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Sample records for abordaje coronal estudio

  1. CORONAL CELLS

    SciTech Connect

    Sheeley, N. R. Jr.; Warren, H. P. E-mail: harry.warren@nrl.navy.mil

    2012-04-10

    We have recently noticed cellular features in Fe XII 193 A images of the 1.2 MK corona. They occur in regions bounded by a coronal hole and a filament channel, and are centered on flux elements of the photospheric magnetic network. Like their neighboring coronal holes, these regions have minority-polarity flux that is {approx}0.1-0.3 times their flux of majority polarity. Consequently, the minority-polarity flux is 'grabbed' by the majority-polarity flux to form low-lying loops, and the remainder of the network flux escapes to connect with its opposite-polarity counterpart in distant active regions of the Sun. As these regions are carried toward the limb by solar rotation, the cells disappear and are replaced by linear plumes projecting toward the limb. In simultaneous views from the Solar Terrestrial Relations Observatory and Solar Dynamics Observatory spacecraft, these plumes project in opposite directions, extending away from the coronal hole in one view and toward the hole in the other view, suggesting that they are sky-plane projections of the same radial structures. We conclude that these regions are composed of closely spaced radial plumes, extending upward like candles on a birthday cake and visible as cells when seen from above. We suppose that a coronal hole has this same discrete, cellular magnetic structure, but that it is not seen until the encroachment of opposite-polarity flux closes part or all of the hole.

  2. Coronal and Prominence Plasmas

    NASA Technical Reports Server (NTRS)

    Poland, Arthur I. (Editor)

    1986-01-01

    Various aspects of solar prominences and the solar corona are discussed. The formation of prominences, prominence diagnostics and structure, prominence dissappearance, large scale coronal structure, coronal diagnostics, small scale coronal structure, and non-equilibrium/coronal heating are among the topics covered.

  3. Can coronal hole spicules reach coronal temperatures?

    NASA Astrophysics Data System (ADS)

    Madjarska, M. S.; Vanninathan, K.; Doyle, J. G.

    2011-08-01

    Aims: The present study aims to provide observational evidence of whether coronal hole spicules reach coronal temperatures. Methods: We combine multi-instrument co-observations obtained with the SUMER/SoHO and with the EIS/SOT/XRT/Hinode. Results: The analysed three large spicules were found to be comprised of numerous thin spicules that rise, rotate, and descend simultaneously forming a bush-like feature. Their rotation resembles the untwisting of a large flux rope. They show velocities ranging from 50 to 250 kms-1. We clearly associated the red- and blue-shifted emissions in transition region lines not only with rotating but also with rising and descending plasmas. Our main result is that these spicules although very large and dynamic, are not present in the spectral lines formed at temperatures above 300 000 K. Conclusions: In this paper we present the analysis of three Ca ii H large spicules that are composed of numerous dynamic thin spicules but appear as macrospicules in lower resolution EUV images. We found no coronal counterpart of these and smaller spicules. We believe that the identification of phenomena that have very different origins as macrospicules is due to the interpretation of the transition region emission, and especially the He ii emission, wherein both chromospheric large spicules and coronal X-ray jets are present. We suggest that the recent observation of spicules in the coronal AIA/SDO 171 Å and 211 Å channels probably comes from the existence of transition region emission there. Movie is available in electronic form at http://www.aanda.org

  4. Episodic coronal heating

    NASA Astrophysics Data System (ADS)

    Sturrock, P. A.; Dixon, W. W.; Klimchuk, J. A.; Antiochos, S. K.

    1990-06-01

    A study is made of the observational consequences of the hypothesis that there is no steady coronal heating, the solar corona instead being heated episodically, such that each short burst of heating is followed by a long period of radiative cooling. The form of the resulting contribution to the differential emission measure (DEM), and to a convenient related function (the differential energy flux, DEF) is calculated. Observational data for the quiet solar atmosphere indicate that the upper branch of the DEM, corresponding to temperatures above 100,000 K, can be interpreted in terms of episodic energy injection at coronal temperatures.

  5. Episodic coronal heating

    NASA Technical Reports Server (NTRS)

    Sturrock, P. A.; Dixon, W. W.; Klimchuk, J. A.; Antiochos, S. K.

    1990-01-01

    A study is made of the observational consequences of the hypothesis that there is no steady coronal heating, the solar corona instead being heated episodically, such that each short burst of heating is followed by a long period of radiative cooling. The form of the resulting contribution to the differential emission measure (DEM), and to a convenient related function (the differential energy flux, DEF) is calculated. Observational data for the quiet solar atmosphere indicate that the upper branch of the DEM, corresponding to temperatures above 100,000 K, can be interpreted in terms of episodic energy injection at coronal temperatures.

  6. Global Coronal Waves

    NASA Astrophysics Data System (ADS)

    Chen, P. F.

    2016-02-01

    After the Solar and Heliospheric Observatory (SOHO) was launched in 1996, the aboard Extreme Ultraviolet Imaging Telescope (EIT) observed a global coronal wave phenomenon, which was initially named ``EIT wave" after the telescope. The bright fronts are immediately followed by expanding dimmings. It has been shown that the brightenings and dimmings are mainly due to plasma density increase and depletion, respectively. Such a spectacular phenomenon sparked long-lasting interest and debates. The debates were concentrated on two topics, one is about the driving source, and the other is about the nature of this wavelike phenomenon. The controversies are most probably because there may exist two types of large-scale coronal waves that were not well resolved before the Solar Dynamics Observatory (SDO) was launched: one is a piston-driven shock wave straddling over the erupting coronal mass ejection (CME), and the other is an apparently propagating front, which may correspond to the CME frontal loop. Such a two-wave paradigm was proposed more than 13 years ago, and now is being recognized by more and more colleagues. In this paper, we review how various controversies can be resolved in the two-wave framework and how important it is to have two different names for the two types of coronal waves.

  7. Solar wind and coronal structure

    NASA Technical Reports Server (NTRS)

    Withbroe, G. L.

    1983-01-01

    Spectroscopic diagnostic techniques used to determine the coronal source region of the solar wind, and results of preliminary applications are examined. The topics reviewed are magnetic fields, coronal mass ejections, coronal holes, flow velocities, coronal temperatures, fine spatial structure, and future observational programs. The physical mechanisms responsible for plasma heating, solar-wind acceleration, the transport of mass momentum and energy, and the spatial differentiation of chemical abundances are also discussed. Among the data presented are Skylab's white-light coronagraph photograph of a coronal transient, X-ray photographs of the corona, and spectroheliograms showing bright points overlying polar plumes, and macrospicules.

  8. Coronal mass ejections and coronal structures

    NASA Technical Reports Server (NTRS)

    Hildner, E.; Bassi, J.; Bougeret, J. L.; Duncan, R. A.; Gary, D. E.; Gergely, T. E.; Harrison, R. A.; Howard, R. A.; Illing, R. M. E.; Jackson, B. V.

    1986-01-01

    Research on coronal mass ejections (CMF) took a variety of forms, both observational and theoretical. On the observational side there were: case studies of individual events, in which it was attempted to provide the most complete descriptions possible, using correlative observations in diverse wavelengths; statistical studies of the properties CMEs and their associated activity; observations which may tell us about the initiation of mass ejections; interplanetary observations of associated shocks and energetic particles even observations of CMEs traversing interplanetary space; and the beautiful synoptic charts which show to what degree mass ejections affect the background corona and how rapidly (if at all) the corona recovers its pre-disturbance form. These efforts are described in capsule form with an emphasis on presenting pictures, graphs, and tables so that the reader can form a personal appreciation of the work and its results.

  9. Chromospheres of Coronal Stars

    NASA Technical Reports Server (NTRS)

    Linsky, Jeffrey L.; Wood, Brian E.

    1996-01-01

    We summarize the main results obtained from the analysis of ultraviolet emission line profiles of coronal late-type stars observed with the Goddard High Resolution Spectrograph (GHRS) on the Hubble Space Telescope. The excellent GHRS spectra provide new information on magnetohydrodynamic phenomena in the chromospheres and transition regions of these stars. One exciting new result is the discovery of broad components in the transition region lines of active stars that we believe provide evidence for microflare heating in these stars.

  10. Coronal mass ejections

    SciTech Connect

    Steinolfson, R.S.

    1990-01-01

    Coronal mass ejections (CMEs) are now recognized as an important component of the large-scale evolution of the solar corona. Some representative observations of CMEs are reviewed with emphasis on more recent results. Recent observations and theory are examined as they relate to the following aspects of CMEs: (1) the role of waves in determining the white-light signature; and (2) the mechanism by which the CME is driven (or launched) into the corona.

  11. CORONAL RAIN AS A MARKER FOR CORONAL HEATING MECHANISMS

    SciTech Connect

    Antolin, P.; Vissers, G.; Shibata, K. E-mail: g.j.m.vissers@astro.uio.n

    2010-06-10

    Reported observations in H{alpha}, Ca II H, and K or other chromospheric lines of coronal rain trace back to the days of the Skylab mission. Corresponding to cool and dense plasma, coronal rain is often observed falling down along coronal loops in active regions. A physical explanation for this spectacular phenomenon has been put forward thanks to numerical simulations of loops with footpoint-concentrated heating, a heating scenario in which cool condensations naturally form in the corona. This effect has been termed 'catastrophic cooling' and is the predominant explanation for coronal rain. In this work, we further investigate the link between this phenomenon and the heating mechanisms acting in the corona. We start by analyzing observations of coronal rain at the limb in the Ca II H line performed by the Hinode satellite, and derive interesting statistical properties concerning the dynamics. We then compare the observations with 1.5-dimensional MHD simulations of loops being heated by small-scale discrete events concentrated toward the footpoints (that could come, for instance, from magnetic reconnection events), and by Alfven waves generated at the photospheric level. Both our observation and simulation results suggest that coronal rain is a far more common phenomenon than previously thought. Also, we show that the structure and dynamics of condensations are far more sensitive to the internal pressure changes in loops than to gravity. Furthermore, it is found that if a loop is predominantly heated from Alfven waves, coronal rain is inhibited due to the characteristic uniform heating they produce. Hence, coronal rain may not only point to the spatial distribution of the heating in coronal loops but also to the agent of the heating itself. We thus propose coronal rain as a marker for coronal heating mechanisms.

  12. Modeling Coronal Jets with FLUX

    NASA Astrophysics Data System (ADS)

    Rachmeler, L. A.; Pariat, E.; Antiochos, S. K.; Deforest, C. E.

    2008-05-01

    We report on a comparative study of coronal jet formation with and without reconnection using two different simulation strategies. Coronal jets are features on the solar surface that appear to have some properties in common with coronal mass ejections, but are less energetic, massive, and broad. Magnetic free energy is built up over time and then suddenly released, which accelerates plasma outward in the form of a coronal jet. We compare results from the ARMS adaptive mesh and FLUX reconnection-less codes to study the role of reconnection in this system. This is the first direct comparison between FLUX and a numerical model with a 3D spatial grid.

  13. Coronal and chromospheric physics

    NASA Technical Reports Server (NTRS)

    Jefferies, J. T.; Landman, D. A.; Orrall, F. Q.

    1983-01-01

    Achievements and completed results are discussed for investigations covering solar activity during the solar maximum mission and the solar maximum year; other studies of solar activity and variability; infrared and submillimeter photometry; solar-related atomic physics; coronal and transition region studies; prominence research; chromospheric research in quiet and active regions; solar dynamics; eclipse studies; and polarimetry and magnetic field measurements. Contributions were also made in defining the photometric filterograph instrument for the solar optical telescope, designing the combined filter spectrograph, and in expressing the scientific aims and implementation of the solar corona diagnostic mission.

  14. Coronal Magnetic Field Models

    NASA Astrophysics Data System (ADS)

    Wiegelmann, Thomas; Petrie, Gordon J. D.; Riley, Pete

    2015-07-01

    Coronal magnetic field models use photospheric field measurements as boundary condition to model the solar corona. We review in this paper the most common model assumptions, starting from MHD-models, magnetohydrostatics, force-free and finally potential field models. Each model in this list is somewhat less complex than the previous one and makes more restrictive assumptions by neglecting physical effects. The magnetohydrostatic approach neglects time-dependent phenomena and plasma flows, the force-free approach neglects additionally the gradient of the plasma pressure and the gravity force. This leads to the assumption of a vanishing Lorentz force and electric currents are parallel (or anti-parallel) to the magnetic field lines. Finally, the potential field approach neglects also these currents. We outline the main assumptions, benefits and limitations of these models both from a theoretical (how realistic are the models?) and a practical viewpoint (which computer resources to we need?). Finally we address the important problem of noisy and inconsistent photospheric boundary conditions and the possibility of using chromospheric and coronal observations to improve the models.

  15. Active region coronal evolution

    NASA Technical Reports Server (NTRS)

    Golub, L.; Noci, G.; Poletto, G.; Vaiana, G. S.

    1982-01-01

    Scaling relations between coronal base pressure and longitudinal photospheric magnetic field strength are tested for the case of a single active region observed for five solar rotations from Skylab. The evolution of measureable quantities, such as coronal thermal energy content, total longitudinal photospheric magnetic flux, region scale size, and peak energy density, is traced throughout the five rotations observed. The theoretically derived scaling law of Golub et al. (1980) is found to provide an acceptable fit to the data throughout the entire evolutionary history of the region from an age of about 3 days to the fully evolved state in which the mature active region merges into the general large-scale structure of the quiet corona. An alternative scaling law obtained by including the results of Galeev et al. (1981), however, is found to provide a somewhat better fit to the data. The study is seen as providing additional justification for the belief that magnetic field-related heating is the operative mechanism in the solar corona.

  16. The Geometric Spreading of Coronal Plumes and Coronal Holes

    NASA Technical Reports Server (NTRS)

    Suess, S. T.; Poletto, G.; Wang, A. - H.; Wu, S. T.; Cuseri, I.

    1997-01-01

    The geometric spreading in plumes and in the interplume region in coronal holes is calculated, using analytic and numerical theoretical models, between 1.0 and 5.0 solar radius. We apply two scale approximation that permits the rapid local spreading at the base of plumes to be evaluated separately from the global spreading imposed by coronal hole geometry. We show that fl can be computed from a potential field model and fg can be computed from global magnetohydrodynamic simulations of coronal structure. The approximations are valid when the plasma beta is small with respect to unity and for a plume separation small with respect to a solar radius.

  17. The Coronal Solar Magnetism Observatory

    NASA Astrophysics Data System (ADS)

    Tomczyk, S.; Landi, E.; Zhang, J.; Lin, H.; DeLuca, E. E.

    2015-12-01

    Measurements of coronal and chromospheric magnetic fields are arguably the most important observables required for advances in our understanding of the processes responsible for coronal heating, coronal dynamics and the generation of space weather that affects communications, GPS systems, space flight, and power transmission. The Coronal Solar Magnetism Observatory (COSMO) is a proposed ground-based suite of instruments designed for routine study of coronal and chromospheric magnetic fields and their environment, and to understand the formation of coronal mass ejections (CME) and their relation to other forms of solar activity. This new facility will be operated by the High Altitude Observatory of the National Center for Atmospheric Research (HAO/NCAR) with partners at the University of Michigan, the University of Hawaii and George Mason University in support of the solar and heliospheric community. It will replace the current NCAR Mauna Loa Solar Observatory (http://mlso.hao.ucar.edu). COSMO will enhance the value of existing and new observatories on the ground and in space by providing unique and crucial observations of the global coronal and chromospheric magnetic field and its evolution. The design and current status of the COSMO will be reviewed.

  18. The coronal fricative problem

    PubMed Central

    Dinnsen, Daniel A.; Dow, Michael C.; Gierut, Judith A.; Morrisette, Michele L.; Green, Christopher R.

    2013-01-01

    This paper examines a range of predicted versus attested error patterns involving coronal fricatives (e.g. [s, z, θ, ð]) as targets and repairs in the early sound systems of monolingual English-acquiring children. Typological results are reported from a cross-sectional study of 234 children with phonological delays (ages 3 years; 0 months to 7;9). Our analyses revealed different instantiations of a putative developmental conspiracy within and across children. Supplemental longitudinal evidence is also presented that replicates the cross-sectional results, offering further insight into the life-cycle of the conspiracy. Several of the observed typological anomalies are argued to follow from a modified version of Optimality Theory with Candidate Chains (McCarthy, 2007). PMID:24790247

  19. The coronal fricative problem.

    PubMed

    Dinnsen, Daniel A; Dow, Michael C; Gierut, Judith A; Morrisette, Michele L; Green, Christopher R

    2013-07-01

    This paper examines a range of predicted versus attested error patterns involving coronal fricatives (e.g. [s, z, θ, ð]) as targets and repairs in the early sound systems of monolingual English-acquiring children. Typological results are reported from a cross-sectional study of 234 children with phonological delays (ages 3 years; 0 months to 7;9). Our analyses revealed different instantiations of a putative developmental conspiracy within and across children. Supplemental longitudinal evidence is also presented that replicates the cross-sectional results, offering further insight into the life-cycle of the conspiracy. Several of the observed typological anomalies are argued to follow from a modified version of Optimality Theory with Candidate Chains (McCarthy, 2007). PMID:24790247

  20. Waves in Solar Coronal Loops

    NASA Astrophysics Data System (ADS)

    Wang, T. J.

    2016-02-01

    The corona is visible in the optical band only during a total solar eclipse or with a coronagraph. Coronal loops are believed to be plasma-filled closed magnetic flux anchored in the photosphere. Based on the temperature regime, they are generally classified into cool, warm, and hot loops. The magnetized coronal structures support propagation of various types of magnetohydrodynamics (MHD) waves. This chapter reviews the recent progress made in studies based on observations of four types of wave phenomena mainly occurring in coronal loops of active regions, including: flare-excited slow-mode waves; impulsively excited kink-mode waves; propagating slow magnetoacoustic waves; and ubiquitous propagating kink (Alfvénic) waves. This review not only comprehensively discusses these waves and coronal seismology but also topics that are newly emerging or hotly debated in order to provide the reader with useful guidance on further studies.

  1. Dynamical behaviour in coronal loops

    NASA Technical Reports Server (NTRS)

    Haisch, Bernhard M.

    1986-01-01

    Rapid variability has been found in two active region coronal loops observed by the X-ray Polychromator (XRP) and the Hard X-ray Imaging Spectrometer (HXIS) onboard the Solar Maximum Mission (SMM). There appear to be surprisingly few observations of the short-time scale behavior of hot loops, and the evidence presented herein lends support to the hypothesis that coronal heating may be impulsive and driven by flaring.

  2. Solar and stellar coronal plasmas

    NASA Technical Reports Server (NTRS)

    Golub, L.

    1985-01-01

    Progress made in describing and interpreting coronal plasma processes and the relationship between the solar corona and its stellar counterparts is reported. Topics covered include: stellar X-ray emission, HEAO 2 X-ray survey of the Pleiades, closed coronal structures, X-ray survey of main-sequence stars with shallow convection zones, implications of the 1400 MHz flare emission, and magnetic field stochasticity.

  3. Coronal structure and the solar wind

    NASA Technical Reports Server (NTRS)

    Roelof, E. C.

    1974-01-01

    Aspects concerning the open coronal structure and geomagnetic disturbances are considered along with the general coronal emission characteristics and relations between the open coronal structure and the interplanetary field. The nonstatistical indicators of coronal structure are examined and questions are investigated regarding the accuracy obtained in the determination of the emission latitude and longitude in the high corona for plasma, fields, and particles. Attention is given to the problem of particle population organization by low-coronal neutral line structures in the absence of a high coronal polarity structure.

  4. The Geometric Spreading of Coronal Plumes and Coronal Holes

    NASA Technical Reports Server (NTRS)

    Suess, S. T.; Poletto, G.; Wang, A.-H.; Wu, S. T.; Cuseri, I.

    1998-01-01

    The geometric spreading in plumes and in the interplume region in coronal holes is calculated, using analytic and numerical theoretical models, between 1.0 and 5.0 solar radius. We apply a two-scale approximation that permits the rapid local spreading at the base of plumes (f(sub t)) to be evaluated separately from the global spreading (f(sub g)) imposed by coronal hole geometry. We show that f(sub t) can be computed from a potential-field model and f(sub g) can be computed from global magnetohydrodynamic simulations of coronal structure. The approximations are valid when the plasma beta is mail with respect to unity and for a plume separation small with respect to a solar radius.

  5. Geometry of solar coronal rays

    NASA Astrophysics Data System (ADS)

    Filippov, B. P.; Martsenyuk, O. V.; Platov, Yu. V.; Den, O. E.

    2016-02-01

    Coronal helmet streamers are the most prominent large-scale elements of the solar corona observed in white light during total solar eclipses. The base of the streamer is an arcade of loops located above a global polarity inversion line. At an altitude of 1-2 solar radii above the limb, the apices of the arches sharpen, forming cusp structures, above which narrow coronal rays are observed. Lyot coronagraphs, especially those on-board spacecrafts flying beyond the Earth's atmosphere, enable us to observe the corona continuously and at large distances. At distances of several solar radii, the streamers take the form of fairly narrow spokes that diverge radially from the Sun. This radial direction displays a continuous expansion of the corona into the surrounding space, and the formation of the solar wind. However, the solar magnetic field and solar rotation complicate the situation. The rotation curves radial streams into spiral ones, similar to water streams flowing from rotating tubes. The influence of the magnetic field is more complex and multifarious. A thorough study of coronal ray geometries shows that rays are frequently not radial and not straight. Coronal streamers frequently display a curvature whose direction in the meridional plane depends on the phase of the solar cycle. It is evident that this curvature is related to the geometry of the global solar magnetic field, which depends on the cycle phase. Equatorward deviations of coronal streamers at solar minima and poleward deviations at solar maxima can be interpreted as the effects of changes in the general topology of the global solar magnetic field. There are sporadic temporal changes in the coronal rays shape caused by remote coronal mass ejections (CMEs) propagating through the corona. This is also a manifestation of the influence of the magnetic field on plasma flows. The motion of a large-scale flux rope associated with a CME away from the Sun creates changes in the structure of surrounding field

  6. Key aspects of coronal heating

    PubMed Central

    Klimchuk, James A.

    2015-01-01

    We highlight 10 key aspects of coronal heating that must be understood before we can consider the problem to be solved. (1) All coronal heating is impulsive. (2) The details of coronal heating matter. (3) The corona is filled with elemental magnetic stands. (4) The corona is densely populated with current sheets. (5) The strands must reconnect to prevent an infinite build-up of stress. (6) Nanoflares repeat with different frequencies. (7) What is the characteristic magnitude of energy release? (8) What causes the collective behaviour responsible for loops? (9) What are the onset conditions for energy release? (10) Chromospheric nanoflares are not a primary source of coronal plasma. Significant progress in solving the coronal heating problem will require coordination of approaches: observational studies, field-aligned hydrodynamic simulations, large-scale and localized three-dimensional magnetohydrodynamic simulations, and possibly also kinetic simulations. There is a unique value to each of these approaches, and the community must strive to coordinate better. PMID:25897094

  7. Solar and stellar coronal plasmas

    NASA Technical Reports Server (NTRS)

    Golub, Leon

    1989-01-01

    Progress in observational, theoretical, and radio studies of coronal plasmas is summarized. Specifically work completed in the area of solar and stellar magnetic fields, related photospheric phenomena and the relationships between magnetism, rotation, coronal and chromospheric emission in solar-like stars is described. Also outlined are theoretical studies carried out in the following areas, among others: (1) neutral beams as the dominant energy transport mechanism in two ribbon-flares; (2) magneto hydrodynamic and circuit models for filament eruptions; and (3) studies of radio emission mechanisms in transient events. Finally, radio observations designed for coronal activity studies of the sun and of solar-type coronae are described. A bibliography of publications and talks is provided along with reprints of selected articles.

  8. Solar Coronal Structure Study

    NASA Technical Reports Server (NTRS)

    Nitta, Nariaki; Bruner, Marilyn E.; Saba, Julia; Strong, Keith; Harvey, Karen

    2000-01-01

    The subject of this investigation is to study the physics of the solar corona through the analysis of the EUV and UV data produced by two flights (12 May 1992 and 25 April 1994) of the Lockheed Solar Plasma Diagnostics Experiment (SPDE) sounding rocket payload, in combination with Yohkoh and ground-based data. Each rocket flight produced both spectral and imaging data. These joint datasets are useful for understanding the physical state of various features in the solar atmosphere at different heights ranging from the photosphere to the corona at the time of the, rocket flights, which took place during the declining phase of a solar cycle, 2-4 years before the minimum. The investigation is narrowly focused on comparing the physics of small- and medium-scale strong-field structures with that of large-scale, weak fields. As we close th is investigation, we have to recall that our present position in the understanding of basic solar physics problems (such as coronal heating) is much different from that in 1995 (when we proposed this investigation), due largely to the great success of SOHO and TRACE. In other words, several topics and techniques we proposed can now be better realized with data from these missions. For this reason, at some point of our work, we started concentrating on the 1992 data, which are more unique and have more supporting data. As a result, we discontinued the investigation on small-scale structures, i.e., bright points, since high-resolution TRACE images have addressed more important physics than SPDE EUV images could do. In the final year, we still spent long time calibrating the 1992 data. The work was complicated because of the old-fashioned film, which had problems not encountered with more modern CCD detectors. After our considerable effort on calibration, we were able to focus on several scientific topics, relying heavily on the SPDE UV images. They include the relation between filaments and filament channels, the identification of hot

  9. CORONAL FOURIER POWER SPECTRA: IMPLICATIONS FOR CORONAL SEISMOLOGY AND CORONAL HEATING

    SciTech Connect

    Ireland, J.; McAteer, R. T. J.; Inglis, A. R.

    2015-01-01

    The dynamics of regions of the solar corona are investigated using Atmospheric Imaging Assembly 171 Å and 193 Å data. The coronal emission from the quiet Sun, coronal loop footprints, coronal moss, and from above a sunspot is studied. It is shown that the mean Fourier power spectra in these regions can be described by a power law at lower frequencies that tails to a flat spectrum at higher frequencies, plus a Gaussian-shaped contribution that varies depending on the region studied. This Fourier spectral shape is in contrast to the commonly held assumption that coronal time series are well described by the sum of a long timescale background trend plus Gaussian-distributed noise, with some specific locations also showing an oscillatory signal. The implications of the observed spectral shape on the fields of coronal seismology and the automated detection of oscillations in the corona are discussed. The power-law contribution to the shape of the Fourier power spectrum is interpreted as being due to the summation of a distribution of exponentially decaying emission events along the line of sight. This is consistent with the idea that the solar atmosphere is heated everywhere by small energy deposition events.

  10. Heating Profiles of Coronal Loops

    NASA Astrophysics Data System (ADS)

    Plowman, Joseph; Kankelborg, Charles C.; Martens, Petrus C.

    2016-05-01

    We analyze the temperature and density profiles of coronal loops, as a function of their length, using data from SDO/AIA and Hinode/EIS. The analysis considers the location of the heating along the loop's length, and we conduct a more throrough investigation of our previous preliminary result that heating is concentrated near the loop footpoints. The work now features a larger selection of coronal loops, compared to our previous presentations, and examines their scale-height temperatures to ascertain the extent to which they are hydrostatic.

  11. Coronal Metallicities of Active Binaries

    NASA Astrophysics Data System (ADS)

    Kashyap, V.; Drake, J. J.; Pease, D. O.; Schmitt, J. H. M. M.

    1998-09-01

    We analyze EUV and X-ray data on a sample of X-ray active binary stars to determine coronal abundances. EUVE spectrometer data are used to obtain line fluxes, which are then used to determine Differential Emission Measures (DEMs). The continuum emission predicted for these DEMs (constrained at high temperatures by measurements in the X-ray regime where available) are then compared with EUVE/DS counts to derive coronal metallicities. These measurements indicate whether the coronae on these stars are metal deficient (the ``MAD Syndrome'') or subject to the FIP-effect (low First Ionization Potential elements have enhanced abundances relative to the photospheres).

  12. CORONAL EMISSION LINES AS THERMOMETERS

    SciTech Connect

    Judge, Philip G.

    2010-01-10

    Coronal emission-line intensities are commonly used to measure electron temperatures using emission measure and/or line ratio methods. In the presence of systematic errors in atomic excitation calculations and data noise, the information on underlying temperature distributions is fundamentally limited. Increasing the number of emission lines used does not necessarily improve the ability to discriminate between different kinds of temperature distributions.

  13. An equatorial coronal hole at solar minimum

    NASA Technical Reports Server (NTRS)

    Bromage, B. J. I.; DelZanna, G.; DeForest, C.; Thompson, B.; Clegg, J. R.

    1997-01-01

    The large transequatorial coronal hole that was observed in the solar corona at the end of August 1996 is presented. It consists of a north polar coronal hole called the 'elephant's trunk or tusk'. The observations of this coronal hole were carried out with the coronal diagnostic spectrometer onboard the Solar and Heliospheric Observatory (SOHO). The magnetic field associated with the equatorial coronal hole is strongly connected to that of the active region at its base, resulting in the two features rotating at almost the same rate.

  14. Coronal Seismology: The Search for Propagating Waves in Coronal Loops

    NASA Astrophysics Data System (ADS)

    Schad, Thomas A.; Seeley, D.; Keil, S. L.; Tomczyk, S.

    2007-05-01

    We report on Doppler observations of the solar corona obtained in the Fe XeXIII 1074.7nm coronal emission line with the HAO Coronal Multi-Channel Polarimeter (CoMP) mounted on the NSO Coronal One Shot coronagraph located in the Hilltop Facility of NSO/Sacramento Peak. The COMP is a tunable filtergraph instrument that records the entire corona from the edge of the occulting disk at approximately 1.03 Rsun out to 1.4 Rsun with a spatial resolution of about 4” x 4”. COMP can be rapidly scanned through the spectral line while recording orthogonal states of linear and circular polarization. The two dimensional spatial resolution allows us to correlate temporal fluctuations observed in one part of the corona with those seen at other locations, in particular along coronal loops. Using cross spectral analysis we find that the observations reveal upward propagating waves that are characterized by Doppler shifts with rms velocities of 0.3 km/s, peak wave power in the 3-5 mHz frequency range, and phase speeds 1-3 Mm/s. The wave trajectories are consistent with the direction of the magnetic field inferred from the linear polarization measurements. We discuss the phase and coherence of these waves as a function of height in the corona and relate our findings to previous observations. The observed waves appear to be Alfvenic in character. "Thomas Schad was supported through the National Solar Observatory Research Experiences for Undergraduate (REU) site program, which is co-funded by the Department of Defense in partnership with the National Science Foundation REU Program." Daniel Seeley was supported through the National Solar Observatory Research Experience for Teachers (RET) site program, which is funded by the National Science Foundation RET program.

  15. HEATCVB: Coronal heating rate approximations

    NASA Astrophysics Data System (ADS)

    Cranmer, Steven R.

    2015-06-01

    HEATCVB is a stand-alone Fortran 77 subroutine that estimates the local volumetric coronal heating rate with four required inputs: the radial distance r, the wind speed u, the mass density ρ, and the magnetic field strength |B0|. The primary output is the heating rate Qturb at the location defined by the input parameters. HEATCVB also computes the local turbulent dissipation rate of the waves, γ = Qturb/(2UA).

  16. The Coronal Loop Inventory Project

    NASA Astrophysics Data System (ADS)

    Schmelz, J. T.; Pathak, S.; Christian, G. M.; Dhaliwal, R. S. S.; Paul, K. S.

    2015-11-01

    Most coronal physicists now seem to agree that loops are composed of tangled magnetic strands and have both isothermal and multithermal cross-field temperature distributions. As yet, however, there is no information on the relative importance of each of these categories, and we do not know how common one is with respect to the other. In this paper, we investigate these temperature properties for all loop segments visible in the 171-Å image of AR 11294, which was observed by the Atmospheric Imaging Assembly (AIA) on 2011 September 15. Our analysis revealed 19 loop segments, but only 2 of these were clearly isothermal. Six additional segments were effectively isothermal, that is, the plasma emission to which AIA is sensitive could not be distinguished from isothermal emission, within measurement uncertainties. One loop had both isothermal transition region and multithermal coronal solutions. Another five loop segments require multithermal plasma to reproduce the AIA observations. The five remaining loop segments could not be separated reliably from the background in the crucial non-171-Å AIA images required for temperature analysis. We hope that the direction of coronal heating models and the efforts modelers spend on various heating scenarios will be influenced by these results.

  17. Impulsively generated fast coronal pulsations

    NASA Technical Reports Server (NTRS)

    Edwin, P. M.; Roberts, B.

    1986-01-01

    Rapid oscillations in the corona are discussed from a theoretical standpoint, developing some previous work on ducted, fast magnetoacoustic waves in an inhomogeneous medium. In the theory, impulsively (e.g., flare) generated mhd (magnetohydrodynamic) waves are ducted by regions of low Alfven speed (high density) such as coronal loops. Wave propagation in such ducts is strongly dispersive and closely akin to the behavior of Love waves in seismology, Pekeris waves in oceanography and guided waves in fiber optics. Such flare-generated magnetoacoustic waves possess distinctive temporal signatures consisting of periodic, quasi-periodic and decay phases. The quasi-periodic phase possesses the strongest amplitudes and the shortest time scales. Time scales are typically of the order of a second for inhomogeneities (coronal loop width) of 1000 km and Alfven speeds of 1000/kms, and pulse duration times are of tens of seconds. Quasi-periodic signatures have been observed in radio wavelengths for over a decade and more recently by SMM. It is hoped that the theoretical ideas outlined may be successfully related to these observations and thus aid the interpretation of oscillatory signatures recorded by SMM. Such signatures may also provide a diagnostic of coronal conditions. New aspects of the ducted mhd waves, for example their behavior in smoothly varying as opposed to tube-like inhomogeneities, are currently under investigation. The theory is not restricted to loops but applied equally to open field regions.

  18. The Structure of Coronal Loops

    NASA Technical Reports Server (NTRS)

    Antiochos, Spiro K.

    2009-01-01

    It is widely believed that the simple coronal loops observed by XUV imagers, such as EIT, TRACE, or XRT, actually have a complex internal structure consisting of many (perhaps hundreds) of unresolved, interwoven "strands". According to the nanoflare model, photospheric motions tangle the strands, causing them to reconnect and release the energy required to produce the observed loop plasma. Although the strands, themselves, are unresolved by present-generation imagers, there is compelling evidence for their existence and for the nanoflare model from analysis of loop intensities and temporal evolution. A problem with this scenario is that, although reconnection can eliminate some of the strand tangles, it cannot destroy helicity, which should eventually build up to observable scales. we consider, therefore, the injection and evolution of helicity by the nanoflare process and its implications for the observed structure of loops and the large-scale corona. we argue that helicity does survive and build up to observable levels, but on spatial and temporal scales larger than those of coronal loops. we discuss the implications of these results for coronal loops and the corona, in general .

  19. Cavernomas de la región temporal mesial: Anatomía microquirúrgica y abordajes

    PubMed Central

    Campero, Alvaro

    2015-01-01

    Objetivo: Describir la anatomía microquirúrgica y los abordajes a la región temporal mesial (RTM), en relación a cavernomas de dicho sector. Materiales y Método: Cinco cabezas de cadáveres adultos, fijadas en formol e inyectadas con silicona coloreada, fueron estudiadas. Además, desde enero de 2007 a junio de 2014, 7 pacientes con cavernomas localizados en la RTM fueron operados por el autor. Resultados: Anatomia: La RTM fue dividida en 3 sectores: Anterior, medio y posterior. Pacientes: 7 enfermos con cavernomas de la RTM fueron operados por el autor. De acuerdo a la ubicacion en la RTM, 4 cavernomas se ubicaron en el sector anterior, 2 cavernomas se localizaron en el sector medio y 1 cavernoma se ubico en el sector posterior. Para el sector anterior de la RTM se utilizo un abordaje transsilviano-transinsular; para el sector medio de la RTM se utilizo un abordaje transtemporal (lobectomia temporal anterior); y para el sector posterior de la RTM se utilizo un abordaje supracerebeloso-transtentorial. Conclusión: Dividir la RTM en 3 sectores nos permite adecuar el abordaje en función a la localización de la lesión. Así, el sector anterior es bien abordable a través de la fisura silviana; el sector medio a través de una vía transtemporal; y el sector posterior por un abordaje supracerebeloso. PMID:26600986

  20. Coronal abundances determined from energetic particles

    NASA Technical Reports Server (NTRS)

    Reames, D. V.

    1995-01-01

    Solar energetic particles (SEPs) provide a measurement of coronal element abundances that is highly independent of the ionization states and temperature of the ions in the source plasma. The most complete measurements come from large 'gradual' events where ambient coronal plasma is swept up by the expanding shock wave from a coronal mass ejection. Particles from 'impulsive' flares have a pattern of acceleration-induced enhancements superimposed on the coronal abundances. Particles accelerated from high-speed solar wind streams at corotating shocks show a different abundance pattern corresponding to material from coronal holes. Large variations in He/O in coronal material are seen for both gradual and impulsive-flare events but other abundance ratios, such as Mg/Ne, are remarkably constant. SEP measurements now include hundreds of events spanning 15 years of high-quality measurement.

  1. EUV Coronal Dimming and its Relationship to Coronal Mass Ejections

    NASA Astrophysics Data System (ADS)

    Mason, James

    2016-05-01

    As a coronal mass ejection (CME) departs from the inner solar atmosphere, it leaves behind a void. This region of depleted plasma results in a corresponding decrease in coronal emissions that can be observed by instruments tuned to measure the extreme ultraviolet (EUV) part of the electromagnetic spectrum. These coronal dimmings can be observed with EUV imagers and EUV spectral irradiance instruments. Onboard the Solar Dynamics Observatory (SDO), the EUV Variability Experiment (EVE) and Atmospheric Imaging Assembly (AIA) provide complementary observations; together they can be used to obtain high spatial and spectral resolution. AIA provides information about the location, extent, and spatial evolution of the dimming while EVE data are important to understand plasma temperature evolution. Concurrent processes with similar timescales to mass-loss dimming also impact the observations, which makes a deconvolution method necessary for the irradiance time series in order to have a “clean” mass-loss dimming light curve that can be parameterized and compared with CME kinematics. This presentation will first provide background on these various physical processes and the deconvolution method developed. Two case studies will then be presented, followed by a semi-statistical study (~30 events) to establish a correlation between dimming and CME parameters. In particular, the slope of the deconvolved irradiance dimming light curve is representative of the CME speed, and the irradiance dimming depth can serve as a proxy for CME mass. Finally, plans and early results from a more complete statistical study of all dimmings in the SDO era, based on an automated detection routine using EVE data, will be described and compared with independently derived dimmings automatically detected with AIA data.

  2. The relationship between coronal streamers and CMEs.

    NASA Astrophysics Data System (ADS)

    Du, Jinsheng; Tong, Yi; Yang, Jing; Eselevich, V. G.

    1999-06-01

    The variation of the polarization brightness of coronal streamer in Carrington Rotations 1591 - 1592 is investigated. The distribution of the polarization brightness along streamer belts is inhomogeneous; the degree of the inhomogeneity is 10% - 50%. In the absence of coronal mass ejection (CME) influence, the distribution of coronal streamers along the streamer belts can persist stable during nearly two Carrington Rotations. The rise velocity of the top of the cusp region in a coronal streamer may be more than 2 km/s, if the longitude angular size is more than 27° associated with a CME occurrence.

  3. THE RELATIONSHIP BETWEEN CORONAL DIMMING AND CORONAL MASS EJECTION PROPERTIES

    SciTech Connect

    Reinard, A. A.

    2009-11-01

    Coronal dimmings are closely related to the footpoints of coronal mass ejections (CMEs) and, as such, offer information about CME origins and evolution. In this paper, we investigate the relationship between CME and dimming properties. In particular, we compare CME quantities for events with and without associated dimmings. We find that dimming-associated CMEs, on average, have much higher speeds than non-dimming-associated events. In fact, CMEs without an associated dimming do not appear to travel faster than 800 km s{sup -1}, i.e., the fast solar wind speed. Dimming-associated events are also more likely to be associated with flares, and those flares tend to have the highest magnitudes. We propose that each of these phenomena is affected by the energy available in the source region. Highly energetic source regions produce fast CMEs that are accompanied by larger flares and visible dimmings, while less energetic source regions produce slow CMEs that are accompanied by smaller flares and may or may not have dimmings. The production of dimmings in the latter case may depend on a number of factors including initiation height of the CME, source region magnetic configuration, and observational effects. These results have important implications for understanding and predicting CME initiations.

  4. On Recurrent/Homologous Coronal Jets Emission: Coronal Geyser Structures

    NASA Astrophysics Data System (ADS)

    Razvan Paraschiv, Alin; Donea, Alina

    2016-05-01

    Active region 11302 has shown a vast display of solar jets during its lifetime. We examine the emission mechanism responsible for multiple coronal jet events occurring at the center-east side of the active region. Identified jet events were detected in extreme-ultraviolet (EUV), hard X-ray (HXR) and radio emissions, observed by dedicated instruments such as SDO's AIA and HMI, STEREO's EUVI and WAVES, and RHESSI, respectively. We report the detection of a base-arch structure in the lower atmosphere. The site was labelled "Coronal Geyser". The structure had emitted jets quasi-periodically for the entire time the AR was visible in SDO'S field of view. The jets expand into the corona with an apparent line of sight velocity of ~200-300$ km/s. To our knowledge the long time-scale behaviour of jet recurrence and base geyser structure was not previously discussed and data analysis of this phenomena will provide new information for theoretical modelling and data interpretation of jets.

  5. Photospheric and coronal magnetic fields

    SciTech Connect

    Sheeley, N.R., Jr. )

    1991-01-01

    Research on small-scale and large-scale photospheric and coronal magnetic fields during 1987-1990 is reviewed, focusing on observational studies. Particular attention is given to the new techniques, which include the correlation tracking of granules, the use of highly Zeeman-sensitive infrared spectral lines and multiple lines to deduce small-scale field strength, the application of long integration times coupled with good seeing conditions to study weak fields, and the use of high-resolution CCD detectors together with computer image-processing techniques to obtain images with unsurpassed spatial resolution. Synoptic observations of large-scale fields during the sunspot cycle are also discussed. 101 refs.

  6. Fishing in the Coronal Graveyard

    NASA Astrophysics Data System (ADS)

    Ayres, T. R.; Brown, A.; Harper, G. M.; Bennett, P. D.; Linsky, J. L.; Carpenter, K. G.; Robinson, R. D.

    1996-12-01

    Hot coronae (T ~ 10(6) K) are thought to be rare among single giant stars to the right of the ``Linsky--Haisch dividing line'' near K0 in the H--R diagram. K and M giants are such slow rotators that absence of dynamo generated magnetic activity would be natural. Nevertheless, gamma Dra (K5 III) unexpectedly was detected in FUV coronal proxies---hot lines Si IV lambda 1393 and C IV lambda 1548---by HST /GHRS during Science Verification, and subsequently was discovered as a faint X-ray source in a deep ROSAT /PSPC pointing. Is gamma Dra anomalous, or is the lack of coronal detections among the K giants simply a matter of insufficient sensitivity? We have used the GHRS low resolution mode to search for additional examples of hot lines among inactive single red giants. Si IV provides a clean diagnostic of subcoronal material because it falls near the peak sensitivity of the G140L mode and does not suffer from abundance depletions that can affect C IV in red giants. X-ray/Si IV ratios are such that HST can reach to much fainter limiting ``coronal'' magnitudes than even very deep ROSAT pointings. In every target so far examined, we find weak---but statistically significant---Si IV emission. These include: the ancient red giant Arcturus (alpha Boo: K1 III), recorded at the end of Cycle 5; and epsilon Crv (K2.5 III) and epsilon Sco (K2 III) observed in Cycle 6. X-ray/Si IV ratios of red giants (for which measurements, or upper limits, of both diagnostics are available) fall on a uniform track, extending downward from active K0 ``Clump'' giants like beta Ceti all the way to Arcturus itself, in the depths of the ``coronal graveyard.'' The systematic behavior argues that magnetic dynamo action continues even when long term angular momentum loss has slowed the stellar spin to a crawl. This work was supported by grant GO-06066.01-94A from STScI.

  7. Anomalous transmission of a coronal "EIT wave" through a nearby coronal hole

    NASA Astrophysics Data System (ADS)

    Long, David; Perez-Suarez, David; Valori, Gherardo

    2016-05-01

    Observations of reflection at coronal hole boundaries and transmission through the coronal hole suggest that "EIT waves" may be interpreted as freely--propagating wave--pulses initially driven by the rapid expansion of a coronal mass ejection (CME) in the low corona. An "EIT wave" observed on 2012 July 07 is seen to impact an adjacent coronal hole. However, rather than reappearing at the far edge of the coronal hole as with previous observations, the "EIT wave" was subsequently observed to reappear ~360 Mm away in the quiet Sun. The non-typical evolution of the "EIT wave" is examined using a combination of observations of the eruption from SDO/AIA and STEREO-A/EUVI as well as extrapolations of the global magnetic field. The observed "jump" in position of the "EIT wave" is shown to be due to the wave pulse traveling along hot coronal loops connecting the edge of the coronal hole with the quiet Sun.

  8. Meterwave observations of a coronal hole

    NASA Technical Reports Server (NTRS)

    Wang, Z.; Schmahl, E. J.; Kundu, M. R.

    1987-01-01

    Meter-wave maps are presented showing a coronal hole at 30.9, 50.0, and 73.8 MHz using the Clark Lake Radioheliograph in October 1984. The coronal hole seen against the disk at all three frequencies shows interesting similarities to, and significant differences from its optical signatures in HeI lambda10830 spectroheliograms. The 73.8 MHz coronal hole, when seen near disk center, appears to coincide with the HeI footprint of the hole. At the lower frequencies, the emission comes from higher levels of the corona, and the hole appears to be displaced, probably due to the non-radial structure of the coronal hole. The contrast of the hole relative to the quiet Sun is much greater than reported previously for a coronal hole observed at 80 MHz. The higher contrast is certainly real, due to the superior dynamic range, sensitivity, and calibration of the Clark Lake instrument. Using a coronal hole model, the electron density is derived from radio observations of the brightness temperature. A very large discrepancy is found between the derived density and that determined from Skylab EUV observations of coronal holes. This discrepancy suggests that much of the physics of coronal holes has yet to be elucidated.

  9. Initiation of Coronal Mass Ejections

    NASA Technical Reports Server (NTRS)

    Moore, Ronald L.; Sterling, Alphonse C.

    2005-01-01

    This paper is a synopsis of the initiation of the strong-field magnetic explosions that produce large, fast coronal mass ejections. Cartoons based on observations are used to describe the inferred basic physical processes and sequences that trigger and drive the explosion. The magnetic field that explodes is a sheared-core bipole that may or may not be embedded in surrounding strong magnetic field, and may or may not contain a flux rope before it starts to explode. We describe three different mechanisms that singly or in combination trigger the explosion: (1) runaway internal tether-cutting reconnection, (2) runaway external tether-cutting reconnection, and (3) ideal MHD instability or loss or equilibrium. For most eruptions, high-resolution, high-cadence magnetograms and chromospheric and coronal movies (such as from TRACE and/or Solar-B) of the pre-eruption region and of the onset of the eruption and flare are needed to tell which one or which combination of these mechanisms is the trigger. Whatever the trigger, it leads to the production of an erupting flux rope. Using a simple model flux rope, we demonstrate that the explosion can be driven by the magnetic pressure of the expanding flux rope, provided the shape of the expansion is "fat" enough.

  10. SPINNING MOTIONS IN CORONAL CAVITIES

    SciTech Connect

    Wang, Y.-M.; Stenborg, G. E-mail: guillermo.stenborg.ctr.ar@nrl.navy.mi

    2010-08-20

    In movies made from Fe XII 19.5 nm images, coronal cavities that graze or are detached from the solar limb appear as continually spinning structures, with sky-plane projected flow speeds in the range 5-10 km s{sup -1}. These whirling motions often persist in the same sense for up to several days and provide strong evidence that the cavities and the immediately surrounding streamer material have the form of helical flux ropes viewed along their axes. A pronounced bias toward spin in the equatorward direction is observed during 2008. We attribute this bias to the poleward concentration of the photospheric magnetic flux near sunspot minimum, which leads to asymmetric heating along large-scale coronal loops and tends to drive a flow from higher to lower latitudes; this flow is converted into an equatorward spinning motion when the loops pinch off to form a flux rope. As sunspot activity increases and the polar fields weaken, we expect the preferred direction of the spin to reverse.

  11. Coronal manifestations of preflare activity

    NASA Technical Reports Server (NTRS)

    Schmahl, E. J.; Webb, D. F.; Woodgate, B.; Waggett, P.; Bentley, R.; Hurford, G.; Schadee, A.; Schrijver, J.; Harrison, R.; Martens, P.

    1986-01-01

    A variety of coronal manifestations of precursors or preheating for flares are discussed. Researchers found that almost everyone with a telescope sees something before flares. Whether an all-encompassing scenario will ever be developed is not at all clear at present. The clearest example of preflare activity appears to be activated filaments and their manifestations, which presumably are signatures of a changing magnetic field. But researchers have seen two similar eruptions, one without any evidence of emerging flux (Kundu et al., 1985) and the other with colliding poles (Simon et al., 1984). While the reconnection of flux is generally agreed to be required to energize a flare, the emergence of flux from below (at least on short timescales and in compact regions) does not appear to be a necessary condition. In some cases the cancelling of magnetic flux (Martin, 1984) by horizontal motions instead may provide the trigger (Priest, 1985) Researchers found similarities and some differences between these and previous observations. The similarities, besides the frequent involvement of filaments, include compact, multiple precursors which can occur both at and near (not at) the flare site, and the association between coronal sources and activity lower in the atmosphere (i.e., transition zone and chromosphere).

  12. Coronal seismology using transverse loop oscillations

    NASA Astrophysics Data System (ADS)

    Verwichte, E.; Foullon, C.; Van Doorsselaere, T.; Smith, H. M.; Nakariakov, V. M.

    2009-12-01

    Coronal seismology exploits the properties of magnetohydrodynamics in the corona of the Sun to diagnose the local plasma. Therefore, seismology complements direct diagnostic techniques, which suffer from line-of-sight integration or may not give access to all physical quantities. In particular, the seismological exploitation of fast magnetoacoustic oscillations in coronal loops provides information about the global magnetic and density structuring of those loops acting as wave guides. From the oscillation period and damping time it is shown how to obtain information about the local coronal magnetic field as well as the longitudinal and transverse structuring. Furthermore, such studies motivate the development of coronal wave theories, which are also relevant to the coronal heating problem.

  13. Network Coronal Bright Points: Coronal Heating Concentrations Found in the Solar Magnetic Network

    NASA Technical Reports Server (NTRS)

    Falconer, D. A.; Moore, R. L.; Porter, J. G.; Hathaway, D.

    1997-01-01

    We examine the magnetic origins of coronal heating in quiet regions by combining SOHO/EIT Fe XII coronal images and Kitt Peak magnetograms. Spatial filtering of the coronal images shows a network of enhanced structures on the scale of the magnetic network in quiet regions. Superposition of the filtered coronal images on maps of the magnetic network extracted from the magnetograms shows that the coronal network does indeed trace and stem from the magnetic network. Network coronal bright points, the brightest features in the network lanes, are found to have a highly significant (8 sigma above random chance) coincidence with polarity dividing lines (neutral lines) in the network, and are often at the feet of enhanced coronal structures that stem from the network and reach out over the cell interiors. These results indicate that, similar to the close linkage of neutral-line core fields with coronal heating in active regions, low-lying core fields encasing neutral lines in the magnetic network often drive noticeable coronal heating both within themselves (the network coronal bright points) and on more extended fields lines rooted around them. This behavior favors the possibility that active core fields in the network are the main drivers of the heating of the bulk of the quiet corona, on scales much larger than the network lanes and cells.

  14. Network Coronal Bright Points: Coronal Heating Concentrations Found in the Solar Magnetic Network

    NASA Technical Reports Server (NTRS)

    Falconer, D. A.; Moore, R. L.; Porter, J. G.; Hathaway, D. H.

    1998-01-01

    We examine the magnetic origins of coronal heating in quiet regions by combining SOHO/EIT Fe xii coronal images and Kitt Peak magnetograms. Spatial filtering of the coronal images shows a network of enhanced structures on the scale of the magnetic network in quiet regions. Superposition of the filtered coronal images on maps of the magnetic network extracted from the magnetograms shows that the coronal network does indeed trace and stem from the magnetic network. Network coronal bright points, the brightest features in the network lanes, are found to have a highly significant coincidence with polarity dividing lines (neutral lines) in the network and are often at the feet of enhanced coronal structures that stem from the network and reach out over the cell interiors. These results indicate that, similar to the close linkage of neutral-line core fields with coronal heating in active regions (shown in previous work), low-lying core fields encasing neutral lines in the magnetic network often drive noticeable coronal heating both within themselves (the network coronal bright points) and on more extended field lines rooted around them. This behavior favors the possibility that active core fields in the network are the main drivers of the heating of the bulk of the quiet corona, on scales much larger than the network lanes and cells.

  15. Fast magnetoacoustic wave trains in coronal holes

    NASA Astrophysics Data System (ADS)

    Pascoe, D. J.; Nakariakov, V. M.; Kupriyanova, E. G.

    2014-08-01

    Context. Rapidly propagating coronal EUV disturbances recently discovered in the solar corona are interpreted in terms of guided fast magnetoacoustic waves. Fast magnetoacoustic waves experience geometric dispersion in waveguides, which causes localised, impulsive perturbations to develop into quasi-periodic wave trains. Aims: We consider the formation of fast wave trains in a super-radially expanding coronal hole modelled by a magnetic funnel with a field-aligned density profile that is rarefied in comparison to the surrounding plasma. This kind of structure is typical of coronal holes, and it forms a fast magnetoacoustic anti-waveguide as a local maximum in the Alfvén speed. Methods: We performed 2D MHD numerical simulations for impulsively generated perturbations to the system. Both sausage and kink perturbations are considered and the role of the density contrast ratio investigated. Results: The anti-waveguide funnel geometry refracts wave energy away from the structure. However, in this geometry the quasi-periodic fast wave trains are found to appear, too, and so can be associated with the observed rapidly propagating coronal EUV disturbances. The wave trains propagate along the external edge of the coronal hole. The fast wave trains generated in coronal holes exhibit less dispersive evolution than in the case of a dense waveguide. Conclusions: We conclude that an impulsive energy release localised in a coronal plasma inhomogeneity develops into a fast wave train for both kink and sausage disturbances and for both waveguide and anti-waveguide transverse plasma profiles.

  16. FORWARD: A toolset for multiwavelength coronal magnetometry

    NASA Astrophysics Data System (ADS)

    Gibson, Sarah; Kucera, Therese; White, Stephen; Dove, James; Fan, Yuhong; Forland, Blake; Rachmeler, Laurel; Downs, Cooper; Reeves, Katharine

    2016-03-01

    Determining the 3D coronal magnetic field is a critical, but extremely difficult problem to solve. Since different types of multiwavelength coronal data probe different aspects of the coronal magnetic field, ideally these data should be used together to validate and constrain specifications of that field. Such a task requires the ability to create observable quantities at a range of wavelengths from a distribution of magnetic field and associated plasma -- i.e., to perform forward calculations. In this paper we describe the capabilities of the FORWARD SolarSoft IDL package, a uniquely comprehensive toolset for coronal magnetometry. FORWARD is a community resource that may be used both to synthesize a broad range of coronal observables, and to access and compare synthetic observables to existing data. It enables forward fitting of specific observations, and helps to build intuition into how the physical properties of coronal magnetic structures translate to observable properties. FORWARD can also be used to generate synthetic test beds from MHD simulations in order to facilitate the development of coronal magnetometric inversion methods, and to prepare for the analysis of future large solar telescope data.

  17. Stability Study of Coronal Cavities and Prominences

    NASA Astrophysics Data System (ADS)

    de Toma, Giuliana; Gibson, Sarah

    2016-05-01

    Cavity/prominence systems are large-scale coronal structures that can live for many weeks and even months and often end their life in the form of large coronal eruptions. To determine the role of the surrounding ambient coronal field in stabilizing thesesystems against eruption, we examined the extent to which the decline with height of the external coronal magnetic field influences their evolution and likelihood to erupt. We selected coronal cavities observed with SDO/AIA during the rising phase of cycle 24 and divided them in two groups, eruptive and non-eruptive. The height of the cavity, both at the cavity center and top, was directly measured from the SDO/AIA images. The ambient coronal field was derived from a PFSS extrapolation of SDO/HMI magnetograms. We find that the decay index of the potential field above the coronal cavity varies significantly in value for both eruptive and non-eruptive cases but stable cavity systems have, on average, a lower decay index and less complex topology than the eruptive ones.

  18. FORWARD: A Toolset for Multiwavelength Coronal Magnetometry

    NASA Technical Reports Server (NTRS)

    Gibson, Sarah E.; Kucera, Therese A.; White, Stephen M.; Dove, James B.; Fan, Yuhong; Forland, Blake C.; Rachmeler, Laurel A.; Downs, Cooper; Reeves, Katharine K.

    2016-01-01

    Determining the 3D coronal magnetic field is a critical, but extremely difficult problem to solve. Since different types of multiwavelength coronal data probe different aspects of the coronal magnetic field, ideally these data should be used together to validate and constrain specifications of that field. Such a task requires the ability to create observable quantities at a range of wavelengths from a distribution of magnetic field and associated plasma i.e., to perform forward calculations. In this paper we describe the capabilities of the FORWARD SolarSoft IDL package, a uniquely comprehensive toolset for coronal magnetometry. FORWARD is a community resource that may be used both to synthesize a broad range of coronal observables, and to access and compare synthetic observables to existing data. It enables forward fitting of specific observations, and helps to build intuition into how the physical properties of coronal magnetic structures translate to observable properties. FORWARD can also be used to generate synthetic test beds from MHD simulations in order to facilitate the development of coronal magnetometric inversion methods, and to prepare for the analysis of future large solar telescope data.

  19. Coronal Structure: Legacy of EUVE

    NASA Technical Reports Server (NTRS)

    Dupree, Andrea K,

    1999-01-01

    During this past school year, the Smithsonian Predoctoral student, Jorge Sanz-Forcada, began work on this Ph.D. thesis research which will focus on the coronal structure of active cool binary stars. He developed a semi-automatic algorithm to derive the emission measure distribution from EUVE spectra using the latest atomic parameters. To date, he has modeled our long EUVE pointing on lambda And that occurred in the fall of 1998, and has reduced and modeled spectra from EUVE pointings on AR Lac and UX Ari. Some of these observations were made simultaneous with the Advanced Satellite for Cosmology and Physics (ASCA) satellite, and the results reported at the HEAD meeting in Spring 1999.

  20. Coronal Diagnostics from Cometary Emission

    NASA Astrophysics Data System (ADS)

    Bryans, Paul; Pesnell, William D; Seaton, Daniel B; West, Matthew J

    2014-06-01

    The extreme ultraviolet (EUV) emission observed from sungrazing comets as they pass through the solar atmosphere can be used to infer the properties of the corona. In this paper we will discuss several of these properties that can be estimated from the EUV observations of Comet Lovejoy from AIA/SDO and SWAP/PROBA2. The longevity of the emission allows us to constrain the coronal electron density through which the comet passes. We will also discuss how dispersion of the emitting cometary material we can be used to estimate the local Alfven speed in the corona. Finally, measuring the deformation of the magnetic field as it is impacted by the comet can be used to estimate the magnetic field strength in this location. In the absence of the comet, none of these parameters are directly measurable in the corona. Sungrazing comets are thus unique probes of the solar atmosphere.

  1. The coronal-sounding experiment

    NASA Technical Reports Server (NTRS)

    Bird, M. K.; Asmar, S. W.; Brenkle, J. P.; Edenhofer, P.; Paetzold, M.; Volland, H.

    1992-01-01

    The main science objective of the Ulysses Solar Corona Experiment is to derive the plasma parameters of the solar atmosphere using established coronal-sounding techniques. Applying appropriate model assumptions, the 3D electron density distribution will be determined from dual-frequency ranging and Doppler measurements recorded at the NASA Deep Space Network during the solar conjunctions. Multi-station observations will be used to derive the plasma bulk velocity at solar distances where the solar wind is expected to undergo its greatest acceleration. As a secondary objective profiting from the favorable geometry during Jupiter encounter, radio-sounding measurements will yield a unique cross-scan of the electron density in the Io Plasma Torus.

  2. Recent advances in coronal heating.

    PubMed

    De Moortel, Ineke; Browning, Philippa

    2015-05-28

    The solar corona, the tenuous outer atmosphere of the Sun, is orders of magnitude hotter than the solar surface. This 'coronal heating problem' requires the identification of a heat source to balance losses due to thermal conduction, radiation and (in some locations) convection. The review papers in this Theo Murphy meeting issue present an overview of recent observational findings, large- and small-scale numerical modelling of physical processes occurring in the solar atmosphere and other aspects which may affect our understanding of the proposed heating mechanisms. At the same time, they also set out the directions and challenges which must be tackled by future research. In this brief introduction, we summarize some of the issues and themes which reoccur throughout this issue. PMID:25897095

  3. Recent advances in coronal heating

    PubMed Central

    De Moortel, Ineke; Browning, Philippa

    2015-01-01

    The solar corona, the tenuous outer atmosphere of the Sun, is orders of magnitude hotter than the solar surface. This ‘coronal heating problem’ requires the identification of a heat source to balance losses due to thermal conduction, radiation and (in some locations) convection. The review papers in this Theo Murphy meeting issue present an overview of recent observational findings, large- and small-scale numerical modelling of physical processes occurring in the solar atmosphere and other aspects which may affect our understanding of the proposed heating mechanisms. At the same time, they also set out the directions and challenges which must be tackled by future research. In this brief introduction, we summarize some of the issues and themes which reoccur throughout this issue. PMID:25897095

  4. Fishing in the Coronal Graveyard

    NASA Astrophysics Data System (ADS)

    Ayres, Thomas

    1996-07-01

    We propose a far-UV spectroscopic survey of K2-K4 giants. Hotcoronae (T> 10^6 K) are rare or absent in single giant starsto the right of a boundary in the H-R diagram near K0(``Linsky-Haisch dividing line''). The early-K giants aresuch slow rotators that the absence of Dynamo-generatedmagnetic activity is natural. Nevertheless, Gamma Draconis(K5 III) unexpectedly was detected in the coronal proxy C IVby HST/GHRS, and subsequently was discovered as a faintX-ray source in a deep ROSAT pointing. The basis for thecoronal emission is unknown, given the presumed lack of Dynamoaction. However, the X-ray/C IV ratio of Gamma Dra falls on acontinuum of values; extending from the active K0 ``Clump''giants like Beta Ceti, down to the old red giant Alpha Boo (K1III) in the depths of the ``coronal graveyard.'' GHRS/G140Lreconnaissance of high-excitation FUV emissions (Si IV, C IV,and N V) can be conducted at sensitivity levels orders ofmagnitude better than possible prior to HST. Such a surveyof single red giants would provide a unique perspective on thebreadth of activity to the right of the L-H boundary. Italso would record the fluoresced 4th-positive system of CO,a key tracer of thermal inhomogeneities in late-typeatmospheres. Seven candidates fall in the magnitude rangeV < 3. Three--Beta UMi, Epsilon Sco, and Epsilon Crv--willbe observed, consistent with the TAC allocation.

  5. Initiation of a coronal transient

    SciTech Connect

    Low, B.C.; Munro, R.H.; Fisher, R.R.

    1982-03-01

    This paper analyzes the coronal transient/eruptive prominence event of 1980 August 5 observed by the Mauna Loa experiment system. This event yielded data on the early development of the transient in the low corona between 1.2 R/sub sun/ and 2.2 R/sub sun/, information which was not available when earlier attempts were made to explain transient phenomena. The transient's initial appearance in the form of a rising density-depleted structure, prior to the eruption of the associated prominence, can be explained as an effect of magnetic buoyancy. The data indicate that this transient has a density depletion of 17% to 33% relative to an undisturbed corona which is approximately isothermal with a temperature of 1.5 x 10/sup 6/ K and a coronal density of 1.0 x 10/sup 9/ cm/sup -3/ at the base of the corona. The height versus base length relationship of the evolving transient resembles, remarkably well, the theoretical predictions obtained from a quasi-static model of a margnetically buoyant loop system. By matching this relationship with the theoretical model, we estimate the magnetic field at the base of the transient to be between 2 and 3 gauss. It is also shown that the initial, nearly constant speed of the top of the transient, 80 +- 20 km s/sup -1/, is consistent with a theoretical estimate calculated from the quasi-static model. These results suggest that some transients are not initiated impulsively, the initial stage of the development being driven by a quasi-static response to a slow change in magnetic field conditions at the base of the corona.

  6. Solar Cycle Variations of Coronal Hole Properties

    NASA Astrophysics Data System (ADS)

    Miralles, M. P.; Cranmer, S. R.; Kohl, J. L.

    2005-05-01

    As of early 2005, we have measured with the SOHO Ultraviolet Coronagraph Spectrometer (UVCS) the physical properties of at least 136 large coronal holes that produced a variety of high-speed solar wind conditions at 1 AU. UVCS has been used to observe O VI (103.2 and 103.7 nm) and H I Lyman alpha (121.6 nm) emission lines as a function of heliocentric distance in coronal holes since 1996. The analysis of their spectroscopic parameters allows us to identify similarities and differences among coronal holes at different phases of the solar cycle. From such measurements we can derive plasma parameters (densities, temperatures, velocity distribution anisotropies, and outflow speeds) for O5+ and protons as a function of heliocentric distance in the coronal holes. These properties, combined with other observed quantities such as white-light polarization brightness and the more-or-less unipolar magnetic fluxes measured on-disk, let us map out the "allowed parameter space" of coronal hole plasma properties more fully than ever before. We will present the solar cycle dependence of the above plasma parameters from the last solar minimum in 1996 to present and compare them, where possible, with the in situ solar wind properties. We will also present an update on the pattern that is beginning to emerge, i.e., coronal holes with lower densities at a given heliocentric distance tend to exhibit faster ion outflow and higher ion temperatures. This information will thus be used to set firm empirical constraints on coronal heating and solar wind acceleration in coronal holes. In 2005, the polar coronal holes have not yet evolved to the fully quiescent minimum state seen in 1996-1997, though the next solar minimum is expected to occur in about 1.5 to 2 years. This work is supported by NASA under Grant NNG04GE84G to the Smithsonian Astrophysical Observatory, by the Italian Space Agency, and by PRODEX (Swiss contribution).

  7. Slipping magnetic reconnection in coronal loops.

    PubMed

    Aulanier, Guillaume; Golub, Leon; Deluca, Edward E; Cirtain, Jonathan W; Kano, Ryouhei; Lundquist, Loraine L; Narukage, Noriyuki; Sakao, Taro; Weber, Mark A

    2007-12-01

    Magnetic reconnection of solar coronal loops is the main process that causes solar flares and possibly coronal heating. In the standard model, magnetic field lines break and reconnect instantaneously at places where the field mapping is discontinuous. However, another mode may operate where the magnetic field mapping is continuous but shows steep gradients: The field lines may slip across each other. Soft x-ray observations of fast bidirectional motions of coronal loops, observed by the Hinode spacecraft, support the existence of this slipping magnetic reconnection regime in the Sun's corona. This basic process should be considered when interpreting reconnection, both on the Sun and in laboratory-based plasma experiments. PMID:18063789

  8. LOW-LATITUDE CORONAL HOLES, DECAYING ACTIVE REGIONS, AND GLOBAL CORONAL MAGNETIC STRUCTURE

    SciTech Connect

    Petrie, G. J. D.; Haislmaier, K. J.

    2013-10-01

    We study the relationship between decaying active-region magnetic fields, coronal holes, and the global coronal magnetic structure using Global Oscillations Network Group synoptic magnetograms, Solar TErrestrial RElations Observatory extreme-ultraviolet synoptic maps, and coronal potential-field source-surface models. We analyze 14 decaying regions and associated coronal holes occurring between early 2007 and late 2010, 4 from cycle 23 and 10 from cycle 24. We investigate the relationship between asymmetries in active regions' positive and negative magnetic intensities, asymmetric magnetic decay rates, flux imbalances, global field structure, and coronal hole formation. Whereas new emerging active regions caused changes in the large-scale coronal field, the coronal fields of the 14 decaying active regions only opened under the condition that the global coronal structure remained almost unchanged. This was because the dominant slowly varying, low-order multipoles prevented opposing-polarity fields from opening and the remnant active-region flux preserved the regions' low-order multipole moments long after the regions had decayed. Thus, the polarity of each coronal hole necessarily matched the polar field on the side of the streamer belt where the corresponding active region decayed. For magnetically isolated active regions initially located within the streamer belt, the more intense polarity generally survived to form the hole. For non-isolated regions, flux imbalance and topological asymmetry prompted the opposite to occur in some cases.

  9. Sept. 28, 2012 Coronal Mass Ejection

    NASA Video Gallery

    This Sept. 28 coronal mass ejection (CME) from the sun, captured by NASA’s Solar Dynamics Observatory (SDO), is the event which caused the near total annihilation of the new radiation belt and sl...

  10. Solar cycle variations of coronal structures

    NASA Astrophysics Data System (ADS)

    Loucif, M. L.; Koutchmy, S.

    1989-01-01

    Using eclipse pictures of the solar corona, properly scaled drawings have been prepared to constitute a short atlas of coronal structures. These drawings have been used to extract 2 parameters which are further considered with respect to the sunspot number and the sunspot cycle: the extension of polar regions free of coronal streamers and the average radial deviation of large streamers. The flattening index deduced from the photometric analysis of a larger number of eclipse pictures is also considered. The out-of-phase behavior of several coronal parameters is confirmed. The results are discussed in the light of the analysis of the green-line activity as observed during 30 years at the Pic du Midi Observatory. The N-S asymmetric behavior of the activity in different solar hemispheres and the occurrence of a powerful secondary maximum of coronal activity are discussed.

  11. Aug. 31, 2012 Coronal Mass Ejection

    NASA Video Gallery

    This two part movie shows an Aug. 31 coronal mass ejection (CME) from the sun , the same event that caused depletion and refilling of the radiation belts just after the Relativistic Electron-Proton...

  12. Coronal magnetic fields and the solar wind

    NASA Technical Reports Server (NTRS)

    Newkirk, G., Jr.

