Science.gov

Sample records for abordaje coronal estudio

  1. Coronal partings

    NASA Astrophysics Data System (ADS)

    Nikulin, Igor F.; Dumin, Yurii V.

    2016-02-01

    The basic observational properties of "coronal partings"-the special type of quasi-one-dimensional magnetic structures, identified by a comparison of the coronal X-ray and EUV images with solar magnetograms-are investigated. They represent the channels of opposite polarity inside the unipolar large-scale magnetic fields, formed by the rows of magnetic arcs directed to the neighboring sources of the background polarity. The most important characteristics of the partings are discussed. It can be naturally assumed that-from the evolutionary and spatial points of view-the partings can transform into the coronal holes and visa versa. The classes of global, intersecting, and complex partings are identified.

  2. 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.

  3. 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.

  4. Coronal Magnetic Field

    NASA Astrophysics Data System (ADS)

    Lin, Haosheng

    2007-05-01

    Centuries after the birth of modern solar astronomy, the Sun's corona still keeps many of its secrets: How is it heated to a million-degree temperature? How does it harbor the cool and dense prominence gas amid the tenuous and hot atmosphere? How does it drive the energetic events that eject particles into interplanetary space with speed exceeding 1% of the speed of light? We have greatly improved our knowledge of the solar corona with decades of space X-ray and EUV coronal observations, and many theories and models were put forward to address these problems. In our current understanding, magnetic fields are undoubtedly the most important fields in the corona, shaping its structure and driving its dynamics. It is clear that the resolution of these important questions all hinge on a better understanding of the organization, evolution, and interaction of the coronal magnetic field. However, as the direct measurement of coronal magnetic field is a very challenging observational problem, most of our theories and models were not experimentally verified. Nevertheless, we have finally overcome the experimental difficulties and can now directly measure the coronal magnetic field with great accuracy. This new capability can now be used to study the static magnetic structure of the corona, and offers hope that we will, in the near future, be able to directly observe the evolution of the coronal magnetic field of energetic solar events. More importantly, it finally allows us to conduct vigorous observational tests of our theories and models. In this lecture, I will review current research activities related to the observation, interpretation, and modeling of the coronal magnetic field, and discuss how they can help us resolve some of the long standing mysteries of the solar corona.

  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. 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.

  7. 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.

  8. 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.

  9. 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.

  10. Magnetic fields and coronal heating

    NASA Technical Reports Server (NTRS)

    Golub, L.; Maxson, C.; Rosner, R.; Vaiana, G. S.; Serio, S.

    1980-01-01

    General considerations concerning the scaling properties of magnetic-field-related coronal heating mechanisms are used to build a two-parameter model for the heating of closed coronal regions. The model predicts the way in which coronal temperature and electron density are related to photospheric magnetic field strength and the size of the region, using the additional constraint provided by the scaling law of Rosner, Tucker, and Vaiana. The model duplicates the observed scaling of total thermal energy content with total longitudinal flux; it also predicts a relation between the coronal energy density (or pressure) and the longitudinal field strength modified by the region scale size.

  11. Key aspects of coronal heating

    NASA Astrophysics Data System (ADS)

    Klimchuk, James A.

    2015-04-01

    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.

  12. Key Aspects of Coronal Heating

    NASA Astrophysics Data System (ADS)

    Klimchuk, James A.

    2015-04-01

    We highlight ten 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 buildup of stress. (6) Nanoflares repeat with different frequencies. (7) What is the characteristic magnitude of energy release? (8) What causes the collective behavior 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 a coordination of approaches: observational studies, field-aligned hydrodynamic simulations, large-scale and localized 3D MHD simulations, and possibly also kinetic simulations. There is a unique value to each of these approaches, and the community must strive to coordinate better.

  13. Coronal heating via nanoflares

    SciTech Connect

    Poletto, G.; Kopp, R.

    1993-10-01

    It has been recently proposed that the coronae of single late-type main sequence stars represent the radiative output from a large number of tiny energy release events, the so-called nanoflares. Although this suggestion is attractive and order of magnitude estimates of the physical parameters involved in the process are consistent with available data, nanoflares have not yet been observed and theoretical descriptions of these phenomena are still very crude. In this paper we examine the temporal behavior of a magnetic flux tube subject to the repeated occurrence of energy release events, randomly distributed in time, and we show that an originally empty cool loop may, in fact, reach typical coronal density and temperature values via nanoflare heating. By choosing physical parameters appropriate to solar conditions we also explore the possibilities for observationally detecting nanoflares. Although the Sun is the only star where nanoflares might be observed, present instrumentation appears to be inadequate for this purpose.

  14. 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

  15. An overview of coronal seismology.

    PubMed

    De Moortel, I

    2005-12-15

    The idea of exploiting observed oscillations as a diagnostic tool for determining the physical conditions of the coronal plasma was first suggested several decades ago (Roberts et al. 1984 Astrophys. J. 279, 857). Until recently, the application of this idea has been very limited by a lack of high-quality observations of coronal oscillations. However, during the last few years, this situation has changed dramatically, especially due to space-based observations by the Solar and Heliospheric Observatory and the Transition Region and Coronal Explorer and waves and oscillations have now been observed in a wide variety of solar structures, such as coronal loops, polar plumes and prominences. This paper will briefly summarize MHD wave theory, which forms the basis for coronal seismology, as well as present an overview of the variety of recently observed waves and oscillations in the solar corona. The present state of coronal seismology will also be discussed. Currently, the uncertainty associated with the obtained parameters is still considerable and, hence, the results require a cautious interpretation. However, these examples do show that coronal seismology is rapidly being transformed from a theoretical possibility to a viable technique.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. Observations of Coronal Mass Ejections with the Coronal Multichannel Polarimeter

    NASA Astrophysics Data System (ADS)

    Tian, H.; Tomczyk, S.; McIntosh, S. W.; Bethge, C.; de Toma, G.; Gibson, S.

    2013-12-01

    The Coronal Multichannel Polarimeter (CoMP) measures not only the polarization of coronal emission, but also the full radiance profiles of coronal emission lines. For the first time, CoMP observations provide high-cadence image sequences of the coronal line intensity, Doppler shift, and line width simultaneously over a large field of view. By studying the Doppler shift and line width we may explore more of the physical processes of the initiation and propagation of coronal mass ejections (CMEs). Here we identify a list of CMEs observed by CoMP and present the first results of these observations. Our preliminary analysis shows that CMEs are usually associated with greatly increased Doppler shift and enhanced line width. These new observations provide not only valuable information to constrain CME models and probe various processes during the initial propagation of CMEs in the low corona, but also offer a possible cost-effective and low-risk means of space-weather monitoring.

  1. 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.

  2. 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.

  3. Coronal Seismology -- Achievements and Perspectives

    NASA Astrophysics Data System (ADS)

    Ruderman, Michael

    Coronal seismology is a new and fast developing branch of the solar physics. The main idea of coronal seismology is the same as of any branches of seismology: to determine basic properties of a medium using properties of waves propagating in this medium. The waves and oscillations in the solar corona are routinely observed in the late space missions. In our brief review we concentrate only on one of the most spectacular type of oscillations observed in the solar corona - the transverse oscillations of coronal magnetic loops. These oscillations were first observed by TRACE on 14 July 1998. At present there are a few dozens of similar observations. Shortly after the first observation of the coronal loop transverse oscillations they were interpreted as kink oscillations of magnetic tubes with the ends frozen in the dense photospheric plasma. The frequency of the kink oscillation is proportional to the magnetic field magnitude and inversely proportional to the tube length times the square root of the plasma density. This fact was used to estimate the magnetic field magnitude in the coronal loops. In 2004 the first simultaneous observation of the fundamental mode and first overtone of the coronal loop transverse oscillation was reported. If we model a coronal loop as a homogeneous magnetic tube, then the ratio of the frequencies of the first overtone and the fundamental mode should be equal to 2. However, the ratio of the observed frequencies was smaller than 2. This is related to the density variation along the loop. If we assume that the corona is isothermal and prescribe the loop shape (usually it is assumed that it has the shape of half-circle), then, using the ratio of the two frequencies, we can determine the temperature of the coronal plasma. The first observation of transverse oscillations of the coronal loops showed that they were strongly damped. This phenomenon was confirmed by the subsequent observations. At present, the most reliable candidate for the

  4. 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

  5. Key aspects of coronal heating.

    PubMed

    Klimchuk, James A

    2015-05-28

    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

  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. Hybrid Stars and Coronal Evolution

    NASA Technical Reports Server (NTRS)

    Mushotzky, Richard (Technical Monitor); Dupree, Andrea K.

    2004-01-01

    This program addresses the evolution of stellar coronas by comparing a solar-like corona in the supergiant Dra (G2 Ib-IIa) to the corona in the allegedly more evolved state of a hybrid star, TrA (K2 11-111). Because the hybrid star has a massive wind, it appears likely that the corona will be cooler and less dense as the magnetic loop structures are no longer closed. By analogy with solar coronal holes, when the topology of the magnetic field is configured with open magnetic structures, both the coronal temperature and density are lower than in atmospheres dominated by closed loops. The hybrid stars assume a pivotal role in the definition of coronal evolution, atmospheric heating processes and mechanisms to drive winds of cool stars.

  9. 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

  10. 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.

  11. Direct coronal body computed tomography.

    PubMed

    van Waes, P F; Zonneveld, F W

    1982-02-01

    Three patient positioning technique have been developed for direct coronal computed tomography (CT) of the body, covering the complete torso: position A, to study pelvis, including retroperitoneal space and lower abdomen; position B, to study upper abdomen and lower chest; and position C, to study upper chest, including neck and posterior fossa. In comparison with multiplanar reformatting (MPR), direct coronal CT has three basic advantages: (a) image quality is improved as a result of a lack of partial volume averaging and patient motion disturbance; (b) the direct coronal planes can be truly parallel to the spinal axis, due to stretching of the lordotic segments of the spine; and (c) examination time is reduced, since a large number of overlapping slices and time consuming MPR effort are not required. Direct coronal CT of the body has been carried out in more than 600 cases and was often uniquely informative. In our institution, use of MPR CT is now restricted to small volumes and/or disabled patients.

  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. IMPLOSION IN A CORONAL ERUPTION

    SciTech Connect

    Liu Rui; Wang Haimin; Alexander, David

    2009-05-01

    We present the observations of the contraction of the extreme-ultraviolet coronal loops overlying the flaring region during the preheating as well as the early impulsive phase of a GOES class C8.9 flare. During the relatively long, 6 minutes, preheating phase, hard X-ray (HXR) count rates at lower energies (below 25 keV) as well as soft X-ray fluxes increase gradually and the flare emission is dominated by a thermal looptop source with the temperature of 20-30 MK. After the onset of impulsive HXR bursts, the flare spectrum is composed of a thermal component of 17-20 MK, corresponding to the looptop emission, and a nonthermal component with the spectral index {gamma} = 3.5-4.5, corresponding to a pair of conjugate footpoints. The contraction of the overlying coronal loops is associated with the converging motion of the conjugate footpoints and the downward motion of the looptop source. The expansion of the coronal loops following the contraction is associated with the enhancement in H{alpha} emission in the flaring region, and the heating of an eruptive filament whose northern end is located close to the flaring region. The expansion eventually leads to the eruption of the whole magnetic structure and a fast coronal mass ejection. It is the first time that such a large scale contraction of the coronal loops overlying the flaring region has been documented, which is sustained for about 10 minutes at an average speed of {approx}5 km s{sup -1}. Assuming that explosive chromospheric evaporation plays a significant role in compensating for the reduction of the magnetic pressure in the flaring region, we suggest that a prolonged preheating phase dominated by coronal thermal emission is a necessary condition for the observation of coronal implosion. The dense plasma accumulated in the corona during the preheating phase may effectively suppress explosive chromospheric evaporation, which explains the continuation of the observed implosion up to {approx}7 minutes into the

  14. 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.

  15. HST STIS Coronal Iron Survey

    NASA Astrophysics Data System (ADS)

    Ayres, T. R.; Brown, A.; Linsky, J. L.

    2001-05-01

    The broad coverage, high sensitivity, and precise wavelength calibration of the Space Telescope Imaging Spectrograph's medium-resolution echelle mode, coupled with the growing collection of GO and GTO E140M exposures, are ideal for surveys of specific spectral diagnostics across a diversity of stellar types, luminosities, and activity levels. Of great current interest are the weak coronal forbidden lines that appear in the far-UV, which are well known from solar flare work. Measuring coronal lines with STIS in the 1150--1700 Å band has significant advantages over using, say, Chandra HETGS or XMM-Newton RGS in the 1 keV range, because the STIS velocity resolution is 40x, or more, higher; STIS has an absolute wavelength calibration established by an onboard emission lamp; and the large effective area of the HST telescope compensates for the faintness of the forbidden lines. Here, we report a survey of Fe XXI λ 1354 in a sample of ~25 stars. The forbidden iron feature forms at a temperature of about 107 K, characteristic of very active or flaring coronal conditions. Clear detections of the coronal iron line are made in active M dwarfs (AU Mic, AD Leo), active giants (α Aur, β Cet, ι Cap, 24 UMa, HR 9024), short-period RS CVn binaries (e.g., HR 1099), and possibly in active solar-type dwarfs (ζ Dor, χ1 Ori). We describe our semi-empirical method for removing the C I blend that partially corrupts the Fe XXI profile, and our measurements of coronal line widths and Doppler shifts. Although α Aur displays clear variability between Fe XXI profiles obtained at the same orbital phase, but four years apart; the hyperactive HR 1099 system showed virtually no change in its coronal iron feature during a sequence of 14 spectra taken over a 7 hr period in 1999 September, despite the occurrence of two large flares in far-UV lines such as Si IV and C IV. This work was supported by grant GO-08280.01-97A from STScI. Observations were from the NASA/ESA HST, collected at the STSc

  16. MICA Observations of Coronal Transients

    NASA Astrophysics Data System (ADS)

    Stenborg, G.; Schwenn, R.; Srivastava, N.

    1999-10-01

    Dynamical processes are well known to occur in the inner solar atmosphere, many of them giving origin to spectacular eruptions known as coronal mass ejections. The projected velocity of propagation of these events ranges from less than 100 km/sec to greater than 1200 km/sec. In order to study the initial evolution of the faster processes it is necessary to image the inner corona at a very high cadence. Although ground-based observations of the corona are strongly affected by sky conditions they allow imaging at a high temporal resolution as compared to coronagraphic observations from space. In the recently inaugurated German-Argentinean Solar-Observatory at El Leoncito, San Juan, Argentina, a mirror coronagraph (MICA) daily images the inner solar corona with high temporal and spatial resolution in two spectral ranges: the well known green (~1.8 MK) and red (~1.0 MK) coronal lines at 5303 A and 6374 A respectively. It is essentially similar in design to LASCO-C1 on board SOHO, its field-of-view ranging from 1.05 to 2.0 solar radii from the sun center. Thus, it is ideally suited to observe the hot material and reveal the fast processes that occur in the coronal plasma. In the last year MICA has recorded several fast and not so fast green line transients at a high temporal resolution. In this work we will present observations of a few such events. This study would allow us to have a better understanding of the conditions that trigger the coronal mass ejections and their propagation in the inner solar corona.

  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 CORONAL LOOP INVENTORY PROJECT

    SciTech Connect

    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.

  19. 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.

  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. A SOLAR CORONAL JET EVENT TRIGGERS A CORONAL MASS EJECTION

    SciTech Connect

    Liu, Jiajia; Wang, Yuming; Shen, Chenglong; Liu, Kai; Pan, Zonghao; Wang, S.

    2015-11-10

    In this paper, we present multi-point, multi-wavelength observations and analysis of a solar coronal jet and coronal mass ejection (CME) event. Employing the GCS model, we obtained the real (three-dimensional) heliocentric distance and direction of the CME and found it to propagate at a high speed of over 1000 km s{sup −1}. The jet erupted before the CME and shared the same source region. The temporal and spacial relationship between these two events lead us to the possibility that the jet triggered the CME and became its core. This scenario hold the promise of enriching our understanding of the triggering mechanism of CMEs and their relations to coronal large-scale jets. On the other hand, the magnetic field configuration of the source region observed by the Solar Dynamics Observatory (SDO)/HMI instrument along with the off-limb inverse Y-shaped configuration observed by SDO/AIA in the 171 Å passband provide the first detailed observation of the three-dimensional reconnection process of a large-scale jet as simulated in Pariat et al. The eruption process of the jet highlights the importance of filament-like material during the eruption of not only small-scale X-ray jets, but likely also of large-scale EUV jets. Based on our observations and analysis, we propose the most probable mechanism for the whole event, with a blob structure overlaying the three-dimensional structure of the jet, to describe the interaction between the jet and the CME.

  2. 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.

  3. 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

  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. Deep coronal hole associated with quiescent filament

    NASA Astrophysics Data System (ADS)

    Kesumaningrum, Rasdewita; Herdiwidjaya, Dhani

    2014-03-01

    We present a study of the morphology of quiescent filament observed by H-alpha Solar Telescope at Bosscha Observatory in association with coronal hole observed by Atmospheric Imaging Assembly (AIA) instrument in 193 Å from Solar Dynamics Observatory. H-alpha images were processed by imaging softwares, namely Iris 5.59 and ImageJ, to enhance the signal to noise ratio and to identify the filament features associated with coronal hole. For images observed on October 12, 2011, November 14, 2011 and January 2, 2012, we identified distinct features of coronal holes above the quiescent filaments. This associated coronal holes have filament-like morphology with a thick long thread as it's `spine', defined as Deep Coronal Hole. Because of strong magnetic field of sunspot, these filaments and coronal holes emerged far from active region and lasted for several days. It is interesting as for segmented filament, deep coronal holes above the filaments lasted for a quite long period of time and merged. This association between filament and deep coronal hole can be explained by filament magnetic loop.

  8. 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.

  9. 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.

  10. 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.

  11. Coronal Modeling and Synchronic Maps

    NASA Astrophysics Data System (ADS)

    Linker, Jon A.; Lionello, R.; Mikic, Z.; Riley, P.; Downs, C.; Henney, C. J.; Arge, C.

    2013-07-01

    MHD simulations of the solar corona rely on maps of the solar magnetic field (typically measured at the photosphere) for input as boundary conditions. These "synoptic" maps (available from a number of ground-based and space-based solar observatories), which are perhaps better described as "diachronic," are built up over a solar rotation. A well-known problem with this approach is that the maps contain data that is as much as 27 days old. The Sun's magnetic flux is always evolving, and these changes in the flux affect coronal and heliospheric structure. Flux evolution models can in principle provide a more accurate specification, by estimating the likely state of the photospheric magnetic field on unobserved portions of the Sun. The Air Force Data Assimilative Photospheric flux Transport (ADAPT) model (Arge et al. 2010), which incorporates data assimilation techniques into the Worden and Harvey (2000) flux evolution model, is especially well-suited for this purpose. In this presentation we describe the use of such "synchronic" maps with coronal models. We compare results using synchronic maps versus the traditional synoptic maps. Research supported by AFOSR, NASA, and NSF.

  12. 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).

  13. 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.

  14. SOLAR WIND AND CORONAL BRIGHT POINTS INSIDE CORONAL HOLES

    SciTech Connect

    Karachik, Nina V.; Pevtsov, Alexei A. E-mail: apevtsov@nso.edu

    2011-07-01

    Observations of 108 coronal holes (CHs) from 1998-2008 were used to investigate the correlation between fast solar wind (SW) and several parameters of CHs. Our main goal was to establish the association between coronal bright points (CBPs; as sites of magnetic reconnection) and fast SW. Using in situ measurements of the SW, we have connected streams of the fast SW at 1 AU with their source regions, CHs. We studied a correlation between the SW speed and selected parameters of CHs: total area of the CH, total intensity inside the CH, fraction of area of the CH associated with CBPs, and their integrated brightness inside each CH. In agreement with previous studies, we found that the SW speed most strongly correlates with the total area of the CHs. The correlation is stronger for the non (de)projected areas of CHs (which are measured in image plane) suggesting that the near-equatorial parts of CHs make a larger contribution to the SW measured at near Earth orbit. This correlation varies with solar activity. It peaks for periods of moderate activity, but decreases slightly for higher or lower levels of activity. A weaker correlation between the SW speed and other studied parameters was found, but it can be explained by correlating these parameters with the CH's area. We also studied the spatial distribution of CBPs inside 10 CHs. We found that the density of CBPs is higher in the inner part of CHs. As such, results suggest that although the reconnection processes occurring in CBPs may contribute to the fast SW, they do not serve as the main mechanism of wind acceleration.

  15. The Problem of Coronal Heating

    SciTech Connect

    Vranjes, J.; Poedts, S.

    2010-12-14

    The inhomogeneous coronal plasma is a perfect environment for fast growing drift waves. The omnipresence of coronal magnetic loops implies gradients of the equilibrium plasma quantities like the density, magnetic field and temperature. These gradients are responsible for the excitation of drift waves that grow both within the two-component fluid description (both in the presence of collisions and without it) and within the two-component kinetic descriptions (due to purely kinetic effects). Some aspects of these phenomena are investigated here. In particular the analysis of the particle dynamics within the growing wave is compared with the corresponding fluid analysis. While both of them predict the stochastic heating, the threshold for the heating obtained from the single particle analysis is higher. The explanation for this effect is given. Also, the effects of the density gradient in the direction perpendicular to the magnetic field vector are investigated within the kinetic theory, in both electrostatic and electromagnetic regimes. The electromagnetic regime implies the coupling of the gradient-driven drift wave with the Alfven wave. The growth rates for the two cases are calculated and compared. It is found that, in general, the electrostatic regime is characterized by stronger growth rates, as compared with the electromagnetic perturbations. The released amount of energy density due to this heating should be more dependent on the magnitude of the background magnetic field than on the coupling of the drift and Alfven waves. The stochastic heating is expected to be much higher in regions with a stronger magnetic field. On the whole, the energy release rate caused by the stochastic heating can be several orders of magnitude above the value presently accepted as necessary for a sustainable coronal heating. The vertical stratification and the very long wavelengths along the magnetic loops imply that a drift-Alfven wave, propagating as a twisted structure along the

  16. 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.

  17. 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.

  18. 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

  19. 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.

  20. 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

  1. 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.

  2. 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.

  3. 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.

  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. 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

  6. Solar Coronal Heating via Alfven Wave Turbulence

    SciTech Connect

    Bigot, B.; Galtier, S.; Politano, H.

    2010-03-25

    A short review is given about the self-consistent MHD model of solar coronal heating recently proposed by Bigot et al.(2008) in which the dynamical effect of the background magnetic field along a coronal structure is taken into account through exact results from Alfven wave turbulence. The main properties of the model are given as well as the heating rate and the microturbulent velocity obtained in the case of coronal loops. The conclusion is that Alfven wave turbulence may produce an efficient background heating for the solar corona.

  7. 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.

  8. 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...

  9. 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...

  10. 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

  11. 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.

  12. 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.

  13. 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...

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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).

  20. 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.

  1. Models for coronal mass ejections

    NASA Astrophysics Data System (ADS)

    Jacobs, Carla; Poedts, Stefaan

    2011-06-01

    Coronal mass ejections (CMEs) play a key role in space weather. The mathematical modelling of these violent solar phenomena can contribute to a better understanding of their origin and evolution and as such improve space weather predictions. We review the state-of-the-art in CME simulations, including a brief overview of current models for the background solar wind as it has been shown that the background solar wind affects the onset and initial evolution of CMEs quite substantially. We mainly focus on the attempt to retrieve the initiation and propagation of CMEs in the framework of computational magnetofluid dynamics (CMFD). Advanced numerical techniques and large computer resources are indispensable when attempting to reconstruct an event from Sun to Earth. Especially the simulations developed in dedicated event studies yield very realistic results, comparable with the observations. However, there are still a lot of free parameters in these models and ad hoc source terms are often added to the equations, mimicking the physics that is not really understood yet in detail.

  2. 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

  3. The coronal temperature and nonthermal motions in a coronal hole compared with other solar regions

    NASA Technical Reports Server (NTRS)

    Doschek, G. A.; Feldman, U.

    1977-01-01

    The coronal lines Si VIII (1446 A), Fe X (1463 A), Fe XI (1467 A), and Fe XII (1242 A and 1349 A) were observed above the limb over a quiet region, a coronal hole, and two active regions. The lines emitted at temperatures greater than 1 million K; i.e., the iron lines, are not observed in the coronal-hole spectra, so the indication is that in the coronal hole most of the plasma is at a temperature of less than 1 million K. The emission measures and column densities of the lines are derived from available atomic cross-section data, and the results are discussed. The nonthermal velocities in the coronal hole and quiet region are about 20 km/s. The velocities in the active regions are substantially less.

