ALBERT

Description: Alfven waves have been invoked as a possible mechanism for the heating of the Sun's outer atmosphere, or corona, to millions of degrees and for the acceleration of the solar wind to hundreds of kilometers per second. However, Alfven waves of sufficient strength have not been unambiguously observed in the solar atmosphere. We used images of high temporal and spatial resolution obtained with the Solar Optical Telescope onboard the Japanese Hinode satellite to reveal that the chromosphere, the region sandwiched between the solar surface and the corona, is permeated by Alfven waves with strong amplitudes on the order of 10 to 25 kilometers per second and periods of 100 to 500 seconds. Estimates of the energy flux carried by these waves and comparisons with advanced radiative magnetohydrodynamic simulations indicate that such Alfven waves are energetic enough to accelerate the solar wind and possibly to heat the quiet corona.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉De Pontieu, B -- McIntosh, S W -- Carlsson, M -- Hansteen, V H -- Tarbell, T D -- Schrijver, C J -- Title, A M -- Shine, R A -- Tsuneta, S -- Katsukawa, Y -- Ichimoto, K -- Suematsu, Y -- Shimizu, T -- Nagata, S -- New York, N.Y. -- Science. 2007 Dec 7;318(5856):1574-7.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Lockheed Martin Solar and Astrophysics Laboratory, 3251 Hanover Street, Organization ADBS, Building 252, Palo Alto, CA 94304, USA. bdp@lmsal.com〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/18063784" target="_blank"〉PubMed〈/a〉

Description: Energy is required to heat the outer solar atmosphere to millions of degrees (refs 1, 2) and to accelerate the solar wind to hundreds of kilometres per second (refs 2-6). Alfven waves (travelling oscillations of ions and magnetic field) have been invoked as a possible mechanism to transport magneto-convective energy upwards along the Sun's magnetic field lines into the corona. Previous observations of Alfvenic waves in the corona revealed amplitudes far too small (0.5 km s(-1)) to supply the energy flux (100-200 W m(-2)) required to drive the fast solar wind or balance the radiative losses of the quiet corona. Here we report observations of the transition region (between the chromosphere and the corona) and of the corona that reveal how Alfvenic motions permeate the dynamic and finely structured outer solar atmosphere. The ubiquitous outward-propagating Alfvenic motions observed have amplitudes of the order of 20 km s(-1) and periods of the order of 100-500 s throughout the quiescent atmosphere (compatible with recent investigations), and are energetic enough to accelerate the fast solar wind and heat the quiet corona.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉McIntosh, Scott W -- De Pontieu, Bart -- Carlsson, Mats -- Hansteen, Viggo -- Boerner, Paul -- Goossens, Marcel -- England -- Nature. 2011 Jul 27;475(7357):477-80. doi: 10.1038/nature10235.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉High Altitude Observatory, National Center for Atmospheric Research, PO Box 3000, Boulder, Colorado 80307, USA. mscott@ucar.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21796206" target="_blank"〉PubMed〈/a〉

Description: It is now apparent that there are at least two heating mechanisms in the Sun's outer atmosphere, or corona. Wave heating may be the prevalent mechanism in quiet solar periods and may contribute to heating the corona to 1,500,000 K (refs 1-3). The active corona needs additional heating to reach 2,000,000-4,000,000 K; this heat has been theoretically proposed to come from the reconnection and unravelling of magnetic 'braids'. Evidence favouring that process has been inferred, but has not been generally accepted because observations are sparse and, in general, the braided magnetic strands that are thought to have an angular width of about 0.2 arc seconds have not been resolved. Fine-scale braiding has been seen in the chromosphere but not, until now, in the corona. Here we report observations, at a resolution of 0.2 arc seconds, of magnetic braids in a coronal active region that are reconnecting, relaxing and dissipating sufficient energy to heat the structures to about 4,000,000 K. Although our 5-minute observations cannot unambiguously identify the field reconnection and subsequent relaxation as the dominant heating mechanism throughout active regions, the energy available from the observed field relaxation in our example is ample for the observed heating.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Cirtain, J W -- Golub, L -- Winebarger, A R -- De Pontieu, B -- Kobayashi, K -- Moore, R L -- Walsh, R W -- Korreck, K E -- Weber, M -- McCauley, P -- Title, A -- Kuzin, S -- DeForest, C E -- England -- Nature. 2013 Jan 24;493(7433):501-3. doi: 10.1038/nature11772.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Marshall Space Flight Center, NASA, Mail Code ZP13, MSFC, Alabama 36812, USA. jonathan.w.cirtain@nasa.gov〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/23344359" target="_blank"〉PubMed〈/a〉

