnesses are comparable to ordinary soft X-ray jets and that occurred in the polar regions near the eclipse period, were observed as eclipse jets. These results suggest that ordinary polar jets generally reach high altitudes and escape from the Sun as part of the solar wind.

https://iopscience.iop.org/article/10.3847/1538-4357/aac49b/pdf

Solar Coronal Jets Extending to High Altitudes Observed during the 2017 August 21 Total Eclipse

Coronal jets, which extend from the solar surface to beyond 2 $R_\odot$, were observed in the polar coronal hole regions during the total solar eclipse on 2017 August 21. In a time-series of white-light images of the corona spanning 70 minutes taken with our multi-site observations of this eclipse, six jets were found as narrow structures upwardly ejected with the apparent speed of about 450 km s$^{-1}$ in polar plumes. On the other hand, extreme-ultraviolet (EUV) images taken with the Atmospheric Image Assembly of the Solar Dynamics Observatory show that all of the eclipse jets were preceded by EUV jets. Conversely, all the EUV jets whose brightness is comparable to ordinary soft X-ray jets and which occurred in the polar regions near the eclipse period were observed as eclipse jets. These results suggest that ordinary polar jets generally reach high altitudes and escape from the Sun as part of the solar wind.

Toshiyuki Toi

Papers

Solar Coronal Jets Extending to High Altitudes Observed during the 2017 August 21 Total Eclipse

Solar Coronal Jets Extending to High Altitudes Observed During the 2017 August 21 Total Eclipse