  4. Coroners and death certification law reform: the Coroners and Justice Act 2009 and its aftermath.

    PubMed

    Luce, Tom

    2010-10-01

    After considering various different options for half a decade, the last Government legislated in 2009 to reform the England and Wales coroner and death certification systems. The Coroners and Justice Act 2009 provides for the creation of a new Chief Coroner post to lead the jurisdiction and for local medical examiners to oversee a new death certification scheme applicable equally to burial and cremation cases. In October 2010 the new Government announced that it judges the main coroner reform to be unaffordable, will not proceed with it and plans to repeal the provisions. It intends to implement the new death certification arrangements, which is welcome. The decision to abort the main coroner reform in spite of longstanding and widespread recognition of the need for major change is deplorable though in line with other failures over the last century to properly modernise this neglected service. PMID:21539281

  5. Coroners and death certification law reform: the Coroners and Justice Act 2009 and its aftermath.

    PubMed

    Luce, Tom

    2010-10-01

    After considering various different options for half a decade, the last Government legislated in 2009 to reform the England and Wales coroner and death certification systems. The Coroners and Justice Act 2009 provides for the creation of a new Chief Coroner post to lead the jurisdiction and for local medical examiners to oversee a new death certification scheme applicable equally to burial and cremation cases. In October 2010 the new Government announced that it judges the main coroner reform to be unaffordable, will not proceed with it and plans to repeal the provisions. It intends to implement the new death certification arrangements, which is welcome. The decision to abort the main coroner reform in spite of longstanding and widespread recognition of the need for major change is deplorable though in line with other failures over the last century to properly modernise this neglected service.

  6. 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.

  7. Using coronal seismology to estimate the magnetic field strength in a realistic coronal model

    NASA Astrophysics Data System (ADS)

    Chen, F.; Peter, H.

    2015-09-01

    Aims: Coronal seismology is used extensively to estimate properties of the corona, e.g. the coronal magnetic field strength is derived from oscillations observed in coronal loops. We present a three-dimensional coronal simulation, including a realistic energy balance in which we observe oscillations of a loop in synthesised coronal emission. We use these results to test the inversions based on coronal seismology. Methods: From the simulation of the corona above an active region, we synthesise extreme ultraviolet emission from the model corona. From this, we derive maps of line intensity and Doppler shift providing synthetic data in the same format as obtained from observations. We fit the (Doppler) oscillation of the loop in the same fashion as done for observations to derive the oscillation period and damping time. Results: The loop oscillation seen in our model is similar to imaging and spectroscopic observations of the Sun. The velocity disturbance of the kink oscillation shows an oscillation period of 52.5 s and a damping time of 125 s, which are both consistent with the ranges of periods and damping times found in observations. Using standard coronal seismology techniques, we find an average magnetic field strength of Bkink = 79 G for our loop in the simulation, while in the loop the field strength drops from roughly 300 G at the coronal base to 50 G at the apex. Using the data from our simulation, we can infer what the average magnetic field derived from coronal seismology actually means. It is close to the magnetic field strength in a constant cross-section flux tube, which would give the same wave travel time through the loop. Conclusions: Our model produced a realistic looking loop-dominated corona, and provides realistic information on the oscillation properties that can be used to calibrate and better understand the result from coronal seismology. A movie associated with Fig. 1 is available in electronic form at http://www.aanda.org

  8. Ectopic folliculosebaceous units at the coronal sulcus.

    PubMed

    Fernandez-Flores, Angel

    2014-12-01

    Tyson glands were described in the 17th century as modified sebaceous glands of the coronal sulcus of the penis. However, this description and other early texts supporting the existence of Tyson glands were not accompanied by illustrations. The existence of such glands has been passing through the literature without adequate graphical demonstration, which has contributed to controversial debates. Herein we present a case of a partial penectomy performed on a 65-year-old man with a squamous cell carcinoma of the penis. In this case we identified sebaceous glands as well as folliculosebaceous units in the coronal sulcus. We also comparatively examined 12 cases of partial penectomy to search for sebaceous glands or folliculosebaceous units in the coronal sulcus or the preputium. We found neither sebaceous glands nor folliculosebaceous units at the coronal sulcus or the mucosal aspect of the prepuce. We conclude that: (1) folliculosebaceous units are possible in the coronal sulcus, as the current case illustrates for the first time in literature and (2) the current case is an oddity, probably induced by the accompanying squamous cell carcinoma, and therefore it may represent an ectopic folliculosebaceous unit rather than an anatomic variation.

  9. CORONAL LOOP EXPANSION PROPERTIES EXPLAINED USING SEPARATORS

    SciTech Connect

    Plowman, Joseph E.; Kankelborg, Charles C.; Longcope, Dana W.

    2009-11-20

    One puzzling observed property of coronal loops is that they are of roughly constant thickness along their length. Various studies have found no consistent pattern of width variation along the length of loops observed by TRACE and SOHO. This is at odds with expectations of magnetic flux tube expansion properties, which suggests that loops are widest at their tops, and significantly narrower at their footpoints. Coronal loops correspond to areas of the solar corona which have been preferentially heated by some process, so this observed property might be connected to the mechanisms that heat the corona. One means of energy deposition is magnetic reconnection, which occurs along field lines called separators. These field lines begin and end on magnetic null points, and loops forming near them can therefore be relatively wide at their bases. Thus, coronal energization by magnetic reconnection may replicate the puzzling expansion properties observed in coronal loops. We present results of a Monte Carlo survey of separator field line expansion properties, comparing them to the observed properties of coronal loops.

  10. DIPOLAR EVOLUTION IN A CORONAL HOLE REGION

    SciTech Connect

    Yang Shuhong; Zhang Jun; Borrero, Juan Manuel E-mail: zjun@ourstar.bao.ac.c

    2009-09-20

    Using observations from the Solar and Heliospheric Observatory, the Solar Terrestrial Relations Observatory, and Hinode, we investigate magnetic field evolution in an equatorial coronal hole region. Two dipoles emerge one by one. The negative element of the first dipole disappears due to the interaction with the positive element of the second dipole. During this process, a jet and a plasma eruption are observed. The opposite polarities of the second dipole separate at first, and then cancel with each other, which is first reported in a coronal hole. With the reduction of unsigned magnetic flux of the second dipole from 9.8 x 10{sup 20} Mx to 3.0 x 10{sup 20} Mx in two days, 171 A brightness decreases by 75% and coronal loops shrink obviously. At the cancellation sites, the transverse fields are strong and point directly from the positive elements to the negative ones, meanwhile Doppler redshifts with an average velocity of 0.9 km s{sup -1} are observed, comparable to the horizontal velocity (1.0 km s{sup -1}) derived from the canceling island motion. Several days later, the northeastern part of the coronal hole, where the dipoles are located, appears as a quiet region. These observations support the idea that the interaction between the two dipoles is caused by flux reconnection, while the cancellation between the opposite polarities of the second dipole is due to the submergence of original loops. These results will help us to understand coronal hole evolution.

  11. 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

  12. 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.

  13. 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

  14. 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).

  15. 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

  16. A two-fluid, MHD coronal model

    NASA Astrophysics Data System (ADS)

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

    1999-03-01

    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 above the streamer (in comparison with the electron temperature). This is consistent with inferences from SOHO/UltraViolet Coronagraph Spectrometer instrument (UVCS) [Kohl et al., 1997], and with the Ulysses/Solar Wind Observations Over the Poles of the Sun instrument (SWOOPS) proton and electron temperature measurements which we show from the fast latitude scan. The density in the coronal hole between 2 and 5 solar radii (2 and 5RS) is similar to the density reported from SPARTAN 201-01 measurements by Fisher and Guhathakurta [1994]. The proton mass flux scaled to 1 AU is 2.4×108cm-2s-1, which is consistent with Ulysses observations [Phillips et al., 1995]. 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. [1998], and the plasma β is larger than unity everywhere above ~1.5RS, as it is in all other MHD coronal streamer models [e.g., Steinolfson et al., 1982; also G. A. Gary and D. Alexander, Constructing the coronal magnetic field, submitted to Solar Physics, 1998].

  17. 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

  18. 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.

  19. FORWARD: Forward modeling of coronal observables

    NASA Astrophysics Data System (ADS)

    Gibson, Sarah E.; Kucera, Therese A.; Casini, Roberto; Dove, James; Forland, Blake; Judge, Philip; Rachmeler, Laurel

    2014-05-01

    FORWARD forward models various coronal observables and can access and compare existing data. Given a coronal model, it can produce many different synthetic observables (including Stokes polarimetry), as well as plots of model plasma properties (density, magnetic field, etc.). It uses the CHIANTI database and CLE polarimetry synthesis code, works with numerical model datacubes, interfaces with the PFSS module of SolarSoft, includes several analytic models, and connects to the Virtual Solar Observatory for downloading data in a format directly comparable to model predictions.

  20. 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.

  1. 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

  2. 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

  3. 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).

  4. 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).

  5. Coronal Bright Points Associated with Minifilament Eruptions

    NASA Astrophysics Data System (ADS)

    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 109 cm-3. These new observational results indicate that CBPs are more complex in dynamical evolution and magnetic structure than previously thought.

  6. Disruption of coronal magnetic field arcades

    NASA Technical Reports Server (NTRS)

    Mikic, Zoran; Linker, Jon A.

    1994-01-01

    The ideal and resistive properties of isolated large-scale coronal magnetic arcades are studied using axisymmetric solutions of the time-dependent magnetohydrodynamic (MHD) equations in spherical geometry. We examine how flares and coronal mass ejections may be initiated by sudden disruptions of the magnetic field. The evolution of coronal arcades in response to applied shearing photospheric flows indicates that disruptive behavior can occur beyond a critical shear. The disruption can be traced to ideal MHD magnetic nonequilibrium. The magnetic field expands outward in a process that opens the field lines and produces a tangential discontinuity in the magnetic field. In the presence of plasma resistivity, the resulting current sheet is the site of rapid reconnection, leading to an impulsive release of magnetic energy, fast flows, and the ejection of a plasmoid. We relate these results to previous studies of force-free fields and to the properties of the open-field configuration. We show that the field lines in an arcade are forced open when the magnetic energy approaches (but is still below) the open-field energy, creating a partially open field in which most of the field lines extend away from the solar surface. Preliminary application of this model to helmet streamers indicates that it is relevant to the initiation of coronal mass ejections.

  7. 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.

  8. 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.

  9. 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.

  10. SYMPATHETIC FILAMENT ERUPTIONS CONNECTED BY CORONAL DIMMINGS

    SciTech Connect

    Jiang Yunchun; Yang Jiayan; Hong Junchao; Bi Yi; Zheng Ruisheng

    2011-09-10

    We present for the first time detailed observations of three successive, interdependent filament eruptions that occurred one by one within 5 hr from different locations beyond the range of a single active region. The first eruption was observed from an active region and was associated with a coronal mass ejection (CME), during which diffuse and complex coronal dimmings formed, largely extending to the two other filaments located in quiet-Sun regions. Then, both quiescent filaments consecutively underwent the second and third eruptions, while the nearby dimmings were persistent. Comparing the result of a derived coronal magnetic configuration, the magnetic connectivity between the dimmings suggested that they were caused by the joint effect of simple expansion of overlying loop systems forced by the first eruption, as well as by its erupting field interacting or reconnecting with the surrounding magnetic structures. Note that the dimming process in the first eruption indicated a weakening and partial removal of an overlying magnetic field constraint on the two other filaments, and thus one can physically connect these eruptions as sympathetic. It appears that the peculiar magnetic field configuration in our event was largely favorable to the occurrence of sympathetic filament eruptions. Because coronal dimmings are frequent and common phenomena in solar eruptions, especially in CME events, it is very likely that they represent a universal agent that can link consecutive eruptions nearby with sympathetic eruptions.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. A Two-Fluid, MHD Coronal Model

    NASA Technical Reports Server (NTRS)

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

    1999-01-01

    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 Corona] 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 above the streamer (in comparison with the electron temperature). This is consistent with inferences from SOHO/UltraViolet Coronagraph Spectrometer instrument (UVCS), and with the Ulysses/Solar Wind Observations Over the Poles of the Sun instrument (SWOOPS) proton and electron temperature measurements which we show from the fast latitude scan. The density in the coronal hole between 2 and 5 solar radii (2 and 5 R(sub S)) is similar to the density reported from SPARTAN 201.-01 measurements by Fisher and Guhathakurta [19941. 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. [1998], 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 [e.g., Steinolfson et al., 1982; also G. A. Gary and D. Alexander, Constructing the coronal magnetic field, submitted to Solar Physics, 1998].

  16. DARK JETS IN SOLAR CORONAL HOLES

    SciTech Connect

    Young, Peter R.

    2015-03-10

    A new solar feature termed a dark jet is identified from observations of an extended solar coronal hole that was continuously monitored for over 44 hr by the Extreme Ultraviolet Imaging Spectrometer on board the Hinode spacecraft in 2011 February 8–10 as part of Hinode Operation Plan No. 177 (HOP 177). Line of sight (LOS) velocity maps derived from the coronal Fe xii λ195.12 emission line, formed at 1.5 MK, revealed a number of large-scale, jet-like structures that showed significant blueshifts. The structures had either weak or no intensity signal in 193 Å filter images from the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory, suggesting that the jets are essentially invisible to imaging instruments. The dark jets are rooted in bright points and occur both within the coronal hole and at the quiet Sun–coronal hole boundary. They exhibit a wide range of shapes, from narrow columns to fan-shaped structures, and sometimes multiple jets are seen close together. A detailed study of one dark jet showed LOS speeds increasing along the jet axis from 52 to 107 km s{sup −1} and a temperature of 1.2–1.3 MK. The low intensity of the jet was due either to a small filling factor of 2% or to a curtain-like morphology. From the HOP 177 sample, dark jets are as common as regular coronal hole jets, but their low intensity suggests a mass flux around two orders of magnitude lower.

  17. Standing sausage modes in curved coronal slabs

    NASA Astrophysics Data System (ADS)

    Pascoe, D. J.; Nakariakov, V. M.

    2016-09-01

    Context. Magnetohydrodynamic waveguides such as dense coronal loops can support standing modes. The ratios of the periods of oscillations for different longitudinal harmonics depend on the dispersive nature of the waveguide and so may be used as a seismological tool to determine coronal parameters. Aims: We extend models of standing sausage modes in low β coronal loops to include the effects of loop curvature. The behaviour of standing sausage modes in this geometry is used to explain the properties of observed oscillations that cannot be accounted for using straight loop models. Methods: We perform 2D numerical simulations of an oscillating coronal loop, modelled as a dense slab embedded in a potential magnetic field. The loop is field-aligned and so experiences expansion with height in addition to being curved. Standing sausage modes are excited by compressive perturbations of the loop and their properties are studied. Results: The spatial profiles of standing sausage modes are found to be modified by the expanding loop geometry typical for flaring loops and modelled by a potential magnetic field in our simulations. Longitudinal harmonics of order n > 1 have anti-nodes that are shifted towards the loop apex and the amplitude of anti-nodes near the loop apex is smaller than those near the loop footpoints. Conclusions: We find that the observation of standing sausage modes by the Nobeyama Radioheliograph in a flaring coronal loop on 12 January 2000 is consistent with interpretation in terms of the global mode (n = 1) and third harmonic (n = 3). This interpretation accounts for the period ratio and spatial structure of the observed oscillations.

  18. 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

  19. 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

  20. 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.

  1. On the Nature of Coronal EIT Waves

    NASA Astrophysics Data System (ADS)

    Ballai, I.; Erdélyi, R.; Pintér, B.

    2005-11-01

    Large-scale eruption events in the solar atmosphere can generate global waves, i.e., waves that propagate over distances comparable to the solar radius. In the low solar corona, global waves observed by SOHO EIT, generated by coronal mass ejections or flares, are usually referred to as ``EIT waves.'' The nature of these global waves is the subject of strong debate, and opinions are divided between different interpretations (e.g., fast magnetohydrodynamic waves, shock waves, nonwave feature, etc.). In the present Letter, we studied TRACE EUV data to show that these global coronal disturbances are indeed waves with a well-defined period. Supposing that the EIT waves transfer all their energy to interacting loops, we also estimate the minimum energy threshold carried by EIT waves.

  2. 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.

  3. Coronal heating by stochastic magnetic pumping

    NASA Technical Reports Server (NTRS)

    Sturrock, P. A.; Uchida, Y.

    1980-01-01

    Recent observational data cast serious doubt on the widely held view that the Sun's corona is heated by traveling waves (acoustic or magnetohydrodynamic). It is proposed that the energy responsible for heating the corona is derived from the free energy of the coronal magnetic field derived from motion of the 'feet' of magnetic field lines in the photosphere. Stochastic motion of the feet of magnetic field lines leads, on the average, to a linear increase of magnetic free energy with time. This rate of energy input is calculated for a simple model of a single thin flux tube. The model appears to agree well with observational data if the magnetic flux originates in small regions of high magnetic field strength. On combining this energy input with estimates of energy loss by radiation and of energy redistribution by thermal conduction, we obtain scaling laws for density and temperature in terms of length and coronal magnetic field strength.

  4. Damped transverse oscillations of interacting coronal loops

    NASA Astrophysics Data System (ADS)

    Soler, Roberto; Luna, Manuel

    2015-10-01

    Damped transverse oscillations of magnetic loops are routinely observed in the solar corona. This phenomenon is interpreted as standing kink magnetohydrodynamic waves, which are damped by resonant absorption owing to plasma inhomogeneity across the magnetic field. The periods and damping times of these oscillations can be used to probe the physical conditions of the coronal medium. Some observations suggest that interaction between neighboring oscillating loops in an active region may be important and can modify the properties of the oscillations. Here we theoretically investigate resonantly damped transverse oscillations of interacting nonuniform coronal loops. We provide a semi-analytic method, based on the T-matrix theory of scattering, to compute the frequencies and damping rates of collective oscillations of an arbitrary configuration of parallel cylindrical loops. The effect of resonant damping is included in the T-matrix scheme in the thin boundary approximation. Analytic and numerical results in the specific case of two interacting loops are given as an application.

  5. 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.

  6. 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.

  7. Coronal Magnetic Structures for Homologous Eruptions

    NASA Astrophysics Data System (ADS)

    Lee, J.; Liu, C.; Jing, J.; Chae, J.

    2015-12-01

    Many studies have been made on homologous eruptions for their importance in understanding the flare energy build-up and release processes. We study the homologous eruptions that occurred in three active regions, NOAA 11444, 11283, and 12192, with emphasis on the coronal quantities derived from the nonlinear force-free field (NLFFF) extrapolation. The quantities include magnetic energy, electric current, and magnetic twist number, and decay index, computed from the high cadence photospheric vector magnetograms of the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamic Observatory (SDO). In addition, photospheric magnetic flux, flare ribbons and overlying field distribution are also examined to determine the changes associated with each eruption. As main results, we will present the difference between the homology of confined eruptions and that of eruptive ones, and variations of the coronal quantities with flare strength.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. THE RELATION BETWEEN MAGNETIC FIELDS AND CORONAL ACTIVITIES IN THE POLAR CORONAL HOLE

    SciTech Connect

    Shimojo, Masumi; Tsuneta, Saku

    2009-11-20

    We investigated the relation between polar magnetic fields and polar coronal activities based on Stokes maps of photospheric and chromospheric lines, simultaneous X-ray and EUV images. These images are taken with Hinode and Solar and Heliospheric Observatory. With careful co-alignment between these images, we found that the X-ray jets, the X-ray bright points, and the coronal loops in the polar coronal hole appear around the relatively large magnetic concentrations near the kG-patches with minority polarity. The magnetic concentrations have magnetic polarity opposite to that of kG-patches, and they are clearly identified in the Stokes-V maps of the Na I line. We also found that such minority magnetic concentrations emerge from below the photosphere in the polar region. Our results suggest that the coronal activities and structures in the polar coronal hole can be used as a tracer of the appearance of the minority polarities in the polar region.

  14. Constructing the Coronal Magnetic Field: by Correlating Parameterized Magnetic Field Lines with Observed Coronal Plasma Structures

    NASA Technical Reports Server (NTRS)

    Gary, G. A.

    1998-01-01

    The reconstruction of the coronal magnetic field is carried out using a perturbation procedure. A set of magnetic field lines generated from magnetogram data is parameterized and then deformed by varying the parameterized values. The coronal fluxtubes associated with this field are adjusted until the correlation between the field lines and the observed coronal loops is maximized. A mathematical formulation is described which ensures (1) that the normal component of the photospheric field remains unchanged, (2) that the field is given in the entire corona, (3) that the field remains divergence free, and (4) that electrical currents are introduced into the field. It is demonstrated that a simple radial parameterization of a potential field, comprising a radial stretching of the field, can provide a match for a simple bipolar active region, AR 7999, which crossed the central meridian on 1996 Nov 26. At a coronal height of 30 km, the resulting magnetic field is a non-force free magnetic field with the maximum Lorentz force being on the order of 2.6 x 10(exp -9) dyn resulting from an electric current density of $0.13 mu A/ sq m. This scheme is an important tool in generating a magnetic field solution consistent with the coronal flux tube observations and the observed photospheric magnetic field.

  15. 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.

  16. ON THE ERUPTION OF CORONAL FLUX ROPES

    SciTech Connect

    Fan, Y.

    2010-08-10

    We present three-dimensional MHD simulations of the evolution of the magnetic field in the corona where the emergence of a twisted magnetic flux tube is driven at the lower boundary into a pre-existing coronal potential arcade field. Through a sequence of simulations in which we vary the amount of twisted flux transported into the corona before the emergence is stopped, we investigate the conditions that lead to a dynamic eruption of the resulting coronal flux rope. It is found that the critical condition for the onset of eruption is for the center of the flux rope to reach a critical height at which the corresponding potential field declines with height at a sufficiently steep rate, consistent with the onset of the torus instability of the flux rope. In some cases, immediately after the emergence is stopped, the coronal flux rope first settles into a quasi-static rise with an underlying sigmoid-shaped current layer developing. Preferential heating of field lines going through this current layer may give rise to the observed quiescent X-ray sigmoid loops before eruption. Reconnections in the current layer during the initial quasi-static stage is found to add detached flux to the coronal flux rope, allowing it to rise quasi-statically to the critical height and dynamic eruption of the flux rope then ensues. By identifying field lines whose tops are in the most intense part of the current layer during the eruption, we deduce the evolution and morphology of the post-flare X-ray loops and the flare ribbons at their footpoints.

  17. 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.

  18. 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.

  19. A coronal plasmoid crossing a magnetic structure.

    NASA Astrophysics Data System (ADS)

    Delannee, C.; Koutchmy, S.

    1996-01-01

    The authors observed, during the solar eclipse in 1991, a coronal plasmoid. They analyzed the trajectory, the dynamic and radiative flux variation of the plasmoid. The motion is upward and decelerated. The flux presents a strong decrease. The plasmoid appears to go across a structure, which is supposed to follow the local magnetic field. It travels across the magnetic field line; this is not in agreement with the theory of the "melon seed" acceleration and additional forces are needed to explain the motion.

  20. 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.

  1. Sunquake Generation by Coronal Magnetic Restructuring

    NASA Astrophysics Data System (ADS)

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

    2016-11-01

    Sunquakes are the surface signatures of acoustic waves in the Sun’s interior that are produced by some but not all flares and coronal mass ejections (CMEs). This paper explores a mechanism for sunquake generation by the changes in magnetic field that occur during flares and CMEs, using MHD simulations with a semiempirical FAL-C atmosphere to demonstrate the generation of acoustic waves in the interior in response to changing magnetic tilt in the corona. We find that Alfvén–sound resonance combined with the ponderomotive force produces acoustic waves in the interior with sufficient energy to match sunquake observations when the magnetic field angle changes of the order of 10° in a region where the coronal field strength is a few hundred gauss or more. The most energetic sunquakes are produced when the coronal field is strong, while the variation of magnetic field strength with height and the timescale of the change in tilt are of secondary importance.

  2. 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.

  3. 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.

  4. 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.

  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. 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.

  7. 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.

  8. 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

  9. 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.