    1972-01-01

    Current information is presented on coronal magnetic fields as they bear on problems of the solar wind. Both steady state fields and coronal transient events are considered. A brief critique is given of the methods of calculating coronal magnetic fields including the potential (current free) models, exact solutions for the solar wind and field interaction, and source surface models. These solutions are compared with the meager quantitative observations which are available at this time. Qualitative comparisons between the shapes of calculated magnetic field lines and the forms visible in the solar corona at several recent eclipses are displayed. These suggest that: (1) coronal streamers develop above extended magnetic arcades which connect unipolar regions of opposite polarity; and (2) loops, arches, and rays in the corona correspond to preferentially filled magnetic tubes in the approximately potential field.

  13. Results of coronal hole research: An overview

    NASA Technical Reports Server (NTRS)

    Wilson, R. M.

    1976-01-01

    An overview of the last 10 years of coronal hole research, in particular since 1970, is presented. The findings of the early investigations and the more recent results obtained with Skylab/Apollo Telescope Mount instrumentation are discussed.

  14. Interpretive Tools for Analysis of Coronal Images

    NASA Technical Reports Server (NTRS)

    Ofman, Leon

    2004-01-01

    Contents include list of publications resulting from grant: Magneto-Hydrodynamic Model of the Solar Corona and Interplanetary Medium. Coronal magnetic field topology and source of fast solar wind. Geophysical Importance of Global Magnetic Field Geometry and Density Distribution in Solar Wind Modeling. Empirical Model of the Corona-Solar Wind with Multiple Current Sheets. Model of the Solar Wind and its Comparison with ULYSSES. Physical properties of a coronal hole from a coronal diagnostic spectrometer, Mauna Loa Coronagraph, and LASCO observations during the Whole Sun Month. Semi-Empirical 2-D MHD Model of the Solar corona and Solar Wind: Energy Flow in the Corona. Source Region of High and Low Speed Wind during the Spartan. Three-dimensional coronal density structure. Cone Model for Halo CME's: Application to Space Weather Forecasting.

  15. Observational Consequences of Coronal Heating Mechanisms

    NASA Technical Reports Server (NTRS)

    Winebarger, Amy R.; Cirtain, Jonathan C.; Golub, Leon; Kobayashi, Ken

    2014-01-01

    The coronal heating problem remains unsolved today, 80 years after its discovery, despite 50 years of suborbital and orbital coronal observatories. Tens of theoretical coronal heating mechanisms have been suggested, but only a few have been able to be ruled out. In this talk, we will explore the reasons for the slow progress and discuss the measurements that will be needed for potential breakthrough, including imaging the solar corona at small spatial scales, measuring the chromospheric magnetic fields, and detecting the presence of high temperature, low emission measure plasma. We will discuss three sounding rocket instruments developed to make these measurements: the High resolution Resolution Coronal Imager (Hi-C), the Chromospheric Lyman-Alpha Spectropolarimeter (CLASP), and the Marshall Grazing Incidence X-ray Spectrometer (MaGIXS).

  16. Solar Coronal Cells as Seen by STEREO

    NASA Video Gallery

    The changes of a coronal cell region as solar rotation carries it across the solar disk as seen with NASA's STEREO-B spacecraft. The camera is fixed on the region (panning with it) and shows the pl...

  17. Relating magnetic reconnection to coronal heating

    PubMed Central

    Longcope, D. W.; Tarr, L. A.

    2015-01-01

    It is clear that the solar corona is being heated and that coronal magnetic fields undergo reconnection all the time. Here we attempt to show that these two facts are related—i.e. coronal reconnection generates heat. This attempt must address the fact that topological change of field lines does not automatically generate heat. We present one case of flux emergence where we have measured the rate of coronal magnetic reconnection and the rate of energy dissipation in the corona. The ratio of these two, , is a current comparable to the amount of current expected to flow along the boundary separating the emerged flux from the pre-existing flux overlying it. We can generalize this relation to the overall corona in quiet Sun or in active regions. Doing so yields estimates for the contribution to coronal heating from magnetic reconnection. These estimated rates are comparable to the amount required to maintain the corona at its observed temperature. PMID:25897089

  18. Coronal Magnetism and Forward Solarsoft Idl Package

    NASA Astrophysics Data System (ADS)

    Gibson, S. E.

    2014-12-01

    The FORWARD suite of Solar Soft IDL codes is a community resource for model-data comparison, with a particular emphasis on analyzing coronal magnetic fields. FORWARD may be used both to synthesize a broad range of coronal observables, and to access and compare to existing data. FORWARD works with numerical model datacubes, interfaces with the web-served Predictive Science Inc MAS simulation datacubes and the Solar Soft IDL Potential Field Source Surface (PFSS) package, and also includes several analytic models (more can be added). It connects to the Virtual Solar Observatory and other web-served observations to download data in a format directly comparable to model predictions. It utilizes the CHIANTI database in modeling UV/EUV lines, and links to the CLE polarimetry synthesis code for forbidden coronal lines. FORWARD enables "forward-fitting" of specific observations, and helps to build intuition into how the physical properties of coronal magnetic structures translate to observable properties.

  19. Energy conversion in the coronal plasma

    NASA Technical Reports Server (NTRS)

    Martens, P. C. H.

    1986-01-01

    Solar and stellar X-ray emission are the observed waste products of the interplay between magnetic fields and the motion of stellar plasma. Theoretical understanding of the process of coronal heating is of utmost importance, since the high temperature is what defines the corona in the first place. Most of the research described deals with the aspects of the several rivalling theories for coronal heating. The rest of the papers deal with processes of energy conversion related to flares.

  20. Dynamic simulation of coronal mass ejections

    NASA Technical Reports Server (NTRS)

    Steinolfson, R. S.; Wu, S. T.

    1980-01-01

    A model is developed for the formation and propagation through the lower corona of the loop-like coronal transients in which mass is ejected from near the solar surface to the outer corona. It is assumed that the initial state for the transient is a coronal streamer. The initial state for the streamer is a polytropic, hydrodynamic solution to the steady-state radial equation of motion coupled with a force-free dipole magnetic field. The numerical solution of the complete time-dependent equations then gradually approaches a stationary coronal streamer configuration. The streamer configuration becomes the initial state for the coronal transient. The streamer and transient simulations are performed completely independent of each other. The transient is created by a sudden increase in the pressure at the base of the closed-field region in the streamer configuration. Both coronal streamers and coronal transients are calculated for values of the plasma beta (the ratio of thermal to magnetic pressure) varying from 0.1 to 100.

  1. MULTIDIMENSIONAL MODELING OF CORONAL RAIN DYNAMICS

    SciTech Connect

    Fang, X.; Xia, C.; Keppens, R.

    2013-07-10

    We present the first multidimensional, magnetohydrodynamic simulations that capture the initial formation and long-term sustainment of the enigmatic coronal rain phenomenon. We demonstrate how thermal instability can induce a spectacular display of in situ forming blob-like condensations which then start their intimate ballet on top of initially linear force-free arcades. Our magnetic arcades host a chromospheric, transition region, and coronal plasma. Following coronal rain dynamics for over 80 minutes of physical time, we collect enough statistics to quantify blob widths, lengths, velocity distributions, and other characteristics which directly match modern observational knowledge. Our virtual coronal rain displays the deformation of blobs into V-shaped features, interactions of blobs due to mostly pressure-mediated levitations, and gives the first views of blobs that evaporate in situ or are siphoned over the apex of the background arcade. Our simulations pave the way for systematic surveys of coronal rain showers in true multidimensional settings to connect parameterized heating prescriptions with rain statistics, ultimately allowing us to quantify the coronal heating input.

  2. Multidimensional Modeling of Coronal Rain Dynamics

    NASA Astrophysics Data System (ADS)

    Fang, X.; Xia, C.; Keppens, R.

    2013-07-01

    We present the first multidimensional, magnetohydrodynamic simulations that capture the initial formation and long-term sustainment of the enigmatic coronal rain phenomenon. We demonstrate how thermal instability can induce a spectacular display of in situ forming blob-like condensations which then start their intimate ballet on top of initially linear force-free arcades. Our magnetic arcades host a chromospheric, transition region, and coronal plasma. Following coronal rain dynamics for over 80 minutes of physical time, we collect enough statistics to quantify blob widths, lengths, velocity distributions, and other characteristics which directly match modern observational knowledge. Our virtual coronal rain displays the deformation of blobs into V-shaped features, interactions of blobs due to mostly pressure-mediated levitations, and gives the first views of blobs that evaporate in situ or are siphoned over the apex of the background arcade. Our simulations pave the way for systematic surveys of coronal rain showers in true multidimensional settings to connect parameterized heating prescriptions with rain statistics, ultimately allowing us to quantify the coronal heating input.

  3. The Global Coronal Structure Investigation

    NASA Technical Reports Server (NTRS)

    Golub, Leon

    1998-01-01

    During the past year we have completed the changeover from the NIXT program to the new TXI sounding rocket program. The NIXT effort, aimed at evaluating the viability of the remaining portions of the NIXT hardware and design, has been finished and the portions of the NIXT which are viable and flightworthy, such as filters, mirror mounting hardware, electronics and telemetry interface systems, are now part of the new rocket payload. The backup NIXT multilayer-coated x-ray telescope and its mounting hardware have been completely fabricated and are being stored for possible future use in the TXI rocket. The H-alpha camera design is being utilized in the TXI program for real-time pointing verification and control via telemetry. A new H-alpha camera has been built, with a high-resolution RS170 CCD camera output. Two papers, summarizing scientific results from the NIXT rocket program, have been written and published this year: 1. "The Solar X-ray Corona," by L. Golub, Astrophysics and Space Science, 237, 33 (1996). 2. "Difficulties in Observing Coronal Structure," Keynote Paper, Proceedings STEPWG1 Workshop on Measurements and Analyses of the Solar 3D Magnetic Field, Solar Physics, 174, 99 (1997).

  4. Characteristics of Coronal Mass Ejections

    NASA Astrophysics Data System (ADS)

    Talukder, F.; Marchese, A. K.; Tulsee, T.

    2014-12-01

    A coronal mass ejection (CME) is a release of charged particles resulting from solar activity. These charged particles can affect electronics on spacecraft, airplanes, global positioning systems, and communication satellites. The purpose of this research was to study CME data from satellites and correlate these to other properties. Solar wind data collected by STEREO A/B and ACE satellites were analyzed. The data consisted of solar wind flux for various elements (helium through iron), as well as the components of the interplanetary magnetic field. CME events are known to cause a surge in the helium flux, as well as other particles. It is hypothesized that a CME event will cause an increase in the number of lighter elements relative to heavier particles. This is because for a given input of energy, lighter elements are expected to be accelerated to a greater extent than heavier elements. A significant increase was observed in the ratio between helium to oxygen (He/O) prior to intense CMEs. A CME event on November 4, 2003 caused an eleven-fold increase in the He/O ratio, while for another event on April 2, 2001 the He/O ratio increased from 80 to 700. A significant increase in He/O ratio is not observed during weaker CMEs. Furthermore, it was also observed that not all increases in the ratio were accompanied by CMEs. The increase in He/O ratio prior to the CME arrival might be used as a way to predict future events.

  5. Composition of Coronal Mass Ejections

    NASA Astrophysics Data System (ADS)

    Zurbuchen, T. H.; Weberg, M.; von Steiger, R.; Mewaldt, R. A.; Lepri, S. T.; Antiochos, S. K.

    2016-07-01

    We analyze the physical origin of plasmas that are ejected from the solar corona. To address this issue, we perform a comprehensive analysis of the elemental composition of interplanetary coronal mass ejections (ICMEs) using recently released elemental composition data for Fe, Mg, Si, S, C, N, Ne, and He as compared to O and H. We find that ICMEs exhibit a systematic abundance increase of elements with first ionization potential (FIP) < 10 eV, as well as a significant increase of Ne as compared to quasi-stationary solar wind. ICME plasmas have a stronger FIP effect than slow wind, which indicates either that an FIP process is active during the ICME ejection or that a different type of solar plasma is injected into ICMEs. The observed FIP fractionation is largest during times when the Fe ionic charge states are elevated above Q Fe > 12.0. For ICMEs with elevated charge states, the FIP effect is enhanced by 70% over that of the slow wind. We argue that the compositionally hot parts of ICMEs are active region loops that do not normally have access to the heliosphere through the processes that give rise to solar wind. We also discuss the implications of this result for solar energetic particles accelerated during solar eruptions and for the origin of the slow wind itself.

  6. Coronal Structures in Cool Stars

    NASA Technical Reports Server (NTRS)

    Oliversen, Ronald (Technical Monitor); Dupree, Andrea K.

    2004-01-01

    Many papers have been published that further elucidate the structure of coronas in cool stars as determined from EUVE, HST, FUSE, Chandra, and XMM-Newton observations. In addition we are exploring the effects of coronas on the He I 1083081 transition that is observed in the infrared. Highlights of these are summarized below including publications during this reporting period and presentations. Ground-based magnetic Doppler imaging of cool stars suggests that active stars have active regions located at high latitudes on their surface. We have performed similar imaging in X-ray to locate the sites of enhanced activity using Chandra spectra. Chandra HETG observations of the bright eclipsing contact binary 44i Boo and Chandra LETG observations for the eclipsing binary VW Cep show X-ray line profiles that are Doppler-shifted by orbital motion. After careful analysis of the spectrum of each binary, a composite line-profile is constructed by adding the individual spectral lines. This high signal-to-noise ratio composite line-profile yields orbital velocities for these binaries that are accurate to 30 km/sec and allows their orbital motion to be studied at higher time resolutions. In conjunction with X-ray lightcurves, the phase-binned composite line-profiles constrain coronal structures to be small and located at high latitudes. These observations and techniques show the power of the Doppler Imaging Technique applied to X-ray line emission.

  7. The Global Coronal Structure Investigation

    NASA Astrophysics Data System (ADS)

    Golub, Leon

    1998-02-01

    During the past year we have completed the changeover from the NIXT program to the new TXI sounding rocket program. The NIXT effort, aimed at evaluating the viability of the remaining portions of the NIXT hardware and design, has been finished and the portions of the NIXT which are viable and flightworthy, such as filters, mirror mounting hardware, electronics and telemetry interface systems, are now part of the new rocket payload. The backup NIXT multilayer-coated x-ray telescope and its mounting hardware have been completely fabricated and are being stored for possible future use in the TXI rocket. The H-alpha camera design is being utilized in the TXI program for real-time pointing verification and control via telemetry. A new H-alpha camera has been built, with a high-resolution RS170 CCD camera output. Two papers, summarizing scientific results from the NIXT rocket program, have been written and published this year: 1. "The Solar X-ray Corona," by L. Golub, Astrophysics and Space Science, 237, 33 (1996). 2. "Difficulties in Observing Coronal Structure," Keynote Paper, Proceedings STEPWG1 Workshop on Measurements and Analyses of the Solar 3D Magnetic Field, Solar Physics, 174, 99 (1997).

  8. Observational characteristics of coronal mass ejections without low-coronal signatures

    SciTech Connect

    D'Huys, E.; Seaton, D. B.; Berghmans, D.; Poedts, S.

    2014-11-01

    Solar eruptions are usually associated with a variety of phenomena occurring in the low corona before, during, and after the onset of eruption. Though easily visible in coronagraph observations, so-called stealth coronal mass ejections (CMEs) do not obviously exhibit any of these low-coronal signatures. The presence or absence of distinct low-coronal signatures can be linked to different theoretical models to establish the mechanisms by which the eruption is initiated and driven. In this study, 40 CMEs without low-coronal signatures occurring in 2012 are identified. Their observational and kinematic properties are analyzed and compared to those of regular CMEs. Solar eruptions without clear on-disk or low-coronal signatures can lead to unexpected space weather impacts, since many early warning signs for significant space weather activity are not present in these events. A better understanding of their initiation mechanism(s) will considerably improve the ability to predict such space weather events.

  9. Comparing semilunar coronally positioned flap to standard coronally positioned flap using periodontal clinical parameters.

    PubMed

    Nassar, Carlos Augusto; da Silva, Wilson Aparecido Dias; Tonet, Karine; Secundes, Mayron Barros; Nassar, Patricia Oehlmeyer

    2014-01-01

    This study compared the effectiveness of 2 surgical root coverage techniques--semilunar coronally positioned flap and coronally advanced flap--using the clinical parameters of periodontal tissues from patients with Miller Class I gingival recession. Twenty patients (20-50 years of age) were selected. Basic periodontal treatment was performed, and plaque index, gingival index, probing depth, clinical attachment level, and height of the attached gingiva were determined. Each patient was placed into 1 of 2 groups: Group 1 patients underwent the semilunar coronally positioned flap technique, and Group 2 patients underwent the coronally advanced flap technique. Patients were assessed for 180 days. Both groups showed significant reduction of plaque and gingival indices and an improvement in clinical attachment levels and probing depth. However, results showed the standard coronally positioned flap technique was deemed more effective due to significant clinical attachment level gains. PMID:24598495

  10. Solar Cycle Dependence of Coronal Hole Properties

    NASA Astrophysics Data System (ADS)

    Miralles, M. P.

    2005-07-01

    The SOHO Ultraviolet Coronagraph Spectrometer (UVCS) has been used to measure the properties of hundreds of large coronal holes, that produced a variety of high-speed solar wind streams, during the past nine years. In the cases where UVCS and in situ measurements were made of the same coronal-hole plasma, high speeds in excess of 600 km/s were found in interplanetary space. UVCS has been used to observe O VI (103.2 and 103.7 nm) and H I Lyman alpha (121.6 nm) emission lines as a function of heliocentric distance. The analysis of their spectroscopic parameters allows us to identify similarities and differences among coronal holes at different phases of the solar cycle. From such measurements we can derive plasma parameters (densities, temperatures, velocity distribution anisotropies, and outflow speeds) for O5+ and protons as a function of heliocentric distance in the coronal holes. These properties, combined with other observed quantities such as white-light polarization brightness and the magnetic fluxes measured on-disk, let us analyze the coronal hole plasma properties more fully than ever before. We will present the solar cycle dependence of the above plasma parameters from the last solar minimum in 1996 to present and compare them, where possible, with the in situ solar wind properties. This work is supported by NASA under Grant NNG04GE84G to the Smithsonian Astrophysical Observatory, by the Italian Space Agency, and by PRODEX (Swiss contribution).

  11. Modeling eruptive coronal magnetohydrodynamic systems with FLUX

    NASA Astrophysics Data System (ADS)

    Rachmeler, L. A.

    In this dissertation I explore solar coronal energetic eruptions in the context of magnetic reconnection, which is commonly thought to be a required trigger mechanism for solar eruptions. Reconnection is difficult to directly observe in the corona, and current numerical methods cannot model reconnectionless control cases. Thus, it is not possible to determine if reconnection is a necessary component of these eruptions. I have executed multiple controlled simulations to determine the importance of reconnection for initiation and evolution of several eruptive systems using FLUX, a numerical model that uses the comparatively new fluxon technique. I describe two types of eruptions modeled with FLUX: a metastable confined flux rope theory for coronal mass ejection (CME) initiation, and symmetrically twisted coronal jets in a uniform vertical background field. In the former, I identified an ideal magnetohydrodynamic (MHD) instability that allows metastable twisted flux rope systems to suddenly lose stability and erupt even in the absence of reconnection, contradicting previous conjecture. The CME result is in contrast to the azimuthally symmetric coronal jet initiation model, where jet-like behavior does not manifest without reconnection. My work has demonstrated that some of the observed eruptive phenomena may be triggered by non-reconnective means such as ideal MHD instabilities, and that magnetic reconnection is not a required element in all coronal eruptions.

  12. Coronal magnetic field modeling using stereoscopy constraints

    NASA Astrophysics Data System (ADS)

    Chifu, I.; Inhester, B.; Wiegelmann, T.

    2015-05-01

    Aims: Nonlinear force-free field (NLFFF) extrapolation has been used extensively in the past to extrapolate solar surface magnetograms to stationary coronal field models. In theoretical tests with known boundary conditions, the nonlinear boundary value problem can be solved reliably. However, if the magnetogram is measured with errors, the extrapolation often yields field lines that disagree with the shapes of simultaneously observed and stereoscopically reconstructed coronal loops. We here propose an extension to an NLFFF extrapolation scheme that remedies this deficiency in that it incorporates the loop information in the extrapolation procedure. Methods: We extended the variational formulation of the NLFFF optimization code by an additional term that monitors and minimizes the difference of the local magnetic field direction and the orientation of 3D plasma loops. We tested the performance of the new code with a previously reported semi-analytical force-free solution. Results: We demonstrate that there is a range of force-free and divergence-free solutions that comply with the boundary measurements within some error bound. With our new approach we can obtain the solution out of this set the coronal fields which is well aligned with given loops. Conclusions: We conclude that the shape of coronal loops reconstructed by stereoscopy may lead to an important stabilization of coronal NLFFF field solutions when, as is typically the case, magnetic surface measurements with limited precision do not allow determining the solution solely from photospheric field measurements.

  13. Blind Stereoscopy of the Coronal Magnetic Field

    NASA Astrophysics Data System (ADS)

    Aschwanden, Markus J.; Schrijver, Carolus J.; Malanushenko, Anna

    2015-10-01

    We test the feasibility of 3D coronal-loop tracing in stereoscopic EUV image pairs, with the ultimate goal of enabling efficient 3D reconstruction of the coronal magnetic field that drives flares and coronal mass ejections (CMEs). We developed an automated code designed to perform triangulation of coronal loops in pairs (or triplets) of EUV images recorded from different perspectives. The automated (or blind) stereoscopy code includes three major tasks: i) automated pattern recognition of coronal loops in EUV images, ii) automated pairing of corresponding loop patterns from two different aspect angles, and iii) stereoscopic triangulation of 3D loop coordinates. We perform tests with simulated stereoscopic EUV images and quantify the accuracy of all three procedures. In addition we test the performance of the blind-stereoscopy code as a function of the spacecraft-separation angle and as a function of the spatial resolution. We also test the sensitivity to magnetic non-potentiality. The automated code developed here can be used for analysis of existing Solar TErrestrial RElationship Observatory (STEREO) data, but primarily serves for a design study of a future mission with dedicated diagnostics of non-potential magnetic fields. For a pixel size of 0.6^'' (corresponding to the Solar Dynamics Observatory (SDO)/ Atmospheric Imaging Assembly (AIA) spatial resolution of 1.4^''), we find an optimum spacecraft-separation angle of αs ≈5°.

  14. Direct Observation of Solar Coronal Magnetic Fields by Vector Tomography of the Coronal Emission Line Polarizations

    NASA Astrophysics Data System (ADS)

    Kramar, M.; Lin, H.; Tomczyk, S.

    2016-03-01

    We present the first direct “observation” of the global-scale, 3D coronal magnetic fields of Carrington Rotation (CR) Cycle 2112 using vector tomographic inversion techniques. The vector tomographic inversion uses measurements of the Fe xiii 10747 Å Hanle effect polarization signals by the Coronal Multichannel Polarimeter (CoMP) and 3D coronal density and temperature derived from scalar tomographic inversion of Solar Terrestrial Relations Observatory (STEREO)/Extreme Ultraviolet Imager (EUVI) coronal emission lines (CELs) intensity images as inputs to derive a coronal magnetic field model that best reproduces the observed polarization signals. While independent verifications of the vector tomography results cannot be performed, we compared the tomography inverted coronal magnetic fields with those constructed by magnetohydrodynamic (MHD) simulations based on observed photospheric magnetic fields of CR 2112 and 2113. We found that the MHD model for CR 2112 is qualitatively consistent with the tomography inverted result for most of the reconstruction domain except for several regions. Particularly, for one of the most noticeable regions, we found that the MHD simulation for CR 2113 predicted a model that more closely resembles the vector tomography inverted magnetic fields. In another case, our tomographic reconstruction predicted an open magnetic field at a region where a coronal hole can be seen directly from a STEREO-B/EUVI image. We discuss the utilities and limitations of the tomographic inversion technique, and present ideas for future developments.

  15. The Fundamental Structure of Coronal Loops

    NASA Technical Reports Server (NTRS)

    Winebarger, Amy; Warren, Harry; Cirtain, Jonathan; Kobayashi, Ken; Korreck, Kelly; Golub, Leon; Kuzin, Sergey; Walsh, Robert; DePontieu, Bart; Title, Alan; Weber, Mark

    2012-01-01

    During the past ten years, solar physicists have attempted to infer the coronal heating mechanism by comparing observations of coronal loops with hydrodynamic model predictions. These comparisons often used the addition of sub ]resolution strands to explain the observed loop properties. On July 11, 2012, the High Resolution Coronal Imager (Hi ]C) was launched on a sounding rocket. This instrument obtained images of the solar corona was 0.2 ]0.3'' resolution in a narrowband EUV filter centered around 193 Angstroms. In this talk, we will compare these high resolution images to simultaneous density measurements obtained with the Extreme Ultraviolet Imaging Spectrograph (EIS) on Hinode to determine whether the structures observed with Hi ]C are resolved.

  16. MHD shocks in coronal mass ejections

    NASA Technical Reports Server (NTRS)

    Steinolfson, R. S.

    1991-01-01

    The primary objective of this research program is the study of the magnetohydrodynamic (MHD) shocks and nonlinear simple waves produced as a result of the interaction of ejected lower coronal plasma with the ambient corona. The types of shocks and nonlinear simple waves produced for representative coronal conditions and disturbance velocities were determined. The wave system and the interactions between the ejecta and ambient corona were studied using both analytic theory and numerical solutions of the time-dependent, nonlinear MHD equations. Observations from the SMM coronagraph/polarimeter provided both guidance and motivation and are used extensively in evaluating the results. As a natural consequence of the comparisons with the data, the simulations assisted in better understanding the physical interactions in coronal mass ejections (CME's).

  17. Free Magnetic Energy and Coronal Heating

    NASA Technical Reports Server (NTRS)

    Winebarger, Amy; Moore, Ron; Falconer, David

    2012-01-01

    Previous work has shown that the coronal X-ray luminosity of an active region increases roughly in direct proportion to the total photospheric flux of the active region's magnetic field (Fisher et al. 1998). It is also observed, however, that the coronal luminosity of active regions of nearly the same flux content can differ by an order of magnitude. In this presentation, we analyze 10 active regions with roughly the same total magnetic flux. We first determine several coronal properties, such as X-ray luminosity (calculated using Hinode XRT), peak temperature (calculated using Hinode EIS), and total Fe XVIII emission (calculated using SDO AIA). We present the dependence of these properties on a proxy of the free magnetic energy of the active region

  18. SUMER Observations of Coronal-Hole Temperatures

    NASA Astrophysics Data System (ADS)

    Wilhelm, Klaus

    2012-11-01

    Observations of emission lines in the vacuum-ultraviolet spectral range with calibrated instrumentation provide crucial information on the prevailing plasma temperatures in the solar atmosphere. Coronal-hole temperatures measured by the SUMER spectrometer on SOHO will be presented in this contribution. Electron temperatures can be estimated from the formation temperatures of the observed emission lines. Line-ratio and emission-measure analyses, however, offer higher accuracies. Typical electron temperatures at altitudes of H<200 Mm in coronal holes are below 1 MK in bright structures—the coronal plumes—with higher values in darker areas—the inter-plume regions. Line-width measurements yield effective ion temperatures, which are much higher than the electron temperatures. Observations of line profiles emitted from species with different masses allow a separation of the effective temperatures into ion temperatures and unresolved non-thermal motions along the line of sight.

  19. A unified theory of coronal heating

    NASA Technical Reports Server (NTRS)

    Ionson, J. A.

    1985-01-01

    Solar coronal heating mechanisms are analyzed within the framework of a unified theory of heating processes. The theory is based on the standing wave equation of Ionson (1982) for the global current driven by emfs from the convection Beta less than 1. The equation has the same form as a driven LRC equation in which the equivalent inductance is scaled with the coronal loop length. The theory is used to classify various heating mechanisms inside the coronal loops. It is shown that the total global current can be obtained from an integration of the local currents, the degree of coherency between local currents being the dominant factor governing the global current amplitude. Active region loops appear to be heated by electrodynamic coupling to p-mode oscillations in the convection Beta less than 1.

  20. A contemporary view of coronal heating.

    PubMed

    Parnell, Clare E; De Moortel, Ineke

    2012-07-13

    Determining the heating mechanism (or mechanisms) that causes the outer atmosphere of the Sun, and many other stars, to reach temperatures orders of magnitude higher than their surface temperatures has long been a key problem. For decades, the problem has been known as the coronal heating problem, but it is now clear that 'coronal heating' cannot be treated or explained in isolation and that the heating of the whole solar atmosphere must be studied as a highly coupled system. The magnetic field of the star is known to play a key role, but, despite significant advancements in solar telescopes, computing power and much greater understanding of theoretical mechanisms, the question of which mechanism or mechanisms are the dominant supplier of energy to the chromosphere and corona is still open. Following substantial recent progress, we consider the most likely contenders and discuss the key factors that have made, and still make, determining the actual (coronal) heating mechanism (or mechanisms) so difficult. PMID:22665900

  1. Interchange Reconnection and Coronal Hole Dynamics

    NASA Technical Reports Server (NTRS)

    Edmondson, J. K.; Antiochos, S. K.; DeVore, C. R.; Lynch, B. J.; Zurbuchen, T. H.

    2011-01-01

    We investigate the effect of magnetic reconnection between open and closed field, (often referred to as "interchange" reconnection), on the dynamics and topology of coronal hole boundaries. The most important and most prevalent 3D topology of the interchange process is that of a small-scale bipolar magnetic field interacting with a large-scale background field. We determine the evolution of such a magnetic topology by numerical solution of the fully 3D MHD equations in spherical coordinates. First, we calculate the evolution of a small-scale bipole that initially is completely inside an open field region and then is driven across a coronal hole boundary by photospheric motions. Next the reverse situation is calculated in which the bipole is initially inside the closed region and driven toward the coronal hole boundary. In both cases we find that the stress imparted by the photospheric motions results in deformation of the separatrix surface between the closed field of the bipole and the background field, leading to rapid current sheet formation and to efficient reconnection. When the bipole is inside the open field region, the reconnection is of the interchange type in that it exchanges open and closed field. We examine, in detail, the topology of the field as the bipole moves across the coronal hole boundary, and find that the field remains well-connected throughout this process. Our results imply that open flux cannot penetrate deeply into the closed field region below a helmet streamer and, hence, support the quasi-steady models in which open and closed flux remain topologically distinct. Our results also support the uniqueness hypothesis for open field regions as postulated by Antiochos et al. We discuss the implications of this work for coronal observations. Subject Headings: Sun: corona Sun: magnetic fields Sun: reconnection Sun: coronal hole

  2. What triggers coronal mass ejections ?

    NASA Astrophysics Data System (ADS)

    Aulanier, Guillaume

    Coronal mass ejections (CMEs) are large clouds of highly magnetized plasma. They are ac-celerated from the solar atmosphere into interplanetary space by the Lorentz force, which is associated to their strong current-carrying magnetic fields. Both theory and observations lead to the inevitable conclusion that the launch of a CME must result from the sudden release of free magnetic energy, which has slowly been accumulated in the corona for a long time before the eruption. Since the incomplete, but seminal, loss-of-equilibrium model was proposed by van Tend and Kuperus (1978), a large variety of analytical and numerical storage-and-release MHD models has been put forward in the past 20 years or so. All these models rely on the slow increase of currents and/or the slow decrease of the restraining magnetic tension preceding the eruption. But they all put the emphazis on different physical mechanisms to achieve this preeruptive evolution, and to suddenly trigger and later drive a CME. Nevertheless, all these models actually share many common features, which all describe many individual observed aspects of solar eruptions. It is therefore not always clear which of all the suggested mecha-nisms do really account for the triggering of observed CMEs in general. Also, these mechanisms should arguably not be as numerous as the models themselves, owing to the common occurence of CMEs. In order to shed some light on this challenging, but unripe, topic, I will attempt to rediscuss the applicability of the models to the Sun, and to rethink the most sensitive ones in a common frame, so as to find their common denominator. I will elaborate on the idea that many of the proposed triggering mechanisms may actually only be considered as different ways to apply a "last push", which puts the system beyond its eruptive threshold. I will argue that, in most cases, the eruptive threshold is determined by the vertical gradient of the magnetic field in the low-β corona, just like the usual

  3. Halo Coronal Mass Ejections and Geomagnetic Storms

    NASA Technical Reports Server (NTRS)

    Gopalswamy, Nat

    2009-01-01

    In this letter, I show that the discrepancies in the geoeffectiveness of halo coronal mass ejections (CMEs) reported in the literature arise due to the varied definitions of halo CMEs used by different authors. In particular, I show that the low geoeffectiveness rate is a direct consequence of including partial halo CMEs. The geoeffectiveness of partial halo CMEs is lower because they are of low speed and likely to make a glancing impact on Earth. Key words: Coronal mass ejections, geomagnetic storms, geoeffectiveness, halo CMEs.

  4. Initiation and Evolution of Global Coronal Waves

    NASA Astrophysics Data System (ADS)

    Vršnak, B.; Muhr, N.; Žic, T.; Lulić, S.; Kienreich, I. W.; Temmer, M.; Veronig, A. M.

    Some essential outcomes of a detailed analysis of the formation and evolution of the coronal EUV wave of 15 February 2011 are presented, focused on the relationship between the source region expansion, wave kinematics, and the evolution of the wave amplitude. The observations are explained in terms of the results of the numerical MHD simulations, providing new insights into the physical background of coronal waves, especially considering the nature of the relationship of the wave amplitude and propagation velocity in different phases of the wave evolution.

  5. On the theory of coronal heating mechanisms

    NASA Technical Reports Server (NTRS)

    Kuperus, M.; Ionson, J. A.; Spicer, D. S.

    1980-01-01

    Theoretical models describing solar coronal heating mechanisms are reviewed in some detail. The requirements of chromospheric and coronal heating are discussed in the context of the fundamental constraints encountered in modelling the outer solar atmosphere. Heating by acoustic processes in the 'nonmagnetic' parts of the atmosphere is examined with particular emphasis on the shock wave theory. Also discussed are theories of heating by electrodynamic processes in the magnetic regions of the corona, either magnetohydrodynamic waves or current heating in the regions with large electric current densities (flare type heating). Problems associated with each of the models are addressed.

  6. Observation of coronal loop torsional oscillation

    NASA Astrophysics Data System (ADS)

    Zaqarashvili, T. V.

    2003-02-01

    We suggest that the global torsional oscillation of solar coronal loop may be observed by the periodical variation of a spectral line width. The amplitude of the variation must be maximal at the velocity antinodes and minimal at the nodes of the torsional oscillation. Then the spectroscopic observation as a time series at different heights above the active region at the solar limb may allow to determine the period and wavelength of global torsional oscillation and consequently the Alfvén speed in corona. From the analysis of early observation (Egan & Schneeberger \\cite{egan}) we suggest the value of coronal Alfvén speed as ~ 500 km s-1.

  7. Pressure structure of solar coronal loops

    NASA Technical Reports Server (NTRS)

    Krishan, V.

    1987-01-01

    The steady state pressure structure of a coronal loop is discussed in terms of the MHD global invariants of an incompressible plasma. The steady state is represented by the superposition of two Chandrasekhar-Kendall functions corresponding to (n=m=0) and (n=m=1) modes. The relative contribution of the two modes (epsilon) is found to depend on the surface pressure of the coronal loop which is also the pressure of the external medium. The mixed mode state does not exist for high values of the external pressure because epsilon becomes complex.

  8. Magnetohydrodynamic Modeling of Coronal Evolution and Disruption

    NASA Technical Reports Server (NTRS)

    Linker, Jon

    2002-01-01

    Flux cancellation, defined observationally as the mutual disappearance of magnetic fields of opposite polarity at the neutral line separating them, has been found to occur frequently at the site of filaments (called prominences when observed on the limb of the Sun). During the second year of this project, we have studied theoretically the role that flux cancellation may play in prominence formation, prominence eruption, and the initiation of coronal mass ejections. This work has been in published in two papers: "Magnetic Field Topology in Prominences" by Lionello, Mikic, Linker, and Amari and "Flux Cancellation and Coronal Mass Ejections" by Linker, Mikic, Riley, Lionello, Amari, and Odstrcil.

  9. Coronal Fractures of the Scaphoid: A Review.

    PubMed

    Slutsky, David J; Herzberg, Guillaume; Shin, Alexander Y; Buijze, Geert A; Ring, David C; Mudgal, Chaitanya S; Leung, Yuen-Fai; Dumontier, Christian

    2016-08-01

    Coronal (or frontal plane) fractures of the scaphoid are distinctly uncommon. There are few published reports of coronal fractures of the scaphoid. This fracture is often missed on the initial X-ray films. A high index of suspicion should exist when there is a double contour of the proximal scaphoid pole on the anteroposterior X-ray view. A computed tomography scan is integral in making the diagnosis. Early recognition is key in salvaging the scaphoid fracture and in preventing articular damage. Level of Evidence IV. Retrospective case series. PMID:27574573

  10. Stereoscopy and Tomography of Coronal Structures

    NASA Astrophysics Data System (ADS)

    de Patoul, J.

    2012-04-01

    The hot solar corona consists of a low density plasma, which is highly structured by the magnetic field. To resolve and study the corona, several solar Ultraviolet (UV) and X-ray telescopes are operated with high spatial and temporal resolution. EUV (Extreme UV) image sequences of the lower solar corona have revealed a wide variety of structures with sizes ranging from the Sun's diameter to the limit of the angular resolution. Active regions can be observed with enhanced temperature and density, as well as 'quiet' regions, coronal holes with lower density and numerous other transient phenomena such as plumes, jets, bright points, flares, filaments, coronal mass ejections, all structured by the coronal magnetic field. In this work, we analyze polar plumes in a sequence of Solar EUV images taken nearly simultaneously by the three telescopes on board of the spacecraft STEREO/SECCHI A and B, and SOHO/EIT. Plumes appear in EUV images as elongated objects starting on the surface of the Sun extending super-radially into the corona. Their formation and contribution to the fast solar wind and other coronal phenomena are still under debate. Knowledge of the polar plume 3-D geometry can help to understand some of the physical processes in the solar corona. In this dissertation we develop new techniques for the characterization of polar plume structures in solar coronal images (Part II) then we analyze these structures using the techniques (Part III): We design a new technique capable of automatically identifying plumes in solar EUV images close to the limb at 1.01-1.39 Ro. This plume identification is based on a multi-scale Hough-wavelet analysis. We show that the method is well adapted to identifying the location, width and orientation of plumes. Starting from Hough-wavelet analysis, we elaborate on two other techniques to determine 3-D plume localization and structure: (i) tomography employing data from a single spacecraft over more than half a rotation and (ii) stereoscopy

  11. Magnetohydrodynamic Simulation of a Streamer Beside a Realistic Coronal Hole

    NASA Technical Reports Server (NTRS)

    Suess, S. T.; Wu, S. T.; Wang, A. H.; Poletto, G.

    1994-01-01

    Existing models of coronal streamers establish their credibility and act as the initial state for transients. The models have produced satisfactory streamer simulations, but unsatisfactory coronal hole simulations. This is a consequence of the character of the models and the boundary conditions. The models all have higher densities in the magnetically open regions than occur in coronal holes (Noci, et al., 1993).

  12. Large-scale Globally Propagating Coronal Waves

    NASA Astrophysics Data System (ADS)

    Warmuth, Alexander

    2015-09-01

    Large-scale, globally propagating wave-like disturbances have been observed in the solar chromosphere and by inference in the corona since the 1960s. However, detailed analysis of these phenomena has only been conducted since the late 1990s. This was prompted by the availability of high-cadence coronal imaging data from numerous spaced-based instruments, which routinely show spectacular globally propagating bright fronts. Coronal waves, as these perturbations are usually referred to, have now been observed in a wide range of spectral channels, yielding a wealth of information. Many findings have supported the "classical" interpretation of the disturbances: fast-mode MHD waves or shocks that are propagating in the solar corona. However, observations that seemed inconsistent with this picture have stimulated the development of alternative models in which "pseudo waves" are generated by magnetic reconfiguration in the framework of an expanding coronal mass ejection. This has resulted in a vigorous debate on the physical nature of these disturbances. This review focuses on demonstrating how the numerous observational findings of the last one and a half decades can be used to constrain our models of large-scale coronal waves, and how a coherent physical understanding of these disturbances is finally emerging.

  13. Coronal Mass Ejections and Their Heliospheric Consequences

    NASA Technical Reports Server (NTRS)

    Gopalswamy, Nat

    2011-01-01

    Coronal mass ejections (CMEs) have been recognized as the most energetic phenomenon in the heliosphere, deriving their energy from the stressed magnetic fields on the Sun. The Solar and Heliospheric Observatory (SOHO) mission has accumulated a wealth of information on CMEs with unprecedented extent, clarity, and uniformity. The CME data base has been useful in confirming results from past missions and obtaining a number of new results on the initiation, propagation, and heliospheric consequences of CMEs. This paper highlights some of the recent results on the morphological, physical, and kinematic properties of CMEs observed during solar cycle 23. White-light signatures of CMEs and their utility in inferring coronal magnetic fields near the Sun will be discussed. Presence of coronal holes near eruption regions have been shown to significantly modify the trajectories of CMEs. New results on the interaction of CMEs with large-scale structures such as coronal holes and other CMEs will be presented. Finally, the CME consequences in the heliosphere such as interplanetary shocks, type II radio bursts, energetic particles, geomagnetic storms, and cosmic ray modulation will be discussed

  14. The Inconvenient Truth About Coronal Dimmings

    NASA Astrophysics Data System (ADS)

    McIntosh, Scott W.

    2009-03-01

    We investigate the occurrence of a coronal mass ejection (CME)-driven coronal dimming using unique high-resolution spectral images of the corona from the Hinode spacecraft. Over the course of the dimming event, we observe the dynamic increase of nonthermal line broadening in the 195.12 Å emission line of Fe XII as the corona opens. As the corona begins to close, refill and brighten, we see a reduction of the nonthermal broadening toward the pre-eruption level. We propose that the dynamic evolution of the nonthermal broadening is the result of the growth of Alfvén wave amplitudes in the magnetically open rarefied dimming region, compared to the dense closed corona prior to the CME. We suggest, based on this proposition, that, as open magnetic regions, coronal dimmings must act just as coronal holes and be sources of the fast solar wind, but only temporarily. Further, we propose that such a rapid transition in the thermodynamics of the corona to a solar wind state may have an impulsive effect on the CME that initiates the observed dimming. This last point, if correct, poses a significant physical challenge to the sophistication of CME modeling and capturing the essence of the source region thermodynamics necessary to correctly ascertain CME propagation speeds, etc.

  15. Modeling Eruptive Coronal Magnetohydrodynamic Systems with FLUX

    NASA Astrophysics Data System (ADS)

    Rachmeler, Laurel

    2010-05-01

    I explore solar coronal energetic eruptions in the context of magnetic reconnection, which is commonly thought to be a required trigger mechanism for solar eruptions. Reconnection is difficult to observe in the corona, and current numerical methods cannot model reconnectionless control cases. Thus, it is not possible to determine if it is a necessary component. I have executed multiple controlled simulations to determine the importance of reconnection for initiation and evolution of several eruptive systems using FLUX, a numerical model that uses the comparatively new fluxon technique. I describe two types of eruptions modeled with FLUX: a confined flux rope theory for CME initiation, and symmetrically twisted coronal jets in a uniform vertical background field. In the former, I identified an ideal MHD instability that allows metastable twisted flux rope systems to suddenly lose stability and erupt even in the absence of reconnection, contradicting previous conjecture. The CME result is in contrast to the azimuthally symmetric coronal jet initiation model, where jet-like behavior does not manifest without reconnection. I demonstrate that some eruptive phenomena may be triggered by non-reconnective means such as ideal MHD instabilities, and that magnetic reconnection is not a required element in all coronal eruptions.

  16. Magnetic Topology of Coronal Hole Linkages

    NASA Technical Reports Server (NTRS)

    Titov, V. S.; Mikic, Z.; Linker, J. A.; Lionello, R.; Antiochos, S. K.

    2010-01-01

    In recent work, Antiochos and coworkers argued that the boundary between the open and closed field regions on the Sun can be extremely complex with narrow corridors of open ux connecting seemingly disconnected coronal holes from the main polar holes, and that these corridors may be the sources of the slow solar wind. We examine, in detail, the topology of such magnetic configurations using an analytical source surface model that allows for analysis of the eld with arbitrary resolution. Our analysis reveals three important new results: First, a coronal hole boundary can join stably to the separatrix boundary of a parasitic polarity region. Second, a single parasitic polarity region can produce multiple null points in the corona and, more important, separator lines connecting these points. Such topologies are extremely favorable for magnetic reconnection, because it can now occur over the entire length of the separators rather than being con ned to a small region around the nulls. Finally, the coronal holes are not connected by an open- eld corridor of finite width, but instead are linked by a singular line that coincides with the separatrix footprint of the parasitic polarity. We investigate how the topological features described above evolve in response to motion of the parasitic polarity region. The implications of our results for the sources of the slow solar wind and for coronal and heliospheric observations are discussed.

  17. Coronal bright points associated with minifilament eruptions

    SciTech Connect

    Hong, Junchao; Jiang, Yunchun; Yang, Jiayan; Bi, Yi; Li, Haidong; Yang, Bo; Yang, Dan

    2014-12-01

    Coronal bright points (CBPs) are small-scale, long-lived coronal brightenings that always correspond to photospheric network magnetic features of opposite polarity. In this paper, we subjectively adopt 30 CBPs in a coronal hole to study their eruptive behavior using data from the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory. About one-quarter to one-third of the CBPs in the coronal hole go through one or more minifilament eruption(s) (MFE(s)) throughout their lifetimes. The MFEs occur in temporal association with the brightness maxima of CBPs and possibly result from the convergence and cancellation of underlying magnetic dipoles. Two examples of CBPs with MFEs are analyzed in detail, where minifilaments appear as dark features of a cool channel that divide the CBPs along the neutral lines of the dipoles beneath. The MFEs show the typical rising movements of filaments and mass ejections with brightenings at CBPs, similar to large-scale filament eruptions. Via differential emission measure analysis, it is found that CBPs are heated dramatically by their MFEs and the ejected plasmas in the MFEs have average temperatures close to the pre-eruption BP plasmas and electron densities typically near 10{sup 9} cm{sup –3}. These new observational results indicate that CBPs are more complex in dynamical evolution and magnetic structure than previously thought.

  18. The topological description of coronal magnetic fields

    NASA Technical Reports Server (NTRS)

    Berger, Mitchell A.

    1986-01-01

    Determining the structure and behavior of solar coronal magnetic fields is a central problem in solar physics. At the photosphere, the field is believed to be strongly localized into discrete flux tubes. After providing a rigorous definition of field topology, how the topology of a finite collection of flux tubes may be classified is discussed.

  19. Modified Coronal Index of the Solar Activity

    NASA Astrophysics Data System (ADS)

    Lukáč, B.; Rybanský, M.

    2010-05-01

    The original coronal index of the solar activity (CI) has been constructed on the basis of ground-based measurements of the intensities of the coronal line of 530.3 nm (Rybanský in Bull. Astron. Inst. Czechoslov., 28, 367, 1975; Rybanský et al. in J. Geophys. Res., 110, A08106, 2005). In this paper, CI is compared with the EUV measurements on the CELIAS/SEM equipment based on the same idea as the original idea of the coronal index. The correlation is very good for the period 1996 - 2005 ( r=0.94 for daily values). The principal result of this paper is the introduction of the modified coronal index (MCI) which in all uses and contexts can replace the existing CI index. Daily MCI values extend over a time period of six solar activity cycles. Future MCI measurements will be derived from more reliable measurements made by space-based observatories that are not influenced by the weather. MCI measurements are and will continue to be archived at the web site of the Slovak Central Observatory in Hurbanovo ( http://www.suh.sk/obs/vysl/MCI.htm ).

  20. Coronal behavior before the large flare onset

    NASA Astrophysics Data System (ADS)

    Imada, Shinsuke; Bamba, Yumi; Kusano, Kanya

    2014-12-01

    Flares are a major explosive event in our solar system. They are often followed by a coronal mass ejection that has the potential to trigger geomagnetic storms. There are various studies aiming to predict when and where the flares are likely to occur. Most of these studies mainly discuss the photospheric and chromospheric activity before the flare onset. In this paper we study the coronal features before the famous large flare occurrence on 2006 December 13. Using the data from Hinode/Extreme ultraviolet Imaging Spectrometer (EIS), X-Ray Telescope (XRT), and Solar and Heliospheric Observatory (SOHO)/Extreme ultraviolet Imaging Telescope (EIT), we discuss the coronal features in the large scale (a few 100″) before the flare onset. Our findings are as follows. (1) The upflows in and around the active region start growing from ˜ 10 to 30 km s-1 a day before the flare. (2) The expanding coronal loops are clearly observed a few hours before the flare. (3) Soft X-ray and extreme ultraviolet intensity are gradually reduced. (4) The upflows are further enhanced after the flare. From these observed signatures, we conclude that the outer part of active region loops with low density was expanding a day before the flare onset, and the inner part with high density was expanding a few hours before the onset.

  1. Relating magnetic reconnection to coronal heating.

    PubMed

    Longcope, D W; Tarr, L A

    2015-05-28

    It is clear that the solar corona is being heated and that coronal magnetic fields undergo reconnection all the time. Here we attempt to show that these two facts are related--i.e. coronal reconnection generates heat. This attempt must address the fact that topological change of field lines does not automatically generate heat. We present one case of flux emergence where we have measured the rate of coronal magnetic reconnection and the rate of energy dissipation in the corona. The ratio of these two, [Formula: see text], is a current comparable to the amount of current expected to flow along the boundary separating the emerged flux from the pre-existing flux overlying it. We can generalize this relation to the overall corona in quiet Sun or in active regions. Doing so yields estimates for the contribution to coronal heating from magnetic reconnection. These estimated rates are comparable to the amount required to maintain the corona at its observed temperature. PMID:25897089

  2. Can Thermal Nonequilibrium Explain Coronal Loops?

    NASA Technical Reports Server (NTRS)

    Klimchuk, James A.; Karpen, Judy T.; Antiochos, Spiro K.

    2010-01-01

    Any successful model of coronal loops must explain a number of observed properties. For warm (approx. 1 MK) loops, these include: 1. excess density, 2. flat temperature profile, 3. super-hydrostatic scale height, 4. unstructured intensity profile, and 5. 1000-5000 s lifetime. We examine whether thermal nonequilibrium can reproduce the observations by performing hydrodynamic simulations based on steady coronal heating that decreases exponentially with height. We consider both monolithic and multi-stranded loops. The simulations successfully reproduce certain aspects of the observations, including the excess density, but each of them fails in at least one critical way. -Xonolithic models have far too much intensity structure, while multi-strand models are either too structured or too long-lived. Storms of nanoflares remain the only viable explanation for warm loops that has been proposed so far. Our results appear to rule out the widespread existence of heating that is both highly concentrated low in the corona and steady or quasi-steady (slowly varying or impulsive with a rapid cadence). Active regions would have a very different appearance if the dominant heating mechanism had these properties. Thermal nonequilibrium may nonetheless play an important role in prominences and catastrophic cooling e(veen.gts..,coronal rain) that occupy a small fraction of the coronal volume. However, apparent inconsistencies between the models and observations of cooling events have yet to be understood.

  3. OBSERVING CORONAL NANOFLARES IN ACTIVE REGION MOSS

    SciTech Connect

    Testa, Paola; DeLuca, Ed; Golub, Leon; Korreck, Kelly; Weber, Mark; De Pontieu, Bart; Martinez-Sykora, Juan; Title, Alan; Hansteen, Viggo; Cirtain, Jonathan; Winebarger, Amy; Kobayashi, Ken; Kuzin, Sergey; Walsh, Robert; DeForest, Craig

    2013-06-10

    The High-resolution Coronal Imager (Hi-C) has provided Fe XII 193A images of the upper transition region moss at an unprecedented spatial ({approx}0.''3-0.''4) and temporal (5.5 s) resolution. The Hi-C observations show in some moss regions variability on timescales down to {approx}15 s, significantly shorter than the minute-scale variability typically found in previous observations of moss, therefore challenging the conclusion of moss being heated in a mostly steady manner. These rapid variability moss regions are located at the footpoints of bright hot coronal loops observed by the Solar Dynamics Observatory/Atmospheric Imaging Assembly in the 94 A channel, and by the Hinode/X-Ray Telescope. The configuration of these loops is highly dynamic, and suggestive of slipping reconnection. We interpret these events as signatures of heating events associated with reconnection occurring in the overlying hot coronal loops, i.e., coronal nanoflares. We estimate the order of magnitude of the energy in these events to be of at least a few 10{sup 23} erg, also supporting the nanoflare scenario. These Hi-C observations suggest that future observations at comparable high spatial and temporal resolution, with more extensive temperature coverage, are required to determine the exact characteristics of the heating mechanism(s).

  4. The evolution of coronal magnetic fields

    NASA Technical Reports Server (NTRS)

    Priest, E. R.; Forbes, T. G.

    1990-01-01

    Slow photospheric motions can produce flow speeds in the corona which are fast enough to violate quasi-static evolution. Therefore, high-speed flows observed in the corona are not necessarily due to a loss of equilibrium or stability. This paper presents an example where the flow speed increases indefinitely with height while the coronal magnetic energy increases quadratically with time.

  5. CAN THERMAL NONEQUILIBRIUM EXPLAIN CORONAL LOOPS?

    SciTech Connect

    Klimchuk, James A.; Karpen, Judy T.; Antiochos, Spiro K.

    2010-05-10

    Any successful model of coronal loops must explain a number of observed properties. For warm ({approx}1 MK) loops, these include (1) excess density, (2) flat temperature profile, (3) super-hydrostatic scale height, (4) unstructured intensity profile, and (5) 1000-5000 s lifetime. We examine whether thermal nonequilibrium can reproduce the observations by performing hydrodynamic simulations based on steady coronal heating that decreases exponentially with height. We consider both monolithic and multi-stranded loops. The simulations successfully reproduce certain aspects of the observations, including the excess density, but each of them fails in at least one critical way. Monolithic models have far too much intensity structure, while multi-strand models are either too structured or too long-lived. Our results appear to rule out the widespread existence of heating that is both highly concentrated low in the corona and steady or quasi-steady (slowly varying or impulsive with a rapid cadence). Active regions would have a very different appearance if the dominant heating mechanism had these properties. Thermal nonequilibrium may nonetheless play an important role in prominences and catastrophic cooling events (e.g., coronal rain) that occupy a small fraction of the coronal volume. However, apparent inconsistencies between the models and observations of cooling events have yet to be understood.

  6. Simulating coronal condensation dynamics in 3D

    NASA Astrophysics Data System (ADS)

    Moschou, S. P.; Keppens, R.; Xia, C.; Fang, X.

    2015-12-01

    We present numerical simulations in 3D settings where coronal rain phenomena take place in a magnetic configuration of a quadrupolar arcade system. Our simulation is a magnetohydrodynamic simulation including anisotropic thermal conduction, optically thin radiative losses, and parametrised heating as main thermodynamical features to construct a realistic arcade configuration from chromospheric to coronal heights. The plasma evaporation from chromospheric and transition region heights eventually causes localised runaway condensation events and we witness the formation of plasma blobs due to thermal instability, that evolve dynamically in the heated arcade part and move gradually downwards due to interchange type dynamics. Unlike earlier 2.5D simulations, in this case there is no large scale prominence formation observed, but a continuous coronal rain develops which shows clear indications of Rayleigh-Taylor or interchange instability, that causes the denser plasma located above the transition region to fall down, as the system moves towards a more stable state. Linear stability analysis is used in the non-linear regime for gaining insight and giving a prediction of the system's evolution. After the plasma blobs descend through interchange, they follow the magnetic field topology more closely in the lower coronal regions, where they are guided by the magnetic dips.

  7. MAGNETIC TOPOLOGY OF CORONAL HOLE LINKAGES

    SciTech Connect

    Titov, V. S.; Mikic, Z.; Linker, J. A.; Lionello, R.; Antiochos, S. K. E-mail: mikicz@predsci.com E-mail: lionel@predsci.com

    2011-04-20

    In recent work, Antiochos and coworkers argued that the boundary between the open and closed field regions on the Sun can be extremely complex with narrow corridors of open flux connecting seemingly disconnected coronal holes from the main polar holes and that these corridors may be the sources of the slow solar wind. We examine, in detail, the topology of such magnetic configurations using an analytical source surface model that allows for analysis of the field with arbitrary resolution. Our analysis reveals three new important results. First, a coronal hole boundary can join stably to the separatrix boundary of a parasitic polarity region. Second, a single parasitic polarity region can produce multiple null points in the corona and, more important, separator lines connecting these points. It is known that such topologies are extremely favorable for magnetic reconnection, because they allow this process to occur over the entire length of the separators rather than being confined to a small region around the nulls. Finally, the coronal holes are not connected by an open-field corridor of finite width, but instead are linked by a singular line that coincides with the separatrix footprint of the parasitic polarity. We investigate how the topological features described above evolve in response to the motion of the parasitic polarity region. The implications of our results for the sources of the slow solar wind and for coronal and heliospheric observations are discussed.

  8. The Role of Active Region Coronal Magnetic Field in Determining Coronal Mass Ejection Propagation Direction

    NASA Astrophysics Data System (ADS)

    Wang, Rui; Liu, Ying D.; Dai, Xinghua; Yang, Zhongwei; Huang, Chong; Hu, Huidong

    2015-11-01

    We study the role of the coronal magnetic field configuration of an active region (AR) in determining the propagation direction of a coronal mass ejection (CME). The CME occurred in the AR 11944 (S09W01) near the disk center on 2014 January 7 and was associated with an X1.2 flare. A new CME reconstruction procedure based on a polarimetric technique is adopted, which shows that the CME changed its propagation direction by around 28° in latitude within 2.5 {R}⊙ and 43° in longitude within 6.5 {R}⊙ with respect to the CME source region. This significant non-radial motion is consistent with the finding of Möstl et al. We use nonlinear force-free field and potential field source surface extrapolation methods to determine the configurations of the coronal magnetic field. We also calculate the magnetic energy density distributions at different heights based on the extrapolations. Our results show that the AR coronal magnetic field has a strong influence on the CME propagation direction. This is consistent with the “channeling” by the AR coronal magnetic field itself, rather than deflection by nearby structures. These results indicate that the AR coronal magnetic field configuration has to be taken into account in order to determine CME propagation direction correctly.

  9. CORONAL SEISMOLOGY USING EIT WAVES: ESTIMATION OF THE CORONAL MAGNETIC FIELD STRENGTH IN THE QUIET SUN

    SciTech Connect

    West, M. J.; Zhukov, A. N.; Dolla, L.; Rodriguez, L.

    2011-04-01

    Coronal EIT waves have been observed for many years. The nature of EIT waves is still contentious, however, there is strong evidence that some of them might be fast magnetosonic waves, or at least have a fast magnetosonic wave component. The fast magnetosonic wave speed is formed from two components; the Alfven speed (magnetic) and the sound speed (thermal). By making measurements of the wave speed, coronal density and temperature it is possible to calculate the quiet-Sun coronal magnetic field strength through coronal seismology. In this paper, we investigate an EIT wave observed on 2009 February 13 by the SECCHI/EUVI instruments on board the STEREO satellites. The wave epicenter was observed at disk center in the STEREO B (Behind) satellite. At this time, the STEREO satellites were separated by approximately 90 deg., and as a consequence the STEREO A (Ahead) satellite observed the wave on the solar limb. These observations allowed us to make accurate speed measurements of the wave. The background coronal density was derived through Hinode/Extreme-ultraviolet Imaging Spectrometer observations of the quiet Sun and the temperature was estimated through the narrow temperature response in the EUVI bandpasses. The density, temperature, and speed measurements allowed us to estimate the quiet-Sun coronal magnetic field strength to be approximately 0.7 {+-} 0.7 G.

  10. Differential Emission Measure Studies of Solar Coronal Loops for AIA

    NASA Astrophysics Data System (ADS)

    Chattopadhyay, D.; Weber, M. A.; Sette, A. L.

    2004-12-01

    The Atmospheric Imaging Assembly (AIA) on the Solar Dynamic Observatory scheduled to launch in 2008 will provide an unprecedented quantity of information about the solar corona at rapid cadence in 6 EUV channels. We discuss the study of coronal loops through differential emission measure (DEM) analysis of coronal plasma using mock AIA observations. We select a loop structure in the coronal model and evaluate various DEM estimation methods (including background subtraction) against the known loop properties. We find that coronal loops can be successfully identified by their DEM signatures. Such signatures provide observational data essential to furthering our understanding of hot coronal plasmas.

  11. Management of distal humeral coronal shear fractures

    PubMed Central

    Yari, Shahram S; Bowers, Nathan L; Craig, Miguel A; Reichel, Lee M

    2015-01-01

    Coronal shear fractures of the distal humerus are rare, complex fractures that can be technically challenging to manage. They usually result from a low-energy fall and direct compression of the distal humerus by the radial head in a hyper-extended or semi-flexed elbow or from spontaneous reduction of a posterolateral subluxation or dislocation. Due to the small number of soft tissue attachments at this site, almost all of these fractures are displaced. The incidence of distal humeral coronal shear fractures is higher among women because of the higher rate of osteoporosis in women and the difference in carrying angle between men and women. Distal humeral coronal shear fractures may occur in isolation, may be part of a complex elbow injury, or may be associated with injuries proximal or distal to the elbow. An associated lateral collateral ligament injury is seen in up to 40% and an associated radial head fracture is seen in up to 30% of these fractures. Given the complex nature of distal humeral coronal shear fractures, there is preference for operative management. Operative fixation leads to stable anatomic reduction, restores articular congruity, and allows initiation of early range-of-motion movements in the majority of cases. Several surgical exposure and fixation techniques are available to reconstruct the articular surface following distal humeral coronal shear fractures. The lateral extensile approach and fixation with countersunk headless compression screws placed in an anterior-to-posterior fashion are commonly used. We have found a two-incision approach (direct anterior and lateral) that results in less soft tissue dissection and better outcomes than the lateral extensile approach in our experience. Stiffness, pain, articular incongruity, arthritis, and ulnohumeral instability may result if reduction is non-anatomic or if fixation fails. PMID:25984515

  12. A Two-Fluid, MHD Coronal Model

    NASA Technical Reports Server (NTRS)

    Suess, Steven T.; Wang, A.-H.; Wu, S. T.; Poletto, G.; McComas, D. J.

    1998-01-01

    We describe first results from a numerical two-fluid MHD model of the global structure of the solar corona. The model is two-fluid in the sense that it accounts for the collisional energy exchange between protons and electrons. As in our single-fluid model, volumetric heat and momentum sources are required to produce high speed wind from coronal holes, low speed wind above streamers, and mass fluxes similar to the empirical solar wind. By specifying different proton and electron heating functions we obtain a high proton temperature in the coronal hole and a relatively low proton temperature in the streamer (in comparison with the electron temperature). This is consistent with inferences from SOHO/UVCS, and with the Ulysses/SWOOPS proton and electron temperature measurements which we show from the fast latitude scan. The density in the coronal hole between 2 solar radii and 5 solar radii (2RS and 5RS) is similar to the density reported from SPARTAN 201-01 measurements by Fisher and Guhathakurta. The proton mass flux scaled to 1 AU is 2.4 x 10(exp 8)/sq cm s, which is consistent with Ulysses observations. Inside the closed field region, the density is sufficiently high so that the simulation gives equal proton and electron temperatures due to the high collision rate. In open field regions (in the coronal hole and above the streamer) the proton and electron temperatures differ by varying amounts. In the streamer, the temperature and density are similar to those reported empirically by Li et al and the plasma beta is larger than unity everywhere above approx. 1.5 R(sub s), as it is in all other MHD coronal streamer models.

  13. Structure and Dynamics of Coronal Plasma

    NASA Technical Reports Server (NTRS)

    Golub, Leon

    1998-01-01

    Brief summaries of the four published papers produced within the present performance period of NASA Grant NAGW-4081 are presented. The full text of the papers are appended to the report. The first paper titled "Coronal Structures Observed in X-rays and H-alpa Structures" was published in the Kofu Symposium proceedings. The study analyzes cool and hot behavior of two x-ray events, a small flare and a surge. It was found that a large H-alpha surge appears in x-rays as a very weak event, while a weak H-alpha feature corresponds to the brightest x-ray emission on the disk at the time of the observation. Calculations of the heating necessary to produce these signatures, and implications for the driving and heating mechanisms of flares vs. surges are presented. The second paper "Differential Magnetic Field Shear in an Active Region" has been published in The Astrophysical Journal. The study compared the three dimensional extrapolation of magnetic fields with the observed coronal structure in an active region. Based on the fit between observed coronal structure throughout the volume of the region and the calculated magnetic field configurations, the authors propose a differential magnetic field shear model for this active region. The decreasing field shear in the outer portions of the AR may indicate a continual relaxation of the magnetic field with time, corresponding to a net transport of helicity outward. The third paper "Difficulties in Observing Coronal Structure" has been published in the journal Solar Physics. This paper discusses the evidence that the temperature and density structure of the corona are far more complicated than had previously been thought. The discussion is based on five studies carried out by the group on coronal plasma properties, showing that any one x-ray instrument does see all of the plasma present in the corona, that hot and cool material may appear to be co-spatial at a given location in the corona, and that simple magnetic field

  14. Magnetism and the Invisible Man: The mysteries of coronal cavities

    NASA Astrophysics Data System (ADS)

    Gibson, Sarah

    2014-01-01

    Magnetism defines the complex and dynamic solar corona. Twists and tangles in coronal magnetic fields build up energy and ultimately erupt, hurling plasma into interplanetary space. These coronal mass ejections (CMEs) are transient riders on the ever-outflowing solar wind, which itself possesses a three-dimensional morphology shaped by the global coronal magnetic field. Coronal magnetism is thus at the heart of any understanding of the origins of space weather at the Earth. However, we have historically been limited by the difficulty of directly measuring the magnetic fields of the corona, and have turned to observations of coronal plasma to trace out magnetic structure. This approach is complicated by the fact that plasma temperatures and densities vary among coronal magnetic structures, so that looking at any one wavelength of light only shows part of the picture. In fact, in some regimes it is the lack of plasma that is a significant indicator of the magnetic field. Such a case is the coronal cavity: a dark, elliptical region in which strong and twisted magnetism dwells. I will elucidate these enigmatic features by presenting observations of coronal cavities in multiple wavelengths and from a variety of observing vantages, including unprecedented coronal magnetic field measurements now being obtained by the Coronal Multichannel Polarimeter (CoMP). These observations demonstrate the presence of twisted magnetic fields within cavities, and also provide clues to how and why cavities ultimately erupt as CMEs.

  15. Loop observations and the coronal heating problem

    NASA Astrophysics Data System (ADS)

    López Fuentes, M. C.; Klimchuk, J. A.

    2015-08-01

    Coronal heating continues to be one of the fundamental problems of solar physics. In recent years, instrumental advances and the availability of data from space observatories produced important progress, imposing restrictions to the models proposed. However, since the physical processes occur at spatial scales below the present instrumental resolution, definitive answers are still due. Since the corona is strongly dominated by the magnetic field, active region plasma is confined in closed structures or loops. These are the basic observable blocks of the corona, so the analysis of their structure and evolution is essential to understand the heating. In this report, mainly addressed to astronomers not necessarily familiarized with the subject, we review some of the proposed heating models and we pay special attention to the sometimes confusing and apparently contradictory observations of coronal loops. We discuss the consequences of these observations for some of the heating models proposed, in particular those based on impulsive events known as nanoflares.

  16. Solar Cycle Changes of Coronal Streamer Properties

    NASA Astrophysics Data System (ADS)

    Strachan, L.; Baham, M.; Miralles, M.; Panasyuk, A.

    2003-12-01

    We have measured UV spectroscopic parameters, as a function of height for more than 30 coronal streamers in order to identify similarities between streamers at different phases of the solar cycle. For the period from 1996-2002, we provide line intensities, line widths, and line ratios for the O VI 1032/1037 doublet and intensities and line widths for the H I Ly-alpha line for these streamers. From such measurements we can derive plasma parameters (densities, temperatures, and outflow velocities) for O5+ and protons as a function of heliocentric height (1.5 > r/Ro > 5) in the streamers. This information is useful for setting empirical constraints on coronal heating and solar wind acceleration in streamers. This work is supported by NASA Grant NAG5-12781 to the Smithsonian Astrophysical Observatory and NASA subcontract OGSP21010200061SAO awarded to SAO through a grant to Southern Universty at Baton Rouge.

  17. MAGNETOHYDRODYNAMIC SIMULATIONS OF INTERPLANETARY CORONAL MASS EJECTIONS

    SciTech Connect

    Lionello, Roberto; Downs, Cooper; Linker, Jon A.; Török, Tibor; Riley, Pete; Mikić, Zoran E-mail: cdowns@predsci.com E-mail: tibor@predsci.com E-mail: mikic@predsci.com

    2013-11-01

    We describe a new MHD model for the propagation of interplanetary coronal mass ejections (ICMEs) in the solar wind. Accurately following the propagation of ICMEs is important for determining space weather conditions. Our model solves the MHD equations in spherical coordinates from a lower boundary above the critical point to Earth and beyond. On this spherical surface, we prescribe the magnetic field, velocity, density, and temperature calculated typically directly from a coronal MHD model as time-dependent boundary conditions. However, any model that can provide such quantities either in the inertial or rotating frame of the Sun is suitable. We present two validations of the technique employed in our new model and a more realistic simulation of the propagation of an ICME from the Sun to Earth.

  18. Geometrical Properties of Coronal Mass Ejections

    NASA Astrophysics Data System (ADS)

    Cremades, Hebe; Bothmer, Volker

    Based on the SOHO/LASCO dataset, a collection of "structured" coronal mass ejections (CMEs) has been compiled within the period 1996-2002, in order to analyze their three-dimensional configuration. These CME events exhibit white-light fine structures, likely indicative of their possible 3D topology. From a detailed investigation of the associated low coronal and photospheric source regions, a generic scheme has been deduced, which considers the white-light topology of a CME projected in the plane of the sky as being primarily dependent on the orientation and position of the source region's neutral line on the solar disk. The obtained results imply that structured CMEs are essentially organized along a symmetry axis, in a cylindrical manner. The measured dimensions of the cylinder's base and length yield a ratio of 1.6. These CMEs seem to be better approximated by elliptic cones, rather than by the classical ice cream cone, characterized by a circular cross section.

