Lucia Kleint

Prevalence of small-scale jets from the networks of the solar transition region and chromosphere

As the interface between the Sun’s photosphere and corona, the chromosphere and transition region play a key role in the formation and acceleration of the solar wind. Observations from the Interface Region Imaging Spectrograph reveal the prevalence of intermittent small-scale jets with speeds of 80 to 250 kilometers per second from the narrow bright network lanes of this interface region. These jets have lifetimes of 20 to 80 seconds and widths of ≤300 kilometers. They originate from small-scale bright regions, often preceded by footpoint brightenings and accompanied by transverse waves with amplitudes of ~20 kilometers per second. Many jets reach temperatures of at least ~105 kelvin and constitute an important element of the transition region structures. They are likely an intermittent but persistent source of mass and energy for the solar wind.

Hot explosions in the cool atmosphere of the Sun

The solar atmosphere was traditionally represented with a simple one-dimensional model. Over the past few decades, this paradigm shifted for the chromosphere and corona that constitute the outer atmosphere, which is now considered a dynamic structured envelope. Recent observations by the Interface Region Imaging Spectrograph (IRIS) reveal that it is difficult to determine what is up and down, even in the cool 6000-kelvin photosphere just above the solar surface: This region hosts pockets of hot plasma transiently heated to almost 100,000 kelvin. The energy to heat and accelerate the plasma requires a considerable fraction of the energy from flares, the largest solar disruptions. These IRIS observations not only confirm that the photosphere is more complex than conventionally thought, but also provide insight into the energy conversion in the process of magnetic reconnection.

On the prevalence of small-scale twist in the solar chromosphere and transition region

The solar chromosphere and transition region (TR) form an interface between the Sun’s surface and its hot outer atmosphere. There, most of the nonthermal energy that powers the solar atmosphere is transformed into heat, although the detailed mechanism remains elusive. High-resolution (0.33–arc second) observations with NASA’s Interface Region Imaging Spectrograph (IRIS) reveal a chromosphere and TR that are replete with twist or torsional motions on sub–arc second scales, occurring in active regions, quiet Sun regions, and coronal holes alike. We coordinated observations with the Swedish 1-meter Solar Telescope (SST) to quantify these twisting motions and their association with rapid heating to at least TR temperatures. This view of the interface region provides insight into what heats the low solar atmosphere.

The Unresolved Fine Structure Resolved: IRIS Observations of the Solar Transition Region

The heating of the outer solar atmospheric layers, i.e., the transition region and corona, to high temperatures is a long-standing problem in solar (and stellar) physics. Solutions have been hampered by an incomplete understanding of the magnetically controlled structure of these regions. The high spatial and temporal resolution observations with the Interface Region Imaging Spectrograph (IRIS) at the solar limb reveal a plethora of short, low-lying loops or loop segments at transition-region temperatures that vary rapidly, on the time scales of minutes. We argue that the existence of these loops solves a long-standing observational mystery. At the same time, based on comparison with numerical models, this detection sheds light on a critical piece of the coronal heating puzzle.The heating of the outer solar atmospheric layers, i.e., the transition region and corona, to high temperatures is a long-standing problem in solar (and stellar) physics. Solutions have been hampered by an incomplete understanding of the magnetically controlled structure of these regions. The high spatial and temporal resolution observations with the Interface Region Imaging Spectrograph (IRIS) at the solar limb reveal a plethora of short, low-lying loops or loop segments at transition-region temperatures that vary rapidly, on the time scales of minutes. We argue that the existence of these loops solves a long-standing observational mystery. At the same time, based on comparison with numerical models, this detection sheds light on a critical piece of the coronal heating puzzle.

The Fast Filament Eruption Leading to the X-flare on 2014 March 29

We investigate the sequence of events leading to the solar X1 flare SOL2014-03-29T17:48. Because of the unprecedented joint observations of an X-flare with the ground-based Dunn Solar Telescope and the spacecraft IRIS, Hinode, RHESSI, STEREO, and the Solar Dynamics Observatory, we can sample many solar layers from the photosphere to the corona. A filament eruption was observed above a region of previous flux emergence, which possibly led to a change in magnetic field configuration, causing the X-flare. This was concluded from the timing and location of the hard X-ray emission, which started to increase slightly less than a minute after the filament accelerated. The filament showed Doppler velocities of ~2–5 km s−1 at chromospheric temperatures for at least one hour before the flare occurred, mostly blueshifts, but also redshifts near its footpoints. Fifteen minutes before the flare, its chromospheric Doppler shifts increased to ~6–10 km s−1 and plasma heating could be observed before it lifted off with at least 600 km s−1 as seen in IRIS data. Compared to previous studies, this acceleration (~3–5 km s−2) is very fast, while the velocities are in the common range for coronal mass ejections. An interesting feature was a low-lying twisted second filament near the erupting filament, which did not seem to participate in the eruption. After the flare ribbons started on each of the second filaments sides, it seems to have untangled and vanished during the flare. These observations are some of the highest resolution data of an X-class flare to date and reveal some small-scale features yet to be explained.

Observations of Subarcsecond Bright Dots in the Transition Region above Sunspots with the Interface Region Imaging Spectrograph

Observations with the Interface Region Imaging Spectrograph (IRIS) have revealed numerous sub-arcsecond bright dots in the transition region above sunspots. These bright dots are seen in the 1400\AA{} and 1330\AA{} slit-jaw images. They are clearly present in all sunspots we investigated, mostly in the penumbrae, but also occasionally in some umbrae and light bridges. The bright dots in the penumbrae typically appear slightly elongated, with the two dimensions being 300--600 km and 250--450 km, respectively. The long sides of these dots are often nearly parallel to the bright filamentary structures in the penumbrae but sometimes clearly deviate from the radial direction. Their lifetimes are mostly less than one minute, although some dots last for a few minutes or even longer. Their intensities are often a few times stronger than the intensities of the surrounding environment in the slit-jaw images. About half of the bright dots show apparent movement with speeds of

HYDROGEN BALMER CONTINUUM IN SOLAR FLARES DETECTED BY THE INTERFACE REGION IMAGING SPECTROGRAPH (IRIS)

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HOMOLOGOUS HELICAL JETS: OBSERVATIONS BY IRIS, SDO, AND HINODE AND MAGNETIC MODELING WITH DATA-DRIVEN SIMULATIONS

10--40~km~s

CO-SPATIAL WHITE LIGHT AND HARD X-RAY FLARE FOOTPOINTS SEEN ABOVE THE SOLAR LIMB

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ON THE ORIGIN OF A SUNQUAKE DURING THE 2014 MARCH 29 X1 FLARE

in the radial direction. Spectra of a few bright dots were obtained and the Si~{\sc{iv}}~1402.77\AA{} line profiles in these dots are significantly broadened. The line intensity can be enhanced by one to two orders of magnitude. Some relatively bright and long-lasting dots are also observed in several passbands of the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory, and they appear to be located at the bases of loop-like structures. Many of these bright dots are likely associated with small-scale energy release events at the transition region footpoints of magnetic loops.