  10. 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

  11. Coroners and medical examiners: mutualism, commensalism or parasitism?

    PubMed

    Furness, Peter

    2012-01-01

    The Coroners and Justice Act 2009 includes provisions for reform of the certification of death and the introduction of "Medical Examiners", who will scrutinise the certification of every death that is not referred to the Coroner for investigation. When these changes are implemented, Coroners and Medical Examiners will have to work closely together. But the boundaries between the two roles are not perfectly defined. Will they work together in synergy, or will they interact unwillingly and abrasively? It is clear which approach will be best for the bereaved and for society, but it is less clear what will actually happen. Medical Examiners will be led by a new Chief Medical Examiner, and Coroners will have a Chief Coroner. But these individuals will have limited powers to oblige Coroners and Medical Examiners to collaborate. It seems inevitable that there will be large variations in practice, at least initially.

  12. Constructing the Coronal Magnetic Field by Correlating Parameterized Magnetic Field Lines with Observed Coronal Plasma Structures

    NASA Technical Reports Server (NTRS)

    Allen, Gary G.; Alexander, David

    1999-01-01

    A method is presented for constructing the coronal magnetic field from photospheric magnetograms and observed coronal loops. A set of magnetic field lines generated from magnetogram data is parameterized and then deformed by varying the parameterized values. The coronal flux tubes associated with this field are adjusted until the correlation between the field lines and the observed coronal loops is maximized. A mathematical formulation is described which ensures that (1) the normal component of the photospheric field remains unchanged, (2) the field is given in the entire corona over an active region, (3) the field remains divergence-free, and 4electric currents are introduced into the field. It is demonstrated that a parameterization of a potential field, comprising a radial stretching of the field, can provide a match for a simple bipolar active region, AR 7999, which crossed the central meridian on 1996 November 26. The result is a non-force-free magnetic field with the Lorentz force being of the order of 10(exp -5.5) g per s(exp 2) resulting from an electric current density of 0.79 micro A per m(exp 2). Calculations show that the plasma beta becomes larger than unity at a strong non-radial currents requires low height of about 0.25 solar radii supporting the non-force-free conclusion. The presence of such strong non-radial currents requires large transverse pressure gradients fo maintain a magnetostatic atmosphere, required by the relatively persistent nature of the coronal structures observed in AR 7999. This scheme is an important tool in generating a magnetic field solution consistent with the coronal flux tube observations and the observed photospheric magnetic field.

  13. 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.

  14. 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.

  15. Determination of the coronal magnetic field from vector magnetograph data

    NASA Technical Reports Server (NTRS)

    Mikic, Zoran

    1991-01-01

    A new algorithm was developed, tested, and applied to determine coronal magnetic fields above solar active regions. The coronal field above NOAA active region AR5747 was successfully estimated on 20 Oct. 1989 from data taken at the Mees Solar Observatory of the Univ. of Hawaii. It was shown that observational data can be used to obtain realistic estimates of coronal magnetic fields. The model has significantly extended the realism with which the coronal magnetic field can be inferred from observations. The understanding of coronal phenomena will be greatly advanced by a reliable technique, such as the one presented, for deducing the detailed spatial structure of the coronal field. The payoff from major current and proposed NASA observational efforts is heavily dependent on the success with which the coronal field can be inferred from vector magnetograms. In particular, the present inability to reliably obtain the coronal field has been a major obstacle to the theoretical advancement of solar flare theory and prediction. The results have shown that the evolutional algorithm can be used to estimate coronal magnetic fields.

  16. 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.

  17. Coronal Structures in Cool Stars: XMM-NEWTON Hybrid Stars and Coronal Evolution

    NASA Technical Reports Server (NTRS)

    Dupree, Andrea K.; Mushotzky, Richard (Technical Monitor)

    2003-01-01

    This program addresses the evolution of stellar coronas by comparing a solar-like corona in the supergiant Beta Dra (G2 Ib-IIa) to the corona in the allegedly more evolved state of a hybrid star, alpha TrA (K2 II-III). Because the hybrid star has a massive wind, it appears likely that the corona will be cooler and less dense as the magnetic loop structures are no longer closed. By analogy with solar coronal holes, when the topology of the magnetic field is configured with open magnetic structures, both the coronal temperature and density are lower than in atmospheres dominated by closed loops. The hybrid stars assume a pivotal role in the definition of coronal evolution, atmospheric heating processes and mechanisms to drive winds of cool stars. We are attempting to determine if this model of coronal evolution is correct by using XMM-NEWTON RGS spectra for the 2 targets we were allocated through the Guest Observer program.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. Stellar Coronal Physics with VLBI Imaging

    NASA Astrophysics Data System (ADS)

    Peterson, William; Mutel, Robert

    2009-11-01

    We present the results of synoptic high-resolution imaging studies of two active binary star systems. Both were conducted using the VLBA-HSA at 15 GHz, making them the first images of extrasolar stars capable of discerning structure at scales smaller than a stellar diameter. Images revealed a giant coronal loop on Algol, filled with gyrosynchrotron flux at high activity levels and emitting from only the feet of the loop during quiescent epochs. UX Ari displays similar activity levels to Algol, but the components do not fill their Roche Lobes, making it an optimal comparison case for the role of mass transfer in the formation of global magnetic fields.

  3. Coronal loop formation resulting from photospheric convection

    NASA Technical Reports Server (NTRS)

    Hoven, G. Van; Mok, Y.; Mikic, Z.

    1995-01-01

    We have demonstrated the dynamic formation of coronal magnetic loops in three dimensions as a result of horizontal vortex-like convection on the photosphere. Localized plasma motions twist bipolar magnetic field lines which are tied to the dense photosphere by high electrical conductivity. The twists propagate into the corona along the field and create a narrow quasi-toroidal region where the field lines interwind. At the same time, this tubeline region rises in altitude, expands in cross section, and distorts into a slight S shape before settling into an equilibrium state. The MHD stability of such line-tied magnetic loop structures is directly exhibited by this dynamic simulation.

  4. Coronal plasma-frequency radio echoes

    SciTech Connect

    Eremin, A.B.

    1986-06-01

    If the mechanism that Zaitsev and the author propose for generating the fundamental mode of type III solar radio bursts is correct, then coronal echo events can occur at the plasma frequency. Certain events recorded during the type IIIb-III storm of July 1974 are identifiable as echoes. Radio-wave reflection from moving solar-wind irregularities consistently shifts the echoes to shorter wavelengths than the primary burst, yielding an estimate of about 10 to the 7th cm/sec for the mean wind velocity 1-2 solar radii from the photosphere. 8 references.

  5. Coronal structure inferred from remote sensing observations

    SciTech Connect

    Feldman, W.C.

    1996-09-01

    Remote-sensing observations of the Sun and inner heliosphere are reviewed to appraise our understanding of the mix of the mechanisms that heat the corona and accelerate the solar wind. An assessment of experimental uncertainties and the basic assumptions needed to translate measurables into physical models, reveals very large fundamental uncertainties in our knowledge of coronal structure near the Sun. We develop a time-dependent, filamentary model of the extended corona that is consistent with a large number of remote sensing observations of the solar atmosphere and the solar wind.

  6. Relationship of EUV Irradiance Coronal Dimming Slope and Depth to Coronal Mass Ejection Speed and Mass

    NASA Astrophysics Data System (ADS)

    Mason, James Paul; Woods, Thomas N.; Webb, David F.; Thompson, Barbara J.; Colaninno, Robin C.; Vourlidas, Angelos

    2016-10-01

    Extreme ultraviolet (EUV) coronal dimmings are often observed in response to solar eruptive events. These phenomena can be generated via several different physical processes. For space weather, the most important of these is the temporary void left behind by a coronal mass ejection (CME). Massive, fast CMEs tend to leave behind a darker void that also usually corresponds to minimum irradiance for the cooler coronal emissions. If the dimming is associated with a solar flare, as is often the case, the flare component of the irradiance light curve in the cooler coronal emission can be isolated and removed using simultaneous measurements of warmer coronal lines. We apply this technique to 37 dimming events identified during two separate two-week periods in 2011 plus an event on 2010 August 7, analyzed in a previous paper to parameterize dimming in terms of depth and slope. We provide statistics on which combination of wavelengths worked best for the flare-removal method, describe the fitting methods applied to the dimming light curves, and compare the dimming parameters with corresponding CME parameters of mass and speed. The best linear relationships found are \\begin{eqnarray*}{v}{CME} ≤ft[\\displaystyle \\frac{{km}}{{{s}}}\\right] & ≈ & 2.36× {10}6 ≤ft[\\displaystyle \\frac{{km}}{ % }\\right]× {s}\\dim ≤ft[\\displaystyle \\frac{ % }{{{s}}}\\right]\\ {m}{CME} [{{g}}] & ≈ & 2.59× {10}15≤ft[\\displaystyle \\frac{g}{ % }\\right]× \\sqrt{{d}\\dim } [ % ].\\end{eqnarray*} These relationships could be used for space weather operations of estimating CME mass and speed using near-real-time irradiance dimming measurements.

  7. A Perceptual Correlate of the Labial-Coronal Effect

    ERIC Educational Resources Information Center

    Sato, Marc; Vallee, Nathalie; Schwartz, Jean-Luc; Rousset, Isabelle

    2007-01-01

    Purpose: Statistical studies conducted in various languages on both infants and adults have revealed an intersyllabic preference for initiating words with a labial consonant-vowel-coronal consonant sequence. Speech motor constraints have been proposed to explain this so-called "labial-coronal effect." This study was designed to test for a possible…

  8. 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...

  9. Segmentation of Coronal Holes Using Active Contours Without Edges

    NASA Astrophysics Data System (ADS)

    Boucheron, L. E.; Valluri, M.; McAteer, R. T. J.

    2016-09-01

    An application of active contours without edges is presented as an efficient and effective means of extracting and characterizing coronal holes. Coronal holes are regions of low-density plasma on the Sun with open magnetic field lines. The detection and characterization of these regions is important for testing theories of their formation and evolution, and also from a space weather perspective because they are the source of the fast solar wind. Coronal holes are detected in full-disk extreme ultraviolet (EUV) images of the corona obtained with the Solar Dynamics Observatory Atmospheric Imaging Assembly (SDO/AIA). The proposed method detects coronal boundaries without determining any fixed intensity value in the data. Instead, the active contour segmentation employs an energy-minimization in which coronal holes are assumed to have more homogeneous intensities than the surrounding active regions and quiet Sun. The segmented coronal holes tend to correspond to unipolar magnetic regions, are consistent with concurrent solar wind observations, and qualitatively match the coronal holes segmented by other methods. The means to identify a coronal hole without specifying a final intensity threshold may allow this algorithm to be more robust across multiple datasets, regardless of data type, resolution, and quality.

  10. Segmentation of Coronal Holes Using Active Contours Without Edges

    NASA Astrophysics Data System (ADS)

    Boucheron, L. E.; Valluri, M.; McAteer, R. T. J.

    2016-10-01

    An application of active contours without edges is presented as an efficient and effective means of extracting and characterizing coronal holes. Coronal holes are regions of low-density plasma on the Sun with open magnetic field lines. The detection and characterization of these regions is important for testing theories of their formation and evolution, and also from a space weather perspective because they are the source of the fast solar wind. Coronal holes are detected in full-disk extreme ultraviolet (EUV) images of the corona obtained with the Solar Dynamics Observatory Atmospheric Imaging Assembly (SDO/AIA). The proposed method detects coronal boundaries without determining any fixed intensity value in the data. Instead, the active contour segmentation employs an energy-minimization in which coronal holes are assumed to have more homogeneous intensities than the surrounding active regions and quiet Sun. The segmented coronal holes tend to correspond to unipolar magnetic regions, are consistent with concurrent solar wind observations, and qualitatively match the coronal holes segmented by other methods. The means to identify a coronal hole without specifying a final intensity threshold may allow this algorithm to be more robust across multiple datasets, regardless of data type, resolution, and quality.

  11. 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.

  12. A Moreton Wave and its Coronal Counterparts

    NASA Astrophysics Data System (ADS)

    Francile, Carlos N.; Mandrini, Cristina H.; Long, David; Cremades, Hebe; Lopez, Fernando M.; Luoni, Maria Luisa

    2016-07-01

    On 29 March 2014, a Moreton wave was detected in AR 12017 with the Halpha Solar Telescope for Argentina (HASTA) in association with an X1 flare. Several phenomena took place in various regimes in connection with this event, such as low coronal waves and a coronal mass ejection (CME). We investigate their role and relationship with the Moreton wave to shed light on issues so far under debate. We analyze its connection with waves observed in the low corona with the Atmospheric Imaging Assembly aboard the Solar Dynamics Observatory (SDO/AIA), as well as with the ensuing CME, via kinematics analyses. We build stack plots from sequences of images obtained at different wavelengths to track wave fronts along several directions and find links between the features observed in the chromosphere and low corona, as well as in the associated CME. We also derive the shock front properties. We propose a geometrical model of the wave to explain the observed wave fronts as the photospheric and chromospheric traces of an expanding and outward-traveling bubble intersecting the Sun.

  13. 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.

  14. 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

  15. 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.

  16. Coronal heating by stochastic magnetic pumping

    NASA Technical Reports Server (NTRS)

    Sturrock, P. A.; Uchida, Y.

    1981-01-01

    Recent observational data cast serious doubt on the widely held view that the sun's corona is heated by traveling waves (acoustic or magnetohydrodynamic). It is here proposed that the energy responsible for heating the corona is derived from the free energy of the coronal magnetic field derived from motion of the 'feet' of magnetic field lines in the photosphere. Stochastic motion of the feet of magnetic field lines leads, on the average, to a linear increase of magnetic free energy with time. This rate of energy input is calculated for a simple model of a single thin flux tube. The model appears to agree well with observational data if the magnetic flux originates in small regions of high magnetic field strength as proposed by Tarbell et al. (1979). On combining this energy input with estimates of energy loss by radiation and of energy redistribution by thermal conduction, scaling laws are obtained for density and temperature in terms of length and coronal magnetic field strength.

  17. Guide Field Reconnection Turbulence and Coronal Heating

    NASA Astrophysics Data System (ADS)

    Pueschel, M. J.; Told, D.; Terry, P. W.; Jenko, F.; Zweibel, E. G.; Zhdankin, V.; Lesch, H.

    2014-10-01

    Magnetic reconnection is a prime contender for explaining plasma heating in the solar corona. This work focuses on turbulent reconnection simulations in the strong-guide-field limit, where the gyrokinetics both captures all relevant physical effects and is numerically efficient. Continuously replenished current sheets force a quasi-stationary turbulent state, where significant levels of j . E heating can be measured. In addition, plasmoids are observed to form in the turbulence, causing secondary reconnection events through mergers. Under coronal conditions, the volumetric heating rate is evaluated as 1 . 5 ×10-3 erg cm-3 s-1, in good agreement with observations. This value scales as, in particular, the reconnecting field to the power of 1 . 8 , and the characteristic current sheet width to the power of 0 . 75 . Moreover, heating bursts associated with plasmoid mergers conform with time scales associated observationally with nanoflares. For further details on this work, as well as on the emergence of temperature anisotropies, see [M.J. Pueschel et al., Magnetic Reconnection Turbulence in Strong Guide Fields: Basic Properties and Application to Coronal Heating, accepted for publication in Astrophys. J. Suppl. Ser.].

  18. 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.

  19. 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.

  20. Data-Driven Global Coronal Models

    NASA Astrophysics Data System (ADS)

    Linker, Jon; Mikic, Zoran; Riley, Pete; Henney, Carl; Arge, Charles; Lionello, Roberto; Downs, Cooper

    MHD simulations of the solar corona based on maps of the solar magnetic field have been demonstrated to describe many aspects of coronal structure. However, these models are typically integrated to steady state, using synoptic or daily-updated magnetic maps to derive the boundary conditions. The Sun's magnetic flux is always evolving, and these changes in the flux affect the structure and dynamics of the corona and heliosphere. In this presentation, we describe an approach to evolutionary models of the corona and solar wind, using time-dependent boundary conditions. A key aspect of our approach is the use of the Air Force Data Assimilative Photospheric flux Transport (ADAPT) model to develop time-evolving boundary conditions for the magnetic field. ADAPT incorporates data assimilation techniques into the Worden and Harvey (2000) flux evolution model, making it an especially suitable candidate for providing boundary conditions to MHD models. We describe initial results and their implications for coronal hole evolution and the origin of the slow solar wind.

  1. 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.

  2. 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.

  3. 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.

  4. OBSERVING EPISODIC CORONAL HEATING EVENTS ROOTED IN CHROMOSPHERIC ACTIVITY

    SciTech Connect

    McIntosh, Scott W.; De Pontieu, Bart E-mail: bdp@lmsal.co

    2009-11-20

    We present the results of a multi-wavelength study of episodic plasma injection into the corona of active region (AR) 10942. We exploit long-exposure images of the Hinode and Transition Region and Coronal Explorer spacecraft to study the properties of faint, episodic, 'blobs' of plasma that are propelled upward along coronal loops that are rooted in the AR plage. We find that the source location and characteristic velocities of these episodic upflow events match those expected from recent spectroscopic observations of faint coronal upflows that are associated with upper chromospheric activity, in the form of highly dynamic spicules. The analysis presented ties together observations from coronal and chromospheric spectrographs and imagers, providing more evidence of the connection of discrete coronal mass heating and injection events with their source, dynamic spicules, in the chromosphere.

  5. 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.

  6. 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.

  7. 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

  8. 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

  9. Measurements of Coronal Proton Velocity Distributions

    NASA Astrophysics Data System (ADS)

    Kohl, J. L.; Panasyuk, A.; Cranmer, S. R.; Gardner, L. D.; Raymond, J. C.

    2007-12-01

    The Ultraviolet Coronagraph Spectrometer (UVCS) on the Solar and Heliospheric Observatory is being used to measure precise coronal H I Ly-alpha spectral line profiles out to several Doppler half widths. Such observations can be used to reveal the proton velocity distribution along the line-of-sight. Departures from a Maxwellian distribution are believed to be needed for the acceleration of solar energetic particles (SEPs) by coronal mass ejection (CME) shocks. Our initial attempt to measure suprathermal proton velocity distributions has been described by Kohl et al. (2006). We have made considerable additional progress on such measurements since then. Improvements include the following: a much more accurate instrument spectral line profile, an increase in the wavelength range used for the observations, an increase in the statistical accuracy of the observations by increasing the observation time, and inclusion of a background measurement as part of every set of observations. We have also investigated the sensitivity to the detector high voltage, investigated the effects of diffraction in the instrument, determined the stray light effects and the Thompson scattering effects, which both turn out to be small except for scattering of Si III 120.6 nm. That scattered light is out of the primary wavelength range of interest. We believe that we have now demonstrated that UVCS has the sensitivity to distinguish between a Gaussian coronal velocity distribution and a kappa = 4 or smaller distribution. It is generally believed that the required seed particle population needed to produce SEPs of interest with a CME shock would have a velocity distribution with 0.001 to 0.01 of the particles with speeds that exceed 1000 km/s. Assuming a kappa distribution that is symmetric in the tangential plane and Maxwellian in the radial direction, this would correspond to a distribution with kappa = 3.5 or smaller. This paper will report the results of examining a fairly large body of new

  10. 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.

  11. Relationship Between a Coronal Mass Ejection-Driven Shock and a Coronal Metric Type II Burst

    NASA Astrophysics Data System (ADS)

    Liu, Y.; Luhmann, J. G.; Bale, S. D.; Lin, R. P.

    2009-02-01

    It has been an intense matter of debate whether coronal metric type II bursts are generated by coronal mass ejection (CME)-driven shocks or flare blast waves. Using unprecedented high-cadence observations from STEREO/SECCHI, we investigate the relationship between a metric type II event and a shock driven by the 2007 December 31 CME. The existence of the CME-driven shock is indicated by the remote deflection of coronal structures, which is in good timing with the metric type II burst. The CME speed is about 600 km s-1 when the metric type II burst occurs, much larger than the Alfvén speed of 419-489 km s-1 determined from band splitting of the type II burst. A causal relationship is well established between the metric and decametric-hectometric type II bursts. The shock height-time curve determined from the type II bands is also consistent with the shock propagation obtained from the streamer deflection. These results provide unambiguous evidence that the metric type II burst is caused by the CME-driven shock.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. Kinematics of Earth Impacting Coronal Mass Ejections

    NASA Astrophysics Data System (ADS)

    Colaninno, R. C.; Vourlidas, A.

    2012-12-01

    With the data from the STEREO mission, we are able to continuously monitor Coronal Mass Ejections (CMEs) as they progress from the Sun to Earth. However, even with continuous monitoring with remote sensing observations, we are still unable to accurately predict the arrival or terrestrial impact of a CME. In this study, we analyze nine CMEs from the Sun to Earth as observed in both the remote sensing and in situ data sets. In this study, we track nine CMEs from the Sun to 70% - 98% of the distance to Earth with the remote sensing data. We use the Graduate Cyclical Shell (GCS) model to estimate the position of each CME as it is observed in the inner heliosphere. From the derived kinematics, we compare the predicted arrival times and impact velocities with the in situ data. We consider different method for fitting the kinematics and the modeled geometry of the CME to improve the predicted arrival time.

  17. 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.

  18. Magnetic fine structure of solar coronal loops

    NASA Technical Reports Server (NTRS)

    Van Ballegooijen, A. A.

    1988-01-01

    A numerical simulation of the effect of a random photospheric flow on the magnetic structure of a coronal loop is presented. An initially uniform field embedded in a perfectly conducting plasma is assumed, extending between two flat parallel plates representing the solar photosphere at both ends of the loop. The field is perturbed by a sequence of randomly phased, sinusoidal flow patterns applied at one of the boundary plates, and the corresponding sequence of force-free fields is determined. It is found that the electric currents generated by these flows develop a fine structure on a scale significantly smaller than the wavelength of the velocity patterns. This suggests that magnetic energy is transferred to smaller scale via a cascade process.

  19. 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

  20. Coronal activity cycles in solar analog stars

    NASA Astrophysics Data System (ADS)

    Favata, Fabio

    2013-10-01

    We propose continuation into AO13 of the ongoing long-term program for the monitoring of coronal cycles in a sample of five solar-type stars in three stellar systems. The targets have been monitored continuously since AO1, yielding the first unambiguous evidence of cyclic behavior in the X-ray emission from the coronae of cool stars. Thanks to the long-term monitoring our program is starting to show evidence of the complex behavior of stellar cycles, with significant cycle-to-cycle variability becoming apparent. The observations requested in AO-13 will allow us to capitalize on our long-term investment of XMM-Newton observing time and to continue assembling a unique long-term data set that is likely to remain unmatched for a long time.

  1. 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

  2. A Catalog of Coronal "EIT Wave" Transients

    NASA Technical Reports Server (NTRS)

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

    2005-01-01

    SOHO Extreme Ultraviolet Imaging Telescope (EIT) data have been visually searched for coronal "EIT wave" transients over the period beginning 24 March 1997 extending through 24 June 1998. The dates covered start at the beginning of regular high-cadence (more than 1 image every 20 minutes) observations, ending at the 4-month interruption of SOHO observations in mid-1998. 176 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 wavefronts and associated active regions, and the speeds of the wavefronts. The measured speeds of the wavefronts varied from less than 50 to over 700 km/sec with "typical" speeds of 200-400 Msec.

  3. 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.

  4. Variability of the coronal line region in NGC 4151

    NASA Astrophysics Data System (ADS)

    Landt, Hermine; Ward, Martin J.; Steenbrugge, Katrien C.; Ferland, Gary J.

    2015-06-01

    We present the first extensive study of the coronal line variability in an active galaxy. Our data set for the nearby source NGC 4151 consists of six epochs of quasi-simultaneous optical and near-infrared spectroscopy spanning a period of about 8 yr and five epochs of X-ray spectroscopy overlapping in time with it. None of the coronal lines showed the variability behaviour observed for the broad emission lines and hot dust emission. In general, the coronal lines varied only weakly, if at all. Using the optical [Fe VII] and X-ray O VII emission lines we estimate that the coronal line gas has a relatively low density of ne ˜ 103 cm-3 and a relatively high ionization parameter of log U ˜ 1. The resultant distance of the coronal line gas from the ionizing source is about two light years, which puts this region well beyond the hot inner face of the obscuring dusty torus. The high ionization parameter implies that the coronal line region is an independent entity rather than part of a continuous gas distribution connecting the broad and narrow emission line regions. We present tentative evidence for the X-ray heated wind scenario of Pier & Voit. We find that the increased ionizing radiation that heats the dusty torus also increases the cooling efficiency of the coronal line gas, most likely due to a stronger adiabatic expansion.