  19. Interplanetary Coronal Mass Ejections detected by HAWC

    NASA Astrophysics Data System (ADS)

    Lara, Alejandro

    The High Altitude Water Cherenkov (HAWC) observatory is being constructed at the volcano Sierra Negra (4100 m a.s.l.) in Mexico. HAWC’s primary purpose is the study of both: galactic and extra-galactic sources of high energy gamma rays. HAWC will consist of 300 large water Cherenkov detectors (WCD), instrumented with 1200 photo-multipliers. The Data taking has already started while construction continues, with the completion projected for late 2014. The HAWC counting rate will be sensitive to cosmic rays with energies above the geomagnetic cutoff of the site (˜ 8 GV). In particular, HAWC will detect solar energetic particles known as Ground Level Enhancements (GLEs), and the effects of Coronal Mass Ejections on the galactic cosmic ray flux, known as Forbush Decreases. In this paper, we present a description of the instrument and its response to interplanetary coronal mass ejections, and other solar wind large scale structures, observed during the August-December 2013 period.

  20. Sunquake Generation by Coronal Magnetic Restructuring

    NASA Astrophysics Data System (ADS)

    Russell, A. J. B.; Mooney, M.; Leake, J. E.; Hudson, H. S.

    2015-12-01

    Solar flares and coronal mass ejections are powered by major restructurings of the coronal magnetic field, which appear to strongly perturb the magnetic field in the photosphere as well. Could the associated Lorentz forces generate sunquakes, as suggested by Hudson et al. 2008? Here, we present the first MHD simulations of sunquake generation by magnetic field perturbations, and explore the details of this mechanism. The downgoing magnetic field change is modelled as an Alfven wave, which propagates into the lower atmosphere. When it reaches the vicinity of the beta=1 layer (where the Alfven and sound speeds are equal), non-linear coupling excites a downgoing acoustic wave, which we interpret as a sunquake. The amplitude of the acoustic wave increases nonlinearly with the amplitude of the magnetic perturbation, reaching a limit where around 35% of the injected Poynting flux is transferred to the seismic wave - enough energy to match sunquake observations.

  1. Solar Energetic Particles: Sampling Coronal Abundances

    NASA Astrophysics Data System (ADS)

    Reames, Donald V.

    1998-05-01

    In the large solar energetic particle (SEP) events, coronal mass ejections (CMEs) drive shock waves out through the corona that accelerate elements of the ambient material to MeV energies in a fairly democratic, temperature-independent manner. These events provide the most complete source of information on element abundances in the corona. Relative abundances of 22 elements from H through Zn display the well-known dependence on the first ionization potential (FIP) that distinguishes coronal and photospheric material. For most elements, the main abundance variations depend upon the gyrofrequency, and hence on the charge-to-mass ratio, Q/A, of the ion. Abundance variations in the dominant species, H and He, are not Q/A dependent, presumably because of non-linear wave-particle interactions of H and He during acceleration. Impulsive flares provide a different sample of material that confirms the Ne:Mg:Si and He/C abundances in the corona.

  2. Interplanetary Coronal Mass Ejections During 1996 - 2007

    NASA Technical Reports Server (NTRS)

    Richardson, I. G.; Cane, H. V.

    2007-01-01

    Interplanetary coronal mass ejections, the interplanetary counterparts of coronal mass ejections at the Sun, are the major drivers of interplanetary shocks in the heliosphere, and are associated with modulations of the galactic cosmic ray intensity, both short term (Forbush decreases caused by the passage of the shock, post-shock sheath, and ICME), and possibly with longer term modulation. Using several in-situ signatures of ICMEs, including plasma temperature, and composition, magnetic fields, and cosmic ray modulations, made by near-Earth spacecraft, we have compiled a "comprehensive" list of ICMEs passing the Earth since 1996, encompassing solar cycle 23. We summarize the properties of these ICMEs, such as their occurrence rate, speeds and other parameters, the fraction of ICMEs that are classic magnetic clouds, and their association with solar energetic particle events, halo CMEs, interplanetary shocks, geomagnetic storms, shocks and cosmic ray decreases.

  3. Longitudinal asymmetries of the coronal line intensities

    NASA Astrophysics Data System (ADS)

    Xanthakis, J.; Petropoulos, B.; Tritakis, V. P.; Mavromichalaki, H.; Marmatsuri, L.

    The analysis of the daily measurements of the coronal green line intensity which have been collected by the Pic-du-Midi Observatory during the period 1944-1974 has led to some very interesting results. The main finding of this analysis is a permanent longitudinal asymmetry of the green line intensity which has been determined all along the data record. In an effort to make this asymmetry certain E-W intensity differences very close to the solar equator where the rotation rate for coronal features is equal to 25.35 days on the average are examined. When these data are examined every 25 days, namely data which almost correspond to the same points of the solar disk, it confirms the above mentioned longitudinal asymmetry.

  4. Solar Coronal Jets: Observations, Theory, and Modeling

    NASA Astrophysics Data System (ADS)

    Raouafi, N. E.; Patsourakos, S.; Pariat, E.; Young, P. R.; Sterling, A. C.; Savcheva, A.; Shimojo, M.; Moreno-Insertis, F.; DeVore, C. R.; Archontis, V.; Török, T.; Mason, H.; Curdt, W.; Meyer, K.; Dalmasse, K.; Matsui, Y.

    2016-07-01

    Coronal jets represent important manifestations of ubiquitous solar transients, which may be the source of significant mass and energy input to the upper solar atmosphere and the solar wind. While the energy involved in a jet-like event is smaller than that of "nominal" solar flares and coronal mass ejections (CMEs), jets share many common properties with these phenomena, in particular, the explosive magnetically driven dynamics. Studies of jets could, therefore, provide critical insight for understanding the larger, more complex drivers of the solar activity. On the other side of the size-spectrum, the study of jets could also supply important clues on the physics of transients close or at the limit of the current spatial resolution such as spicules. Furthermore, jet phenomena may hint to basic process for heating the corona and accelerating the solar wind; consequently their study gives us the opportunity to attack a broad range of solar-heliospheric problems.

  5. Empirical scaling laws for coronal heating

    NASA Technical Reports Server (NTRS)

    Golub, L.

    1983-01-01

    The origins and uses of scaling laws in studies of stellar outer atmospheres are reviewed with particular emphasis on the properties of coronal loops. Some evidence is presented for a fundamental structuring of the solar corona and the thermodynamics of scaling laws are discussed. It is found that magnetic field-related scaling laws can be obtained by relating coronal pressure, temperature, and magnetic field strength. Available data validate this method. Some parameters of the theory, however, must be treated as adjustable, and it is considered necessary to examine data from other stars in order to determine the validity of the parameters. Using detailed observational data, the applicability of single loop models is examined.

  6. STATISTICAL STUDY OF CORONAL MASS EJECTIONS WITH AND WITHOUT DISTINCT LOW CORONAL SIGNATURES

    SciTech Connect

    Ma, S.; Attrill, G. D. R.; Golub, L.; Lin, J.

    2010-10-10

    Taking advantage of the two viewpoints of the STEREO spacecraft, we present a statistical study of coronal mass ejections (CMEs) with and without distinct low coronal signatures (LCSs) from 2009 January 1 to August 31. During this period, the lines of sight from STEREO A and B are almost perpendicular and nearly a quarter of the Sun was observed by both. We identified 34 CMEs that originated from around this area and find that (1) about 1 out of 3 CMEs that were studied during 8 months of solar minimum activity are stealth CMEs; a CME is stealth if no distinct LCS (such as coronal dimming, coronal wave, filament eruption, flare, post-eruptive arcade) can be found on the disk. (2) The speeds of the stealth CMEs without LCSs are typically below 300 km s{sup -1}. Comparing with the slow CMEs with LCSs, the stealth CMEs did not show any clear differences in their velocity and acceleration evolution. (3) The source regions of the stealth CMEs are usually located in the quiet Sun rather than active regions. Detailed study indicates that more than half of the stealth CMEs in this paper showed some faint change of the coronal structures (likely parts of flux ropes) when they could be observed over the solar limb before or during the CME evolution. Finally, we note that space weather detection systems based on LCSs totally independent of coronagraph data may fail to detect a significant proportion of CMEs.

  7. Structure and dynamics of coronal plasmas

    NASA Technical Reports Server (NTRS)

    Golub, Leon

    1995-01-01

    The Normal Incidence X-ray Telescope (NIXT) obtained a unique set of high resolution full disk solar images which were exposed simultaneously by X-rays in a passband at 63.5 A and by visible light. The perfect alignment of a photospheric visible light image with a coronal X-ray image enables us to present observations of X-ray intensity vs an accurately determined height above the visible limb. The height at which the observed X-ray intensity peak varies from 4000 km in active regions to 9000 km in quiet regions of the sun. The interpretation of the observations stems from the previously established fact that, for the coronal loops, emission in the NIXT bandpass peaks sharply just above the footpoints. Because there is not a sharp peak in the observed X-ray intensity vs off limb height, we conclude that the loop footpoints, when viewed at the limb, are obscured by absorption in chromospheric material along the line of sight. We calculate the X-ray intensity vs height predicted by a number of different idealizations of the solar atmosphere, and we compare these calculations with the observed X-ray intensity vs height. The calculations use existing coronal and chromospheric models. In order for the calculations to reproduce the observed off limb X-ray intensities, we are forced to assume an atmosphere in which the footpoints of coronal loops are interspersed along the line of sight with cooler chromospheric material extending to heights well above the loop footpoints. We argue that the absorption coefficient for NIXT X-rays by chromospheric material is roughly proportional to the neutral hydrogen density, and we estimate an average neutral hydrogen density and scale height implied by the data.

  8. Equilibrium and Stability of Coronal Helmet Streamers

    NASA Astrophysics Data System (ADS)

    Glukhov, Vyacheslav Sergeevich

    1997-05-01

    Equilibrium states and stability of partially open magentic field structures in the solar corona are studied. Soft X-ray observations of the birth and evolution of a giant coronal helmet streamer suggest that the energy source responsible for the X-ray manifestation of the structure is most probably located in the lower corona. The downward heat flux is the indication that a significant part of the source's energy is transported to the top of the structure and converted there to a disposable form. It is shown that by applying the thermodynamic equilibrium model of the corona to the two-dimensional X-ray data it is possible to reconstruct the three-dimensional form of the coronal helmet. The general significance of the projective geometry effects for the observation of the solar corona is discussed. The hypothesis of thermal pressure increase as the cause of the observed helmet expansion is verified numerically. It is shown that in the solar corona a relatively small variations of the pressure distribution in the closed field region can cause huge variations in the geometry of a coronal helmet streamer. Numerical simulations of the morphology and energy accumulation in helmet-like structures subject to photospheric shear motion show that the magnetic field surrounding a partially open structure can inhibit catastrophic expansion of the structure as its energy grows. Stability of a coronal streamer in the framework of the neutral current sheet model is studied theoretically. It is shown that effects of viscosity and the finite Larmor radius dominate effects of inertial fluid motion in the tearing mode instability of a neutral current sheet. Two new regimes of the instability are discovered. It is proven that in the solar corona the rates of growth of the neutral current sheet instability are much smaller than previously believed. Implications of the obtained results are discussed.

  9. The transition region and coronal explorer (TRACE)

    NASA Technical Reports Server (NTRS)

    Title, Alan; Bruner, M.; Jurcevich, B.; Lemen, J.; Strong, K.; Tarbell, Ted; Wolfson, C. Jacob; Golub, L.; Bookbinder, J.; Fisher, R.

    1995-01-01

    The transition region and coronal explorer (TRACE) NASA small explorer mission and instrument are presented. The TRACE scientific investigation explores the relationships between fine-scale magnetic fields and the associated solar plasma structures. The instrument collects images of solar plasmas at temperatures from 10(exp 4) to 10(exp 7) K with one arcsec spatial resolution. The design specifications of the trace instrument are presented.

  10. Structure and dynamics of coronal plasmas

    NASA Technical Reports Server (NTRS)

    Golub, Leon (Principal Investigator)

    1996-01-01

    Progress for the period July 1995 - June 1996 included work on the differential magnetic field shear in an active region; observations and modeling of the solar chromosphere seen in soft X-ray absorption by NIXT; and modeling magnetic flux emergence. These were the subjects of three papers. The plans for the current year include projects on a converging flux model for point-like brightenings around sunspots, and difficulties in observing coronal structure.

  11. The Near-Infrared Coronal Spectrum

    NASA Astrophysics Data System (ADS)

    Kuhn, J. R.; Penn, M. J.; Mann, I.

    1996-01-01

    Sensitive measurements of the near-infrared coronal spectrum were obtained from the 1994 total solar eclipse. A new [S IX] emission line at 1.25249 +/- 0.00003 mu m has been detected, and a bright, potentially important diagnostic, [Si X] line at 1.43 mu m has been confirmed. Upper limits on the intensity of several other predicted IR emission lines have been established. Also, diffuse He I emission, perhaps geocoronal, has been observed with a significant heliocentric redshift.

  12. Coronal Plumes in the Fast Solar Wind

    NASA Technical Reports Server (NTRS)

    Velli, Marco; Lionello, Roberto; Linker, Jon A.; Mikic, Zoran

    2011-01-01

    The expansion of a coronal hole filled with a discrete number of higher density coronal plumes is simulated using a time-dependent two-dimensional code. A solar wind model including an exponential coronal heating function and a flux of Alfven waves propagating both inside and outside the structures is taken as a basic state. Different plasma plume profiles are obtained by using different scale heights for the heating rates. Remote sensing and solar wind in situ observations are used to constrain the parameter range of the study. Time dependence due to plume ignition and disappearance is also discussed. Velocity differences of the order of approximately 50 km/s, such as those found in microstreams in the high-speed solar wind, may be easily explained by slightly different heat deposition profiles in different plumes. Statistical pressure balance in the fast wind data may be masked by the large variety of body and surface waves which the higher density filaments may carry, so the absence of pressure balance in the microstreams should not rule out their interpretation as the extension of coronal plumes into interplanetary space. Mixing of plume-interplume material via the Kelvin-Helmholtz instability seems to be possible within the parameter ranges of the models defined here, only at large di stances from the Sun, beyond 0.2-0.3 AU. Plasma and composition measurements in the inner heliosphere, such as those which will become available with Solar Orbiter and Solar Probe Plus, should therefore definitely be able to identify plume remnants in the solar wind.

  13. CORONAL PLUMES IN THE FAST SOLAR WIND

    SciTech Connect

    Velli, Marco; Lionello, Roberto; Linker, Jon A.; Mikic, Zoran E-mail: lionel@predsci.com E-mail: mikicz@predsci.com

    2011-07-20

    The expansion of a coronal hole filled with a discrete number of higher density coronal plumes is simulated using a time-dependent two-dimensional code. A solar wind model including an exponential coronal heating function and a flux of Alfven waves propagating both inside and outside the structures is taken as a basic state. Different plasma plume profiles are obtained by using different scale heights for the heating rates. Remote sensing and solar wind in situ observations are used to constrain the parameter range of the study. Time dependence due to plume ignition and disappearance is also discussed. Velocity differences of the order of {approx}50 km s{sup -1}, such as those found in microstreams in the high-speed solar wind, may be easily explained by slightly different heat deposition profiles in different plumes. Statistical pressure balance in the fast wind data may be masked by the large variety of body and surface waves which the higher density filaments may carry, so the absence of pressure balance in the microstreams should not rule out their interpretation as the extension of coronal plumes into interplanetary space. Mixing of plume-interplume material via the Kelvin-Helmholtz instability seems to be possible within the parameter ranges of the models defined here, only at large distances from the Sun, beyond 0.2-0.3 AU. Plasma and composition measurements in the inner heliosphere, such as those which will become available with Solar Orbiter and Solar Probe Plus, should therefore definitely be able to identify plume remnants in the solar wind.

  14. Coronal microleakage: an online study guide.

    PubMed

    2008-05-01

    The Editorial Board of the Journal of Endodontics has developed a literature-based study guide of topical areas related to endodontics. This study guide is intended to give the reader a focused review of the essential endodontic literature and does not cite all possible articles related to each topic. Although citing all articles would be comprehensive, it would defeat the idea of a study guide. This section will cover coronal microleakage. PMID:18457692

  15. Coronal structure of low-mass stars

    NASA Astrophysics Data System (ADS)

    Lang, Pauline; Jardine, Moira; Donati, Jean-François; Morin, Julien; Vidotto, Aline

    2012-08-01

    We investigate the change in stellar magnetic topology across the fully convective boundary and its effects on coronal properties. We consider both the magnitude of the open flux that influences angular momentum loss in the stellar wind and X-ray emission measure. We use reconstructed maps of the radial magnetic field at the stellar surface and the potential-field source surface method to extrapolate a 3D coronal magnetic field for a sample of early-to-mid M dwarfs. During the magnetic reconstruction process it is possible to force a solution towards field geometries that are symmetric or antisymmetric about the equator but we demonstrate that this has only a modest impact on the coronal tracers mentioned above. We find that the dipole component of the field, which governs the large-scale structure, becomes increasingly strong as the stellar mass decreases, while the magnitude of the open (wind-bearing) magnetic flux is proportional to the magnitude of the reconstructed magnetic flux. By assuming a hydrostatic and isothermal corona, we calculate X-ray emission measures (in magnitude and rotational modulation) for each star and, using observed stellar densities as a constraint, we reproduce the observed X-ray saturation at Ro≤ 0.1. We find that X-ray rotational modulation is not a good indicator of magnetic structure as it shows no trend with Rossby number but can be useful in discriminating between different assumptions on the field geometry.

  16. Coronal Heating Observed with Hi-C

    NASA Technical Reports Server (NTRS)

    Winebarger, Amy R.

    2013-01-01

    The recent launch of the High-Resolution Coronal Imager (Hi-C) as a sounding rocket has offered a new, different view of the Sun. With approx 0.3" resolution and 5 second cadence, Hi-C reveals dynamic, small-scale structure within a complicated active region, including coronal braiding, reconnection regions, Alfven waves, and flows along active region fans. By combining the Hi-C data with other available data, we have compiled a rich data set that can be used to address many outstanding questions in solar physics. Though the Hi-C rocket flight was short (only 5 minutes), the added insight of the small-scale structure gained from the Hi-C data allows us to look at this active region and other active regions with new understanding. In this talk, I will review the first results from the Hi-C sounding rocket and discuss the impact of these results on the coronal heating problem.

  17. Thermal Analysis of CDS Coronal Loops

    NASA Astrophysics Data System (ADS)

    Kimble, J. A.; Schmelz, J. T.; Nasraoui, K.; Rightmire, L. A.; Andrews, J. M.; Cirtain, J. W.

    2008-05-01

    The coronal loop data used for this analysis was obtained using the Coronal Diagnostic Spectrometer (CDS) aboard the Solar and Heliospheric Observatory on 2003 January 17 at 14:24:43 UT. We use the Chianti atomic physics database and the hybrid coronal abundances to determine temperatures and densities for positions along several loops. We chose six pixels along each loop as well as background pixels. The intensities of the background pixels are subtracted from each loop pixel to isolate the emission from the loop pixel, and then spectral lines with significant contributions to the loop intensities are selected. The loops were then analyzed with a forward folding process to produce differential emission measure (DEM) curves. Emission measure loci plots and DEM automatic inversions are then used to verify those conclusions. We find different results for each of these loops. One appears to be isothermal at each loop position, and the temperature does not change with height. The second appears to be multithermal at each position and the third seems to be consistent with two DEM spikes, which might indicate that there are two isothermal loops so close together, that they are not resolved by CDS. Solar physics research at the University of Memphis is supported by a Hinode subcontract from NASA/SAO as well as NSF ATM-0402729.

  18. Forward Modeling of a Coronal Cavity

    NASA Technical Reports Server (NTRS)

    Kucera, T. A.; Gibson, S. E.; Schmit, D. J.

    2011-01-01

    We apply a forward model of emission from a coronal cavity in an effort to determine the temperature and density distribution in the cavity. Coronal cavities are long, low-density structures located over filament neutral lines and are often seen as dark elliptical features at the solar limb in white light, EUV and X-rays. When these structures erupt they form the cavity portions of CMEs The model consists of a coronal streamer model with a tunnel-like cavity with elliptical cross-section and a Gaussian variation of height along the tunnel length. Temperature and density can be varied as a function of altitude both in the cavity and streamer. We apply this model to a cavity observed in Aug. 2007 by a wide array of instruments including Hinode/EIS, STEREO/EUVI and SOHO/EIT. Studies such as these will ultimately help us understand the the original structures which erupt to become CMEs and ICMES, one of the prime Solar Orbiter objectives.

  19. The Coronal X-ray Deficiency Syndrome

    NASA Astrophysics Data System (ADS)

    Ayres, Thomas R.

    Something strange happens to M ~ 3 M(sun) stars during their post-MS evolution through the Hertzsprung gap (F--G0), on their way ultimately to the post-helium-flash ``Clump (G8--K0). The subcoronal emissions of the H-gap stars (traced by Mg II and C IV) appear to be normal for fast-rotating giants, but their coronal X-ray luminosities are depressed by an order of magnitude or more. The nearby binary Capella is the archetype: the G0 secondary has a C IV flux 10 times that of the G8 primary, and rotates faster by a similar factor. Yet, evidence points to near equality of the coronal X-ray fluxes. We propose to continue our broad-reaching exploration of the dichotomy (and its implications for coronal heating and the evolution of Dynamo action) through EUVE spectroscopy of key stars along the post-Main-Sequence trajectories connecting the Hertzsprung gap and the Clump.

  20. Fast Waves in Smooth Coronal Slab

    NASA Astrophysics Data System (ADS)

    Lopin, I.; Nagorny, I.

    2015-03-01

    This work investigates the effect of transverse density structuring in coronal slab-like waveguides on the properties of fast waves. We generalized previous results obtained for the exponential and Epstein profiles to the case of an arbitrary transverse density distribution. The criteria are given to determine the possible (trapped or leaky) wave regime, depending on the type of density profile function. In particular, there are plasma slabs with transverse density structuring that support pure trapped fast waves for all wavelengths. Their phase speed is nearly equal to the external Alfvén speed for the typical parameters of coronal loops. Our findings are obtained on the basis of Kneser’s oscillation theorem. To confirm the results, we analytically solved the wave equation evaluated at the cutoff point and the original wave equation for particular cases of transverse density distribution. We also used the WKB method and obtained approximate solutions of the wave equation at the cutoff point for an arbitrary transverse density profile. The analytic results were supplemented by numerical solutions of the obtained dispersion relations. The observed high-quality quasi-periodic pulsations of flaring loops are interpreted in terms of the trapped fundamental fast-sausage mode in a slab-like coronal waveguide.

  1. Solar Sources of Coronal Mass Ejections

    NASA Astrophysics Data System (ADS)

    Li, Y.

    2014-12-01

    Coronal mass ejections (CMEs) originate in the solar corona.Due to recent ample solar images from space missions, especially the STEREO mission, we know that CMEs initiate not only from flaring active regions of strong magnetic field, prominence (filaments) in decayed active regions, but also from coronal structures in higher coronaover regions no apparent strong magnetic fields on the solar disk. Regardless the differences of their appearances, these regionsmust all include non-potential magnetic field or free magnetic energy in order to produce CMEs. When an energized magnetic structure erupts, the free magnetic energy converts to kinetic energy and few other types ofenergy, and the magnetic structure leaves the corona and propagates into the interplanetary space. At the source regions, the initiations of CMEs often accompany with solar flares, filament eruptions, coronalEUV dimmings and waves, and post eruption loop brightennings. Studying the CME source regions and the processes is essential for the understanding of CME initiation and their interplanetary consequences.

  2. THE CORONAL ABUNDANCE ANOMALIES OF M DWARFS

    SciTech Connect

    Wood, Brian E.; Laming, J. Martin; Karovska, Margarita

    2012-07-01

    We analyze Chandra X-ray spectra of the M0 V+M0 V binary GJ 338. As quantified by X-ray surface flux, these are the most inactive M dwarfs ever observed with X-ray grating spectroscopy. We focus on measuring coronal abundances, in particular searching for evidence of abundance anomalies related to first ionization potential (FIP). In the solar corona and wind, low-FIP elements are overabundant, which is the so-called FIP effect. For other stars, particularly very active ones, an 'inverse FIP effect' is often observed, with low-FIP elements being underabundant. For both members of the GJ 338 binary, we find evidence for a modest inverse FIP effect, consistent with expectations from a previously reported correlation between spectral type and FIP bias. This amounts to strong evidence that all M dwarfs should exhibit the inverse FIP effect phenomenon, not just the active ones. We take the first step toward modeling the inverse FIP phenomenon in M dwarfs, building on past work that has demonstrated that MHD waves coursing through coronal loops can lead to a ponderomotive force that fractionates elements in a manner consistent with the FIP effect. We demonstrate that in certain circumstances this model can also lead to an inverse FIP effect, pointing the way to more detailed modeling of M dwarf coronal abundances in the future.

  3. The Coronal Abundance Anomalies of M Dwarfs

    NASA Astrophysics Data System (ADS)

    Wood, Brian E.; Laming, J. Martin; Karovska, Margarita

    2012-07-01

    We analyze Chandra X-ray spectra of the M0 V+M0 V binary GJ 338. As quantified by X-ray surface flux, these are the most inactive M dwarfs ever observed with X-ray grating spectroscopy. We focus on measuring coronal abundances, in particular searching for evidence of abundance anomalies related to first ionization potential (FIP). In the solar corona and wind, low-FIP elements are overabundant, which is the so-called FIP effect. For other stars, particularly very active ones, an "inverse FIP effect" is often observed, with low-FIP elements being underabundant. For both members of the GJ 338 binary, we find evidence for a modest inverse FIP effect, consistent with expectations from a previously reported correlation between spectral type and FIP bias. This amounts to strong evidence that all M dwarfs should exhibit the inverse FIP effect phenomenon, not just the active ones. We take the first step toward modeling the inverse FIP phenomenon in M dwarfs, building on past work that has demonstrated that MHD waves coursing through coronal loops can lead to a ponderomotive force that fractionates elements in a manner consistent with the FIP effect. We demonstrate that in certain circumstances this model can also lead to an inverse FIP effect, pointing the way to more detailed modeling of M dwarf coronal abundances in the future.

  4. Coronal heating in multiple magnetic threads

    NASA Astrophysics Data System (ADS)

    Tam, K. V.; Hood, A. W.; Browning, P. K.; Cargill, P. J.

    2015-08-01

    Context. Heating the solar corona to several million degrees requires the conversion of magnetic energy into thermal energy. In this paper, we investigate whether an unstable magnetic thread within a coronal loop can destabilise a neighbouring magnetic thread. Aims: By running a series of simulations, we aim to understand under what conditions the destabilisation of a single magnetic thread can also trigger a release of energy in a nearby thread. Methods: The 3D magnetohydrodynamics code, Lare3d, is used to simulate the temporal evolution of coronal magnetic fields during a kink instability and the subsequent relaxation process. We assume that a coronal magnetic loop consists of non-potential magnetic threads that are initially in an equilibrium state. Results: The non-linear kink instability in one magnetic thread forms a helical current sheet and initiates magnetic reconnection. The current sheet fragments, and magnetic energy is released throughout that thread. We find that, under certain conditions, this event can destabilise a nearby thread, which is a necessary requirement for starting an avalanche of energy release in magnetic threads. Conclusions: It is possible to initiate an energy release in a nearby, non-potential magnetic thread, because the energy released from one unstable magnetic thread can trigger energy release in nearby threads, provided that the nearby structures are close to marginal stability.

  5. Solar origins of coronal mass ejections

    NASA Technical Reports Server (NTRS)

    Kahler, Stephen

    1987-01-01

    The large scale properties of coronal mass ejections (CMEs), such as morphology, leading edge speed, and angular width and position, have been cataloged for many events observed with coronagraphs on the Skylab, P-78, and SMM spacecraft. While considerable study has been devoted to the characteristics of the SMEs, their solar origins are still only poorly understood. Recent observational work has involved statistical associations of CMEs with flares and filament eruptions, and some evidence exists that the flare and eruptive-filament associated CMEs define two classes of events, with the former being generally more energetic. Nevertheless, it is found that eruptive-filament CMEs can at times be very energetic, giving rise to interplanetary shocks and energetic particle events. The size of the impulsive phase in a flare-associated CME seems to play no significant role in the size or speed of the CME, but the angular sizes of CMEs may correlate with the scale sizes of the 1-8 angstrom x-ray flares. At the present time, He 10830 angstrom observations should be useful in studying the late development of double-ribbon flares and transient coronal holes to yield insights into the CME aftermath. The recently available white-light synoptic maps may also prove fruitful in defining the coronal conditions giving rise to CMEs.

  6. On the structure of coronal streamer belts

    NASA Astrophysics Data System (ADS)

    Eselevich, V. G.

    1998-02-01

    In an attempt to separate the temporal and spatial variations in polarization brightness (plasma density) along the coronal streamer belt, a study is made of the parts of the belt which are longitudinally aligned with the west or east limb of the sun. It is shown that the brightness distribution along streamer belts is inhomogeneous with relative brightness variations of about 1.1-2.0. Streamer belts consist of a sequence of coronal rays (streamers), each of which at distances of greater than 3 solar radii from the solar center has a cross section with a typical angular size of about 10-70 deg along the belt and about 10-30 deg across the belt with neighboring rays separated by L of about 10-70. Examples from CRs 1591 and 1592 show that in the absence of the influence of coronal mass ejection, the distribution of streamer rays along the streamer belt can be stable for nearly two complete Carrington rotations.

  7. EIT Observations of Coronal Mass Ejections

    NASA Technical Reports Server (NTRS)

    Gurman, J. B.; Fisher, Richard B. (Technical Monitor)

    2000-01-01

    Before the Solar and Heliospheric Observatory (SOHO), we had only the sketchiest of clues as to the nature and topology of coronal mass ejections (CMEs) below 1.1 - 1.2 solar radii. Occasionally, dimmings (or 'transient coronal holes') were observed in time series of soft X-ray images, but they were far less frequent than CME's. Simply by imaging the Sun frequently and continually at temperatures of 0.9 - 2.5 MK we have stumbled upon a zoo of CME phenomena in this previously obscured volume of the corona: (1) waves, (2) dimmings, and (3) a great variety of ejecta. In the three and a half years since our first observations of coronal waves associated with CME's, combined Large Angle Spectroscopic Coronagraph (LASCO) and extreme ultra-violet imaging telescope (EIT) synoptic observations have become a standard prediction tool for space weather forecasters, but our progress in actually understanding the CME phenomenon in the low corona has been somewhat slower. I will summarize the observations of waves, hot (> 0.9 MK) and cool ejecta, and some of the interpretations advanced to date. I will try to identify those phenomena, analysis of which could most benefit from the spectroscopic information available from ultraviolet coronograph spectrometer (UVCS) observations.

  8. Simulations of Emerging Magnetic Flux. II. The Formation of Unstable Coronal Flux Ropes and the Initiation of Coronal Mass Ejections

    NASA Technical Reports Server (NTRS)

    Leake, James E.; Linton, Mark G.; Antiochos, Spiro K.

    2014-01-01

    We present results from three-dimensional magnetohydrodynamic simulations of the emergence of a twisted convection zone flux tube into a pre-existing coronal dipole field. As in previous simulations, following the partial emergence of the sub-surface flux into the corona, a combination of vortical motions and internal magnetic reconnection forms a coronal flux rope. Then, in the simulations presented here, external reconnection between the emerging field and the pre-existing dipole coronal field allows further expansion of the coronal flux rope into the corona. After sufficient expansion, internal reconnection occurs beneath the coronal flux rope axis, and the flux rope erupts up to the top boundary of the simulation domain (approximately 36 Mm above the surface).We find that the presence of a pre-existing field, orientated in a direction to facilitate reconnection with the emerging field, is vital to the fast rise of the coronal flux rope. The simulations shown in this paper are able to self-consistently create many of the surface and coronal signatures used by coronal mass ejection (CME) models. These signatures include surface shearing and rotational motions, quadrupolar geometry above the surface, central sheared arcades reconnecting with oppositely orientated overlying dipole fields, the formation of coronal flux ropes underlying potential coronal field, and internal reconnection which resembles the classical flare reconnection scenario. This suggests that proposed mechanisms for the initiation of a CME, such as "magnetic breakout," are operating during the emergence of new active regions.

  9. Simulations of emerging magnetic flux. II. The formation of unstable coronal flux ropes and the initiation of coronal mass ejections

    SciTech Connect

    Leake, James E.; Linton, Mark G.; Antiochos, Spiro K.

    2014-05-20

    We present results from three-dimensional magnetohydrodynamic simulations of the emergence of a twisted convection zone flux tube into a pre-existing coronal dipole field. As in previous simulations, following the partial emergence of the sub-surface flux into the corona, a combination of vortical motions and internal magnetic reconnection forms a coronal flux rope. Then, in the simulations presented here, external reconnection between the emerging field and the pre-existing dipole coronal field allows further expansion of the coronal flux rope into the corona. After sufficient expansion, internal reconnection occurs beneath the coronal flux rope axis, and the flux rope erupts up to the top boundary of the simulation domain (∼36 Mm above the surface). We find that the presence of a pre-existing field, orientated in a direction to facilitate reconnection with the emerging field, is vital to the fast rise of the coronal flux rope. The simulations shown in this paper are able to self-consistently create many of the surface and coronal signatures used by coronal mass ejection (CME) models. These signatures include surface shearing and rotational motions, quadrupolar geometry above the surface, central sheared arcades reconnecting with oppositely orientated overlying dipole fields, the formation of coronal flux ropes underlying potential coronal field, and internal reconnection which resembles the classical flare reconnection scenario. This suggests that proposed mechanisms for the initiation of a CME, such as 'magnetic breakout', are operating during the emergence of new active regions.

  10. TRACE observation of damped coronal loop oscillations: implications for coronal heating

    PubMed

    Nakariakov; Ofman; DeLuca; Roberts; Davila

    1999-08-01

    The imaging telescope on board the Transition Region and Coronal Explorer (TRACE) spacecraft observed the decaying transversal oscillations of a long [(130 +/- 6) x 10(6) meters], thin [diameter (2.0 +/- 0.36) x 10(6) meters], bright coronal loop in the 171 angstrom Fe(IX) emission line. The oscillations were excited by a solar flare in the adjacent active region. The decay time of the oscillations is 14.5 +/- 2.7 minutes for an oscillation with a frequency 3.90 +/- 0.13 millihertz. The coronal dissipation coefficient is estimated to be eight to nine orders of magnitude larger than the theoretically predicted classical value. The larger dissipation coefficient may solve existing difficulties with wave heating and reconnection theories. PMID:10436148

  11. A CORONAL HOLE'S EFFECTS ON CORONAL MASS EJECTION SHOCK MORPHOLOGY IN THE INNER HELIOSPHERE

    SciTech Connect

    Wood, B. E.; Wu, C.-C.; Howard, R. A.; Socker, D. G.; Rouillard, A. P.

    2012-08-10

    We use STEREO imagery to study the morphology of a shock driven by a fast coronal mass ejection (CME) launched from the Sun on 2011 March 7. The source region of the CME is located just to the east of a coronal hole. The CME ejecta is deflected away from the hole, in contrast with the shock, which readily expands into the fast outflow from the coronal hole. The result is a CME with ejecta not well centered within the shock surrounding it. The shock shape inferred from the imaging is compared with in situ data at 1 AU, where the shock is observed near Earth by the Wind spacecraft, and at STEREO-A. Shock normals computed from the in situ data are consistent with the shock morphology inferred from imaging.

  12. A unified theory of electrodynamic coupling in coronal magnetic loops - The coronal heating problem

    NASA Technical Reports Server (NTRS)

    Ionson, J. A.

    1984-01-01

    The coronal heating problem is studied, and it is demonstrated that Ionson's (1982) LRC approach results in a unified theory of coronal heating which unveils a variety of new heating mechanisms and which links together previously proposed mechanisms. Ionson's LRC equation is rederived, focusing on various aspects that were not clarified in the original article and incorporating new processes that were neglected. A parameterized heating rate is obtained. It is shown that Alfvenic surface wave heating, stochastic magnetic pumping, resonant electrodynamic heating, and dynamical dissipation emerge as special cases of a much more general formalism. This generalized theory is applied to solar coronal loops and it is found that active region and large scale loops are underdamped systems. Young active region loops and (possibly) bright points are found to be overdamped systems.

  13. Recent VLA Observations of Coronal Faraday Rotation

    NASA Astrophysics Data System (ADS)

    Kooi, Jason E.; Fischer, P. D.; Buffo, J. J.; Spangler, S. R.

    2014-01-01

    Proposed mechanisms for coronal heating and acceleration of the fast solar wind, such as Joule heating by coronal currents or dissipation of Alfvén waves, depend on the magnetic field structure and plasma characteristics of the corona within heliocentric distances of 5 solar radii. Faraday rotation observations can provide unique information on the magnetic field in this region of the corona. We report on sensitive full-polarization observations of the radio galaxy 3C228 through the solar corona at heliocentric distances of 4.6 - 5.0 solar radii. The observations were made with the VLA in August of 2011. We performed these observations at 5.0 and 6.1 GHz (each with a bandwidth of 128 MHz), permitting measurements deeper in the corona than previous VLA observations at 1.4 and 1.7 GHz. While the measured Faraday rotation was lower than our a priori expectations, we can understand the magnitude of the observed Faraday rotation in terms of observed properties of the corona on the day of observation. For coronal remote sensing, an advantage of using extended extragalactic radio sources such as 3C228 is that such observations provide multiple lines of sight through the corona. Our data provide two lines of sight (separated by 46″, 33,000 km in the corona), one to a northern hotspot and the other to a southern hotspot with fractional polarizations of 14% and 8% respectively. We detected three periods over the eight-hour observing session during which there appeared to be a difference in the Faraday rotation between these two closely spaced lines of sight. These measurements yield an estimate of 2 - 4 GA for coronal currents. We did not directly detect rotation measure fluctuations. Our data impose upper limits on rotation measure fluctuations caused by coronal waves. The observed upper limits were 3.3 and 6.4 rad/m2 and are comparable to and not inconsistent with some models for Alfvén wave heating. This research was supported at the University of Iowa by grants ATM09

  14. Structure and Dynamics of Coronal Plasmas

    NASA Technical Reports Server (NTRS)

    Golub, Leon

    1997-01-01

    During the past year this grant has funded research in the interaction between magnetic fields and the hot plasma in the solar outer atmosphere. The following is a brief summary of the published papers, abstracts and talks which have been supported. The paper 'Coronal Structures Observed in X-rays and H-alpha Structures' was published in the Kofu Symposium proceedings. The study analyzes cool and hot behavior of two x-ray events, a small flare and a surge. We find that a large H-alpha surge appears in x-rays as a very weak event, while a weak H-alpha feature corresponds to the brightest x-ray emission on the disk at the time of the observation. Calculations of the heating necessary to produce these signatures, and implications for the driving and heating mechanisms of flares vs. surges are presented. A copy of the paper is appended to this report. The paper 'Differential Magnetic Field Shear in an Active Region' has been published in The Astrophysical Journal. We have compared the 3D extrapolation of magnetic fields with the observed coronal structure in an active region. Based on the fit between observed coronal structure throughout the volume of the region and the calculated magnetic field configurations, we propose a differential magnetic field shear model for this active region. The decreasing field shear in the outer portions of the AR may indicate a continual relaxation of the magnetic field with time, corresponding to a net transport of helicity outward. The paper 'Difficulties in Observing Coronal Structure' has been accepted for publication in the journal Solar Physics. In this paper we discuss the evidence that the temperature and density structure of the corona are far more complicated than had previously been thought. The discussion is based on five studies carried out by our group on coronal plasma properties, showing that any one x-ray instrument does see all of the plasma present in the corona, that hot and cool material may appear to be co

  15. Spatial and Temporal Scales of Coronal Magnetic Restructuring in the Development of Coronal Mass Ejections

    NASA Astrophysics Data System (ADS)

    Wen, Yayuan; Wang, Jingxiu; Maia, Dalmiro Jorge Filipe; Zhang, Yuzong; Zhao, Hui; Zhou, Guiping

    2006-12-01

    It has been commonly accepted that coronal mass ejections (CMEs) result from the restructuring or reconfiguring of large-scale coronal magnetic fields. In this paper, we analyzed four CME events using Nançay Radioheliograph (NRH) images and the experiments onboard the Solar and Heliospheric Observatory (SOHO) spacecraft to understand the coronal restructuring leading to CME initiation. We investigated the onset, duration, and position of the radio emissions in relation to EUV dimming and the inferred CME onset. It has been identified that the early CME development on the solar disk is characterized by a series of distinct radio bursts. These nonthermal radio sources appeared in phase with coronal dimming shown by SOHO-EIT images and are located within the EUV dimming or ongoing dimming regions. Three time scales are identified: the duration, the separation of individual radio bursts, and the overall time scale of all of the nonthermal sources. They fall in the ranges of approximately tens of seconds to three minutes, one to three minutes, and 15 20 minutes, respectively. The individual radio emission seems to shift and expand at the speed of the fast magnetoacoustic waves in the corona; while the nonthermal radio emissions as a whole appear episodically to correspond to the successive coronal restructuring. If we define the triggering speed by dividing the overall spatial scale by the temporal scale of all the radio bursts, then the triggering speed falls in the range of 300 400 km s-1. This implies that the general process of coronal restructuring and reconfiguring takes place at a speed slower than either the Alvfenic or acoustic speed in the corona. This is a type of speed of “topology waves,” i. e., the speed of successive topology changes from closed to open field configuration.

  16. THE COOLING OF CORONAL PLASMAS. IV. CATASTROPHIC COOLING OF LOOPS

    SciTech Connect

    Cargill, P. J.; Bradshaw, S. J.

    2013-07-20

    We examine the radiative cooling of coronal loops and demonstrate that the recently identified catastrophic cooling is due to the inability of a loop to sustain radiative/enthalpy cooling below a critical temperature, which can be >1 MK in flares, 0.5-1 MK in active regions, and 0.1 MK in long tenuous loops. Catastrophic cooling is characterized by a rapid fall in coronal temperature, while the coronal density changes by a small amount. Analytic expressions for the critical temperature are derived and show good agreement with numerical results. This effect considerably limits the lifetime of coronal plasmas below the critical temperature.

  17. The cooling and condensation of flare coronal plasma

    NASA Technical Reports Server (NTRS)

    Antiochos, S. K.; Sturrock, P. A.

    1981-01-01

    A model is investigated for the decay of flare heated coronal loops in which rapid radiative cooling at the loop base creates strong pressure gradients which, in turn, generate large (supersonic) downward flows. The coronal material cools and 'condenses' onto the flare chromosphere. The features which distinguish this model from previous models of flare cooling are: (1) most of the thermal energy of the coronal plasma may be lost by mass motion rather than by conduction or coronal radiation; (2) flare loops are not isobaric during their decay phase, and large downward velocities are present near the footpoints; (3) the differential emission measure q has a strong temperature dependence.

  18. Evidence linking coronal transients to the evolution of coronal holes. [solar X-ray observations on Skylab

    NASA Technical Reports Server (NTRS)

    Webb, D. F.; Nolte, J. T.; Solodyna, C. V.; Mcintosh, P. S.

    1978-01-01

    The positions of X-ray coronal transients outside of active regions observed during Skylab were superposed on H-alpha synoptic charts and coronal hole boundaries for seven solar rotations. A detailed spatial association between the transients and neutral lines was confirmed. It was found that most of the transients were related to large-scale changes in coronal hole area and tended to occur on the borders of evolving equatorial holes.

  19. Computerized tomography myelography with coronal and oblique coronal view for diagnosis of nerve root avulsion in brachial plexus injury

    PubMed Central

    2007-01-01

    Background The authors describe a new computerized tomography (CT) myelography technique with coronal and oblique coronal view to demonstrate the status of the cervical nerve rootlets involved in brachial plexus injury. They discuss the value of this technique for diagnosis of nerve root avulsion compared with CT myelography with axial view. Methods CT myelography was performed with penetration of the cervical subarachnoid space by the contrast medium. Then the coronal and oblique coronal reconstructions were created. The results of CT myelography were evaluated and classified with presence of pseudomeningocele, intradural ventral nerve rootlets, and intradural dorsal nerve rootlets. The diagnosis was by extraspinal surgical exploration with or without spinal evoked potential measurements and choline acetyl transferase activity measurement in 25 patients and recovery by a natural course in 3 patients. Its diagnostic accuracy was compared with that of CT myelography with axial view, correlated with surgical findings or a natural course in 57 cervical roots in 28 patients. Results Coronal and oblique coronal views were superior to axial views in visualization of the rootlets and orientation of the exact level of the root. Sensitivity and specificity for coronal and oblique coronal views of unrecognition of intradural ventral and dorsal nerve root shadow without pseudomeningocele in determining pre-ganglionic injury were 100% and 96%, respectively. There was no statistically significant difference between coronal and oblique coronal views and axial views. Conclusion The information by the coronal and oblique coronal slice CT myelography enabled the authors to assess the rootlets of the brachial plexus and provided valuable data for helping to decide whether to proceed with exploration, nerve repair, primary reconstruction. PMID:17651476

  20. Impact of the growing use of narrative verdicts by coroners on geographic variations in suicide: analysis of coroners' inquest data

    PubMed Central

    Carroll, R.; Hawton, K.; Kapur, N.; Bennewith, O.; Gunnell, D.

    2012-01-01

    Background Coroners' death certificates form the basis of suicide statistics in England and Wales. Recent increases in coroners' use of narrative verdicts may affect the reliability of local and national suicide rates. Method We used Ministry of Justice data on inquests held between 2008 and 2009 and Local Authority suicide data (2001–02 and 2008–09) to investigate variations between coroners in their use of narrative verdicts and the impact of these on suicide rates, using ‘other’ verdicts (79% of which are narratives) as a proxy for narrative verdicts. Results There was wide geographic variation in Coroners' use of ‘other’ (mainly narrative) verdicts—they comprised between 0 and 50% (median = 9%) of verdicts given by individual coroners in 2008–09. Coroners who gave more ‘other’ verdicts gave fewer suicide verdicts (r = − 0.41; P< 0.001). In the 10 English Coroners' jurisdictions where the highest proportion of ‘other’ verdicts were given, the incidence of suicide decreased by 16% between 2001–02 and 2008–09, whereas it did not change in areas served by the 10 coroners who used narratives the least. Conclusions Variation in Coroners' use of narrative verdicts influences the validity of reported regional suicide rates. Small-area suicide rates, and changes in these rates over time in the last decade, should be interpreted with caution. PMID:22085685

  1. MxCSM: A massively-multiplexed coronal spectropolarimetric magnetometer for spaced-based coronal magnetometry

    NASA Astrophysics Data System (ADS)

    Lin, Haosheng

    2016-07-01

    This paper presents the conceptual design of a new coronal spectropolarimeter that employs large-scale multiplexing strategy to enable small coronagraphs to perform high-sensitivity measurements of the polarizations of multiple coronal emission lines (CELs) of the whole corona. The massively multiplexed coronal spectropolarimetric magnetometer (mxCSM) is a 25 cm catadioptric off-axis Gregorian coronagraph equipped with two 3-wavelength, 100-slit spectrographs to measure the polarization of six CELs simultaneously at 100 slits over a 1.2 degree x 1.0 degree (2.4 Rsun x 2.0 Rsun ) field of view. The large multiplexing capability of this design allows small coronagraphs to perform high sensitivity spectropolarimetric observations over a large FOV that until now is possible only with large aperture telescopes. Therefore, this design is ideally suited for space missions in which payload size and weight are important considerations. Future space missions with multiple mxCSMs in circumsolar orbits can provide polarization measurements of CELs from multiple lines of sight to enable true tomographic inversion of the coronal magnetic fields.

  2. Solar Jet-Coronal Hole Collision and a Closely Related Coronal Mass Ejection

    NASA Astrophysics Data System (ADS)

    Zheng, Ruisheng; Chen, Yao; Du, Guohui; Li, Chuanyang

    2016-03-01

    Jets are defined as impulsive, well-collimated upflows, occurring in different layers of the solar atmosphere with different scales. Their relationship with coronal mass ejections (CMEs), another type of solar impulsive events, remains elusive. Using high-quality imaging data from the Atmospheric Imaging Assembly/Solar Dynamics Observatory, we show a well-observed coronal jet event, in which the part of the jet with embedding coronal loops runs into a nearby coronal hole (CH) and gets bounced in the opposite direction. This is evidenced by the flat shape of the jet front during its interaction with the CH and the V-shaped feature in the time-slice plot of the interaction region. About a half-hour later, a CME with an initially narrow and jet-like front is observed by the LASCO C2 coronagraph propagating along the direction of the post-collision jet. We also observe some 304 Å dark material flowing from the jet-CH interaction region toward the CME. We thus suggest that the jet and the CME are physically connected, with the jet-CH collision and the large-scale magnetic topology of the CH being important in defining the eventual propagating direction of this particular jet-CME eruption.

  3. Standing Slow-Mode Waves in Hot Coronal Loops: Observations, Modeling, and Coronal Seismology

    NASA Astrophysics Data System (ADS)

    Wang, Tongjiang

    2011-07-01

    Strongly damped Doppler shift oscillations are observed frequently associated with flarelike events in hot coronal loops. In this paper, a review of the observed properties and the theoretical modeling is presented. Statistical measurements of physical parameters (period, decay time, and amplitude) have been obtained based on a large number of events observed by SOHO/SUMER and Yohkoh/BCS. Several pieces of evidence are found to support their interpretation in terms of the fundamental standing longitudinal slow mode. The high excitation rate of these oscillations in small- or micro-flares suggest that the slow mode waves are a natural response of the coronal plasma to impulsive heating in closed magnetic structure. The strong damping and the rapid excitation of the observed waves are two major aspects of the waves that are poorly understood, and are the main subject of theoretical modelling. The slow waves are found mainly damped by thermal conduction and viscosity in hot coronal loops. The mode coupling seems to play an important role in rapid excitation of the standing slow mode. Several seismology applications such as determination of the magnetic field, temperature, and density in coronal loops are demonstrated. Further, some open issues are discussed.

  4. Coronal Loops: Evolving Beyond the Isothermal Approximation

    NASA Astrophysics Data System (ADS)

    Schmelz, J. T.; Cirtain, J. W.; Allen, J. D.

    2002-05-01

    Are coronal loops isothermal? A controversy over this question has arisen recently because different investigators using different techniques have obtained very different answers. Analysis of SOHO-EIT and TRACE data using narrowband filter ratios to obtain temperature maps has produced several key publications that suggest that coronal loops may be isothermal. We have constructed a multi-thermal distribution for several pixels along a relatively isolated coronal loop on the southwest limb of the solar disk using spectral line data from SOHO-CDS taken on 1998 Apr 20. These distributions are clearly inconsistent with isothermal plasma along either the line of sight or the length of the loop, and suggested rather that the temperature increases from the footpoints to the loop top. We speculated originally that these differences could be attributed to pixel size -- CDS pixels are larger, and more `contaminating' material would be expected along the line of sight. To test this idea, we used CDS iron line ratios from our data set to mimic the isothermal results from the narrowband filter instruments. These ratios indicated that the temperature gradient along the loop was flat, despite the fact that a more complete analysis of the same data showed this result to be false! The CDS pixel size was not the cause of the discrepancy; rather, the problem lies with the isothermal approximation used in EIT and TRACE analysis. These results should serve as a strong warning to anyone using this simplistic method to obtain temperature. This warning is echoed on the EIT web page: ``Danger! Enter at your own risk!'' In other words, values for temperature may be found, but they may have nothing to do with physical reality. Solar physics research at the University of Memphis is supported by NASA grant NAG5-9783. This research was funded in part by the NASA/TRACE MODA grant for Montana State University.

  5. Ultraviolet Spectroscopy of Narrow Coronal Mass Ejections

    NASA Astrophysics Data System (ADS)

    Dobrzycka, D.; Raymond, J. C.; Biesecker, D. A.; Li, J.; Ciaravella, A.

    2003-05-01

    We present Ultraviolet Coronagraph Spectrometer (UVCS) observations of five narrow coronal mass ejections (CMEs) that were among 15 narrow CMEs originally selected by Gilbert and coworkers. Two events (1999 March 27, April 15) were ``structured,'' i.e., in white-light data they exhibited well-defined interior features, and three (1999 May 9, May 21, June 3) were ``unstructured,'' i.e., appeared featureless. In UVCS data the events were seen as 4°-13° wide enhancements of the strongest coronal lines H I Lyα and O VI λλ1032, 1037. We derived electron densities for several of the events from the Large Angle and Spectrometric Coronagraph Experiment (LASCO) C2 white-light observations. They are comparable to or smaller than densities inferred for other CMEs. We modeled the observable properties of examples of the structured (1999 April 15) and unstructured (1999 May 9) narrow CMEs at different heights in the corona between 1.5 and 2 Rsolar. The derived electron temperatures, densities, and outflow speeds are similar for those two types of ejections. They were compared with properties of polar coronal jets and other CMEs. We discuss different scenarios of narrow CME formation as either a jet formed by reconnection onto open field lines or a CME ejected by expansion of closed field structures. Overall, we conclude that the existing observations do not definitively place the narrow CMEs into the jet or the CME picture, but the acceleration of the 1999 April 15 event resembles acceleration seen in many CMEs, rather than constant speeds or deceleration observed in jets.

  6. Coronal plasma diagnostics from eclipse observations

    NASA Astrophysics Data System (ADS)

    Landi, E.; Habbal, S. R.; Tomczyk, S.

    2015-12-01

    In this talk we will discuss the diagnostic potential of observationsof visible spectral lines formed in the extended solar corona that canbe obtained during eclipses. We will discuss the possible diagnosticapplications of visible eclipse observations to measure the physicalparameters of the extended corona, to understand solar wind origin andacceleration, and to determine the evolution of Coronal Mass Ejectionsduring onset.We will first review the mechanisms of formation of spectral lineintensities, we will then illustrate their diagnostic applications,and show some results from recent eclipse observations. We will alsoreview the spectral lines that are most likely to be observed inthe extended solar corona during the upcoming 2017 eclipse in thecontinental United States.

  7. Coronal Heating, Spicules, and Solar-B

    NASA Technical Reports Server (NTRS)

    Moore, Ron; Falconer, David; Porter, Jason; Hathaway, David; Yamauchi, Yohei

    2003-01-01

    Falconer et al. investigated the heating of the quiet corona by measuring the increase of coronal luminosity with the amount of the magnetic flux in the underlying network at solar minimum when there were no active regions on the face of the Sun. The coronal luminosity was measured from Fe IX/X - Fe XII pairs of coronal images from SOHO/EIT, under the assumption that practically all of the coronal luminosity in these very quiet regions came from plasma in the temperature range 0.9 x 10(exp 6) K is less than or equal to T is less than or equal to 1.3 x 10(exp 6) K. The network magnetic flux content was measured from SOHO/MDI magnetograms. It was found that luminosity of the corona in these quiet regions increased roughly in proportion to the square root of the magnetic flux content of the network and roughly in proportion to the length of the perimeter of the network flux clumps. From 1) this result; 2) the observed occurrence of many fine-scale explosive events (e.g., spicules) at the edges of network flux clumps; and 3) a demonstration that it is energetically feasible for the heating of the corona in quiet regions to be driven by explosions of granule-sized sheared-core magnetic bipoles embedded in the edges of the network flux clumps, Falconer et al. infer that in quiet regions that are not influenced by active regions the corona is mainly heated by such magnetic activity in the edges of the network flux clumps. From their observational results together with their feasibility analysis, Falconer et al. predict that 1) At the edges of the network flux clumps there are many transient sheared core bipoles of the size and lifetime of granules and having transverse field strengths greater than approx. 100 G; 2) Approx. 30 of these bipoles are present per supergranule; and 3) Most spicules are produced by explosions of these bipoles. The photospheric vector magnetograms, chromospheric filtergrams, and EUV spectra from Solar-B are expected to have sufficient sensitivity

  8. Interacting active regions and coronal holes: implications for coronal outflows and solar wind structure

    NASA Astrophysics Data System (ADS)

    Culhane, J. Leonard; Baker, Deborah; Rouillard, Alexis; van Driel-Gesztelyi, Lidia

    When active regions are adjacent to coronal holes a variety of magnetic field interactions can result. These may include the interchange reconnection between the closed active region (AR) fields and the open field of the coronal hole (CH), leading to fast and significant evolution of coronal hole boundaries. Outcomes may include variability of -or changes in, active region-associated hot plasma outflows seen with Hinode/EIS and the modulation of the solar wind flows on open field lines. Depending on their relative positions on the Sun, the AR-CH interactions may have their signatures embedded in co-rotating interaction regions (CIRs) or rarefaction regions. During two intervals -8/11 January, 2008 and 7/9 December, 2008, we have made observations with Hinode of two oppositely configured situations on the Sun. For 8/11 January, the coronal hole leads the active region while for 7/9 December the order is reversed. The Hinode EIS instrument is used to locate outflows and measure their velocities while the XRT is used to image the source regions, including the variable nature of the outflows. SOHO EIT imaging is used to follow the longer-term evolution of the coronal hole boundaries while MDI is used to observe changes in the magnetic field. STEREO imaging and in-situ data are also employed -as are ACE observations, to assess the resulting impacts on interplanetary solar wind structures. The contrasting behaviour that results from magnetic interactions in the two different configurations is described and assessed.

  9. Observaciones de la corona solar interior con un coronógrafo de espejo

    NASA Astrophysics Data System (ADS)

    Stenborg, G.; Schwenn, R.; Francile, C.; Rovira, M.

    El plasma de la corona solar es un buen indicador de las líneas de fuerza del campo magnético. Por lo tanto, el análisis de estructuras coronales cuasiestacionarias en la corona da importante información sobre el campo magnético y la actividad asociada. Se trata de poner límites a los modelos teóricos existentes mediante el estudio de distintas estructuras en la corona interior. En agosto de 1997 comenzó a operar el coronógrafo solar (MICA) en El Leoncito como parte del Observatorio Solar Alemán-Argentino. Desde su instalación obtiene imágenes de la corona solar (1.05 a 2.0 radios solares) en 2 líneas espectrales correspondientes a la emisión de Fe XIV y Fe X. El instrumento puede obtener imágenes cada minuto por lo que es ideal para estudiar procesos rápidos. Presentamos observaciones recientes que muestran la capacidad del coronógrafo así como la evolución de algunos eventos dinámicos observados por MICA.

  10. NASA’s SDO Spies an Elongated Coronal Hole

    NASA Video Gallery

    A long coronal hole can be seen right down the middle of the sun in this video captured by NASA’s Solar Dynamics Observatory on March 23-25, 2016. Coronal holes are areas on the sun where the solar...

  11. GALEX Observes Nearby Cool Stars: Constraints on Ultraviolet Coronal Activity

    NASA Astrophysics Data System (ADS)

    Wheatley, Jonathan; Welsh, Barry

    2016-01-01

    The GALEX ultraviolet mission (1350-2800A) has detected many late-type dwarf stars. Numerous M-type dwarf stars exhibit flaring and coronal activity; we use GALEX UV photometry to measure the variability of coronal emission in the GALEX NUV and FUV wavebands.

  12. Magnetism Matters: Coronal Magnetometry Using Multi-Wavelength Polarimetry

    NASA Astrophysics Data System (ADS)

    Gibson, Sarah E.

    2015-08-01

    The solar coronal magnetic field is key both to solving fundamental problems in solar physics such as coronal heating and solar wind acceleration, and to predicting the internal magnetic structure and thus space-weather impact of coronal mass ejections. I will describe the current state of the art in coronal magnetometry, and present results from the Coronal Multichannel Polarimeter (CoMP) at Mauna Loa Solar Observatory (MLSO), which since 2011 has taken polarimetric observations of the solar corona in the near-infrared on a near-daily basis. I will discuss work in progress that utilizes forward modeling to synthesize polarimetric data at multiple heights and vantage points, and at wavelengths from radio to infrared to visible to ultraviolet. The goal is to use such synthetic testbeds to determine the ideal set of observations for constraining the coronal magnetic field, and to establish a Data-Optimized Coronal Field Model (DOC-FM) that efficiently incorporates these data into global magnetic models. This work will provide essential tools and motivation for the planning and implementation of future coronal polarimetric projects and missions spanning a broad range of wavelengths.

  13. Streamer Waves Driven by Coronal Mass Ejections

    NASA Astrophysics Data System (ADS)

    Chen, Y.; Song, H. Q.; Li, B.; Xia, L. D.; Wu, Z.; Fu, H.; Li, Xing

    2010-05-01

    Between 2004 July 5 and July 7, two intriguing fast coronal mass ejection (CME)-streamer interaction events were recorded by the Large Angle and Spectrometric Coronagraph. At the beginning of the events, the streamer was pushed aside from its equilibrium position upon the impact of the rapidly outgoing and expanding ejecta; then, the streamer structure, mainly the bright streamer belt, exhibited elegant large-scale sinusoidal wavelike motions. The motions were apparently driven by the restoring magnetic forces resulting from the CME impingement, suggestive of magnetohydrodynamic kink mode propagating outward along the plasma sheet of the streamer. The mode is supported collectively by the streamer-plasma sheet structure and is therefore named "streamer wave" in the present study. With the white light coronagraph data, we show that the streamer wave has a period of about 1 hr, a wavelength varying from 2 to 4 solar radii, an amplitude of about a few tens of solar radii, and a propagating phase speed in the range 300-500 km s-1. We also find that there is a tendency for the phase speed to decline with increasing heliocentric distance. These observations provide good examples of large-scale wave phenomena carried by coronal structures and have significance in developing seismological techniques for diagnosing plasma and magnetic parameters in the outer corona.

  14. Low-coronal Sources of Stealth CMEs

    NASA Astrophysics Data System (ADS)

    Alzate, Nathalia; Morgan, Huw

    2016-01-01

    Coronal mass ejections (CMEs) are eruptions in the solar atmosphere which expand and propagate into space. They are generally associated with eruptive phenomena in the lower corona such as solar flares, filament eruptions, EUV waves or jets, known as low-coronal signatures (LCS). Recent studies have observed CMEs without a LCS which have been referred to as stealth CMEs. Through new image processing applied to EUV images we find clear evidence of LCS leading to stealth CMEs. In this work, the new processing methods are applied to some of the data identified to contain stealth CMEs in previous studies to investigate the possible existence of observable LCS. The LCS of stealth CMEs are fairly sizeable yet faint eruptions with structure consistent with a rising flux tube, possibly formed higher in the corona in regions of weaker magnetic field. We believe these flux tubes are formed mostly in polar regions due to the larger shear resulting from the slowly-rotating lower atmosphere below the more rapidly rotating corona. This would allow the formation of large flux tubes in weaker field regions, leading to low-energy and low-density flux tube eruptions.

  15. Chromospheric and Coronal Emission in DM Stars

    NASA Astrophysics Data System (ADS)

    Giampapa, Mark S.

    We propose to obtain low dispersion, large aperture LWP spectra of the Mg II h+k chromospheric resonance lines for a volume limited sample of mainly single dM (i.e., nondMe) stars for which X-ray data are available. The combination of the IUE data-set we propose herein to obtain and the previously acquired X-ray data-set (Bookbinder 1985) will yield further insights on the nature of chromospheric and coronal heating in the ordinary, inactive (quiescent) dM stars. In particular, if the X-ray heating hypothesis for the source of chromospheric heating in the dMe stars, as advanced by Cram (1982), is also applicable to the dM stars then we would expect to find a linear correlation between the luminosity in the Mg II lines and the X-ray luminosity. In general, if a common source of in situ heating in the chromospheres and coronae of the dM stars is present then we would expect to find a linear relationship between the observed Mg II emission and the X-ray emission. Conversely, if the sources of chromospheric and coronal heating are different between these atmospheric regions in the dM stars then we expect to find a departure from a simple linear relationship. The results to be obtained in this program will yield critical observational constraints on the possible mechanisms for atmospheric heating in the dM stars.

  16. Particle Heating Resulting from Coronal Mass Ejection

    NASA Astrophysics Data System (ADS)

    Paul, Suman; Sundar De, Syam; Guha, Gautam

    2016-07-01

    Coronal Mass Ejection (CME) is a continuous phenomena occurring from the entire solar coronal zone responsible for the outflow of solar masses, viz., protons, electrons, neutrons and solar wind in the form of plasma. These perturb the Earth's atmosphere via magnetopause. Very high temperature plasma generator in the solar atmosphere produces huge magnetic dipoles with intense magnetic field. It traps the energetic charged particles released from the solar corona. These particles gyrate along the magnetic field lines and are gradually elongated outwards from the Sun. Due to this, the field lines get detached at some critical limit thereby enhancing the magnetic reconnection with the interplanetary magnetic field releasing huge energy in the form of X-rays and γ-rays. This perturbs the Earth's atmosphere. In this work, the situation has been investigated by momentum balance equation, energy balance equation along with the equations of continuity and states. From the analyses, the dispersive nature of the thermospheric medium is studied. Variation of normalized electron temperature with dimensionless time has been critically contemplated. The altitude dependent electric field in the medium is also investigated.

  17. Coronal loops - Current-based heating processes

    NASA Technical Reports Server (NTRS)

    Beaufume, P.; Coppi, B.; Golub, L.

    1992-01-01

    Based on new observations, a theoretical model of magnetic-field related heating processes in the solar corona is given. In this model, field-aligned currents are induced along coronal loops in thin current sheaths. Excitation of instabilities involving magnetic reconnection converts the energy associated with the current-related magnetic field directly into particle energy, where the heating process proceeds via short bursts corresponding to an intermittent disruption of the current sheath configuration. Because of the relatively low transverse thermal conduction, only a small fraction of the loop volume is heated to a much higher temperature than the average value. This is consistent with experimental observations of low filling factors of hot plasmas in coronal loops. Thus the model involves a repeated sequence of dynamic events taking into account the observed loop topology, the differential emission measure distribution in the 10 exp 6 - 10 exp 7 K range, the energy balance requirements in the loop, and the probable duty cycles involved in the heating processes.

  18. STREAMER WAVES DRIVEN BY CORONAL MASS EJECTIONS

    SciTech Connect

    Chen, Y.; Song, H. Q.; Li, B.; Xia, L. D.; Wu, Z.; Fu, H.; Li Xing

    2010-05-01

    Between 2004 July 5 and July 7, two intriguing fast coronal mass ejection (CME)-streamer interaction events were recorded by the Large Angle and Spectrometric Coronagraph. At the beginning of the events, the streamer was pushed aside from its equilibrium position upon the impact of the rapidly outgoing and expanding ejecta; then, the streamer structure, mainly the bright streamer belt, exhibited elegant large-scale sinusoidal wavelike motions. The motions were apparently driven by the restoring magnetic forces resulting from the CME impingement, suggestive of magnetohydrodynamic kink mode propagating outward along the plasma sheet of the streamer. The mode is supported collectively by the streamer-plasma sheet structure and is therefore named 'streamer wave' in the present study. With the white light coronagraph data, we show that the streamer wave has a period of about 1 hr, a wavelength varying from 2 to 4 solar radii, an amplitude of about a few tens of solar radii, and a propagating phase speed in the range 300-500 km s{sup -1}. We also find that there is a tendency for the phase speed to decline with increasing heliocentric distance. These observations provide good examples of large-scale wave phenomena carried by coronal structures and have significance in developing seismological techniques for diagnosing plasma and magnetic parameters in the outer corona.

  19. Low-Coronal Sources of Stealth CMEs

    NASA Astrophysics Data System (ADS)

    Alzate, Nathalia; Morgan, Huw

    2016-05-01

    Coronal mass ejections (CMEs) are eruptions in the solar atmosphere, which expand and propagate into space. They are generally associated with eruptive phenomena in the lower corona such as solar flares, filament eruptions, EUV waves or jets, known as low-coronal signatures (LCS). Recent studies have observed CMEs without a LCS and these have been referred to as stealth CMEs. Through new image processing applied to EUV images we find clear evidence of LCS leading to stealth CMEs. In this work, the new processing methods are applied to some of the data identified to contain stealth CMEs in previous studies to investigate the possible existence of observable LCS. The LCS of stealth CMEs are fairly sizeable yet faint eruptions with structure consistent with a rising flux tube, possibly formed higher in the corona in regions of weaker magnetic field. We believe these flux tubes are formed mostly in polar regions due to the larger shear resulting from the more slowly rotating lower atmosphere below the more rapidly rotating corona. This would allow the formation of large flux tubes in weaker field regions, leading to low-energy and low-density flux tube eruptions

  20. Interplanetary Propagation of Coronal Mass Ejections

    NASA Technical Reports Server (NTRS)

    Gopalswamy, Nat

    2011-01-01

    Although more than ten thousand coronal mass ejections (CMEs) are produced during each solar cycle at the Sun, only a small fraction hits the Earth. Only a small fraction of the Earth-directed CMEs ultimately arrive at Earth depending on their interaction with the solar wind and other large-scale structures such as coronal holes and CMEs. The interplanetary propagation is essentially controlled by the drag force because the propelling force and the solar gravity are significant only near the Sun. Combined remote-sensing and in situ observations have helped us estimate the influence of the solar wind on the propagation of CMEs. However, these measurements have severe limitations because the remote-sensed and in-situ observations correspond to different portions of the CME. Attempts to overcome this problem are made in two ways: the first is to model the CME and get the space speed of the CME, which can be compared with the in situ speed. The second method is to use stereoscopic observation so that the remote-sensed and in-situ observations make measurements on the Earth-arriving part of CMEs. The Solar Terrestrial Relations Observatory (STEREO) mission observed several such CMEs, which helped understand the interplanetary evolution of these CMEs and to test earlier model results. This paper discusses some of these issues and updates the CME/shock travel time estimates for a number of CMEs.

  1. Multi-instrument observations of coronal loops

    NASA Astrophysics Data System (ADS)

    Scott, Jason Terrence

    This document exhibits results of analysis from data collected with multiple EUV satellites (SOHO, TRACE, STEREO, Hinode, and SDO). The focus is the detailed observation of coronal loops using multiple instruments, i.e. filter imagers and spectrometers. Techniques for comparing the different instruments and deriving loop parameters are demonstrated. Attention is given to the effects the different instruments may introduce into the data and their interpretation. The assembled loop parameters are compared to basic energy balance equations and scaling laws. Discussion of the blue-shifted, asymmetric, and line broadened spectral line profiles near the footpoints of coronal loops is made. The first quantitative analysis of the anti-correlation between intensity and spectral line broadening for isolated regions along loops and their footpoints is presented. A magnetic model of an active region shows where the separatrices meet the photospheric boundary. At the boundary, the spectral data reveal concentrated regions of increased blue-shifted outflows, blue wing asymmetry, and line broadening. This is found just outside the footpoints of bright loops. The intensity and line broadening in this region are anti-correlated. A comparison of the similarities in the spectroscopic structure near the footpoints of the arcade loops and more isolated loops suggests the notion of consistent structuring for the bright loops forming an apparent edge of an active region core.