Description: The Sun's outer atmosphere, or corona, is heated to millions of degrees, considerably hotter than its surface or photosphere. Explanations for this enigma typically invoke the deposition in the corona of nonthermal energy generated by magnetoconvection. However, the coronal heating mechanism remains unknown. We used observations from the Solar Dynamics Observatory and the Hinode solar physics mission to reveal a ubiquitous coronal mass supply in which chromospheric plasma in fountainlike jets or spicules is accelerated upward into the corona, with much of the plasma heated to temperatures between ~0.02 and 0.1 million kelvin (MK) and a small but sufficient fraction to temperatures above 1 MK. These observations provide constraints on the coronal heating mechanism(s) and highlight the importance of the interface region between photosphere and corona.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉De Pontieu, B -- McIntosh, S W -- Carlsson, M -- Hansteen, V H -- Tarbell, T D -- Boerner, P -- Martinez-Sykora, J -- Schrijver, C J -- Title, A M -- New York, N.Y. -- Science. 2011 Jan 7;331(6013):55-8. doi: 10.1126/science.1197738.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Lockheed Martin Solar and Astrophysics Laboratory, 3251 Hanover Street, Organization ADBS, Building 252, Palo Alto, CA 94304, USA. bdp@lmsal.com〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21212351" target="_blank"〉PubMed〈/a〉

Description: 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.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Peter, H -- Tian, H -- Curdt, W -- Schmit, D -- Innes, D -- De Pontieu, B -- Lemen, J -- Title, A -- Boerner, P -- Hurlburt, N -- Tarbell, T D -- Wuelser, J P -- Martinez-Sykora, Juan -- Kleint, L -- Golub, L -- McKillop, S -- Reeves, K K -- Saar, S -- Testa, P -- Kankelborg, C -- Jaeggli, S -- Carlsson, M -- Hansteen, V -- New York, N.Y. -- Science. 2014 Oct 17;346(6207):1255726. doi: 10.1126/science.1255726. Epub 2014 Oct 16.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Max Planck Institute for Solar System Research, 37077 Gottingen, Germany. peter@mps.mpg.de. ; Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA. ; Max Planck Institute for Solar System Research, 37077 Gottingen, Germany. ; Lockheed Martin Solar and Astrophysics Laboratory (LMSAL), 3251 Hanover Street, Building 252, Palo Alto, CA 94304, USA. Institute of Theoretical Astrophysics, University of Oslo, Post Office Box 1029, Blindern, NO-0315 Oslo, Norway. ; Lockheed Martin Solar and Astrophysics Laboratory (LMSAL), 3251 Hanover Street, Building 252, Palo Alto, CA 94304, USA. ; Lockheed Martin Solar and Astrophysics Laboratory (LMSAL), 3251 Hanover Street, Building 252, Palo Alto, CA 94304, USA. Bay Area Environmental Research Institute, 596 1st Street West, Sonoma, CA 95476, USA. ; Lockheed Martin Solar and Astrophysics Laboratory (LMSAL), 3251 Hanover Street, Building 252, Palo Alto, CA 94304, USA. Bay Area Environmental Research Institute, 596 1st Street West, Sonoma, CA 95476, USA. NASA Ames Research Center, Moffett Field, CA 94305, USA. ; Department of Physics, Montana State University, Bozeman, Post Office Box 173840, Bozeman, MT 59717, USA. ; Institute of Theoretical Astrophysics, University of Oslo, Post Office Box 1029, Blindern, NO-0315 Oslo, Norway.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25324397" target="_blank"〉PubMed〈/a〉

Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉De Pontieu, Bart -- Title, Alan -- Carlsson, Mats -- New York, N.Y. -- Science. 2014 Oct 17;346(6207):315. doi: 10.1126/science.346.6207.315.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Lockheed Martin Solar & Astrophysics Laboratory, Palo Alto, CA, USA. ; Institute of Theoretical Astrophysics, University of Oslo, Norway.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25324380" target="_blank"〉PubMed〈/a〉

Description: 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.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉De Pontieu, B -- van der Voort, L Rouppe -- McIntosh, S W -- Pereira, T M D -- Carlsson, M -- Hansteen, V -- Skogsrud, H -- Lemen, J -- Title, A -- Boerner, P -- Hurlburt, N -- Tarbell, T D -- Wuelser, J P -- De Luca, E E -- Golub, L -- McKillop, S -- Reeves, K -- Saar, S -- Testa, P -- Tian, H -- Kankelborg, C -- Jaeggli, S -- Kleint, L -- Martinez-Sykora, J -- New York, N.Y. -- Science. 2014 Oct 17;346(6207):1255732. doi: 10.1126/science.1255732. Epub 2014 Oct 16.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Lockheed Martin Solar and Astrophysics Laboratory (LMSAL), 3251 Hanover Street, Organization A021S, Building 252, Palo Alto, CA 94304, USA. Institute of Theoretical Astrophysics, University of Oslo, Post Office Box 1029, Blindern, N-0315 Oslo, Norway. bdp@lmsal.com. ; Institute of Theoretical Astrophysics, University of Oslo, Post Office Box 1029, Blindern, N-0315 Oslo, Norway. ; High Altitude Observatory, National Center for Atmospheric Research, Post Office Box 3000, Boulder, CO 80307, USA. ; Lockheed Martin Solar and Astrophysics Laboratory (LMSAL), 3251 Hanover Street, Organization A021S, Building 252, Palo Alto, CA 94304, USA. ; Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA. ; Department of Physics, Montana State University, Bozeman, Post Office Box 173840, Bozeman, MT 59717, USA. ; Bay Area Environmental Research Institute, 596 1st Street West, Sonoma, CA 95476, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25324398" target="_blank"〉PubMed〈/a〉