  5. Improving Heliospheric Field Models with Optimized Coronal Models

    NASA Astrophysics Data System (ADS)

    Jones, S. I.; Davila, J. M.; Uritsky, V. M.

    2015-12-01

    The Solar Orbiter and Solar Probe Plus missions will travel closer to the sun than any previous mission, collecting unprecedented in situ data. This data can provide insight into coronal structure, energy transport, and evolution in the inner heliosphere. However, in order to take full advantage of this data, researchers need quality models of the inner heliosphere to connect the in situ observations to their coronal and photospheric sources. Developing quality models for this region of space has proved difficult, in part because the only part of the field that is accessible for routine measurement is the photosphere. The photospheric field measurements, though somewhat problematic, are used as boundary conditions for coronal models, which often neglect or over-simplify chromospheric conditions, and these coronal models are then used as boundary conditions to drive heliospheric models. The result is a great deal of uncertainty about the accuracy and reliability of the heliospheric models. Here we present a technique we are developing for improving global coronal magnetic field models by optimizing the models to conform to the field morphology observed in coronal images. This agreement between the coronal model and the basic morphology of the corona is essential for creating accurate heliospheric models. We will present results of early tests of two implementations of this idea, and its first application to real-world data.

  6. 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.

  7. Stealth Coronal Mass Ejections: A Perspective

    NASA Astrophysics Data System (ADS)

    Howard, Timothy A.; Harrison, Richard A.

    2013-07-01

    "Stealth CME" has become a commonly used term in recent studies of solar activity. It refers to a coronal mass ejection (CME) with no apparent solar surface association, and therefore has no easily identifiable signature to locate the region on the Sun from which the CME erupted. We review the literature and express caution in categorising CMEs in this way. CMEs were discovered some 40 years ago and there have been numerous statistical studies of associations with phenomena in the solar atmosphere which clearly identify a range of associations, from bright flares and large prominence eruptions to small flares, and even a lack of flares or any identifiable surface activity at all. In this sense the stealth CME concept is not new. One major question relates to whether the range of associations reveal different CME classes, i.e. different CME launch processes, or are indicative of a spectrum of coronal responses to one common process. We favour the latter and stress that this spectrum must be considered in the description of the CME launch, meaning that the physics of a so-called stealth CME must not be fundamentally different from a CME associated with major surface events. On the other hand we also stress that the use of a stealth CME category implies that all surface activity could indeed be detected using modern instrumentation. We argue that this may not be the case, and that even in the SDO era of full-Sun, high resolution imaging, we are restricted by instrument sensitivity and bandwidth issues. Thus, having reviewed the case for stealth CMEs as a distinct category, we stress the need to keep the concept in perspective.

  8. 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.

  9. Observational Signatures of Coronal Heating Mechanisms

    NASA Astrophysics Data System (ADS)

    Judge, Philip

    1998-11-01

    Many mechanisms for heating the corona have been proposed since the problem was identified by Edlen more than 50 years ago. Identifying those that are important is a challenging problem that has so far not been resolved. One thing is clear: based upon a variety of observations, the corona is heated by conversion of magnetic flux into thermal energy. The flux emerges from sub-photospheric layers and is buffeted by photospheric dynamics. The ``coronal heating problem'' is to identify how, given the high conductivities of coronal plasma, the magnetic energy is dissipated. After reviewing some basic observational facts and placing the corona into appropriate physical regimes, I will focus on two pieces of information recently obtained from spacecraft. In one, I will discuss the interpretation of line profiles from the UVCS instrument on the SOHO spacecraft, presented by Kohl and colleagues. These observations indicate the presence of asymmetric particle distribution functions low in the solar wind, so I will discuss implications for heating mechanisms for plasma on these ``open'' field lines, in terms of ion cyclotron resonant heating by high frequency Alfven waves. In the other, I will try to review evidence for the ``nano-flare'' heating mechanism proposed by Parker to explain the heating of plasma along closed field lines, such as are present in active regions, based upon data from the SOHO and TRACE spacecraft. Parker's picture is one of slow field line ``braiding'', driven by random footpoint motions, with sudden energy release at critical energies. An attempt will be made to relate these different mechanisms by looking for the source of the high frequency waves implied by the UVCS observations.

  10. 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.

  11. 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.

  12. 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.

  13. 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

  14. 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.

  15. 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.

  16. 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.

  17. Fine thermal structure of a coronal active region.

    PubMed

    Reale, Fabio; Parenti, Susanna; Reeves, Kathy K; Weber, Mark; Bobra, Monica G; Barbera, Marco; Kano, Ryouhei; Narukage, Noriyuki; Shimojo, Masumi; Sakao, Taro; Peres, Giovanni; Golub, Leon

    2007-12-01

    The determination of the fine thermal structure of the solar corona is fundamental to constraining the coronal heating mechanisms. The Hinode X-ray Telescope collected images of the solar corona in different passbands, thus providing temperature diagnostics through energy ratios. By combining different filters to optimize the signal-to-noise ratio, we observed a coronal active region in five filters, revealing a highly thermally structured corona: very fine structures in the core of the region and on a larger scale further away. We observed continuous thermal distribution along the coronal loops, as well as entangled structures, and variations of thermal structuring along the line of sight.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. Estudio del CH interestelar

    NASA Astrophysics Data System (ADS)

    Olano, C.; Lemarchand, G.; Sanz, A. J.; Bava, J. A.

    El objetivo principal de este proyecto consiste en el estudio de la distribución y abundancia del CH en nubes interestelares a través de la observación de las líneas hiperfinas del CH en 3,3 GHz. El CH es una molécula de amplia distribución en el espacio interestelar y una de las pocas especies que han sido observadas tanto con técnicas de radio como ópticas. Desde el punto de vista tecnológico se ha desarrollado un cabezal de receptor que permitirá la realización de observaciones polarimétricas en la frecuencia de 3,3 GHz, con una temperatura del sistema de 60 K y un ancho de banda de 140 MHz, y que será instalado en el foco primario de la antena parabólica del IAR. El cabezal del receptor es capaz de detectar señales polarizadas, separando las componentes de polarización circular derecha e izquierda. Para tal fin el cabezal consta de dos ramas receptoras que amplificarán la señal y la trasladarán a una frecuencia más baja (frecuencia intermedia), permitiendo de esa forma un mejor transporte de la señal a la sala de control para su posterior procesamiento. El receptor además de tener características polarimétricas, podrá ser usado en el continuo y en la línea, utilizando las ventajas observacionales y de procesamiento de señal que actualmente posee el IAR.

  3. 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.

  4. Solar coronal holes as sources of recurrent geomagnetic disturbances

    NASA Technical Reports Server (NTRS)

    Neupert, W. M.; Pizzo, V.

    1974-01-01

    Observations of the solar corona by Oso 7 have been used in a superposed epoch analysis to study the relationships between classes of coronal features and geomagnetic activity. Both bright coronal regions and regions of less than average brightness were investigated. It was found that for the period from January 1972 through January 1973, a significant enhancement in geomagnetic activity occurred 2-3 days after central meridian passage of large coronal holes that extended to within 5 deg of the solar subearth point when they were on the meridian. Large coronal holes appear to satisfy the requirements for 'M regions' which were hypothesized to be responsible for recurrent geomagnetic disturbances (Bartels, 1934). If solar wind high-speed streams originate preferentially in these regions, their velocity at the base of the corona will be substantially higher than that expected from an axisymmetric solar wind model.

  5. 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.

  6. 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).

  7. 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

  8. 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

  9. MHD Modeling of Differential Rotation in Coronal Holes

    NASA Technical Reports Server (NTRS)

    Lionello, Roberto; Linker, Jon A.; Mikic, Zoran; Riley, Pete

    2004-01-01

    The photosphere and the magnetic flux therein undergo differential rotation. Coronal holes appear to rotate almost rigidly. Magnetic reconnection has been invoked to reconcile these phenomena. Mechanism relevant to the formation of the slow solar wind. We have used our MHD model in spherical coordinates to study the effect of differential rotation on coronal holes. We have imposed a magnetic flux distribution similar to and applied differential rotation for the equivalent of 5 solar rotations.

  10. 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.

  11. 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.

  12. 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.

  13. Strong variability of the coronal line region in NGC 5548

    NASA Astrophysics Data System (ADS)

    Landt, Hermine; Ward, Martin J.; Steenbrugge, Katrien C.; Ferland, Gary J.

    2015-12-01

    We present the second extensive study of the coronal line variability in an active galaxy. Our data set for the well-studied Seyfert galaxy NGC 5548 consists of five epochs of quasi-simultaneous optical and near-infrared spectroscopy spanning a period of about five years and three epochs of X-ray spectroscopy overlapping in time with it. Whereas the broad emission lines and hot dust emission varied only moderately, the coronal lines varied strongly. However, the observed high variability is mainly due to a flux decrease. Using the optical [Fe VII] and X-ray O VII emission lines we estimate that the coronal line gas has a relatively low density of ne ˜ 103 cm-3 and a relatively high ionisation parameter of log U ˜ 1. The resultant distance of the coronal line gas from the ionizing source of about eight light-years places this region well beyond the hot inner face of the dusty torus. These results imply that the coronal line region is an independent entity. We find again support for the X-ray heated wind scenario of Pier & Voit; the increased ionizing radiation that heats the dusty torus also increases the cooling efficiency of the coronal line gas, most likely due to a stronger adiabatic expansion. The much stronger coronal line variability of NGC 5548 relative to that of NGC 4151 can also be explained within this picture. NGC 5548 has much stronger coronal lines relative to the low-ionization lines than NGC 4151 indicating a stronger wind, in which case a stronger adiabatic expansion of the gas and so fading of the line emission is expected.

  14. The Contribution of Coronal Jets to the Solar Wind

    NASA Astrophysics Data System (ADS)

    Lionello, R.; Török, T.; Titov, V. S.; Leake, J. E.; Mikić, Z.; Linker, J. A.; Linton, M. G.

    2016-11-01

    Transient collimated plasma eruptions in the solar corona, commonly known as coronal (or X-ray) jets, are among the most interesting manifestations of solar activity. It has been suggested that these events contribute to the mass and energy content of the corona and solar wind, but the extent of these contributions remains uncertain. We have recently modeled the formation and evolution of coronal jets using a three-dimensional (3D) magnetohydrodynamic (MHD) code with thermodynamics in a large spherical domain that includes the solar wind. Our model is coupled to 3D MHD flux-emergence simulations, i.e., we use boundary conditions provided by such simulations to drive a time-dependent coronal evolution. The model includes parametric coronal heating, radiative losses, and thermal conduction, which enables us to simulate the dynamics and plasma properties of coronal jets in a more realistic manner than done so far. Here, we employ these simulations to calculate the amount of mass and energy transported by coronal jets into the outer corona and inner heliosphere. Based on observed jet-occurrence rates, we then estimate the total contribution of coronal jets to the mass and energy content of the solar wind to (0.4–3.0)% and (0.3–1.0)%, respectively. Our results are largely consistent with the few previous rough estimates obtained from observations, supporting the conjecture that coronal jets provide only a small amount of mass and energy to the solar wind. We emphasize, however, that more advanced observations and simulations (including parametric studies) are needed to substantiate this conjecture.

  15. 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.

  16. Coronal transverse magnetohydrodynamic waves in a solar prominence.

    PubMed

    Okamoto, T J; Tsuneta, S; Berger, T E; Ichimoto, K; Katsukawa, Y; Lites, B W; Nagata, S; Shibata, K; Shimizu, T; Shine, R A; Suematsu, Y; Tarbell, T D; Title, A M

    2007-12-01

    Solar prominences are cool 10(4) kelvin plasma clouds supported in the surrounding 10(6) kelvin coronal plasma by as-yet-undetermined mechanisms. Observations from Hinode show fine-scale threadlike structures oscillating in the plane of the sky with periods of several minutes. We suggest that these represent Alfvén waves propagating on coronal magnetic field lines and that these may play a role in heating the corona.

  17. 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.

  18. 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

  19. 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

  20. Inferences on Coronal Magnetic Fields from SOHO UVCS Observations

    NASA Technical Reports Server (NTRS)

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

    1996-01-01

    The characteristics of the magnetic field ubiquitously permeating the coronal plasma are still largely unknown. In this paper we analyze some aspects of coronal physics, related to the magnetic field behavior, which forthcoming SOHO UVCS observations can help better understand. To this end, three coronal structures will be examined: streamers, coronal mass ejections (CME's) and coronal holes. As to streamers and CME's, we show, via simulations of the Ly-alpha and white light emission from these objects, calculated on the basis of recent theoretical models, how new data from SOHO can help advancing our knowledge of the streamer/CME magnetic configuration. Our discussion highlights also those observational signatures which might offer clues on reconnection processes in streamers' current sheets. Coronal holes (CH's) are discussed in the last section of the paper. Little is known about CH flux tube geometry, which is closely related to the behavior of the solar wind at small heliocentric distances. Indirect evidence for the flux tube spreading factors, within a few solar radii, is here examined.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. Radio-quiet Fast Coronal Mass Ejections

    NASA Astrophysics Data System (ADS)

    Gopalswamy, N.; Aguilar-Rodriguez, E.; Kaiser, M. L.; Howard, R. A.

    2004-12-01

    Coronal mass ejections (CMEs) drive shocks in the interplanetary medium that produce type II radio emission. These CMEs are faster and wider on the average, than the general population of CMEs. However, when we start from fast (speed > 900 km/s) and wide (angular width > 60 degrees), more than half of them are not associated with radio bursts. In order to understand why these CMEs are radio quiet, we collected all the fast and wide (FW) CMEs detected by the Solar and Heliospheric Observatory (SOHO) mission's Large Angle and Spectrometric Coronagraph (LASCO) and isolated those without associated type II radio bursts. The radio bursts were identified in the dynamic spectra of the Radio and Plasma Wave (WAVES) Experiment on board the Wind spacecraft. We also checked the list against metric type II radio bursts reported in Solar Geophysical Data and isolated those without any radio emission. This exercise resulted in about 140 radio-quiet FW CMEs. We identified the source regions of these CMEs using the Solar Geophysical Data listings, cross-checked against the eruption regions in the SOHO/EIT movies. We explored a number of possibilities for the radio-quietness: (i) Source region being too far behind the limb, (ii) flare size, (iii) brightness of the CME, and (iv) the density of the ambient medium. We suggest that a combination of CME energy and the Alfven speed profile of the ambient medium is primarily responsible for the radio-quietness of these FW CMEs.

  8. 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.

  9. 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.

  10. 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.

  11. Why are halo coronal mass ejections faster?

    NASA Astrophysics Data System (ADS)

    Zhang, Qing-Min; Guo, Yang; Chen, Peng-Fei; Ding, Ming-De; Fang, Cheng

    2010-05-01

    Halo coronal mass ejections (CMEs) have been to be significantly faster than normal CMEs, which is a long-standing puzzle. In order to solve the puzzle, we first investigate the observed properties of 31 limb CMEs that clearly display loop-shaped frontal loops. The observational results show a strong tendency that slower CMEs are weaker in white-light intensity. Then, we perform a Monte Carlo simulation of 20000 artificial limb CMEs that have an average velocity of ~523 km s-1. The Thomson scattering of these events is calculated when they are assumed to be observed as limb and halo events, respectively. It is found that the white-light intensity of many slow CMEs becomes remarkably reduced when they turn from being viewed as a limb event to being viewed as a halo event. When the intensity is below the background solar wind fluctuation, it is assumed that they would be missed by coronagraphs. The average velocity of “detectable" halo CMEs is ~922 km s-1 very close to the observed value. This also indicates that wider events are more likely to be recorded. The results soundly suggest that the higher average velocity of halo CMEs is due to that a majority of slow events and some of narrow fast events carrying less material are so faint that they are blended with the solar wind fluctuations, and therefore are not observed.

  12. 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.

  13. Numerical simulation of solar coronal magnetic fields

    NASA Technical Reports Server (NTRS)

    Dahlburg, Russell B.; Antiochos, Spiro K.; Zang, T. A.

    1990-01-01

    Many aspects of solar activity are believed to be due to the stressing of the coronal magnetic field by footpoint motions at the photosphere. The results are presented of a fully spectral numerical simulation which is the first 3-D time dependent simulation of footpoint stressing in a geometry appropriate for the corona. An arcade is considered that is initially current-free and impose a smooth footpoint motion that produces a twist in the field of approx 2 pi. The footprints were fixed and the evolution was followed until the field relaxes to another current-free state. No evidence was seen for any instability, either ideal or resistive and no evidence for current sheet formation. The most striking feature of the evolution is that in response to photospheric motions, the field expands rapidly upward to minimize the stress. The expansion has two important effects. First, it suppresses the development of dips in the field that could support dense, cool material. For the motions assumed, the magnetic field does not develop a geometry suitable for prominence formation. Second, the expansion inhibits ideal instabilities such as kinking. The results indicate that simple stearing of a single arcade is unlikely to lead to solar activity such as flares or prominences. Effects are discussed that might possibly lead to such activity.

  14. Coronal Kink Instability With Parallel Thermal Conduction

    NASA Astrophysics Data System (ADS)

    Botha, Gert J. J.; Arber, Tony D.; Hood, Alan W.; Srivastava, A. K.

    2012-01-01

    Thermal conduction along magnetic field lines plays an important role in the evolution of the kink instability in coronal loops. In the nonlinear phase of the instability, local heating occurs due to reconnection, so that the plasma reaches high temperatures. To study the effect of parallel thermal conduction in this process, the 3D nonlinear magnetohydrodynamic (MHD) equations are solved for an initially unstable equilibrium. The initial state is a cylindrical loop with zero net current. Parallel thermal conduction reduces the local temperature, which leads to temperatures that are an order of magnitude lower than those obtained without thermal conduction. This process is important on the timescale of fast MHD phenomena; it reduces the kinetic energy released by an order of magnitude. The impact of this process on observational signatures is presented. Synthetic observables are generated that include spatial and temporal averaging to account for the resolution and exposure times of TRACE images. It was found that the inclusion of parallel thermal conductivity does not have as large an impact on observables as the order of magnitude reduction in the maximum temperature would suggest. The reason is that response functions sample a broad range of temperatures, so that the net effect of parallel thermal conduction is a blurring of internal features of the loop structure.

  15. L-alpha intensity in coronal streamers

    NASA Astrophysics Data System (ADS)

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

    1993-09-01

    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.

  16. A Catalog of Coronal "EIT Wave" Transients

    NASA Technical Reports Server (NTRS)

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

    2009-01-01

    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 one 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(exp -1) with "typical" speeds of 200-400 km s(exp -1).

  17. 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

  18. 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

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. Projection effects in coronal mass ejections

    NASA Astrophysics Data System (ADS)

    Vršnak, B.; Sudar, D.; Ruždjak, D.; Žic, T.

    2007-07-01

    Context: Basic observational parameters of a coronal mass ejection (CME) are its speed and angular width. Measurements of the CME speed and angular width are severely influenced by projection effects. Aims: The goal of this paper is to investigate a statistical relationship between the plane-of-sky speeds of CMEs and the direction of their propagation, hopefully providing an estimate of the true speeds of CMEs. Methods: We analyze the correlation between the plane-of-sky velocity and the position of the CME source region, employing several non-halo CME samples. The samples are formed applying various restrictions to avoid crosstalk of relevant parameters. For example, we select only CMEs observed to radial distances larger than 10 solar radii; we omit CMEs showing a considerable acceleration in the considered distance range and treat CMEs of different angular widths separately. Finally, we combine these restriction criteria, up to the limits beyond which the statistical significance of the results becomes ambiguous. Results: A distinct anti-correlation is found between the angular width of CMEs and their source-region position, clearly showing an increasing trend towards the disc center. Similarly, all of the considered subsamples show a correlation between the CME projected speed and the distance of the source region from the disc center. On average, velocities of non-halo limb-CMEs are 1.5-2 times higher than in the case of non-halo CMEs launched from regions located close to the disc center. Conclusions: Unfortunately, the established empirical relationships provide only a rough estimate of the velocity correction as a function of the source-region location. To a certain degree, the results can be explained in terms of CME cone models, but only after taking crosstalk of various parameters and observational artifacts into account.

  4. 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.

  5. Magnetic Flux Supplement to Coronal Bright Points

    NASA Astrophysics Data System (ADS)

    Mou, Chaozhou; Huang, Zhenghua; Xia, Lidong; Madjarska, Maria S.; Li, Bo; Fu, Hui; Jiao, Fangran; Hou, Zhenyong

    2016-02-01

    Coronal bright points (BPs) are associated with magnetic bipolar features (MBFs) and magnetic cancellation. Here we investigate how BP-associated MBFs form and how the consequent magnetic cancellation occurs. We analyze longitudinal magnetograms from the Helioseismic and Magnetic Imager to investigate the photospheric magnetic flux evolution of 70 BPs. From images taken in the 193 Å passband of the Atmospheric Imaging Assembly (AIA) we dermine that the BPs’ lifetimes vary from 2.7 to 58.8 hr. The formation of the BP MBFs is found to involve three processes, namely, emergence, convergence, and local coalescence of the magnetic fluxes. The formation of an MBF can involve more than one of these processes. Out of the 70 cases, flux emergence is the main process of an MBF buildup of 52 BPs, mainly convergence is seen in 28, and 14 cases are associated with local coalescence. For MBFs formed by bipolar emergence, the time difference between the flux emergence and the BP appearance in the AIA 193 Å passband varies from 0.1 to 3.2 hr with an average of 1.3 hr. While magnetic cancellation is found in all 70 BPs, it can occur in three different ways: (I) between an MBF and small weak magnetic features (in 33 BPs); (II) within an MBF with the two polarities moving toward each other from a large distance (34 BPs); (III) within an MBF whose two main polarities emerge in the same place simultaneously (3 BPs). While an MBF builds up the skeleton of a BP, we find that the magnetic activities responsible for the BP heating may involve small weak fields.

  6. 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.

  7. 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.

  8. The Importance of Geometric Effects in Coronal Loop Models

    NASA Astrophysics Data System (ADS)

    Mikić, Zoran; Lionello, Roberto; Mok, Yung; Linker, Jon A.; Winebarger, Amy R.

    2013-08-01

    We systematically investigate the effects of geometrical assumptions in one-dimensional (1D) models of coronal loops. Many investigations of coronal loops have been based on restrictive assumptions, including symmetry in the loop shape and heating profile, and a uniform cross-sectional area. Starting with a solution for a symmetric uniform-area loop with uniform heating, we gradually relax these restrictive assumptions to consider the effects of nonuniform area, nonuniform heating, a nonsymmetric loop shape, and nonsymmetric heating, to show that the character of the solutions can change in important ways. We find that loops with nonuniform cross-sectional area are more likely to experience thermal nonequilibrium, and that they produce significantly enhanced coronal emission, compared with their uniform-area counterparts. We identify a process of incomplete condensation in loops experiencing thermal nonequilibrium during which the coronal parts of loops never fully cool to chromospheric temperatures. These solutions are characterized by persistent siphon flows. Their properties agree with observations (Lionello et al.) and may not suffer from the drawbacks that led Klimchuk et al. to conclude that thermal nonequilibrium is not consistent with observations. We show that our 1D results are qualitatively similar to those seen in a three-dimensional model of an active region. Our results suggest that thermal nonequilibrium may play an important role in the behavior of coronal loops, and that its dismissal by Klimchuk et al., whose model suffered from some of the restrictive assumptions we described, may have been premature.

  9. THE IMPORTANCE OF GEOMETRIC EFFECTS IN CORONAL LOOP MODELS

    SciTech Connect

    Mikic, Zoran; Lionello, Roberto; Linker, Jon A.; Mok, Yung; Winebarger, Amy R.

    2013-08-20

    We systematically investigate the effects of geometrical assumptions in one-dimensional (1D) models of coronal loops. Many investigations of coronal loops have been based on restrictive assumptions, including symmetry in the loop shape and heating profile, and a uniform cross-sectional area. Starting with a solution for a symmetric uniform-area loop with uniform heating, we gradually relax these restrictive assumptions to consider the effects of nonuniform area, nonuniform heating, a nonsymmetric loop shape, and nonsymmetric heating, to show that the character of the solutions can change in important ways. We find that loops with nonuniform cross-sectional area are more likely to experience thermal nonequilibrium, and that they produce significantly enhanced coronal emission, compared with their uniform-area counterparts. We identify a process of incomplete condensation in loops experiencing thermal nonequilibrium during which the coronal parts of loops never fully cool to chromospheric temperatures. These solutions are characterized by persistent siphon flows. Their properties agree with observations (Lionello et al.) and may not suffer from the drawbacks that led Klimchuk et al. to conclude that thermal nonequilibrium is not consistent with observations. We show that our 1D results are qualitatively similar to those seen in a three-dimensional model of an active region. Our results suggest that thermal nonequilibrium may play an important role in the behavior of coronal loops, and that its dismissal by Klimchuk et al., whose model suffered from some of the restrictive assumptions we described, may have been premature.