  2. BAYESIAN MAGNETOHYDRODYNAMIC SEISMOLOGY OF CORONAL LOOPS

    SciTech Connect

    Arregui, I.; Asensio Ramos, A. E-mail: aasensio@iac.es

    2011-10-10

    We perform a Bayesian parameter inference in the context of resonantly damped transverse coronal loop oscillations. The forward problem is solved in terms of parametric results for kink waves in one-dimensional flux tubes in the thin tube and thin boundary approximations. For the inverse problem, we adopt a Bayesian approach to infer the most probable values of the relevant parameters, for given observed periods and damping times, and to extract their confidence levels. The posterior probability distribution functions are obtained by means of Markov Chain Monte Carlo simulations, incorporating observed uncertainties in a consistent manner. We find well-localized solutions in the posterior probability distribution functions for two of the three parameters of interest, namely the Alfven travel time and the transverse inhomogeneity length scale. The obtained estimates for the Alfven travel time are consistent with previous inversion results, but the method enables us to additionally constrain the transverse inhomogeneity length scale and to estimate real error bars for each parameter. When observational estimates for the density contrast are used, the method enables us to fully constrain the three parameters of interest. These results can serve to improve our current estimates of unknown physical parameters in coronal loops and to test the assumed theoretical model.

  3. Small-Scale Magnetic Reconnection at Equatorial Coronal Hole Boundaries

    NASA Astrophysics Data System (ADS)

    Lamb, Derek; DeForest, C. E.

    2011-05-01

    Coronal holes have long been known to be the source of the fast solar wind at both high and low latitudes. The equatorial extensions of polar coronal holes have long been assumed to have substantial magnetic reconnection at their boundaries, because they rotate more rigidly than the underlying photosphere. However, evidence for this reconnection has been sparse until very recently. We present some evidence that reconnection due to the evolution of small-scale magnetic fields may be sufficient to drive coronal hole boundary evolution. We hypothesize that a bias in the direction of that reconnection is sufficient to give equatorial coronal holes their rigid rotation. We discuss the prospects for investigating this using FLUX, a reconnection-controlled coronal MHD simulation framework. This work was funded by the NASA SHP-GI program.

  4. A DATA-DRIVEN MODEL FOR THE GLOBAL CORONAL EVOLUTION

    SciTech Connect

    Feng Xueshang; Jiang Chaowei; Xiang Changqing; Zhao Xuepu; Wu, S. T. E-mail: cwjiang@spaceweather.ac.cn E-mail: xpzhao@sun.stanford.edu

    2012-10-10

    This work is devoted to the construction of a data-driven model for the study of the dynamic evolution of the global corona that can respond continuously to the changing of the photospheric magnetic field. The data-driven model consists of a surface flux transport (SFT) model and a global three-dimensional (3D) magnetohydrodynamic (MHD) coronal model. The SFT model is employed to produce the global time-varying and self-consistent synchronic snapshots of the photospheric magnetic field as the input to drive our 3D numerical global coronal AMR-CESE-MHD model on an overset grid of Yin-Yang overlapping structure. The SFT model and the 3D global coronal model are coupled through the boundary condition of the projected characteristic method. Numerical results of the coronal evolution from 1996 September 4 to October 29 provide a good comparison with multiply observed coronal images.

  5. A Data-driven Model for the Global Coronal Evolution

    NASA Astrophysics Data System (ADS)

    Feng, Xueshang; Jiang, Chaowei; Xiang, Changqing; Zhao, Xuepu; Wu, S. T.

    2012-10-01

    This work is devoted to the construction of a data-driven model for the study of the dynamic evolution of the global corona that can respond continuously to the changing of the photospheric magnetic field. The data-driven model consists of a surface flux transport (SFT) model and a global three-dimensional (3D) magnetohydrodynamic (MHD) coronal model. The SFT model is employed to produce the global time-varying and self-consistent synchronic snapshots of the photospheric magnetic field as the input to drive our 3D numerical global coronal AMR-CESE-MHD model on an overset grid of Yin-Yang overlapping structure. The SFT model and the 3D global coronal model are coupled through the boundary condition of the projected characteristic method. Numerical results of the coronal evolution from 1996 September 4 to October 29 provide a good comparison with multiply observed coronal images.

  6. Determination of coronal magnetic fields from vector magnetograms

    NASA Technical Reports Server (NTRS)

    Mikic, Zoran

    1993-01-01

    This report covers technical progress during the second year of the contract entitled 'Determination of Coronal Magnetic Fields from Vector Magnetograms,' NASW-4728, between NASA and Science Applications International Corporation, and covers the period January 1, 1993 to December 31, 1993. Under this contract SAIC has conducted research into the determination of coronal magnetic fields from vector magnetograms, including the development and application of algorithms to determine force-free coronal fields above selected observations of active regions. The contract began on June 30, 1992 and has a completion date of December 31, 1994. This contract is a continuation of work started in a previous contract, NASW-4571, which covered the period November 15, 1990 to December 14, 1991. During this second year we have concentrated on studying additional active regions and in using the estimated coronal magnetic fields to compare to coronal features inferred from observations.

  7. Coronal disturbances and their terrestrial effects /Tutorial Lecture/

    NASA Technical Reports Server (NTRS)

    Rust, D. M.

    1983-01-01

    An assessment is undertaken of recent approaches to the prediction of the interplanetary consequences of coronal disturbances, with attention to the relationships of shocks and energetic particles to coronal transients, of proton events to gamma-ray and microwave bursts, of geomagnetic storms to filament eruptions, and of solar wind increases to the flare site magnetic field direction. A discussion is given concerning the novel phenomenon of transient coronal holes, which appear astride the long decay enhancements of 2-50 A X-ray emission following H-alpha filament eruptions. These voids in the corona are similar to long-lived coronal holes, which are the sources of high speed solar wind streams. The transient coronal holes may also be associated with transient solar wind speed increases.

  8. Solar Wind Associated with Near Equatorial Coronal Hole

    NASA Astrophysics Data System (ADS)

    Hegde, M.; Hiremath, K. M.; Doddamani, Vijayakumar H.; Gurumath, Shashanka R.

    2015-09-01

    Present study probes temporal changes in the area and radiative flux of near equatorial coronal hole associated with solar wind parameters such as wind speed, density, magnetic field and temperature. Using high temporal resolution data from SDO/AIA for the two wavelengths 193 Å and 211 Å, area and radiative flux of coronal holes are extracted and are examined for the association with high speed solar wind parameters. We find a strong association between different parameters of coronal hole and solar wind. For both the wavelength bands, we also compute coronal hole radiative energy near the earth and it is found to be of similar order as that of solar wind energy. However, for the wavelength 193 Å, owing to almost similar magnitudes of energy emitted by coronal hole and energy due to solar wind, it is conjectured that solar wind might have originated around the same height where 193 Å line is formed in the corona.

  9. SEISMOLOGY OF TRANSVERSELY OSCILLATING CORONAL LOOPS WITH SIPHON FLOWS

    SciTech Connect

    Terradas, J.; Arregui, I.; Verth, G.; Goossens, M.

    2011-03-10

    There are ubiquitous flows observed in the solar atmosphere of sub-Alfvenic speeds; however, after flaring and coronal mass ejection events flows can become Alfvenic. In this Letter, we derive an expression for the standing kink mode frequency due to siphon flow in coronal loops, valid for both low and high speed regimes. It is found that siphon flow introduces a linear, spatially dependent phase shift along coronal loops and asymmetric eigenfunctions. We demonstrate how this theory can be used to determine the kink and flow speed of oscillating coronal loops with reference to an observational case study. It is shown that the presence of siphon flow can cause the underestimation of magnetic field strength in coronal loops using the traditional seismological methods.

  10. Low-latitude Coronal Holes during Solar Maximum

    NASA Astrophysics Data System (ADS)

    Miralles, M.; Cranmer, S.; Kohl, J.

    Analyses of in situ observations have shown that some small coronal holes are sources of slow solar wind near solar maximum when polar coronal holes become smaller and disappear. However, not all coronal holes at solar maximum produce slow wind. The Ultraviolet Coronagraph Spectrometer (UVCS) aboard SOHO has been used to observe large low-latitude coronal holes during solar maximum that produced fast solar wind. UVCS observations show that large equatorial holes at solar maximum have plasma properties that seem to bridge the gap between solar minimum polar coronal holes and streamers. The ion kinetic temperatures in equatorial holes are about 2 times larger than those in a solar minimum equatorial streamer, and about a factor of 2 smaller than those in polar coronal holes above 2 R . The outflow speeds for the large equatorial holes observed by UVCS are only about 100 km s-1 , a factor of 4 smaller than those in polar holes, at 3 R . However, in situ data corresponding to these equatorial coronal holes showed asymptotic wind speeds of 600-700 km s-1 . These wind speeds are similar to those observed over polar coronal holes at solar minimum. In contrast to the polar coronal holes, the bulk of the solar wind acceleration in large equatorial coronal holes at solar maximum must occur above 3 R . Thus, the combination of spectroscopic measurements in the extended corona, where the primary solar wind acceleration occurs, and in situ measurements made in the solar wind can be used to obtain the solar wind acceleration as a function of heliocentric distance. These observations provide detailed empirical constraints for theoretical models and may be key to understanding how the various types of solar wind plasma are heated and accelerated. This work is supported by NASA under Grant NAG5-11420 to the Smithsonian Astrophysical Observatory, by the Italian Space Agency and by PRODEX (Swiss contribution).

  11. Coronal Heating and the Magnetic Flux Content of the Network

    NASA Technical Reports Server (NTRS)

    Falconer, D. A.; Moore, R. L.; Porter, J. G.; Hathaway, D. H.; Rose, M. Franklin (Technical Monitor)

    2001-01-01

    Previously, from analysis of SOHO coronal images in combination with Kitt Peak magnetograms, we found that the quiet corona is the sum of two components: the large-scale corona and the coronal network. The large-scale corona consists of all coronal-temperature (T approximately 10(exp 6) K) structures larger than supergranules (greater than approximately 30,000 kilometers). The coronal network (1) consists of all coronal-temperature structures smaller than supergranules, (2) is rooted in and loosely traces the photospheric magnetic network, (3) has its brightest features seated on polarity dividing lines (neutral lines) in the network magnetic flux, and (4) produces only about 5% of the total coronal emission in quiet regions. The heating of the coronal network is apparently magnetic in origin. Here, from analysis of EIT coronal images of quiet regions in combination with magnetograms of the same quiet regions from SOHO/MDI and from Kitt Peak, we examine the other 95% of the quiet corona and its relation to the underlying magnetic network. We find: (1) Dividing the large-scale corona into its bright and dim halves divides the area into bright "continents" and dark "oceans" having spans of 2-4 supergranules. (2) These patterns are also present in the photospheric magnetograms: the network is stronger under the bright half and weaker under the dim half. (3) The radiation from the large-scale corona increases roughly as the cube root of the magnetic flux content of the underlying magnetic network. In contrast, the coronal radiation from an active region increases roughly linearly with the magnetic flux content of the active region. We assume, as is widely held, that nearly all of the large-scale corona is magnetically rooted in the network. Our results suggest that either the coronal heating in quiet regions has a large non-magnetic component, or, if the heating is predominantly produced via the magnetic field, the mechanism is significantly different than in active

  12. SOLAR CYCLE VARIATIONS OF CORONAL NULL POINTS: IMPLICATIONS FOR THE MAGNETIC BREAKOUT MODEL OF CORONAL MASS EJECTIONS

    SciTech Connect

    Cook, G. R.; Mackay, D. H.; Nandy, Dibyendu E-mail: duncan@mcs.st-and.ac.u

    2009-10-20

    In this paper, we investigate the solar cycle variation of coronal null points and magnetic breakout configurations in spherical geometry, using a combination of magnetic flux transport and potential field source surface models. Within the simulations, a total of 2843 coronal null points and breakout configurations are found over two solar cycles. It is found that the number of coronal nulls present at any time varies cyclically throughout the solar cycle, in phase with the flux emergence rate. At cycle maximum, peak values of 15-17 coronal nulls per day are found. No significant variation in the number of nulls is found from the rising to the declining phase. This indicates that the magnetic breakout model is applicable throughout both phases of the solar cycle. In addition, it is shown that when the simulations are used to construct synoptic data sets, such as those produced by Kitt Peak, the number of coronal nulls drops by a factor of 1/6. The vast majority of the coronal nulls are found to lie above the active latitudes and are the result of the complex nature of the underlying active region fields. Only 8% of the coronal nulls are found to be connected to the global dipole. Another interesting feature is that 18% of coronal nulls are found to lie above the equator due to cross-equatorial interactions between bipoles lying in the northern and southern hemispheres. As the majority of coronal nulls form above active latitudes, their average radial extent is found to be in the low corona below 1.25 R {sub sun} (175, 000 km above the photosphere). Through considering the underlying photospheric flux, it is found that 71% of coronal nulls are produced though quadrupolar flux distributions resulting from bipoles in the same hemisphere interacting. When the number of coronal nulls present in each rotation is compared to the number of bipoles emerging, a wide scatter is found. The ratio of coronal nulls to emerging bipoles is found to be approximately 1/3. Overall

  13. Determination of Coronal Magnetic Fields from Vector Magnetograms

    NASA Technical Reports Server (NTRS)

    Mikic, Zoran

    1997-01-01

    During the course of the present contract we developed an 'evolutionary technique' for the determination of force-free coronal magnetic fields from vector magnetograph observations. The method can successfully generate nonlinear force- free fields (with non-constant-a) that match vector magnetograms. We demonstrated that it is possible to determine coronal magnetic fields from photospheric measurements, and we applied it to vector magnetograms of active regions. We have also studied theoretical models of coronal fields that lead to disruptions. Specifically, we have demonstrated that the determination of force-free fields from exact boundary data is a well-posed mathematical problem, by verifying that the computed coronal field agrees with an analytic force-free field when boundary data for the analytic field are used; demonstrated that it is possible to determine active-region coronal magnetic fields from photospheric measurements, by computing the coronal field above active region 5747 on 20 October 1989, AR6919 on 15 November 1991, and AR7260 on 18 August 1992, from data taken with the Stokes Polarimeter at Mees Solar Observatory, University of Hawaii; started to analyze active region 7201 on 19 June 1992 using measurements made with the Advanced Stokes Polarimeter at NSO/Sac Peak; investigated the effects of imperfections in the photospheric data on the computed coronal magnetic field; documented the coronal field structure of AR5747 and compared it to the morphology of footpoint emission in a flare, showing that the 'high- pressure' H-alpha footpoints are connected by coronal field lines; shown that the variation of magnetic field strength along current-carrying field lines is significantly different from the variation in a potential field, and that the resulting near-constant area of elementary flux tubes is consistent with observations; begun to develop realistic models of coronal fields which can be used to study flare trigger mechanisms; demonstrated that

  14. A gigantic coronal jet ejected from a compact active region in a coronal hole

    NASA Technical Reports Server (NTRS)

    Shibata, K.; Nitta, N.; Strong, K. T.; Matsumoto, R.; Yokoyama, T.; Hirayama, T.; Hudson, H.; Ogawara, Y.

    1994-01-01

    A gigantic coronal jet greater than 3 x 10(exp 5) km long (nearly half the solar radius) has been found with the soft X-ray telescope (SXT) on board the solar X-ray satellite, Yohkoh. The jet was ejected on 1992 January 11 from an 'anemone-type' active region (AR) appearing in a coronal hole and is one of the largest coronal X-ray jets observed so far by SXT. This gigantic jet is the best observed example of many other smaller X-ray jets, because the spatial structures of both the jet and the AR located at its base are more easily resolved. The range of apparent translational velocities of the bulk of the jet was between 90 and 240 km s(exp -1), with the corresponding kinetic energy estimated to be of order of 10(exp 28) ergs. A detailed analysis reveals that the jet was associated with a loop brightening (a small flare) that occurred in the active region. Several features of this observation suggest and are consistent with a magnetic reconnection mechanism for the production of such a 'jet-loop-brightening' event.

  15. Magnetic Topology of Active Regions and Coronal Holes: Implications for Coronal Outflows and the Solar Wind

    NASA Astrophysics Data System (ADS)

    van Driel-Gesztelyi, L.; Culhane, J. L.; Baker, D.; Démoulin, P.; Mandrini, C. H.; DeRosa, M. L.; Rouillard, A. P.; Opitz, A.; Stenborg, G.; Vourlidas, A.; Brooks, D. H.

    2012-11-01

    During 2 - 18 January 2008 a pair of low-latitude opposite-polarity coronal holes (CHs) were observed on the Sun with two active regions (ARs) and the heliospheric plasma sheet located between them. We use the Hinode/EUV Imaging Spectrometer (EIS) to locate AR-related outflows and measure their velocities. Solar-Terrestrial Relations Observatory (STEREO) imaging is also employed, as are the Advanced Composition Explorer (ACE) in-situ observations, to assess the resulting impacts on the solar wind (SW) properties. Magnetic-field extrapolations of the two ARs confirm that AR plasma outflows observed with EIS are co-spatial with quasi-separatrix layer locations, including the separatrix of a null point. Global potential-field source-surface modeling indicates that field lines in the vicinity of the null point extend up to the source surface, enabling a part of the EIS plasma upflows access to the SW. We find that similar upflow properties are also observed within closed-field regions that do not reach the source surface. We conclude that some of plasma upflows observed with EIS remain confined along closed coronal loops, but that a fraction of the plasma may be released into the slow SW. This suggests that ARs bordering coronal holes can contribute to the slow SW. Analyzing the in-situ data, we propose that the type of slow SW present depends on whether the AR is fully or partially enclosed by an overlying streamer.

  16. A gigantic coronal jet ejected from a compact active region in a coronal hole

    NASA Astrophysics Data System (ADS)

    Shibata, K.; Nitta, N.; Strong, K. T.; Matsumoto, R.; Yokoyama, T.; Hirayama, T.; Hudson, H.; Ogawara, Y.

    1994-08-01

    A gigantic coronal jet greater than 3 x 105 km long (nearly half the solar radius) has been found with the soft X-ray telescope (SXT) on board the solar X-ray satellite, Yohkoh. The jet was ejected on 1992 January 11 from an 'anemone-type' active region (AR) appearing in a coronal hole and is one of the largest coronal X-ray jets observed so far by SXT. This gigantic jet is the best observed example of many other smaller X-ray jets, because the spatial structures of both the jet and the AR located at its base are more easily resolved. The range of apparent translational velocities of the bulk of the jet was between 90 and 240 km s-1, with the corresponding kinetic energy estimated to be of order of 1028 ergs. A detailed analysis reveals that the jet was associated with a loop brightening (a small flare) that occurred in the active region. Several features of this observation suggest and are consistent with a magnetic reconnection mechanism for the production of such a 'jet-loop-brightening' event.

  17. COMBINING PARTICLE ACCELERATION AND CORONAL HEATING VIA DATA-CONSTRAINED CALCULATIONS OF NANOFLARES IN CORONAL LOOPS

    SciTech Connect

    Gontikakis, C.; Efthymiopoulos, C.; Georgoulis, M. K.; Patsourakos, S.; Anastasiadis, A.

    2013-07-10

    We model nanoflare heating of extrapolated active-region coronal loops via the acceleration of electrons and protons in Harris-type current sheets. The kinetic energy of the accelerated particles is estimated using semi-analytical and test-particle-tracing approaches. Vector magnetograms and photospheric Doppler velocity maps of NOAA active region 09114, recorded by the Imaging Vector Magnetograph, were used for this analysis. A current-free field extrapolation of the active-region corona was first constructed. The corresponding Poynting fluxes at the footpoints of 5000 extrapolated coronal loops were then calculated. Assuming that reconnecting current sheets develop along these loops, we utilized previous results to estimate the kinetic energy gain of the accelerated particles. We related this energy to nanoflare heating and macroscopic loop characteristics. Kinetic energies of 0.1-8 keV (for electrons) and 0.3-470 keV (for protons) were found to cause heating rates ranging from 10{sup -6} to 1 erg s{sup -1} cm{sup -3}. Hydrodynamic simulations show that such heating rates can sustain plasma in coronal conditions inside the loops and generate plasma thermal distributions that are consistent with active-region observations. We concluded the analysis by computing the form of X-ray spectra generated by the accelerated electrons using the thick-target approach. These spectra were found to be in agreement with observed X-ray spectra, thus supporting the plausibility of our nanoflare-heating scenario.

  18. Coronal Holes During the Past Solar Cycle [Invited

    NASA Astrophysics Data System (ADS)

    Miralles, M. P.

    2003-06-01

    Analyses of UVCS/SOHO observations during different phases of Solar Cycle 23 have shown marked variations of ion properties in the acceleration region of the high-speed solar wind in large coronal holes. In 1996--1997 at solar minimum, UVCS observations revealed fast, hot flows coming from polar coronal holes. Around solar maximum, UVCS observations showed slower, cooler flows coming from coronal holes at the Sun's equator. In 2001 and 2002, UVCS observations evidenced the reappearance of the coronal holes at the north and south poles for the next solar cycle. We present empirical models for the physical properties of large coronal holes and the acceleration of the associated high-speed solar wind derived from ultraviolet coronagraphic spectroscopy. We discuss the role of solar cycle trends and the variation of ambient coronal-hole properties (e.g., magnetic field, geometry, density). We use these observations to test phenomenological models of coronal heating and solar wind acceleration. This work is supported by NASA under Grant NAG5-11420 to the Smithsonian Astrophysical Observatory, by the Italian Space Agency and by PRODEX (Swiss contribution).

  19. Possible evidence for coronal Alfven waves

    NASA Technical Reports Server (NTRS)

    Hollweg, J. V.; Bird, M. K.; Volland, H.; Edenhofer, P.; Stelzried, C. T.; Seidel, B. L.

    1982-01-01

    A statistical ray analysis is used to analyze observed electron content and Faraday rotation fluctuations in the 2.29 GHz S band carrier signals of the two Helios spacecraft probing the magnetic and density structures of the solar corona inside 0.05 AU. It is found that (1) the observed Faraday rotation fluctuations cannot be due only to electron density fluctuations in the corona, unless the coronal magnetic field is about five times stronger than suggested by current estimates; and (2) the observed Faraday rotation fluctuations are consistent with the hypothesis that the sun radiates Alfven waves whose energies are great enough to heat and accelerate high-speed solar wind streams.

  20. Driving mechanisms for coronal mass ejections.

    NASA Astrophysics Data System (ADS)

    Steinolfson, R. S.

    Mass ejections are new bright features observed in white-light that give the appearance of outward moving material. An acknowledged key ingredient in both the ejection and its progenitor is the magnetic field, although the precise nature of its role, particularily in the driving mechanism, remains unclear. The author begins by reviewing analyses of coordinated data sets that establish the relative time sequence and spatial location of individually identified phenomena (such as the flare impulsive phase, eruptive prominence, CME trajectory, etc.) that better define potential drivers. Some of the models and numerical simulations that have been developed with the intent of determining the physical interactions in the driving mechanism and coronal mass ejection are then considered.

  1. Low-coronal Sources of Stealth CMEs

    NASA Astrophysics Data System (ADS)

    Alzate, N.; Morgan, H.

    2015-10-01

    Coronal mass ejections (CMEs) usually exhibit lower-corona dynamics such as flares, magnetic reconfiguration, EUV waves, jets or filaments. Recent studies have observed CMEs without a lowcoronal signatures (LCS) which have been referred to as stealth CMEs. Through new image processing applied to EUV images we find clear evidence of LCS leading to stealth CMEs. The LCS of stealth CMEs are fairly sizeable yet faint eruptions with structure consistent with a rising flux tube, possibly formed higher in the corona in regions of weaker magnetic field. We believe these flux tubes are formed mostly in polar regions due to the large shear resulting from the slowly-rotating lower atmosphere below the more rapidly rotating corona. This would allow the formation of large flux tubes in weaker field regions, leading to low-energy and low-density flux tube eruptions.

  2. Global Acceleration of Coronal Mass Ejections

    NASA Technical Reports Server (NTRS)

    Gopalswamy, Nat; Lara, Alejandro; Lepping, Ronald; Kaiser, Michael; Berdichevsky, Daniel; St. Cyr, O. Chris; Lazarus, Al

    1999-01-01

    Using the observed relation between speeds of coronal mass ejections (CMEs) near the Sun and in the solar wind, we estimate a global acceleration acting on the CMEs. Our study quantifies the qualitative results of Gosling [1997] and numerical simulations that CMEs at 1 AU with speeds closer to the solar wind. We found a linear relation between the global acceleration and the initial speed of the CMEs and the absolute value of the acceleration is similar to the slow solar wind acceleration. Our study naturally divides CMEs into fast and slow ones, the dividing line being the solar wind speed. Our results have important implications to space weather prediction models which need to incorporate this effect in estimating the CME arrival time at 1 AU. We show that the arrival times of CMEs at 1 AU are drastically different from the zero acceleration case.

  3. Solar wind origin in coronal funnels.

    PubMed

    Tu, Chuan-Yi; Zhou, Cheng; Marsch, Eckart; Xia, Li-Dong; Zhao, Liang; Wang, Jing-Xiu; Wilhelm, Klaus

    2005-04-22

    The origin of the solar wind in solar coronal holes has long been unclear. We establish that the solar wind starts flowing out of the corona at heights above the photosphere between 5 megameters and 20 megameters in magnetic funnels. This result is obtained by a correlation of the Doppler-velocity and radiance maps of spectral lines emitted by various ions with the force-free magnetic field as extrapolated from photospheric magnetograms to different altitudes. Specifically, we find that Ne7+ ions mostly radiate around 20 megameters, where they have outflow speeds of about 10 kilometers per second, whereas C3+ ions with no average flow speed mainly radiate around 5 megameters. Based on these results, a model for understanding the solar wind origin is suggested. PMID:15845846

  4. Solar Eruptions: Coronal Mass Ejections and Flares

    NASA Technical Reports Server (NTRS)

    Gopalswamy, Nat

    2012-01-01

    This lecture introduces the topic of Coronal mass ejections (CMEs) and solar flares, collectively known as solar eruptions. During solar eruptions, the released energy flows out from the Sun in the form of magnetized plasma and electromagnetic radiation. The electromagnetic radiation suddenly increases the ionization content of the ionosphere, thus impacting communication and navigation systems. Flares can be eruptive or confined. Eruptive flares accompany CMEs, while confined flares hav only electromagnetic signature. CMEs can drive MHD shocks that accelerate charged particles to very high energies in the interplanetary space, which pose radiation hazard to astronauts and space systems. CMEs heading in the direction of Earth arrive in about two days and impact Earth's magnetosphere, producing geomagnetic storms. The magnetic storms result in a number of effects including induced currnts that can disrupt power grids, railroads, and underground pipelines

  5. Coronal Loops: New Insights from EIS Observations

    NASA Astrophysics Data System (ADS)

    Del Zanna, G.; Bradshaw, S. J.

    2009-12-01

    Multi-instrument observations of coronal loops of different active regions have been studied. The general features discussed in Del Zanna (2003) and Del Zanna and Mason (2003) based on SOHO/CDS are confirmed. Hinode/EIS high-cadence observations clearly show how dynamic loops are at all temperatures. This clearly reflects the fast changes in the photospheric magnetic fields measured by SOT over a minute timescale. Despite that, persistent patterns are present. In particular, the pattern of Doppler shifts and non-thermal widths, found for the first time in NOAA 10926 (cf. Del Zanna 2007, 2008), is actually a common feature in all active regions. It is likely that the majority of cool (0.5--1 MK) loops are observed during their radiatively cooling phase.

  6. Differential flow: Locally Generated or Coronal Artifact?

    NASA Astrophysics Data System (ADS)

    Alterman, B. L.; Kasper, J. C.; Stevens, M. L.; Szabo, A.; Koval, A.

    2015-12-01

    Alpha particles and proton beams differentially flow in the solar wind with respect to the proton core by about an Alfvén speed. Whether differential flow is an artifact of coronal physics or a signature of local acceleration as the solar wind propagates earthward is undetermined. A new analysis of Wind spacecraft observations in the solar wind combines Faraday Cup ion distribution functions with vector magnetic field measurements to characterize the bulk properties of the proton core, proton beam, and alpha particles with 92s time resolution. We utilize this data set to examine the occurrence of differential flow at 1 AU as a function of solar wind conditions and other parameters. We discuss the implications of observed trends on our understanding of differential flow's origin.

  7. On the theory of coronal heating mechanisms

    NASA Technical Reports Server (NTRS)

    Kuperus, M.; Ionson, J. A.; Spicer, D. S.

    1981-01-01

    The present state-of-the-art of two classes of theories of coronal heating is examined: (1) heating by acoustic processes in the 'nonmagnetic' parts of the atmosphere (the shock-wave theory is an example); and (2) heating by electrodynamic processes in the magnetic regions of the corona (beta much less than 1) either by MHD waves or current heating in regions with high electric current densities (flare-type heating). It is concluded that the mechanism of the heating of the solar chromosphere and corona remains an open question, especially in explaining detailed atmospheric structures. The acoustic theory might be correct with little modification for most of the chromosphere, but as soon as the atmosphere shows a high degree of structure as in the corona and transition layer the magnetic field must play a dominant role. It appears that the current heating theories have a small range of applicability, while the MHD-wave theories are the most promising.

  8. Characteristics of polar coronal hole jets

    NASA Astrophysics Data System (ADS)

    Chandrashekhar, K.; Bemporad, A.; Banerjee, D.; Gupta, G. R.; Teriaca, L.

    2014-01-01

    Context. High spatial- and temporal-resolution images of coronal hole regions show a dynamical environment where mass flows and jets are frequently observed. These jets are believed to be important for the coronal heating and the acceleration of the fast solar wind. Aims: We studied the dynamics of two jets seen in a polar coronal hole with a combination of imaging from EIS and XRT onboard Hinode. We observed drift motions related to the evolution and formation of these small-scale jets, which we tried to model as well. Methods: Stack plots were used to find the drift and flow speeds of the jets. A toymodel was developed by assuming that the observed jet is generated by a sequence of single reconnection events where single unresolved blobs of plasma are ejected along open field lines, then expand and fall back along the same path, following a simple ballistic motion. Results: We found observational evidence that supports the idea that polar jets are very likely produced by multiple small-scale reconnections occurring at different times in different locations. These eject plasma blobs that flow up and down with a motion very similar to a simple ballistic motion. The associated drift speed of the first jet is estimated to be ≈27 km s-1. The average outward speed of the first jet is ≈171 km s-1, well below the escape speed, hence if simple ballistic motion is considered, the plasma will not escape the Sun. The second jet was observed in the south polar coronal hole with three XRT filters, namely, C-poly, Al-poly, and Al-mesh filters. Many small-scale (≈3″-5″) fast (≈200-300 km s-1) ejections of plasma were observed on the same day; they propagated outwards. We observed that the stronger jet drifted at all altitudes along the jet with the same drift speed of ≃7 km s-1. We also observed that the bright point associated with the first jet is a part of sigmoid structure. The time of appearance of the sigmoid and that of the ejection of plasma from the bright

  9. Reduced Coronal Emission Above Large Isolated Sunspots

    NASA Astrophysics Data System (ADS)

    Ryabov, B. I.; Gary, D. E.; Peterova, N. G.; Shibasaki, K.; Topchilo, N. A.

    2015-01-01

    We analysed specific regions of reduced soft X-ray and microwave emission in five large isolated sunspots. The Nobeyama Radioheliograph 17 GHz observations reveal a local depression of microwave brightness in the peripheral area of the sunspots. The depression regions appear light (weak absorption) in the He 10830 Å line in areas with extended (open) field lines, as indicated by potential field source surface model (PFSS) extrapolations up to 1.5 R⊙. The observed depressions of 3 - 8 % in ordinary mode at 17 GHz are interpreted as resulting from free-free emission when the plasma density is lower by 5 - 10 %. Our model estimates show that the decrease in density in both the coronal and the lower layers above the depression region accounts for the depression. These depression regions lend themselves well to marking the location of outward plasma motions.

  10. Coronal Mass Ejections: From Sun to Earth

    NASA Astrophysics Data System (ADS)

    Patsourakos, S.

    2016-06-01

    Coronal Mass Ejections (CMEs) are gigantic expulsions of magnetized plasmas from the solar corona into the interplanetary (IP) space. CMEs spawn ~ 1015 gr of mass and reach speeds ranging between several hundred to a few thousand km/s (e.g., Gopalswamy et al. 2009; Vourlidas et al. 2010). It takes 1-5 days for a CME to reach Earth. CMEs are one of the most energetic eruptive manifestations in the solar system and are major drivers of space weather via their magnetic fields and energetic particles, which are accelerated by CME-driven shocks. In this review we give a short account of recent, mainly observational, results on CMEs from the STEREO and SDO missions which include the nature of their pre-eruptive and eruptive configurations and the CME propagation from Sun to Earth. We conclude with a discussion of the exciting capabilities in CME studies that will soon become available from new solar and heliospheric instrumentation.

  11. A catastrophe mechanism for coronal mass ejections

    NASA Technical Reports Server (NTRS)

    Forbes, T. G.; Isenberg, P. A.

    1991-01-01

    The ideal-MHD equations are used to show that a coronal current filament can suddenly lose equilibrium if its magnetic energy exceeds a critical value. The loss of equilibrium in the configuration results from an imbalance between magnetic tension and compression, and this imbalance ejects the filament upwards. Near the critical value, the equilibrium configuration develops a vertical current sheet attached to the photosphere at the point directly below the filament. When equilibrium is lost, field lines anchored to the photosphere are stretched upwards, and the current sheet rapidly grows longer. Without reconnection in the current sheet, the filament travels only a short distance before reaching a new equilibrium, and the net magnetic energy released is less than 1 percent of the stored magnetic energy. However, with reconnection, the filament travels upwards indefinitely, and all of the stored energy is released.

  12. A magnetohydrodynamic theory of coronal loop transients

    NASA Technical Reports Server (NTRS)

    Yeh, T.

    1982-01-01

    The physical and geometrical characteristics of solar coronal loop transients are described in an MHD model based on Archimedes' MHD buoyancy force. The theory was developed from interpretation of coronagraphic data, particularly from Skylab. The brightness of a loop is taken to indicate the electron density, and successive pictures reveal the electron enhancement in different columns. The forces which lift the loop off the sun surface are analyzed as an MHD buoyancy force affecting every mass element by imparting an inertial force necessary for heliocentrifugal motion. Thermal forces are responsible for transferring the ambient stress to the interior of the loop to begin the process. The kinematic and hydrostatic buoyancy overcome the gravitational force, and a flux rope can then curve upward, spiralling like a corkscrew with varying cross section around the unwinding solar magnetic field lines.

  13. Turbulent resistive heating of solar coronal arches

    NASA Technical Reports Server (NTRS)

    Benford, G.

    1983-01-01

    The possibility that coronal heating occurs by means of anomalous Joule heating by electrostatic ion cyclotron waves is examined, with consideration given to currents running from foot of a loop to the other. It is assumed that self-fields generated by the currents are absent and currents follow the direction of the magnetic field, allowing the plasma cylinder to expand radially. Ion and electron heating rates are defined within the cylinder, together with longitudinal conduction and convection, radiation and cross-field transport, all in terms of Coulomb and turbulent effects. The dominant force is identified as electrostatic ion cyclotron instability, while ion acoustic modes remain stable. Rapid heating from an initial temperature of 10 eV to 100-1000 eV levels is calculated, with plasma reaching and maintaining a temperature in the 100 eV range. Strong heating is also possible according to the turbulent Ohm's law and by resistive heating.

  14. A Model for Stealth Coronal Mass Ejections

    NASA Astrophysics Data System (ADS)

    Lynch, Benjamin J.; Masson, Sophie; Li, Yan; DeVore, C. Richard; Luhmann, Janet; Antiochos, Spiro K.; Fisher, George H.

    2016-05-01

    Stealth coronal mass ejections (CMEs) are events in which there are almost no observable signatures of the CME eruption in the low corona but often a well-resolved slow flux rope CME observed in the coronagraph data. We present results from a three-dimensional numerical magnetohydrodynamics (MHD) simulation of the 2008 June 1-2 slow streamer blowout CME that Robbrecht et al. [2009] called “the CME from nowhere.” We model the global coronal structure using a 1.4 MK isothermal solar wind and a low-order potential field source surface representation of the Carrington Rotation 2070 magnetogram synoptic map. The bipolar streamer belt arcade is energized by simple shearing flows applied in the vicinity of the helmet streamer’s polarity inversion line. The slow expansion of the energized helmet-streamer arcade results in the formation of a radial current sheet. The subsequent onset of expansion-driven flare reconnection initiates the stealth CME while gradually releasing ~1.5E+30 erg of stored magnetic energy over the 20+ hour eruption duration. We show the energy flux available for flare heating and flare emission during the eruption is approximately two orders of magnitude below the energy flux required to heat the ambient background corona, thus confirming the “stealth” character of the 2008 June 1-2 CME’s lack of observable on disk signatures. We also present favorable comparisons between our simulation results and the multi-viewpoint SOHO-LASCO and STEREO-SECCHI coronagraph observations of the pre-eruption streamer structure and the initiation and evolution of the stealth streamer blowout CME.

  15. FOXSI-2 Observations and Coronal Heating

    NASA Astrophysics Data System (ADS)

    Christe, S.; Glesener, L.; Krucker, S.; Ramsey, B.; Ishikawa, S. N.; Buitrago Casas, J. C.; Takahashi, T.; Foster, N.

    2015-12-01

    Energy release and particle acceleration on the Sun is a frequent occurrence associated with a number of different solar phenomenon including but not limited to solar flares, coronal mass ejections and nanoflares. The exact mechanism through which particles are accelerated and energy is released is still not well understood. This issue is related to the unsolved coronal heating problem, the mystery of the heating mechanism for the million degree solar corona. One prevalent theory posits the existence of a multitude of small flares, dubbed nanoflares. Recent observations of active region AR11890 by IRIS (Testa et al. 2014) are consistent with numerical simulations of heating by impulsive beams of nonthermal electrons, suggesting that nanoflares may be similar to large flares in that they accelerate particles. Furthermore, observations by the EUNIS sounding rocket (Brosius et al. 2014) of faint Fe XIX (592.2 Angstrom) emission in an active region is indicative of plasma at temperatures of at least 8.9 MK providing further evidence of nanoflare heating. One of the best ways to gain insight into accelerated particles on the Sun and the presence of hot plasma is by observing the Sun in hard X-rays (HXR). We present on observations taken during the second successful flight of the Focusing Optics X-ray Solar Imager (FOXSI-2). FOXSI flew on December 11, 2014 with upgraded optics as well as new CdTe strip detectors. FOXSI-2 observed thermal emission (4-15 keV) from at least three active regions (AR#12234, AR#12233, AR#12235) and observed regions of the Sun without active regions. We present on using FOXSI observations to test the presence of hot temperatures in and outside of active regions.

  16. The Dynamics of Coronal-Hole Boundaries

    NASA Astrophysics Data System (ADS)

    Higginson, A. K.; Antiochos, S. K.; DeVore, C. R.; Wyper, P. F.; Zurbuchen, T.

    2015-12-01

    The source of the slow solar wind at the Sun is the subject of intense debate in solar and heliospheric physics. Because the majority of the solar wind observed at Earth is slow wind, understanding its origin is essential for understanding and predicting Earth's space weather environment. In-situ and remote observations show that, compared to the fast wind, the slow solar wind corresponds to higher freeze-in temperatures, as indicated by charge-state ratios, and more corona-like elemental abundances. These results indicate that the most likely source for the slow wind is the hot plasma in the closed-field corona; however, the release mechanism for the wind from the closed-field regions is far from understood. Here we present the first fully dynamic, 3D MHD simulations of a coronal-hole boundary driven by photospheric convective flows. We determine in detail the opening and closing of coronal flux due to photospheric motions at the base of a helmet streamer. These changes should lead to the release of plasma from the closed magnetic field at the edge of the streamer. Our analysis demonstrates that the bulk of the release is due to interchange reconnection. We calculate the effective of numerical Lundquist number on the dynamics and discuss the implications of our results for theories of slow-wind origin, in particular the S-Web model. We also discuss the implications of our results for observations, in particular from the upcoming Solar Orbiter and Solar Probe Plus missions. This work was supported by the NASA SR&T and TR&T Programs.

  17. Numerical Simulation of DC Coronal Heating

    NASA Astrophysics Data System (ADS)

    Dahlburg, Russell B.; Einaudi, G.; Taylor, Brian D.; Ugarte-Urra, Ignacio; Warren, Harry; Rappazzo, A. F.; Velli, Marco

    2016-05-01

    Recent research on observational signatures of turbulent heating of a coronal loop will be discussed. The evolution of the loop is is studied by means of numerical simulations of the fully compressible three-dimensional magnetohydrodynamic equations using the HYPERION code. HYPERION calculates the full energy cycle involving footpoint convection, magnetic reconnection, nonlinear thermal conduction and optically thin radiation. The footpoints of the loop magnetic field are convected by random photospheric motions. As a consequence the magnetic field in the loop is energized and develops turbulent nonlinear dynamics characterized by the continuous formation and dissipation of field-aligned current sheets: energy is deposited at small scales where heating occurs. Dissipation is non-uniformly distributed so that only a fraction of thecoronal mass and volume gets heated at any time. Temperature and density are highly structured at scales which, in the solar corona, remain observationally unresolved: the plasma of the simulated loop is multi thermal, where highly dynamical hotter and cooler plasma strands are scattered throughout the loop at sub-observational scales. Typical simulated coronal loops are 50000 km length and have axial magnetic field intensities ranging from 0.01 to 0.04 Tesla. To connect these simulations to observations the computed number densities and temperatures are used to synthesize the intensities expected in emission lines typically observed with the Extreme ultraviolet Imaging Spectrometer (EIS) on Hinode. These intensities are then employed to compute differential emission measure distributions, which are found to be very similar to those derived from observations of solar active regions.

  18. Measurements of EUV coronal holes and open magnetic flux

    SciTech Connect

    Lowder, C.; Qiu, J.; Leamon, R.; Liu, Y.

    2014-03-10

    Coronal holes are regions on the Sun's surface that map the footprints of open magnetic field lines. We have developed an automated routine to detect and track boundaries of long-lived coronal holes using full-disk extreme-ultraviolet (EUV) images obtained by SOHO/EIT, SDO/AIA, and STEREO/EUVI. We measure coronal hole areas and magnetic flux in these holes, and compare the measurements with calculations by the potential field source surface (PFSS) model. It is shown that, from 1996 through 2010, the total area of coronal holes measured with EIT images varies between 5% and 17% of the total solar surface area, and the total unsigned open flux varies between (2-5)× 10{sup 22} Mx. The solar cycle dependence of these measurements is similar to the PFSS results, but the model yields larger hole areas and greater open flux than observed by EIT. The AIA/EUVI measurements from 2010-2013 show coronal hole area coverage of 5%-10% of the total surface area, with significant contribution from low latitudes, which is under-represented by EIT. AIA/EUVI have measured much enhanced open magnetic flux in the range of (2-4)× 10{sup 22} Mx, which is about twice the flux measured by EIT, and matches with the PFSS calculated open flux, with discrepancies in the location and strength of coronal holes. A detailed comparison between the three measurements (by EIT, AIA-EUVI, and PFSS) indicates that coronal holes in low latitudes contribute significantly to the total open magnetic flux. These low-latitude coronal holes are not well measured with either the He I 10830 line in previous studies, or EIT EUV images; neither are they well captured by the static PFSS model. The enhanced observations from AIA/EUVI allow a more accurate measure of these low-latitude coronal holes and their contribution to open magnetic flux.

  19. Effects of Large-Scale Flows on Coronal Abundances: Multispecies Models and TRACE Observations

    NASA Astrophysics Data System (ADS)

    Lenz, D. D.

    2003-05-01

    Understanding coronal abundances is crucial for interpreting coronal observations and for understanding coronal physical processes and heating. Bulk flows and gravity, both unmistakably present in the corona, significantly affect abundances. We present multispecies simulations of long-lived coronal structures and compare model results with TRACE observations, focusing on abundance variations and flows.

  20. Unilateral coronal craniosynostosis in Abraham Lincoln and his family.

    PubMed

    Fishman, Ronald S

    2010-09-01

    Premature closure of one coronal skull suture produces a characteristic arching or relative elevation of the superior orbital rim on the involved side. This sign is associated with facial asymmetry, and both signs are usually the most conspicuous features in patients with mild unilateral coronal craniosynostosis. Photographs suggest that at least 9 individuals over 5 generations of the Abraham Lincoln family had premature closure of 1 coronal suture. In 8 males, there was involvement of the left side; in 1 female, there was involvement of the right side. PMID:20856045

  1. EUV Coronal Waves: Atmospheric and Heliospheric Connections and Energetics

    NASA Astrophysics Data System (ADS)

    Patsourakos, S.

    2015-12-01

    Since their discovery in late 90's by EIT on SOHO, the study EUV coronal waves has been a fascinating andfrequently strongly debated research area. While it seems as ifan overall consensus has been reached about the nurture and nature of this phenomenon,there are still several important questions regarding EUV waves. By focusing on the most recentobservations, we will hereby present our current understanding about the nurture and nature of EUV waves,discuss their connections with other atmospheric and heliospheric phenomena (e.g.,flares and CMEs, Moreton waves, coronal shocks, coronal oscillations, SEP events) and finallyassess their possible energetic contribution to the overall budget of relatederuptive phenomena.

  2. Atlas of Skylab ATM/S056 coronal hole observations

    NASA Technical Reports Server (NTRS)

    Wilson, R. M.

    1976-01-01

    An atlas of coronal hole observations (Patrol Long and Single Frame Long Filter 3) recorded by the Skylab Apollo Telescope Mount/SO56 X-ray Telescope during the first two manned missions is presented. A total of 279 operations (excluding super long frames) were determined. Comparisons are made between coronal hole observations performed in the first manned mission and those in the second manned mission, and between a super long filter 3 image and a typical single frame (or Patrol) long image. Additional studies to enhance the S056 coronal hole observations and perhaps to extend coverage into the last manned mission are suggested. The data presented are in preliminary form.

  3. Guided MHD waves as a coronal diagnostic tool

    NASA Technical Reports Server (NTRS)

    Roberts, B.

    1986-01-01

    A description is provided of how fast magnetoacoustic waves are ducted along regions of low Alfven velocity (high density) in the corona, exhibiting a distinctive wave signature which may be used as a diagnostic probe of in situ coronal conditions (magnetic field strength, density inhomogeneity, etc.). Some observational knowledge of the start time of the impulsive wave source, possibly a flare, the start and end times of the generated wave event, and the frequency of the pulsations in that event permits a seismological deduction of the physical properties of the coronal medium in which the wave propagated. With good observations the theory offers a new means of probing the coronal atmosphere.

  4. Temperature, Density, and Heating Profiles of Coronal Loops

    NASA Astrophysics Data System (ADS)

    Plowman, Joseph; Martens, P. C.; Kankelborg, C.; Ritchie, M.; Scott, J.; Sharma, R.

    2013-07-01

    We show detailed results of a combined DEM and density-sensitive line ratio analysis of coronal loops observed simultaneously by EIS and AIA. The temperature and density profiles of the loop are compared to and isolated from those of the surrounding material, and these properties are fit to an analytic strand heating model developed by Martens (2010). This research builds on our previously reported work by analyzing a number of coronal loops (including one observed by the Hi-C rocket), improved background subtraction and loop fitting. These improvements allow us to place significant constraints on the heating distribution of coronal loops.

  5. Magnetohydrodynamic waves and coronal seismology: an overview of recent results.

    PubMed

    De Moortel, Ineke; Nakariakov, Valery M

    2012-07-13

    Recent observations have revealed that magnetohydrodynamic (MHD) waves and oscillations are ubiquitous in the solar atmosphere, with a wide range of periods. We give a brief review of some aspects of MHD waves and coronal seismology that have recently been the focus of intense debate or are newly emerging. In particular, we focus on four topics: (i) the current controversy surrounding propagating intensity perturbations along coronal loops, (ii) the interpretation of propagating transverse loop oscillations, (iii) the ongoing search for coronal (torsional) Alfvén waves, and (iv) the rapidly developing topic of quasi-periodic pulsations in solar flares. PMID:22665899

  6. Long-term Trend of Solar Coronal Hole Distribution from 1975 to 2014

    NASA Astrophysics Data System (ADS)

    Fujiki, K.; Tokumaru, M.; Hayashi, K.; Satonaka, D.; Hakamada, K.

    2016-08-01

    We developed an automated prediction technique for coronal holes using potential magnetic field extrapolation in the solar corona to construct a database of coronal holes appearing from 1975 February to 2015 July (Carrington rotations from 1625 to 2165). Coronal holes are labeled with the location, size, and average magnetic field of each coronal hole on the photosphere and source surface. As a result, we identified 3335 coronal holes and found that the long-term distribution of coronal holes shows a similar pattern known as the magnetic butterfly diagram, and polar/low-latitude coronal holes tend to decrease/increase in the last solar minimum relative to the previous two minima.

  7. HINODE/XRT AND STEREO OBSERVATIONS OF A DIFFUSE CORONAL 'WAVE'-CORONAL MASS EJECTION-DIMMING EVENT

    SciTech Connect

    Attrill, Gemma D. R.; Engell, Alexander J.; Wills-Davey, Meredith J.; Grigis, Paolo; Testa, Paola

    2009-10-20

    We report on observations of the first diffuse coronal wave detected by Hinode/XRT. The event occurred near the west solar limb on 2007 May 23, originating from active region (AR) 10956 and was associated with a coronal mass ejection (CME) and coronal dimmings. The bright emission forming the coronal wave expanded predominantly to the east and south of the AR. We use X-Ray Telescope (XRT) and STEREO Behind (B) data combined with a potential magnetic field extrapolation to derive an understanding of the global magnetic field connectivity. We attribute the brightening to the east of the AR to compression and channeling of the plasma along large-scale loops. The brightening to the south of the AR expands across the quiet Sun, making the southern component a likely candidate for identification as a diffuse coronal wave. We analyze the bright front in STEREO/EUVI (B) 171, 195, and 284 A images, as well as in XRT data, finding the strongest components to be largely cospatial in all bandpasses. We also exploit the near-limb location of this event by combining STEREO/COR1 and Extreme Ultra-Violet Imaging Telescope (EUVI) data. Using all the data, we derive a full picture of the low-coronal development of the eruption. The COR1 data show that the southernmost outer edge of the CME is progressively displaced southward during the expansion. EUVI data below the COR1 occulting disk show that the CME is significantly distorted in the low corona as a result of the associated filament eruption. The core coronal dimmings map to the core of the CME; the secondary coronal dimmings map to the CME cavity; and the diffuse coronal wave maps to the outermost edge of the expanding CME shell. The analysis of this near-limb event has important implications for understanding earlier eruptions originating from the same AR on 2007 May 16, 19, and 20.

  8. Coronal heating experiments of the Williams College Group at Mukandgarh Fort, Rajasthan.

    NASA Astrophysics Data System (ADS)

    Pasachoff, J. M.; Babcock, B. A.; Diaz, S.; Reardon, K. P.; Kutner, E. R.

    The authors report on the Williams College expedition to Mukandgarh Fort, Rajasthan, for the total solar eclipse of 24 October 1995. The main experiments were a search for 1 Hz oscillations in coronal loops as an indication of magnetohydrodynamic theories of coronal heating and a mapping of the coronal temperature through comparison of images at specific ultraviolet wavelengths, measuring the difference between the photospheric and coronal continuum. The authors also obtained a variety of coronal images.

  9. Towards a Physical Characterization of Large Coronal Holes

    NASA Astrophysics Data System (ADS)

    Miralles, M. P.; Cranmer, S. R.; Kohl, J. L.

    2004-05-01

    The Ultraviolet Coronagraph Spectrometer (UVCS) aboard SOHO was used to observe O VI (103.2 and 103.7 nm) and H I Lyman alpha (121.6 nm) emission lines as a function of heliocentric distance in more than 85 coronal holes, in order to characterize the physical properties of coronal holes at different phases of the solar cycle. Our previous analyses of UVCS observations have shown that polar and equatorial coronal holes produce different acceleration profiles and have different oxygen kinetic temperatures. We examine the variation in the characteristics of representative large coronal holes producing a variety of high-speed conditions at 1 AU. This work is supported by NASA under Grant NAG5-12865 to the Smithsonian Astrophysical Observatory, by the Italian Space Agency and by PRODEX (Swiss contribution).

  10. Propagation and Dissipation of MHD Waves in Coronal Holes

    NASA Astrophysics Data System (ADS)

    Dwivedi, B. N.

    2006-11-01

    bholadwivedi@gmail.com In view of the landmark result on the solar wind outflow, starting between 5 Mm and 20 Mm above the photosphere in magnetic funnels, we investigate the propagation and dissipation of MHD waves in coronal holes. We underline the importance of Alfvén wave dissipation in the magnetic funnels through the viscous and resistive plasma. Our results show that Alfvén waves are one of the primary energy sources in the innermost part of coronal holes where the solar wind outflow starts. We also consider compressive viscosity and thermal conductivity to study the propagation and dissipation of long period slow longitudinal MHD waves in polar coronal holes. We discuss their likely role in the line profile narrowing, and in the energy budget for coronal holes and the solar wind. We compare the contribution of longitudinal MHD waves with high frequency Alfvén waves.

  11. Braided coronal loops: equilibria, heating, and observational signatures

    NASA Astrophysics Data System (ADS)

    Pontin, David Iain; Hornig, Gunnar; Candelaresi, Simon

    2016-05-01

    We examine the dynamics of coronal loops containing non-trivial magnetic field line braiding. We discuss the existence of braided force-free equilibria, and demonstrate that these equilibria must contain current layers whose thickness becomes increasingly small for increasing field complexity. In practical terms, the implication is that if one considers a line-tied coronal loop that is driven by photospheric motions, then the eventual onset of reconnection and energy release is inevitable. Once the initial reconnection event is triggered a turbulent relaxation ensues. We discuss the relation with Parker’s braiding mechanism for coronal heating, and go on to describe the expected observational signatures of energy release in such a braided coronal loop.

  12. The helium chromosphere, coronal holes, and stellar X-rays

    NASA Technical Reports Server (NTRS)

    Zirin, H.

    1975-01-01

    The solar chromosphere at the limb seen in D3 is an irregular bright band 1000 km thick with a dark band 1000 km thick beneath. The D3 chromosphere disappears in coronal holes. It is shown that the D3 emission, as well as the other He I and He II lines, can be explained quantitatively by photoionization by coronal back-radiation. A Chapman layer with N(He)H = 5 times 10 to the 17th power is formed near tau = 1 in the He I and He II continua. The chromospheric He emission or absorption is weak in coronal holes because there is no coronal back-radiation. Based on this model, the soft X-ray flux from stars with He 10830-A absorption lines is estimated as proportional to the 10830-A equivalent width and the apparent area.

  13. Energy released by the interaction of coronal magnetic fields

    NASA Technical Reports Server (NTRS)

    Sheeley, N. R., Jr.

    1976-01-01

    Comparisons between coronal spectroheliograms and photospheric magnetograms are presented to support the idea that as coronal magnetic fields interact, a process of field-line reconnection usually takes place as a natural way of preventing magnetic stresses from building up in the lower corona. This suggests that the energy which would have been stored in stressed fields is continuously released as kinetic energy of material being driven aside to make way for the reconnecting fields. However, this kinetic energy is negligible compared with the thermal energy of the coronal plasma. Therefore, it appears that these slow adjustments of coronal magnetic fields cannot account for even the normal heating of the corona, much less the energetic events associated with solar flares.

  14. New Instruments to Isolate the Coronal Heating Mechanism

    NASA Technical Reports Server (NTRS)

    Winebarger, Amy

    2014-01-01

    The coronal heating problem remains unsolved today, 80 years after its discovery, despite 50 years of suborbital and orbital coronal observatories. Tens of theoretical coronal heating mechanisms have been suggested, but only a few have been able to be ruled out. In this talk, we will explore the reasons for the slow progress and discuss the measurements that will be needed for potential breakthrough, including imaging the solar corona at small spatial scales, measuring the chromospheric magnetic fields, and detecting the presence of high temperature, low-emission measure plasma. We will discuss three sounding rocket instruments developed to make these measurements: the High-resolution Resolution Coronal Imager (Hi-C), the Chromospheric Lyman-Alpha Spectropolarimeter (CLASP), and the Marshall Grazing Incidence X-ray Spectrometer (MaGIXS).

  15. Nobeyama/SOHO/BBSO Comparison of Solar Polar Coronal Holes

    NASA Astrophysics Data System (ADS)

    Gary, D. E.; Enome, S.; Shibasaki, K.; Gurman, J. B.; Shine, R. A.

    1997-05-01

    Although it is not widely known outside the discipline of solar radiophysics, a long-standing puzzle exists: the poles of the Sun appear brighter than the rest of the quiet Sun in a restricted range of wavelengths roughly from 15 GHz to about 48 GHz (cf. Kosugi et al. 1986). At somewhat lower radio frequencies the poles appear darker than the quiet Sun due to a deficit of coronal material, while at mm-wavelengths the polar and non-polar quiet Sun appear quite uniform due to the similarity of the atmospheric structure at lower heights in the chromosphere. The excess brightness at the poles has also been reported in coronal holes on the disk, and so is apparently related to the phenomenon of coronal holes. The brightening likely corresponds to an elevated temperature in the upper chromosphere in coronal holes relative to normal quiet Sun. The phenomenon is especially well suited to study via radio emission due to the unique sensitivity of radio waves to this height range in the chromosphere. The possibility exists that the different chromospheric structure for coronal holes implied by the radio brightening may offer some clue to the origin of the fast solar wind, which is now well established to arise in coronal holes. Radio brightening of coronal holes is a difficult observational problem because an instrument is needed that can image large areas of the Sun at relatively high resolution. The Nobeyama Radioheliograph has the required capability and operates at 17 and 34 GHz, nicely within the frequency range where the brightening occurs. We compare Nobeyama radio synthesis images on several days in 1996 with images from the EIT, CDS, and MDI experiments on the Solar and Heliospheric Observatory (SOHO) spacecraft, and with high resolution images from the Big Bear Solar Observatory, with the aim of determining the spatial and temporal characteristics of the brightening. We compare the extent of the radio brightening with the boundaries of the coronal holes seen from

  16. Coronal Activity and Extended Solar Cycles

    NASA Astrophysics Data System (ADS)

    Altrock, R. C.

    2012-12-01

    Wilson et al. (1988, Nature 333, 748) discussed a number of solar parameters, which appear at high latitudes and gradually migrate towards the equator, merging with the sunspot "butterfly diagram". They found that this concept had been identified by earlier investigators extending back to 1957. They named this process the "Extended Solar Cycle" (ESC). Altrock (1997, Solar Phys. 170, 411) found that this process continued in Fe XIV 530.3 nm emission features. In cycles 21 - 23 solar maximum occurred when the number of Fe XIV emission regions per day > 0.19 (averaged over 365 days and both hemispheres) first reached latitudes 18°, 21° and 21°, for an average of 20° ± 1.7°. Other recent studies have shown that Torsional Oscillation (TO) negative-shear zones are co-located with the ESC from at least 50° down to the equator and also in the zones where the Rush to the Poles occur. These phenomena indicate that coronal activity occurring up to 50° and higher latitudes is related to TO shear zones, another indicator that the ESC is an important solar process. Another high-latitude process, which appears to be connected with the ESC, is the "Rush to the Poles" ("Rush") of polar crown prominences and their associated coronal emission, including Fe XIV. The Rush is is a harbinger of solar maximum (cf. Altrock, 2003, Solar Phys. 216, 343). Solar maximum in cycles 21 - 23 occurred when the center line of the Rush reached a critical latitude. These latitudes were 76°, 74° and 78°, respectively, for an average of 76° ± 2°. Applying the above conclusions to Cycle 24 is difficult due to the unusual nature of this cycle. Cycle 24 displays an intermittent "Rush" that is only well-defined in the northern hemisphere. In 2009 an initial slope of 4.6°/yr was found in the north, compared to an average of 9.4 ± 1.7 °/yr in the previous three cycles. This early fit to the Rush would have reached 76° at 2014.6. However, in 2010 the slope increased to 7.5°/yr (an increase

  17. Coronal magnetic structure at a solar sector boundary

    NASA Technical Reports Server (NTRS)

    Wilcox, J. M.; Svalgaard, L.

    1973-01-01

    The persistent large-scale coronal magnetic structure associated with a sector boundary appears to consist of a magnetic arcade loop structure extending from one solar polar region to the other in approximately the North-South direction. This structure was inferred from computer coronal magnetic field maps for days on which a stable magnetic sector boundary was near central meridian, based on an interplanetary sector boundary observed to recur during much of 1968 and 1969.

  18. Coronal and interplanetary transport of solar energetic protons and electrons

    NASA Astrophysics Data System (ADS)

    Wibberenz, G.; Kunow, H.; Iwers, B.; Kecskemety, K.; Somogyi, A.

    1989-09-01

    Data from the Helios 1 and 2 and the Prognoz 6 spacecraft are used to separate coronal and interplanetary propagation effects for two solar particle events on December 27, 1977 and January 1, 1978. The results confirm the concept of two different coronal propagation regimes. In both regimes electrons are transported more efficiently than protons. Possible explanations for the fast transport of electrons and the different behavior of electrons and protons are considered.

  19. Associations between coronal mass ejections and interplanetary shocks

    NASA Technical Reports Server (NTRS)

    Sheeley, N. R., Jr.; Howard, R. A.; Koomen, M. J.; Michels, D. J.; Schwenn, R.; Muhlhauser, K. H.; Rosenbauer, H.

    1983-01-01

    Nearly continuous complementary coronal observations and interplanetary plasma measurements for the years 1979-1982 are compared. It is shown that almost all low latitude high speed coronal mass ejections (CME's) were associated with shocks at HELIOS 1. Some suitably directed low speed CME's were clearly associated with shocks while others may have been associated with disturbed plasma (such as NCDE's) without shocks. A few opposite hemisphere CME's associated with great flares seem to be associated with shocks at HELIOS.

  20. Exploración del modelo coronal MHD de Uchida

    NASA Astrophysics Data System (ADS)

    Francile, C.; Castro, J. I.; Flores, M.

    We present an analysis of the MHD model of an isothermal solar corona with radially symmetrical magnetic field and gravity. The solution in the approximation "WKB" was presented by Uchida (1968). The model is ex- plored for different coronal conditions and heights of initial perturbation to study the propagation of coronal waves and reproduce the observed char- acteristics of phenomena such as Moreton waves. Finally we discuss the obtained results. FULL TEXT IN SPANISH

  1. Are Spicules the Primary Source of Hot Coronal Plasma?

    NASA Technical Reports Server (NTRS)

    Klimchuk, James A.

    2011-01-01

    The recent discovery of Type II spicules has generated considerable excitement. It has even been suggested that these ejections can account for a majority of the hot plasma observed in the corona, thus obviating the need for "coronal" heating. If this is the case, however, then there should be observational consequences. We have begun to examine some of these consequences and find reason to question the idea that spicules are the primary source of hot coronal plasma.

  2. Radio Coronal Magnetography of a Large Active Region

    NASA Astrophysics Data System (ADS)

    Bastian, Timothy S.; Gary, Dale E.; White, Stephen; Fleishman, Gregory; Chen, Bin

    2015-04-01

    Quantitative knowledge of coronal magnetic fields is fundamental to understanding energetic phenomena such as solar flares. Flares occur in solar active regions where strong, non-potential magnetic fields provide free energy. While constraints on the coronal magnetic field topology are readily available through high resolution SXR and EUV imaging of solar active regions, useful quantitative measurements of coronal magnetic fields have thus far been elusive. Recent progress has been made at infrared (IR) wavelengths in exploiting both the Zeeman and Hanle effects to infer the line-of-sight magnetic field strength or the orientation of the magnetic field vector in the plane of the sky above the solar limb. However, no measurements of coronal magnetic fields against the solar disk are possible using IR observations. Radio observations of gyroresonance emission from active regions offer the means of measuring coronal magnetic fields above the limb and on the solar disk. In particular, for plasma plasma conditions in the solar corona, active regions typically become optically thick to emission over a range of radio frequencies through gyroresonance absorption at a low harmonic of the electron gyrofrequency. The specific range of resonant frequencies depends on the range of coronal magnetic field strengths present in the active region.The Karl G. Jansky Very Large Array was used in November 2014 to image NOAA/USAF active region AR12209 over a continuous frequency range of 1-8 GHz, corresponding to a wavelength range of 3.75-30 cm. This frequency range is sensitive to coronal magnetic field strengths ranging from ~120-1400G. The active region was observed on four different dates - November 18, 20, 22, and 24 - during which the active region longitude ranged from -15 to +70 degrees, providing a wide range of aspect angles. In this paper we provide a preliminary description of the coronal magnetic field measurements derived from the radio observations.

  3. The Multithermal and Multi-stranded Nature of Coronal Rain

    NASA Astrophysics Data System (ADS)

    Antolin, P.; Vissers, G.; Pereira, T. M. D.; Rouppe van der Voort, L.; Scullion, E.

    2015-06-01

    We analyze coordinated observations of coronal rain in loops, spanning chromospheric, transition region (TR), and coronal temperatures with sub-arcsecond spatial resolution. Coronal rain is found to be a highly multithermal phenomenon with a high degree of co-spatiality in the multi-wavelength emission. EUV darkening and quasi-periodic intensity variations are found to be strongly correlated with coronal rain showers. Progressive cooling of coronal rain is observed, leading to a height dependence of the emission. A fast-slow two-step catastrophic cooling progression is found, which may reflect the transition to optically thick plasma states. The intermittent and clumpy appearance of coronal rain at coronal heights becomes more continuous and persistent at chromospheric heights just before impact, mainly due to a funnel effect from the observed expansion of the magnetic field. Strong density inhomogeneities of 0\\buildrel{\\prime\\prime}\\over{.} 2-0\\buildrel{\\prime\\prime}\\over{.} 5 are found, in which a transition from temperatures of 105 to 104 K occurs. The 0\\buildrel{\\prime\\prime}\\over{.} 2-0\\buildrel{\\prime\\prime}\\over{.} 8 width of the distribution of coronal rain is found to be independent of temperature. The sharp increase in the number of clumps at the coolest temperatures, especially at higher resolution, suggests that the bulk distribution of the rain remains undetected. Rain clumps appear organized in strands in both chromospheric and TR temperatures. We further find structure reminiscent of the magnetohydrodynamic (MHD) thermal mode (also known as entropy mode), thereby suggesting an important role of thermal instability in shaping the basic loop substructure. Rain core densities are estimated to vary between 2 × 1010 and 2.5× {{10}11} cm-3, leading to significant downward mass fluxes per loop of 1-5 × 109 g s-1, thus suggesting a major role in the chromosphere-corona mass cycle.

  4. Coronal propagation of flare associated electrons and protons

    NASA Technical Reports Server (NTRS)

    Schellert, G.; Wibberenz, G.; Kunow, H.

    1985-01-01

    A statistical study of characteristic times and intensities of 36 solar particle events observed between 1977 and 1979 by the Kiel Cosmic Ray Experiment on board HELIOS-1 and -2 has been carried out. For approx. 0.5 MeV electrons we order the times of maximum and the absolute intensities with respect to angular distance from the parent flare. Discussion of coronal parameters in terms of Reid's model leads to typical time constants for coronal diffusion and escape.

  5. Coroner consistency - The 10-jurisdiction, 10-year, postcode lottery?

    PubMed

    Mclean, Maxwell

    2015-04-01

    The investigation and classification of deaths in England and Wales relies upon the application by medical practitioners of diverse reporting standards set locally by coroners and thereafter upon the effectively unconstrained decision process of those same coroners. The author has conducted extensive comparative analysis of Ministry of Justice data on reports to the coroner and their inquest and verdict returns alongside Office of National Statistics data pertaining to the numbers of registered deaths in equivalent local jurisdictions. Here, he analyses 10 jurisdictions characterised by almost identical inquest return numbers in 2011. Substantial variation was found in reporting rates to the coroner and in the profile of inquest verdicts. The range of deaths reported varied from 34% to 62% of all registered deaths. Likewise only 2 of the 10 jurisdictions shared the same ranking of proportions in which the six common verdicts were reached. Individual jurisdictions tended to be consistent over time in their use of verdicts. In all cases, proportionately more male deaths were reported to the coroner. Coroners generally seemed prima facie to be 'gendered' in their approach to verdicts; that is, they were consistently more likely to favour a particular verdict when dealing with a death, according to the sex of the deceased. The extent to which coroners seemed gendered varied widely. While similar services such as the criminal courts or the Crown Prosecution Service are subject to extensive national guidance in an attempt to constrain idiosyncratic decision making, there seems no reason why this should apply less to the process of death investigation and classification. Further analysis of coroners' local practices and their determinants seems necessary. PMID:24644227

  6. Coronal Dynamics at Recent Total Solar Eclipses

    NASA Astrophysics Data System (ADS)

    Pasachoff, J. M.; Lu, M.; Davis, A. B.; Demianski, M.; Rusin, V.; Saniga, M.; Seaton, D. B.; Lucas, R.; Babcock, B. A.; Dantowitz, R.; Gaintatzis, P.; Seeger, C. H.; Malamut, C.; Steele, A.

