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Item 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.Item 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.Item 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.Item 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, SarahThe 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.