  10. 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.

  11. SLOW MAGNETOACOUSTIC WAVE OSCILLATION OF AN EXPANDING CORONAL LOOP

    SciTech Connect

    Schmidt, J. M.; Ofman, L.

    2011-10-01

    We simulated an expanding loop or slow coronal mass ejection (CME) in the solar corona dimensioned with size parameters taken from real coronal expanding loops observed with the STEREO spacecraft. We find that the loop expands to Sun's size within about one hour, consistent with slow CME observations. At the top of the loop, plasma is being blown off the loop, enabled with the reconnection between the loop's flux rope magnetic field and the radial magnetic field of the Sun, thus yielding feeding material for the formation of the slow solar wind. This mechanism is in accordance with the observed blob formation of the slow solar wind. We find wave packets traveling with local sound speed downward toward the footpoints of the loop, already seen in coronal seismology observations and simulations of stationary coronal loops. Here, we generalize these results for an expanding medium. We also find a reflection of the wave packets, identified as slow magnetoacoustic waves, at the footpoints of the loop. This confirms the formation of standing waves within the coronal loop. In particular, the reflected waves can partly escape the loop top and contribute to the heating of the solar wind. The present study improves our understanding on how loop material can emerge to form blobs, major ingredients of slow CMEs, and how the release of the wave energy stored in slow magnetoacoustic waves, and transported away from the Sun within expanding loops, contributes to the acceleration and formation of the slow solar wind.

  12. Development of coronal cementum in hypsodont horse cheek teeth.

    PubMed

    Sahara, Noriyuki

    2014-04-01

    The horse is a grazing herbivore whose cheek teeth are hypsodon; that is, they possess long crowns that are completely covered by coronal cement at eruption. For elucidation of the sequential events in the formation of this coronal cementum in the mandibular horse cheek teeth, in the present study the lower 3rd permanent premolar teeth (PM4 ) from 3.5-, 4-, and 5-year-old horses were compared by using radiography, microcomputed tomography (Miro-CT), light microscopy (LM), and scanning electron microscopy (SEM). The present study clearly showed that prior to coronal cementogenesis tartrate-resistant acid phosphatase (TRAP)-positive odontoclasts resorbed on the enamel surface of the reserve crown in horse cheek tooth. Enamel resorption areas were relatively narrow, and started from the cuspal tips, and moved in the apical direction during tooth development. A primary cementum was initially deposited on the irregularly pitted enamel-cementum junction (ECJ) of the infolding and peripheral enamel. The infolding cementum filled grooves completely by the time of tooth eruption. On the other hand, in the peripheral cementum, the secondary and tertiary cementum layers were sequentially deposited on the primary cementum. These two cementum layers were sites for the insertion of the periodontal ligaments, and were continually laid down on the primary cementum coronally rather than apically throughout the life. The results of the present study suggest that the coronal cementum of horse cheek teeth is a multistructural and multifunctional tissue, meeting the requirements of its many different functions.

  13. 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.

  14. 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.

  15. Identification of the Coronal Sources of the Fast Solar Wind.

    PubMed

    Giordano; Antonucci; Noci; Romoli; Kohl

    2000-03-01

    The present spectroscopic study of the ultraviolet coronal emission in a polar hole, detected on 1996 April 6-9 with the Ultraviolet Coronagraph Spectrometer aboard the Solar and Heliospheric Observatory spacecraft, identifies the interplume lanes and background coronal hole regions as the channels in which the fast solar wind is preferentially accelerated. In interplume lanes, at heliocentric distance 1.7 R middle dot in circle, the corona expands at a rate between 105 and 150 km s-1, that is, much faster than in plumes in which the outflow velocity is between 0 and 65 km s-1. The wind velocity is inferred from the Doppler dimming of the O vi lambdalambda1032, 1037 lines, within a range of values, whose lower and upper limit corresponds to anisotropic and isotropic velocity distribution of the oxygen coronal ions, respectively.

  16. 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.

  17. 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.

  18. The privilege against self-incrimination in coroners' inquests.

    PubMed

    Freckelton, Ian

    2015-03-01

    The privilege against self-incrimination has a venerable history in the conduct of coroners' inquests. However, recent statutory reforms to the privilege in coroners' courts, which have had disuniform outcomes throughout Australia, have complicated the circumstances in which the privilege is extended to those claiming its protection. This editorial reviews the evolving law on the privilege generally and rulings that have been made in high-profile coronial inquests, as well as the modest volume of appellate litigation on this important issue. It identifies that the emerging law on the area prioritises amongst relevant factors for the coroner's discretion to exercise coercive powers over witnesses' objections to give evidence the fact that they are charged with serious criminal offences, and that the need for and utility of the evidence are also functioning as important considerations. PMID:25980183

  19. 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.

  20. 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.

  1. 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.

  2. FORWARD: A toolset for analyzing coronal magnetic fields

    NASA Astrophysics Data System (ADS)

    Gibson, Sarah

    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 Solar Soft IDL Potential Field Source Surface (PFSS) package, and also includes several analytic models (more can be added). It utilizes the Chianti database, and connects to the Virtual Solar Observatory to download data in a format directly comparable to model predictions. 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.

  3. 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.

  4. 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.

  5. Are halo coronal mass ejections special events?

    NASA Astrophysics Data System (ADS)

    Lara, Alejandro; Gopalswamy, Nat; Xie, Hong; Mendoza-Torres, Eduardo; PéRez-EríQuez, RomáN.; Michalek, Gregory

    2006-06-01

    We revisited the properties of wide coronal mass ejections (CMEs) called halo CMEs. Using the large LASCO/SOHO CMEs data set, from 1996 to 2004, we examined the statistical properties of (partial and full) halo CMEs and compare with the same properties of "normal" width (lower than 120°) CMEs. We found that halo CMEs have different properties than "normal" CMEs, which cannot be explained merely by the current geometric interpretation that they are seen as halos because they are traveling in the Sun Earth direction. We found that the CME width distribution is formed by, at least, three different populations: Two gaussians: a narrow and a medium distribution centered at ˜17° and ˜38°, respectively; the narrow population most likely corresponds to the "true" observed widths, whereas the medium width population is the product of projection effects. The third distribution corresponds to wider CMEs (80° < W < 210°) which behaves as a power law. Partial and full halo CMEs wider than these do not follow any particular distribution. This lack of regularity may be due to the small number of such events. In particular, we found (and test by a statistical approach) that the number of observed full halo CMEs is lower than expected. The CME speed follows a log-normal distribution, except for the very low speed CME population, which follows a gaussian distribution centered at ˜100 km/s and is probably due to projection effects. When the CMEs are divided by width into nonhalo, partial halo, and full halo, we found that the peaks of the distributions are shifted toward higher speeds, ˜300, ˜400 and ˜600 km/s for nonhalo, partial halo, and full halo CMEs, respectively. This confirms that halo CMEs tend to be high speed CMEs. The acceleration of full halo CMEs tends to be more negative compared with nonhalo and partial halo CMEs. We introduce a new observational CME parameter: The final observed distance (FOD), i.e., the highest point within the coronograph field of view

  6. UPFLOWS IN FUNNEL-LIKE LEGS OF CORONAL MAGNETIC LOOPS

    SciTech Connect

    Tian Hui; Marsch, Eckart; Curdt, Werner; He, Jiansen

    2009-10-10

    The prominent blueshifts of Ne VIII associated with the junctions of the magnetic network in the quiet Sun are still not well understood. By comparing the coronal magnetic-field structures as obtained by a potential-field reconstruction with the conspicuous blueshift patches on the Dopplergram of Ne VIII as observed in an equatorial quiet-Sun region, we find that most of the regions with significant upflow are associated with the funnel-like legs of magnetic loops and cospatial with increments of the line width. These quasi-steady upflows can be regarded as the signatures of mass supply to coronal loops. By using the square root of the line intensity as a proxy for the plasma density, the mass flux of the upflow in each funnel can be estimated. We find that the mass flux is anti-correlated with the funnel's expansion factor as determined from the extrapolated magnetic field. One of the loop systems is associated with a coronal bright point, which was observed by several instruments and exhibited various morphologies in different wavelengths and viewing directions. A remarkable agreement between its magnetic structure and the associated EUV emission pattern was found, suggesting an almost potential-field nature of the coronal magnetic field. We also report the direct detection of a small-scale siphon flow by both STEREO satellites. However, this transient siphon flow occurred in a weak mixed-polarity-field region, which was outside the adjacent magnetic funnel, and thus it is perhaps not related to plasma upflow in the funnel. Based on these observations, we suggest that at upper transition region (TR) temperatures the dominant flows in quiet-Sun coronal loops are long-lasting upflows rather than siphon flows. We also discuss the implications of our results for coronal heating and unresolved magnetic structures.

  7. 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.

  8. 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).

  9. (abstract) The Initiation of Quiescent-Filament Associated Coronal Mass Ejections by New Active Regions

    NASA Technical Reports Server (NTRS)

    Feynman, J.; Martin, S. F.

    1993-01-01

    We will present observational evidence that the eruption of filaments and coronal mass ejections (CMEs) occur as a consequence of the destabilization of large scale coronal arcades due to newly emerging magnetic flux reconnecting with the preexisting arcades.

  10. 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.

  11. Coronal mass ejections and magnetic flux ropes in interplanetary space

    NASA Technical Reports Server (NTRS)

    Gosling, J. T.

    1990-01-01

    Coronal mass ejections (CMEs) are formed in the solar corona by the ejection of material from closed field regions that were not previously participating in the solar wind expansion. CMEs commonly exhibit a signature consisting of a counterstreaming flux of suprathermal electrons with energies above about 80 eV, indicating closed field structures that are either rooted at both ends in the sun or entirely disconnected from it. About 30 percent of all CME events at 1 AU exhibit large, coherent internal field rotations typical of magnetic flux ropes. It is suggested that interplanetary magnetic flux ropes form as a result of reconnection within rising, previously sheared coronal magnetic loops.

  12. MHD stability of incompressible coronal loops with radiative energy loss

    NASA Technical Reports Server (NTRS)

    An, C.-H.

    1983-01-01

    Previous studies of the magnetohydrodynamic (MHD) stability of solar coronal loops have not taken into account the effects of radiative energy loss in the energy equation. However, since coronal loops continuously lose energy by radiation and heat conduction, it is important to understand how these energy loss mechanisms affect MHD stability. We investigate the problem assuming that a magnetic loop has cylindrical geometry. As a first step, stability is studied for a localized mode, and the result is applied to a specific equilibrium. We find that the radiative energy loss effect not only changes the growth rate of ideally unstable modes, but also alters the stability boundary predicted by ideal MHD theory.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. Excitation of kink oscillations of coronal loops: statistical study

    NASA Astrophysics Data System (ADS)

    Zimovets, I. V.; Nakariakov, V. M.

    2015-05-01

    Context. Solar flares are often accompanied by kink (transverse) oscillations of coronal loops. Despite intensive study of these oscillations in recent years, the mechanisms that excite them are still not known. Aims: We aim to clarify the excitation mechanisms for these kink oscillations of coronal loops. Methods: We analysed 58 kink-oscillation events observed by the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) during its first four years (2010-2014) with the use of the JHelioviewer. Association of these oscillation events with flares, lower coronal (r ≲ 1.4 R⊙) eruptions and plasma ejections, coronal mass ejections (CMEs), and coronal Type-II radio bursts is studied. Results: We find that 44 of these 58 oscillation events (76%) were associated with CMEs observed in the white light emission. Moreover, 57 events (98%) were accompanied by lower coronal eruptions/ejections (LCEs) observed in the extreme-ultraviolet band in the parental active regions. In the remaining event an LCE was not clearly seen, but it was definitely associated with a CME too. The main observational finding is that the kink oscillations were excited by the deviation of loops from their equilibria by a nearby LCE in 55 events (95%). In three remaining events, it was difficult to reliably determine the cause of the oscillations because of limitations in the observational data. We also found that 53 events (91%) were associated with flares. In five remaining events, the parental active regions were behind the limb and we could not directly see flare sites. It indicates that there is a close relationship between these two kinds of solar activity. However, the estimated speeds of a hypothetical driver of kink oscillations by flares were found to be lower than 500 km s-1 in 80% of the cases. Such low speeds do not favour the association of the oscillation excitation with a shock wave, as usually assumed. That only 23 (40%) of the oscillation events were found

  18. 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.

  19. 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

  20. 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)

  1. 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.

  2. Initiation of Coronal Mass Ejections by Tether-Cutting Reconnection

    NASA Technical Reports Server (NTRS)

    Moore, Ronald L.; Sterling, Alphonse C.; Falconer, David A.; Six, N. Frank (Technical Monitor)

    2002-01-01

    We present and interpret examples of the eruptive motion and flare brightening observed in the onset of magnetic explosions that produce coronal mass ejections. The observations are photospheric magnetograms and sequences of coronal and/or chromospheric images. In our examples, the explosion is apparently driven by the ejective eruption of a sigmoidal sheared-field flux rope from the core of an initially closed bipole. This eruption is initiated (triggered and unleashed) by reconnection located either (1) internally, low in the sheared core field, or (2) externally, at a magnetic null above the closed bipole. The internal reconnection is commonly called 'tether-cutting" reconnection, and the external reconnection is commonly called "break-out' reconnection. We point out that break-out reconnection amounts to external tether cutting. In one example, the eruptive motion of the sheared core field starts several minutes prior to any detectable brightening in the coronal images. We suggest that in this case the eruption is triggered by internal tether-cutting reconnection that at first is too slow and/or too localized to produce detectable heating in the coronal images. This work is supported by NASA's Office of Space Science through its Solar & Heliospheric Physics Supporting Research & Technology program and its Sun-Earth Connection Guest Investigator program.

  3. More Macrospicule Jets in On-Disk Coronal Holes

    NASA Astrophysics Data System (ADS)

    Adams, Mitzi; Sterling, Alphonse; Moore, Ronald

    2015-04-01

    We examine the magnetic structure and dynamics of multiple jets found in coronal holes close to or at 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 Å, 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, ~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.

  4. OBSERVATIONAL SIGNATURES OF THE CORONAL KINK INSTABILITY WITH THERMAL CONDUCTION

    SciTech Connect

    Botha, G. J. J.; Arber, T. D.; Srivastava, Abhishek K. E-mail: T.D.Arber@warwick.ac.uk

    2012-01-20

    It is known from numerical simulations that thermal conduction along magnetic field lines plays an important role in the evolution of the kink instability in coronal loops. This study presents the observational signatures of the kink instability in long coronal loops when parallel thermal conduction is included. The three-dimensional nonlinear magnetohydrodynamic equations are solved numerically to simulate the evolution of a coronal loop that is initially in an unstable equilibrium. The loop has length 80 Mm, width 8 Mm, and an initial maximum twist of {Phi} = 11.5{pi}, where {Phi} is a function of the radius. The initial loop parameters are obtained from a highly twisted loop observed in the Transition Region and Coronal Explorer (TRACE) 171 A wave band. Synthetic observables are generated from the data. These observables include spatial and temporal averaging to account for the resolution and exposure times of TRACE images. Parallel thermal conduction reduces the maximum local temperature by up to an order of magnitude. This means that different spectral lines are formed and different internal loop structures are visible with or without the inclusion of thermal conduction. However, the response functions sample a broad range of temperatures. The result is that the inclusion of parallel thermal conductivity does not have as large an impact on observational signatures as the order of magnitude reduction in the maximum temperature would suggest; the net effect is a blurring of internal features of the loop structure.

  5. The Swelling and Destabilization of a Coronal Mass Ejection (abstract)

    NASA Technical Reports Server (NTRS)

    Martin, S. F.; Feynman, J.

    1993-01-01

    We will present and discuss data for a bugle that was particularly well observed. Apparently the swelling of the bugle and its destabilization were caused by the newly emerging flux and its interaction with the pre-existing active regions and coronal structures.

  6. 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.

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

    NASA Astrophysics Data System (ADS)

    Matsumoto, Takuma

    2016-11-01

    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 this 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 per cent 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 this study would significantly impact on the prospects of successful MHD turbulence theory in the solar chromosphere.

  8. Heating of minor ions by the coronal slow shock

    NASA Technical Reports Server (NTRS)

    Whang, Y. C.; Zhao, Xuepu; Ogilvie, K. W.

    1990-01-01

    The coronal slow shock has been predicted to exist embedded in large coronal holes at 4-10 solar radii. In this paper, a three-fluid model is used to study the jumps in minor ion properties across a slow shock such as the coronal slow shock. The jump conditions are formulated in the de Hoffmann-Teller frame of reference. The Rankine-Hugoniot solution determines the MHD flow and the magnetic field across the shocks. For each minor ion species, the fluid equations for the conservation of mass, momentum, and energy can be solved to determine the velocity and the temperature of the ions across the shock. Also obtained is a similarity solution for heavy ions. The results show that, on the downstream side of the slow shock, the ion temperatures are nearly proportional to the ion masses for He, O, Si, and Fe, in agreement with observed ion temperatures in the inner solar wind. This indicates that the possibly existing coronal slow shock can be responsible for the observed heating of minor ions in the solar wind.

  9. 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

  10. 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.

  11. Do Coronal Holes Cause 27 Day Recurring Geomagnetic Storms?

    NASA Technical Reports Server (NTRS)

    Tsurutani, Bruce T.; Gonzalez, Walter D.; Gonzalez, Alicia L. C.; Tang, Frances; Park, Dan; Okada, Masaki; Arballo, John

    1994-01-01

    We examine 3 years of interplanetary data and geomagnetic activity indices (1973-1975) to determine the causes of geomagnetic storms and substorms during the descending phase of the solar cycle. In this paper, we specifically studied the year 1974 where two long lasting coronating streams existed.

  12. 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.

  13. 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.

  14. 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

  15. 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 .

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. Magnetic Field in the Gravitationally Stratified Coronal Loops

    NASA Astrophysics Data System (ADS)

    Dwivedi, B. N.; Srivastava, A. K.

    2015-03-01

    We study the effect of gravitational stratification on the estimation of magnetic fields in the coronal loops. By using the method of MHD seismology of kink waves for the estimation of magnetic field of coronal loops, we derive a new formula for the magnetic field considering the effect of gravitational stratification. The fast-kink wave is a potential diagnostic tool for the estimation of magnetic field in fluxtubes. We consider the eleven kink oscillation cases observed by TRACE between July 1998 and June 2001. We calculate magnetic field in the stratified loops ( B str) and compare them with the previously calculated absolute magnetic field ( B abs). The gravitational stratification efficiently affects the magnetic field estimation in the coronal loops as it affects also the properties of kink waves. We find ≈22% increment in the magnetic field for the smallest ( L = 72 Mm) while ≈ 42% increment in the absolute magnetic field for the longest ( L = 406 Mm) coronal loops. The magnetic fields B str and B abs also increase with the number density, if the loop length does not vary much. The increment in the magnetic field due to gravitational stratification is small at the lower number densities, however, it is large at the higher number densities. We find that damping time of kink waves due to phase-mixing is less in the case of gravitationally stratified loops compared to nonstratified ones. This indicates the more rapid damping of kink waves in the stratified loops. In conclusion, we find that the gravitational stratification efficiently affects the estimation of magnetic field and damping time estimation especially in the longer coronal loops.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. Drawing inferences about solar wind acceleration from coronal minor ion observations

    SciTech Connect

    Esser, R.; Holzer, T.E.; Leer, E.

    1987-12-01

    A parameter study is designed and carried out to illustrate the physical effects that can be studied through analysis and interpretation of coronal minor ion spectral line observations. It is shown that minor ion line width, together with the coronal Ly..cap alpha.. line width and coronal white light observations, can yield important information concerning the transport and dissipation of energy carried outward from the coronal base by hydromagnetic waves. Although it is difficult to infer minor ion velocities through the Doppler dimming technique, the application of this technique using both radiatively and collisionally excited lines can provide constraints on the acceleration of coronal minor ions. It is concluded tha the observation of coronal minor ion spectral lines represents an important component of a concerted observational approach to the solar wind acceleration problem. It must be emphasized, however, that the measurement of line widths is the most important coronal minor ion observation to obtain. copyright American Geophysical Union 1987

  8. PHYSICAL CONDITIONS OF CORONAL PLASMA AT THE TRANSIT OF A SHOCK DRIVEN BY A CORONAL MASS EJECTION

    SciTech Connect

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

    2015-10-20

    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{sub ⊙} 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 M{sub A} and strength of coronal magnetic fields at the shock's heights. We found that in the early phases (2–4 R{sub ⊙}) 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{sub ⊙} altitude and ∼110° latitude.

  9. 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

  10. Characteristics of EUV Coronal Jets Observed with STEREO/SECCHI

    NASA Astrophysics Data System (ADS)

    Nisticò, G.; Bothmer, V.; Patsourakos, S.; Zimbardo, G.

    2009-10-01

    In this paper we present the first comprehensive statistical study of EUV coronal jets observed with the SECCHI (Sun Earth Connection Coronal and Heliospheric Investigation) imaging suites of the two STEREO spacecraft. A catalogue of 79 polar jets is presented, identified from simultaneous EUV and white-light coronagraph observations, taken during the time period March 2007 to April 2008, when solar activity was at a minimum. The twin spacecraft angular separation increased during this time interval from 2 to 48 degrees. The appearances of the coronal jets were always correlated with underlying small-scale chromospheric bright points. A basic characterization of the morphology and identification of the presence of helical structure were established with respect to recently proposed models for their origin and temporal evolution. Though each jet appeared morphologically similar in the coronagraph field of view, in the sense of a narrow collimated outward flow of matter, at the source region in the low corona the jet showed different characteristics, which may correspond to different magnetic structures. A classification of the events with respect to previous jet studies shows that amongst the 79 events there were 37 Eiffel tower-type jet events, commonly interpreted as a small-scale (˜35 arc sec) magnetic bipole reconnecting with the ambient unipolar open coronal magnetic fields at its loop tops, and 12 lambda-type jet events commonly interpreted as reconnection with the ambient field happening at the bipole footpoints. Five events were termed micro-CME-type jet events because they resembled the classical coronal mass ejections (CMEs) but on much smaller scales. The remaining 25 cases could not be uniquely classified. Thirty-one of the total number of events exhibited a helical magnetic field structure, indicative for a torsional motion of the jet around its axis of propagation. A few jets are also found in equatorial coronal holes. In this study we present sample

  11. 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

  12. 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

  13. 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.

  14. 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.

  15. How Do Coronal Hole Storms Affect the Upper Atmosphere?

    NASA Astrophysics Data System (ADS)

    Mannucci, A. J.; Tsurutani, B. T.; Solomon, S. C.; Verkhoglyadova, O. P.; Thayer, J. P.

    2012-02-01

    The solar cycle, often described as an increase and decrease of solar activity with a period of about 11 years, can strongly affect Earth's thermosphere and ionosphere. Although the longest direct record of solar activity is based on sunspot number, a more quantifiable parameter is solar irradiance at extreme ultraviolet (EUV) wavelengths, which varies by more than a factor of 3 over the sunspot cycle. To first order, upper atmospheric variation is a result of changes in ionizing fluxes at EUV wavelengths. As the solar cycle passes its EUV peak and approaches minimum, the number of solar active regions declines, leading to a reduction and then a near absence of coronal mass ejections (CMEs)—episodic events of high-energy bursts of solar plasma that cause geomagnetic storms at Earth. During the solar cycle's declining phase, coronal holes begin to occupy lower latitudes on the solar surface and fall in line with the ecliptic plane.

  16. Coronal Mass Ejections and Non-recurrent Forbush Decreases

    NASA Astrophysics Data System (ADS)

    Belov, A.; Abunin, A.; Abunina, M.; Eroshenko, E.; Oleneva, V.; Yanke, V.; Papaioannou, A.; Mavromichalaki, H.; Gopalswamy, N.; Yashiro, S.