    2014-12-01

    Our composite images of the solar corona based on extensive imaging at the total solar eclipses of 2010 (Easter Island), 2012 (Australia), and 2013 (Gabon) reveal several coronal mass ejections and other changes in coronal streamers and in polar plumes. Our resultant spatial resolution is finer than that available in imaging from spacecraft, including that from SOHO/LASCO or STEREO. We trace the eruptions back to their footpoints on the sun using imaging from SDO and SWAP, and follow them upwards through the corona, measuring velocities. The high-resolution computer compositing by Miloslav Druckmüller and Hana Druckmüllerová (2010 and 2013) and Pavlos Gaintatzis (2012) allows comparison of our images with those taken at intervals of minutes or hours along the totality path. Williams College's 2013 eclipse expedition was supported in part by grant 9327-13 from National Geographic Society/Committee for Research and Exploration. Our work on the 2012 eclipse is supported in part by grant AGS-1047726 from Solar Terrestrial Research/NSF AGS. V.R. and M.S. were partially supported by the VEGA grant agency project 2/0098/10 and 2/0003/13 (Slovak Academy of Sciences) and Grant 0139-12 from NG/CRE, and Hana Druckmüllerová by grant 205/09/1469 of the Czech Science Foundation. M.L. was supported by Sigma Xi. C.M. was a Keck Northeast Astronomy Consortium Summer Fellow, supported at Williams College by REU/NSF grant AST-1005024. Partial support was provided by U.S. Department of Defense's ASSURE program. J.M.P. thanks Caltech's Planetary Sciences Department for hospitality. Support for D.B.S. and SWAP came from PRODEX grant C90345 managed by ESA in collaboration with the Belgian Federal Science Policy Office (BELSPO) in support of the PROBA2/SWAP mission, and from the EC's Seventh Framework Programme (FP7/2007-2013) under grant 218816 (SOTERIA project, www.soteria-space.eu). SWAP is a project of the Centre Spatial de Liège and the Royal Observatory of Belgium funded by

  7. TRANSVERSE OSCILLATIONS OF A COOLING CORONAL LOOP

    SciTech Connect

    Morton, R. J.; Erdelyi, R. E-mail: Robertus@sheffield.ac.u

    2009-12-10

    Here we present an investigation into how cooling of the plasma influences the oscillation properties (e.g., eigenfunctions and eigenfrequencies) of transverse (i.e., kink) magnetohydrodynamic (MHD) waves in a compressible magnetic flux tube embedded in a gravitationally stratified and uniformly magnetized atmosphere. The cooling is introduced via a temperature-dependent density profile. A time-dependent governing equation is derived and an approximate zeroth-order solution is then obtained. From this the influence of cooling on the behavior of the eigenfrequencies and eigenfunctions of the transverse MHD waves is determined for representative cooling timescales. It is shown analytically, as the loop cools, how the amplitude of the perturbations is found to decrease as time increases. For cooling timescales of 900-2000 s (as observed in typical EUV loops), it is shown that the cooling has important and relevant influence on the damping times of loop oscillations. Next, the theory is put to the test. The damping due to cooling is fitted to a representative observation of standing kink oscillation of EUV loops. It is also shown with an explicit approximate analytical form, how the period of the fundamental and first harmonic of the kink mode changes with time as the loop cools. A consequence of this is that the value of the period ratio P {sub 1}/P {sub 2}, a tool that is popular in magneto-seismological studies in coronal diagnostics, decreases from the value of a uniform loop, 2, as the temperature decreases. The rate of change in P {sub 1}/P {sub 2} is dependent upon the cooling timescale and is well within the observable range for typical EUV loops. Further to this, the magnitude of the anti-node shift of the eigenfunctions of the first harmonic is shown to continually increase as the loop cools, giving additional impetus to the use of spatial magneto-seismology of the solar atmosphere. Finally, we suggest that measurements of the rate of change in the

  8. TRANSVERSE OSCILLATIONS OF A LONGITUDINALLY STRATIFIED CORONAL LOOP SYSTEM

    SciTech Connect

    Fathalian, N.; Safari, H. E-mail: safari@znu.ac.i

    2010-11-20

    Collective transverse coronal loop oscillations seem to be detected in observational studies. In this regard, Luna et al. modeled the collective kink-like normal modes of several cylindrical loop systems using the T-matrix theory. This paper investigates the effects of longitudinal density stratification along the loop axis on the collective kink-like modes of the system of coronal loops. The coronal loop system is modeled as cylinders of parallel flux tubes, with two ends of each loop at the dense photosphere. The flux tubes are considered as uniform magnetic fields, with stratified density along the loop axis which changes discontinuously at the lateral surface of each cylinder. The MHD equations are reduced to solve a set of two coupled dispersion relations for frequencies and wavenumbers, in the presence of a stratification parameter. The fundamental and first overtone frequencies and longitudinal wavenumbers are computed. The previous results are verified for an unstratified coronal loop system. Finally, we conclude that an increased longitudinal density stratification parameter will result in an increase of the frequencies. The frequency ratios, first overtones to fundamentals, are very sensitive functions of the density scale height parameter. Therefore, stratification should be included in dynamics of coronal loop systems. For unstratified coronal loop systems, these ratios are the same as monoloop ones.

  9. Differences in Plasma Conditions Among 85 Large Coronal Holes

    NASA Astrophysics Data System (ADS)

    Miralles, M. P.; Cranmer, S. R.; Kohl, J. L.

    2004-05-01

    We have measured ultraviolet spectroscopic parameters as a function of heliocentric distance for more than 85 coronal holes, in order to characterize the physical properties of coronal holes at different phases of the solar cycle. The Ultraviolet Coronagraph Spectrometer (UVCS) aboard SOHO was used to observed O VI (103.2 and 103.7 nm) and H I Lyman alpha (121.6 nm) emission lines to determine kinetic temperatures, average densities, and outflow speeds in coronal holes. UVCS observations provide unique information on the heating and acceleration processes in the corona. Our previous analyses of UVCS observations have shown that solar minimum (polar) and solar maximum (equatorial) coronal holes produce different acceleration profiles and have different oxygen kinetic temperatures. We also examine the differences in the characteristics of representative coronal holes producing a variety of high-speed conditions (550-800 km/s) at 1 AU. These analyses provide limits on the coronal plasma properties and put constraints on the physical processes that are responsible for the heating of the extended corona and the acceleration of the solar wind. This work is supported by NASA under Grant NAG5-12865 to the Smithsonian Astrophysical Observatory, by the Italian Space Agency and by PRODEX (Swiss contribution).

  10. Coronal Magnetism: Hanle Effect in UV and IR Spectral Lines

    NASA Astrophysics Data System (ADS)

    Raouafi, N. E.; Riley, P.

    2014-12-01

    The plasma thermodynamics in the solar upper atmosphere, particularly in the corona, are dominated by the magnetic field, which controls the flow and dissipation of energy. The relative lack of knowledge of the coronal vector magnetic field is a major handicap for the progress in coronal physics. This makes the development of measurement methods of coronal magnetic fields a high priority in solar physics. The Hanle effect in the UV and IR spectral lines is a largely unexplored diagnostic. Here we use magnetohydrodynamic (MHD) simulations to study the magnitude of the signal to be expected for typical coronal magnetic fields for selected spectral lines in the UV and IR wavelength ranges, namely the H I Lyman series (i.e., α, β, and γ), O VI 103.2 nm line, and the He I 1083 nm line. We show that the selected lines may be useful for the diagnostic of coronal magnetic fields. We also show that the combination of polarization measurements of spectral lines with different sensitivities to the Hanle effect may be most appropriate for the interpretation of the data. We propose that UV coronal magnetic field mapper should be a central part of the science payload of any future spacebased solar observatory.

  11. The Coronal Abundances of Mid-F Dwarfs

    NASA Astrophysics Data System (ADS)

    Wood, Brian E.; Laming, J. Martin

    2013-05-01

    A Chandra spectrum of the moderately active nearby F6 V star π3 Ori is used to study the coronal properties of mid-F dwarfs. We find that π3 Ori's coronal emission measure distribution is very similar to those of moderately active G and K dwarfs, with an emission measure peak near log T = 6.6 seeming to be ubiquitous for such stars. In contrast to coronal temperature, coronal abundances are known to depend on spectral type for main sequence stars. Based on this previously known relation, we expected π3 Ori's corona to exhibit an extremely strong "first ionization potential (FIP) effect," a phenomenon first identified on the Sun where elements with low FIP are enhanced in the corona. We instead find that π3 Ori's corona exhibits a FIP effect essentially identical to that of the Sun and other early G dwarfs, perhaps indicating that the increase in FIP bias toward earlier spectral types stops or at least slows for F stars. We find that π3 Ori's coronal characteristics are significantly different from two previously studied mid-F stars, Procyon (F5 IV-V) and τ Boo (F7 V). We believe π3 Ori is more representative of the coronal characteristics of mid-F dwarfs, with Procyon being different because of luminosity class, and τ Boo being different because of the effects of one of two close companions, one stellar (τ Boo B: M2 V) and one planetary.

  12. Evidence linking coronal mass ejections with interplanetary magnetic clouds

    NASA Technical Reports Server (NTRS)

    Wilson, R. M.; Hildner, E.

    1983-01-01

    Using proxy data for the occurrence of those mass ejections from the solar corona which are directed earthward, we investigate the association between the post-1970 interplanetary magnetic clouds of Klein and Burlaga and coronal mass ejections. The evidence linking magnetic clouds following shocks with coronal mass ejections is striking; six of nine clouds observed at Earth were preceded an appropriate time earlier by meter-wave type II radio bursts indicative of coronal shock waves and coronal mass ejections occurring near central meridian. During the selected periods when no clouds were detected near Earth, the only type II bursts reported were associated with solar activity near the limbs. Where the proxy solar data to be sought are not so clearly suggested, that is, for clouds preceding interaction regions and clouds within cold magnetic enhancements, the evidence linking the clouds and coronal mass ejections is not as clear; proxy data usually suggest many candidate mass-ejection events for each cloud. Overall, the data are consistent with and support the hypothesis suggested by Klein and Burlaga that magnetic clouds observed with spacecraft at 1 AU are manifestations of solar coronal mass ejection transients.

  13. Are chromospheric nanoflares a primary source of coronal plasma?

    SciTech Connect

    Klimchuk, J. A.; Bradshaw, S. J. E-mail: stephen.bradshaw@rice.edu

    2014-08-10

    It has been suggested that the hot plasma of the solar corona comes primarily from impulsive heating events, or nanoflares, that occur in the lower atmosphere, either in the upper part of the ordinary chromosphere or at the tips of type II spicules. We test this idea with a series of hydrodynamic simulations. We find that synthetic Fe XII (195) and Fe XIV (274) line profiles generated from the simulations disagree dramatically with actual observations. The integrated line intensities are much too faint; the blueshifts are much too fast; the blue-red asymmetries are much too large; and the emission is confined to low altitudes. We conclude that chromospheric nanoflares are not a primary source of hot coronal plasma. Such events may play an important role in producing the chromosphere and powering its intense radiation, but they do not, in general, raise the temperature of the plasma to coronal values. Those cases where coronal temperatures are reached must be relatively uncommon. The observed profiles of Fe XII and Fe XIV come primarily from plasma that is heated in the corona itself, either by coronal nanoflares or a quasi-steady coronal heating process. Chromospheric nanoflares might play a role in generating waves that provide this coronal heating.

  14. Coronal seismology of flare-excited longitudinal slow magnetoacoustic waves in hot coronal loops

    NASA Astrophysics Data System (ADS)

    Wang, T.; Ofman, L.; Sun, X.; Provornikova, E. A.; Davila, J. M.

    2015-12-01

    The flare-excited longitudinal intensity oscillations in hot flaring loops have been recently detected by SDO/AIA in 94 and 131 bandpasses. These oscillations show similar physical properties (such as period, decay time, and trigger) as those slow-mode standing waves previously detected by the SOHO/SUMER spectrometer in Doppler shift of flare lines formed above 6 MK. The multi-wavelength AIA observations with high spatio-temporal resolution and wide temperature coverage enable us to measure both thermal and wave properties of the oscillating hot plasma with unprecedented accuracy. These new measurements can be used to diagnose the complicated energy transport processes in flare plasma by a technique called coronal seismology based on the combination of observations and MHD wave theory. From a detailed case study we have found evidence for thermal conduction suppression in hot loops by measuring the polytropic index and analyzing the phase relationship between the temperature and density wave signals. This result is not only crucial for better understanding the wave dissipation mechanism but also provides an alternative mechanism to explain the puzzles of long-duration events and X-ray loop-top sources which show much slower cooling than expected by the classical Spitzer conductive cooling. This finding may also shed a light on the coronal heating problem because weak thermal conductivity implies slower cooling of hot plasma in nanoflares, so increasing the average coronal temperature for the same heating rate. We will discuss the effects of thermal conduction suppression on the wave damping and loop cooling based on MHD simulations.

  15. Understanding Coronal Heating with Emission Measure Distributions

    NASA Technical Reports Server (NTRS)

    Klimchik, James A.; Tripathi, Durgesh; Bradshaw, Stephen J.; Mason, Helen E.

    2011-01-01

    It is widely believed that the cross-field spatial scale of coronal heating is small, so that the fundamental plasma structures (loop strands) are spatially unresolved. We therefore must appeal to diagnostic techniques that are not strongly affected by spatial averaging. One valuable observable is the emission measure distribution, EM(T), which indicates how much material is present at each temperature. Using data from the Extreme-ultraviolet Imaging Spectrograph on the Hinode mission, we have determined emission measure distributions in the cores of two active regions. The distributions have power law slopes of approximately 2.4 coolward of the peak. We compare these slopes, as well as the amount of emission measure at very high temperature, with the predictions of a series of models. The models assume impulsive heating (nanoflares) in unresolved strands and take full account of non equilibrium ionization. A variety of nanoflare properties and initial conditions are considered. We also comment on the selection of spectral lines for upcoming missions like Solar Orbiter.

  16. A CATALOG OF CORONAL 'EIT WAVE' TRANSIENTS

    SciTech Connect

    Thompson, B. J.; Myers, D. C.

    2009-08-01

    Solar and Heliospheric Observatory (SOHO) Extreme ultraviolet Imaging Telescope (EIT) data have been visually searched for coronal 'EIT wave' transients over the period beginning from 1997 March 24 and extending through 1998 June 24. The dates covered start at the beginning of regular high-cadence (more than 1 image every 20 minutes) observations, ending at the four-month interruption of SOHO observations in mid-1998. One hundred and seventy six events are included in this catalog. The observations range from 'candidate' events, which were either weak or had insufficient data coverage, to events which were well defined and were clearly distinguishable in the data. Included in the catalog are times of the EIT images in which the events are observed, diagrams indicating the observed locations of the wave fronts and associated active regions, and the speeds of the wave fronts. The measured speeds of the wave fronts varied from less than 50 to over 700 km s{sup -1} with 'typical' speeds of 200-400 km s{sup -1}.

  17. Potential Method of Predicting Coronal Mass Ejection

    NASA Astrophysics Data System (ADS)

    Imholt, Timothy

    2001-10-01

    Coronal Mass Ejections (CME) may be described as a blast of gas and highly charged solar mass fragments ejected into space. These ejections, when directed toward Earth, have many different effects on terrestrial systems ranging from the Aurora Borealis to changes in wireless communication. The early prediction of these solar events cannot be overlooked. There are several models currently accepted and utilized to predict these events, however, with earlier prediction of both the event and the location on the sun where the event occurs allows us to have earlier warnings as to when they will affect man-made systems. A better prediction could perhaps be achieved by utilizing low angular resolution radio telescope arrays to catalog data from the sun at different radio frequencies on a regular basis. Once this data is cataloged a better predictor for these CME’s could be found. We propose a model that allows a prediction to be made that appears to be longer than 24 hours.

  18. Potential Method of Predicting Coronal Mass Ejection

    NASA Astrophysics Data System (ADS)

    Imholt, Timothy; Roberts, J. A.; Scott, J. B.; University Of North Texas Team

    2000-10-01

    Coronal Mass Ejections (CME) may be described as a blast of gas and highly charged solar mass fragments ejected into space. These ejections, when directed toward Earth, have many different effects on terrestrial systems ranging from the Aurora Borealis to changes in wireless communications. The importance of an early prediction of these solar events cannot be overlooked. There are several models currently accepted and utilized to predict these events, however, with earlier prediction of both the event and the location on the sun where the event occur allows us to have earlier warnings as to when they will effect man-made systems. A better prediction could perhaps be achieved by utilizing low angular resolution radio telescope arrays to catalog data from the sun at different radio frequencies on a regular basis. Once this data is cataloged a better predictor for these CME's could be found. We propose a model that allows a prediction to be made that appears to be longer than 24 hours.

  19. Multithermal Analysis of EIS Coronal Loops

    NASA Astrophysics Data System (ADS)

    Worley, Brian T.; Schmelz, J. T.; Pathak, S.

    2012-05-01

    Four separate active regions containing multiple coronal loops were selected for Differential Emission Measure (DEM) analysis from Hinode Extreme ultraviolet Imaging Spectrometer (EIS) data. Each loop was chosen based on its location and our ability to find a clean nearby area for background subtraction. Our analysis uses iron lines with ionization stages from Fe VIII to Fe XVI in the wavelength ranges 170 - 210 and 250 - 290 A. The twelve selected loops were then analyzed to determine if their cross-field temperature was isothermal or multithermal. This was accomplished by averaging the intensities of ten individual pixels along the length of each loop and subtracting the average intensity of ten nearby background pixels. We then used these background-subtracted values, the density from a density-sensitive line ratio, and the atomic data from the CHIANTI database to create a DEM curve for each loop. Solar physics research at the University of Memphis is supported by NSF ATM-0402729 as well as a Hinode subcontract from NASA/SAO.

  20. Streamer Waves Driven by Coronal Mass Ejections

    NASA Astrophysics Data System (ADS)

    Chen, Yao; Song, Hong-Qiang; Li, Bo; Xia, Li-Dong; Wu, Zhao; Fu, Hui

    Between July 5th and July 7th 2004, two intriguing fast coronal mass ejection(CME)-streamer interaction events were recorded by the Large Angle and Spectrometric Coronagraph (LASCO). At the beginning of the events, the streamer was pushed aside from their equilibrium position upon the impact of the rapidly outgoing and expanding ejecta; then, the streamer structure, mainly the bright streamer belt, exhibited elegant large scale sinusoidal wavelike motions. The motions were apparently driven by the restoring magnetic forces resulting from the CME impingement, suggestive of magnetohydrodynamic kink mode propagating outwards along the plasma sheet of the streamer. The mode is supported collectively by the streamer structure and is therefore named "streamer wave" in the present study. With the whitelight coronagraph data, we show that the streamer wave has a period of about 1 hour, a wavelength varying from 2 to 4 solar radii, an amplitude of about a few tens of solar radii, and a propagating phase speed in the range 300 to 500 km/s. We also find that there is a tendency for the phase speed to decline with increasing heliocentric distance. These observations provide good examples of large scale wave phenomena carried by corona structures, and have significance in developing seismological techniques for diagnosing plasma and magnetic parameters in the outer corona.

  1. L-alpha intensity in coronal streamers

    NASA Technical Reports Server (NTRS)

    Noci, G.; Poletto, G.; Suess, S. T.; Wang, A.-H.; Wu, S. T.

    1993-01-01

    White-light images are presently the primary source of information on physical conditions in the solar corona at distances greater than a few tenths of a solar radius above the limb. As a consequence, we still only have an incomplete description of structures extending beyond the solar limb. In particular, streamers, although observed for decades, represent a poorly known phenomenon. SOHO, to be launched in 1995, will be able to make long-term observations of these features up to heights of a few solar radii, both in white light and UV. In this paper we present simulations of L-alpha intensity in coronal streamers, based on the two-dimensional (2D) model developed by Wang et at. (1992, 1993) via a time-dependent numerical relaxation approach. Because the model is 2D, we make an a priori hypothesis about the extension of streamers in the third dimension. L-alpha data, obtained from a rocket (Kohl et al., 1983), allowed us to identify a shape which fits the observations.

  2. Coronal Mass Ejections and Solar Radio Emissions

    NASA Technical Reports Server (NTRS)

    Gopalswamy, Nat

    2010-01-01

    Coronal mass ejections (CMEs) have important connections to various types of radio emissions from the Sun. The persistent noise storm radiation (type I storm at metric wavelengths, type III storms at longer wavelengths) can be clearly interrupted by the occurrence of a CME in the active region that produces the storm. Sometimes the noise storm completely disappears and other times, it reappears in the active region. Long-lasting type III bursts are associated with CME eruption, thought to be due to the reconnection process taking place beneath the erupting CME. Type II bursts are indicative of electron acceleration in the CME-driven shocks and hence considered to be the direct response of the CME propagation in the corona and interplanetary medium. Finally type IV bursts indicate large-scale post-eruption arcades containing trapped electrons that produce radio emission. This paper summarizes some key results that connect CMEs to various types of radio emission and what we can learn about particle acceleration in the corona) and interplanetary medium. Particular emphasis will be placed on type If bursts because of their connection to interplanetary shocks detected in situ.

  3. Multiscale Modeling of Solar Coronal Magnetic Reconnection

    NASA Technical Reports Server (NTRS)

    Antiochos, Spiro K.; Karpen, Judith T.; DeVore, C. Richard

    2010-01-01

    Magnetic reconnection is widely believed to be the primary process by which the magnetic field releases energy to plasma in the Sun's corona. For example, in the breakout model for the initiation of coronal mass ejections/eruptive flares, reconnection is responsible for the catastrophic destabilizing of magnetic force balance in the corona, leading to explosive energy release. A critical requirement for the reconnection is that it have a "switch-on' nature in that the reconnection stays off until a large store of magnetic free energy has built up, and then it turn on abruptly and stay on until most of this free energy has been released. We discuss the implications of this requirement for reconnection in the context of the breakout model for CMEs/flares. We argue that it imposes stringent constraints on the properties of the flux breaking mechanism, which is expected to operate in the corona on kinetic scales. We present numerical simulations demonstrating how the reconnection and the eruption depend on the effective resistivity, i.e., the effective Lundquist number, and propose a model for incorporating kinetic flux-breaking mechanisms into MHO calculation of CMEs/flares.

  4. Geometric Model of a Coronal Cavity

    NASA Technical Reports Server (NTRS)

    Kucera, Therese A.; Gibson, S. E.; Ratawicki, D.; Dove, J.; deToma, G.; Hao, J.; Hudson, H. S.; Marque, C.; McIntosh, P. S.; Reeves, K. K.; Schmidt, D. J.; Sterling, A. C.; Tripathi, D. K.; Williams, D. R.; Zhang, M.

    2010-01-01

    We observed a coronal cavity from August 8-18 2007 during a multi-instrument observing campaign organized under the auspices of the International Heliophysical Year (IHY). Here we present initial efforts to model the cavity with a geometrical streamer-cavity model. The model is based the white-light streamer mode] of Gibson et a]. (2003 ), which has been enhanced by the addition of a cavity and the capability to model EUV and X-ray emission. The cavity is modeled with an elliptical cross-section and Gaussian fall-off in length and width inside the streamer. Density and temperature can be varied in the streamer and cavity and constrained via comparison with data. Although this model is purely morphological, it allows for three-dimensional, multi-temperature analysis and characterization of the data, which can then provide constraints for future physical modeling. Initial comparisons to STEREO/EUVI images of the cavity and streamer show that the model can provide a good fit to the data. This work is part of the effort of the International Space Science Institute International Team on Prominence Cavities

  5. The solar probe and coronal dynamics

    NASA Technical Reports Server (NTRS)

    Belcher, J.; Heinemann, M.; Goodrich, C.

    1978-01-01

    The discovery of coronal holes led to basic changes in ideas about the structure of the low corona and its expansion into the solar wind. The nature of the energy flux is not understood. Current ideas include enhanced thermal conductivities, extended MHD wave heating, and wave momentum transfer, all in rapidly diverging geometries. There is little feel for the relative importance of these processes. The Solar Probe, with its penetration deep into the solar corona, could lead to observational constraints on their relative importance, and thus to an understanding of the origin of the solar wind. Observations from the Solar Probe will also bear on such questions as to whether small scale "intrastream" structure is common close to the Sun in open field-line regions, whether the properties of the wind are pronouncedly different over closed and open field-line regions at five solar radii, and many others. The resolution of these questions requires measurements of the magnetic field and of the proton and electron distribution functions.

  6. Surface Flux Emergence and Coronal Eruption

    NASA Astrophysics Data System (ADS)

    Fang, Fang

    2016-05-01

    Among various active regions, delta-sunspots of aggregated spots of opposite polarities, are of particular interest due to their high productivity in energetic and recurrent eruptive events, such as X-class flares and homologous eruptions. We here study the formation of such complex magnetic structures by numerical simulations of magnetic flux emergence from the convection zone into the corona in an active-region scale domain. In our simulation, two pairs of bipolar sunspots form on the surface, originating from two buoyant segments of a single subsurface twisted flux rope. Expansion and rotation of the emerging fields in the two bipoles drive the two opposite polarities into each other with apparent rotating motion, producing a compact delta-sunspot with a sharp polarity inversion line (PIL). The formation of the delta-sunspot in such a realistic-scale domain produces emerging patterns similar to those formed in observations, e.g. the inverted polarity against Hale’s law, the curvilinear motion of the spot, strong transverse field with highly sheared magnetic and velocity fields at the PIL. Strong current builds up at the PIL, giving rise to reconnection, which produces a complex coronal magnetic connectivity with non-potential fields in the delta-spot overlaid by more relaxed fields connecting the two polarities at the two ends.

  7. Coronal Neutrino Emission in Hypercritical Accretion Flows

    NASA Astrophysics Data System (ADS)

    Kawabata, R.; Mineshige, S.; Kawanaka, N.

    2008-03-01

    Hypercritical accretion flows onto stellar mass black holes (BHs) are commonly believed to be as a promising model of central engines of gamma-ray bursts (GRBs). In this model a certain fraction of the gravitational binding energy of accreting matter is deposited to the energy of relativistic jets via neutrino annihilation and/or magnetic fields. However, some recent studies have indicated that the energy deposition rate by neutrino annihilation is somewhat smaller than that needed to power a GRB. To overcome this difficulty, Ramirez-Ruiz and Socrates proposed that high-energy neutrinos from the hot corona above the accretion disk might enhance the efficiency of the energy deposition. We elucidate the disk corona model in the context of hypercritical accretion flows. From the energy balance in the disk and the corona, we can calculate the disk and coronal temperature, Td and Tc, and neutrino spectra, taking into account the neutrino cooling processes by neutrino-electron scatterings and neutrino pair productions. The calculated neutrino spectra consist of two peaks: one by the neutrino emission from the disk and the other by that from the corona. We find that the disk corona can enhance the efficiency of energy release but only by a factor of 1.5 or so, unless the height of the corona is very small, Hll r. This is because the neutrino emission is very sensitive to the temperature of the emitting region, and then the ratio Tc/Td cannot be very large.

  8. Coronal Jets in Closed Magnetic Regions on the Sun

    NASA Astrophysics Data System (ADS)

    Wyper, Peter Fraser; DeVore, C. R.

    2015-04-01

    Coronal jets are dynamic, collimated structures observed in solar EUV and X-ray emission. They appear predominantly in the open field of coronal holes, but are also observed in areas of closed field, especially active regions. A common feature of coronal jets is that they originate from the field above a parasitic polarity of opposite sign to the surrounding field. Some process - such as instability onset or flux emergence - induces explosive reconnection between the closed “anemone” field and the surrounding open field that generates the jet. The lesser number of coronal jets in closed-field regions suggests a possible stabilizing effect of the closed configuration with respect to coronal jet formation. If the scale of the jet region is small compared with the background loop length, as in for example type II spicules, the nearby magnetic field may be treated as locally open. As such, one would expect that if a stabilizing effect exists it becomes most apparent as the scale of the anemone region approaches that of the background coronal loops.To investigate if coronal jets are indeed suppressed along shorter coronal loops, we performed a number of simulations of jets driven by a rotation of the parasitic polarity (as in the previous open-jet calculations by Pariat et. al 2009, 2010, 2015) embedded in a large-scale closed bipolar field. The simulations were performed with the state of the art Adaptively Refined Magnetohydrodynamics Solver. We will report here how the magnetic configuration above the anemone region determines the nature of the jet, when it is triggered, and how much of the stored magnetic energy is released. We show that regions in which the background field and the parasitic polarity region are of comparable scale naturally suppress explosive energy release. We will also show how in the post-jet relaxation phase a combination of confined MHD waves and weak current layers are generated by the jet along the background coronal loops, both of which

  9. Coronal Heating and the Magnetic Flux Content of the Network

    NASA Technical Reports Server (NTRS)

    Falconer, D. A.; Moore, R. L.; Porter, J. G.; Hathaway, D. H.; Whitaker, Ann F. (Technical Monitor)

    2001-01-01

    Previously, from analysis of SOHO/EIT coronal images in combination with Kitt Peak magnetograms (Falconer et al 1998, ApJ, 501, 386-396), we found that the quiet corona is the sum of two components: the e-scale corona and the coronal network. The large-scale corona consists of all coronal-temperature (T approx. 10(exp 6) K) structures larger than supergranules (>approx.30,000 km). The coronal network (1) consists of all coronal-temperature structures smaller than supergranules, (2) is rooted in and loosely traces the photospheric magnetic network, (3) has its brightest features seated on polarity dividing fines (neutral lines) in the network magnetic flux, and (4) produces only about 5% of the total coronal emission in quiet regions. The heating of the coronal network is apparently magnetic in origin. Here, from analysis of EIT coronal images of quiet regions in combination with magnetograms of the same quiet regions from SOHO/MDI and from Kitt Peak, we examine the other 95% of the quiet corona and its relation to the underlying magnetic network. We find: (1) Dividing the large-scale corona into its bright and dim halves divides the area into bright "continents" and dark "oceans" having spans of 2-4 supergranules. (2) These patterns are also present in the photospheric magnetograms: the network is stronger under the bright half and weaker under the dim half. (3) The radiation from the large-scale corona increases roughly as the cube root of the magnetic flux content of the underlying magnetic network. In contrast, Fisher et A (1998, ApJ, 508, 985-998) found that the coronal radiation from an active region increases roughly linearly with the magnetic flux content of the active region. We assume, as is widely held, that nearly all of the large-scale corona is magnetically rooted in the network. Our results, together with the result of Fisher et al (1999), suggest that either the coronal heating in quiet regions has a large non-magnetic component, or, if the heating

  10. ORIGIN OF CORONAL SHOCK WAVES ASSOCIATED WITH SLOW CORONAL MASS EJECTIONS

    SciTech Connect

    Magdalenic, J.; Marque, C.; Zhukov, A. N.; Vrsnak, B.; Zic, T.

    2010-07-20

    We present a multiwavelength study of five coronal mass ejection/flare events (CME/flare) and associated coronal shock waves manifested as type II radio bursts. The study is focused on the events in which the flare energy release, and not the associated CME, is the most probable source of the shock wave. Therefore, we selected events associated with rather slow CMEs (reported mean velocity below 500 km s{sup -1}). To ensure minimal projection effects, only events related to flares situated close to the solar limb were included in the study. We used radio dynamic spectra, positions of radio sources observed by the Nancay Radioheliograph, GOES soft X-ray flux measurements, Large Angle Spectroscopic Coronagraph, and Extreme-ultraviolet Imaging Telescope observations. The kinematics of the shock wave signatures, type II radio bursts, were analyzed and compared with the flare evolution and the CME kinematics. We found that the velocities of the shock waves were significantly higher, up to one order of magnitude, than the contemporaneous CME velocities. On the other hand, shock waves were closely temporally associated with the flare energy release that was very impulsive in all events. This suggests that the impulsive increase of the pressure in the flare was the source of the shock wave. In four events the shock wave was most probably flare-generated, and in one event results were inconclusive due to a very close temporal synchronization of the CME, flare, and shock.

  11. Coronal evolution during the sunspot cycle: Coronal holes observed with the Mauna Loa K-coronameters

    SciTech Connect

    Hundhausen, A.J.; Hansen, R.T.; Hansen, S.F.

    1981-04-01

    The white-light corona was observed regularly at the Mauna Loa Observatory during the years 1965--1967 and 1969--1978. Display of the measured polarization brightness in the form of synoptic maps permits the identification of large coronal holes and the study of their slow evolution during the sunspot cycle. The polar coronal holes were clearly seen to shrink in size during the ascending phase of cycle 20 (1965--1967), to be absent during a two-year period (1969--1970) just after sunspot maximum, to reappear near the end of 1970, and to remain as prominent features of the corona for the years 1971--1978. During the sunspot maximum epoch the corona was dominated by 'mid-latitude' holes, elongated in the direction parallel to the solar equator. Large equatorial holes or equatorward extensions of the polar holes were observed during the ascending, maximum, and descending phases of cycle 20 and appear to be sources of solar wind streams with maximum speeds over 600 km s/sup -1/ at all of these epochs. The lifetimes of these holes and streams were greatest during the descending phase of the cycle, or in 1974--1975.

  12. ON THE RELATIONSHIP BETWEEN THE CORONAL MAGNETIC DECAY INDEX AND CORONAL MASS EJECTION SPEED

    SciTech Connect

    Xu Yan; Liu Chang; Jing Ju; Wang Haimin

    2012-12-10

    Numerical simulations suggest that kink and torus instabilities are two potential contributors to the initiation and prorogation of eruptive events. A magnetic parameter called the decay index (i.e., the coronal magnetic gradient of the overlying fields above the eruptive flux ropes) could play an important role in controlling the kinematics of eruptions. Previous studies have identified a threshold range of the decay index that distinguishes between eruptive and confined configurations. Here we advance the study by investigating if there is a clear correlation between the decay index and coronal mass ejection (CME) speed. Thirty-eight CMEs associated with filament eruptions and/or two-ribbon flares are selected using the H{alpha} data from the Global H{alpha} Network. The filaments and flare ribbons observed in H{alpha} associated with the CMEs help to locate the magnetic polarity inversion line, along which the decay index is calculated based on the potential field extrapolation using Michelson Doppler Imager magnetograms as boundary conditions. The speeds of CMEs are obtained from the LASCO C2 CME catalog available online. We find that the mean decay index increases with CME speed for those CMEs with a speed below 1000 km s{sup -1} and stays flat around 2.2 for the CMEs with higher speeds. In addition, we present a case study of a partial filament eruption, in which the decay indices show different values above the erupted/non-erupted part.

  13. CME Interaction with Coronal Holes and Their Interplanetary Consequences

    NASA Technical Reports Server (NTRS)

    Gopalswamy, N.; Makela, P.; Xie, H.; Akiyama, S.; Yashiro, S.

    2008-01-01

    A significant number of interplanetary (IP) shocks (-17%) during cycle 23 were not followed by drivers. The number of such "driverless" shocks steadily increased with the solar cycle with 15%, 33%, and 52% occurring in the rise, maximum, and declining phase of the solar cycle. The solar sources of 15% of the driverless shocks were very close the central meridian of the Sun (within approx.15deg), which is quite unexpected. More interestingly, all the driverless shocks with their solar sources near the solar disk center occurred during the declining phase of solar cycle 23. When we investigated the coronal environment of the source regions of driverless shocks, we found that in each case there was at least one coronal hole nearby suggesting that the coronal holes might have deflected the associated coronal mass ejections (CMEs) away from the Sun-Earth line. The presence of abundant low-latitude coronal holes during the declining phase further explains why CMEs originating close to the disk center mimic the limb CMEs, which normally lead to driverless shocks due to purely geometrical reasons. We also examined the solar source regions of shocks with drivers. For these, the coronal holes were located such that they either had no influence on the CME trajectories. or they deflected the CMEs towards the Sun-Earth line. We also obtained the open magnetic field distribution on the Sun by performing a potential field source surface extrapolation to the corona. It was found that the CMEs generally move away from the open magnetic field regions. The CME-coronal hole interaction must be widespread in the declining phase, and may have a significant impact on the geoeffectiveness of CMEs.

  14. The composition of a coronal active region

    NASA Technical Reports Server (NTRS)

    Waljeski, K.; Moses, D.; Dere, K. P.; Saba, J. L. R.; Strong, K. T.; Webb, D. F.; Zarro, D. M.

    1994-01-01

    The relative abundances of iron, oxygen, magnesium, and neon in a coronal active region are determined from measurements of soft X-ray line and broadband intensities. The emission measure, temperature, and column density are derived from these measured intensities and are used to place a constraint on the abundances of the heavier elements relative to hydrogen in the corona. The intensity measurements were made on 1987 December 11, when an active region was observed jointly by the American Science and Engineering (AS&E) High Resolution Soft X-Ray Imaging Sounding-Rocket Payload and the X-Ray Polychromator Flat Crystal Spectrometer (FCS) onboard the Solar Maximum Mission spacecraft. The coordinated observations include images through two broadband filters (8 to 29 A and 8 to 39, 44 to 60 A) and profiles of six emission lines: Fe XVII (15.01 A), FE VIII (15.26 A), O VIII (18.97 A), Mg XI (9.17 A), Ne IX (13.44 A), and Fe XVIII (14.21 A). The effects of resonance scattering are considered in the interpretation of the FCS line intensities. We calculated the expected intensity ratio of the two Fe XVII lines as a function of optical depth and compared this ratio with the observed intensity ratio to obtain the optical depths of each of the lines and the column density. The line intensities and the broadband filtered images are consistent with the emission from a thermal plasma where Fe, O, Mg, and Ne have the 'adopted coronal' abundances of Meyer (1985b) relative to one another, but are not consistent with the emission from a plasma having photospheric abundances: The ratios of the abundances of the low first ionization potential (FIP) elements (Fe and Mg) to the abundances of the high-FIP elements (Ne and O) are higher than the ratios seen in the photosphere by a factor of about 3.5. This conclusion is independent of the assumption of either an isothermal or a multithermal plasma. The column densities derived from the Fe XVII line ratio and the geometry of the active

  15. Statistical Properties of Solar Coronal Bright Points

    NASA Astrophysics Data System (ADS)

    Alipour, N.; Safari, H.

    2015-07-01

    Here, we aim to study the statistical properties (i.e., spatial, temporal, and magnetic structures) of extreme ultraviolet coronal bright points (CBPs) observed by SDO during a 4.4 yr period (2010 June 1 to 2014 October 31). We developed the automatic detection method for CBPs based on the machine-learning technique and Zernike image moments. The average number and the mean density of CBPs are estimated to be about 572 (per full disk image taken at 193 Å) and 1.9× {10}-4 Mm-2, respectively. There is a negative correlation (-0.7) between the number of CBPs and the number of sunspots. The size and lifetime frequency distribution of CBPs show the lognormal and power-law (exponent equal to -1.6) behaviors, respectively. The relationship between the lifetime and size of CBPs is clearly treated by a power-law function with an exponent equal to 0.13. Around 1.3% of the solar surface is covered by the bright cores of CBPs and 2.6% of that is covered by their total area. About 52% of CBPs have lifetimes of less than 20 minutes and the remaining 48% have mean lifetimes of 6 hr. More than 95% of CBPs with lifetimes of less than 20 hr and nine CBPs with lifetimes of more than 72 hr are detected. The average number of the new CBPs emerging every 45 s in the whole of the Sun is about 27 ± 3. The temporal self-affinity of the time series of CBPs that emerged, indexed by the Hurst exponent determined using both detrended fluctuation analysis and R/S analysis, is 0.78. This long-temporal correlation suggests that CBPs form a system of self-organized criticality.

  16. ROTATION OF CORONAL MASS EJECTIONS DURING ERUPTION

    SciTech Connect

    Lynch, B. J.; Li, Y.; Luhmann, J. G.; Antiochos, S. K.; DeVore, C. R. E-mail: yanli@ssl.berkeley.edu E-mail: spiro.k.antiochos@nasa.gov

    2009-06-01

    Understanding the connection between coronal mass ejections (CMEs) and their interplanetary counterparts (ICMEs) is one of the most important problems in solar-terrestrial physics. We calculate the rotation of erupting field structures predicted by numerical simulations of CME initiation via the magnetic breakout model. In this model, the initial potential magnetic field has a multipolar topology and the system is driven by imposing a shear flow at the photospheric boundary. Our results yield insight on how to connect solar observations of the orientation of the filament or polarity inversion line (PIL) in the CME source region, the orientation of the CME axis as inferred from coronagraph images, and the ICME flux rope orientation obtained from in situ measurements. We present the results of two numerical simulations that differ only in the direction of the applied shearing motions (i.e., the handedness of the sheared-arcade systems and their resulting CME fields). In both simulations, eruptive flare reconnection occurs underneath the rapidly expanding sheared fields transforming the ejecta fields into three-dimensional flux rope structures. As the erupting flux ropes propagate through the low corona (from 2 to 4 R{sub sun}) the right-handed breakout flux rope rotates clockwise and the left-handed breakout flux rope rotates counterclockwise, in agreement with recent observations of the rotation of erupting filaments. We find that by 3.5 R {sub sun} the average rotation angle between the flux rope axes and the active region PIL is approximately 50 deg. We discuss the implications of these results for predicting, from the observed chirality of the pre-eruption filament and/or other properties of the CME source region, the direction and amount of rotation that magnetic flux rope structures will experience during eruption. We also discuss the implications of our results for CME initiation models.

  17. Probing Coronal Mass Ejections with Faraday Rotation

    NASA Astrophysics Data System (ADS)

    Spangler, Steven R.; Fischer, P. D.; Kooi, J. E.; Buffo, J. J.

    2013-07-01

    Coronal Mass Ejections (CMEs) are one of the most important solar phenomena in affecting conditions on Earth. There is not a consensus as to the physical mechanisms responsible for ejecting CME material from the solar atmosphere. Measurements that specify basic physical properties close to the Sun, when the CME is still evolving, should be useful in determining the correct theoretical model. One of the best observational techniques is that of Faraday rotation, a rotation in the plane of polarization of radio waves when propagating through a magnetized medium like the corona. The importance of Faraday rotation in determining the structure and evolutionary history of CMEs was discussed in Liu et al (ApJ 665, 1439, 2007). In this paper, we report Faraday rotation observations of ``constellations'' of background extragalactic radio sources near the Sun on three days in August, 2012, with the intention of observing a source occulted by a CME. Observations were made with the Jansky Very Large Array (VLA) of the National Radio Astronomy Observatory. We made polarization measurements at 6 frequencies between 1.31 and 1.94 GHz. On August 2, 2012, a CME clearly visible on the LASCO C3 coronagraph occulted a radio source from our sample, 0843+1547. Preliminary data analysis shows a Faraday rotation transient for 0843+1547 which appears to be associated with the CME. The Faraday rotation measure changes from nearly 0 before CME passage, to a value of about -12 radians/square-meter before declining after CME passage. We will discuss the interpretation of these data in terms of models for CME structure, as well as the status of our observations of other sources on August 2, and on other days. This work was supported at the University of Iowa by grant ATM09-56901.

  18. A New Way to Identify Coronal Holes.

    NASA Astrophysics Data System (ADS)

    Malanushenko, O.; Jones, H. P.

    2003-05-01

    The location of a coronal hole (CH) in the upper chromosphere is usually based on equivalent width (EqW) images in the He 1083 nm line. A CH is seen on these images as bright areas, which represents low values of EqW. But sometimes it is difficult to differentiate a CH from the bright centers of chromospheric network, or filament channels, without complementary data and the skill of an experienced of observer. To remove the above ambiguity we apply a new spectral analysis technique for the He I 1083 nm line to imaging spectroscopy of several CHs obtained with the NASA/NSO spectromagnetograph (Malanushenko and Jones, 2002, BAAS 33, 700). Reduction includes making dark and flat-field corrections; normalization to a non-linear continuum on the basis of a comparison to a spectral standard; a differential method for the de-blending of spectra; and multi-profile fitting to define the He line components. We fit a Gaussian profile to the main component of the He line and deduce the parameters of central intensity (I) and half width at half maximum (HW). On the HW-images, CHs are distinguished from the surrounding regions as bright areas; similarly, they are also seen as bright on the I-images. Chromospheric network is seen on W-images as opposite in contrast to the I-images, and this distinction is the basis for our CH identification method. We normalize the I- and HW-images by subtracting their respective quiet-sun means and dividing by the corresponding standard deviations. The sum of the normalized I- and HW-images shows increasing contrast of the CH and a depression of contrast in the network and can be used as an independent CH diagnostic.

  19. Magnetic Reconnection in Interplanetary Coronal Mass Ejections

    NASA Astrophysics Data System (ADS)

    Fermo, R. L.; Opher, M.; Drake, J. F.

    2014-12-01

    Magnetic reconnection is a ubiquitous phenomenon in many varied space and astrophysical plasmas, and as such plays an important role in the dynamics of interplanetary coronal mass ejections (ICMEs). It is widely regarded that reconnection is instrumental in the formation and ejection of the initial CME flux rope, but reconnection also continues to affect the dynamics as it propagates through the interplanetary medium. For example, reconnection on the leading edge of the ICME, by which it interacts with the interplanetary medium, leads to flux erosion. However, recent in situ observations by Gosling et al. found signatures of reconnection exhausts in the interior. In light of this data, we consider the stability properties of systems with this flux rope geometry with regard to their minimum energy Taylor state. Variations from this state will result in the magnetic field relaxing back towards the minimum energy state, subject to the constraints that the toroidal flux and magnetic helicity remain invariant. In reversed field pinches, this relaxation is mediated by reconnection in the interior of the system, as has been shown theoretically and experimentally. By treating the ICME flux rope in a similar fashion, we show analytically that the the elongation of the flux tube cross section in the latitudinal direction will result in a departure from the Taylor state. The resulting relaxation of the magnetic field causes reconnection to commence in the interior of the ICME, in agreement with the observations of Gosling et al. We present MHD simulations in which reconnection initiates at a number of rational surfaces, and ultimately produces a stochastic magnetic field. If the time scales for this process are shorter than the propagation time to 1 AU, this result explains why many ICME flux ropes no longer exhibit the smooth, helical flux structure characteristic of a magnetic cloud.

  20. Quiet Sun coronal heating: A statistical model

    NASA Astrophysics Data System (ADS)

    Krasnoselskikh, V.; Podladchikova, O.; Lefebvre, B.; Vilmer, N.

    2002-02-01

    Recent observations of Krucker & Benz (\\cite{Krucker98}) give strong support to Parker's hypothesis (\\cite∥) that small-scale dissipative events make up the main contribution to quiet Sun coronal heating. They also showed that these small-scale events are associated not only with the magnetic network, but also with the cell interiors (Benz & Krucker \\cite{Benz98}). Taking into account in addition the results of the analysis performed by Priest with co-authors (\\cite{pr1}) who demonstrated that the heating is quasi-homogeneous along the arcs, we come to the conclusion that the sources driving these dissipative events are also small-scale sources. Typically they are of the order of or smaller than the linear scale of the events observed, that is <2000 km. To describe statistical properties of quiet Sun corona heating by microflares, nanoflares, and even smaller events, we consider a cellular automata model subject to uniform small-scale driving and dissipation. The model consists of two elements, the magnetic field source supposed to be associated with the small scale hydrodynamic turbulence convected from the photosphere and local dissipation of small scale currents. The dissipation is assumed to be provided by either anomalous resistivity, when the current density exceeds a certain threshold value, or by the magnetic reconnection. The main problem considered is how the statistical characteristics of dissipated energy flow depend upon characteristics of the magnetic field source and on physical mechanism responsible for the magnetic field dissipation. As the threshold value of current is increased, we observe the transition from Gaussian statistics to power-law type. In addition, we find that the dissipation provided by reconnection results in stronger deviations from Gaussian distribution.

  1. Coronal Seismology: Inferring Magnetic Fields and Exploring Damping Mechanisms

    NASA Astrophysics Data System (ADS)

    McAteer, R. T. James; Ireland, Jack

    2015-08-01

    Recent observations in extreme ultra-violet wavelengths have shown that the solar corona oscillates at many different spatial sizes and temporal size scales. However, much remains unknown about many of these oscillations; they are intermittent for unknown reasons, appear on some coronal features and not on other, similar, neighboring features, and may (or may not) be magnetohydrodynamic (MHD) wave modes. Definitive causes of the structure and origins of these oscillations are still largely lacking. Here, we use automated oscillation detection routines to study a large sample of oscillations, inferring physical mechanisms as to how and why the corona varies.First, we measure the oscillation content of different physical regions on the Sun in SDO AIA data, using two different automated oscillation detection algorithms. This shows a power-law distribution in oscillatory frequency, disagreeing with strong historical assumptions about the nature of coronal heating and coronal seismology. We show how such disagreements can be reconciled by using a power-law background for oscillatory signals.Second we use coronal seismology to provide a means to infer coronal plasma parameters and to differentiate between potential damping mechanisms. Recent sets of kink-mode observations (usually 5-8 loops) have come insights into how the coronal is structured and how it evolves. We present a complex set of flare-induced, off-limb, coronal kink-mode oscillations of almost 100 loops. These display a spread of periods, amplitudes, and damping times, allowing us to probe the spatial distribution of these parameters for the first time. Both Fourier and Wavelet routines are used to automatically extract and characterize these oscillations. An initial period of P~500s, results in an inferred coronal magnetic field of B~20G. The decrease in the oscillation period of the loop position corresponds to a drop in number density inside the coronal loop, as predicted by MHD. As the the period drops

  2. Coronal Energy Release via Explosive Three-Dimensional Instability

    NASA Astrophysics Data System (ADS)

    Dahlburg, R. B.; Klimchuk, J. A.; Antiochos, S. K.

    2003-05-01

    It is widely believed that most coronal phenomena involve the release of magnetic free energy that is stored within stressed magnetic field configurations. The availability of sufficient free energy to explain everything from coronal heating to flares and coronal mass ejections is well established, but how this energy is released remains a major puzzle. Observations reveal that an important property of the energy release mechanism is its ``switch on" character. The mechanism must remain dormant for long periods of time to allow the magnetic stresses build, then it must operate very vigorously once it finally turns on. We discuss a mechanism called the ``secondary instability" which exhibits this behavior. It is essentially the ideal kinking of thin twisted magnetic flux tubes that form from the resistive instability of current sheets. We relate the mechanism to the coronal heating idea of Parker in which the coronal magnetic field becomes tangled by random motions of the photospheric footpoints. Global energy balance considerations imply that magnetic energy dissipation occurs at a particular angle in the field, and the secondary instability offers the first quantitative explanation for why this should be. It thus places Parker's popular idea on a much firmer physical footing. This research was funded by NASA.

  3. Solar wind heavy ions from flare-heated coronal plasma

    NASA Technical Reports Server (NTRS)

    Bame, S. J.; Asbridge, J. R.; Feldman, W. C.; Fenimore, E. E.; Gosling, J. T.

    1979-01-01

    Information concerning the coronal expansion is carried by solar-wind heavy ions. Distinctly different energy-per-charge ion spectra are found in two classes of solar wind having the low kinetic temperatures necessary for E/q resolution of the ion species. Heavy-ion spectra which can be resolved are most frequently observed in the low-speed interstream (IS) plasma found between high speed streams; the streams are thought to originate from coronal holes. Although the sources of the IS plasma are uncertain, the heavy-ion spectra found there contain identifiable peaks of O, Si, and Fe ions. Such spectra indicate that the IS ionization state of O is established in coronal gas at a temperature of approximately 1.6 million K, while that of Fe is frozen in farther out at about 1.5 million K. On occasion anomalous spectra are found outside IS flows in solar wind with abnormally depressed local kinetic temperatures. The anomalous spectra contain Fe(16+) ions, not usually found in IS flows, and the derived coronal freezing-in temperatures are significantly higher. The coronal sources of some of these ionizationally hot flows are identified as solar flares.

  4. Standing Kink modes in three-dimensional coronal loops

    SciTech Connect

    Pascoe, D. J.; De Moortel, I.

    2014-04-01

    So far, the straight flux tube model proposed by Edwin and Roberts is the most commonly used tool in practical coronal seismology, in particular, to infer values of the (coronal) magnetic field from observed, standing kink mode oscillations. In this paper, we compare the period predicted by this basic model with three-dimensional (3D) numerical simulations of standing kink mode oscillations, as the period is a crucial parameter in the seismological inversion to determine the magnetic field. We perform numerical simulations of standing kink modes in both straight and curved 3D coronal loops and consider excitation by internal and external drivers. The period of oscillation for the displacement of dense coronal loops is determined by the loop length and the kink speed, in agreement with the estimate based on analytical theory for straight flux tubes. For curved coronal loops embedded in a magnetic arcade and excited by an external driver, a secondary mode with a period determined by the loop length and external Alfvén speed is also present. When a low number of oscillations is considered, these two periods can result in a single, non-resolved (broad) peak in the power spectrum, particularly for low values of the density contrast for which the two periods will be relatively similar. In that case (and for this particular geometry), the presence of this additional mode would lead to ambiguous seismological estimates of the magnetic field strength.

  5. Coronal Loop Evolution Observed with AIA and Hi-C

    NASA Technical Reports Server (NTRS)

    Mulu-Moore, Fana; Winebarger, A.; Cirtain, J.; Kobayashi, K.; Korreck, K.; Golub, L.; Kuzin. S.; Walsh, R.; DeForest, C.; DePontieu, B.; Weber, M.

    2012-01-01

    Despite much progress toward understanding the dynamics of the solar corona, the physical properties of coronal loops are not yet fully understood. Recent investigations and observations from different instruments have yielded contradictory results about the true physical properties of coronal loops. In the past, the evolution of loops has been used to infer the loop substructure. With the recent launch of High Resolution Coronal Imager (Hi-C), this inference can be validated. In this poster we discuss the first results of loop analysis comparing AIA and Hi-C data. We find signatures of cooling in a pixel selected along a loop structure in the AIA multi-filter observations. However, unlike previous studies, we find that the cooling time is much longer than the draining time. This is inconsistent with previous cooling models.

  6. The First Decade of UVCS/SOHO: Coronal Hole Properties

    NASA Astrophysics Data System (ADS)

    Miralles, Mari Paz; Cranmer, S. R.; Kohl, J. L.

    2006-06-01

    We have measured with the SOHO Ultraviolet Coronagraph Spectrometer (UVCS) the physical properties of over 155 large coronal holes that produced a variety of high-speed solar wind conditions at 1 AU. This data set includes observations of coronal holes of different sizes and latitudinal locations present throughout solar cycle 23.In the spring of 2006, the polar coronal holes have not yet evolved to the fully quiescent minimum state seen in 1996-1997, although the next solar minimum is expected to occur during 2006-2007. We will present the solar cycle dependence of the derived plasma parameters for O5+ and protons from the last solar minimum in 1996 to present and compare them, where possible, with the in situ solar wind properties.This work is supported by NASA under Grant NNG05GG38G tothe Smithsonian Astrophysical Observatory, by the Italian Space Agency, and by PRODEX (Swiss contribution).

  7. Coronal holes - Mass loss driven by magnetic reconnection

    NASA Technical Reports Server (NTRS)

    Mullan, D. J.; Ahmad, I. A.

    1982-01-01

    A nonthermal mechanism for driving coronal hole mass loss is proposed. Three empirical results are noted, namely (1) that polar plumes with short-lived X-ray bright points (XBP) at their base are sites of matter flow sufficient to account for the total solar mass flux, (2) that solar wind densities are positively correlated with the number of XBP in coronal holes, and (3) that XBP are associated with newly emerged magnetic flux. It is noted that since the dynamical development following the onset of nonequilibrium is a hitherto unsolved problem, subsequent features in the scenario described here are relatively speculative. It is proposed that bubbles of matter ejected from magnetic reconnection sites in polar plumes drive the solar wind in coronal holes.

  8. Development of coronal mass ejections and association with interplanetary events

    NASA Technical Reports Server (NTRS)

    Pick, M.; Maia, D.; Howard, R.; Thompson, B.; Lanzerotti, L. J. L.; Bothmer, V.; Lamy, P.

    1997-01-01

    Results are presented on the development of two coronal mass ejections (CMEs) obtained by comparing the observations of the large angle spectroscopic coronagraph (LASCO) and the extreme ultraviolet imaging telescope (EIT) instrument onboard the SOHO with those of the Nancay radioheliograph. The radioheliograph provides images at five levels in the corona. An excellent spatial association is found between the position and extent of the type 4 radio sources and the CMEs seen by LASCO. One result is the existence for these two events of discrete successive phases in their development. For these events, Ulysses and SOHO missions measured interplanetary particles of coronal origin. The coronal acceleration site was attempted to be identified, as well as the path of these particles from the corona to the interplanetary medium.

  9. Observations of the birth of a small coronal hole

    NASA Technical Reports Server (NTRS)

    Solodyna, C. V.; Krieger, A. S.; Nolte, J. T.

    1977-01-01

    Using soft X-ray data from the S-054 X-ray spectrographic telescope aboard Skylab, we observed temporal changes in the emission structure of the X-ray corona associated with the birth of a small coronal hole. Designated as CH6, this coronal hole was born near the equator in a time interval less than 9-1/2 hr. By constructing a light curve for a point near the center of CH6, we observed a sudden 40% decrease in X-ray emission associated with the birth of this coronal hole. On a time scale of hours, the growth of CH6 in area proceeded faster than the average rate predicted by the diffusion of solar fields. The short term decay of CH6 followed the diffusive rate to within experimental uncertainty. On a time scale of one rotation, the subsequent development of CH6 was not consistent with steady growth at the average rate predicted by diffusion.

  10. Shock Formation of Slow Magnetosonic Waves in Coronal Plumes

    NASA Technical Reports Server (NTRS)

    Cuntz, Manfred; Suess, Steve; Rose, M. Franklin (Technical Monitor)

    2000-01-01

    We investigate the height of shock formation in coronal plumes for slow magnetosonic waves. The models take into account plume geometric spreading, heat conduction, and radiative damping. The wave parameters as well as the spreading functions of the plumes and the base magnetic field strengths are given by empirical constraints mostly from Solar and Heliospheric Observatory (SOHO)/ Ultraviolet Coronograph Spectrometer (UVCS), Extreme Ultraviolet Imaging Telescope (EIT), Michelson Doppler Imager (MDI), and Large Angle Spectrometric Coronagraph (LASCO). Our models show that shock formation occurs at relatively low coronal heights, typically within 1.2 RsuN, depending on the model parameters. The shock formation is calculated using the well-established wave breaking criterion given by the intersection of C+ characteristics in the space-time plane. Our models show that shock heating by slow magnetosonic waves is expected to be relevant at most heights in solar coronal plumes, although such waves are probably not the main energy supply mechanism.

  11. Shock Formation of Slow Magnetosonic Waves in Coronal Plumes

    NASA Technical Reports Server (NTRS)

    Cuntz, Manfred; Suess, Steven T.; Rose, M. Franklin (Technical Monitor)

    2001-01-01

    We investigate the height of shock formation in coroner plumes for slow magnetosonic waves. The models take into account plume geometric spreading, heat conduction and radiative damping. The wave parameters as well as the spreading functions of the plumes and the base magnetic field strengths are given by empirical constraints mostly from Solar and Heliospheric Observatory/Ultraviolet Coronagraph Spectrometer (SOHO/UVCS). Our models show that shock formation occurs at low coronal heights, i.e., within 1.3 solar radius, depending on the model parameters. The shock formation is calculated using the well-established wave breaking condition given by the intersection of C+ characteristics in the space-time plane. Our models show that shock heating by slow magnetosonic waves is expected to be relevant at most heights in solar coronal plumes, although slow magnetosonic waves are most likely not a solely operating energy supply mechanism.

  12. Examining the Properties of Jets in Coronal Holes

    NASA Technical Reports Server (NTRS)

    Gaulle, Owen; Adams, Mitzi L.; Tennant, A. F.

    2012-01-01

    We examined both X-ray and Magnetic field data in order to determine if there is a correlation between emerging magnetic flux and the production of Coronal jets. It was proposed that emerging flux can be a trigger to a coronal jet. The jet is thought to be caused when local bipoles reconnect or when a region of magnetic polarity emerges through a uniform field. In total we studied 15 different jets that occurred over a two day period starting 2011-02-27 00:00:00 UTC and ending 2011-02-28 23:59:55 UTC. All of the jets were contained within a coronal hole that was centered on the disk. Of the 15 that we studied 6 were shown to have an increase of magnetic flux within one hour prior to the creation of the jet and 10 were within 3 hours before the event.

  13. Extreme-ultraviolet observations of global coronal wave rotation

    SciTech Connect

    Attrill, G. D. R.; Long, D. M.; Green, L. M.; Harra, L. K.; Van Driel-Gesztelyi, L.

    2014-11-20

    We present evidence of global coronal wave rotation in EUV data from SOHO/EIT, STEREO/EUVI, and SDO/AIA. The sense of rotation is found to be consistent with the helicity of the source region (clockwise for positive helicity, anticlockwise for negative helicity), with the source regions hosting sigmoidal structures. We also study two coronal wave events observed by SDO/AIA where no clear rotation (or sigmoid) is observed. The selected events show supporting evidence that they all originate with flux rope eruptions. We make comparisons across this set of observations (both with and without clear sigmoidal structures). On examining the magnetic configuration of the source regions, we find that the nonrotation events possess a quadrupolar magnetic configuration. The coronal waves that do show a rotation originate from bipolar source regions.

  14. Flux Rope Formation Preceding Coronal Mass Ejection Onset

    NASA Astrophysics Data System (ADS)

    Kliem, Bernhard; Green, L. M.

    2009-12-01

    We analyse the evolution of a sigmoidal (S shaped) active region toward eruption, which includes a coronal mass ejection (CME) but leaves part of the filament in place. The X-ray sigmoid is found to trace out three different magnetic topologies in succession: a highly sheared arcade of coronal loops in its long-lived phase, a bald-patch separatrix surface (BPSS) in the hours before the CME, and the first flare loops in its major transient intensity enhancement. The coronal evolution is driven by photospheric changes which involve the convergence and cancellation of flux elements under the sigmoid and filament. The data yield unambiguous evidence for the existence of a BPSS, and hence a flux rope, in the corona prior to the onset of the CME.

  15. Flux Rope Formation Preceding Coronal Mass Ejection Onset

    NASA Astrophysics Data System (ADS)

    Green, L. M.; Kliem, B.

    2009-08-01

    We analyze the evolution of a sigmoidal (S-shaped) active region toward eruption, which includes a coronal mass ejection (CME) but leaves part of the filament in place. The X-ray sigmoid is found to trace out three different magnetic topologies in succession: a highly sheared arcade of coronal loops in its long-lived phase, a bald-patch separatrix surface (BPSS) in the hours before the CME, and the first flare loops in its major transient intensity enhancement. The coronal evolution is driven by photospheric changes which involve the convergence and cancellation of flux elements under the sigmoid and filament. The data yield unambiguous evidence for the existence of a BPSS, and hence a flux rope, in the corona prior to the onset of the CME.

  16. Coronal element abundances derived from solar energetic particles

    NASA Technical Reports Server (NTRS)

    Reames, Donald V.

    1994-01-01

    The large gradual solar-energetic-particle (SEP) events, where abundances are commonly measured, are produced when coronal mass ejections (CMEs) drive shock waves through the corona and the interplanetary medium. The shock accelerates particles from the highly-ionized, approximately 1.5 MK, plasma in a manner that depends only weakly upon the Q/A of the ion, except at very high energies. Averaging the approximately 1 MeV/amu abundances over many events compensates for the acceleration effects to produce abundances that appear to correspond directly to those in the coronal source for all observed elements, including H. The resulting abundances reflect the 4 x enhancement of ions with low values of first ionization potential (FIP) arising from ion-neutral fractionation that occurs as the atoms are transported up from the photosphere. A different pattern of fractionation is found for ions that are shock-accelerated from the high speed solar wind emerging from coronal holes.

  17. Exploring the Spectral Type Dependence of Coronal Abundance Anomalies

    NASA Astrophysics Data System (ADS)

    Wood, Brian

    2010-09-01

    We propose to improve our empirical understanding of how coronal abundance anomalies, such as the solar "FIP effect," vary with spectral type by observing the X-ray spectra of Pi3 Ori (F6 V) and GJ 338 (M0 V+K7 V) with LETGS. No high resolution X-ray spectrum has ever been taken of a coronal main sequence star with a spectral type as early as that of Pi3 Ori. A known correlation between spectral type and FIP effect suggests that Pi3 Ori's X-ray spectrum should show the strongest solar-like FIP effect ever observed. The observation of the GJ 338 binary will efficiently provide two stellar spectra in one exposure, which we will use to test whether stars with modest coronal activity can possess an "inverse FIP effect," a phenomenon generally associated only with very active stars.

  18. FLUX ROPE FORMATION PRECEDING CORONAL MASS EJECTION ONSET

    SciTech Connect

    Green, L. M.; Kliem, B. E-mail: bhk@mssl.ucl.ac.uk

    2009-08-01

    We analyze the evolution of a sigmoidal (S-shaped) active region toward eruption, which includes a coronal mass ejection (CME) but leaves part of the filament in place. The X-ray sigmoid is found to trace out three different magnetic topologies in succession: a highly sheared arcade of coronal loops in its long-lived phase, a bald-patch separatrix surface (BPSS) in the hours before the CME, and the first flare loops in its major transient intensity enhancement. The coronal evolution is driven by photospheric changes which involve the convergence and cancellation of flux elements under the sigmoid and filament. The data yield unambiguous evidence for the existence of a BPSS, and hence a flux rope, in the corona prior to the onset of the CME.

  19. Eruptions that Drive Coronal Jets in a Solar Active Region

    NASA Technical Reports Server (NTRS)

    Sterling, Alphonse C.; Moore, Ronald L.; Falconer, David A.; Panesar, Navdeep K.; Akiyama, Sachiko; Yashiro, Seiji; Gopalswamy, Nat

    2016-01-01

    Solar coronal jets are common in both coronal holes and in active regions (e.g., Shibata et al. 1992, Shimojo et al. 1996, Cirtain et al. 2007. Savcheva et al. 2007). Recently, Sterling et al. (2015), using data from Hinode/XRT and SDO/AIA, found that coronal jets originating in polar coronal holes result from the eruption of small-scale filaments (minifilaments). The jet bright point (JBP) seen in X-rays and hotter EUV channels off to one side of the base of the jet's spire develops at the location where the minifilament erupts, consistent with the JBPs being miniature versions of typical solar flares that occur in the wake of large-scale filament eruptions. Here we consider whether active region coronal jets also result from the same minifilament-eruption mechanism, or whether they instead result from a different mechanism (e.g. Yokoyama & Shibata 1995). We present observations of an on-disk active region (NOAA AR 11513) that produced numerous jets on 2012 June 30, using data from SDO/AIA and HMI, and from GOES/SXI. We find that several of these active region jets also originate with eruptions of miniature filaments (size scale 20'') emanating from small-scale magnetic neutral lines of the region. This demonstrates that active region coronal jets are indeed frequently driven by minifilament eruptions. Other jets from the active region were also consistent with their drivers being minifilament eruptions, but we could not confirm this because the onsets of those jets were hidden from our view. This work was supported by funding from NASA/LWS, NASA/HGI, and Hinode. A full report of this study appears in Sterling et al. (2016).

  20. DICHOTOMY OF SOLAR CORONAL JETS: STANDARD JETS AND BLOWOUT JETS

    SciTech Connect

    Moore, Ronald L.; Cirtain, Jonathan W.; Sterling, Alphonse C.; Falconer, David A.

    2010-09-01

    By examining many X-ray jets in Hinode/X-Ray Telescope coronal X-ray movies of the polar coronal holes, we found that there is a dichotomy of polar X-ray jets. About two thirds fit the standard reconnection picture for coronal jets, and about one third are another type. We present observations indicating that the non-standard jets are counterparts of erupting-loop H{alpha} macrospicules, jets in which the jet-base magnetic arch undergoes a miniature version of the blowout eruptions that produce major coronal mass ejections. From the coronal X-ray movies we present in detail two typical standard X-ray jets and two typical blowout X-ray jets that were also caught in He II 304 A snapshots from STEREO/EUVI. The distinguishing features of blowout X-ray jets are (1) X-ray brightening inside the base arch in addition to the outside bright point that standard jets have, (2) blowout eruption of the base arch's core field, often carrying a filament of cool (T {approx} 10{sup 4} - 10{sup 5} K) plasma, and (3) an extra jet-spire strand rooted close to the bright point. We present cartoons showing how reconnection during blowout eruption of the base arch could produce the observed features of blowout X-ray jets. We infer that (1) the standard-jet/blowout-jet dichotomy of coronal jets results from the dichotomy of base arches that do not have and base arches that do have enough shear and twist to erupt open, and (2) there is a large class of spicules that are standard jets and a comparably large class of spicules that are blowout jets.

  1. THE CORONAL ABUNDANCES OF MID-F DWARFS

    SciTech Connect

    Wood, Brian E.; Laming, J. Martin

    2013-05-10

    A Chandra spectrum of the moderately active nearby F6 V star {pi}{sup 3} Ori is used to study the coronal properties of mid-F dwarfs. We find that {pi}{sup 3} Ori's coronal emission measure distribution is very similar to those of moderately active G and K dwarfs, with an emission measure peak near log T = 6.6 seeming to be ubiquitous for such stars. In contrast to coronal temperature, coronal abundances are known to depend on spectral type for main sequence stars. Based on this previously known relation, we expected {pi}{sup 3} Ori's corona to exhibit an extremely strong ''first ionization potential (FIP) effect'', a phenomenon first identified on the Sun where elements with low FIP are enhanced in the corona. We instead find that {pi}{sup 3} Ori's corona exhibits a FIP effect essentially identical to that of the Sun and other early G dwarfs, perhaps indicating that the increase in FIP bias toward earlier spectral types stops or at least slows for F stars. We find that {pi}{sup 3} Ori's coronal characteristics are significantly different from two previously studied mid-F stars, Procyon (F5 IV-V) and {tau} Boo (F7 V). We believe {pi}{sup 3} Ori is more representative of the coronal characteristics of mid-F dwarfs, with Procyon being different because of luminosity class, and {tau} Boo being different because of the effects of one of two close companions, one stellar ({tau} Boo B: M2 V) and one planetary.

  2. Simulations of Solar Jets Confined by Coronal Loops

    NASA Astrophysics Data System (ADS)

    Wyper, P. F.; DeVore, C. R.

    2016-03-01

    Coronal jets are collimated, dynamic events that occur over a broad range of spatial scales in the solar corona. In the open magnetic field of coronal holes, jets form quasi-radial spires that can extend far out into the heliosphere, while in closed-field regions the jet outflows are confined to the corona. We explore the application of the embedded-bipole model to jets occurring in closed coronal loops. In this model, magnetic free energy is injected slowly by footpoint motions that introduce twist within the closed dome of the jet source region, and is released rapidly by the onset of an ideal kink-like instability. Two length scales characterize the system: the width (N) of the jet source region and the footpoint separation (L) of the coronal loop that envelops the jet source. We find that both the conditions for initiation and the subsequent dynamics are highly sensitive to the ratio L/N. The longest-lasting and most energetic jets occur along long coronal loops with large L/N ratios, and share many of the features of open-field jets, while smaller L/N ratios produce shorter-duration, less energetic jets that are affected by reflections from the far-loop footpoint. We quantify the transition between these behaviors and show that our model replicates key qualitative and quantitative aspects of both quiet Sun and active-region loop jets. We also find that the reconnection between the closed dome and surrounding coronal loop is very extensive: the cumulative reconnected flux at least matches the total flux beneath the dome for small L/N, and is more than double that value for large L/N.

