Browsing by Author "Wuelser, Jean-Pierre"

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Evidence of nonthermal particles in coronal loops heated impulsively by nanoflares
(2014-10) Testa, Paola; De Pontieu, Bart; Allred, J.; Carlsson, Mats; Reale, F.; Daw, A.; Hansteen, Viggo H.; Martinez-Sykora, J.; Liu, W.; DeLuca, E.E.; Golub, Leon; McKillop, Sean; Reeves, Kathy K.; Saar, Steven; Tian, Hui; Lemen, James; Title, Alan M.; Boerner, P.; Hurlburt, Neal E.; Tarbell, Ted D.; Wuelser, Jean-Pierre; Kleint, Lucia; Kankelborg, Charles; Jaeggli, Sarah
The physical processes causing energy exchange between the Sun’s hot corona and its cool lower atmosphere remain poorly understood. The chromosphere and transition region (TR) form an interface region between the surface and the corona that is highly sensitive to the coronal heating mechanism. High-resolution observations with the Interface Region Imaging Spectrograph (IRIS) reveal rapid variability (~20 to 60 seconds) of intensity and velocity on small spatial scales (≲500 kilometers) at the footpoints of hot and dynamic coronal loops. The observations are consistent with numerical simulations of heating by beams of nonthermal electrons, which are generated in small impulsive (≲30 seconds) heating events called “coronal nanoflares.” The accelerated electrons deposit a sizable fraction of their energy (≲1025 erg) in the chromosphere and TR. Our analysis provides tight constraints on the properties of such electron beams and new diagnostics for their presence in the nonflaring corona.
Hot Explosions in the Cool Atmoshere of the Sun
(2014-10) Peter, H.; Tian, Hui; Curdt, W.; Schmidt, D.; Innes, D.; De Pontieu, Bart; Lemen, James; Title, Alan M.; Boerner, P.; Hurlburt, Neal E.; Tarbell, Ted D.; Wuelser, Jean-Pierre; Martinez-Sykora, J.; Kleint, Lucia; Golub, Leon; McKillop, Sean; Reeves, Kathy K.; Saar, Steven; Testa, Paola; Kankelborg, Charles; Jaeggli, Sarah; Carlsson, Mats; Hansteen, Viggo H.
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.
Internetwork Chromospheric Bright Grains Observed with IRIS and SST
(2015-04) Martínez-Sykora, Juan; van der Voort, Luc Rouppe; Carlsson, Mats; De Pontieu, Bart; Pereira, Tiago M. D.; Boerner, P.; Hurlburt, Neal E.; Kleint, Lucia; Lemen, James; Tarbell, Ted D.; Title, Alan M.; Wuelser, Jean-Pierre; Hansteen, Viggo H.; Golub, Leon; McKillop, Sean; Reeves, Kathy K.; Saar, Steven; Testa, Paola; Tian, Hui; Jaeggli, Sarah; Kankelborg, Charles
The Interface Region Imaging Spectrograph (IRIS) reveals small-scale rapid brightenings in the form of bright grains all over coronal holes and the quiet Sun. These bright grains are seen with the IRIS 1330, 1400, and 2796 Ã… slit-jaw filters. We combine coordinated observations with IRIS and from the ground with the Swedish 1 m Solar Telescope (SST) which allows us to have chromospheric (Ca ii 8542 Ã…, Ca ii H 3968 Ã…, HÎ±, and Mg ii k 2796 Ã…) and transition region (C ii 1334 Ã…, Si iv 1403 Ã…) spectral imaging, and single-wavelength Stokes maps in Fe i 6302 Ã… at high spatial ($0\\buildrel{\\prime\\prime}\\over{.} 33$), temporal, and spectral resolution. We conclude that the IRIS slit-jaw grains are the counterpart of so-called acoustic grains, i.e., resulting from chromospheric acoustic waves in a non-magnetic environment. We compare slit-jaw images (SJIs) with spectra from the IRIS spectrograph. We conclude that the grain intensity in the 2796 Ã… slit-jaw filter comes from both the Mg ii k core and wings. The signal in the C ii and Si iv lines is too weak to explain the presence of grains in the 1300 and 1400 Ã… SJIs and we conclude that the grain signal in these passbands comes mostly from the continuum. Although weak, the characteristic shock signatures of acoustic grains can often be detected in IRIS C ii spectra. For some grains, a spectral signature can be found in IRIS Si iv. This suggests that upward propagating acoustic waves sometimes reach all the way up to the transition region.
On the prevalence of small-scale twist in the solar chromosphere and transition region
(De Pontieu, B., L. Rouppe van der Voort, S. W. McIntosh, T. M. D. Pereira, M. Carlsson, V. Hansteen, H. Skogsrud, et al. “On the Prevalence of Small-Scale Twist in the Solar Chromosphere and Transition Region.” Science 346, no. 6207 (October 16, 2014): 1255732–1255732. doi:10.1126/science.1255732., 2014-10) De Pontieu, Bart; Rouppe van der Voort, L.; McIntosh, Scott W.; Pereira, Tiago M. D.; Carlsson, Mats; Hansteen, Viggo H.; Skogsrud, H.; Lemen, James; Title, Alan M.; Boerner, P.; Hurlburt, Neal E.; Tarbell, Ted D.; Wuelser, Jean-Pierre; DeLuca, E.E.; Golub, Leon; McKillop, Sean; Reeves, Kathy K.; Saar, Steven; Testa, Paola; Tian, Hui; Kankelborg, Charles; Jaeggli, Sarah; Kleint, Lucia; Martinez-Sykora, J.
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.
Prevalence of small-scale jets from the networks of the solar transition region and chromosphere
(2014-10) Tian, Hui; DeLuca, E.E.; Cranmer, S.R.; De Pontieu, Bart; Peter, H.; Martinez-Sykora, J.; Golub, Leon; McKillop, Sean; Reeves, Kathy K.; Miralles, M.P.; McCauley, P.; Saar, Steven; Testa, Paola; Weber, Mark A.; Murphy, N.; Lemen, James; Title, Alan M.; Boerner, P.; Hurlburt, Neal E.; Tarbell, Ted D.; Wuelser, Jean-Pierre; Kleint, Lucia; Kankelborg, Charles; Jaeggli, Sarah; Carlsson, Mats; Hansteen, Viggo H.; McIntosh, Scott W.
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.
The Unresolved Fine Structure Resolved: IRIS Observations of the Solar Transition Region
(2014-10) Hansteen, Viggo H.; De Pontieu, B.; Carlsson, Mats; Lemen, James; Title, Alan M.; Boerner, P.; Hurlburt, Neal E.; Tarbell, Ted D.; Wuelser, Jean-Pierre; Pereira, Tiago M. D.; De Luca, E.E.; Golub, Leon; McKillop, Sean; Reeves, Kathy K.; Saar, Steven; Testa, Paola; Tian, Hui; Kankelborg, Charles; Jaeggli, Sarah; Kleint, Lucia; Martínez-Sykora, J.
The heating of the outer solar atmospheric layers, i.e., the transition region and corona, to high temperatures is a longstanding 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, lowlying loops or loop segments at transitionregion temperatures that vary rapidly, on the time scales of minutes. We argue that the existence of these loops solves a longstanding 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.