    2014-10-01

    Coronal mass ejections (CMEs) and their interplanetary counterparts (interplanetary coronal mass ejections, ICMEs) are responsible for large solar energetic particle events and severe geomagnetic storms. They can modulate the intensity of Galactic cosmic rays, resulting in non-recurrent Forbush decreases (FDs). We investigate the connection between CME manifestations and FDs. We used specially processed data from the worldwide neutron monitor network to pinpoint the characteristics of the recorded FDs together with CME-related data from the detailed online catalog based upon the Solar and Heliospheric Observatory (SOHO)/ Large Angle and Spectrometric Coronagraph (LASCO) data. We report on the correlations of the FD magnitude to the CME initial speed, the ICME transit speed, and the maximum solar wind speed. Comparisons between the features of CMEs (mass, width, velocity) and the characteristics of FDs are also discussed. FD features for halo, partial halo, and non-halo CMEs are presented and discussed.

  17. Inferring the Coronal Density Irregularity from EUV Spectra

    NASA Astrophysics Data System (ADS)

    Hahn, M.; Savin, D. W.

    2016-09-01

    Understanding the density structure of the solar corona is important for modeling both coronal heating and the solar wind. Direct measurements are difficult because of line-of-sight integration and possible unresolved structures. We present a new method for quantifying such structures using density-sensitive extreme ultraviolet line intensities to derive a density irregularity parameter, a relative measure of the amount of structure along the line of sight. We also present a simple model to relate the inferred irregularities to physical quantities, such as the filling factor and density contrast. For quiet-Sun regions and interplume regions of coronal holes, we find a density contrast of at least a factor of 3-10 and corresponding filling factors of about 10%-20%. Our results are in rough agreement with other estimates of the density structures in these regions. The irregularity diagnostic provides a useful relative measure of unresolved structure in various regions of the corona.

  18. 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

  19. Solar cycle changes in coronal holes and space weather cycles

    NASA Astrophysics Data System (ADS)

    Luhmann, J. G.; Li, Y.; Arge, C. N.; Gazis, P. R.; Ulrich, R.

    2002-08-01

    Potential field source surface models of the coronal magnetic field, based on Mt. Wilson Observatory synoptic magnetograms, are used to infer the coronal hole sources of low-heliolatitude solar wind over approximately the last three solar cycles. Related key parameters like interplanetary magnetic field and bulk velocity are also calculated. The results illustrate how the evolving contribution of the polar hole sources relative to that from low-latitude and midlatitude active region hole sources can explain solar magnetic field control of long-term interplanetary variations. In particular, the enduring consistent magnetogram record and continuous model displays produce a useful overview of the solar control of interplanetary cycles and trends that affect space weather.

  20. Long-term containment of energetic particles in coronal loops

    NASA Technical Reports Server (NTRS)

    Lau, Yun-Tung; Northrop, Theodore G.; Finn, John M.

    1993-01-01

    Recent observation from the Compton Gamma-Ray Observatory shows that gamma-ray emission after a solar flare can last for as long as 8 hours. There is also evidence that electrons and protons are accelerated only during the impulsive phase of the flare and are subsequently mirror trapped in coronal magnetic loops. This poses the following dilemma: if the magnetic field lines in the loop are simple plane arches, the protons will drift across the cross section of the loop in seconds to minutes, rather than hours. To solve the dilemma, we use guiding center theory to show that long-term containment of energetic protons in a coronal loop is possible if magnetic field lines have enough twist. We also find that in the trapped region of the loop, the twist angle of field lines between the mirror points of a bounce orbit is approximately 2 pi.

  1. 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.

  2. 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.

  3. Imprints of coronal temperature disturbances on type III bursts

    NASA Astrophysics Data System (ADS)

    Li, Bo; Robinson, Peter

    The electron temperature Te and ion temperature Ti in the corona vary with time and loca-tion, due to transient and persistent activity on the Sun. The effects of spatially localized disturbances in Te and Ti on coronal type III radio bursts are simulated. The disturbances are superimposed on monotonically varying temperature backgrounds and arise from spatially confined solar activity. Qualitatively and quantitatively different imprints are found on the curve of the maximum flux versus frequency of type III bursts, because of the disturbances in Te and Ti . The results indicate that nonthermal coronal type III bursts offer a new tool to probe and distinguish between spatially localized structures of Te and Ti along the paths of type III beams. Furthermore, localized temperature disturbances may be responsible for some fine structures in type III bursts, e.g., striae in type IIIb bursts in the presence of multiple, localized temperature disturbances.

  4. 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

  5. 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.

  6. Magnetic reconnection between a solar filament and nearby coronal loops

    NASA Astrophysics Data System (ADS)

    Li, Leping; Zhang, Jun; Peter, Hardi; Priest, Eric; Chen, Huadong; Guo, Lijia; Chen, Feng; Mackay, Duncan

    2016-09-01

    Magnetic reconnection is difficult to observe directly but coronal structures on the Sun often betray the magnetic field geometry and its evolution. Here we report the observation of magnetic reconnection between an erupting filament and its nearby coronal loops, resulting in changes in the filament connection. X-type structures form when the erupting filament encounters the loops. The filament becomes straight, and bright current sheets form at the interfaces. Plasmoids appear in these current sheets and propagate bi-directionally. The filament disconnects from the current sheets, which gradually disperse and disappear, then reconnects to the loops. This evolution suggests successive magnetic reconnection events predicted by theory but rarely detected with such clarity in observations. Our results confirm the three-dimensional magnetic reconnection theory and have implications for the evolution of dissipation regions and the release of magnetic energy for reconnection in many magnetized plasma systems.

  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. Flux Emergence as a Trigger of Coronal Mass Ejections

    NASA Astrophysics Data System (ADS)

    Linton, Mark; Torok, T.

    2009-05-01

    We will present preliminary results from an investigation of Coronal Mass Ejections (CMEs) triggered by flux emergence. Related numerical simulations rely so far mostly on the kinematic, i.e. boundary-driven, emergence of magnetic flux at a photospheric boundary into the corona. We are investigating the viability of these models by studying the dynamical emergence of flux from a convection zone, through a temperature minimum photospheric region, into the corona. We are focusing on two CME models: the magnetic breakout model, and the ideal MHD torus instability model. Results from the breakout CME study will be shown at this meeting in the presentation by Leake et al. Here, we will show first results from the torus CME model. We build on recent simulations by Torok, where the torus instability of a pre-existing, stable coronal flux rope is triggered by kinematic flux emergence. We will report on our work to emerge flux dynamically in an equivalent configuration.

  9. 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.

  10. 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.

  11. 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.

  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. Estimate of Coronal Magnetic Field Strength Using Plasmoid Acceleration Measurement

    NASA Astrophysics Data System (ADS)

    Choe, G.; Lee, K.; Jang, M.

    2010-12-01

    A method of estimating the lower bound of coronal magnetic field strength in the neighborhood of an ejecting plasmoid is presented. Based on the assumption that the plasma ejecta is within a magnetic island, an analytical expression for the force acting on the ejecta is derived. A rather simple calculation shows that the vertical force acting on a cylinder-like volume, whose lateral surface is a flux surface and whose magnetic axis is parallel to the horizontal, is just the difference in total pressure (magnetic pressure plus plasma pressure) below and above the volume. The method is applied to a limb coronal mass ejection event, and a lower bound of the magnetic field strength just below the CME core is estimated. The method is expected to provide useful information on the strength of reconnecting magnetic field if applied to X-ray plasma ejecta.

  14. 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.

  15. 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.

  16. 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.

  17. 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

  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. Energetic characterisation and statistics of solar coronal brightenings

    NASA Astrophysics Data System (ADS)

    Buchlin, Eric; Solomon, Jacques; Joulin, Vincent; Guennou, Chloé

    2016-07-01

    To explain the high temperature of the corona, much attention has been paid to the distribution of energy in dissipation events, which might be caused by turbulent reconnection. 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. We aim at getting a better estimate of the distributions of the energy dissipated in coronal heating events using high-resolution, multi-channel Extreme Ultra-Violet (EUV) data. To estimate the energies corresponding to heating events and deduce their distribution, we detect brightenings in five EUV channels of the Atmospheric Imaging Assembly (AIA) on-board the Solar Dynamics Observatory (SDO). We combine the results of these detections and we use maps of temperature and emission measure derived from the same observations to compute the energies. We obtain distributions of areas, durations, intensities, and energies (thermal, radiative, and conductive) of events. These distributions are power-laws, and we find also power-law correlations between event parameters. 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.

  20. 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.

  1. 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.

  2. 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.

  3. Evolving Magnetic Structures and Their Relation to Coronal Mass Ejections

    NASA Technical Reports Server (NTRS)

    Feynman, J.

    1996-01-01

    Solar activity regions are frequently concentrated into cluster which persist for many solar rotations. These activity complexes are associated with weak dispersed magnetic fields which are most apparent after the activity itself has ceased. We call this combination of persistent activity and dispersed Evolving Magnetic Structures (EMS). Here we show examples of EMSs and describe the evolution of an EMS associated with major Coronal Mass Ejections (CME) and other solar and magnetic disturbances.

  4. Projection Effects in Coronal Dimmings and Associated EUV Wave Event

    NASA Astrophysics Data System (ADS)

    Dissauer, K.; Temmer, M.; Veronig, A. M.; Vanninathan, K.; Magdalenić, J.

    2016-10-01

    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 on 2011 September 6 (SOL2011-09-06T22:12). This EUV wave features peculiar on-disk signatures in particular, we observe an intermittent “disappearance” of the front for 120 s in Solar Dynamics Observatory (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. The eruption was also accompanied by localized coronal dimming regions. 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 and reconstruct the SDO line-of-sight (LOS) direction of the identified coronal dimming regions in STEREO-A. We show that the observed intensities of the dimming regions in SDO/AIA depend on the structures that are lying along their LOS and are the combination of their individual intensities, e.g., the expanding CME body, the enhanced EUV wave, and the CME front. In this context, we conclude that the intermittent disappearance of the EUV wave in the AIA 171, 193, and 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.

  5. 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

  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. Nonthermal Linewidths from Serts: Implications for Coronal Heating Models

    NASA Technical Reports Server (NTRS)

    Davila, Joseph M.

    1999-01-01

    Observations from Solar Extreme-ultraviolet Research Telescope and Spectrograph (SERTS) are used to determine the nonthermal velocity in the corona for active and quiet Sun regions in 1991 and 1993. A nonthermal velocity of 20-30 km/s is obtained in all solar structures observed at both observing times. These observations can be used to constrain coronal heating models. The idea that magnetic reconnection could provide energy to heat the non-transient corona is not supported by the data.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. Solar wind and coronal rotation during an activity cycle

    NASA Astrophysics Data System (ADS)

    Pinto, Rui; Brun, Allan Sacha

    The properties of the solar wind flow are strongly affected by the time-varying strength and geometry of the global background magnetic field. The wind velocity and mass flux depend directly on the size and position of the wind sources at the surface, and on the geometry of the magnetic flux-tubes along which the wind flows. We address these problems by performing numerical simulations coupling a kinematic dynamo code (STELEM) evolve in a 2.5D axisymmetric coronal MHD code (DIP) covering an 11 yr activity cycle. The latitudinal distribution of the calculated wind velocities agrees with in-situ (ULYSSES, HELIO) and radio measurements (IPS). The transition from fast to slow wind flows can be explained in terms of the high overall flux-tube superradial expansion factors in the vicinities of coronal streamer boundaries. We found that the Alfvén radii and the global Sun's mass loss rate vary considerably throughout the cycle (by a factor 4.5 and 1.6, respectively), leading to strong temporal modulations of the global angular momentum flux and magnetic braking torque. The slowly varying magnetic topology introduces strong non-uniformities in the coronal rotation rate in the first few solar radii. Finally, we point out directions to assess the effects of surface transient phenomena on the global properties of the solar wind.

  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. Coronal Observations at the Siberian 2008 Total Solar Eclipse

    NASA Astrophysics Data System (ADS)

    Pasachoff, Jay M.; Babcock, B. A.; Freeman, M. J.; DuPré, K. M.; Demianski, M.; Nesterenko, A.; Nesterenko, I.; Schneider, G.

    2009-12-01

    We successfully observed the 1 August 2008 total solar eclipse from the rooftop observatory of the State University of Novosibirsk in Akademgorodok, Siberia, latitude 55° N at 10:45 UT in clear skies and also from an airplane at 83° N latitude north of Svalbard at 9:43 UT. Our prime experiment in Akademgorodok was a set of high-cadence, 10 Hz, observations in the coronal green line at 530.3 nm from [Fe XIV] to verify and extend our previous findings of excess power in the 0.5 Hz to 1 Hz region as predicted by a subset of coronal-heating theories. We used twin 0.2-m telescopes with narrow-band interference filters and our POETS frame-transfer CCD's on the university's Paramount ME. Additional photography included graded-exposure sets of images meant for post-processing to compare with images taken earlier from the airplane and later from the ground in Mongolia and China to provide time differences of over 90 minutes. We also obtained HD video. Our comparison of the images from the airplane and from Siberia will be used to search for coronal motions.

  15. 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.

  16. 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

  17. 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.

  18. 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.

  19. A RECONNECTION-DRIVEN RAREFACTION WAVE MODEL FOR CORONAL OUTFLOWS

    SciTech Connect

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

    2011-12-10

    We conduct numerical experiments to determine whether interchange reconnection at high altitude coronal null points can explain the outflows observed as blueshifts in coronal emission lines at the boundaries between open and closed magnetic field regions. In this scenario, a strong, post-reconnection pressure gradient forms in the field-aligned direction when dense and hot, active region core loops reconnect with neighboring tenuous and cool, open field lines. We find that the pressure gradient drives a supersonic outflow and a rarefaction wave develops in both the open and closed post-reconnection magnetic field regions. We forward-model the spectral line profiles for a selection of coronal emission lines to predict the spectral signatures of the rarefaction wave. We find that the properties of the rarefaction wave are consistent with the observed velocity versus temperature structure of the corona in the outflow regions, where the velocity increases with the formation temperature of the emission lines. In particular, we find excellent agreement between the predicted and observed Fe XII 195.119 A spectral line profiles in terms of the blueshift (10 km s{sup -1}), full width at half-maximum (83 mA) and symmetry. Finally, we find that T{sub i} < T{sub e} in the open field region, which indicates that the interchange reconnection scenario may provide a viable mechanism and source region for the slow solar wind.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. Coronal Physics and the Chandra Emission Line Project

    NASA Technical Reports Server (NTRS)

    Brickhouse, N. S.; Drake, J. J.

    2000-01-01

    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 Capella, Procyon, and HR 1099 are providing not only invaluable calibration data, but also benchmarks for plasma spectral models. These models are needed to interpret data from stellar coronae, galaxies and clusters of galaxies, supernova, remnants and other astrophysical sources. They have been called into question in recent years as problems with understanding low resolution ASCA and moderate resolution Extreme Ultraviolet Explorer Satellite (EUVE) data have arisen. The Emission Line Project is a collaborative effort, to improve the models, with Phase I 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, negligible optical depth) apply. We will discuss recent, advances in our understanding of stellar coronae, in this context.

  7. 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.

  8. A Solar Type II Radio Burst from Coronal Mass Ejection-Coronal Ray Interaction: Simultaneous Radio and Extreme Ultraviolet Imaging

    NASA Astrophysics Data System (ADS)

    Chen, Yao; Du, Guohui; Feng, Li; Feng, Shiwei; Kong, Xiangliang; Guo, Fan; Wang, Bing; Li, Gang

    2014-05-01

    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.

  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. THERMAL SIGNATURES OF TETHER-CUTTING RECONNECTIONS IN PRE-ERUPTION CORONAL FLUX ROPES: HOT CENTRAL VOIDS IN CORONAL CAVITIES

    SciTech Connect

    Fan, Y.

    2012-10-10

    Using a three-dimensional MHD simulation, we model the quasi-static evolution and the onset of eruption of a coronal flux rope. The simulation begins with a twisted flux rope emerging at the lower boundary and pushing into a pre-existing coronal potential arcade field. At a chosen time the emergence is stopped with the lower boundary taken to be rigid. Then the coronal flux rope settles into a quasi-static rise phase during which an underlying, central sigmoid-shaped current layer forms along the so-called hyperbolic flux tube (HFT), a generalization of the X-line configuration. Reconnections in the dissipating current layer effectively add twisted flux to the flux rope and thus allow it to rise quasi-statically, even though the magnetic energy is decreasing as the system relaxes. We examine the thermal features produced by the current layer formation and the associated 'tether-cutting' reconnections as a result of heating and field aligned thermal conduction. It is found that a central hot, low-density channel containing reconnected, twisted flux threading under the flux rope axis forms on top of the central current layer. When viewed in the line of sight roughly aligned with the hot channel (which is roughly along the neutral line), the central current layer appears as a high-density vertical column with upward extensions as a {sup U-}shaped dense shell enclosing a central hot, low-density void. Such thermal features have been observed within coronal prominence cavities. Our MHD simulation suggests that they are the signatures of the development of the HFT topology and the associated tether-cutting reconnections, and that the central void grows and rises with the reconnections, until the flux rope reaches the critical height for the onset of the torus instability and dynamic eruption ensues.

  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. Diagnostics of Coronal Heating in Solar Active Regions

    NASA Astrophysics Data System (ADS)

    Fludra, Andrzej; Hornsey, Christopher; Nakariakov, Valery

    2015-04-01

    We aim to develop a diagnostic method for the coronal heating mechanism in active region loops. Observational constraints on coronal heating models have been sought using measurements in the X-ray and EUV wavelengths. Statistical analysis, using EUV emission from many active regions, was done by Fludra and Ireland (2008) who studied power-law relationships between active region integrated magnetic flux and emission line intensities. A subsequent study by Fludra and Warren (2010) for the first time compared fully resolved images in an EUV spectral line of OV 63.0 nm with the photospheric magnetic field, leading to the identification of a dominant, ubiquitous variable component of the transition region EUV emission and a discovery of a steady basal heating, and deriving the dependence of the basal heating rate on the photospheric magnetic flux density. In this study, we compare models of single coronal loops with EUV observations. We assess to what degree observations of individual coronal loops made in the EUV range are capable of providing constraints on the heating mechanism. We model the coronal magnetic field in an active region using an NLFF extrapolation code applied to a photospheric vector magnetogram from SDO/HMI and select several loops that match an SDO/AIA 171 image of the same active region. We then model the plasma in these loops using a 1D hydrostatic code capable of applying an arbitrary heating rate as a function of magnetic field strength along the loop. From the plasma parameters derived from this model, we calculate the EUV emission along the loop in AIA 171 and 335 bands, and in pure spectral lines of Fe IX 17.1 nm and Fe XVI 33.5 nm. We use different spatial distributions of the heating function: concentrated near the loop top, uniform and concentrated near the footpoints, and investigate their effect on the modelled EUV intensities. We find a diagnostics based on the dependence of the total loop intensity on the shape of the heating function

  13. Imaging solar coronal magnetic structures in 3D

    NASA Astrophysics Data System (ADS)

    Cartledge, N. P.

    The study of solar coronal structures and, in particular prominences, is a key part of understanding the highly complex physical mechanisms occurring in the Sun's atmosphere. Solar prominences are important in their own right and some of the most puzzling questions in solar theory have arisen through their study. For example, how do they form and how is their mass continuously replenished? How can the magnetic field provide their continuous support against gravity over time periods of several months? How can such cool, dense material exist in thermal equilibrium in the surrounding coronal environment? Why do they erupt? A study of their structure and that of the surrounding medium is important in determining the nature of the coronal plasma and magnetic field. Also, prominences are closely associated with other key phenomena such as coronal mass ejections and eruptive solar flares which occur as a prominence loses equilibrium and rises from the solar surface. Our current understanding of these fascinating structures is extremely limited and we know very little about their basic global structure. In fact, recent prominence observations have caused our basic paradigms to be challenged (Priest, 1996) and so we must set up new models in order to gain even a fundamental understanding. Prominences are highly nonlinear, three-dimensional structures. Large feet (or barbs) reach out from the main body of a prominence and reach down to the photosphere where the dense material continuously drains away. These provide a real clue to the three-dimensional nature of the coronal field and its relation to the photospheric field. It is important, therefore, to make stereographic observations of prominences in order to gain a basic understanding of their essentially three-dimensional nature and attempt to formulate new paradigms for their structure and evolution. There is no doubt that the study of prominences in three dimensions is a crucial exercise if we are to develop a better

  14. 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.

  15. Coronal Magnetic Structures Observing Campaign. 3: Coronal plasma and magnetic field diagnostics derived from multiwaveband active region observations

    NASA Technical Reports Server (NTRS)

    Schmelz, J. T.; Holman, G. D.; Brosius, J. W.; Willson, R. F.

    1994-01-01

    Simultaneous soft X-ray, microwave, and photospheric magnetic field observations were taken during the Coronal Magnetic Structures Observing Campaign (CoMStOC '87). The plasma electron temperature and emission measures determined from the X-ray data are used to predict the free-free emission expected at 20 and 6 cm. Comparing these predictions with the microwave observations, it is found that the predicted 20 cm brightness temperatures are higher than the observed, requiring cool absorbing material between the hot X-ray plasma and the observer. The model that is most consistent with all the observations and minimizes the required coronal fields indicates that this 20 cm emission is either free-free or a combination of free-free and fourth harmonic cyclotron emanating from the X-ray plasma with an electron temperature of approximately 3.1 x 10(exp 6) K and an emission measure of approximately 1.3 x 10(exp 29)/cm(exp 5). The observed 20 cm polarization requires a field strength of greater than or equal to 150 G. In addition, the 6 cm emission is free-free, emanating from cooler plasma with an electron temperature of approximately 1.5 x 10(exp 6) K and an emission measure of approximately 3-6 x 10(exp 29)/cm(exp 5). This model is consistent with the rather unusual combination of high 20 cm and low 6 cm polarization as well as the low extrapolated coronal fields.

  16. 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).

  17. 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.

  18. 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.

  19. 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

  20. A TYPE II RADIO BURST WITHOUT A CORONAL MASS EJECTION

    SciTech Connect

    Su, W.; Cheng, X.; Ding, M. D.; Chen, P. F.; Sun, J. Q. E-mail: dmd@nju.edu.cn

    2015-05-10

    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{sup −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.

  1. 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.

  2. 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.

  3. THE TEMPERATURE-DEPENDENT NATURE OF CORONAL DIMMINGS

    SciTech Connect

    Robbrecht, Eva; Wang Yiming E-mail: Yi.Wang@nrl.navy.mi

    2010-09-01

    The opening-up of the magnetic field during solar eruptive events is often accompanied by a dimming of the local coronal emission. From observations of filament eruptions recorded with the Extreme-Ultraviolet Imager on STEREO during 2008-2009, it is evident that these dimmings are much more pronounced in 19.5 nm than in the lower-temperature line 17.1 nm, as viewed either on the disk or above the limb. We conclude that most of the cooler coronal plasma is not ejected but remains gravitationally bound when the loops open up. This result is consistent with Doppler measurements by Imada and coworkers, who found that the upflow speeds in a transient coronal hole increased dramatically above a temperature of 1 MK; it is also consistent with the quasistatic behavior of polar plumes, as compared with the hotter interplume regions that are the main source of the fast solar wind. When the open flux reconnects and closes down again, the trapped plasma is initially heated to such high temperatures that it is no longer visible at Fe IX 17.1 nm. Correspondingly, 17.1 nm images show a dark ribbon or 'heat wave' propagating away from the polarity inversion line and coinciding with the brightened Fe XV 28.4 nm and Fe XII 19.5 nm post-eruptive loops and their footpoint areas. Such dark ribbons provide a clear example of dimmings that are not caused by a density depletion. The propagation of the 'heat wave' is driven by the closing-down, not the opening-up, of the flux and can be observed both off-limb and on-disk.

  4. SYMPATHETIC MAGNETIC BREAKOUT CORONAL MASS EJECTIONS FROM PSEUDOSTREAMERS

    SciTech Connect

    Lynch, B. J.; Edmondson, J. K. E-mail: jkedmond@umich.edu

    2013-02-10

    We present high-resolution 2.5D MHD simulation results of magnetic breakout-initiated coronal mass ejections (CMEs) originating from a coronal pseudostreamer configuration. The coronal null point in the magnetic topology of pseudostreamers means that the initiation of consecutive sympathetic eruptions is a natural consequence of the system's evolution. A generic source region energization process-ideal footpoint shearing parallel to the pseudostreamer arcade polarity inversion lines-is all that is necessary to store sufficient magnetic energy to power consecutive CME eruptions given that the pseudostreamer topology enables the breakout initiation mechanism. The second CME occurs because the eruptive flare reconnection of the first CME simultaneously acts as the overlying pre-eruption breakout reconnection for the sympathetic eruption. We examine the details of the magnetic and kinetic energy evolution and the signatures of the overlying null point distortion, current sheet formation, and magnetic breakout reconnection giving rise to the runaway expansion that drives the flare reconnection below the erupting sheared field core. The numerical simulation's spatial resolution and output cadence are sufficient to resolve the formation of magnetic islands during the reconnection process in both the breakout and eruptive flare current sheets. We quantify the flux transfer between the pseudostreamer arcades and show that the eruptive flare reconnection processes flux {approx}10 times faster than the pre-eruption breakout reconnection. We show that the breakout reconnection jets cause bursty, intermittent upflows along the pseudostreamer stalk, as well as downflows in the adjacent pseudostreamer arcade, both of which may be observable as pre-eruption signatures. Finally, we examine the flux rope CME trajectories and show that the breakout current sheet provides a path of least resistance as an imbalance in the surrounding magnetic energy density and results in a non

  5. 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.