  3. Rendering Three-Dimensional Solar Coronal Structures

    NASA Technical Reports Server (NTRS)

    Gary, G. Allen

    1997-01-01

    An X-ray or EUV image of the corona or chromosphere is a 2D representation of an extended 3D complex for which a general inversion process is impossible. A specific model must be incorporated in order to understand the full 3D structure. We approach this problem by modeling a set of optically-thin 3D plasma flux tubes which we render these as synthetic images. The resulting images allow the interpretation of the X-ray/EUV observations to obtain information on (1) the 3D structure of X-ray images, i.e., the geometric structure of the flux tubes, and on (2) the internal structure using specific plasma characteristics, i.e., the physical structure of the flux tubes. The data-analysis technique uses magnetograms to characterize photospheric magnetic fields and extrapolation techniques to form the field lines. Using a new set of software tools, we have generated 3D flux tube structures around these field lines and integrated the plasma emission along the line of sight to obtain a rendered image. A set of individual flux-tube images is selected by a non-negative least-squares technique to Provide a match with an observed X-ray image. The scheme minimizes the squares of the differences between the synthesized image and the observed image with a non-negative constraint on the coefficients of the brightness of the individual flux-tube loops. The derived images are used to determine the specific photospheric foot points and physical data, i.e., scaling laws for densities and loop lengths. The development has led to Computer efficient integration and display software that is compatible for comparison with observations (e.g., Yohkoh SXT data, NIXT, or EIT). This analysis is important in determining directly the magnetic field configuration, which provides the structure of coronal loops, and indirectly the electric currents or waves, which provide the energy for the heating of the plasma. We have used very simple assumptions (i.e., potential magnetic fields and isothermal

  4. Coronal Reconstruction using LASCO and UVCS Observations

    NASA Technical Reports Server (NTRS)

    Hick, P. P.

    2000-01-01

    The main goal of the research described in the original proposal was to develop methods to quantify coronal and inner-heliospheric velocity fields of the 'quiet' solar wind. For this we planned to use several sources of observations:(1) SOHO/UVCS velocity information in the range 1.5-3 Solar Radii obtained from Doppler dimming observations; (2) projected solar wind velocities (into the plane of the sky) obtained from SOHO/ LASCO images (1.1-30 Solar Radii), primarily derived from two-dimensional correlation tracking techniques; (3) Interplanetary scintillation observations of the heliospheric (> 26 Solar Radii) solar wind velocity from the Solar-Terrestrial Environment Laboratory (STELab) in Nagoya, Japan; (4) Ecliptic in situ observations: data for the ecliptic solar wind are available from the MIT and Los Alamos plasma experiments on the Earth-orbiting IMP-8 spacecraft, from the Cellas instrument on SOHO near the LI Lagrange point, and from the WIND spacecraft; (5) Out-of-ecliptic in situ observations: these data are available primarily from the Los Alamos SWOOPS instrument on Ulysses, which passed over the solar north pole in August 1995, about one year prior to the Whole Sun Month period. Where ever possible we planned to use the first Whole Sun Month as the main time period for the analysis, since we expected that for this period it would be easiest to obtain adequate coverage over the extended period of time required to analyze 'quiet' solar wind patterns. Beyond the observations mentioned above (primarily SOHO data) we extended our selection of data to several events identified in the Yohkoh/SXT data base which directly promised to provide us with clues about the connection between the slow solar wind observed by IPS in the inner heliosphere and their sources in the low corona, in particular active regions. We also obtained valuable results using SWOOPS ill situ observations from the pole-to-pole passage of Ulysses in a comparison with solar wind velocities

  5. A Doppler dimming determination of coronal outflow velocity

    NASA Technical Reports Server (NTRS)

    Strachan, Leonard; Kohl, John L.; Weiser, Heinz; Withbroe, George L.; Munro, Richard H.

    1993-01-01

    Outflow velocities in a polar coronal hole are derived from observations made during a 1982 sounding rocket flight. The velocity results are derived from a Doppler dimming analysis of resonantly scattered H I Ly-alpha. This analysis indicates radial outflow velocities of 217 km/s at 2 solar radii from sun-center with an uncertainty range of 153 to 251 km/s at a confidence level of 67 percent. These results are best characterized as strong evidence for supersonic outflow within 2 solar radii of sun-center in a polar coronal hole. Several means for obtaining improved accuracy in future observations are discussed.

  6. Predicting Ly-alpha intensities in coronal streamers

    NASA Technical Reports Server (NTRS)

    Noci, Giancarlo; Poletto, Giannina; Suess, Steven T.; Wang, A.-H.; Wu, S. T.

    1992-01-01

    SOHO (Solar and Heliospheric Observatory) UVCS (Ultraviolet Coronagraph Spectrometer) will make long term observations of coronal streamers in UV lines, providing a new tool for the analysis of structures which have been known for decades but are still far from being adequately described. Work to evaluate the Lyman alpha brightness of coronal streamers is reported, adopting the streamer models obtained, via a time dependent numerical relaxation technique. This will yield understanding on the role of geometric versus physical factors in determining the streamer lyman alpha intensity and provide guidelines for UVCS observational operations. Future prospects along this line of research are summarized.

  7. Solar coronal and photospheric abundances from solar energetic particle measurements

    NASA Technical Reports Server (NTRS)

    Breneman, H. H.; Stone, E. C.

    1985-01-01

    Solar energetic particle (SEP) elemental abundance data from the cosmic ray subsystem (CRS) aboard the Voyager 1 and 2 spacecraft are used to derive unfractionated coronal and photospheric abundances for elements with Z = 6-30. It is found that the ionic charge-to-mass ratio (Q/M) is the principal organizing parameter for the fractionation of SEPs by acceleration and propagation processes and for flare-to-flare variability, making possible a single-parameter Q/M-dependent correction to the average SEP abundances to obtain unfractionated coronal abundances. A further correction based on first ionization potential allows the determination of unfractionated photospheric abundances.

  8. Solar Coronal and photospheric abundances from solar energetic particle measurements

    NASA Technical Reports Server (NTRS)

    Breneman, H.; Stone, E. C.

    1985-01-01

    Solar energetic particle (SEP) elemental abundance data from the cosmic ray subsystem (CRS) aboard the Voyager 1 and 2 spacecraft are used to derive unfractionated coronal and photospheric abundances for elements with 3 Z or = 30. It is found that the ionic charge-to-mass ratio (Q/M) is the principal organizing parameter for the fractionation of SEPs by acceleration and propagation processes and for flare-to-flare variability, making possible a single-parameter Q/M-dependent correction to the average SEP abundances to obtain unfractionated coronal abundances. A further correction based on first ionization potential allows the determination of unfractionated photospheric abundances.

  9. Solar coronal and photospheric abundances from solar energetic particle measurements

    NASA Technical Reports Server (NTRS)

    Breneman, H.; Stone, E. C.

    1985-01-01

    Solar energetic particle (SEP) elemental abundance data from the Cosmic Ray Subsystem (CRS) aboard the Voyager 1 and 2 spacecraft are used to derive unfractionated coronal and photospheric abundances for elements with 3 = or Z or = 30. The ionic charge-to-mass ratio (Q/M) is the principal organizing parameter for the fractionation of SEPs by acceleration and propagation processes and for flare-to-flare variability, making possible a single-parameter Q/M-dependent correction to the average SEP abundances to obtain unfractionated coronal abundances. A further correction based on first ionization potential allows the determination of unfractionated photospheric abundances.

  10. Was the eclipse comet of 1893 a disconnected coronal transient?

    NASA Technical Reports Server (NTRS)

    Cliver, E. W.

    1987-01-01

    The comet-like feature obsereved in the solar corona by the Lick Observatory eclipse expedition to Chile in 1893 bears an interesting resemblance to the disconnection coronal transient reported by Illing and Hundhausen. Reports of possibly-related limb activity are reviewed to see whether a pre-discovery observation of a relatively rare type of coronal mass ejection was mis-interpreted. The goal of this study is to learn more about the morphology of mass ejections by examining observations that extend down to the low corona of a disconnection event.

  11. Low transition-region characteristics of equatorial coronal holes

    NASA Technical Reports Server (NTRS)

    Patsourakos, S.; Bocchialini, K.; Vial, J.-C.

    1997-01-01

    The results of observations concerning the low transition region of equatorial coronal holes, performed by the Solar and Heliospheric Observatory (SOHO), are discussed. A study performed by other authors led to the conclusion that the chromospheric network corresponding to an equatorial hole is brighter in some lines than the one corresponding to the quiet sun. A statistical study on equatorial holes using the Lyman beta lines from the solar ultraviolet measurements of emitted radiation (SUMER), onboard SOHO, is presented. The mean profiles of cell, network and bright points in and out of the coronal holes are discussed, together with the possible implications of the observations.

  12. Non-local heat transport in static solar coronal loops

    NASA Astrophysics Data System (ADS)

    Ciaravella, A.; Peres, G.; Serio, S.

    1991-04-01

    The limits of applicability of the Spitzer-Harm thermal conductivity in solar coronal loops is investigated, and it is shown that the ratio of electron mean-free path to temperature scale height in large-scale structures can approach the limits of the Spitzer-Harm theory. A nonlocal formulation of heat transport is used to compute a grid of loop models: the effects of nonlocal transport on the distribution of differential emission measure are particularly important in the coronal part of loops longer than the pressure scale height.

  13. The New Zealand Coroners Amendment Bill's proposed approach to health care-related deaths that are reportable to the coroner.

    PubMed

    Moore, Jennifer; Stokes, Tim; Gray, Ben

    2016-03-01

    When must a death that occurs in a health care setting be reported to the coroner? This article explores this question by analysing the Coroners Act 2006 (NZ) and the amendments to the health care-related deaths provisions in the Coroners Amendment Bill 2014 (NZ). At the time of writing, the Bill was at the Select Committee stage. This article examines whether the amendments may improve the inconsistent clinical and coronial practices with respect to reportable health care-related deaths. It concludes that, while the proposed amendments are an improvement on the current legislative drafting, doubt remains about whether they will solve the challenges presented by health care-related reportable deaths. The second and third readings of the Bill should give serious consideration to the submissions received by the New Zealand Law Commission that express the view that the Queensland and Victorian legislation should be used as models. PMID:27323634

  14. A new way to convert Alfven waves into heat in solar coronal holes - Intermittent magnetic levitation

    NASA Technical Reports Server (NTRS)

    Moore, R. L.; Hammer, R.; Musielak, Z. E.; Suess, S. T.; An, C.-H.

    1992-01-01

    In our recent analysis of Alfven wave reflection in solar coronal holes, we found evidence that coronal holes are heated by reflected Alfven waves. This result suggests that the reflection is inherent to the process that dissipates these Alfven waves into heat. We propose a novel dissipation process that is driven by the reflection, and that plausibly dominates the heating in coronal holes.

  15. UVCS/SOHO Observations of Equatorial and Polar Coronal Holes

    NASA Astrophysics Data System (ADS)

    Kohl, J. L.; Miralles, M. P.; Cranmer, S. R.; Suleiman, R. M.

    2000-05-01

    A large equatorial coronal hole was observed above the west limb with the Ultraviolet Coronagraph Spectrometer (UVCS) on SOHO from November 1999 to March 2000. Observations in H I Lyα and O VI 103.2, 103.7 nm provided spectroscopic diagnostics of proton and O5+ velocity distributions and outflow velocities. These properties will be compared to those of the large polar coronal holes observed near solar minimum. The equatorial coronal hole corresponded to a high-speed solar wind stream at 1 AU, but there were significant differences between the interplanetary properties of this stream and the steady high-speed wind seen over the poles at solar minimum. The several obvious differences between the two structures in the extended corona may be associated with the different densities and magnetic field configurations and flux tube expansion factors. Preliminary results from a detailed empirical model of the equatorial coronal hole will be presented. This work is supported by NASA under Grant NAG5-7822 to the Smithsonian Astrophysical Observatory, by the Italian Space Agency and by PRODEX (Swiss contribution).

  16. Ultraviolet Spectroscopy of Coronal Jets Within the Fast Solar Wind

    NASA Astrophysics Data System (ADS)

    Dobrzycka, D.; Cranmer, S. R.; Raymond, J. C.; Biesecker, D. A.; Gurman, J. B.

    2001-05-01

    The coronal jets are spectacular dynamic events originating from different structures in the solar corona. We present UVCS/SOHO observations of polar coronal jets. They appear to originate near flaring ultraviolet bright points within polar coronal holes that are source regions of the fast solar wind. UVCS recorded the jets as a significant enhancement in the integrated intensities of the strongest coronal emission lines: mostly H~I Lyα and O~VI λ λ 1032,1037. A number of detected jets are correlated with the EIT Fe~XII 195~Å and LASCO C2 white-light events. Typically, the observed H~I Lyα enhancement was up to a factor of 1.3-1.7 over the ambient corona and lasted for 20-30 minutes. The narrow profiles of the emission lines indicate that the material in the jets is cooler than the underlying corona. We modeled the observable properties of the jets to get estimates on jet plasma conditions. We discuss the model results, the initial electron temperature and the heating rate required to reproduce the observed O~VI ionization state. We also discuss connection of the polar jets to the fast solar wind. This work is supported by the National Aeronautics and Space Administration under grant NAG5--7822 to the Smithsonian Astrophysical Observatory, by Agenzia Spaziale Italiana, and by the ESA PRODEX program (Swiss contribution).

  17. What can observations tell us about coronal heating?

    PubMed

    Schmelz, J T; Winebarger, A R

    2015-05-28

    The actual source of coronal heating is one of the longest standing unsolved mysteries in all of astrophysics, but it is only in recent years that observations have begun making significant contributions. Coronal loops, their structure and sub-structure, their temperature and density details, and their evolution with time, may hold the key to solving this mystery. Because spatial resolution of current observatories cannot resolve fundamental scale lengths, information about the heating of the corona must be inferred from indirect observations. Loops with unexpectedly high densities and multi-thermal cross-field temperatures were not consistent with results expected from steady uniform heating models. The hot (T>5 MK) plasma component of loops may also be a key observation; a new sounding rocket instrument called the Marshall Grazing Incidence X-ray Spectrometer will specifically target this observable. Finally, a loop is likely to be a tangle of magnetic strands. The High Resolution Coronal Imager observed magnetic braids untwisting and reconnecting, dispersing enough energy to heat the surrounding plasma. The existence of multi-thermal, cooling loops and hot plasma provides observational constraints that all viable coronal heating models will need to explain. PMID:25897090

  18. More Macrospicule Jets in On-Disk Coronal Holes

    NASA Technical Reports Server (NTRS)

    Adams, M. L.; Sterling, A. C.; Moore, R. L.

    2015-01-01

    We examine the magnetic structure and dynamics of multiple jets found in coronal holes close to or on disk center. All data are from the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager (HMI) of the Solar Dynamics Observatory (SDO). We report on observations of about ten jets in an equatorial coronal hole spanning 2011 February 27 and 28. We show the evolution of these jets in AIA 193 A, examine the magnetic field configuration and flux changes in the jet area, and discuss the probable trigger mechanism of these events. We reported on another jet in this same coronal hole on 2011 February 27, (is) approximately 13:04 UT (Adams et al 2014, ApJ, 783: 11). That jet is a previously-unrecognized variety of blowout jet, in which the base-edge bright point is a miniature filament-eruption flare arcade made by internal reconnection of the legs of the erupting field. In contrast, in the presently-accepted 'standard' picture for blowout jets, the base-edge bright point is made by interchange reconnection of initially-closed erupting jet-base field with ambient open field. This poster presents further evidence of the production of the base-edge bright point in blowout jets by internal reconnection. Our observations suggest that most of the bigger and brighter EUV jets in coronal holes are blowout jets of the new-found variety.

  19. Intermittent Coronal Loop Oscillations by Random Energy Releases

    NASA Astrophysics Data System (ADS)

    Mendoza-Briceño, César A.; Erdélyi, Robert

    2006-09-01

    High-resolution observations by the SOHO and TRACE spacecraft have confirmed the existence of coronal loop oscillations and waves. In a recent work, Mendoza-Briceño et al. studied the heating response of coronal plasma to energy pulses randomly distributed in time and space along coronal loops. In this paper we focus on the oscillatory patterns and other features, such as cool gas blobs traveling along the loop, during the evolution of spatiotemporal randomly heated flux tubes in the corona. The nature of these oscillatory patterns is investigated using wavelet analysis. Periodic features, such as wave packets, with periods of 150-220, 500-600, and 800-1000 s are found. It is also found that the periods increase with the loop length and decrease with the length of the loop segments along which the pulses are injected. On the other hand, the randomly driven intermittent cool plasma blobs that propagate from one footpoint to the other are analyzed. Although plenty of coronal loop oscillations are detected by the cohort of the current high-resolution satellites, there are more controversial observational evidences about the predicted cold plasma blobs.

  20. Competition between shock and turbulent heating in coronal loop system

    NASA Astrophysics Data System (ADS)

    Matsumoto, Takuma

    2016-08-01

    2.5-dimensional magnetohydrodynamic (MHD) simulations are performed with high spatial resolution in order to distinguish between competing models of the coronal heating problem. A single coronal loop powered by Alfvén waves excited in the photosphere is the target of the present study. The coronal structure is reproduced in our simulations as a natural consequence of the transportation and dissipation of Alfvén waves. Further, the coronal structure is maintained as the spatial resolution is changed from 25 to 3 km, although the temperature at the loop top increases with the spatial resolution. The heating mechanisms change gradually across the magnetic canopy at a height of 4 Mm. Below the magnetic canopy, both the shock and the MHD turbulence are dominant heating processes. Above the magnetic canopy, the shock heating rate reduces to less than 10 % of the total heating rate while the MHD turbulence provides significant energy to balance the radiative cooling and thermal conduction loss or gain. The importance of compressibility shown in the present study would significantly impact on the prospects of successful MHD turbulence theory in the solar chromosphere.

  1. Closed Field Coronal Heating Models Inspired by Wave Turbulence

    NASA Astrophysics Data System (ADS)

    Downs, C.; Lionello, R.; Mikic, Z.; Linker, J.; Velli, M. M.

    2013-12-01

    To simulate the energy balance of coronal plasmas on macroscopic scales, we often require the specification of the coronal heating mechanism in some functional form. To go beyond empirical formulations and to build a more physically motivated heating function, we investigate the wave-turbulence dissipation (WTD) phenomenology for the heating of closed coronal loops. To do so, we employ an implementation of non-WKB equations designed to capture the large-scale propagation, reflection, and dissipation of wave turbulence along a loop. The parameter space of this model is explored by solving the coupled WTD and hydrodynamic equations in 1D for an idealized loop, and the relevance to a range of solar conditions is established by computing solutions for several hundred loops extracted from a realistic 3D coronal field. Due to the implicit dependence of the WTD heating model on loop geometry and plasma properties along the loop and at the footpoints, we find that this model can significantly reduce the number of free parameters when compared to traditional empirical heating models, and still robustly describe a broad range of quiet-sun and active region conditions. The importance of the self-reflection term in producing realistic heating scale heights and thermal non-equilibrium cycles is discussed, and preliminary 3D thermodynamic MHD simulations using this formulation are presented. Research supported by NASA and NSF.

  2. Quantifying the Significance of Substructure in Coronal Loops

    NASA Astrophysics Data System (ADS)

    McKeough, K. B. D.; Kashyap, V.; McKillop, S.

    2014-12-01

    A method to infer the presence of small-scale substructure in SDO/AIA (Atmospheric Imaging Assembly on the Solar Dynamics Observatory) images of coronal loops is developed. We can classify visible loop structure based on this propensity to show substructure which puts constraints on contemporary solutions to the coronal heating problem. The method uses the Bayesian algorithm Low-count Image Reconstruction and Analysis (LIRA) to infer the multi-scale component of the loops which describes deviations from a smooth model. The increase in contrast of features in this multi-scale component is determined using a statistic that estimates the sharpness across the image. Regions with significant substructure are determined using p-value upper bounds. We are able to locate substructure visible in Hi-C (High-Resolution Coronal Imager) data that are not salient features in the corresponding AIA image. Looking at coronal loops at different regions of the Sun (e.g., low-lying structure and loops in the upper corona) we are able to map where detectable substructure exists and thus the influence of the nanoflare heating process. We acknowledge support from AIA under contract SP02H1701R from Lockheed-Martin to SAO.

  3. Investigation of Coronal Large Scale Structures Utilizing Spartan 201 Data

    NASA Technical Reports Server (NTRS)

    Guhathakurta, Madhulika

    1998-01-01

    Two telescopes aboard Spartan 201, a small satellite has been launched from the Space Shuttles, on April 8th, 1993, September 8th, 1994, September 7th, 1995 and November 20th, 1997. The main objective of the mission was to answer some of the most fundamental unanswered questions of solar physics-What accelerates the solar wind and what heats the corona? The two telescopes are 1) Ultraviolet Coronal Spectrometer (UVCS) provided by the Smithsonian Astrophysical Observatory which uses ultraviolet emissions from neutral hydrogen and ions in the corona to determine velocities of the coronal plasma within the solar wind source region, and the temperature and density distributions of protons and 2) White Light Coronagraph (WLC) provided by NASA's Goddard Space Flight Center which measures visible light to determine the density distribution of coronal electrons within the same region. The PI has had the primary responsibility in the development and application of computer codes necessary for scientific data analysis activities, end instrument calibration for the white-light coronagraph for the entire Spartan mission. The PI was responsible for the science output from the WLC instrument. PI has also been involved in the investigation of coronal density distributions in large-scale structures by use of numerical models which are (mathematically) sufficient to reproduce the details of the observed brightness and polarized brightness distributions found in SPARTAN 201 data.

  4. Coronal Activity in the R CrA T Association

    NASA Technical Reports Server (NTRS)

    Patten, Brian M.; Oliversen, Ronald J. (Technical Monitor)

    2005-01-01

    Brian Patten is the Principal Investigator of the NASA ROSS-ADP project Coronal Activity in the R CrA T Association. For this project we have extracted net counts and variability information for all of the X-ray sources found in 23 archival ROSAT PSPC and HRI images in the region of the R CrA T association. These data have been merged with an extensive database of optical and near-infrared photometry, optical spectroscopy, and parallax data. These data have been used to (1) identify new association members and clarify the membership status of a number of previously suspected members of the association, and (2) derive, for the first time, an accurate coronal luminosity function for the T Tauri members of this T association and make direct comparisons between the coronal luminosity functions for other T associations and those of large clusters. We have used our survey data to assess (a) the importance of the star-formation environment in initial coronal activity levels, (b) the effects of PMS evolution on dynamo activity as a function of mass and age, and (c) the level of contamination by field post-T Tauri stars on association membership surveys.

  5. Preguntas y respuestas acerca del Estudio del

    Cancer.gov

    El Estudio del Tamoxifeno y Raloxifeno (STAR, por sus siglas en ingls) es un estudio clnico (un estudio de investigacin conducido con voluntarios) diseado para ver cómo el medicamento raloxifeno (Evista) se compara con el medicamento tamoxifeno (Nolvadex)

  6. Coronal shock acceleration and heliospheric transport of solar energetic protons

    NASA Astrophysics Data System (ADS)

    Kozarev, Kamen Asenov

    Solar flares and coronal mass ejections (CME) in the Sun's atmosphere produce highly energetic charged particles during violent bursts of activity. Protons, the most numerous and important species of these solar energetic particles (SEP), accelerate and propagate throughout the heliosphere, probing the interplanetary transport conditions. They also present a significant radiation hazard to space operations. Nevertheless, SEP acceleration in the low corona is currently not well constrained and poorly understood. In this dissertation, I examine off-limb extreme ultraviolet (EUV) wave dynamics between 1.3 and 2.0 solar radii in the corona, and I show that the EUV signatures are consistent with CME-driven shocks. Therefore, such shocks may form very low in the corona. I also develop a data-driven model for estimating the maximum energy to which protons may be accelerated in coronal shocks. I apply it to an observed shock and show that it may accelerate protons up to tens of MeV during its fast coronal passage, consistent with in-situ observations. To explore further coronal SEP acceleration by CME-driven shocks, I modify a global, 3D numerical model for interplanetary SEP transport for the coronal conditions, and adapt it to incorporate results from a realistic magnetohydrodynamic coronal and CME model. Furthermore, I apply a diffusive shock acceleration model, which explicitly treats proton energization at traveling shocks, to an MHD simulation of a real CME event. I find that the source population becomes strongly accelerated. In addition, I simulate the proton transport between the Sun and Earth, and find that the modeled fluxes are consistent with particle observations near Earth. Results suggest that CME-driven shocks in the corona may be the primary source of SEPs in solar storms. In addition, conditions along coronal shock fronts vary greatly, influencing the amount of acceleration. Finally, I model the global proton transport between Earth and 5 AU during a

  7. Jets and Plumes: What scale coronal phenomenal can be seen by SWEAP on Solar Probe Plus?

    NASA Astrophysics Data System (ADS)

    Korreck, Kelly E.; Case, Anthony; Kasper, Justin C.; Stevens, Michael L.; Whittlesey, Phyllis

    2016-05-01

    Coronal jets are reconnection events that are found most easily in coronal holes both polar and equatorial. Previous studies of coronal jets have associated the jets with microstream peaks in Ulysses solar wind data (Neugebauer, 2012 ). Plumes have been thought to contribute to both the slow and fast solar wind. Utilizing long-term studies of jets and plumes in x-ray and extreme ultraviolet coronal observations, we examine the signatures of these coronal features as seen in simulated Solar Probe Cup data. Simulated moment data representing density, velocity and temperature are created for the first Solar Probe Plus orbit.

  8. CME Interaction with Large-Scale Coronal Structures

    NASA Technical Reports Server (NTRS)

    Gopalswarny, Nat

    2012-01-01

    This talk presents some key observations that highlight the importance of CME interaction with other large scale structures such as CMEs and coronal holes . Such interactions depend on the phase of the solar cycle: during maximum, CMEs are ejected more frequently, so CME-CME interaction becomes dominant. During the rise phase, the polar coronal holes are strong, so the interaction between polar coronal holes and CMEs is important, which also leads to a possible increase in the number of interplanetary CMEs observed as magnetic clouds. During the declining phase, there are more equatorial coronal holes, so CMEs originating near these coronal holes are easily deflected. CMEs can be deflected toward and away from the Sun-Earth line resulting in interesting geospace consequences. For example, the largest geomagnetic storm of solar cycle 23 was due to a CME that was deflected towards the Sun-earth line from E22. CME deflection away from the Sun-Earth line diminishes the chance of a CME producing a geomagnetic storm. CME interaction in the coronagraphic field of view was first identified using enhanced radio emission, which is an indication of acceleration of low energy (approx.10 keV) electrons in the interaction site. CME interaction, therefore, may also have implications for proton acceleration. For example, solar energetic particle events typically occur with a higher intensity, whenever multiple CMEs occur in quick succession from the same source region. CME deflection may also have implications to the arrival of energetic particles to earth because magnetic connectivity may be changed by the interaction. I illustrate the above points using examples from SOHO, STEREO, Wind, and ACE data .

  9. Latitudinal Dependence of Coronal Hole-Associated Fast Solar Wind

    NASA Astrophysics Data System (ADS)

    Zhao, L.; Landi, E.

    2014-05-01

    The fast solar wind can have at least two different coronal sources: high-latitude, polar coronal holes (PCH) and low-latitude, equatorial coronal holes (ECH). The in-situ differences in the PCH and ECH winds have not been well studied, nor have the differences in their evolution over the solar cycles. Ulysses' 19 years of observations from 1990 to 2009, combined with ACE observations from 1998 to the present, provide us with measurements of solar wind properties that span two entire solar cycles, which allow us to study the in-situ properties and evolution of the coronal hole-associated solar wind at different latitudes. In this work, we focus on the PCH and ECH solar winds during the minima between solar cycles 22-23 and 23-24. We use data from SWICS, SWOOPS, and VHM/FGM on board Ulysses, and SWICS, SWEPAM, and MAG on board ACE to analyze the proton dynamics, heavy ion composition, elemental abundance, and magnetic field properties of the PCH wind and ECH wind, with a special focus on their differences during the recent two solar minima. We also include the slow and hot, streamer-associated (ST) wind as a reference in the comparison. The comparison of PCH and ECH wind shows that: 1) the in-situ properties of ECH and PCH winds are significantly different during the two solar minima, and 2) the two types of coronal hole-associated solar wind respond differently to changes in solar activity strength from cycle 23 to cycle 24.

  10. FAST CONTRACTION OF CORONAL LOOPS AT THE FLARE PEAK

    SciTech Connect

    Liu Rui; Wang Haimin

    2010-05-01

    On 2005 September 8, a coronal loop overlying the active region NOAA 10808 was observed in TRACE 171 A to contract at {approx}100 km s{sup -1} at the peak of an X5.4-2B flare at 21:05 UT. Prior to the fast contraction, the loop underwent a much slower contraction at {approx}6 km s{sup -1} for about 8 minutes, initiating during the flare preheating phase. The sudden switch to fast contraction is presumably corresponding to the onset of the impulsive phase. The contraction resulted in the oscillation of a group of loops located below, with the period of about 10 minutes. Meanwhile, the contracting loop exhibited a similar oscillatory pattern superimposed on the dominant downward motion. We suggest that the fast contraction reflects a suddenly reduced magnetic pressure underneath due either to (1) the eruption of magnetic structures located at lower altitudes or to (2) the rapid conversion of magnetic free energy in the flare core region. Electrons accelerated in the shrinking trap formed by the contracting loop can theoretically contribute to a late-phase hard X-ray burst, which is associated with Type IV radio emission. To complement the X5.4 flare which was probably confined, a similar event observed in SOHO/EIT 195 A on 2004 July 20 in an eruptive, M8.6 flare is briefly described, in which the contraction was followed by the expansion of the same loop leading up to a halo coronal mass ejection. These observations further substantiate the conjecture of coronal implosion and suggest coronal implosion as a new exciter mechanism for coronal loop oscillations.

  11. AGN coronal emission models - I. The predicted radio emission

    NASA Astrophysics Data System (ADS)

    Raginski, I.; Laor, Ari

    2016-06-01

    Accretion discs in active galactic nucleus (AGN) may be associated with coronal gas, as suggested by their X-ray emission. Stellar coronal emission includes radio emission, and AGN corona may also be a significant source for radio emission in radio quiet (RQ) AGN. We calculate the coronal properties required to produce the observed radio emission in RQ AGN, either from synchrotron emission of power-law (PL) electrons, or from cyclosynchrotron emission of hot mildly relativistic thermal electrons. We find that a flat spectrum, as observed in about half of RQ AGN, can be produced by corona with a disc or a spherical configuration, which extends from the innermost regions out to a pc scale. A spectral break to an optically thin power-law emission is expected around 300-1000 GHz, as the innermost corona becomes optically thin. In the case of thermal electrons, a sharp spectral cut-off is expected above the break. The position of the break can be measured with very long baseline interferometry observations, which exclude the cold dust emission, and it can be used to probe the properties of the innermost corona. Assuming equipartition of the coronal thermal energy density, the PL electrons energy density, and the magnetic field, we find that the energy density in a disc corona should scale as ˜R-1.3, to get a flat spectrum. In the spherical case the energy density scales as ˜R-2, and is ˜4 × 10-4 of the AGN radiation energy density. In Paper II we derive additional constraints on the coronal parameters from the Gudel-Benz relation, Lradio/LX-ray ˜ 10- 5, which RQ AGN follow.

  12. Dichotomy of Solar Coronal Jets: Standard Jets and Blowout Jets

    NASA Technical Reports Server (NTRS)

    Moore, R. L.; Cirtain, J. W.; Sterling, A. C.; Falconer, D. A.

    2010-01-01

    By examining many X-ray jets in Hinode/XRT coronal X-ray movies of the polar coronal holes, we found that there is a dichotomy of polar X-ray jets. About two thirds fit the standard reconnection picture for coronal jets, and about one third are another type. We present observations indicating that the non-standard jets are counterparts of erupting-loop H alpha macrospicules, jets in which the jet-base magnetic arch undergoes a miniature version of the blowout eruptions that produce major CMEs. From the coronal X-ray movies we present in detail two typical standard X-ray jets and two typical blowout X-ray jets that were also caught in He II 304 Angstrom snapshots from STEREO/EUVI. The distinguishing features of blowout X-ray jets are (1) X-ray brightening inside the base arch in addition to the outside bright point that standard jets have, (2) blowout eruption of the base arch's core field, often carrying a filament of cool (T 10(exp 4) - 10(exp 5) K) plasma, and (3) an extra jet-spire strand rooted close to the bright point. We present cartoons showing how reconnection during blowout eruption of the base arch could produce the observed features of blowout X-ray jets. We infer that (1) the standard-jet/blowout-jet dichotomy of coronal jets results from the dichotomy of base arches that do not have and base arches that do have enough shear and twist to erupt open, and (2) there is a large class of spicules that are standard jets and a comparably large class of spicules that are blowout jets.

  13. Towards a Data-Optimized Coronal Magnetic Field Model (DOC-FM): statistical method for diagnosing the coronal magnetic field

    NASA Astrophysics Data System (ADS)

    Dalmasse, Kevin; Nychka, Doug; Gibson, Sarah; Fan, Yuhong; Flyer, Natasha

    2016-05-01

    Knowing the 3D coronal magnetic field prior to the trigger of a CME is one of the key features for predicting their geomagnetic effect. Since the magnetic field is essentially measured at the photosphere, one must rely on reconstruction models to obtain the 3D magnetic field in the corona. Hence, obtaining an accurate model of the real 3D coronal magnetic field is one of the cornerstones for precise Space Weather Forecasting. In this work, we propose a new method for data-constrained reconstruction of the 3D coronal magnetic field. Model-data fitting is achieved by optimizing a user-specified log-likelihood, quantifying the difference between a dataset (including e.g. polarization, extreme-ultraviolet emission, X-ray emission) and its synthetic analogue. The synthetic data is produced by forward calculations applied to a 3D magnetic model that depends upon a finite set of parameters. After introducing the method, we present its validation on a synthetic test bed consisting of a coronal magnetic flux rope assumed to depend on three parameters, i.e. latitude, longitude, and tilt angle. A specific value of each parameter is used to generate a ground truth and the corresponding synthetic data. We show that our method performs well and the best-fit parameters provide a good approximation of the ground-truth parameters. We discuss future plans for validation and application of our method to solar observations.

  14. The Relation between Coronal Holes and Coronal Mass Ejections during the Rise, Maximum, and Declining Phases of Solar Cycle 23

    NASA Technical Reports Server (NTRS)

    Mohamed, A. A.; Gopalswamy, N; Yashiro, S.; Akiyama, S.; Makela, P.; Xie, H.; Jung, H.

    2012-01-01

    We study the interaction between coronal holes (CHs) and coronal mass ejections (CMEs) using a resultant force exerted by all the coronal holes present on the disk and is defined as the coronal hole influence parameter (CHIP). The CHIP magnitude for each CH depends on the CH area, the distance between the CH centroid and the eruption region, and the average magnetic field within the CH at the photospheric level. The CHIP direction for each CH points from the CH centroid to the eruption region. We focus on Solar Cycle 23 CMEs originating from the disk center of the Sun (central meridian distance =15deg) and resulting in magnetic clouds (MCs) and non-MCs in the solar wind. The CHIP is found to be the smallest during the rise phase for MCs and non-MCs. The maximum phase has the largest CHIP value (2.9 G) for non-MCs. The CHIP is the largest (5.8 G) for driverless (DL) shocks, which are shocks at 1 AU with no discernible MC or non-MC. These results suggest that the behavior of non-MCs is similar to that of the DL shocks and different from that of MCs. In other words, the CHs may deflect the CMEs away from the Sun-Earth line and force them to behave like limb CMEs with DL shocks. This finding supports the idea that all CMEs may be flux ropes if viewed from an appropriate vantage point.

  15. Hanle Effect Diagnostics of the Coronal Magnetic Field: A Test Using Realistic Magnetic Field Configurations

    NASA Astrophysics Data System (ADS)

    Raouafi, N.-E.; Solanki, S. K.; Wiegelmann, T.

    2009-06-01

    Our understanding of coronal phenomena, such as coronal plasma thermodynamics, faces a major handicap caused by missing coronal magnetic field measurements. Several lines in the UV wavelength range present suitable sensitivity to determine the coronal magnetic field via the Hanle effect. The latter is a largely unexplored diagnostic of coronal magnetic fields with a very high potential. Here we study the magnitude of the Hanle-effect signal to be expected outside the solar limb due to the Hanle effect in polarized radiation from the H I Lyα and β lines, which are among the brightest lines in the off-limb coronal FUV spectrum. For this purpose we use a magnetic field structure obtained by extrapolating the magnetic field starting from photospheric magnetograms. The diagnostic potential of these lines for determining the coronal magnetic field, as well as their limitations are studied. We show that these lines, in particular H I Lyβ, are useful for such measurements.

  16. IMPULSIVE ACCELERATION OF CORONAL MASS EJECTIONS. I. STATISTICS AND CORONAL MASS EJECTION SOURCE REGION CHARACTERISTICS

    SciTech Connect

    Bein, B. M.; Berkebile-Stoiser, S.; Veronig, A. M.; Temmer, M.; Muhr, N.; Kienreich, I.; Utz, D.

    2011-09-10

    We use high time cadence images acquired by the STEREO EUVI and COR instruments to study the evolution of coronal mass ejections (CMEs) from their initiation through impulsive acceleration to the propagation phase. For a set of 95 CMEs we derived detailed height, velocity, and acceleration profiles and statistically analyzed characteristic CME parameters: peak acceleration, peak velocity, acceleration duration, initiation height, height at peak velocity, height at peak acceleration, and size of the CME source region. The CME peak accelerations we derived range from 20 to 6800 m s{sup -2} and are inversely correlated with the acceleration duration and the height at peak acceleration. Seventy-four percent of the events reach their peak acceleration at heights below 0.5 R{sub sun}. CMEs that originate from compact sources low in the corona are more impulsive and reach higher peak accelerations at smaller heights. These findings can be explained by the Lorentz force, which drives the CME accelerations and decreases with height and CME size.

  17. Coronal Outflow Velocities in a 3D Coronal Model Determined from UVCS Doppler Dimming Observations

    NASA Astrophysics Data System (ADS)

    Strachan, L.; Panasyuk, A. V.; Dobrzycka, D.; Gibson, S.; Biesecker, D. A.; Ko, Y.-K.; Galvin, A. B.; Romoli, M.; Kohn, J. L.

    1998-04-01

    We constrain coronal outflow velocity solutions, resolved along the line-of-sight, by using Doppler dimming models of H I Lyman alpha and O VI 1032/1037 Angstrom emissivities obtained with data from the Ultraviolet Coronagraph Spectrometer (UVCS) on SOHO. The local emissivities, from heliocentric heights of 1.5 to 3.0 radii, were determined from 3-D reconstructions of line-of-sight intensities obtained during the Whole Sun Month Campaign (10 Aug. -- 8 Sep. 1996). The models use electron densities derived from polarized brightness measurements made with the visible light coronagraphs on UVCS and LASCO, supplemented with data from Mark III at NCAR/MLSO. Electron temperature profiles are derived from `freezing-in' temperatures obtained from an analysis of charge state data from SWICS/Ulysses. The work concentrates on O5+ outflow velocities which are determined from an analysis of the the O VI line ratios. This analysis is less sensitive to the uncertainties in the electron density and independent of the ionization balance and elemental abundance than the analyses which use individual spectral lines. This work is supported in part by NASA under grant NAG-3192 to the Smithsonian Astrophysical Observatory, by the Italian Space Agency and by Swiss funding agencies.

  18. Physical Conditions of Coronal Plasma at the Transit of a Shock Driven by a Coronal Mass Ejection

    NASA Astrophysics Data System (ADS)

    Susino, R.; Bemporad, A.; Mancuso, S.

    2015-10-01

    We report here on the determination of plasma physical parameters across a shock driven by a coronal mass ejection using white light (WL) coronagraphic images and radio dynamic spectra (RDS). The event analyzed here is the spectacular eruption that occurred on 2011 June 7, a fast CME followed by the ejection of columns of chromospheric plasma, part of them falling back to the solar surface, associated with a M2.5 flare and a type-II radio burst. Images acquired by the Solar and Heliospheric Observatory/LASCO coronagraphs (C2 and C3) were employed to track the CME-driven shock in the corona between 2-12 R⊙ in an angular interval of about 110°. In this interval we derived two-dimensional (2D) maps of electron density, shock velocity, and shock compression ratio, and we measured the shock inclination angle with respect to the radial direction. Under plausible assumptions, these quantities were used to infer 2D maps of shock Mach number MA and strength of coronal magnetic fields at the shock's heights. We found that in the early phases (2-4 R⊙) the whole shock surface is super-Alfvénic, while later on (i.e., higher up) it becomes super-Alfvénic only at the nose. This is in agreement with the location for the source of the observed type-II burst, as inferred from RDS combined with the shock kinematic and coronal densities derived from WL. For the first time, a coronal shock is used to derive a 2D map of the coronal magnetic field strength over intervals of 10 R⊙ altitude and ˜110° latitude.

  19. Deriving the Coronal Magnetic Field Using Parametric Transformation Analysis

    NASA Technical Reports Server (NTRS)

    Gary, G. Allen; Rose, M. Franklin (Technical Monitor)

    2001-01-01

    When plasma-beta greater than 1 then the gas pressure dominates over the magnetic pressure. This ratio as a function along the coronal magnetic field lines varies from beta greater than 1 in the photosphere at the base of the field lines, to beta much less than 1 in the mid-corona, to beta greater than 1 in the upper corona. Almost all magnetic field extrapolations do not or cannot take into account the full range of beta. They essentially assume beta much less than 1, since the full boundary conditions do not exist in the beta greater than 1 regions. We use a basic parametric representation of the magnetic field lines such that the field lines can be manipulated to match linear features in the EUV and SXR coronal images in a least squares sense. This research employs free-form deformation mathematics to generate the associated coronal magnetic field. In our research program, the complex magnetic field topology uses Parametric Transformation Analysis (PTA) which is a new and innovative method to describe the coronal fields that we are developing. In this technique the field lines can be viewed as being embedded in a plastic medium, the frozen-in-field-line concept. As the medium is deformed the field lines are similarly deformed. However the advantage of the PTA method is that the field line movement represents a transformation of one magnetic field solution into another magnetic field solution. When fully implemented, this method will allow the resulting magnetic field solution to fully match the magnetic field lines with EUV/SXR coronal loops by minimizing the differences in direction and dispersion of a collection of PTA magnetic field lines and observed field lines. The derived magnetic field will then allow beta greater than 1 regions to be included, the electric currents to be calculated, and the Lorentz force to be determined. The advantage of this technique is that the solution is: (1) independent of the upper and side boundary conditions, (2) allows non

  20. Standing sausage modes in coronal loops with plasma flow

    NASA Astrophysics Data System (ADS)

    Li, Bo; Chen, Shao-Xia; Xia, Li-Dong; Yu, Hui

    2014-08-01

    Context. Magnetohydrodynamic waves are important for diagnosing the physical parameters of coronal plasmas. Field-aligned flows appear frequently in coronal loops. Aims: We examine the effects of transverse density and plasma flow structuring on standing sausage modes trapped in coronal loops, and examine their observational implications in the context of coronal seismology. Methods: We model coronal loops as straight cold cylinders with plasma flow embedded in a static corona. An eigen-value problem governing propagating sausage waves is formulated and its solutions are employed to construct standing modes. Two transverse profiles are distinguished, and are called profiles E and N. A parameter study is performed on the dependence of the maximum period Pmax and cutoff length-to-radius ratio (L/a)cutoff in the trapped regime on the density parameters (ρ0/ρ∞ and profile steepness p) and the flow parameters (its magnitude U0 and profile steepness u). Results: For either profile, introducing a flow reduces Pmax obtainable in the trapped regime relative to the static case. The value of Pmax is sensitive to p for profile N, but is insensitive to p for profile E. By far the most important effect a flow introduces is to reduce the capability for loops to trap standing sausage modes: (L/a)cutoff may be substantially reduced in the case with flow relative to the static one. In addition, (L/a)cutoff is smaller for a stronger flow, and for a steeper flow profile when the flow magnitude is fixed. Conclusions: If the density distribution can be described by profile N, then measuring the sausage mode period can help deduce the density profile steepness. However, this practice is not feasible if profile E more accurately describes the density distribution. Furthermore, even field-aligned flows with magnitudes substantially smaller than the ambient Alfvén speed can make coronal loops considerably less likely to support trapped standing sausage modes. Appendix A is available in

  1. Coronal Abundance Anomalies in Solar-Like Stars

    NASA Astrophysics Data System (ADS)

    Laming, John

    We propose to model the trend of coronal abundance anomalies observed in a sample of solar-like stars by Wood & Linsky (2010). Dwarf stars of similar spectral type to the Sun show what has become known as a FIP (First Ionization Potential) Effect, where elements with first ionization potential below about 10 eV are enhanced in abundance in the corona by a factor of about 3 - 4. Stars of later spectral type show a diminished FIP effect, with the anomaly disappearing at about K5 spectral type. Beyond this, M dwarf stars show an inverse FIP effect, with the low FIP ions becoming depleted in the stellar corona, by factors of order 2.5 - 3. The solar case of positive FIP effect has been successfully interpreted as being due to the action of the ponderomotive force associated with chromospheric Alfven waves. In conditions in which upgoing Alfven waves are transmitted into coronal loops, or in which coronally generated waves reflect at loop footpoints, the ponderomotive force is directed upwards, and accelerates chromospheric ions (the low FIP elements) into the corona. Neutral atoms are not affected. The inverse FIP effect can arise when upward propagating chromospheric Alfven waves are reflected back down again at coronal loop footpoints, due to a mismatch between the wave frequency and the loop resonance. We propose to study stars for which parameters like asteroseismic oscillation frequencies, coronal abundance anomalies, and chromospheric structure are known. As well as constraining coronal magnetic fields and loop resonances in these stars, we expect important insights into the nature of stellar dynamos since the M dwarfs in the sample (with inverse FIP effect) are at or near the fully convective limit. Finally, we will be able to assess potential fractionation in the O/Ne abundance ratio. Drake & Testa (2005) argued that Ne is depleted in the solar corona relative to O, but not in the coronae of more active stars. Our FIP models provide some support for this in the

  2. Coronal/Hemicoronal Approach – A Gateway to Craniomaxillofacial Region

    PubMed Central

    Tauro, David; Bagulkar, Bhupesh; Vyas, Anuj

    2015-01-01

    Aims The coronal incision with its various modifications provides the most versatile approach to various areas in the craniomaxillofacial region coupled with excellent exposure. The aesthetic advantage of a hidden scar in the hairline, accounts for its continued popularity. The aim of this study was to review the surgical anatomy, technique and problems of post-operative morbidity pertinent to coronal approach in various clinical situations such as craniofacial trauma, tumour resections and reconstructive craniofacial procedures. Materials and Methods In this study, ten patients who presented to Oral and maxillofacial surgery department with various craniofacial problems requiring the use of coronal and hemicoronal approach for treatment were evaluated over a period of two years. Five patients needed coronal approach and another five underwent the surgical procedures through hemicoronal approach. This was an observational study. Results It was observed that a well-planned and carefully designed coronal/hemicoronal incision with strict adherence to surgical principles posed minimal complication during surgery as well as post-operatively. None of the patients developed infection or heamatoma in the postoperative period. Sensory nerve deficits along the distribution of supraorbital nerve was observed in four patients of bicoronal approach and three patients of hemicoronal approach which completely resolved at the end of six months. Motor nerve weakness was observed in four patients in immediate postoperative period which gradually improved. But it persisted in one patient even after six months who had pathology of temporo-orbital region. All the patients had transient alopecia along the line of incision which improved at the end of six months. No other significant disadvantages or complications were noted. Conclusion This approach offers widest accessibility and visibility to the entire upper and middle one third of the face in less than twenty minutes as observed in

  3. Coronal Faraday Rotation Observations: Measurements and Limits on Plasma Inhomogeneities

    NASA Astrophysics Data System (ADS)

    Mancuso, Salvatore; Spangler, Steven R.

    1999-11-01

    We report Faraday rotation measurements of the extended radio galaxy J0039+0319 (4C+03.01) seen through the solar corona when the source was at an average distance of 8.6 Rsolar from the center of the Sun. Nearly continuous polarimetric observations were made over an 11 hour period on 1997 March 28 with the NRAO Very Large Array at frequencies of 1465 and 1635 MHz. The observations were made near solar minimum conditions. Observations of radio galaxies have two advantages with respect to spacecraft transmitter signals. (1) The λ2 dependence of the polarization position angle expected of Faraday rotation can be verified. (2) Observations of spatially extended radio galaxies have the potential of directly measuring the propagation speed of coronal MHD irregularities. With the use of observations made when the source was far from the Sun, we measure an average rotation measure of +6.2+/-1.0 rad m-2 attributable to the corona. A rotation-measure time series was obtained for the most polarized component of the source. This rotation-measure time series showed slow variations during the observing session, with a total change of about 3 rad m-2. This variation is attributed to large-scale gradients and static plasma structures in the corona. We also obtain a weak detection of rotation-measure fluctuations on timescales of 15 minutes to 1 hour, which may be due to coronal Alfvén waves. This fluctuating component of the coronal rotation measure has an rms value <=0.40 rad m-2, comparable to previously reported detections. This measurement is then used to place model-dependent upper limits to the Alfvén wave flux at the coronal base. Depending on the precise geometry of the solar wind flow from the coronal base to 8.6 Rsolar, the inferred wave flux at the coronal base ranges from 2.4×104 to 2.3×105 ergs s-1 cm-2. These values range from slightly below to more than an order of magnitude below the wave flux needed to heat and accelerate the solar wind to its observed

  4. Gradual Inflation of Coronal Arcades Building up to Coronal Mass Ejections

    NASA Astrophysics Data System (ADS)

    Liu, Rui; Liu, C.; Park, S.; Wang, H.

    2010-05-01

    The pre-CME structure is of great importance to understanding the origin of CMEs, which, however, has been largely unknown for CMEs originating from active regions. In this presentation, we investigate this issue using the wavelet-enhanced EUV Imaging Telescope observations combined with the Large Angle and Spectrometric Coronagraph, Michelson Doppler Imager, and GOES soft X-ray observations. Two types of active-region coronal arcades whose gradual inflation may build up to CMEs are identified, namely, post-eruptive arcades and overlying arcades. The observed inflation of 16 selected events sustains for 8.7 +/- 4.1 hours, with the arcade rising from 1.15 +/- 0.06 to 1.36 +/- 0.07 solar radii at a speed of less than 5 km/s, which eventually blast up as a CME similar in morphology to the pre-CME arcade. For the 4 events that were observed on the disk, it is found that the gradual inflation of the arcade is temporally associated with the helicity injection from photosphere. This pre-CME structure is apparently unaffected by the flares occurring during its quasi-static inflation phase, but is closely coupled with the flare occurring during its acceleration phase. In particular, a swirling structure, which is reminiscent of a magnetic flux rope, was observed in one of the arcades over 4 hrs prior to the subsequent CME, and the growth of the arcade is temporally associated with the injection of helicity of opposite sense into the active region via flux emergence. We propose a four-phase evolution paradigm for the observed CMEs, i.e., a quasi-static inflation phase which corresponds to the buildup of magnetic free energy in the corona, followed by the frequently observed three-phase paradigm, including an initial phase, an acceleration phase and a gradual phase.

  5. Solar wind flow upstream of the coronal slow shock

    NASA Technical Reports Server (NTRS)

    Whang, Y. C.

    1986-01-01

    Slow shocks have been predicted to exist embedded in large coronal holes at low altitude. Two or more curved slow shocks may link together to form a composite discontinuity surface around the sun which may be called the coronal slow shock (CSS). Here a solar-wind model is studied under the assumption that a standing CSS exists and cororates with the sun at a constant angular velocity. A steady, axisymmetrical one-fluid model is introduced to study the expansion of solar wind in the open-field region upstream of the CSS. The model requires that the conditions downstream of the CSS near the equatorial plane can produce a solar wind agreeable with the observations made near the earth's orbit. The paper presents an illustrative calculation in which the polar caps within 60 deg of the polar angle are assumed to be the source region of the solar wind.

  6. Stellar activity and coronal heating: an overview of recent results.

    PubMed

    Testa, Paola; Saar, Steven H; Drake, Jeremy J

    2015-05-28

    Observations of the coronae of the Sun and of solar-like stars provide complementary information to advance our understanding of stellar magnetic activity, and of the processes leading to the heating of their outer atmospheres. While solar observations allow us to study the corona at high spatial and temporal resolution, the study of stellar coronae allows us to probe stellar activity over a wide range of ages and stellar parameters. Stellar studies therefore provide us with additional tools for understanding coronal heating processes, as well as the long-term evolution of solar X-ray activity. We discuss how recent studies of stellar magnetic fields and coronae contribute to our understanding of the phenomenon of activity and coronal heating in late-type stars. PMID:25897087

  7. Modeling of transient disturbances in coronal-streamer configurations

    NASA Technical Reports Server (NTRS)

    Steinolfson, R. S.

    1983-01-01

    Numerical simulations of the formation and propagation of mass ejection, loop transients in coronal streamers are discussed. The simulations are accomplished with numerical solutions of the single fluid, ideal MHD equations of motion in the meridional plane. The streamer is produced by simulating the relaxation of an initially radial hydrodynamic flow coupled with a dipole magnetic field. The simulated transient then results from an energy release at the base of the streamer. The legs of the loop transient produced remain essentially stationary while the loop expands mainly in the radial direction with velocities of 400 to 750 km s-1. Once the leading edge of the transient has passed out of the lower corona, the initial streamer configuration is restored after 15 to 24 hours. A second energy release 2 hours later than, and with an energy release identical to, the first does not produce a significant coronal disturbance.

  8. Shear-induced inflation of coronal magnetic fields

    NASA Technical Reports Server (NTRS)

    Klimchuk, James A.

    1990-01-01

    Using numerical models of force-free magnetic fields, the shearing of footprints in arcade geometries leading to an inflation of the coronal magnetic field was examined. For each of the shear profiles considered, all of the field lines become elevated compared with the potential field. This includes cases where the shear is concentrated well away from the arcade axis, such that B(sub z), the component of field parallel to the axis, increases outward to produce an inward B(sub z) squared/8 pi magnetic pressure gradient force. These results contrast with an earlier claim, shown to be incorrect, that field lines can sometimes become depressed as a result of shear. It is conjectured that an inflation of the entire field will always result from the shearing of simple arcade configurations. These results have implications for prominence formation, the interplanetary magnetic flux, and possibly also coronal holes.

  9. Shear-induced inflation of coronal magnetic fields

    NASA Technical Reports Server (NTRS)

    Klimchuk, James A.

    1989-01-01

    Using numerical models of force-free magnetic fields, the shearing of footprints in arcade geometries leading to an inflation of the coronal magnetic field was examined. For each of the shear profiles considered, all of the field lines become elevated compared with the potential field. This includes cases where the shear is concentrated well away from the arcade axis, such that B(sub z), the component of field parallel to the axis, increases outward to produce an inward B(sub z)squared/8 pi magnetic pressure gradient force. These results contrast with an earlier claim, shown to be incorrect, that field lines can sometimes become depressed as a result of shear. It is conjectured that an inflation of the entire field will always result from the shearing of simple arcade configurations. These results have implications for prominence formation, the interplanetary magnetic flux, and possibly also coronal holes.

  10. Three-dimensional reconstruction of coronal mass ejections

    NASA Technical Reports Server (NTRS)

    Jackson, Bernard V.; Hick, Paul

    1994-01-01

    Computer assisted tomography (CAT) techniques are used to reconstruct the three dimensional shape of coronal mass ejections in the interplanetary medium. Both the Helios 2 spacecraft zodiacal-light photometers and the Solwind coronograph measure changes in Thomson scattering of sunlight from electrons. The technique from near-perpendicular Solwind and Helios views are applied to determine the density of a mass ejection which left the solar surface on 24 May 1979. The coronograph and the Helios perspective views are not simultaneous; the Solwind observations extend outward to sky plane distances of only 10 of the solar radius, whereas the Helios 16 photometer observes to as close as 17 of the solar radius from the sun. The solution is obtained by assuming outward radial expansion and that the coronal mass ejections (CME's) have the same speed everywhere at the same height. The analyses show that CME's are extensive three dimensional structures (the CME of 24 May appears approximately shell) like in three dimensions.

  11. Coronal plasmas on the sun and nearby stars

    NASA Technical Reports Server (NTRS)

    Lang, Kenneth R.

    1986-01-01

    The current understanding of the quiescent, or non-flaring, microwave emission from solar active regions is summarized. The thermal radiation mechanisms that account for most of the quiescent emission is reviewed, while it is also pointed out that current-amplified magnetic fields or non-thermal radiation may be required in some instances. The 20 cm radiation of coronal loops and the thermal cyclotron lines that accurately specify their magnetic field strength are discussed. The 20 cm and X ray emission of the coronal plasma are then compared. The coronae of nearby stars is next discussed, where coherent radiation processes seem to prevail. Some thoughts toward directions for future exploration are given.

  12. Signatures of Nonlinear Waves in Coronal Plumes and Holes

    NASA Technical Reports Server (NTRS)

    Ofman, Leon

    1999-01-01

    In recent Ultraviolet Coronagraph Spectrometer/Solar and Heliospheric Observatory (UVCS/SOHO) White Light Channel (WLC) observations we found quasi-periodic variations in the polarized brightness (pB) in the polar coronal holes at heliocentric distances of 1.9-2.45 solar radii. The motivation for the observation is the 2.5D Magnetohydrodynamics (MHD) model of solar wind acceleration by nonlinear waves, that predicts compressive fluctuations in coronal holes. To help identify the waves observed with the UVCS/WLC we model the propagation and dissipation of slow magnetosonic waves in polar plumes using 1D MHD code in spherical geometry, We find that the slow waves nonlinearly steepen in the gravitationally stratified plumes. The nonlinear steepening of the waves leads to enhanced dissipation due to compressive viscosity at the wave-fronts.

  13. A Survey of Interplanetary Coronal Mass Ejections During 1996 - 2007

    NASA Technical Reports Server (NTRS)

    Richardson, Ian; Cane, Hilary

    2007-01-01

    Interplanetary coronal mass ejections, the interplanetary counterparts of coronal mass ejections at the Sun, are the major drivers of interplanetary shocks in the heliosphere, and are associated with modulations of the galactic cosmic ray intensity, both short term (Forbush decreases caused by the passage of the shock, post-shock sheath, and ICME) and possibly with longer term modulation. Using several in-situ signatures of ICMEs, including plasma temperature, and composition, magnetic fields, and cosmic ray modulations, made by near-Earth spacecraft, we have compiled a "comprehensive" list of ICMEs passing the Earth since 1996, encompassing solar cycle 23. We summarize the properties of these ICMEs, such as their occurrence rate, speeds, association with solar energetic particle events, shocks and cosmic ray decreases.

  14. Radio and white-light observations of coronal transients

    NASA Technical Reports Server (NTRS)

    Dulk, G. A.

    1980-01-01

    Optical, radio and X-ray evidence of violent mass motions in the corona has existed for some years but only recently have the form, nature, frequency and implication of the transients become obvious. In this paper the observed properties of coronal transients are reviewed, with concentration on the white-light and radio manifestations. The classification according to speeds seems to be meaningful, with the slow transients having thermal emissions at radio wavelengths and the fast ones nonthermal. The possible mechanisms involved in the radio bursts are then discussed and estimates of various forms of energy are reviewed. It appears that the magnetic energy transported from the sun by the transient exceeds that of any other form, and that magnetic forces dominate in the dynamics of the motions. The conversion of magnetic energy into mechanical energy, by expansion of the field, provides a possible driving force for the coronal and interplanetary shock waves.

  15. Stellar activity and coronal heating: an overview of recent results

    PubMed Central

    Testa, Paola; Saar, Steven H.; Drake, Jeremy J.

    2015-01-01

    Observations of the coronae of the Sun and of solar-like stars provide complementary information to advance our understanding of stellar magnetic activity, and of the processes leading to the heating of their outer atmospheres. While solar observations allow us to study the corona at high spatial and temporal resolution, the study of stellar coronae allows us to probe stellar activity over a wide range of ages and stellar parameters. Stellar studies therefore provide us with additional tools for understanding coronal heating processes, as well as the long-term evolution of solar X-ray activity. We discuss how recent studies of stellar magnetic fields and coronae contribute to our understanding of the phenomenon of activity and coronal heating in late-type stars. PMID:25897087

  16. On the thermal stability of coronal loop plasma

    NASA Technical Reports Server (NTRS)

    Antiochos, S. K.; Emslie, A. G.; Shoub, E. C.; An, C. H.

    1982-01-01

    The stability to thermal perturbation of static models of coronal loops is considered including the effects of cool, radiatively stable material at the loop base. The linear stability turns out to be sensitive only to the boundary conditions assumed on the velocity at the loop base. The question of the appropriate boundary conditions is discussed, and it is concluded that the free surface condition (the pressure perturbation vanishes), rather than the rigid wall (the velocity vanishes), is relevant to the solar case. The static models are found to be thermally unstable, with a growth time of the order of the coronal cooking time. The physical implications of these results for the solar corona and transition region are examined.

  17. Coronal sources of the intrastream structure of the solar wind

    NASA Technical Reports Server (NTRS)

    Sullivan, J. D.; Bridge, H. S.

    1983-01-01

    Short time scale changes in the bulk speed were found not to coincide with X-ray transients near the sub-earth point nor with the number of X-ray bright points within a coronal hole and near the equator. The changes in bulk speed, it is shown, are associated with changes in light areas in a hole which may be associated with the opening or closing of magnetic field lines within the coronal hole. That there is a causal connection between these sudden changes (apperance or disappearance) in light area and sudden changes in the bulk speed of the solar wind is further evidenced by the spatial proximity on the Sun of these changing light regions to the source position of stream lines from Levine's model that connect into the same solar wind streams.

  18. Coronal Rotation at Solar Minimum from UV Observations

    NASA Technical Reports Server (NTRS)

    Mancuso, S.

    2008-01-01

    UVCS/SOHO observations have been analyzed to reconstruct intensity time series of the O VI 1032 A and H 11216 A spectral lines at different coronal heliolatitudes from 1.5 to 3.0 solar radii from Sun center. Evidence was found for coronal differential rotation that differs significantly from that of the photospheric plasma. The study of the latitudinal variation shows that the UV corona decelerates toward the photospheric rates from the equator up to the poleward boundary 2 of the midlatitude streamers, reaching a peak of 28.16+/-0.20 days around +30 from the equator at 1.5 solar radii, while a less evident peak is observed in the northern hemisphere. This result suggests a real north-south rotational asymmetry as a consequence of different activity and weak coupling between the magnetic fields of the two hemispheres. The study of the radial rotation profiles shows that the corona is rotating almost rigidly with height.

  19. Magnetic helicity as a constraint on coronal dissipation

    NASA Technical Reports Server (NTRS)

    Choudhuri, Arnab Rai

    1986-01-01

    The Taylor hypothesis has provided a model for the relaxed magnetic configurations of not only laboratory plasmas, but also of astrophysical plasmas. However, energy dissipation is possible only for systems which depart from a strict Taylor state, and hence a parameter describing that departure must be introduced, when the Taylor hypothesis is used to estimate the dissipation. An application of the Taylor hypothesis to the problem of coronal heating provides an insight into this difficult problem. When particular sorts of footpoint motions put energy and helicity in the corona, the conservation of helicity puts a constraint on how much of the energy can be dissipated. However, on considering a random distribution of footpoint motions, this constraint gets washed away, and the Taylor hypothesis is probably not going to play any significant role in the actual calculation of relevant physical quantities in the coronal heating problem.

  20. Coronal Streamers and Their Associated Solar Wind Streams

    NASA Astrophysics Data System (ADS)

    Miralles, M. P.; Landi, E.; Cranmer, S. R.; Cohen, O.; Raymond, J. C.

    2012-12-01

    We use the EUV spectrometers aboard SOHO and Hinode and white-light coronagraphs to characterize the physical properties of coronal streamers during Earth/Ulysses quadrature configurations for the previous two solar minimum periods. In addition, comparisons between coronal observations and in situ measurements of solar wind plasma properties are being used to further characterize the origins of slow wind streams. In order to investigate slow solar wind heating and acceleration, we also compare with predictions from three-dimensional MHD models. We aim to use the empirical measurements to distinguish between different proposed physical processes for slow wind acceleration (e.g., waves/turbulence versus reconnection). This work is supported by NASA grant NNX10AQ58G to the Smithsonian Astrophysical Observatory.

  1. Spectroscopic Capabilities of XMM for Stellar Coronal Studies

    NASA Astrophysics Data System (ADS)

    Pallavicini, R.

    The turn of the millennium will be a marvelous time for X-ray astronomy with the launch of powerful missions such as AXAF, XMM, and ASTRO-E. Stellar coronae, with their spectra rich in emission lines, will be primary targets to exploit the spectroscopic capabilities of these missions. In particular, the CCD cameras and reflection gratings on XMM will allow us to address a number of key questions in stellar coronal physics. The capabilities of XMM for the study of stellar coronae are illustrated by means of simulations of EPIC and RGS spectra for a variety of typical stellar coronal sources. The mission time-line and the policy for accessing the data are also briefly illustrated.

  2. Role of Coronal Mass Ejections in the Heliospheric Hale Cycle

    NASA Technical Reports Server (NTRS)

    Owens, M. J.; Schwardron, N. A.; Crooker, N. U.; Hughes, W. J.; Spence, H. E.

    2007-01-01

    The 11-year solar cycle variation in the heliospheric magnetic field strength can be explained by the temporary buildup of closed flux released by coronal mass ejections (CMEs). If this explanation is correct, and the total open magnetic flux is conserved, then the interplanetary-CME closed flux must eventually open via reconnection with open flux close to the Sun. In this case each CME will move the reconnected open flux by at least the CME footpoint separation distance. Since the polarity of CME footpoints tends to follow a pattern similar to the Hale cycle of sunspot polarity, repeated CME eruption and subsequent reconnection will naturally result in latitudinal transport of open solar flux. We demonstrate how this process can reverse the coronal and heliospheric fields, and we calculate that the amount of flux involved is sufficient to accomplish the reversal within the 11 years of the solar cycle.

  3. A model for radio emission from solar coronal shocks

    SciTech Connect

    Zhao, G. Q.; Chen, L.; Wu, D. J.

    2014-05-01

    Solar coronal shocks are very common phenomena in the solar atmosphere and are believed to be the drivers of solar type II radio bursts. However, the microphysical nature of these emissions is still an open question. This paper proposes that electron cyclotron maser (ECM) emission is responsible for the generation of radiation from the coronal shocks. In the present model, an energetic ion beam accelerated by the shock first excites the Alfvén wave (AW), then the excited AW leads to the formation of a density-depleted duct along the foreshock boundary of the shock. In this density-depleted duct, the energetic electron beam produced via the shock acceleration can effectively excite radio emission by ECM instability. Our results show that this model may potentially be applied to solar type II radio bursts.

  4. Energetic characterisation and statistics of solar coronal brightenings

    NASA Astrophysics Data System (ADS)

    Joulin, V.; Buchlin, E.; Solomon, J.; Guennou, C.

    2016-07-01

    Context. To explain the high temperature of the corona, much attention has been paid to the distribution of energy in dissipation events. Indeed, if the event energy distribution is steep enough, the smallest, unobservable events could be the largest contributors to the total energy dissipation in the corona. Previous observations have shown a wide distribution of energies but remain inconclusive about the precise slope. Furthermore, these results rely on a very crude estimate of the energy. On the other hand, more detailed spectroscopic studies of structures such as coronal bright points do not provide enough statistical information to derive their total contribution to heating. Aims: We aim at getting a better estimate of the distributions of the energy dissipated in coronal heating events using high-resolution, multi-channel extreme ultraviolet (EUV) data. Methods: To estimate the energies corresponding to heating events and deduce their distribution, we detected brightenings in five EUV channels of the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). We combined the results of these detections and used maps of temperature and emission measure derived from the same observations to compute the energies. Results: We obtain distributions of areas, durations, intensities, and energies (thermal, radiative, and conductive) of events. These distributions are power laws and we also find power-law correlations between event parameters. Conclusions: The energy distributions indicate that the energy from a population of events like the ones we detect represents a small contribution to the total coronal heating, even when extrapolating to smaller scales. The main explanations for this are how heating events can be extracted from observational data, and the incomplete knowledge of the thermal structure and processes in the coronal plasma attainable from available observations. Two movies attached to Fig. 3 are available in electronic form at

  5. UV and Soft X-ray Polar Coronal Jets

    NASA Astrophysics Data System (ADS)

    Dobrzycka, D.; Raymond, J. C.; Cranmer, S. R.; Li, J.

    2002-01-01

    Coronal jets are spectacular dynamic events originating from different structures in the solar corona. Jetlike phenomena were observed by various instruments aboard SOHO, and the X--ray jets were discovered by Yohkoh's soft X--ray telescope (SXT). The relation among the different types of jets is still not yet clear. We present ultraviolet spectroscopy of polar coronal jets obtained by the Ultraviolet Coronagraph Spectrometer (UVCS/SOHO) at heights in the corona ranging from 1.5 Rodot to 2.5 Rodot. The jets appear to originate near flaring ultraviolet bright points within polar coronal holes and were recorded by UVCS as a significant enhancement in the integrated intensities of the strongest coronal emission lines: mainly H I Ly alpha and O VI lambda lambda 1032,1037. A number of the detected jets are correlated with EIT Fe XII 195Å and LASCO C2 white-light events. Our modeling of the jet's observable properties provided estimates of the jet plasma conditions, as well as the initial electron temperature and heating rate required to reproduce the observed O VI ionization state. We discuss possible relationship between the polar ultraviolet and X--ray jets based on the results of coordinated SXT and UVCS observations in December 1996. We compare their properties and consider the magnetic reconnection models, developed for X--ray jets, as a model for UV jet formation. This work is supported by the National Aeronautics and Space Administration under grant NAG5--10093 to the Smithsonian Astrophysical Observatory, by Agenzia Spaziale Italiana, and by the ESA PRODEX program (Swiss contribution).