Description: 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.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Hansteen, V -- De Pontieu, B -- Carlsson, M -- Lemen, J -- Title, A -- Boerner, P -- Hurlburt, N -- Tarbell, T D -- Wuelser, J P -- Pereira, T M D -- De Luca, E E -- Golub, L -- McKillop, S -- Reeves, K -- Saar, S -- Testa, P -- Tian, H -- Kankelborg, C -- Jaeggli, S -- Kleint, L -- Martinez-Sykora, J -- New York, N.Y. -- Science. 2014 Oct 17;346(6207):1255757. doi: 10.1126/science.1255757.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Institute of Theoretical Astrophysics, University of Oslo, Post Office Box 1029, Blindern, NO-0315, Oslo, Norway. viggoh@astro.uio.no. ; Institute of Theoretical Astrophysics, University of Oslo, Post Office Box 1029, Blindern, NO-0315, Oslo, Norway. Lockheed Martin Solar and Astrophysics Laboratory, 3251 Hanover Street, Org. A021S, Building 252, Palo Alto, CA 94304, USA. ; Institute of Theoretical Astrophysics, University of Oslo, Post Office Box 1029, Blindern, NO-0315, Oslo, Norway. ; Lockheed Martin Solar and Astrophysics Laboratory, 3251 Hanover Street, Org. A021S, Building 252, Palo Alto, CA 94304, USA. ; Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA. ; Department of Physics, Montana State University, Bozeman, Post Office Box 173840, Bozeman, MT 59717, USA. ; Bay Area Environmental Research Institute, 596 1st Street West, Sonoma, CA 95476, USA. Lockheed Martin Solar and Astrophysics Laboratory, 3251 Hanover Street, Org. A021S, Building 252, Palo Alto, CA 94304, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25324399" target="_blank"〉PubMed〈/a〉

Description: 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 ( less, similar500 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 ( less, similar30 seconds) heating events called "coronal nanoflares." The accelerated electrons deposit a sizable fraction of their energy ( less, similar10(25) 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.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Testa, P -- De Pontieu, B -- Allred, J -- Carlsson, M -- Reale, F -- Daw, A -- Hansteen, V -- Martinez-Sykora, J -- Liu, W -- DeLuca, E E -- Golub, L -- McKillop, S -- Reeves, K -- Saar, S -- Tian, H -- Lemen, J -- Title, A -- Boerner, P -- Hurlburt, N -- Tarbell, T D -- Wuelser, J P -- Kleint, L -- Kankelborg, C -- Jaeggli, S -- New York, N.Y. -- Science. 2014 Oct 17;346(6207):1255724. doi: 10.1126/science.1255724.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA. ptesta@cfa.harvard.edu. ; Lockheed Martin Solar and Astrophysics Laboratory, 3251 Hanover Street, Org. A021S, Building 252, Palo Alto, CA 94304, USA. Institute of Theoretical Astrophysics, University of Oslo, Post Office Box 1029, Blindern, N-0315, Oslo, Norway. ; NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA. ; Institute of Theoretical Astrophysics, University of Oslo, Post Office Box 1029, Blindern, N-0315, Oslo, Norway. ; Dipartimento di Fisica e Chimica, Universita' di Palermo and Istituto Nazionale di Astrofisica (INAF)/Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy. ; Bay Area Environmental Research Institute 596 1st Street West, Sonoma, CA 95476, USA. ; Lockheed Martin Solar and Astrophysics Laboratory, 3251 Hanover Street, Org. A021S, Building 252, Palo Alto, CA 94304, USA. W. W. Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA 94305, USA. ; Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA. ; Lockheed Martin Solar and Astrophysics Laboratory, 3251 Hanover Street, Org. A021S, Building 252, Palo Alto, CA 94304, USA. ; Lockheed Martin Solar and Astrophysics Laboratory, 3251 Hanover Street, Org. A021S, Building 252, Palo Alto, CA 94304, USA. Bay Area Environmental Research Institute 596 1st Street West, Sonoma, CA 95476, USA. ; Department of Physics, Montana State University, Bozeman, Post Office Box 173840, Bozeman, MT 59717, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25324396" target="_blank"〉PubMed〈/a〉