  6. Acceleration of Ions and Electrons by Coronal Shocks

    NASA Astrophysics Data System (ADS)

    Sandroos, A.

    2013-12-01

    Diffusive shock acceleration (DSA) of particles at collisionless shock waves driven by coronal mass ejections (CMEs) is the best developed theory for the genesis of gradual solar energetic particle (SEP) events. According to DSA, particles scatter from fluctuations present in the ambient magnetic field, which causes some particles to encounter the shock front repeatedly and to gain energy during each crossing. DSA operating in solar corona is a complex process whose outcome depends on multiple parameters such as shock speed and strength, magnetic geometry, and composition of seed particles. Currently, STEREO and other near-Earth spacecraft are providing valuable multi-point information on how SEP properties, such as composition and energy spectra, vary in longitude. Initial results have shown that longitude distributions of large CME-associated SEP events are much wider than previously thought. These findings have many important consequences on SEP modeling. For example, it is important to extend the present models into two or three spatial coordinates to properly account for the effects of coronal and interplanetary magnetic geometry and the evolution of the CME-driven shock wave on the acceleration and transport of SEPs. We present a new model for the shock acceleration of ions and electrons in the solar corona and discuss implications for particle properties (energy spectra, longitudinal distribution, composition) in the resulting gradual SEP events. We also discuss the possible emission of type II radio waves by the accelerated coronal electrons. In the new model, the ion pitch angle scattering rate is calculated from modeled Alfvén wave power spectra using quasilinear theory. The energy gained by ions in scatterings are self-consistently removed from waves so that total energy (ions+waves) is conserved. New model has been implemented on massively parallel simulation platform Corsair.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. Driving Coronal MHD Simulations with Flux Evolution Models

    NASA Astrophysics Data System (ADS)

    Linker, J.; Lionello, R.; Mikic, Z.; Riley, P.; Downs, C.; Arge, C. N.; Henney, C. J.

    2013-12-01

    The solar corona and solar wind strongly influences space weather at Earth. While coronal mass ejections (CMEs) are the most obvious source of this influence, the structure and dynamics of the ambient solar corona and solar wind also play an important role. Coronal structure leads to the partitioning of the solar wind into fast and slow streams, which are the source of recurrent geomagnetic activity. The geo-effectiveness of CMEs is in part determined by their interaction with the ambient wind, and the connection of the ambient interplanetary magnetic field to CME-related shocks and impulsive solar flares determines where solar energetic particles propagate. MHD simulations of the solar corona based on maps of the solar magnetic field have been demonstrated to describe many aspects of coronal structure. However, these models are typically integrated to steady state, using synoptic or daily-updated magnetic maps to derive the boundary conditions. The Sun's magnetic flux is always evolving, and these changes in the flux affect the structure and dynamics of the corona and heliosphere. In this presentation, we describe an approach to evolutionary models of the corona and so wind, using time-dependent boundary conditions. A key aspect of our approach is the use of the Air Force Data Assimilative Photospheric flux Transport (ADAPT) model to develop time-evolving boundary conditions for the magnetic field. ADAPT incorporates data assimilation techniques into the Worden and Harvey (2000) flux evolution model, making it an especially suitable candidate for providing boundary conditions to MHD models. We describe initial results and compare them with more traditional approaches. Research supported by AFOSR, NASA, and NSF.

  13. 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.

  14. The stellar coronal X-ray Explorer: STCOEX

    NASA Technical Reports Server (NTRS)

    Vaiana, G. S.

    1981-01-01

    The status of the newly born field of stellar X-ray astronomy is considered. The need for further observational capability, the study of stellar surface activity and the development of design criteria for a follow-up mission, with primary emphasis on stellar observations and with general capabilities within the scope of the Explorer program are examined. The criteria which lead to the desired instrumental capabilities are reviewed; and an overview of the proposed instrument and some of its capabilities, as indicated by simulations is presented. Two versions of a trial payload the stellar coronal. Explorer (STCOEX) which meet the observational desirable are developed.

  15. The stellar coronal X-ray Explorer: STCOEX

    NASA Astrophysics Data System (ADS)

    Vaiana, G. S.

    1981-11-01

    The status of the newly born field of stellar X-ray astronomy is considered. The need for further observational capability, the study of stellar surface activity and the development of design criteria for a follow-up mission, with primary emphasis on stellar observations and with general capabilities within the scope of the Explorer program are examined. The criteria which lead to the desired instrumental capabilities are reviewed; and an overview of the proposed instrument and some of its capabilities, as indicated by simulations is presented. Two versions of a trial payload the stellar coronal. Explorer (STCOEX) which meet the observational desirable are developed.

  16. 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.

  17. 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.

  18. 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.

  19. Coronal X-Ray Flares on Active Stars

    NASA Astrophysics Data System (ADS)

    Nordon, Raanan

    2008-09-01

    Stellar coronae are the hot (kT>0.1 keV) tenuous regions in the outer atmospheres of cool-stars. Stellar coronae have been researched for many years, and yet they are poorly understood. In particular, the deviation of coronal chemical composition from photospheric elemental abundances is a long standing mystery. In the solar case, this was labeled the first ionization potential (FIP) effect. While some stellar coronae show a solar-like FIP effect, others show no FIP effect, or an inverse effect, although difficulties in measuring stellar photospheric abundances cast some doubt on these results. A correlation between coronal activity and abundance patterns led to a suggestion that flares affect coronal abundances. However, different variations were observed during flares, with no clear pattern emerging. We investigate a full sample of X-ray flares on stellar coronae from the archives of XMM-Newton and Chandra space observatories. We develop a method for reconstructing emission measure distribution, EMD(T), and abundances that is optimized to reduce systematic uncertainties. We measure variations of coronal abundances during flares, relative to quiescence abundances. This measurement is independent of the photospheric abundances and their related uncertainties. A theoretical analysis of the EMD(T) degeneracy problem is also presented. We find excess emission during flares originates predominantly from temperatures of kT>2 keV, while the low-T emission is very close to quiescence. This result cannot be reconciled with pure radiative-cooling or simple conductive-cooling. Evaporation from low dense regions into higher, thinner corona may aid in explaining this observed behavior. We define a relative measure for the FIP bias and compare the FIP bias of flare vs. quiescence with that of quiescence vs. photospheric (solar). We discovered a general trend where the relative FIP bias during flares is opposite to the quiescence FIP bias, meaning that the flares tend to

  20. The heating of coronal loops by MHD waves

    NASA Technical Reports Server (NTRS)

    Davila, Joseph M.

    1988-01-01

    A detailed derivation of the MHD wave equation appropriate for solar coronal conditions is presented. Some general concepts are discussed regarding the propagation of MHD waves in regions where gradients in the Alfven speed exist. A solution of the ideal equation is discussed, and the ideal solution near the surface of the resonance layer is obtained. The dissipative solution is found and the matching between the ideal and dissipative solutions is demonstrated. The heating rate is calculated and the expression for the heating rate is used to estimate the wave amplitude which is necessary in the corona to explain the observed active region heating rate on the sun.

  1. 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

  2. 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.

  3. 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).

  4. LOOPREF: A Fluid Code for the Simulation of Coronal Loops

    NASA Technical Reports Server (NTRS)

    deFainchtein, Rosalinda; Antiochos, Spiro; Spicer, Daniel

    1998-01-01

    This report documents the code LOOPREF. LOOPREF is a semi-one dimensional finite element code that is especially well suited to simulate coronal-loop phenomena. It has a full implementation of adaptive mesh refinement (AMR), which is crucial for this type of simulation. The AMR routines are an improved version of AMR1D. LOOPREF's versatility makes is suitable to simulate a wide variety of problems. In addition to efficiently providing very high resolution in rapidly changing regions of the domain, it is equipped to treat loops of variable cross section, any non-linear form of heat conduction, shocks, gravitational effects, and radiative loss.

  5. Faraday rotation as a probe of coronal and astrophysical plasmas

    NASA Astrophysics Data System (ADS)

    Mancuso, Salvatore

    Faraday rotation observations of polarized radiation from natural radio sources yield a unique diagnostic of coronal and astrophysical plasmas. We made observations of the radiogalaxy 4C+03.01 seen through the solar corona when the source was at a distance of 8.6 solar radii from the Sun. Nearly continuous polarimetric observations were made on March 28, 1997 with the Very Large Array (VLA) at frequencies of 1465 and 1635 MHz. Dual frequency polarization measurements yield the rotation measure, a quantity that is proportional to the product along the line of sight of the electron density and the line-of-sight component of the magnetic field. We measure a rotation measure of +6.2 +/- 1.0 rad m-2 attributable to the corona. We obtain a weak detection of rotation measure fluctuations which may be due to coronal Alfvén waves and derive model-dependent upper limits to the Alfvén wave flux at the coronal base. We also report dual frequency linear polarization observations of thirteen polarized radio sources made on four days in May 1997 at elongations ranging from 5 to 14 solar radii. A tridimensional model of the solar minimum corona was found to be in excellent agreement with the observed rotation measures and deviations from the values predicted by the model were suggestive of long wavelength coronal Alfvén waves. These observations were also used for detection of high frequency magnetohydrodynamic waves. These waves can be detected through a Faraday screen depolarization mechanism, that is a reduction of the observed degree of linear polarization of an extended polarized source when viewed through a medium in which the Faraday rotation varies randomly. The observations show no detectable depolarization, and rule out some turbulence models. Finally we derive expressions for auto- and cross- correlation functions of the Stokes parameters Q and U of the galactic synchrotron radiation. Fluctuations in the polarization characteristics of the galactic synchrotron

  6. 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

  7. 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.

  8. Coronal holes inferred from the Fleurs East-West solar scans

    NASA Technical Reports Server (NTRS)

    Ferguson, B. G.

    1979-01-01

    East-West solar scans produced daily on 692 and 1415 MHz are analyzed for the period 1968 to 1973. The analysis confirms that coronal holes are stable features displaying significantly reduced electromagnetic emission which can persist for many solar rotations. The coronal hole observations are summarized in a series of tables.

  9. Deprivation of liberty safeguard deaths to be reported to the coroner.

    PubMed

    Griffith, Richard

    2015-12-10

    The Chief Coroner has issued guidance that all deaths where a person is subject to a deprivation of liberty safeguard or Court of Protection welfare order allowing a deprivation of liberty must be reported to the coroner and an inquest held. In this article the author considers the impact of the guidance.

  10. 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.

  11. 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.

  12. Fast-mode magnetohydrodynamic waves in coronal holes and the solar wind

    NASA Technical Reports Server (NTRS)

    Fla, T.; Habbal, S. R.; Holzer, T. E.; Leer, E.

    1984-01-01

    Fast-mode MHD waves in the solar corona can propagate in any direction relative to the background magnetic field. In coronal holes, they refract into regions of low Alfven speed and are relatively difficult to damp. These characteristics lead to the possibility that fast-mode waves transport energy from magnetically closed coronal regions into coronal holes, that they are refracted into the central regions of coronal holes, and that they deposit most of their energy in the region of supersonic flow of high-speed solar wind streams emanating from coronal holes. To investigate whether this possibility might be realized and fast-mode waves might play a significant role in driving high-speed streams, a parameter study is carried out to examine the propagation and damping of fast-mode waves in various coronal hole models. This study indicates a broad range of coronal hole parameters for which fast-mode waves can play such a role and emphasizes the need for an improved knowledge of large-scale coronal magnetic structure, which is required before any firm conclusions can be drawn.

  13. 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…

  14. 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.

  15. Coronal electron temperature in the protracted solar minimum, the cycle 24 mini maximum, and over centuries

    NASA Astrophysics Data System (ADS)

    Schwadron, N. A.; Goelzer, M. L.; Smith, C. W.; Kasper, J. C.; Korreck, K.; Leamon, R. J.; Lepri, S. T.; Maruca, B. A.; McComas, D.; Steven, M. L.

    2014-03-01

    Recent in situ observations of the solar wind show that charge states (e.g., the O7+/O6+and C6+/C5+abundance ratios) evolved through the extended, deep solar minimum between solar cycles 23 and 24 (i.e., from 2006 to 2009) reflecting cooler electron temperatures in the corona. We extend previous analyses to study the evolution of the coronal electron temperature through the protracted solar minimum and observe not only the reduction in coronal temperature in the cycles 23-24 solar minimum but also a small increase in coronal temperature associated with increasing activity during the "mini maximum" in cycle 24. We use a new model of the interplanetary magnetic flux since 1749 to estimate coronal electron temperatures over more than two centuries. The reduction in coronal electron temperature in the cycles 23-24 protracted solar minimum is similar to reductions observed at the beginning of the Dalton Minimum (˜1805-1840). If these trends continue to reflect the evolution of the Dalton Minimum, we will observe further reductions in coronal temperature in the cycles 24-25 solar minimum. Preliminary indications in 2013 do suggest a further post cycle 23 decline in solar activity. Thus, we extend our understanding of coronal electron temperature using the solar wind scaling law and compare recent reductions in coronal electron temperature in the protracted solar minimum to conditions that prevailed in the Dalton Minimum.

  16. '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.

  17. Converging Supergranular Flows and the Formation of Coronal Plumes

    NASA Astrophysics Data System (ADS)

    Wang, Y.-M.; Warren, H. P.; Muglach, K.

    2016-02-01

    Earlier studies have suggested that coronal plumes are energized by magnetic reconnection between unipolar flux concentrations and nearby bipoles, even though magnetograms sometimes show very little minority-polarity flux near the footpoints of plumes. Here we use high-resolution extreme-ultraviolet (EUV) images and magnetograms from the Solar Dynamics Observatory (SDO) to clarify the relationship between plume emission and the underlying photospheric field. We find that plumes form where unipolar network elements inside coronal holes converge to form dense clumps, and fade as the clumps disperse again. The converging flows also carry internetwork fields of both polarities. Although the minority-polarity flux is sometimes barely visible in the magnetograms, the corresponding EUV images almost invariably show loop-like features in the core of the plumes, with the fine structure changing on timescales of minutes or less. We conclude that the SDO observations are consistent with a model in which plume emission originates from interchange reconnection in converging flows, with the plume lifetime being determined by the ∼1 day evolutionary timescale of the supergranular network. Furthermore, the presence of large EUV bright points and/or ephemeral regions is not a necessary precondition for the formation of plumes, which can be energized even by the weak, mixed-polarity internetwork fields swept up by converging flows.

  18. MHD Simulations of the Initiation of Coronal Mass Ejections

    NASA Astrophysics Data System (ADS)

    Fan, Yuhong; Chatterjee, Piyali

    Using three-dimensional MHD simulations, we model the quasi-static evolution and the onset of eruption of twisted magnetic flux ropes in the solar corona. We present simulations where the eruption is triggered by either the onset of the torus instability or the helical kink instability of the line-tied coronal flux rope. The simulations show that S (or inverse S) shaped current sheets develop along topological structures identified as Quasi Separatrix Layers (QSLs), during the quasi-static phase before the eruption. Reconnections in the current sheets effectively add twisted flux to the flux rope and thus allow it to rise quasi-statically to the critical height for the onset of the torus instability. We examine the thermal features produced by the current sheet formation and the associated reconnections and found that they can explain some of the observed features in coronal prominence cavities as well as in pre-eruption active regions. We also present simulations of the development of a homologous sequence of CMEs caused by the repeated formation and partial eruption of kink unstable flux ropes as a result of continued flux emergence. It is found that such homologous CMEs tend to be cannibalistic, leading to the formation of more energetic, highly twisted ejecta.

  19. Converging Supergranular Flows and the Formation of Coronal Plumes

    NASA Technical Reports Server (NTRS)

    Wang, Y.-M.; Warren, H. P.; Muglach, K.

    2016-01-01

    Earlier studies have suggested that coronal plumes are energized by magnetic reconnection between unipolar flux concentrations and nearby bipoles, even though magnetograms sometimes show very little minority-polarity flux near the footpoints of plumes. Here we use high-resolution extreme-ultraviolet (EUV) images and magnetograms from the Solar Dynamics Observatory (SDO) to clarify the relationship between plume emission and the underlying photospheric field. We find that plumes form where unipolar network elements inside coronal holes converge to form dense clumps, and fade as the clumps disperse again. The converging flows also carry internetwork fields of both polarities. Although the minority-polarity flux is sometimes barely visible in the magnetograms, the corresponding EUV images almost invariably show loop-like features in the core of the plumes, with the fine structure changing on timescales of minutes or less. We conclude that the SDO observations are consistent with a model in which plume emission originates from interchange reconnection in converging flows, with the plume lifetime being determined by the approximately 1-day evolutionary timescale of the supergranular network. Furthermore, the presence of large EUV bright points and/or ephemeral regions is not a necessary precondition for the formation of plumes, which can be energized even by the weak, mixed-polarity internetwork fields swept up by converging flows.

  20. Models of coronal heating, turbulence and fast reconnection.

    PubMed

    Velli, M; Pucci, F; Rappazzo, F; Tenerani, A

    2015-05-28

    Coronal heating is at the origin of the EUV and X-ray emission and mass loss from the sun and many other stars. While different scenarios have been proposed to explain the heating of magnetically confined and open regions of the corona, they must all rely on the transfer, storage and dissipation of the abundant energy present in photospheric motions, which, coupled to magnetic fields, give rise to the complex phenomenology seen at the chromosphere and transition region (i.e. spicules, jets, 'tornadoes'). Here we discuss models and numerical simulations which rely on magnetic fields and electric currents both for energy transfer and for storage in the corona. We will revisit the sources and frequency spectrum of kinetic and electromagnetic energies, the role of boundary conditions, and the routes to small scales required for effective dissipation. Because reconnection in current sheets has been, and still is, one of the most important processes for coronal heating, we will also discuss recent aspects concerning the triggering of reconnection instabilities and the transition to fast reconnection. PMID:25897086

  1. Scientific objectives and capabilities of the Coronal Solar Magnetism Observatory

    NASA Astrophysics Data System (ADS)

    Tomczyk, S.; Landi, E.; Burkepile, J. T.; Casini, R.; DeLuca, E. E.; Fan, Y.; Gibson, S. E.; Lin, H.; McIntosh, S. W.; Solomon, S. C.; Toma, G.; Wijn, A. G.; Zhang, J.

    2016-08-01

    Magnetic influences increase in importance in the solar atmosphere from the photosphere out into the corona, yet our ability to routinely measure magnetic fields in the outer solar atmosphere is lacking. We describe the scientific objectives and capabilities of the COronal Solar Magnetism Observatory (COSMO), a proposed synoptic facility designed to measure magnetic fields and plasma properties in the large-scale solar atmosphere. COSMO comprises a suite of three instruments chosen to enable the study of the solar atmosphere as a coupled system: (1) a coronagraph with a 1.5 m aperture to measure the magnetic field, temperature, density, and dynamics of the corona; (2) an instrument for diagnostics of chromospheric and prominence magnetic fields and plasma properties; and (3) a white light K-coronagraph to measure the density structure and dynamics of the corona and coronal mass ejections. COSMO will provide a unique combination of magnetic field, density, temperature, and velocity observations in the corona and chromosphere that have the potential to transform our understanding of fundamental physical processes in the solar atmosphere and their role in the origins of solar variability and space weather.

  2. QUASI-PERIODIC OSCILLATION OF A CORONAL BRIGHT POINT

    SciTech Connect

    Samanta, Tanmoy; Banerjee, Dipankar; Tian, Hui E-mail: hui.tian@cfa.harvard.edu

    2015-06-20

    Coronal bright points (BPs) are small-scale luminous features seen in the solar corona. Quasi-periodic brightenings are frequently observed in the BPs and are generally linked with underlying magnetic flux changes. We study the dynamics of a BP seen in the coronal hole using the Atmospheric Imaging Assembly images, the Helioseismic and Magnetic Imager magnetogram on board the Solar Dynamics Observatory, and spectroscopic data from the newly launched Interface Region Imaging Spectrograph (IRIS). The detailed analysis shows that the BP evolves throughout our observing period along with changes in underlying photospheric magnetic flux and shows periodic brightenings in different EUV and far-UV images. With the highest possible spectral and spatial resolution of IRIS, we attempted to identify the sources of these oscillations. IRIS sit-and-stare observation provided a unique opportunity to study the time evolution of one footpoint of the BP as the slit position crossed it. We noticed enhanced line profile asymmetry, enhanced line width, intensity enhancements, and large deviation from the average Doppler shift in the line profiles at specific instances, which indicate the presence of sudden flows along the line-of-sight direction. We propose that transition region explosive events originating from small-scale reconnections and the reconnection outflows are affecting the line profiles. The correlation between all these parameters is consistent with the repetitive reconnection scenario and could explain the quasi-periodic nature of the brightening.

  3. Dichotomy of X-Ray Jets in Solar Coronal Holes

    NASA Astrophysics Data System (ADS)

    Robe, D. M.; Moore, R. L.; Falconer, D. A.

    2012-12-01

    It has been found that there are two different types of X-ray jets observed in the Sun's polar coronal holes: standard jets and blowout jets. A proposed model of this dichotomy is that a standard jet is produced by a burst of reconnection of the ambient magnetic field with the opposite-polarity leg of the base arcade. In contrast, it appears that a blowout jet is produced when the interior of the arcade has so much pent-up free magnetic energy in the form of shear and twist in the interior field that the external reconnection unleashes the interior field to erupt open. In this project, X-ray movies of the polar coronal holes taken by Hinode were searched for X-ray jets. Co-temporal movies taken by the Solar Dynamics Observatory in 304 Å emission from He II, showing solar plasma at temperatures around 80,000 K, were examined for whether the identified blowout jets carry much more He II plasma than the identified standard jets. It was found that though some jets identified as standard from the X-ray movies could be seen in the He II 304 Å movies, the blowout jets carried much more 80,000 K plasma than did most standard jets. This finding supports the proposed model for the morphology and development of the two types of jets.

  4. SAUSAGE WAVES IN TRANSVERSELY NONUNIFORM MONOLITHIC CORONAL TUBES

    SciTech Connect

    Lopin, I.; Nagorny, I.

    2015-09-10

    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.

  5. In What Magnetic Environment Are Coronal Loop Plasmas Located?

    NASA Astrophysics Data System (ADS)

    Lim, Daye; Choe, Gwangson; Yi, Sibaek

    2016-04-01

    Coronal loop plasmas are often regarded to be confined within magnetic flux ropes as in the case of laboratory plasmas. However, a plasma pressure profile, which decreases from the center of a flux rope to its periphery, can be ideal MHD interchange unstable if individual flux tubes constituting the flux rope are freely movable. In the solar corona, the strong line-tying condition impedes the interchange of flux tube positions, but ubiquitous magnetic reconnection processes can change plasma distribution in such a way that the system moves to a possible lower energy state. In this paper, we present a 2.5D MHD simulation study of the plasma redistribution in the merging process of many small flux ropes possibly representing loop strands. We have found that the redistributed plasma is more concentrated between flux ropes rather than near the center of flux ropes. When flux ropes initially have different amounts of twists, the plasma tends to accumulate in less twisted regions. As larger and larger flux ropes are formed by successive merging processes, the toroidal field of the flux ropes become stronger and stronger, i.e., field lines are less and less twisted. Our study may explain why the observed coronal loops appear very little twisted and quite well ordered in spite of continuous entangling motions in the photosphere and below.

  6. Forbush decreases associated to Stealth Coronal Mass Ejections

    NASA Astrophysics Data System (ADS)

    Heber, B.; Wallmann, C.; Galsdorf, D.; Herbst K.; Kühl, P.; Dumbovic, M.; Vršnak, B.; Veronig, A.; Temmer, M.; Möstl, C.; Dalla, S.