  6. ON THE 'EXTENDED' SOLAR CYCLE IN CORONAL EMISSION

    SciTech Connect

    Robbrecht, E.; Wang, Y.-M.; Sheeley, N. R.; Rich, N. B. E-mail: yi.wang@nrl.navy.mi E-mail: nathan.rich@nrl.navy.mi

    2010-06-10

    Butterfly diagrams (latitude-time plots) of coronal emission show a zone of enhanced brightness that appears near the poles just after solar maximum and migrates toward lower latitudes; a bifurcation seems to occur at sunspot minimum, with one branch continuing to migrate equatorward with the sunspots of the new cycle and the other branch heading back to the poles. The resulting patterns have been likened to those seen in torsional oscillations and have been taken as evidence for an extended solar cycle lasting over {approx}17 yr. In order to clarify the nature of the overlapping bands of coronal emission, we construct butterfly diagrams from green-line simulations covering the period 1967-2009 and from 19.5 nm and 30.4 nm observations taken with the Extreme-Ultraviolet Imaging Telescope during 1996-2009. As anticipated from earlier studies, we find that the high-latitude enhancements mark the footpoint areas of closed loops with one end rooted outside the evolving boundaries of the polar coronal holes. The strong underlying fields were built up over the declining phase of the cycle through the poleward transport of active-region flux by the surface meridional flow. Rather than being a precursor of the new-cycle sunspot activity zone, the high-latitude emission forms a physically distinct, U-shaped band that curves upward again as active-region fields emerge at midlatitudes and reconnect with the receding polar-hole boundaries. We conclude that the so-called extended cycle in coronal emission is a manifestation not of early new-cycle activity, but of the poleward concentration of old-cycle trailing-polarity flux by meridional flow.

  7. Parameterisation of coronal heating: spatial distribution and observable consequences

    NASA Astrophysics Data System (ADS)

    van Wettum, T.; Bingert, S.; Peter, H.

    2013-06-01

    Aims: We investigate the difference in the spatial distribution of the energy input for parameterisations of different mechanisms to heat the corona of the Sun and possible impacts on the coronal emission. Methods: We use a 3D magneto-hydrodynamic (MHD) model of a solar active region as a reference and compare the Ohmic-type heating in this model to parameterisations for alternating current (AC) and direct current (DC) heating models; in particular, we use Alfvén wave and MHD turbulence heating. We extract the quantities needed for these two parameterisations from the reference model and investigate the spatial distribution of the heat input in all three cases, globally and along individual field lines. To study differences in the resulting coronal emission, we employ 1D loop models with a prescribed heat input based on the heating rate we extracted along a bundle of field lines. Results: On average, all heating implementations show a rough drop of the heating rate with height. This also holds for individual field lines. While all mechanisms show a concentration of the energy input towards the low parts of the atmosphere, for individual field lines the concentration towards the foot points is much stronger for the DC mechanisms than for the Alfvén wave AC case. In contrast, the AC model gives a stronger concentration of the emission towards the foot points. This is because the more homogeneous distribution of the energy input leads to higher coronal temperatures and a more extended transition region. Conclusions: The significant difference in the concentration of the heat input towards the foot points for the AC and DC mechanisms and the pointed difference in the spatial distribution of the coronal emission for these cases show that the two mechanisms should be discriminable by observations. Before drawing final conclusions, these parameterisations should be implemented in new 3D models in a more self-consistent way.

  8. Numerical simulations of transverse oscillations in radiatively cooling coronal loops

    NASA Astrophysics Data System (ADS)

    Magyar, Norbert; Van Doorsselaere, Tom; Marcu, Alexandru

    2016-05-01

    We aim to study the influence of radiative cooling on the standing kink oscillations of coronal loops. To solve the 3D MHD ideal problem, we use the FLASH code. Our model consists of a straight, density enhanced and gravitationally stratified magnetic flux tube. We perturbed the system initially, leading to a transverse oscillation of the structure, and followed its evolution for a number of periods. A realistic radiative cooling is implemented. Results are compared to available analytical theory. We find that in the linear regime (i.e. low amplitude perturbation and slow cooling) the obtained period and damping time are in good agreement with theory. The cooling leads to an amplification of the oscillation amplitude. However, the difference between the cooling and non-cooling cases is small (around 6% after 6 oscillations). In high amplitude runs with realistic cooling, instabilities deform the loop, leading to increased damping. In this case, the difference between cooling and non-cooling is still negligible at around 12%. A set of simulations with higher density loops are also performed, to explore what happens when the cooling takes place in a very short time (t cool ≈ 100 s). In this case, the difference in amplitude after nearly 3 oscillation periods for the low amplitude case is 21% between cooling and non-cooling cases. We strengthen the results of previous analytical studies that state that the amplification due to cooling is ineffective, and its influence on the oscillation characteristics is small, at least for the cases shown here. Furthermore, the presence of a relatively strong damping in the high amplitude runs even in the fast cooling case indicates that it is unlikely that cooling could alone account for the observed, flare-related undamped oscillations of coronal loops. These results may be significant in the field of coronal seismology, allowing its application to coronal loop oscillations with observed fading-out or cooling behaviour.

  9. Determining the full halo coronal mass ejection characteristics

    NASA Astrophysics Data System (ADS)

    Fainshtein, V. G.

    2009-03-01

    In this paper we determined the parameters of 45 full halo coronal mass ejections (HCMEs) for various modifications of their cone forms (“ice cream cone models”). We show that the CME determined characteristics depend significantly on the CME chosen form. We show that, regardless of the CME chosen form, the trajectory of practically all the considered HCMEs deviate from the radial direction to the Sun-to-Earth axis at the initial stage of their movement.

  10. Numerical simulations of transverse oscillations in radiatively cooling coronal loops

    NASA Astrophysics Data System (ADS)

    Magyar, N.; Van Doorsselaere, T.; Marcu, A.

    2015-10-01

    Aims: We aim to study the influence of radiative cooling on the standing kink oscillations of a coronal loop. Methods: Using the FLASH code, we solved the 3D ideal magnetohydrodynamic equations. Our model consists of a straight, density enhanced and gravitationally stratified magnetic flux tube. We perturbed the system initially, leading to a transverse oscillation of the structure, and followed its evolution for a number of periods. A realistic radiative cooling is implemented. Results are compared to available analytical theory. Results: We find that in the linear regime (i.e. low amplitude perturbation and slow cooling) the obtained period and damping time are in good agreement with theory. The cooling leads to an amplification of the oscillation amplitude. However, the difference between the cooling and non-cooling cases is small (around 6% after 6 oscillations). In high amplitude runs with realistic cooling, instabilities deform the loop, leading to increased damping. In this case, the difference between cooling and non-cooling is still negligible at around 12%. A set of simulations with higher density loops are also performed, to explore what happens when the cooling takes place in a very short time (tcool ≈ 100 s). In this case, the difference in amplitude after nearly 3 oscillation periods for the low amplitude case is 21% between cooling and non-cooling cases. We strengthen the results of previous analytical studies that state that the amplification due to cooling is ineffective, and its influence on the oscillation characteristics is small, at least for the cases shown here. Furthermore, the presence of a relatively strong damping in the high amplitude runs even in the fast cooling case indicates that it is unlikely that cooling could alone account for the observed, flare-related undamped oscillations of coronal loops. These results may be significant in the field of coronal seismology, allowing its application to coronal loop oscillations with observed

  11. Spatial Relationship of Signatures of Interplanetary Coronal Mass Ejections

    NASA Technical Reports Server (NTRS)

    Richardson, I. G.; Cane, H. V.; Lepri, S. T.; Zurbuchen, T. H.; Gosling, J. T.

    2003-01-01

    Interplanetary coronal mass ejections (ICMEs) are characterized by a number of signatures. In particular, we examine the relationship between Fe charge states and other signatures during ICMEs in solar cycle 23. Though enhanced Fe charge states characterize many ICMEs, average charge states vary from event to event, are more likely to be enhanced in faster or flare-related ICMEs, and do not appear to depend on whether the ICME is a magnetic cloud.

  12. Simulations of Filament Channel Formation in a Coronal Magnetic Field

    NASA Astrophysics Data System (ADS)

    Knizhnik, Kalman; DeVore, C. Richard; Antiochos, Spiro K.

    2016-05-01

    A major unanswered problem in solar physics has been explaining the presence of sheared filament channels above photospheric polarity inversion lines (PILs) and the simultaneous lack of structure in the ‘loop’ portion of the coronal magnetic field. The shear inherent in filament channels represents not only a form of magnetic energy, but also magnetic helicity. As a result, models of filament channel formation need to explain not only why helicity is observed above PILs, but also why it is apparently not observed anywhere else in the corona. Previous results (Knizhnik, Antiochos & DeVore, 2015) have suggested that any helicity injected into the coronal field inverse-cascades in scale, a process known as magnetic helicity condensation (Antiochos, 2013). In this work, we present high resolution numerical simulations of photospheric helicity injection into a coronal magnetic field that contains both a PIL and a coronal hole (CH). We show conclusively that the inverse cascade of magnetic helicity terminates at the PIL, resulting in the formation of highly sheared filament channels and a smooth, untwisted corona. We demonstrate that even though magnetic helicity is injected throughout the flux system, it accumulates only at the PIL, where it manifests itself in the form of highly sheared filament channels, while any helicity obtained by the CH is ejected out of the system. We show that the formation of filament channels is both qualitatively and quantitatively in agreement with observations and discuss the implications of our simulations for observations.This work was supported by the NASA Earth and Space Science Fellowship, LWS TR&T and H-SR Programs.

  13. Extended HXR Sources - Albedo Patches or Coronal Sources

    NASA Technical Reports Server (NTRS)

    Dennis, Brian R.

    2011-01-01

    Extended HXR sources in the presence of compact footpoints have been reported based on visibility amplitudes from different detectors. Attempts have been made to determine the location and extent of these sources through direct imaging. Results of this work will be described for simulated sources and for specific flares at different solar longitudes, with a discussion of the possible nature of the extended sources as either albedo patches or coronal sources or a combination of the two.

  14. Solar cycle variation of large-scale coronal structures

    NASA Technical Reports Server (NTRS)

    Antonucci, E.; Duvall, T. L.

    1974-01-01

    A green line intensity variation is associated with the interplanetary and photospheric magnetic sector structure. This effect depends on the solar cycle and occurs with the same amplitude in the latitude range 60 deg N - 60 deg S. Extended longitudinal coronal structures are suggested, which indicate the existence of closed magnetic field lines over the neutral line, separating adjacent regions of opposite polarities on the photospheric surface.

  15. Coronal transient--eruptive prominence of 1980 August 5

    SciTech Connect

    Fisher, R.; Garcia, C.J.; Seagraves, P.

    1981-06-15

    A coronal transient was observed in association with an eruptive prominence event using the Mauna Loa experiment system. The transient, a rarefaction, formed before the acceleration of the eruptive prominence. Upward velocities of various features, as seen in the plane of the sky, show a marked difference as a function of time between the transient and the eruptive prominence. A region of enhanced electron density formed slowly in front of the rarefaction.

  16. Effects of calcium hydroxide paste medication on coronal leakage.

    PubMed

    Sevimay, S; Oztan, M D; Dalat, D

    2004-03-01

    The purpose of this in vitro study was to examine the coronal leakage of canals medicated with Ca(OH)(2) compared with the canals which did not receive Ca(OH)(2) medication before obturation with laterally condensed gutta-percha points and sealer. Sixty-one single rooted permanent canines and premolars were used. The crowns were removed from the cemento-enamel junction. After the canals were chemomechanically prepared, the roots were divided into three experimental groups as group 1, 2 and 3. The canals in group 1 and 2 were treated with ethylenediaminetetraacetic acid (EDTA) and NaOCl in order to remove the smear layer and then the canals were filled with Ca(OH)(2) paste. The coronal 3 mm of the cavities were sealed with Cavit and the samples were kept in an incubator at 37 degrees C for 7 days. No intra-canal medication was applied in group 3. The root canals were irrigated with NaOCl in group 1 and with EDTA and NaOCl in group 2, in order to remove Ca(OH)(2) before obturation. Two samples from group 1 and two from group 2 were examined under SEM in order to reveal the removal of Ca(OH)(2) paste. Following this, the canals in the experimental groups were obturated with gutta-percha and sealer. The roots were placed in India ink for 7 days and the linear dye penetration was evaluated. No significant statistical difference was found in the amount of coronal dye leakage between experimental groups (P > 0.05). The results of the present study indicated that the application of Ca(OH)(2) as a temporary dressing material had no effect on coronal leakage. PMID:15025656

  17. Constraints on Solar Coronal Heating from the FIP Effect

    NASA Astrophysics Data System (ADS)

    Laming, J. M.

    2012-12-01

    The solar composition is now known to vary with location on the sun. The solar corona was first observed in 1963 to exhibit what has now become known as the "FIP Effect". Elements with First Ionization Potential (FIP) less than about 10 eV are enhanced in their abundance relative to hydrogen by a factor of 3-4, relative to values in the solar photosphere. These low FIP elements include Fe, Si, Mg. Modern observations indicate that similar abundance anomalies apply in the corona and slow speed solar wind. High FIP elements are relatively less affected, although He and possibly Ne exhibit abundance depletions from their photospheric values. These fractionations are best explained within the context of a model where Alfvén waves propagating in the chromosphere interact with chromospheric ions (i.e. the low FIP elements), but not neutrals, through the ponderomotive force. Alfvén waves may originate either in the low chromosphere, as upward propagating sound waves mode convert at the layer where sound and Alfvén speeds are equal, or in the corona, as a byproduct of coronal heating by e.g. nanoflares or resonant absorption. In the former case resonance with an overlying coronal loop is not guaranteed, but in the latter case, it should be expected. Alfvén waves in resonance, or close to resonance with an overlying coronal loop produce a subtly different fractionation pattern to that found in the nonresonant case, and it is closer to that observed in several important respects, particularly the depletion of He. We therefore suggest that the ponderomotive model of the FIP Effect is more consistent with models of coronal heating such as nanoflares or Alfvén resonance, and permit ourselves some further speculation on the nature of such energy release.

  18. Coronal and heliospheric imagers for solar wind phenomena

    NASA Astrophysics Data System (ADS)

    Middleton, Kevin F.; Bourdelle, Anthony; Davies, Jackie A.; Eyles, Chris J.; Griffin, Doug K.; Harrison, Richard A.; Richards, Tony R.; Rogers, J. Kevin; Tappin, S. James; Tosh, Ian A. J.; Waltham, Nick R.

    2015-09-01

    RAL Space is enhancing its program to lead the development of European capabilities in space-based visible-light coronal and heliospheric imaging instrumentation in the light of emerging opportunities such as the European Space Agency's Space Situational Awareness program and recent S2 small-mission call. Visible-light coronal and heliospheric imaging of solar wind phenomena, such as coronal mass ejections and interaction regions, is of critical importance to space weather studies, both operationally and in terms of enabling the underpinning science. This work draws on heritage from scientific instruments such as LASCO (Large Angle and Spectrometric Coronagraph) on the SOHO spacecraft, SMEI (Solar Mass Ejection Imager) on the Coriolis spacecraft and the HI (Heliospheric Imager) instruments on STEREO. Such visible-light observation of solar wind structures relies on the detection of sunlight that has been Thomson-scattered by electrons (the so-called K-corona). The Thomson-scattered signal must be extracted from other signals that can be many orders of magnitude greater (such as that from the F-corona and the solar disc itself) and this places stringent constraints on stray-light rejection, as well as pointing stability and accuracy. We discuss the determination of instrument requirements, key design trade-offs and the evolution of base-line designs for the coronal and heliospheric regimes. We explain how the next generation of instruments will build on this heritage while also, in some cases, meeting the challenges on resources imposed on operational space weather imagers. In particular, we discuss the optical engineering challenges involved in the design of these instruments.

  19. THE ROLE OF TORSIONAL ALFVEN WAVES IN CORONAL HEATING

    SciTech Connect

    Antolin, P.; Shibata, K. E-mail: shibata@kwasan.kyoto-u.ac.j

    2010-03-20

    In the context of coronal heating, among the zoo of magnetohydrodynamic (MHD) waves that exist in the solar atmosphere, Alfven waves receive special attention. Indeed, these waves constitute an attractive heating agent due to their ability to carry over the many different layers of the solar atmosphere sufficient energy to heat and maintain a corona. However, due to their incompressible nature these waves need a mechanism such as mode conversion (leading to shock heating), phase mixing, resonant absorption, or turbulent cascade in order to heat the plasma. Furthermore, their incompressibility makes their detection in the solar atmosphere very difficult. New observations with polarimetric, spectroscopic, and imaging instruments such as those on board the Japanese satellite Hinode, or the Crisp spectropolarimeter of the Swedish Solar Telescope or the Coronal Multi-channel Polarimeter, are bringing strong evidence for the existence of energetic Alfven waves in the solar corona. In order to assess the role of Alfven waves in coronal heating, in this work we model a magnetic flux tube being subject to Alfven wave heating through the mode conversion mechanism. Using a 1.5 dimensional MHD code, we carry out a parameter survey varying the magnetic flux tube geometry (length and expansion), the photospheric magnetic field, the photospheric velocity amplitudes, and the nature of the waves (monochromatic or white-noise spectrum). The regimes under which Alfven wave heating produces hot and stable coronae are found to be rather narrow. Independently of the photospheric wave amplitude and magnetic field, a corona can be produced and maintained only for long (>80 Mm) and thick (area ratio between the photosphere and corona >500) loops. Above a critical value of the photospheric velocity amplitude (generally a few km s{sup -1}) the corona can no longer be maintained over extended periods of time and collapses due to the large momentum of the waves. These results establish several

  20. ANALYSIS OF CORONAL GREEN LINE PROFILES: EVIDENCE OF EXCESS BLUESHIFTS

    SciTech Connect

    Raju, K. P.; Chandrasekhar, T.; Ashok, N. M. E-mail: chandra@prl.res.in

    2011-08-01

    Coronal green line (Fe XIV 5303 A) profiles were obtained from Fabry-Perot interferometric observations of the solar corona during the total solar eclipse of 2001 June 21 from Lusaka, Zambia. The instrumental width is about 0.2 A and the spectral resolution is about 26,000. About 300 line profiles were obtained within a radial range of 1.0-1.5 R{sub sun} and a position angle coverage of about 240{sup 0}. The line profiles were fitted with single Gaussians, and their intensities, Doppler velocities, and line widths were obtained. Also obtained were the centroids of the line profiles, which give a measure of line asymmetry. The histograms of Doppler velocity show excess blueshifts, while the centroids reveal a predominant blue wing in the line profiles. It was found that the centroids and the Doppler velocities are highly correlated. This points to the presence of multiple components in the line profiles, with an excess of blueshifted components. We then obtained the (Blue-Red) wing intensities, which clearly reveal the secondary components, the majority of which are blueshifted. This confirms that the coronal green line profiles often contain multicomponents with excess blueshifts, which also depend on the solar activity. The magnitude of the Doppler velocity of the secondary components is in the range of 20-40 km s{sup -1} and shows an increase toward the poles. Possible explanations of the multicomponents are the type II spicules that were recently found to be important to coronal heating or the nascent solar wind flow, but the cause of the blue asymmetry in the coronal lines above the limb remains unclear.

  1. On the "Extended" Solar Cycle in Coronal Emission

    NASA Astrophysics Data System (ADS)

    Robbrecht, E.; Wang, Y.-M.; Sheeley, N. R., Jr.; Rich, N. B.

    2010-06-01

    Butterfly diagrams (latitude-time plots) of coronal emission show a zone of enhanced brightness that appears near the poles just after solar maximum and migrates toward lower latitudes; a bifurcation seems to occur at sunspot minimum, with one branch continuing to migrate equatorward with the sunspots of the new cycle and the other branch heading back to the poles. The resulting patterns have been likened to those seen in torsional oscillations and have been taken as evidence for an extended solar cycle lasting over ~17 yr. In order to clarify the nature of the overlapping bands of coronal emission, we construct butterfly diagrams from green-line simulations covering the period 1967-2009 and from 19.5 nm and 30.4 nm observations taken with the Extreme-Ultraviolet Imaging Telescope during 1996-2009. As anticipated from earlier studies, we find that the high-latitude enhancements mark the footpoint areas of closed loops with one end rooted outside the evolving boundaries of the polar coronal holes. The strong underlying fields were built up over the declining phase of the cycle through the poleward transport of active-region flux by the surface meridional flow. Rather than being a precursor of the new-cycle sunspot activity zone, the high-latitude emission forms a physically distinct, U-shaped band that curves upward again as active-region fields emerge at midlatitudes and reconnect with the receding polar-hole boundaries. We conclude that the so-called extended cycle in coronal emission is a manifestation not of early new-cycle activity, but of the poleward concentration of old-cycle trailing-polarity flux by meridional flow.

  2. Breakout coronal mass ejections from solar active regions

    NASA Astrophysics Data System (ADS)

    DeVore, C. Richard; Lynch, Benjamin; MacNeice, Peter; Olson, Kevin; Antiochos, Spiro

    We are performing magnetohydrodynamic simulations of single bipolar active regions (ARs) embedded in the Sun's global background field and of pairs of ARs interacting with each other. The magnetic flux near the polarity inversion lines (PILs) of the ARs is subjected to twisting footpoint displacements that introduce strong magnetic shear between the two polarities and gradually inflate the coronal volume occupied by the AR fields. If the initially current-free coronal field contains a magnetic null, then it is vulnerable to eruptions triggered by magnetic breakout, which reconnects aside the previously restraining field lines overhead. The sheared core flux promptly expands outward at the Alfven speed, opening the magnetic field in the vicinity of the PIL. Flare reconnection below the ejecta, across the vertical current sheet thus established, thereafter reforms the magnetic-null configuration above the AR. This reformation sets the stage for subsequent homologous episodes of breakout reconnection and eruption, if the energizing footpoint motions are sustained. The magnetic flux and energy of an isolated AR, relative to those of the background field, determine whether the eruption is confined or ejective, as the sheared flux either comes to rest in the corona or escapes the Sun to interplanetary space, respectively. In the latter case, the field lines accompanying the coronal mass ejection can comprise a weakly twisted "magnetic bottle" as readily as a strongly twisted flux rope, both of which are observed routinely in situ. The latest developments in this research will be reported. In particular, we will emphasize the observational signatures inferred from the simulations that could be sought in STEREO data, such as multiple three-dimensional views, EUV brightenings at reconnection sites, and coronal dimmings in regions of strong expansion. Our research is sponsored by NASA and ONR.

  3. Longitudinal magnetohydrodynamics oscillations in dissipative, cooling coronal loops

    SciTech Connect

    Al-Ghafri, K. S.; Ruderman, M. S.; Williamson, A.; Erdélyi, R. E-mail: m.s.ruderman@sheffield.ac.uk E-mail: robertus@sheffield.ac.uk

    2014-05-01

    This paper investigates the effect of cooling on standing slow magnetosonic waves in coronal magnetic loops. The damping mechanism taken into account is thermal conduction that is a viable candidate for dissipation of slow magnetosonic waves in coronal loops. In contrast to earlier studies, here we assume that the characteristic damping time due to thermal conduction is not small, but arbitrary, and can be of the order of the oscillation period, i.e., a temporally varying plasma is considered. The approximation of low-beta plasma enables us to neglect the magnetic field perturbation when studying longitudinal waves and consider, instead, a one-dimensional motion that allows a reliable first insight into the problem. The background plasma temperature is assumed to be decaying exponentially with time, with the characteristic cooling timescale much larger than the oscillation period. This assumption enables us to use the WKB method to study the evolution of the oscillation amplitude analytically. Using this method we obtain the equation governing the oscillation amplitude. The analytical expressions determining the wave properties are evaluated numerically to investigate the evolution of the oscillation frequency and amplitude with time. The results show that the oscillation period increases with time due to the effect of plasma cooling. The plasma cooling also amplifies the amplitude of oscillations in relatively cool coronal loops, whereas, for very hot coronal loop oscillations the damping rate is enhanced by the cooling. We find that the critical point for which the amplification becomes dominant over the damping is in the region of 4 MK. These theoretical results may serve as impetus for developing the tools of solar magneto-seismology in dynamic plasmas.

  4. The Solar Non-activity Cycle of Polar Coronal Holes

    NASA Astrophysics Data System (ADS)

    Kirk, M. S.; Pesnell, W. D.; Young, C. A.

    2015-12-01

    After the unusually extended minimum in 2008 and 2009, solar cycle 24 continues to be an exceptionally weak cycle both in sunspot number and number of large magnetic storms. Coronal holes offer a direct measurement of the non-activity solar cycle, a missing link in our understanding of solar cycle progression. They are prevalent during solar minimum, non-axisymmetric, and are stable. Polar coronal holes are regularly observed capping the northern and southern solar poles in EUV images of the corona and are understood as the primary source of the fast solar wind. We make measurements of these features from 1996 through 2015 using four different NASA imagers: SOHO EIT, STEREO A and B EUVI, and SDO AIA. A measurement of the axial symmetry of the polar holes is seen to have clear solar cycle dependence. Polar coronal holes are aligned with the solar rotation axis during minimum and have a maximum asymmetry between holes of about 14 degrees in the declining phase of the current solar cycle.

  5. Temperature and Density Analysis of a Coronal Loop Using EIS

    NASA Astrophysics Data System (ADS)

    Garst, J. W.; Schmelz, J. T.

    2008-05-01

    The temperature analysis of coronal loops has produced contradictory results. Image ratios from TRACE show substantially smaller temperature gradients than predicted by standard models for loops in hydrodynamic equilibrium. TRACE has state-of-the-art spatial resolution but limited temperature coverage. On the other hand, the pixels of the Coronal Diagnostics Spectrometer (CDS) on SOHO are larger but its temperature resolution is state-of-the-art. Loop results from differential emission measure analyses from CDS data have been questioned due to the resolving power. Loop analysis could benefit greatly from observations by an instrument with the spatial resolution of TRACE and the temperature coverage of CDS. A spectrometer with (almost) these characteristics was launched in September 2006 on the Japanese/USA/UK Hinode mission. The EUV Imaging Spectrometer (EIS) is similar to CDS, observing emission lines originating from the solar corona and upper transition region at wavelength intervals in the extreme ultraviolet, but with a spatial resolution that is almost as good as TRACE. Differential emission measure and density analysis is done on the coronal loop data observed by EIS on 01 June 2007. Results from CDS and TRACE analysis are compared and discussed qualitatively. Solar physics research at the University of Memphis is supported by a Hinode subcontract from NASA/SAO as well as NSF ATM-0402729.

  6. More of the Inconvenient Truth About Coronal Dimmings

    NASA Astrophysics Data System (ADS)

    McIntosh, S. W.; Burkepile, J.; Leamon, R. J.

    2009-12-01

    We continue the investigation of a CME-driven coronal dimming from December 14 2006 using unique high resolution imaging of the chromosphere and corona from the Hinode spacecraft. Over the course of the dimming event we observe the dynamic increase of non-thermal line broadening of multiple emission lines as the CME is released and the corona opens; reaching levels seen in coronal holes. As the corona begins to close, refill and brighten, we see a reduction of the non-thermal broadening towards the pre-eruption level. The dynamic evolution of non-thermal broadening is consistent with the expected change of Alfvén wave amplitudes in the magnetically open rarefied dimming region, compared to the dense closed corona prior to the CME. The presented data reinforce the belief that coronal dimmings must be temporary sources of the fast solar wind. It is unclear if such a rapid transition in the thermodynamics of the corona to a solar wind state has an effect on the CME itself.

  7. POST-CORONAL MASS EJECTION PLASMA OBSERVED BY HINODE

    SciTech Connect

    Landi, E.; Raymond, J. C.; Miralles, M. P.; Hara, H.

    2012-05-20

    In the present work we study the evolution of an active region after the eruption of a coronal mass ejection (CME) using observations from the EIS and XRT instruments on board Hinode. The field of view includes a post-eruption arcade, a current sheet, and a coronal dimming. The goal of this paper is to provide a comprehensive set of measurements for all these aspects of the CME phenomenon made on the same CME event. The main physical properties of the plasma along the line of sight-electron density, thermal structure, plasma composition, size, and, when possible, mass-are measured and monitored with time for the first three hours following the CME event of 2008 April 9. We find that the loop arcade observed by EIS and XRT may not be related to the post-eruption arcade. Post-CME plasma is hotter than the surrounding corona, but its temperature never exceeds 3 MK. Both the electron density and thermal structure do not show significant evolution with time, while we found that the size of the loop arcade in the Hinode plane of the sky decreased with time. The plasma composition is the same in the current sheet, in the loop arcade, and in the ambient plasma, so all these plasmas are likely of coronal origin. No significant plasma flows were detected.

  8. The Nature of CME-flare-Associated Coronal Dimming

    NASA Astrophysics Data System (ADS)

    Cheng, J. X.; Qiu, J.

    2016-07-01

    Coronal mass ejections (CMEs) are often accompanied by coronal dimming that is evident in extreme ultraviolet (EUV) and soft X-ray observations. The locations of dimming are sometimes considered to map footpoints of the erupting flux rope. As the emitting material expands in the corona, the decreased plasma density leads to reduced emission observed in spectral and irradiance measurements. Therefore, signatures of dimming may reflect the properties of CMEs in the early phase of their eruption. In this study, we analyze the event of flare, CME, and coronal dimming on 2011 December 26. We use the data from the Atmospheric Imaging Assembly on the Solar Dynamics Observatory for disk observations of the dimming, and analyze images taken by EUVI, COR1, and COR2 on board the Solar Terrestrial Relations Observatory to obtain the height and velocity of the associated CMEs observed at the limb. We also measure the magnetic reconnection rate from flare observations. Dimming occurs in a few locations next to the flare ribbons, and it is observed in multiple EUV passbands. Rapid dimming starts after the onset of fast reconnection and CME acceleration, and its evolution tracks the CME height and flare reconnection. The spatial distribution of dimming exhibits cores of deep dimming with a rapid growth, and their light curves are approximately linearly scaled with the CME height profile. From the dimming analysis we infer the process of the CME expansion, and estimate properties of the CME.

  9. Coronal Physics and the Chandra Emission Line Project

    NASA Technical Reports Server (NTRS)

    Brickhouse, Nancy

    1999-01-01

    With the launch of the Chandra X-ray Observatory, high resolution X-ray spectroscopy of cosmic sources has begun. Early, deep observations of three stellar coronal sources will provide not only invaluable calibration data, but will also give us benchmarks for plasma spectral modeling codes. These codes are to interpret data from stellar coronae, galaxies and clusters of galaxies. supernova remnants and other astrophysical sources, but they have been called into question in recent years as problems with understanding moderate resolution ASCA and EUVE data have arisen. The Emission Line Project is a collaborative effort to improve the models, with Phase 1 being the comparison of models with observed spectra of Capella, Procyon, and HR, 1099. Goals of these comparisons are (1) to determine and verify accurate and robust diagnostics and (2) to identify and prioritize issues in fundamental spectroscopy which will require further theoretical and/or laboratory work. A critical issue in exploiting the coronal data for these purposes is to understand the extent to which common simplifying assumptions (coronal equilibrium, time-independence, negligible optical depth) apply. We will discuss recent advances in our understanding of stellar coronae in this context.

  10. Macrospicule Jets in On-Disk Coronal Holes

    NASA Technical Reports Server (NTRS)

    Adams, M. L.; Sterling, A. C.; Moore, R. L.

    2014-01-01

    We examine the magnetic structure and dynamics of multiple jets found in coronal holes close to or on disk center. All data are from the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager (HMI) of the Solar Dynamics Observatory (SDO). We report on observations of six jets in an equatorial coronal hole spanning 2011 February 27 and 28. We show the evolution of these jets in AIA 193 A, examine the magnetic field configuration, and postulate the probable trigger mechanism of these events. We recently reported on another jet in the same coronal hole on 2011 February 27, approximately 13:04 Universal Time (Adams et al 2014, Astrophysical Journal, 783: 11); this jet is a previously-unrecognized variety of blowout jet. In this variety, the reconnection bright point is not made by interchange reconnection of initially-closed erupting field in the base of the jet with ambient open field. Instead, there is a miniature filament-eruption flare arcade made by internal reconnection of the legs of the erupting field.

  11. Numerically modelling the large scale coronal magnetic field

    NASA Astrophysics Data System (ADS)

    Panja, Mayukh; Nandi, Dibyendu

    2016-07-01

    The solar corona spews out vast amounts of magnetized plasma into the heliosphere which has a direct impact on the Earth's magnetosphere. Thus it is important that we develop an understanding of the dynamics of the solar corona. With our present technology it has not been possible to generate 3D magnetic maps of the solar corona; this warrants the use of numerical simulations to study the coronal magnetic field. A very popular method of doing this, is to extrapolate the photospheric magnetic field using NLFF or PFSS codes. However the extrapolations at different time intervals are completely independent of each other and do not capture the temporal evolution of magnetic fields. On the other hand full MHD simulations of the global coronal field, apart from being computationally very expensive would be physically less transparent, owing to the large number of free parameters that are typically used in such codes. This brings us to the Magneto-frictional model which is relatively simpler and computationally more economic. We have developed a Magnetofrictional Model, in 3D spherical polar co-ordinates to study the large scale global coronal field. Here we present studies of changing connectivities between active regions, in response to photospheric motions.

  12. Mission Prospects: Remote Sensing of Coronal Suprathermal Seed Particles

    NASA Astrophysics Data System (ADS)

    Moses, J.; Laming, J. M.; Ko, Y.

    2013-12-01

    A new perspective on the feasibility of remote sensing detection and characterization of suprathermal particles serving the role of seeds in solar energetic particle (SEP) acceleration has recently been achieved via a combination of theoretical (Laming et al. 2013 http://dx.doi.org/10.1088/0004-637X/770/1/73) and experimental (Kohl et al. 2011 http://arxiv.org/abs/1104.3817, Moses et al. 2011 http://dx.doi.org/10.1117/12.896868) developments. The location, density and velocity distribution of these seed particles can now be established as science observing requirements for instrument specification. The most promising instrumentation for these observations is a UV coronal spectrometer. While the spectroscopic and spatial resolution of the one existing, spaceflight UV coronal spectrometer - SOHO UVCS - meets this specification; the effective area of this instrument is two orders of magnitude too low. Initial attempts at achieving increased effective area by directly scaling UVCS have not been successfully transitioned into flight programs (e.g. Gardner et al. 1999, 'Advanced Solar Coronal Explorer Mission (ASCE)', SPIE 3764, 134). With the recent development of instrument designs achieving the requisite increase in effective area within a volume envelope comparable to UVCS, the options for achieving a successful flight program have been increased. This work is supported in part by the Office of Naval Research/Naval Research Laboratory Basic Research (6.1) Program and NASA-DoD PR 12SHP12/2-0151.

  13. Single-point inversion of the coronal magnetic field

    SciTech Connect

    Plowman, Joseph

    2014-09-01

    The Fe XIII 10747 and 10798 Å lines observed in the solar corona are sensitive to the coronal magnetic field in such a way that, in principle, the full vector field at a point on the line of sight can be inferred from their combined polarization signals. This paper presents analytical inversion formulae for the field parameters and analyzes the uncertainty of magnetic field measurements made from such observations, assuming emission dominated by a single region along the line of sight. We consider the case of the current Coronal Multi-channel Polarimeter (CoMP) instrument as well as the future Coronal Solar Magnetism Observatory (COSMO) and Advanced Technology Solar Telescope (ATST) instruments. Uncertainties are estimated with a direct analytic inverse and with a Markov Chain Monte Carlo algorithm. We find that (in effect) two components of the vector field can be recovered with CoMP, and well recovered with COSMO or ATST, but that the third component can only be recovered when the solar magnetic field is strong and optimally oriented.

  14. Spatial damping of propagating sausage waves in coronal cylinders

    NASA Astrophysics Data System (ADS)

    Guo, Ming-Zhe; Chen, Shao-Xia; Li, Bo; Xia, Li-Dong; Yu, Hui

    2015-09-01

    Context. Sausage modes are important in coronal seismology. Spatially damped propagating sausage waves were recently observed in the solar atmosphere. Aims: We examine how wave leakage influences the spatial damping of sausage waves propagating along coronal structures modeled by a cylindrical density enhancement embedded in a uniform magnetic field. Methods: Working in the framework of cold magnetohydrodynamics, we solve the dispersion relation (DR) governing sausage waves for complex-valued, longitudinal wavenumber k at given real angular frequencies ω. For validation purposes, we also provide analytical approximations to the DR in the low-frequency limit and in the vicinity of ωc, the critical angular frequency separating trapped from leaky waves. Results: In contrast to the standing case, propagating sausage waves are allowed for ω much lower than ωc. However, while able to direct their energy upward, these low-frequency waves are subject to substantial spatial attenuation. The spatial damping length shows little dependence on the density contrast between the cylinder and its surroundings, and depends only weakly on frequency. This spatial damping length is of the order of the cylinder radius for ω ≲ 1.5vAi/a, where a and vAi are the cylinder radius and the Alfvén speed in the cylinder, respectively. Conclusions: If a coronal cylinder is perturbed by symmetric boundary drivers (e.g., granular motions) with a broadband spectrum, wave leakage efficiently filters out the low-frequency components.

  15. Expansion and broadening of coronal loop transients - A theoretical explanation

    NASA Technical Reports Server (NTRS)

    Mouschovias, T. CH.; Poland, A. I.

    1978-01-01

    Consequences are examined of the assumption that an observed coronal loop transient is a twisted rope of magnetic-field lines expanding and broadening in the background coronal plasma and magnetic field. It is shown that the expansion can be accounted for by the azimuthal component of the field; the observed broadening of the loop as it moves outward can be accounted for by the longitudinal component of the field. In order to have a net outward force and at the same time avoid a classical pinch (sausage) instability, the two components of the field must satisfy a certain inequality. It is predicted that, as the loop rises, the width (h) of its top portion should vary proportionally with distance (R) from the sun's center. This is in good agreement with measurements that show h is proportional to the 0.8 power of R. The prediction that the radius of curvature of the top portion of the loop should be proportional to R differs from the measured variation. The difference could be accounted for by a drag due to the background coronal field that flattens the loop's top.

  16. Fast-sausage oscillations in coronal loops with smooth boundary

    NASA Astrophysics Data System (ADS)

    Lopin, I.; Nagorny, I.

    2014-12-01

    Aims: The effect of the transition layer (shell) in nonuniform coronal loops with a continuous radial density profile on the properties of fast-sausage modes are studied analytically and numerically. Methods: We modeled the coronal waveguide as a structured tube consisting of a cord and a transition region (shell) embedded within a magnetic uniform environment. The derived general dispersion relation was investigated analytically and numerically in the context of frequency, cut-off wave number, and the damping rate of fast-sausage oscillations for various values of loop parameters. Results: The frequency of the global fast-sausage mode in the loops with a diffuse (or smooth) boundary is determined mainly by the external Alfvén speed and longitudinal wave number. The damping rate of such a mode can be relatively low. The model of coronal loop with diffuse boundary can support a comparatively low-frequency, global fast-sausage mode of detectable quality without involving extremely low values of the density contrast. The effect of thin transition layer (corresponds to the loops with steep boundary) is negligible and produces small reductions of oscillation frequency and relative damping rate in comparison with the case of step-function density profile. Seismological application of obtained results gives the estimated Alfvén speed outside the flaring loop about 3.25 Mm/s.

  17. Coronal Current Sheet Evolution in the Aftermath of a CME

    NASA Technical Reports Server (NTRS)

    Bemporad, A.; Poletto, G.; Suess, S. T.; Ko, Y.-K.; Schwadron, N. A.; Elliott, H. A.; Raymond, J. C.

    2005-01-01

    We report on SOHO-UVCS observations of coronal restructuring following a Coronal Mass Ejection (CME) on November 26, 2002, at the time of a SOHO-Ulysses quadrature campaign. Starting about 3 hours after the CME, which was directed towards Ulysses, UVCS began taking spectra at 1.7 solar radii, covering emission from both cool and hot plasma. Observations continued, with occasional gaps, for more than 2 days. Emission in the 974.8 Angstrom line of [Fe XVIII], indicating temperatures above 6x10(6) K, was observed throughout the campaign in a spatially limited location. Comparison with EIT images shows the [Fe XVIII] emission to overlie a growing post-flare loop system formed in the aftermath of the CME. The emission most likely originates in a current sheet overlying the arcade. Analysis of the [Fe XVIII] emission allows us to infer the evolution of physical parameters in the current sheet over the entire span of our observations: in particular, we give the temperature vs. time in the current sheet and estimate the density. Ulysses was directly above the location of the CME and intercepted the ejecta. High ionization state Fe was detected by SWICS throughout the magnetic cloud associated with the CME, although the rapid temporal variation suggests bursty, rather than smooth, reconnection in the coronal current sheet. Both the remote and in situ observations are compared with predictions of theoretical CME models.

  18. Coronal Shock Waves and Solar Energetic Particle Events

    NASA Astrophysics Data System (ADS)

    Cliver, Edward

    Recent evidence supports the view first expressed by Wild, Smerd, and Weiss in 1963 that large solar energetic particle (SEP) events are a consequence of shock waves manifested by radio type II bursts. Following Tylka et al. (ApJ 625, 474, 2005), our picture of SEP acceleration at shocks now includes the effects of variable seed particle population and shock geometry. By taking these factors into account, Tylka and Lee (ApJ 646, 1319, 2006; see also Sandroos Vainio, ApJ 662, L127, 2007; AA 507, L21, 2009) were able to account for the charge-to-mass variability in high-Z ions first reported by Breneman and Stone in 1985. Recent studies of electron-to-proton ratios, both in interplanetary space (Cliver Ling, ApJ 658, 1349, 2007; Dietrich et al., in preparation, 2010) and in gamma-ray-line events (Shih et al., ApJ 698, L152, 2009), also support the view that large SEP events originate in coronal shocks and not in solar flares. Concurrent with the above developments, there is growing evidence that coronal shocks are driven by coronal mass ejections rather than by flare pressure pulses.

  19. Coronal Heating, Weak MHD Turbulence, and Scaling Laws

    NASA Technical Reports Server (NTRS)

    Rappazzo, A. F.; Velli, M.; Einaudi, G.; Dahlburg, R. B.

    2007-01-01

    Long-time high-resolution simulations of the dynamics of a coronal loop in Cartesian geometry are carried out, within the framework of reduced magnetohydrodynamics (RMHD), to understand coronal heating driven by the motion of field lines anchored in the photosphere. We unambiguously identify MHD anisotropic turbulence as the physical mechanism responsible for the transport of energy from the large scales, where energy is injected by photospheric motions, to the small scales, where it is dissipated. As the loop parameters vary, different regimes of turbulence develop: strong turbulence is found for weak axial magnetic fields and long loops, leading to Kolmogorov-like spectra in the perpendicular direction, while weaker and weaker regimes (steeper spectral slopes of total energy) are found for strong axial magnetic fields and short loops. As a consequence we predict that the scaling of the heating rate with axial magnetic field intensity B, which depends on the spectral index of total energy for given loop parameters, must vary from B3/2 for weak fields to B2 for strong fields at a given aspect ratio. The predicted heating rate is within the lower range of observed active region and quiet-Sun coronal energy losses.

  20. Projection effects in coronal dimmings and associated EUV wave event

    NASA Astrophysics Data System (ADS)

    Dissauer, Karin; Temmer, Manuela; Veronig, Astrid; Vanninathan, Kamalam; Magdalenic, Jasmina

    2016-04-01

    We investigate the high-speed (v > 1000 km s‑1) extreme-ultraviolet (EUV) wave associated with an X1.2 flare and coronal mass ejection (CME) from NOAA active region 11283. This EUV wave features peculiar on-disk signatures, in particular we observe an intermittent "disappearance" of the front for 120 s in SDO/AIA 171, 193, 211 Å data, whereas the 335 Å filter, sensitive to hotter plasmas (T˜ 2.5 MK), shows a continuous evolution of the wave front. We exploit the multi-point quadrature position of SDO and STEREO-A, to make a thorough analysis of the EUV wave evolution, with respect to its kinematics and amplitude evolution. We identify on-disk coronal dimming regions in SDO/AIA, reminiscent of core dimmings, that have no corresponding on-disk dimming signatures in STEREO-A/EUVI. Reconstructing the SDO line-of-sight (LOS) direction in STEREO-A clearly shows that the observed SDO on-disk dimming areas are not the footprints of the erupting fluxrope but result from decreased emission from the expanding CME body integrated along the LOS. In this context, we conclude that the intermittent disappearance of the EUV wave in the AIA 171, 193, 211 Å filters, which are channels sensitive to plasma with temperatures below ˜ 2 MK is also caused by such LOS integration effects. These observations clearly demonstrate that single-view image data provide us with limited insight to correctly interpret coronal features.

  1. MHD simulations of homologous and cannibalistic coronal mass ejections

    NASA Astrophysics Data System (ADS)

    Fan, Yuhong; Chatterjee, Piyali

    2014-06-01

    We present magneto-hydrodynamic simulations of the development of a homologous sequence of coronal mass ejections (CMEs) and demonstrate their so-called cannibalistic behavior. These CMEs originate from the repeated formations and partial eruptions of kink unstable flux ropes as a result of the continued emergence of a twisted flux rope across the lower boundary into a pre-existing coronal potential arcade field. The simulations show that a CME erupting into the open magnetic field created by a preceding CME has a higher speed, and therefore tends to be cannibalistic, catching up and merging with the preceding one into a single fast CME. All the CMEs attained speeds of about 1000 km/s as they exit the domain. The reformation of a twisted flux rope after each CME eruption during the sustained flux emergence can naturally explain the X-ray observations of repeated reformations of sigmoids and “sigmoid-under-cusp” configurations at a low-coronal source of homologous CMEs.

  2. Bashful ballerina unveiled: Multipole analysis of the coronal magnetic field

    NASA Astrophysics Data System (ADS)

    Virtanen, I.; Mursula, K.

    2012-12-01

    Heliospheric current sheet (HCS) is the continuum of the coronal magnetic equator, dividing the heliospheric magnetic field (HMF) into two sectors (polarities). Because of its wavy structure, the HCS is often called the ballerina skirt. Several studies have proven that the HCS is southward shifted during about three years in the solar declining phase. This persistent phenomenon, called the bashful ballerina, has been verified by geomagnetic indices since 1930s, by OMNI data base since 1960s, by the WSO PFSS model since mid-1970s and by the Ulysses probe measurements during the fast latitude scans in 1994-1995 and 2007. We study here the Wilcox Solar Observatory measurements of the photospheric magnetic field and the PFSS extrapolation of the coronal magnetic field. We show that the quadrupole moment of the photospheric magnetic field, which is important for the HCS asymmetry (bashful ballerina), mainly arises from the difference between northern and southern polar field strengths. According to the WSO data the minimum time quadrupole is mainly due to the difference between the highest northern and southern latitude bins. Related studies imply that the southward shift of the HCS is related to the delayed development of southern coronal holes. We also discuss the suggested connection of the HCS asymmetry to sunspot hemispheric asymmetry.

  3. Revealing the Spectral Type Dependence of the Coronal FIP Effect

    NASA Astrophysics Data System (ADS)

    Wood, B.; Linsky, J. L.

    2011-12-01

    The most widely studied coronal abundance anomaly is the so-called "FIP effect", where the abundances of elements with low First Ionization Potential (FIP) are enhanced relative to the photosphere. Many studies in the past have reported a tendency for more active stars to have less of a FIP effect, and for particularly active stars to even exhibit an inverse FIP effect, where low FIP elements are depleted in the corona instead of enhanced. However, we find that this activity dependence is nonexistent among main sequence stars when the most active stars with log LX > 29 are excluded. Extremely active stars normally dominate coronal surveys since active stars are brighter and more easily observed in X-rays, but by avoiding such extremes and focusing solely on more normal stars we find a very different empirical view of the FIP effect, one in which FIP bias is dependent on spectral type instead of activity. This dependence indicates a strong connection between coronal abundance and basic photospheric characteristics.

  4. A large coronal loop in the Algol system.

    PubMed

    Peterson, W M; Mutel, R L; Güdel, M; Goss, W M

    2010-01-14

    The close binary Algol system contains a radio-bright KIV subgiant star in a very close (0.062 astronomical units) and rapid (2.86 day) orbit with a main sequence B8 star. Because the rotation periods of the two stars are tidally locked to the orbital period, the rapid rotation drives a magnetic dynamo. A large body of evidence points to the existence of an extended, complex coronal magnetosphere originating at the cooler K subgiant. The detailed morphology of the subgiant's corona and its possible interaction with its companion are unknown, though theory predicts that the coronal plasma should be confined in a magnetic loop structure, as seen on the Sun. Here we report multi-epoch radio imaging of the Algol system, in which we see a large, persistent coronal loop approximately one subgiant diameter in height, whose base is straddling the subgiant and whose apex is oriented towards the B8 star. This suggests that a persistent asymmetric magnetic field structure is aligned between the two stars. The loop is larger than anticipated theoretically, but the size may be the result of a magnetic interaction between the two stars. PMID:20075916

  5. Solar Coronal Plumes and the Fast Solar Wind

    NASA Astrophysics Data System (ADS)

    Dwivedi, Bhola N.; Wilhelm, Klaus

    2015-03-01

    The spectral profiles of the coronal Ne viii line at 77 nm have different shapes in quiet-Sun regions and Coronal Holes (CHs). A single Gaussian fit of the line profile provides an adequate approximation in quiet-Sun areas, whereas, a strong shoulder on the long-wavelength side is a systematic feature in CHs. Although this has been noticed since 1999, no physical reason for the peculiar shape could be given. In an attempt to identify the cause of this peculiarity, we address three problems that could not be conclusively resolved, in a review article by a study team of the International Space Science Institute (ISSI) (Wilhelm et al. 2011): (1) The physical processes operating at the base and inside of plumes, as well as their interaction with the Solar Wind (SW). (2) The possible contribution of plume plasma to the fast SW streams. (3) The signature of the First-Ionization Potential (FIP) effect between plumes and inter-plume regions (IPRs). Before the spectroscopic peculiarities in IPRs and plumes in Polar Coronal Holes (PCHs) can be further investigated with the instrument Solar Ultraviolet Measurements of Emitted Radiation (SUMER) aboard the Solar and Heliospheric Observatory (SOHO), it is mandatory to summarize the results of the review to place the spectroscopic observations into context. Finally, a plume model is proposed that satisfactorily explains the plasma flows up and down the plume field lines and leads to the shape of the neon line in PCHs.

  6. MHD Modeling of Coronal Loops: the Transition Region Throat

    NASA Technical Reports Server (NTRS)

    Guarrasi, M.; Reale, F.; Orlando, S.; Mignone, A.; Klimchuk, J. A.

    2014-01-01

    Context. The expansion of coronal loops in the transition region may considerably influence the diagnostics of the plasma emission measure. The cross-sectional area of the loops is expected to depend on the temperature and pressure, and might be sensitive to the heating rate. Aims. The approach here is to study the area response to slow changes in the coronal heating rate, and check the current interpretation in terms of steady heating models. Methods. We study the area response with a time-dependent 2D magnetohydrodynamic (MHD) loop model, including the description of the expanding magnetic field, coronal heating and losses by thermal conduction, and radiation from optically thin plasma. We run a simulation for a loop 50 Mm long and quasi-statically heated to about 4 millikelvin. Results. We find that the area can change substantially with the quasi-steady heating rate, e.g., by approx. 40% at 0.5 millikelvin as the loop temperature varies between 1 millikelvin and 4 millikelvin, and, therefore, affects the interpretation of the differential emission measure vs. temperature (DEM(T)) curves.

  7. Effect of coronal structure on loop oscillations: exponential profiles

    NASA Astrophysics Data System (ADS)

    Díaz, A. J.; Donnelly, G. R.; Roberts, B.

    2007-12-01

    Aims:The role of longitudinal structuring of the surrounding corona on the modes of oscillation of a coronal magnetic flux tube was studied in Donnelly et al. (2006) for a piecewise uniform profile. Here we investigate whether a more realistic continuous exponential profile changes the conclusions drawn from that paper. Methods: A partial differential equation is derived for the total pressure perturbation of the fast modes, which is then decomposed by separation of variables. The longitudinal part is solved numerically, obtaining a dispersion relation. These results are supported by an analytical investigation in terms of Bessel functions of purely imaginary order. Results: Structure in the interior of the loop shifts the frequencies of the modes (and may trap higher harmonics), an effect which can be understood by taking an averaged profile with a suitable weight. Structure in the environment modifies only slightly the frequencies, but displaces the cutoff frequency. The shift due to the structure in the fundamental period is small, but the ratio between the periods of the fundamental mode and its harmonics can be used to probe the structure. Conclusions: The results support our previous study in a more realistic, continuously varying profile and provide limits to the conclusions drawn in coronal seismology if an unstructured loop is used. Also, the ratio between the period of the fundamental kink (even) mode and its first (odd) harmonic is proven as an extra seismological tool for coronal loops.

  8. Validation of the Coronal Thick Target Source Model

    NASA Astrophysics Data System (ADS)

    Fleishman, Gregory D.; Xu, Yan; Nita, Gelu N.; Gary, Dale E.

    2016-01-01

    We present detailed 3D modeling of a dense, coronal thick-target X-ray flare using the GX Simulator tool, photospheric magnetic measurements, and microwave imaging and spectroscopy data. The developed model offers a remarkable agreement between the synthesized and observed spectra and images in both X-ray and microwave domains, which validates the entire model. The flaring loop parameters are chosen to reproduce the emission measure, temperature, and the nonthermal electron distribution at low energies derived from the X-ray spectral fit, while the remaining parameters, unconstrained by the X-ray data, are selected such as to match the microwave images and total power spectra. The modeling suggests that the accelerated electrons are trapped in the coronal part of the flaring loop, but away from where the magnetic field is minimal, and, thus, demonstrates that the data are clearly inconsistent with electron magnetic trapping in the weak diffusion regime mediated by the Coulomb collisions. Thus, the modeling supports the interpretation of the coronal thick-target sources as sites of electron acceleration in flares and supplies us with a realistic 3D model with physical parameters of the acceleration region and flaring loop.

  9. A solar type II radio burst from coronal mass ejection-coronal ray interaction: Simultaneous radio and extreme ultraviolet imaging

    SciTech Connect

    Chen, Yao; Du, Guohui; Feng, Shiwei; Kong, Xiangliang; Wang, Bing; Feng, Li; Guo, Fan; Li, Gang

    2014-05-20

    Simultaneous radio and extreme ultraviolet (EUV)/white-light imaging data are examined for a solar type II radio burst occurring on 2010 March 18 to deduce its source location. Using a bow-shock model, we reconstruct the three-dimensional EUV wave front (presumably the type-II-emitting shock) based on the imaging data of the two Solar TErrestrial RElations Observatory spacecraft. It is then combined with the Nançay radio imaging data to infer the three-dimensional position of the type II source. It is found that the type II source coincides with the interface between the coronal mass ejection (CME) EUV wave front and a nearby coronal ray structure, providing evidence that the type II emission is physically related to the CME-ray interaction. This result, consistent with those of previous studies, is based on simultaneous radio and EUV imaging data for the first time.

  10. Energy and momentum deposition in coronal holes. Solar coronal hole simulations compared with interpretations of YOHKOH SXT observations

    NASA Astrophysics Data System (ADS)

    Tziotziou, K.; Martens, P. C. H.; Hearn, A. G.

    1998-12-01

    A grid of 74 coronal models with parameterized heating distribution, representing a wide range of physical parameters, has been calculated. We find that three of these models reproduce the recent observations made by Hara et al. (\\cite{hara:tsun}) with the soft X-ray telescope aboard the Japanese satellite Yohkoh, which indicate a temperature of 1.8 ~ 2.4 x es 10(6) { K with an emission measure of 10(25.5) to 10(26.2) cm^{-5}, while other solutions reproduce the more standard Yohkoh and Skylab observations, which have a temperature of about 1.4 x es 10(6) { K The best fit for the coronal temperature and emission measure gives a velocity at the Earth's orbit of only 10 {km s^{-1}. A model including acceleration by Alfven waves gives a final velocity of 630 km s^{-1} which is in agreement with the observations. The mechanical heating flux at the transition region is 2.1 x es 10(5) ergcms with a weighted average dissipation scale length of 0.1 R_{\\odot}. The flux of Alfven waves is 1 x es 10(5) ergcms . In our models the velocity of the solar wind from coronal holes is completely determined by the Alfven wave acceleration, in contrast to previous models in which the Alfven wave acceleration increased the velocity of the purely thermal model only by a factor 2. Observations of the non thermal broadening of the coronal red and green lines are consistent with this model.

  11. From SOHO to STEREO: Understanding Propagation of Coronal Mass Ejections

    NASA Astrophysics Data System (ADS)

    Gopalswamy, N.

    2011-12-01

    Direct comparison between coronal mass ejections (CMEs) from near the Sun and their solar wind counterparts became possible roughly a decade after the discovery of CMEs (Lindsay et al. 1999). This comparison revealed that fast CMEs decelerate and slow CMEs accelerate due to the interaction with the solar wind. Gopalswamy et al. (2000) quantified this interaction as an interplanetary acceleration which is useful in predicting the arrival time and speed of CMEs at 1 AU. The interplanetary acceleration is essentially due to the aerodynamic drag between the CME and the solar wind because the propelling force and the solar gravity are effective only near the Sun. Combined remote-sensing and in situ observations from SOHO and Wind/ACE have helped us estimate the influence of the solar wind on the propagation of CMEs. However, these measurements have severe limitations because the remote-sensed and in-situ observations correspond to different portions of the CME. Furthermore, the true speeds of Earth-directed CMEs cannot be measured accurately from a spacecraft located along the Sun-Earth line. There have been attempts to model the CME as a cone and get the space speed of the CME, which did improve the travel time predictions. Instruments on board the Solar Terrestrial Relations Observatory (STEREO) mission were able to provide observations of Earth-arriving CMEs without projection effects, while the same CMEs were observed at Sun-Earth L1 by Wind and ACE spacecraft. The quadrature between STEREO and L1 spacecraft presented an ideal situation to study the interplanetary evolution of CMEs and test earlier model results. The quadrature observations did improve the CME travel time predictions, but additional factors such as the unusually slow solar wind, CME cannibalism, and coronal-hole deflection need to be considered to reconcile the difference between observed and predicted travel times. This point is illustrated using the 2011 February 15 CME. References Gopalswamy, N

  12. Field Topology Analysis of a Long-lasting Coronal Sigmoid

    NASA Astrophysics Data System (ADS)

    Savcheva, A. S.; van Ballegooijen, A. A.; DeLuca, E. E.

    2012-01-01

    We present the first field topology analysis based on nonlinear force-free field (NLFFF) models of a long-lasting coronal sigmoid observed in 2007 February with the X-Ray Telescope on Hinode. The NLFFF models are built with the flux rope insertion method and give the three-dimensional coronal magnetic field as constrained by observed coronal loop structures and photospheric magnetograms. Based on these models, we have computed horizontal maps of the current and the squashing factor Q for 25 different heights in the corona for all six days of the evolution of the region. We use the squashing factor to quantify the degree of change of the field line linkage and to identify prominent quasi-separatrix layers (QSLs). We discuss the major properties of these QSL maps and devise a way to pick out important QSLs since our calculation cannot reach high values of Q. The complexity in the QSL maps reflects the high degree of fragmentation of the photospheric field. We find main QSLs and current concentrations that outline the flux rope cavity and that become characteristically S-shaped during the evolution of the sigmoid. We note that, although intermittent bald patches exist along the length of the sigmoid during its whole evolution, the flux rope remains stable for several days. However, shortly after the topology of the field exhibits hyperbolic flux tubes (HFT) on February 7 and February 12 the sigmoid loses equilibrium and produces two B-class flares and associated coronal mass ejections (CMEs). The location of the most elevated part of the HFT in our model coincides with the inferred locations of the two flares. Therefore, we suggest that the presence of an HFT in a coronal magnetic configuration may be an indication that the system is ready to erupt. We offer a scenario in which magnetic reconnection at the HFT drives the system toward the marginally stable state. Once this state is reached, loss of equilibrium occurs via the torus instability, producing a CME.

  13. DISPELLING ILLUSIONS OF REFLECTION: A NEW ANALYSIS OF THE 2007 MAY 19 CORONAL 'WAVE' EVENT

    SciTech Connect

    Attrill, Gemma D. R.

    2010-07-20

    A new analysis of the 2007 May 19 coronal wave-coronal mass ejection-dimmings event is offered employing base difference extreme-ultraviolet (EUV) images. Previous work analyzing the coronal wave associated with this event concluded strongly in favor of purely an MHD wave interpretation for the expanding bright front. This conclusion was based to a significant extent on the identification of multiple reflections of the coronal wave front. The analysis presented here shows that the previously identified 'reflections' are actually optical illusions and result from a misinterpretation of the running difference EUV data. The results of this new multiwavelength analysis indicate that two coronal wave fronts actually developed during the eruption. This new analysis has implications for our understanding of diffuse coronal waves and questions the validity of the analysis and conclusions reached in previous studies.

  14. Optimizing Global Coronal Magnetic Field Models Using Image-based Constraints

    NASA Astrophysics Data System (ADS)

    Jones, Shaela I.; Davila, Joseph M.; Uritsky, Vadim

    2016-04-01

    The coronal magnetic field directly or indirectly affects a majority of the phenomena studied in the heliosphere. It provides energy for coronal heating, controls the release of coronal mass ejections, and drives heliospheric and magnetospheric activity, yet the coronal magnetic field itself has proven difficult to measure. This difficulty has prompted a decades-long effort to develop accurate, timely, models of the field—an effort that continues today. We have developed a method for improving global coronal magnetic field models by incorporating the type of morphological constraints that could be derived from coronal images. Here we report promising initial tests of this approach on two theoretical problems, and discuss opportunities for application.

  15. Analysis and Modeling of Coronal Holes Observed by CORONAS-1. 1; Morphology and Magnetic Field Configuration

    NASA Technical Reports Server (NTRS)

    Obridko, Vladmir; Formichev, Valery; Kharschiladze, A. F.; Zhitnik, Igor; Slemzin, Vladmir; Hathaway, David H.; Wu, Shi T.

    1998-01-01

    Two low-latitude coronal holes observed by CORONAS-1 in April and June 1994 are analyzed together with magnetic field measurements obtained from Wilcox and Kitt Peak Solar Observatories. To estimate the comparable temperature of these two coronal holes, the YOHKOH observations are also utilized. Using this information, we have constructed three-dimensional magnetic field lines to illustrate the geometrical configuration of these coronal holes. The calculated synoptic maps are used to determine the existence of closed and open field regions of the hole. Finally, we have correlated the characteristics of two coronal holes with observed solar wind speed. We found that the brighter coronal hole has high speed solar wind, and the dimmer coronal hole has low speed solar wind.

  16. NO TRACE LEFT BEHIND: STEREO OBSERVATION OF A CORONAL MASS EJECTION WITHOUT LOW CORONAL SIGNATURES

    SciTech Connect

    Robbrecht, Eva; Patsourakos, Spiros; Vourlidas, Angelos

    2009-08-10

    The availability of high-quality synoptic observations of the extreme-ultraviolet (EUV) and visible corona during the SOHO mission has advanced our understanding of the low corona manifestations of coronal mass ejections (CMEs). The EUV imager/white light coronagraph connection has been proven so powerful, it is routinely assumed that if no EUV signatures are present when a CME is observed by a coronagraph, then the event must originate behind the visible limb. This assumption carries strong implications for space weather forecasting but has not been put to the test. This paper presents the first detailed analysis of a frontside, large-scale CME that has no obvious counterparts in the low corona as observed in EUV and H{alpha} wavelengths. The event was observed by the SECCHI instruments onboard the STEREO mission. The COR2A coronagraph observed a slow flux-rope-type CME, while an extremely faint partial halo was observed in COR2B. The event evolved very slowly and is typical of the streamer-blowout CME class. EUVI A 171 A images show a concave feature above the east limb, relatively stable for about two days before the eruption, when it rises into the coronagraphic fields and develops into the core of the CME. None of the typical low corona signatures of a CME (flaring, EUV dimming, filament eruption, waves) were observed in the EUVI B images, which we attribute to the unusually large height from which the flux rope lifted off. This interpretation is supported by the CME mass measurements and estimates of the expected EUV dimming intensity. Only thanks to the availability of the two viewpoints we were able to identify the likely source region. The event originated along a neutral line over the quiet-Sun. No active regions were present anywhere on the visible (from STEREO B) face of the disk. Leaving no trace behind on the solar disk, this observation shows unambiguously that a CME eruption does not need to have clear on-disk signatures. Also it sheds light on the

  17. Coronal mass ejection rate and the evolution of the large-scale K-coronal density distribution

    SciTech Connect

    Sime, D.G.

    1989-01-01

    Recently reported occurrence rates of coronal mass ejections (CMEs) are compared with the time scale for the long-term evolution of the global white light coronal density distribution. This time scale is estimated from the synoptic observations of the corona made from Mauna Loa, Hawaii, by a seies of K-coronameters. The data span a period of more than 20 years and show evolution rates which vary with time roughly in phase with the solar activity cycle. However, there are detailed differences between the sunspot number curve and the long-term behavior of this quantity. When the occurrence rates of CMEs observed from orbiting coronagraphs, available mainly during the descending phase of the activity cycle, are compared with this evolution time, it is found that the two quantities are inversely proportional. From energy considerations, it is unlikely that there is a causal relationship between CMEs and this coronal evolution. Rather, the result indicates that the processes which lead to the global evolution are intimately related to those which give rise to CMEs, a hypothesis consistent with current theories that CMEs arise from preexisting magnetic structures which become stressed by the global magnetic field rearrangement to the point of instability. copyright American Geophysical Union 1989

  18. Newborn Coronal Holes Associated with the Disappearance of Polarity Reversal Boundaries (P46)

    NASA Astrophysics Data System (ADS)

    Shelke, R.

    2006-11-01

    rajendra_shelke@yahoo.co.in Coronal holes play an important role in the occurrence of various kinds of solar events. The geomagnetic activity, coronal transients, type II radio bursts, and soft X ray blowouts have shown their strong association with coronal holes (Webb et al., 1978; Shelke and Pande, 1985; Bhatnagar, 1996; Hewish and Bravo, 1986). Recently, Shelke (2006) has linked the onset of interplanetary erupting stream disturbances with the evolutionary changes in the coronal holes. The present study reveals that there exists some physical relationship between the formation of new coronal holes and the disappearance of polarity reversal boundaries with or without the overlying prominences. About 124 new coronal holes are found to emerge at the locations where polarity reversal boundaries existed prior to their disappearance. Among them, nearly 66% and 18% newborn coronal holes have been associated with disappearing prominences and disappearing small unipolar magnetic regions (UMRs) with encircled polarity reversal boundaries respectively. Coronal holes and quiescent prominences are stable solar features that last for many solar rotations. A coronal hole is indicative of a radial magnetic field of a predominant magnetic polarity at the photosphere, whereas solar prominence overlying the polarity reversal boundary straddles both the polarities of a bipolar magnetic region. The new coronal hole emerges on the Sun, owing to the changes in magnetic field configuration leading to the opening of closed magnetic structure into the corona. The mechanism that leads to the eruption of polarity reversal boundaries with or without prominences seems to be interlinked with the mechanism that converts bipolar magnetic regions into unipolar magnetic regions characterizing coronal holes. The fundamental activity for the onset of erupting polarity reversal boundary seems to be the opening of preexisting closed magnetic structures into a new coronal hole, which can support mass

  19. Coronal temperatures of selected active cool stars as derived from low resolution Einstein observations

    NASA Technical Reports Server (NTRS)

    Vilhu, Osmi; Linsky, Jeffrey L.

    1990-01-01

    Mean coronal temperatures of some active G-K stars were derived from Rev1-processed Einstein-observatory's IPC-spectra. The combined X-ray and transition region emission line data are in rough agreement with static coronal loop models. Although the sample is too small to derive any statistically significant conclusions, it suggests that the mean coronal temperature depends linearly on the inverse Rossby-number, with saturation at short rotation periods.

  20. Coronal holes, solar wind streams, and recurrent geomagnetic disturbances - 1973-1976

    NASA Technical Reports Server (NTRS)

    Sheeley, N. R., Jr.; Harvey, J. W.; Feldman, W. C.

    1976-01-01

    Observations of coronal holes, solar-wind streams, and geomagnetic disturbances during 1973-1976 are compared in a 27-day pictorial format which shows their long-term evolution. The results leave little doubt that coronal holes are related to the high-speed streams and their associated recurrent geomagnetic disturbances. In particular, these observations strongly support the hypothesis that coronal holes are the solar origin of the high-speed streams observed in the solar wind near the ecliptic plane.

  1. General practitioner's knowledge of when to refer deaths to a coroner.

    PubMed Central

    Start, R D; Usherwood, T P; Carter, N; Dorries, C P; Cotton

    1995-01-01

    BACKGROUND--In 1992 about 179,000 deaths were reported to coroners in England and Wales and these represented 32% of the total number of registered deaths. Many of these cases were referred to coroners by general practitioners who certify the vast majority of deaths which occur outside hospitals. The safeguards to society which are provided by the coroner system in England and Wales are undermined if doctors fail to recognize those deaths which should be reported for further investigation. AIM--A study was undertaken to assess the ability of general practitioners to recognize deaths which require referral to a coroner. METHOD-A postal questionnaire consisting of 12 fictitious case histories was sent to all 323 general practitioners in Sheffield and the senior staff of the local coroner's office (two coroner's officers and two deputy coroners). Ten of the case histories contained a clear indication for referral to the coroner. RESULTS--A total fo 196 general practitioners (61%) and all the coroner's office staff returned the questionnaire. General practitioners correctly identified whether or not referral was indicated, with reasons, in a mean of 8.5 cases (range 4-12). Only six general practitioners (3%) were correct in all 12 cases. All of the coroner's staff were correct in all cases. CONCLUSION--General practitioners may be failing to bring certain categories of cases to the attention of coroners because of misconceptions of ignorance of their medico-legal responsibilities. General practitioner education in this area, and a closer working relationship between general practitioners and coroners may improve the situation. PMID:7612320

  2. Differentiation between coronal holes and filament channels from SDO image data using machine learning algorithms

    NASA Astrophysics Data System (ADS)

    Reiss, Martin; Hofmeister, Stefan; DeVisscher, Ruben; Temmer, Manuela; Veronig, Astrid; Delouille, Veronique; Rotter, Thomas

    2015-04-01

    In combination with the Sun's rotation, coronal holes and their associated high speed solar wind streams (HSSs) shape the solar wind distribution in the interplanetary space. The structuring of interplanetary space is especially important for deriving changes in the kinematics of coronal mass ejections. In order to forecast HSSs we empirically relate the fractional coronal hole area to the solar wind speed at 1AU. We apply an automated method for the identification and extraction of coronal hole regions in SDO/AIA 193Å images. Due to the almost equal low intensity of coronal holes and filament channels the intensity-based detection method cannot differentiation filament channels from coronal holes. Hence, to improve the HSS forecasting method we need to distinguish filament channels from coronal holes. Compared to coronal holes, filament channels are regions of closed magnetic field lines along a polarity inversion line and are therefore different in their magnetic field configuration. Acting on this physical background we investigate the benefits of using Haralick's textural features to analyze the intrinsic texture information contained with coronal holes and filament channels in AIA and HMI images. In combination with first order statistics and shape measures, we tested several classifiers to find the most suitable decision rule for a differentiation. In order to evaluate the performance of each classifier the Hanssen-Kuiper skill score, also called True Skill Statistic, was calculated. The results reveal that all classifiers, including Support Vector Machine (SVM), Linear SVM, Decision Tree and Random Forest classifier provide good results in general.

  3. UVCS/SOHO Observations of Coronal Holes from Solar Minimum to Solar Maximum

    NASA Astrophysics Data System (ADS)

    Miralles, M. P.; Cranmer, S. R.; Esser, R.; Kohl, J. L.

    2001-12-01

    Coronal holes are open field, low-density source regions of the solar wind. At solar minimum, large coronal holes are present at the poles and are the dominant source of the solar wind flow for this part of the solar cycle. At solar maximum, coronal holes of varying sizes and shapes appear at all latitudes and last for several rotations. During this stage of the cycle, the dominant component is mainly slow wind, but fast wind streams are generated by large coronal holes. UVCS/SOHO has been used to measure the plasma properties in several types of coronal holes from 1996 to 2001. Spectroscopic diagnostics of O5+ velocity distributions and outflow velocities are derived from measurements of intensities and line widths for O~VI 103.2 and 103.7 nm as a function of height. We compare the plasma properties of coronal holes from solar minimum to solar maximum and discuss the evolution of coronal holes during the solar cycle. We also study the compatibility between the growing database of coronal hole plasma properties and theoretical models of extended coronal heating via ion cyclotron resonance. This work is supported by NASA under Grant NAG5-10093 to the Smithsonian Astrophysical Observatory, by the Italian Space Agency and by PRODEX (Swiss contribution).

  4. A STATISTICAL STUDY OF CORONAL ACTIVE EVENTS IN THE NORTH POLAR REGION

    SciTech Connect

    Sako, Nobuharu; Shimojo, Masumi; Watanabe, Tetsuya; Sekii, Takashi

    2013-09-20

    In order to study the relationship between characteristics of polar coronal active events and the magnetic environment in which such events take place, we analyze 526 X-ray jets and 1256 transient brightenings in the polar regions and in regions around the equatorial limbs. We calculate the occurrence rates of these polar coronal active events as a function of distance from the boundary of coronal holes, and find that most events in the polar quiet regions occur adjacent to and equatorward of the coronal hole boundaries, while events in the polar coronal holes occur uniformly within them. Based primarily on the background intensity, we define three categories of regions that produce activity: polar coronal holes, coronal hole boundary regions, and polar quiet regions. We then investigate the properties of the events produced in these regions. We find no significant differences in their characteristics, for example, length and lifetime, but there are differences in the occurrence rates. The mean occurrence rate of X-ray jets around the boundaries of coronal holes is higher than that in the polar quiet regions, equatorial quiet regions, and polar coronal holes. Furthermore, the mean occurrence rate of transient brightenings is also higher in these regions. We make comparison with the occurrence rates of emerging and canceling magnetic fields in the photosphere reported in previous studies, and find that they do not agree with the occurrence rates of transient brightenings found in this study.

  5. Comparison of mucogingival changes following treatment with coronally positioned flap and guided tissue regeneration procedures.

    PubMed

    Trombelli, L; Tatakis, D N; Scabbia, A; Zimmerman, G J

    1997-10-01

    This study compared the variation in anatomic width of the mucogingival unit following coronally positioned flap or guided tissue regeneration procedures in deep (greater than or equal to 4 mm) buccal maxillary gingival recession defects 12 months postsurgery. Eighteen patients, 10 treated with guided tissue regeneration procedures and eight treated with coronally positioned flap procedures, were retrospectively analyzed. The results demonstrated that both treatments led to consistent recession depth reduction and coronal shift of the mucogingival junction. A significant increase in the amount of keratinized gingiva was observed for the guided tissue regeneration procedure, but a decrease that was not statistically significant was observed for the coronally positioned flap procedure. PMID:9497733

  6. Estudio de Salud Agrícola

    Cancer.gov

    En 1993, científicos del Instituto Nacional del Cáncer, Instituto Nacional de Ciencias Ambientales y la Agencia de Protección Ambiental de Estados Unidos iniciaron un estudio conocido como Estudio de Salud Agrícola (AHS).

  7. Reexamination of the coronal index of solar activity

    NASA Astrophysics Data System (ADS)

    Rybanský, M.; Rušin, V.; Minarovjech, M.; Klocok, L.; Cliver, E. W.

    2005-08-01

    The coronal index (CI) of solar activity is the irradiance of the Sun as a star in the coronal green line (Fe XIV, 530.3 nm or 5303 Å). It is derived from ground-based observations of the green corona made by the network of coronal stations (currently Kislovodsk, Lomnický Štít, Norikura, and Sacramento Peak). The CI was introduced by Rybanský (1975) to facilitate comparison of ground-based green line measurements with satellite-based extreme ultraviolet and soft X-ray observations. The CI since 1965 is based on the Lomnický Štít photometric scale; the CI was extended to earlier years by Rybanský et al. (1994) based on cross-calibrations of Lomnický Štít data with measurements made at Pic du Midi and Arosa. The resultant 1939-1992 CI had the interesting property that its value at the peak of the 11-year cycle increased more or less monotonically from cycle 18 through cycle 22 even though the peak sunspot number of cycle 20 exhibited a significant local minimum between that of cycles 19 and 21. Rušin and Rybanský (2002) recently showed that the green line intensity and photospheric magnetic field strength were highly correlated from 1976 to 1999. Since the photospheric magnetic field strength is highly correlated with sunspot number, the lack of close correspondence between the sunspot number and the CI from 1939 to 2002 is puzzling. Here we show that the CI and sunspot number are highly correlated only after 1965, calling the previously-computed coronal index for earlier years (1939-1965) into question. We can use the correlation between the CI and sunspot number (also the 2800 MHz radio flux and the cosmic ray intensity) to recompute daily values of the CI for years before 1966. In fact, this method can be used to obtain CI values as far back as we have reliable sunspot observations (˜1850). The net result of this exercise is a CI that closely tracks the sunspot number at all times. We can use the sunspot-CI relationship (for 1966-2002) to identify

  8. Structure and dynamics of the coronal magnetic field

    NASA Technical Reports Server (NTRS)

    VanHoven, Gerard; Schnack, Dalton D.

    1996-01-01

    The last few years have seen a marked increase in the sophistication of models of the solar corona. This has been brought about by a confluence of three key elements. First, the collection of high-resolution observations of the Sun, both in space and time, has grown tremendously. The SOHO (Solar Heliospheric Observatory) mission is providing additional correlated high-resolution magnetic, white-light and spectroscopic observations. Second, the power and availability of supercomputers has made two- and three-dimensional modeling routine. Third, the sophistication of the models themselves, both in their geometrical realism and in the detailed physics that has been included, has improved significantly. The support from our current Space Physics Theory grant has allowed us to exploit this confluence of capabilities. We have carried out direct comparisons between observations and models of the solar corona. The agreement between simulated coronal structure and observations has verified that the models are mature enough for detailed analysis, as we will describe. The development of this capability is especially timely, since observations obtained from three space missions that are underway (Ulysses, WIND and SOHO) offer an opportunity for significant advances in our understanding of the corona and heliosphere. Through this interplay of observations and theory we can improve our understanding of the Sun. Our achievements thus far include progress modeling the large-scale structure of the solar corona, three-dimensional models of active region fields, development of emerging flux and current, formation and evolution of coronal loops, and coronal heating by current filaments.

  9. Intermediate inclinations of type 2 Coronal-Line Forest AGN

    NASA Astrophysics Data System (ADS)

    Rose, Marvin; Elvis, Martin; Crenshaw, Michael; Glidden, Ana

    2015-07-01

    Coronal-Line Forest Active Galactic Nuclei (CLiF AGN) are remarkable in the sense that they have a rich spectrum of dozens of coronal emission lines (e.g. [Fe VII], [Fe X] and [Ne V]) in their spectra. Rose, Elvis & Tadhunter suggest that the inner obscuring torus wall is the most likely location of the coronal line region in CLiF AGN, and the unusual strength of the forbidden high-ionization lines is due to a specific AGN-torus inclination angle. Here, we test this suggestion using mid-IR colours (4.6-22 μm) from the Wide-Field Infrared Survey Explorer for the CLiF AGN. We use the Fischer et al. result that showed that as the AGN-torus inclination becomes more face on, the Spitzer 5.5-30 μm colours become bluer. We show that the [W2-W4] colours for the CLiF AGN (<[W2-W4]> = 5.92 ± 0.12) are intermediate between Sloan Digital Sky Survey (SDSS) type 1 (<[W2-W4]> = 5.22 ± 0.01) and type 2 AGN (<[W2-W4]> = 6.35 ± 0.03). This implies that the AGN-torus inclinations for the CLiF AGN are indeed intermediate, supporting the work of Rose, Elvis & Tadhunter. The confirmed relation between CLiF AGN and their viewing angle shows that CLiF AGN may be useful for our understanding of AGN unification.

  10. On the Nature of the Solar Wind from Coronal Pseudostreamers

    NASA Astrophysics Data System (ADS)

    Wang, Y.-M.; Grappin, R.; Robbrecht, E.; Sheeley, N. R., Jr.

    2012-04-01

    Coronal pseudostreamers, which separate like-polarity coronal holes, do not have current sheet extensions, unlike the familiar helmet streamers that separate opposite-polarity holes. Both types of streamers taper into narrow plasma sheets that are maintained by continual interchange reconnection with the adjacent open magnetic field lines. White-light observations show that pseudostreamers do not emit plasma blobs; this important difference from helmet streamers is due to the convergence of like-polarity field lines above the X-point, which prevents the underlying loops from expanding outward and pinching off. The main component of the pseudostreamer wind has the form of steady outflow along the open field lines rooted just inside the boundaries of the adjacent coronal holes. These flux tubes are characterized by very rapid expansion below the X-point, followed by reconvergence at greater heights. Analysis of an idealized pseudostreamer configuration shows that, as the separation between the underlying holes increases, the X-point rises and the expansion factor f ss at the source surface increases. In situ observations of pseudostreamer crossings indicate wind speeds v ranging from ~350 to ~550 km s-1, with O7 +/O6 + ratios that are enhanced compared with those in high-speed streams but substantially lower than in the slow solar wind. Hydrodynamic energy-balance models show that the empirical v-f ss relation overestimates the wind speeds from nonmonotonically expanding flux tubes, particularly when the X-point is located at low heights and f ss is small. We conclude that pseudostreamers produce a "hybrid" type of outflow that is intermediate between classical slow and fast solar wind.

  11. Interpretation of the coronal magnetic field configuration of the Sun

    NASA Astrophysics Data System (ADS)

    Li, Bo; Li, Xing; Yu, Hui

    2012-12-01

    The origin of the heliospheric magnetic flux on the Sun, and hence the origin of the solar wind, is a topic of hot debate. While the prevailing view is that the solar wind originates from outside the coronal streamer helmets, there also exists the suggestion that the open magnetic field spans a far wider region. Without the definitive measurement of the coronal magnetic field, it is difficult to unambiguously resolve the conflict between the two scenarios. We present two 2-dimensional, Alfvénic-turbulence-based models of the solar corona and solar wind, one with and the other without a closed magnetic field region in the inner corona. The purpose of the latter model is to test whether it is possible to realize a picture suggested by polarimetric measurements of the corona using the Fe XIII 10747 Å line, where open magnetic field lines seem to penetrate the streamer base. The boundary conditions at the coronal base are able to account for important observational constraints, especially those on the magnetic flux distribution. Interestingly, the two models provide similar polarized brightness (pB) distributions in the field of view (FOV) of SOHO/LASCO C2 and C3 coronagraphs. In particular, a dome-shaped feature is present in the C2 FOV even for the model without a closed magnetic field. Moreover, both models fit the Ulysses data scaled to 1 AU equally well. We suggest that: 1) The pB observations cannot be safely taken as a proxy for the magnetic field topology, as is often implicitly assumed. 2) The Ulysses measurements, especially the one showing a nearly uniform distribution with heliocentric latitude of the radial magnetic field, do not rule out the ubiquity of open magnetic fields on the Sun.

  12. ON THE NATURE OF THE SOLAR WIND FROM CORONAL PSEUDOSTREAMERS

    SciTech Connect

    Wang, Y.-M.; Sheeley, N. R. J.R.; Grappin, R.; Robbrecht, E. E-mail: neil.sheeley@nrl.navy.mil E-mail: eva.robbrecht@oma.be

    2012-04-20

    Coronal pseudostreamers, which separate like-polarity coronal holes, do not have current sheet extensions, unlike the familiar helmet streamers that separate opposite-polarity holes. Both types of streamers taper into narrow plasma sheets that are maintained by continual interchange reconnection with the adjacent open magnetic field lines. White-light observations show that pseudostreamers do not emit plasma blobs; this important difference from helmet streamers is due to the convergence of like-polarity field lines above the X-point, which prevents the underlying loops from expanding outward and pinching off. The main component of the pseudostreamer wind has the form of steady outflow along the open field lines rooted just inside the boundaries of the adjacent coronal holes. These flux tubes are characterized by very rapid expansion below the X-point, followed by reconvergence at greater heights. Analysis of an idealized pseudostreamer configuration shows that, as the separation between the underlying holes increases, the X-point rises and the expansion factor f{sub ss} at the source surface increases. In situ observations of pseudostreamer crossings indicate wind speeds v ranging from {approx}350 to {approx}550 km s{sup -1}, with O{sup 7+}/O{sup 6+} ratios that are enhanced compared with those in high-speed streams but substantially lower than in the slow solar wind. Hydrodynamic energy-balance models show that the empirical v-f{sub ss} relation overestimates the wind speeds from nonmonotonically expanding flux tubes, particularly when the X-point is located at low heights and f{sub ss} is small. We conclude that pseudostreamers produce a 'hybrid' type of outflow that is intermediate between classical slow and fast solar wind.

  13. Transverse, propagating velocity perturbations in solar coronal loops

    NASA Astrophysics Data System (ADS)

    De Moortel, I.; Pascoe, D. J.; Wright, A. N.; Hood, A. W.

    2016-01-01

    As waves and oscillations carry both energy and information, they have enormous potential as a plasma heating mechanism and, through seismology, to provide estimates of local plasma properties which are hard to obtain from direct measurements. Being sufficiently near to allow high-resolution observations, the atmosphere of the Sun forms a natural plasma laboratory. Recent observations have revealed that an abundance of waves and oscillations is present in the solar atmosphere, leading to a renewed interest in wave heating mechanisms. This short review paper gives an overview of recently observed transverse, propagating velocity perturbations in coronal loops. These ubiquitous perturbations are observed to undergo strong damping as they propagate. Using 3D numerical simulations of footpoint-driven transverse waves propagating in a coronal plasma with a cylindrical density structure, in combination with analytical modelling, it is demonstrated that the observed velocity perturbations can be understood in terms of coupling of different wave modes in the inhomogeneous boundaries of the loops. Mode coupling in the inhomogeneous boundary layers of the loops leads to the coupling of the transversal (kink) mode to the azimuthal (Alfvén) mode, observed as the decay of the transverse kink oscillations. Both the numerical and analytical results show the spatial profile of the damped wave has a Gaussian shape to begin with, before switching to exponential decay at large heights. In addition, recent analysis of CoMP (Coronal Multi-channel Polarimeter) Doppler shift observations of large, off-limb, trans-equatorial loops shows that Fourier power at the apex appears to be higher in the high-frequency part of the spectrum than expected from theoretical models. This excess high-frequency FFT power could be tentative evidence for the onset of a cascade of the low-to-mid frequency waves into (Alfvénic) turbulence.

  14. A Type II Radio Burst without a Coronal Mass Ejection

    NASA Astrophysics Data System (ADS)

    Su, W.; Cheng, X.; Ding, M. D.; Chen, P. F.; Sun, J. Q.

    2015-05-01

    Type II radio bursts are thought to be a signature of coronal shocks. In this paper, we analyze a short-lived type II burst that started at 07:40 UT on 2011 February 28. By carefully checking white-light images, we find that the type II radio burst is not accompanied by a coronal mass ejection, only by a C2.4 class flare and narrow jet. However, in the EUV images provided by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory, we find a wave-like structure that propagated at a speed of ∼600 km s‑1 during the burst. The relationship between the type II radio burst and the wave-like structure is, in particular, explored. For this purpose, we first derive the density distribution under the wave by the differential emission measure method, which is used to restrict the empirical density model. We then use the restricted density model to invert the speed of the shock that produces the observed frequency drift rate in the dynamic spectrum. The inverted shock speed is similar to the speed of the wave-like structure. This implies that the wave-like structure is most likely a coronal shock that produces the type II radio burst. We also examine the evolution of the magnetic field in the flare-associated active region and find continuous flux emergence and cancellation taking place near the flare site. Based on these facts, we propose a new mechanism for the formation of the type II radio burst, i.e., the expansion of the strongly inclined magnetic loops after reconnecting with a nearby emerging flux acts as a piston to generate the shock wave.

  15. Analysis of the Deflection of CMEs by Coronal Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Liewer, Paulett C.; Panasenco, O.; Vourlidas, A.

    2013-07-01

    Understanding coronal influences on the direction of propagation of CMEs is important for space weather prediction. It is well known that CMEs often propagate non-radially, e.g., they do not move out radially from the location of the solar source (see, e.g., Cremades and Bothmer, A&A, 2004; Panasenco et al., Sol. Phys. 2013). There is evidence that most CMEs exit the corona in the minimum field region surrounding the coronal/heliospheric current sheet (HCS). If this is the case, then the degree of deflection should reflect the distance of the source region from the current sheet region. Here we study the observed deflection in latitude of four CMEs using STEREO/SECCHI’s EUV and white light observations to trace the deflection. A potential-field source surface (PFSS) model (Schrijver & DeRosa, Sol. Phys. 2003) is used to give information on the magnetic forces acting on the CME at different heights in the lower corona. This model, as well as the PFSS model results at the GONG website (http://gong.nso.edu/data/magmap/archive.html) and the coronal observations from STEREO, are used to try to determine the location of the HCS. For the events studied, we find cases when the deflection is gradual (occurring between the surface at several solar radii) and cases where the deflection is immediate (within ~1.5 solar radii). There are many cases in the literature where CMEs originating at high latitude are deflected towards the ecliptic and eventually impact Earth. Several of the CMEs we analyzed were later detected in situ at ~1 AU and we compare the near-Sun trajectory information to the trajectory information determine from the in situ information.

  16. Coronal Loops: Observations and Modeling of Confined Plasma

    NASA Astrophysics Data System (ADS)

    Reale, Fabio

    2014-07-01

    Coronal loops are the building blocks of the X-ray bright solar corona. They owe their brightness to the dense confined plasma, and this review focuses on loops mostly as structures confining plasma. After a brief historical overview, the review is divided into two separate but not independent parts: the first illustrates the observational framework, the second reviews the theoretical knowledge. Quiescent loops and their confined plasma are considered and, therefore, topics such as loop oscillations and flaring loops (except for non-solar ones, which provide information on stellar loops) are not specifically addressed here. The observational section discusses the classification, populations, and the morphology of coronal loops, its relationship with the magnetic field, and the loop stranded structure. The section continues with the thermal properties and diagnostics of the loop plasma, according to the classification into hot, warm, and cool loops. Then, temporal analyses of loops and the observations of plasma dynamics, hot and cool flows, and waves are illustrated. In the modeling section, some basics of loop physics are provided, supplying fundamental scaling laws and timescales, a useful tool for consultation. The concept of loop modeling is introduced and models are divided into those treating loops as monolithic and static, and those resolving loops into thin and dynamic strands. More specific discussions address modeling the loop fine structure and the plasma flowing along the loops. Special attention is devoted to the question of loop heating, with separate discussion of wave (AC) and impulsive (DC) heating. Large-scale models including atmosphere boxes and the magnetic field are also discussed. Finally, a brief discussion about stellar coronal loops is followed by highlights and open questions.

  17. Role of Transients in the Sustainability of Solar Coronal Plumes

    NASA Astrophysics Data System (ADS)

    Raouafi, N.-E.; Stenborg, G.

    2014-06-01

    We report on the role of small-scale, transient magnetic activity in the formation and evolution of solar coronal plumes. Three plumes within equatorial coronal holes are analyzed over the span of several days based on the Solar Dynamic Observatory (SDO)/Atmospheric Imaging Assembly 171 Å and 193 Å images and SDO/Helioseismic and Magnetic Imager line-of-sight magnetograms. The focus is on the role of transient structures at the footpoints in sustaining coronal plumes for relatively long periods of time (i.e., several days). The appearance of plumes is a gradual and lengthy process. In some cases, the initial stages of plume formation are marked by the appearance of pillar-like structures whose footpoints are the sources of transient brightenings. In addition to nominal jets occurring prior to and during the development of plumes, the data show that a large number of small jets (i.e., "jetlets") and plume transient bright points (PTBPs) occur on timescales of tens of seconds to a few minutes. These features are the result of quasi-random cancellations of fragmented and diffuse minority magnetic polarity with the dominant unipolar magnetic field concentration over an extended period of time. They unambiguously reflect a highly dynamical evolution at the footpoints and are seemingly the main energy source for plumes. This suggests a tendency for plumes to be dependent on the occurrence of transients (i.e., jetlets, and PTBPs) resulting from low-rate magnetic reconnection. The decay phase of plumes is characterized by gradual fainting and multiple rejuvenations as a result of the dispersal of the unipolar magnetic concentration and its precipitation into multiple magnetic centers.

  18. Finding X-ray Coronal Cycles in Low Mass Stars

    NASA Astrophysics Data System (ADS)

    Wilson, Maurice; Guenther, Hans Moritz; Auchettl, Katie

    2015-01-01

    We seek to increase the number of stars known to have an X-ray coronal cycle. Four stars (including the Sun) are known to experience periodic long-term coronal flux variability but the statistics are not superb. In this analysis, we analyze four stellar sources that have been observed frequently by Chandra and XMM-Newton over the last ~11 years. These four sources were the brightest among numerous stellar point sources within the Chandra Deep Field South. Solar flares can dramatically increase the flux measured for our stars on short time intervals and, in observations with insufficient time coverage, can be confused for the maximum of the stars' magnetic cycles (if they have one). We have discarded times where solar proton flares are detected in the data. We utilize an APEC model, which represents the coronal plasma, to fit our stellar spectra. As our sources are very faint, we do not subtract the background, but instead we fit the background and source spectra simultaneously. We use the chi-squared statistic to evaluate the confidence of our fits. We present four light curves which suggest that a long-term X-ray flux variability similar to our Sun (the solar X-ray flux can vary by a factor of 10 over ~11 years) is not present in these stellar sources. None of our stars experienced a flux variability exceeding a factor of 3 over an 11 year time scale but one of the four stars in our sample exhibits short term variability over a one year period. However, our stellar sources are too faint to conclusively state that the flux remains constant throughout all epochs.This work is supported by the National Science Foundation REU and Department of Defense AS-SURE programs under NSF Grant no. 1262851 and by the Smithsonian Institution.

  19. Role of transients in the sustainability of solar coronal plumes

    SciTech Connect

    Raouafi, N.-E.; Stenborg, G.

    2014-06-01

    We report on the role of small-scale, transient magnetic activity in the formation and evolution of solar coronal plumes. Three plumes within equatorial coronal holes are analyzed over the span of several days based on the Solar Dynamic Observatory (SDO)/Atmospheric Imaging Assembly 171 Å and 193 Å images and SDO/Helioseismic and Magnetic Imager line-of-sight magnetograms. The focus is on the role of transient structures at the footpoints in sustaining coronal plumes for relatively long periods of time (i.e., several days). The appearance of plumes is a gradual and lengthy process. In some cases, the initial stages of plume formation are marked by the appearance of pillar-like structures whose footpoints are the sources of transient brightenings. In addition to nominal jets occurring prior to and during the development of plumes, the data show that a large number of small jets (i.e., {sup j}etlets{sup )} and plume transient bright points (PTBPs) occur on timescales of tens of seconds to a few minutes. These features are the result of quasi-random cancellations of fragmented and diffuse minority magnetic polarity with the dominant unipolar magnetic field concentration over an extended period of time. They unambiguously reflect a highly dynamical evolution at the footpoints and are seemingly the main energy source for plumes. This suggests a tendency for plumes to be dependent on the occurrence of transients (i.e., jetlets, and PTBPs) resulting from low-rate magnetic reconnection. The decay phase of plumes is characterized by gradual fainting and multiple rejuvenations as a result of the dispersal of the unipolar magnetic concentration and its precipitation into multiple magnetic centers.

  20. About the magnetic origin of Chromospheric Spicules and Coronal Jets

    NASA Astrophysics Data System (ADS)

    Koutchmy, S.; Filippov, B.; Tavabi, E.

    2012-06-01

    Observations of jet- like phenomena near the solar limb are reported for a long time, first in Hα (Secchi observations of spicules in the 1870 ies), and after, from eclipse high resolution coronal images taken in white-light (1920-1973) as spiky structures. EUV jets were reported in the 70 ies from rocket and space-borne CIV filtergrams and finally X-EUV jets were reported from SXT observations of Yohkoh and from EIT and CDS SoHO observations. There is now little doubt that they are of magnetic origin although no magnetic field measurements exist for these regions and thermo-dynamical models are still work out. New observations of both spicules and jets with the SOT/SXT of Hinode were subjected to an analysis showing the influence of the null point(s) of the magnetic field. The collective behavior of the H CaII SOT(Hinode) time sequences of processed with the Madmax operator images of limb spicules show the torsional effects which were partly suggested before from the interpretation of high resolution limb spectra taken on Russian coronagraphs and the VTT at SacPeak. 100 s and shorter period waves are recorded. We propose a reconnection process occurring at the top of an emerging twisted flux tube for explaining some peculiarities of the spicular eruptions and possibly, as a viable mechanism for explaining the SXR jet eruptions. The result of a numerical 3D modeling illustrates this erupting mechanism although the behavior of the magneto-plasma structure near a null point, as shown by coronal filtergrams, does not necessary imply reconnections, especially the case of jets making a long coronal ray we observed in white-light with Lasco C2.

  1. Structure and dynamics of the coronal magnetic field

    NASA Astrophysics Data System (ADS)

    Vanhoven, Gerard; Schnack, Dalton D.

    1996-07-01

    The last few years have seen a marked increase in the sophistication of models of the solar corona. This has been brought about by a confluence of three key elements. First, the collection of high-resolution observations of the Sun, both in space and time, has grown tremendously. The SOHO (Solar Heliospheric Observatory) mission is providing additional correlated high-resolution magnetic, white-light and spectroscopic observations. Second, the power and availability of supercomputers has made two- and three-dimensional modeling routine. Third, the sophistication of the models themselves, both in their geometrical realism and in the detailed physics that has been included, has improved significantly. The support from our current Space Physics Theory grant has allowed us to exploit this confluence of capabilities. We have carried out direct comparisons between observations and models of the solar corona. The agreement between simulated coronal structure and observations has verified that the models are mature enough for detailed analysis, as we will describe. The development of this capability is especially timely, since observations obtained from three space missions that are underway (Ulysses, WIND and SOHO) offer an opportunity for significant advances in our understanding of the corona and heliosphere. Through this interplay of observations and theory we can improve our understanding of the Sun. Our achievements thus far include progress modeling the large-scale structure of the solar corona, three-dimensional models of active region fields, development of emerging flux and current, formation and evolution of coronal loops, and coronal heating by current filaments.

  2. Effect of Thermal Conduction on Acoustic Waves in Coronal Loops

    NASA Astrophysics Data System (ADS)

    Bogdan, T. J.

    2006-05-01

    The influence of classical (Spitzer) thermal conduction on longitudinal acoustic waves in a coronal loop is determined through an idealized but exactly solvable model. The model consists of an isothermal, stratified (constant gravity) atmosphere in which a monochromatic acoustic wave, traveling in the direction of decreasing density, is imposed throughout the lower half of the atmosphere. Based on the linearized equations of motion, the complete steady state (t-->∞) solution is obtained. In addition to the imposed driving wave, the solution also contains reflected and transmitted acoustic and thermal conduction waves. The mode transformation and mixing occurs in the vicinity of the atmospheric layer where the gas pressure passes through a critical value set by the magnitude of the thermal conduction and other model parameters. For 5 minute waves in a million degree loop, this critical pressure is on the order of 8×10-4 in cgs units. Since the apex gas pressure of many coronal loops of current interest is thought to be comfortably in excess of this value, mode mixing and transformation is not likely to be a relevant factor for understanding acoustic waves in these structures. On the other hand, enhanced thermal conductivity as a result of plasma instabilities, for example, could revive the importance of this mechanism for coronal loops. If this mixing layer is present, the calculations show that the pair of thermal conduction waves invariably gains the overwhelming majority of the energy flux of the incoming acoustic wave. This energy is rapidly dissipated in the neighborhood of the mixing layer.

  3. Coronal Heating and the Magnetic Flux Content of the Network

    NASA Astrophysics Data System (ADS)

    Moore, R. L.; Falconer, D. A.; Porter, J. G.; Hathaway, D. H.

    2003-05-01

    We investigate the heating of the quiet corona by measuring the increase of coronal luminosity with the amount of magnetic flux in the underlying network at solar minimum when there were no active regions on the face of the Sun. The coronal luminosity is measured from Fe IX/X-Fe XII pairs of coronal images from SOHO/EIT. The network magnetic flux content is measured from SOHO/MDI magnetograms. We find that the luminosity of the corona in our quiet regions increases roughly in proportion to the square root of the magnetic flux content of the network and roughly in proportion to the length of the perimeter of the network magnetic flux clumps. From (1) this result, (2) other observations of many fine-scale explosive events at the edges of network flux clumps, and (3) a demonstration that it is energetically feasible for the heating of the corona in quiet regions to be driven by explosions of granule-sized sheared-core magnetic bipoles embedded in the edges of network flux clumps, we infer that in quiet regions that are not influenced by active regions the corona is mainly heated by such magnetic activity in the edges of the network flux clumps. Our observational results together with our feasibility analysis allow us to predict that (1) at the edges of the network flux clumps there are many transient sheared-core bipoles of the size and lifetime of granules and having transverse field strengths > 100 G, (2) 30 of these bipoles are present per supergranule, and (3) most spicules are produced by explosions of these bipoles. This work was supported by NASA's Office of Space Science through its Solar and Heliospheric Physics Supporting Research and Technology Program and its Sun-Earth Connection Guest Investigator Program.

  4. Flux-Rope Structure of Coronal Mass Ejections

    NASA Technical Reports Server (NTRS)

    Gopalswamy, N.; Nieves-Chinchilla, T.; Hidalgo, M.; Zhang, J.; Riley, P.; van Driel-Gesztelyi, L.; Mandrini, C. H.

    2013-01-01

    This Topical Issue (TI) of Solar Physics, devoted to the study of flux-rope structure in coronal mass ejections (CMEs), is based on two Coordinated Data Analysis Workshops (CDAWs) held in 2010 (20-23 September in Dan Diego, California, USA) and 2011 (5-9 September in Alcala, Spain). The primary purpose of the CDAWs was to address the question whether all CMEs have a flux rope structure. Each CDAW was attended by about 50 scientists interested in the origin, propagation, and interplanetary manifestation of CME phenomena.

  5. The Radiation, Interplanetary Shocks, and Coronal Sources (RISCS) Toolset

    NASA Technical Reports Server (NTRS)

    Zank, G. P.; Spann, James F.

    2014-01-01

    The goal of this project is to serve the needs of space system designers and operators by developing an interplanetary radiation environment model within 10 AU:Radiation, Interplanetary Shocks, and Coronal Sources (RISCS) toolset: (1) The RISCS toolset will provide specific reference environments for space system designers and nowcasting and forecasting capabilities for space system operators; (2) We envision the RISCS toolset providing the spatial and temporal radiation environment external to the Earth's (and other planets') magnetosphere, as well as possessing the modularity to integrate separate applications (apps) that can map to specific magnetosphere locations and/or perform the subsequent radiation transport and dosimetry for a specific target.

  6. Findings from a Three Year Survey of Coronal Null Points

    NASA Astrophysics Data System (ADS)

    Freed, Michael; Longcope, Dana; McKenzie, David Eugene

    2014-06-01

    We report the findings from a comprehensive coronal magnetic null point survey created by Potential Field Source Surface (PFSS) modeling & Solar Dynamic Observatory/Atmospheric Imaging Assembly (SDO/AIA) observations. Locations of magnetic null points in the corona were predicted from the PFSS model from Carrington Rotation 2098 to 2139 and manually compared to contrast enhanced SDO/AIA images in 171 angstroms. Statistical results will be presented that illustrate the characteristics associated with the observed and predicted null points. These characteristics include the radial & latitudinal distribution; eigenvalues associated with null point structure; and the effect spine orientation has on observability.

  7. The Expansion and Radial Speeds of Coronal Mass Ejections

    NASA Astrophysics Data System (ADS)

    Gopalswamy, N.; Dal Lago, A.; Yashiro, S.; Akiyama, S.

    We show the relation between radial (V_{rad}) and expansion (V_{exp}) speeds of coronal mass ejections (CMEs) depends on the CME width. As CME width increases, {V_{rad}/V_{exp}} decreases from a value >1 to <1. For widths approaching 180°, the ratio approaches 0 if the cone has a flat base, while it approaches 0.5 if the base has a bulge (ice cream cone). The speed difference between the limb and disk halos and the spherical expansion of super fast CMEs can be explained by the width dependence.

  8. Solar coronal bright points observed with the VLA

    NASA Technical Reports Server (NTRS)

    Habbal, S. R.; Ronan, R. S.; Withbroe, G. L.; Shevgaonkar, R. K.; Kundu, M. R.

    1986-01-01

    The first observations of solar coronal bright points made at 20-cm wavelength with the VLA are reported. The brightness temperature of the sources observed varies between 1 and 5 x 10 to the 5th K. The observations indicate that significant fluctuations in the brightness temperature as well as in the spatial extent of these sources can occur over a few minutes. These fluctuations are shown to be due to density and temperature fluctuations at transition region heights combined with either plasma motions along magnetic field lines or changes in magnetic field topology, or both.

  9. The structure, stability and flaring of solar coronal loops

    NASA Technical Reports Server (NTRS)

    Van Hoven, G.

    1982-01-01

    A review is given of recent progress in the theory of the magnetohydrodynamic behavior of coronal loops, beginning with a brief characterization of thy observations. The equilibrium magnetic field is described, along with the consequences of the empirical requirement for short-term, or infinite-conductivity, stability which is shown to be dominated by the end-effect influence of thy quasi-rigid photosphere. A new loop-flare model is then developed, which takes account of the finite loop length. The primary resistive-sausage-mode instability exhibits the necessary threshold behavior, and produces a number of spatially and energetically distinct flare-release manifestations.

  10. Particle Acceleration by Magnetic Reconnection in a Twisted Coronal Loop

    NASA Astrophysics Data System (ADS)

    Gordovskyy, Mykola; Browning, Philippa K.

    2011-03-01

    Photospheric motions may lead to twisted coronal magnetic fields which contain free energy that can be released by reconnection. Browning & Van der Linden suggested that such a relaxation event may be triggered by the onset of ideal kink instability. In the present work, we study the evolution of a twisted magnetic flux tube with zero net axial current following Hood et al. Based on the obtained magnetic and electric fields, proton and electron trajectories are calculated using the test-particle approach. We discuss resulting particle distributions and possible observational implications, for example, for small solar flares.

  11. Stellar coronal magnetic fields and star-planet interaction

    NASA Astrophysics Data System (ADS)

    Lanza, A. F.

    2009-10-01

    Context: Evidence of magnetic interaction between late-type stars and close-in giant planets is provided by the observations of stellar hot spots rotating synchronously with the planets and showing an enhancement of chromospheric and X-ray fluxes. Possible photospheric signatures of such an interaction have also been reported. Aims: We investigate star-planet interaction in the framework of a magnetic field model of a stellar corona, considering the interaction between the coronal field and that of a planetary magnetosphere moving through the corona. This is motivated, among other reasons, by the difficulty of accounting for the energy budgets of the interaction phenomena with previous models. Methods: A linear force-free model is applied to describe the coronal field and study the evolution of its total magnetic energy and relative helicity according to the boundary conditions at the stellar surface and the effects related to the planetary motion through the corona. Results: The energy budget of the star-planet interaction is discussed, assuming that the planet may trigger a release of the energy of the coronal field by decreasing its relative helicity. The observed intermittent character of the star-planet interaction is explained by a topological change in the stellar coronal field, induced by a variation in its relative helicity. The model predicts the formation of many prominence-like structures in the case of highly active stars owing to the accumulation of matter evaporated from the planet inside an azimuthal flux rope in the outer corona. Moreover, the model can explain why stars accompanied by close-in planets have a higher X-ray luminosity than those with distant planets. It predicts that the best conditions for detecting radio emission from the exoplanets and their host stars are achieved when the field topology is characterized by field lines connected to the surface of the star, leading to a chromospheric hot spot rotating synchronously with the planet

  12. The COronal Solar Magnetism Observatory (COSMO) Large Aperture Coronagraph

    NASA Astrophysics Data System (ADS)

    Tomczyk, Steve; Gallagher, Dennis; Wu, Zhen; Zhang, Haiying; Nelson, Pete; Burkepile, Joan; Kolinksi, Don; Sutherland, Lee

    2013-04-01

    The COSMO is a facility dedicated to observing coronal and chromospheric magnetic fields. It will be located on a mountaintop in the Hawaiian Islands and will replace the current Mauna Loa Solar Observatory (MLSO). COSMO will provide unique observations of the global coronal magnetic fields and its environment to enhance the value of data collected by other observatories on the ground (e.g. SOLIS, BBO NST, Gregor, ATST, EST, Chinese Giant Solar Telescope, NLST, FASR) and in space (e.g. SDO, Hinode, SOHO, GOES, STEREO, Solar-C, Solar Probe+, Solar Orbiter). COSMO will employ a fleet of instruments to cover many aspects of measuring magnetic fields in the solar atmosphere. The dynamics and energy flow in the corona are dominated by magnetic fields. To understand the formation of CMEs, their relation to other forms of solar activity, and their progression out into the solar wind requires measurements of coronal magnetic fields. The large aperture coronagraph, the Chromospheric and Prominence Magnetometer and the K-Coronagraph form the COSMO instrument suite to measure magnetic fields and the polarization brightness of the low corona used to infer electron density. The large aperture coronagraph will employ a 1.5 meter fuse silica singlet lens, birefringent filters, and a spectropolarimeter to cover fields of view of up to 1 degree. It will observe the corona over a wide range of emission lines from 530.3 nm through 1083.0 nm allowing for magnetic field measurements over a wide range of coronal temperatures (e.g. FeXIV at 530.3 nm, Fe X at 637.4 nm, Fe XIII at 1074.7 and 1079.8 nm. These lines are faint and require the very large aperture. NCAR and NSF have provided funding to bring the large aperture coronagraph to a preliminary design review state by the end of 2013. As with all data from Mauna Loa, the data products from COSMO will be available to the community via the Mauna Loa website: http://mlso.hao.ucar.edu

  13. 3D reconstruction methods of coronal structures by radio observations

    NASA Astrophysics Data System (ADS)

    Aschwanden, Markus J.; Bastian, T. S.; White, Stephen M.

    1992-11-01

    The ability to carry out the three dimensional (3D) reconstruction of structures in the solar corona would represent a major advance in the study of the physical properties in active regions and in flares. Methods which allow a geometric reconstruction of quasistationary coronal structures (for example active region loops) or dynamic structures (for example flaring loops) are described: stereoscopy of multi-day imaging observations by the VLA (Very Large Array); tomography of optically thin emission (in radio or soft x-rays); multifrequency band imaging by the VLA; and tracing of magnetic field lines by propagating electron beams.

  14. The thermal stability of coronal loops by nonlinear diffusion asymptotics

    NASA Technical Reports Server (NTRS)

    Pakkert, J. W.; Verhulst, F.; Martens, P. C. H.

    1987-01-01

    A nonlinear reaction-diffusion equation and some additional constraints are derived which describe the time-dependent behavior of the temperature structure of the plasma in coronal loops. The equation is analyzed using nonlinear diffusion asymptotics, in particular singular perturbation techniques, and the results are interpreted in the context of the physical problem of the thermal stability and temporal behavior of the plasma. The results are consistent with the possibility of cyclic thermal behavior of the plasma, as suggested by Kuin and Martens (1982).

  15. The Source of 3 Minute Magnetoacoustic Oscillations in Coronal Fans

    NASA Astrophysics Data System (ADS)

    Jess, D. B.; De Moortel, I.; Mathioudakis, M.; Christian, D. J.; Reardon, K. P.; Keys, P. H.; Keenan, F. P.

    2012-10-01

    We use images of high spatial, spectral, and temporal resolution, obtained using both ground- and space-based instrumentation, to investigate the coupling between wave phenomena observed at numerous heights in the solar atmosphere. Analysis of 4170 Å continuum images reveals small-scale umbral intensity enhancements, with diameters ~0farcs6, lasting in excess of 30 minutes. Intensity oscillations of ≈3 minutes are observed to encompass these photospheric structures, with power at least three orders of magnitude higher than the surrounding umbra. Simultaneous chromospheric velocity and intensity time series reveal an 87° ± 8° out-of-phase behavior, implying the presence of standing modes created as a result of partial wave reflection at the transition region boundary. We find a maximum waveguide inclination angle of ≈40° between photospheric and chromospheric heights, combined with a radial expansion factor of <76%. An average blueshifted Doppler velocity of ≈1.5 km s-1, in addition to a time lag between photospheric and chromospheric oscillatory phenomena, confirms the presence of upwardly propagating slow-mode waves in the lower solar atmosphere. Propagating oscillations in EUV intensity are detected in simultaneous coronal fan structures, with a periodicity of 172 ± 17 s and a propagation velocity of 45 ± 7 km s-1. Numerical simulations reveal that the damping of the magnetoacoustic wave trains is dominated by thermal conduction. The coronal fans are seen to anchor into the photosphere in locations where large-amplitude umbral dot (UD) oscillations manifest. Derived kinetic temperature and emission measure time series display prominent out-of-phase characteristics, and when combined with the previously established sub-sonic wave speeds, we conclude that the observed EUV waves are the coronal counterparts of the upwardly propagating magnetoacoustic slow modes detected in the lower solar atmosphere. Thus, for the first time, we reveal how the

  16. Calibration of the LASCO C3 Coronal Images

    NASA Astrophysics Data System (ADS)

    Morrill, J.; Biesecker, D.; Esfandiari, A.; Korendyke, C.; Moses, D.; Rich, N.; Vourlidas, A.; Wang, D.; Howard, R. A.; Lamy, P.; Llebaria, A.; Thernisien, A.

    2002-05-01

    The LASCO C3 coronagraph has provided coronal observations since May, 1996. Preliminary calibrations have been available during most of this time period. However, some aspects of the calibration have required re-evaluation and we are just completing a complete review of the calibration procedure for these images. In this presentation we will discuss the steps required to correct LASCO C3 images. This includes corrections required by both optical and electrical characteristics of the instrument as well as timimg and spacecraft pointing driven correctons.

  17. 3D reconstruction methods of coronal structures by radio observations

    NASA Technical Reports Server (NTRS)

    Aschwanden, Markus J.; Bastian, T. S.; White, Stephen M.

    1992-01-01

    The ability to carry out the three dimensional (3D) reconstruction of structures in the solar corona would represent a major advance in the study of the physical properties in active regions and in flares. Methods which allow a geometric reconstruction of quasistationary coronal structures (for example active region loops) or dynamic structures (for example flaring loops) are described: stereoscopy of multi-day imaging observations by the VLA (Very Large Array); tomography of optically thin emission (in radio or soft x-rays); multifrequency band imaging by the VLA; and tracing of magnetic field lines by propagating electron beams.

  18. The Interaction between Coronal Mass Ejections (CMEs) and Coronal Holes (CHs) during the Solar Cycle 23 and its Geomagnetic Consequences

    NASA Astrophysics Data System (ADS)

    Mohamed, Amaal; Gopalswamy, Nat

    2016-07-01

    The interactions between the two large scale phenomena, coronal holes (CHs) and coronal mass ejections (CMEs) maybe considered as one of the most important relations that having a direct impact not only on space weather but also on the relevant plasma physics. Many observations have shown that throughout their propagation from the Sun to interplanetary space, CMEs interact with the heliospheric structures (e.g., other CMEs, Corotating interaction regions (CIRs), helmet streamers, and CHs). Such interactions could enhance the southward magnetic field component, which has important implications for geomagnetic storm generation. These interactions imply also a significant energy and momentum transfer between the interacting systems where magnetic reconnection is taking place. When CHs deflect CMEs away from or towards the Sun-Earth line, the geomagnetic response of the CME is highly affected. Gopalswamy et al. [2009] have addressed the deflection of CMEs due to the existence of CHs that are in close proximity to the eruption regions. They have shown that CHs can act as magnetic barriers that constrain CMEs propagation and can significantly affect their trajectories. Here, we study the interaction between coronal holes (CHs) and coronal mass ejections (CMEs) using a resultant force exerted by all coronal holes present on the disk and is defined as the coronal hole influence parameter (CHIP). The CHIP magnitude for each CH depends on the CH area, the distance between the CH centroid and the eruption region, and the average magnetic field within the CH at the photospheric level. The CHIP direction for each CH points from the CH centroid to the eruption region. We focus on Solar Cycle 23 CMEs originating from the disk center of the Sun (central meridian distance < 15 °). We present an extensive statistical study via compiling data sets of observations of CMEs and their interplanetary counterparts; known as interplanetary CMEs (ICMEs). There are 2 subsets of ICMEs

  19. The Usefulness of Coroners' Data on Suicides for Providing Information Relevant to Prevention

    ERIC Educational Resources Information Center

    Bennewith, Olive; Hawton, Keith; Simkin, Sue; Sutton, Lesley; Kapur, Navneet; Turnbull, Pauline; Gunnell, David

    2005-01-01

    Coroners' records are an accessible source of information on suicides. To assess their usefulness in relation to the investigation of specific methods of suicide, we examined coroners records for 492 suicides across 24 jurisdictions in England. Generally data on demographic variables were well recorded. Information on contact with general…

  20. Computed tomography of the orbit with special emphasis on coronal sections: Part II. Pathological anatomy.

    PubMed

    Tadmor, R; New, P F

    1978-01-01

    Visualization of orbital soft tissue structures by computed tomography in direct coronal and axial studies is extremely useful in diagnosis. Direct enlargement viewing of scans has disclosed minute anatomical details. This study reviews some of our experiences in the investigation of a variety of lesions within the orbit and attempts, in particular, to illustrate the value of direct coronal studies. PMID:670469

  1. The observation of possible reconnection events in the boundary changes of solar coronal holes

    NASA Technical Reports Server (NTRS)

    Kahler, S. W.; Moses, J. Daniel

    1989-01-01

    Coronal holes are large scale regions of magnetically open fields which are easily observed in solar soft X-ray images. The boundaries of coronal holes are separatrices between large scale regions of open and closed magnetic fields where one might expect to observe evidence of solar magnetic reconnection. Previous studies by Nolte and colleagues using Skylab X-ray images established that large scale (greater than or equal to 9 x 10(4) km) changes in coronal hole boundaries were due to coronal processes, i.e., magnetic reconnection, rather than to photospheric motions. Those studies were limited to time scales of about one day, and no conclusion could be drawn about the size and time scales of the reconnection process at hole boundaries. Sequences of appropriate Skylab X-ray images were used with a time resolution of about 90 min during times of the central meridian passages of the coronal hole labelled Coronal Hole 1 to search for hole boundary changes which can yield the spatial and temporal scales of coronal magnetic reconnection. It was found that 29 of 32 observed boundary changes could be associated with bright points. The appearance of the bright point may be the signature of reconnection between small scale and large scale magnetic fields. The observed boundary changes contributed to the quasi-rigid rotation of Coronal Hole 1.

  2. Acceleration of the Fast Solar Wind by Solitary Waves in Coronal Holes

    NASA Technical Reports Server (NTRS)

    Ofman, Leon

    2001-01-01

    The purpose of this investigation is to develop a new model for the acceleration of the fast solar wind by nonlinear. time-dependent multidimensional MHD simulations of waves in solar coronal holes. Preliminary computational studies indicate that nonlinear waves are generated in coronal holes by torsional Alfv\\'{e}n waves. These waves in addition to thermal conduction may contribute considerably to the accelerate the solar wind. Specific goals of this proposal are to investigate the generation of nonlinear solitary-like waves and their effect on solar wind acceleration by numerical 2.5D MHD simulation of coronal holes with a broad range of plasma and wave parameters; to study the effect of random disturbances at the base of a solar coronal hole on the fast solar wind acceleration with a more advanced 2.5D MHD model and to compare the results with the available observations; to extend the study to a full 3D MHD simulation of fast solar wind acceleration with a more realistic model of a coronal hole and solar boundary conditions. The ultimate goal of the three year study is to model the, fast solar wind in a coronal hole, based on realistic boundary conditions in a coronal hole near the Sun, and the coronal hole structure (i.e., density, temperature. and magnetic field geometry,) that will become available from the recently launched SOHO spacecraft.

  3. The Labial-Coronal Effect Revisited: Japanese Adults Say Pata, but Hear Tapa

    ERIC Educational Resources Information Center

    Tsuji, Sho; Gomez, Nayeli Gonzalez; Medina, Victoria; Nazzi, Thierry; Mazuka, Reiko

    2012-01-01

    The labial-coronal effect has originally been described as a bias to initiate a word with a labial consonant-vowel-coronal consonant (LC) sequence. This bias has been explained with constraints on the human speech production system, and its perceptual correlates have motivated the suggestion of a perception-production link. However, previous…

  4. Acceleration of the Fast Solar Wind by Solitary Waves in Coronal Holes

    NASA Technical Reports Server (NTRS)

    Ofman, Leon

    2000-01-01

    The purpose of this investigation is to develop a new model for the acceleration of the fast solar wind by nonlinear, time-dependent multidimensional MHD simulations of waves in solar coronal holes. Preliminary computational studies indicate that solitary-like waves are generated in coronal holes nonlinearly by torsional Alfven waves. These waves in addition to thermal conduction may contribute considerably to the accelerate the solar wind. Specific goals of this proposal are to investigate the generation of nonlinear solitary-like waves and their effect on solar wind acceleration by numerical 2.5D MHD simulation of coronal holes with a broad range of plasma and wave parameters; to study the effect of random disturbances at the base of a solar coronal hole on the fast solar wind acceleration with a more advanced 2.5D MHD model and to compare the results with the available observations; to extend the study to a full 3D MHD simulation of fast solar wind acceleration with a more realistic model of a coronal hole and solar boundary conditions. The ultimate goal of the three year study is to model the fast solar wind in a coronal hole, based on realistic boundary conditions in a coronal hole near the Sun, and the coronal hole structure (i.e., density, temperature, and magnetic field geometry) that will become available from the recently launched SOHO spacecraft.

  5. Coronal Loop Mapping to Infer the Best Magnetic Field Models for Active Region Prominences

    NASA Astrophysics Data System (ADS)

    Gary, G. Allen; Hu, Qiang; Lee, Jong Kwan

    2014-01-01

    This article comments on the results of a new, rapid, and flexible manual method to map on-disk individual coronal loops of a two-dimensional EUV image into the three-dimensional coronal loops. The method by Gary, Hu, and Lee (2013) employs cubic Bézier splines to map coronal loops using only four free parameters per loop. A set of 2D splines for coronal loops is transformed to the best 3D pseudo-magnetic field lines for a particular coronal model. The results restrict the magnetic field models derived from extrapolations of magnetograms to those admissible and inadmissible via a fitness parameter. This method uses the minimization of the misalignment angles between the magnetic field model and the best set of 3D field lines that match a set of closed coronal loops. We comment on the implication of the fitness parameter in connection with the magnetic free energy and comment on extensions of our earlier work by considering the issues of employing open coronal loops or employing partial coronal loop.

  6. World data center a for solar-terrestrial physics. Catalog of coronal holes, 1970-1991

    SciTech Connect

    Sanchez-Ibarra, A.; Barraza-Paredes, M.

    1992-10-01

    Coronal Holes were first noted as 'M' regions that produced periodic geomagnetic disturbances. These were first observed in 1970 by instruments on the Orbiting Solar Observatory (OSO) satellites, and also were noted with optical observations during the total solar eclipse of March 7, 1970. The Apollo Telescope Mount (ATM) on the Skylab manned mission observed in short wavelengths the real nature of Coronal Holes as regions of lower density and temperature than the rest of the solar corona. Three observational periods from Skylab produced substantial data on the development of Coronal Holes as well as their relationship with other types of solar activity. After Skylab, although Coronal Holes were later deduced from radio observations, the main data were obtained by observing the He l 10830A line at the Vacuum Solar Telescope at Kitt Peak National Observatory. These data, continuous from 1977 to date, were published in Solar-Geophysical Data (SGD) as Helium synoptic charts by Carrington Rotation or as Coronal Hole contours plotted on H-alpha synoptic charts. The Skylab observations of Coronal Holes were the subject of exhaustive examination. However, the main data source on Coronal Holes currently are the synoptic maps published in SGD. This catalogue was motivated by the lack of a global reference guide. This catalogue is based only on summary data for each Carrington Rotation, it presents interesting values and enough data to analyze several aspects of the evolution of Coronal Holes.

  7. 'Hurricane Season' in the Inner Heliosphere: Observations of Coronal Mass

    NASA Astrophysics Data System (ADS)

    Vourlidas, A.

    2013-09-01

    The current solar cycle, albeit low in sunspot numbers, is not lacking in coronal explosive activity. The solar corona has produced several spectacular Coronal Mass Ejections (CMEs) directed at Earth and other planets. In addition, this is the first time in human history that we are able to image continuously the full 360 degree corona and the full inner heliosphere from the Sun to Earth, and beyond. In addition, a host of inner heliospheric spacecraft can directly probe the quiescent and transient solar wind at several locations around Mercury, Venus, Earth, and Mars. These unprecedented observational capabilities offer us a unique opportunity to study the solar maximum activity and in particular CMEs and their impact on Earth and the other planets. The new field of Interplanetary Space Weather is being born. In this talk, I review our progress (sometimes) and befuddlement (more often) towards understanding the evolution of CMEs in the inner heliosphere. I discuss how this knowledge is shaping Space Weather efforts around the world, including a comprehensive approach from a large group of Greek solar and space physicists under the THALIS aegis. I will also present ideas for future missions and instrumentation to improve our Space Weather predictive capabilities.

  8. Tracking of Coronal White-Light Events by Texture

    NASA Astrophysics Data System (ADS)

    Goussies, N.; Stenborg, G.; Vourlidas, A.; Howard, R.

    2010-04-01

    The extraction of the kinematic properties of coronal mass ejections (CMEs) from white-light coronagraph images involves a significant degree of user interaction: defining the edge of the event, separating the core from the front or from nearby unrelated structures, etc. To contribute towards a less subjective and more quantitative definition, and therefore better kinematic characterization of such events, we have developed a novel image-processing technique based on the concept of “texture of the event”. The texture is defined by the so-called gray-level co-occurrence matrix, and the technique consists of a supervised segmentation algorithm to isolate a particular region of interest based upon its similarity with a pre-specified model. Once the event is visually defined early in its evolution, it is possible to automatically track the event by applying the segmentation algorithm to the corresponding time series of coronagraph images. In this paper we describe the technique, present some examples, and show how the coronal background, the core of the event, and even the associated shock (if one exists) can be identified for different kind of CMEs detected by the LASCO and SECCHI coronagraphs.

  9. An Imaging Study of a Complex Solar Coronal Radio Eruption

    NASA Astrophysics Data System (ADS)

    Feng, S. W.; Chen, Y.; Song, H. Q.; Wang, B.; Kong, X. L.

    2016-08-01

    Solar coronal radio bursts are enhanced radio emission excited by energetic electrons accelerated during solar eruptions. Studying these bursts is important for investigating the origin and physical mechanism of energetic particles and further diagnosing coronal parameters. Earlier studies suffered from a lack of simultaneous high-quality imaging data of the radio burst and the eruptive structure in the inner corona. Here we present a study on a complex solar radio eruption consisting of a type II burst and three reversely drifting type III bursts, using simultaneous EUV and radio imaging data. It is found that the type II burst is closely associated with a propagating and evolving CME-driven EUV shock structure, originated initially at the northern shock flank and later transferred to the top part of the shock. This source transfer is coincident with the presence of shock decay and enhancing signatures observed at the corresponding side of the EUV front. The electron energy accelerated by the shock at the flank is estimated to be ˜0.3 c by examining the imaging data of the fast-drifting herringbone structure of the type II burst. The reverse-drifting type III sources are found to be within the ejecta and correlated with a likely reconnection event therein. The implications for further observational studies and relevant space weather forecasting techniques are discussed.

  10. Hinode XRT and EIS Multithermal Analysis of a Coronal Loop

    NASA Astrophysics Data System (ADS)

    Schmelz, Joan T.; Saar, S.; Kashyap, V.

    2010-05-01

    Data from the X-Ray Telescope (XRT) and the EUV Imaging Spectrometer (EIS) on Hinode were used to investigate the spatial and thermal properties of an isolated quiescent coronal loop. We constructed Differential Emission Measure (DEM) curves using Monte Carlo based reconstruction algorithms. We studied the loop as a whole, in segments, in transverse cuts, and point-by-point, always with some form of background subtraction, and find that the loop DEM is neither isothermal nor extremely broad, with 96% of the EM between 6.2 < log T < 6.7, and an EM weighted average temperature of log T = 6.48 +/- 0.16. We find evidence for a gradual change in temperature along the loop, with log T increasing by 0.1 from the footpoints to the peak. The combined XRT-EIS data can do a good job of constraining the temperature distribution for coronal loop plasma, but strong high- and low- temperature constraints are crucial. Solar physics research at the University of Memphis is supported by a Hinode subcontract from NASA/SAO as well as NSF ATM-0402729.

  11. Sausage Waves in Transversely Nonuniform Monolithic Coronal Tubes

    NASA Astrophysics Data System (ADS)

    Lopin, I.; Nagorny, I.

    2015-09-01

    We investigate fast sausage waves in a monolithic coronal magnetic tube, modeled as a local density inhomogeneity with a continuous radial profile. This work is a natural extension of our previous results, obtained for a slab loop model for the case of cylindrical geometry. Using Kneser’s oscillating theorem, we provided the criteria for the existence of trapped and leaky wave regimes as a function of the profile features. For a number of density profiles there are only trapped modes for the entire range of longitudinal wave numbers. The phase speed of these modes tends toward the external Alfvén speed in the long wavelength limit. The generalized results were supported by the analytic solution of the wave equation for the specific density profiles. The approximate Wentzel-Kramers-Brillouin solutions allowed us to obtain the desired dispersion relations and to study their properties as a function of the profile parameters. The multicomponent quasi-periodic pulsations in flaring loops, observed on 2001 May 2 and 2002 July 3, are interpreted in terms of the transversely fundamental trapped fast sausage mode with several longitudinal harmonics in a smooth coronal waveguide.

  12. Visibility of Extended Coronal Structures and CMEs in the EUV

    NASA Astrophysics Data System (ADS)

    Schanche, Nicole; Golub, Leon

    2014-06-01

    Extended coronal structures around active regions and coronal mass ejections (CMEs) have often been seen in the extreme-ultraviolet (EUV) channels to the full extent of the AIA and SWAP field of views 1.3 and 1.7 Rsun). Using off-pointed comet data in AIA we sum a large number of frames to evaluate the off-limb distance to which streamers can be detected. For CMEs, we compared the events classified as halo CMEs in the white-light LASCO CACTus catalog from July-September 2013 to the AIA and SWAP data collected around those events. We discovered that roughly 80% of events could be seen in the EUV using both regular and running difference movies, with the most effective channels being the 193 and 304Å channels. By projecting out the signal strength of several of these events, we conclude that these EUV events can in many cases be detected to over 2.5 Rsun. A larger field-of-view telescope would make it possible to track the development of these structures and events from the disk out to several solar radii, complementing the traditional white-light methods.

  13. An empirical study of coronal observations at the solar limb

    NASA Astrophysics Data System (ADS)

    Freed, Michael Scott

    Solar observations were employed in this work to quantify motion and structures seen in the sun's corona with particular attention given to features found at the solar limb. These features consist of coronal magnetic-null points, quiescent prominences, and post flare eruption plasma sheets. Extreme-ultraviolet (EUV) observations from the Solar Dynamics Observatory (SDO) spacecraft were used to determine the fidelity of the commonly used potential field source surface (PFSS) model for predicting the location of coronal magnetic-null-points. Several properties of the null points were also investigated to ascertain if they had any effect on their observability. Next, quiescent prominence observations from the Hinode/Solar Optical Telescope satellite were used to create velocity maps of the plasma found in these structures. The derived velocities provided insight into the vorticity, kinetic energy, and oscillations that reside in these prominences. Primarily, this investigation was concerned with determining the distribution of velocity and vorticity at different length scales by applying a power spectral density analysis. All of this information is intended to strengthen our understanding on how these prominences evolve and potentially become unstable. An identical analysis is then conducted on post-flare-eruption plasma sheets observed in EUV by the space based SDO and TRACE satellites. Investigating the dynamics that reside in these plasma sheets are crucial for understanding the conditions that trigger and accelerate the magnetic reconnection responsible for producing these energetic solar flares.

  14. Prospective study of coroner's autopsies in Benin City, Nigeria.

    PubMed

    Aligbe, J U; Akhiwu, W O; Nwosu, S O

    2002-10-01

    A prospective study of 726 cases of coroner's autopsies carried out over a period of two years (1st January, 1996 - 31st December, 1997) was reviewed. The causes and circumstances of death are defined and classified into natural and unnatural deaths. Fifty cases (6.3%) were children while the remaining 676 cases (93.1%) were adults in a male to female ratio of 2.6 to 1. The most common indications for coroner's autopsies were sudden unnatural deaths (SUDs) accounting for 485 cases (66.8%) and also sudden unexpected natural deaths (SUNDs) (241 cases) accounting for 33.2%. In the first category, road traffic accidents accounted for 86.7% of cases with deaths involving motor vehicle drivers and their passengers (41.8%); pedestrians (37.1%); and motorcyclists and their passengers (18.6%). The commonest causes of death in all road traffic accidents were craniocerebral injuries and haemorrhagic shock. In the second category the most common causes of sudden unexpected natural death were cardiovascular diseases resulting from complications of hypertension (54.7%) occurring in apparently healthy individuals. Other causes of death were pneumonia, pulmonary tuberculosis, typhoid fever and neoplastic diseases. This study showed that in Nigeria, with an increasing acquisition of dietary and life style habits of the developed western world, there is becoming a concomitant risk of deaths from road traffic accidents and sudden unexpected natural deaths from hypertensive cardiovascular disease. PMID:12487517

  15. Old and New Aspects of Prominence Physics from Coronal Observations

    NASA Astrophysics Data System (ADS)

    Koutchmy, S.; Filippov, B.; Lamy, P.

    2007-05-01

    Classical W-L eclipse observations at typical spatial resolution of 10 arcsec show dark cavities surrounding prominences. Images at higher spatial resolution processed with a spatial filter reveal small dynamical cool clouds moving inside the inner corona around prominences. More recently EIT/SoHO observations taken using the 304 Å channel showed He+ prominences sometimes not seen in cooler lines. TRACE movies of the Fe IX and XI emissions where prominences are seen in absorption also bring appreciable informations on the dynamical surrounding of prominences, without showing obvious correlations between prominence and coronal structures. Accordingly, we re-examine the significance of the cavity and propose a possible interpretation as magnetic interlaced 3-D flux ropes and loops evacuating the corona, in addition to twisted flux ropes where the prominence plasma is condensing. Future space missions like ASPIICS should pay more attention to cavities and emptiness, to coronal dynamics around prominences, in order to resolve the long-standing problem of the origin of prominences and perhaps, perform a new diagnostic of the erupting process responsible for many CMEs.

  16. CORONAL ELECTRON DISTRIBUTION IN SOLAR FLARES: DRIFT-KINETIC MODEL

    SciTech Connect

    Minoshima, Takashi; Kusano, Kanya; Masuda, Satoshi; Miyoshi, Yoshizumi

    2011-05-10

    Using a model of particle acceleration and transport in solar flares, we investigate the height distribution of coronal electrons by focusing on the energy-dependent pitch-angle scattering. When pitch-angle scattering is not included, the peak heights of loop-top electrons are constant, regardless of their energy, owing to the continuous acceleration and compression of the electrons via shrinkage of magnetic loops. On the other hand, under pitch-angle scattering, the electron heights are energy-dependent: intermediate-energy electrons are at a higher altitude, whereas lower and higher energy electrons are at lower altitudes. This implies that the intermediate-energy electrons are inhibited from following the shrinking field lines to lower altitudes because pitch-angle scattering causes efficient precipitation of these electrons into the footpoint and their subsequent loss from the loop. This result is qualitatively consistent with the position of the above-the-loop-top hard X-ray (HXR) source that is located above coronal HXR loops emitted by lower energy electrons and microwaves emitted by higher energy electrons. Quantitative agreement with observations might be achieved by considering primary acceleration before the onset of loop shrinkage and additional pitch-angle scattering via wave-particle interactions.

  17. Asymmetries in coronal spectral lines and emission measure distribution

    SciTech Connect

    Tripathi, Durgesh; Klimchuk, James A.

    2013-12-10

    It has previously been argued that (1) spicules do not provide enough pre-heated plasma to fill the corona, and (2) even if they did, additional heating would be required to keep the plasma hot as it expands upward. Here we address whether spicules play an important role by injecting plasma at cooler temperatures (<2 MK), which then gets heated to coronal values at higher altitudes. We measure red-blue asymmetries in line profiles formed over a wide range of temperatures in the bright moss areas of two active regions. We derive emission measure distributions from the excess wing emission. We find that the asymmetries and emission measures are small and conclude that spicules do not inject an important (dominant) mass flux into the cores of active regions at temperatures >0.6 MK (log T > 5.8). These conclusions apply not only to spicules but also to any process that suddenly heats and accelerates chromospheric plasma (e.g., a chromospheric nanoflare). The traditional picture of coronal heating and chromospheric evaporation appears to remain the most likely explanation of the active region corona.

  18. Symmetric Coronal Jets: A Reconnection-controlled Study

    NASA Astrophysics Data System (ADS)

    Rachmeler, L. A.; Pariat, E.; DeForest, C. E.; Antiochos, S.; Török, T.

    2010-06-01

    Current models and observations imply that reconnection is a key mechanism for destabilization and initiation of coronal jets. We evolve a system described by the theoretical symmetric jet formation model using two different numerical codes with the goal of studying the role of reconnection in this system. One of the codes is the Eulerian adaptive mesh code ARMS, which simulates magnetic reconnection through numerical diffusion. The quasi-Lagrangian FLUX code, on the other hand, is ideal and able to evolve the system without reconnection. The ideal nature of FLUX allows us to provide a control case of evolution without reconnection. We find that during the initial symmetric and ideal phase of evolution, both codes produce very similar morphologies and energy growth. The symmetry is then broken by a kink-like motion of the axis of rotation, after which the two systems diverge. In ARMS, current sheets formed and reconnection rapidly released the stored magnetic energy. In FLUX, the closed field remained approximately constant in height while expanding in width and did not release any magnetic energy. We find that the symmetry threshold is an ideal property of the system, but the lack of energy release implies that the observed kink is not an instability. Because of the confined nature of the FLUX system, we conclude that reconnection is indeed necessary for jet formation in symmetric jet models in a uniform coronal background field.

  19. Low frequency radio observations of coronal magnetic field

    NASA Astrophysics Data System (ADS)

    Ramesh, R.; Kathiravan, C.

    2012-07-01

    Magnetic fields play an important role in the dynamics as well as the formation of the structures in the solar corona. Despite its fundamental importance, only a few direct measurements of the coronal magnetic field are available. The existing direct estimates using optical/infrared and radio emissions are limited to the inner corona, i.e., r < 1.2 R , where R is the radius of the Sun. In the outer corona beyond r > 3 R , Faraday rotation observations are used to derive the magnetic field. But due to lack of observational techniques, measurements in the range 1.2 R < r > 3 R (middle corona) are not available until now. As the photosphere, chromosphere, and corona are coupled by the solar magnetic field, the magnetic field strength at these distances is generally obtained by mathematical extrapolation of the observed line-of-sight component of the photospheric magnetic field assuming a potential or force-free model. The Indian Institute of Astrophysics has recently commissioned a radio polarimeter (based on inteferometer techniques) for dedicated obervations of the polarized radio emission from the solar corona. The frequency range of observation is 120-30 MHz which corresponds to a radial distance range of about 1.2-1.8 R. Estimates of weak magnetic fields in the 'undisturbed' Sun (non-flaring sunspot active regions, coronal streamers, etc.) obtained from observations with the above instrument will be presented.

  20. Coronal Diagnostics from Narrowband Images Around 30.4 nm

    NASA Astrophysics Data System (ADS)

    Andretta, V.; Telloni, D.; Del Zanna, G.

    2012-07-01

    Images taken in the band centered at 30.4 nm are routinely used to map the radiance of the He ii Ly α line on the solar disk. That line is one of the strongest, if not the strongest, line in the EUV observed in the solar spectrum, and one of the few lines in that wavelength range providing information on the upper chromosphere or lower transition region. However, when observing the off-limb corona, the contribution from the nearby Si xi 30.3 nm line can become significant. In this work we aim at estimating the relative contribution of those two lines in the solar corona around the minimum of solar activity. We combine measurements from CDS taken in August 2008 with temperature and density profiles from semiempirical models of the corona to compute the radiances of the two lines, and of other representative coronal lines ( e.g. Mg x 62.5 nm, Si xii 52.1 nm). Considering both diagnosed quantities from line ratios (temperatures and densities) and line radiances in absolute units, we obtain a good overall match between observations and models. We find that the Si xi line dominates the He ii line from just above the limb up to ≈ 2 R ⊙ in streamers, while its contribution to narrowband imaging in the 30.4 nm band is expected to become smaller, even negligible in the corona beyond ≈ 2 - 3 R ⊙, the precise value being strongly dependent on the coronal temperature profile.