    Interplanetary coronal mass ejections (ICMEs) are structures in the solar wind that are the counterparts of coronal mass ejections (CMEs) at the Sun. It is commonly believed that enhanced magnetic fields in interplanetary shocks and solar ejecta as well as the increased turbulence in the solar wind sheath region are the cause of Forbush decreases (FDs) representing decreases of galactic cosmic ray (GCR) intensities. Recently, stealth CMEs i.e.~CMEs with no apparent solar surface association have become a subject in recent studies of solar activity. Whether all of such stealth CMEs can drive a FD is difficult to investigate on the basis of neutron monitor NM measurements because these measurements not only reflect the GCR intensity variation in interplanetary space but also the variation of the geomagnetic field as well as the conditions in the Earth atmosphere. Single detector counter from spacecraft instrumentation, here SOHO and Chandra EPHIN, exceed counting statistic of NMs allowing to determine intensity variation of less than 1 permil in interplanetary space on the basis of 30 minute count rate averages. Here we present the ongoing analysis of eleven stealth CMEs.

  7. Magnetic Interaction: An Erupting Filament and a Remote Coronal Hole

    NASA Astrophysics Data System (ADS)

    Jiang, Yunchun; Yang, Liheng; Li, Kejun; Shen, Yuandeng

    2007-09-01

    For the first time, we present a rare observation of direct magnetic interaction between an erupting filament and a coronal hole (CH). The small active region filament obliquely erupted toward the CH getting in the way, met and interacted with it, and then was deflected back. The erupting filament thus underwent a distinct to-and-fro motion in the visible disk, while the CH was clearly disturbed by the interaction. Brightenings in Hα and EUV and darkenings in He I 10830 Å appeared at the boundaries and in the interior of the CH. This eruption was closely associated with the initiation of a halo-type coronal mass ejection (CME). The direction of the CME, despite being greatly different from that of the initial filament eruption, was consistent with that of the reflected filament. Moreover, when the CME was seen in the limb, the filament was still in the process of the return journey in the visible disk. Therefore, it appears that the large-scale structure of the CME was bounced against and then reflected away from the CH along with the filament, and the eruptive filament represented only a very small part in the CME.

  8. The Radiation, Interplanetary Shocks, and Coronal Sources (RISCS) Toolset

    NASA Technical Reports Server (NTRS)

    Zank, G. P.; Spann, J.

    2014-01-01

    We outline a plan to develop a physics based predictive toolset RISCS to describe the interplanetary energetic particle and radiation environment throughout the inner heliosphere, including at the Earth. To forecast and "nowcast" the radiation environment requires the fusing of three components: 1) the ability to provide probabilities for incipient solar activity; 2) the use of these probabilities and daily coronal and solar wind observations to model the 3D spatial and temporal heliosphere, including magnetic field structure and transients, within 10 AU; and 3) the ability to model the acceleration and transport of energetic particles based on current and anticipated coronal and heliospheric conditions. We describe how to address 1) - 3) based on our existing, well developed, and validated codes and models. The goal of RISCS toolset is to provide an operational forecast and "nowcast" capability that will a) predict solar energetic particle (SEP) intensities; b) spectra for protons and heavy ions; c) predict maximum energies and their duration; d) SEP composition; e) cosmic ray intensities, and f) plasma parameters, including shock arrival times, strength and obliquity at any given heliospheric location and time. The toolset would have a 72 hour predicative capability, with associated probabilistic bounds, that would be updated hourly thereafter to improve the predicted event(s) and reduce the associated probability bounds. The RISCS toolset would be highly adaptable and portable, capable of running on a variety of platforms to accommodate various operational needs and requirements.

  9. Sunquakes and their relationship with coronal magnetic topology

    NASA Astrophysics Data System (ADS)

    Green, Lucie; Zharkov, Sergei; Matthews, Sarah; Zharkova, Valentina

    2015-08-01

    Sunquakes were first predicted in 1972 by Wolff and are seen in the Sun’s photosphere as a burst of outwardly emanating ripples, caused by sudden a release of energy below the surface that produces sound waves. Typically the formation of a sunquake is discussed in the context of a solar flare in which a propagation of energy and momentum downward from the corona occurs via accelerated particles, Lorentz force transients, MHD wave conversion or so-called back-warming from coronal and chromospheric radiation at the footpoints of the flare loops. But many sunquakes also occur in concert with a coronal mass ejection and therefore within a magnetic field that is evolving on an active region-wide scale. More specifically, the locations of some of these sunquakes have a magnetic connection to the erupting magnetic field rather than the flare loops themselves.So, how can the sunquake generation scenarios be informed/constrained by considering the overall magnetic field configuration in which they are formed? This talk will use data spanning the photosphere to corona to reveal the magnetic field configuration and its evolution, so that sunquake generation scenarios can be placed in the context of an erupting magnetic configuration with associated energy and momentum transport.

  10. COUPLED ALFVEN AND KINK OSCILLATIONS IN CORONAL LOOPS

    SciTech Connect

    Pascoe, D. J.; Wright, A. N.; De Moortel, I.

    2010-03-10

    Observations have revealed ubiquitous transverse velocity perturbation waves propagating in the solar corona. However, there is ongoing discussion regarding their interpretation as kink or Alfven waves. To investigate the nature of transverse waves propagating in the solar corona and their potential for use as a coronal diagnostic in MHD seismology, we perform three-dimensional numerical simulations of footpoint-driven transverse waves propagating in a low beta plasma. We consider the cases of both a uniform medium and one with loop-like density structure and perform a parametric study for our structuring parameters. When density structuring is present, resonant absorption in inhomogeneous layers leads to the coupling of the kink mode to the Alfven mode. The decay of the propagating kink wave as energy is transferred to the local Alfven mode is in good agreement with a modified interpretation of the analysis of Ruderman and Roberts for standing kink modes. Numerical simulations support the most general interpretation of the observed loop oscillations as a coupling of the kink and Alfven modes. This coupling may account for the observed predominance of outward wave power in longer coronal loops since the observed damping length is comparable to our estimate based on an assumption of resonant absorption as the damping mechanism.

  11. Development of a tunable filter for coronal polarimetry

    NASA Astrophysics Data System (ADS)

    Tomczyk, S.; Mathew, S. K.; Gallagher, D.

    2016-07-01

    Measuring magnetic fields in the solar corona is crucial to understanding and predicting the Sun's generation of space weather that affects communications, GPS systems, space flight, and power transmission. The Coronal Solar Magnetism Observatory Large Coronagraph (COSMO LC) is a proposed 1.5 m aperture coronagraph designed to synoptically observe magnetic fields and plasma properties in the large-scale corona to improve our understanding of solar processes that cause space weather. The LC will observe coronal emission lines over the wavelength range from 500 to 1100 nm with a field of view of 1° and a spatial resolution of 2 arcsec. A spectral resolution greater than 8000 over the wavelength range is needed to resolve the polarization signatures of magnetic fields in the emission line profiles. The aperture and field of view of the LC set an étendue requirement of 1.39 m2 deg2 for the postfocus instrumentation. We find that a tunable wide-field birefringent filter using Lithium Niobate crystals can meet the étendue and spectral resolution requirements for the LC spectrometer. We have tested a number of commercially available crystals and verify that crystals of the required size and birefringence uniformity are available. We also evaluate electro-optical tuning of a Lithium Niobate birefringent filter by the application of high voltage. This tunable filter represents a key enabling technology for the COSMO LC.

  12. Straight line access and coronal flaring: effect on canal length.

    PubMed

    Schroeder, Kyle P; Walton, Richard E; Rivera, Eric M

    2002-06-01

    The object of this study was to determine if canal length is altered as a result of straight-line access (SLA) and coronal flaring (CF). Selected were 86 canals of extracted molars and premolars from two groups: straight or severely curved (Schneider curvature <5 degrees and >20 degrees). The reference cusp tip and root-end were flattened to produce reproducible measurements. A #10 file was placed such that the tip extended slightly beyond the apex, with the handle on the referenced cusp. The amount of file protrusion was measured with a stereomicroscope. Then, SLA and CF were performed and the corresponding file replaced to the same coronal reference position. Apical file protrusion was measured again. The change in canal length was determined by the difference in the pre- and post-SLA/CF measurements. A Wilcoxon signed rank test statistically verified that there was a measurable, significant (p < 0.001) change in canal length after SLA and CF. The mean change overall was slight, with a decrease of 0.17 mm. Severe curvature had a slightly greater, significant effect on the amount of change. Tooth type had no significant effect. Changes in working length from SLA and CF, although statistically significant, were very small and clinically unimportant.

  13. WARM CORONAL RAIN ON YOUNG SOLAR ANALOG EK DRACONIS?

    SciTech Connect

    Ayres, Thomas; France, Kevin E-mail: Kevin.France@Colorado.ed

    2010-11-01

    We report a moderate-resolution, 1290-1430 A spectrum of young solar analog EK Draconis (HD 129333: G1.5 V), obtained by Cosmic Origins Spectrograph on Hubble Space Telescope. The 20 minute observation, remarkably, captured two distinct 'flares' in the Si IV 1400 A doublet (T {approx} 6 x 10{sup 4} K); very broad profiles of Si IV and the C II 1335 A multiplet (T {approx} 3 x 10{sup 4} K); and prominent Fe XXI {lambda}1354 coronal forbidden line emission (T {approx} 10 MK). The bright Si IV features are significantly redshifted compared to the milder, although still redshifted, equivalent components of solar-twin {alpha}{sup 1} Cen (HD 128620: G2 V). The broad, shifted, flaring hot-line profiles of EK Dra indicate not only that the subcoronal plasma of the young sun is highly dynamic, but also that the Si IV-bearing gas must be continually accreting onto the lower atmosphere, perhaps the stellar equivalent of warm 'coronal rain'.

  14. Automated Coronal Loop Identification Using Digital Image Processing Techniques

    NASA Technical Reports Server (NTRS)

    Lee, Jong K.; Gary, G. Allen; Newman, Timothy S.

    2003-01-01

    The results of a master thesis project on a study of computer algorithms for automatic identification of optical-thin, 3-dimensional solar coronal loop centers from extreme ultraviolet and X-ray 2-dimensional images will be presented. These center splines are proxies of associated magnetic field lines. The project is pattern recognition problems in which there are no unique shapes or edges and in which photon and detector noise heavily influence the images. The study explores extraction techniques using: (1) linear feature recognition of local patterns (related to the inertia-tensor concept), (2) parametric space via the Hough transform, and (3) topological adaptive contours (snakes) that constrains curvature and continuity as possible candidates for digital loop detection schemes. We have developed synthesized images for the coronal loops to test the various loop identification algorithms. Since the topology of these solar features is dominated by the magnetic field structure, a first-order magnetic field approximation using multiple dipoles provides a priori information in the identification process. Results from both synthesized and solar images will be presented.

  15. 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.

  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. On the observability of optically thin coronal hyperfine structure lines

    SciTech Connect

    Chatzikos, M.; Ferland, G. J.; Williams, R. J. R.; Fabian, A. C.

    2014-06-01

    We present CLOUDY calculations for the intensity of coronal hyperfine lines in various environments. We model indirect collisional and radiative transitions, and quantify the collisionally excited line emissivity in the density-temperature phase space. As an observational aid, we also express the emissivity in units of that in the 0.4-0.7 keV band. For most hyperfine lines, knowledge of the X-ray surface brightness and the plasma temperature is sufficient for rough estimates. We find that the radiation fields of both Perseus A and Virgo A can enhance the populations of highly ionized species within 1 kpc. They can also enhance line emissivity within the cluster core. This could have implications for the interpretation of spectra around bright active galactic nuclei. We find the intensity of the {sup 57}Fe XXIV λ3.068 mm line to be about two orders of magnitude fainter than previously thought, at ∼20 μK. Comparably bright lines may be found in the infrared. Finally, we find the intensity of hyperfine lines in the Extended Orion Nebula to be low, due to the shallow sightline. Observations of coronal hyperfine lines will likely be feasible with the next generation of radio and submillimeter telescopes.

  18. Coronal Modeling with Flux-Evolved Maps: Comparison with Observations

    NASA Astrophysics Data System (ADS)

    Linker, J.; Downs, C.; Lionello, R.; Caplan, R. M.; Mikic, Z.; Riley, P.; Henney, C. J.; Arge, C. N.

    2014-12-01

    MHD simulations of the solar corona rely on maps of the solar magnetic field for input as boundary conditions. These "synoptic" maps (available from a number of ground-based and space-based solar observatories) are built up over a solar rotation. A well-known problem with this approach is that the maps contain data that is as much as 27 days old. The Sun's magnetic flux is always evolving, and these changes in the flux affect coronal and heliospheric structure. Flux evolution models can in principle provide a more accurate specification, by estimating the likely state of the photospheric magnetic field on unobserved portions of the Sun. The Air Force Data Assimilative Photospheric flux Transport (ADAPT) model (Arge et al. 2010) is especially well suited for this purpose. ADAPT can also incorporate information from helioseismic acoustic images to estimate the emergence of new active regions on the Sun's far side. In this presentation we describe MHD models with boundary conditions derived from ADAPT maps. We investigate the June-August 2010 time period, when there was significant coronal hole evolution observed by the STEREO and SDO spacecraft. We compare model results using ADAPT maps, including those with far side data, as well as models using traditional synoptic maps, to STEREO EUVI and SDO AIA data. Research supported by AFOSR & NASA.

  19. On the Fourier and Wavelet Analysis of Coronal Time Series

    NASA Astrophysics Data System (ADS)

    Auchère, F.; Froment, C.; Bocchialini, K.; Buchlin, E.; Solomon, J.

    2016-07-01

    Using Fourier and wavelet analysis, we critically re-assess the significance of our detection of periodic pulsations in coronal loops. We show that the proper identification of the frequency dependence and statistical properties of the different components of the power spectra provides a strong argument against the common practice of data detrending, which tends to produce spurious detections around the cut-off frequency of the filter. In addition, the white and red noise models built into the widely used wavelet code of Torrence & Compo cannot, in most cases, adequately represent the power spectra of coronal time series, thus also possibly causing false positives. Both effects suggest that several reports of periodic phenomena should be re-examined. The Torrence & Compo code nonetheless effectively computes rigorous confidence levels if provided with pertinent models of mean power spectra, and we describe the appropriate manner in which to call its core routines. We recall the meaning of the default confidence levels output from the code, and we propose new Monte-Carlo-derived levels that take into account the total number of degrees of freedom in the wavelet spectra. These improvements allow us to confirm that the power peaks that we detected have a very low probability of being caused by noise.

  20. 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.

  1. Imprints of coronal temperature disturbances on type III bursts

    NASA Astrophysics Data System (ADS)

    Li, B.; Cairns, I. H.; Robinson, P. A.

    2010-02-01

    The electron temperature T_e and ion temperature T_i in the corona vary with time and location, due to transient and persistent activity on the Sun. The effects of spatially localized disturbances in T_e and T_i on coronal type III radio bursts are simulated. The disturbances are superimposed on monotonically varying temperature backgrounds and arise from spatially confined solar activity, Qualitatively and quantitatively different imprints are found on the curve of the maximum flux versus frequency of type III bursts, because of the disturbances in T_e and T_i. The results indicate that nonthermal coronal type III bursts offer a new tool to probe and distinguish between spatially localized structures of T_e and T_i along the paths of type III beams. Furthermore, localized temperature disturbances may be responsible for some fine structures in type III bursts, e.g., striae in type IIIb bursts in the presence of multiple, localized temperature disturbances.

  2. 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.

  3. 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.

  4. 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.

  5. Solar coronal loop heating by cross-field wave transport

    NASA Technical Reports Server (NTRS)

    Amendt, Peter; Benford, Gregory

    1989-01-01

    Solar coronal arches heated by turbulent ion-cyclotron waves may suffer significant cross-field transport by these waves. Nonlinear processes fix the wave-propagation speed at about a tenth of the ion thermal velocity, which seems sufficient to spread heat from a central core into a large cool surrounding cocoon. Waves heat cocoon ions both through classical ion-electron collisions and by turbulent stochastic ion motions. Plausible cocoon sizes set by wave damping are in roughly kilometers, although the wave-emitting core may be only 100 m wide. Detailed study of nonlinear stabilization and energy-deposition rates predicts that nearby regions can heat to values intermediate between the roughly electron volt foot-point temperatures and the about 100 eV core, which is heated by anomalous Ohmic losses. A volume of 100 times the core volume may be affected. This qualitative result may solve a persistent problem with current-driven coronal heating; that it affects only small volumes and provides no way to produce the extended warm structures perceptible to existing instruments.

  6. 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.

  7. What is the Most Important Origin of the Coronal Helicity?

    NASA Astrophysics Data System (ADS)

    Tian, L.

    23 active regions (ARs) with well-defined SXR sigmoids are selected to study which is the more important origin of the coronal helicity -- the emergence of magnetic fields or photospheric horizontal motions. The radial magnetic flux of each polarity, the helicity injection rate, and total helicity flux (Δ Hlct) are calculated using local correlation tracking technique and {MDI 96m} line-of-sight magnetograms, and the helicity budget of the differential rotation (Δ Hrot) is also estimated. It is found that six ARs inject helicity flux greater than 1.0× 1043 {Mx}^2 (Δ H=Δ Hlct-Δ Hrot), in a sample of seven ARs with emerging magnetic flux greater than 1.0× 1022 Mx. On the other hand, in sixteen ARs with emerging magnetic flux less than 1.0× 1022 Mx, only four ARs inject helicity flux greater than 1.0× 1043 Mx^2, which denotes the main contribution of the horizontal motions. The statistical results suggest that the horizontal motions are not important to the coronal helicity injection when there is little magnetic field emergence.

  8. 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.

  9. The 3D structure of Coronal Mass Ejections

    NASA Astrophysics Data System (ADS)

    Patsourakos, Spiros

    2016-07-01

    Coronal Mass Ejections (CMEs) represent one of the most powerful energy release phenomena in the entire solar system and are a major driver of space weather. Prior to 2006, our observational access to CMEs was limited to single viewpoint remote sensing observations in the inner/outer corona, and in-situ observations further away, e.g. at 1 AU. Taking all these factors together, turned out to be a major obstacle in our understanding and characterizing of the 3D structure and evolution of CMEs. The situation improved dramatically with the availability of multi-viewpoint imaging observations of CMEs, all way through from the Sun to 1 AU, from the STEREO mission since 2006, combined with observations from other missions (SOHO, Hinode, SDO, IRIS). With this talk we will discuss several key recent results in CME science resulting from the analysis of multi-viewpoint observations. This includes: (1) shape and structure; (2) kinematics and energetics; (3) trajectories, deflections and rotations; (4) arrival times and velocities at 1 AU; (5) magnetic field structure; (6) relationships with coronal and interplanetary shocks and solar energetic particles. The implications of these results in terms of CME theories and models will be also addressed. We will conclude with a discussion of important open issues in our understanding of CMEs and how these could be addressed with upcoming (Solar Orbiter, Solar Probe Plus) and under-study missions (e.g., L5).

  10. ISOTHERMAL AND MULTITHERMAL ANALYSIS OF CORONAL LOOPS OBSERVED WITH AIA

    SciTech Connect

    Schmelz, J. T.; Jenkins, B. S.; Worley, B. T.; Anderson, D. J.; Pathak, S.; Kimble, J. A.

    2011-04-10

    The coronal filters in the Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Observatory peak at different temperatures; the series covers the entire active region temperature range, making AIA ideal for multithermal analysis. Here, we analyze coronal loops from several active regions that have been observed by AIA. We have specifically targeted cool loops (or at least loops with a cool component) that were chosen in the 171 A channel of AIA, which has a peak response temperature of log T = 5.8. We wanted to determine if the loops could be described as isothermal or multithermal. We find that several of our 12 loops have narrow temperature distributions, which may be consistent with isothermal plasma; these can be modeled with a single flux tube. Other loops have intermediate-width temperature distributions, appear well-constrained, and should be multi-stranded. The remaining loops, however, have unrealistically broad differential emission measures. We find that this problem is the result of missing low-temperature lines in the AIA 131 A channel. If we repeat the analysis without the 131 A data, these loops also appear to be well-constrained and multi-stranded.

  11. Charge state composition in coronal hole and CME related solar wind: Latitudinal variations observed by Ulysses and WIND

    NASA Technical Reports Server (NTRS)

    Galvin, A. B.; Gloeckler, G.

    1997-01-01

    Iron charge states in recurrent coronal hole-associated solar wind flows are obtained in the ecliptic by WIND/SMS, while measurements of iron and silicon from the polar coronal holes are available from Ulysses/SWICS. Ulysses/SWICS also provides ion composition of coronal mass ejection (CME)-related solar wind. Both coronal hole-associated and CME-related solar wind charge charges show heliographic latitudinal variations.

  12. The solar origins of solar wind interstream flows - Near-equatorial coronal streamers

    NASA Technical Reports Server (NTRS)

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

    1981-01-01

    A class of low-speed solar wind flows with velocities of 450 km/s and less, ion temperatures of 40,000 K and less, and heavy ion distributions indicating moderate coronal freezing in temperatures in the range from 1 million to 2.5 millions K is considered. For brevity this class is termed interstream. Interstream flows have as yet, not firm identification with a coronal origin. The considered investigation is concerned with the identification of the coronal origins of interstream flows. It is found that major sources of low speed solar wind are the quiescent, near-equatorial coronal streamers. Such an identification provides a natural explanation for the long term variations of solar wind electron temperature and density observed at 1 AU by Feldman et al. (1979) in terms of the concurrent long term morphological variation in the coronal equatorial streamer belt observed using the Mauna Loa K-coronameters.

  13. High-spatial-resolution microwave and related observations as diagnostics of coronal loops

    NASA Technical Reports Server (NTRS)

    Holman, Gordon D.

    1986-01-01

    High spatial resolution microwave observations of coronal loops, together with theoretical models for the loop emission, can provide detailed information about the temperature, density, and magnetic field within the loop, as well as the environment around the loop. The capability for studying magnetic fields is particularly important, since there is no comparable method for obtaining direct information about coronal magnetic fields. Knowledge of the magnetic field strength and structure in coronal loops is important for understanding both coronal heating and flares. With arc-second-resolution microwave observations from the Very Large Array (VLA), supplemental high-spectral-resolution microwave data from a facility such as the Owens Valley frequency-agile interferometer, and the ability to obtain second-of-arc resolution EUV aor soft X ray images, the capability already exists for obtaining much more detailed information about coronal plasma and magnetic structures than is presently available. This capability is discussed.

  14. PUTTING CORONAL SEISMOLOGY ESTIMATES OF THE MAGNETIC FIELD STRENGTH TO THE TEST

    SciTech Connect

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

    2009-07-10

    The magnetic field strength inside a model coronal loop is 'estimated' using coronal seismology, to examine the reliability of magnetic field strengths derived from observed, transverse coronal loop oscillations. Three-dimensional numerical simulations of the interaction of an external pressure pulse with a coronal loop (modeled as a three-dimensional density enhancement inside a two-dimensional magnetic arcade) are analyzed and the 'observed' properties of the excited transverse loop oscillations are used to derive the value of the local magnetic field strength, following the method of Nakariakov and Ofman. Due to the (unexpected) change in periodicity, the magnetic field derived from our 'observed' oscillation is substantially different from the actual (input) magnetic field value (approximately 50%). Coronal seismology can derive useful information about the local magnetic field, but the combined effect of the loop curvature, the density ratio, and aspect ratio of the loop appears to be more important than previously expected.

  15. Self-Regulation of Solar Coronal Heating Process via the Collisionless Reconnection Condition

    SciTech Connect

    Uzdensky, Dmitri A.

    2007-12-31

    I propose a new paradigm for solar coronal heating viewed as a self-regulating process keeping the plasma marginally collisionless. The mechanism is based on the coupling between two effects. First, coronal density controls the plasma collisionality and hence the transition between the slow collisional Sweet-Parker and the fast collisionless reconnection regimes. In turn, coronal energy release leads to chromospheric evaporation, increasing the density and thus inhibiting subsequent reconnection of the newly reconnected loops. As a result, statistically, the density fluctuates around some critical level, comparable to that observed in the corona. In the long run, coronal heating can be represented by repeating cycles of fast reconnection events (nanoflares), evaporation episodes, and long periods of slow magnetic stress buildup and radiative cooling of the coronal plasma.

  16. Self-regulation of solar coronal heating process via the collisionless reconnection condition.

    PubMed

    Uzdensky, Dmitri A

    2007-12-31

    I propose a new paradigm for solar coronal heating viewed as a self-regulating process keeping the plasma marginally collisionless. The mechanism is based on the coupling between two effects. First, coronal density controls the plasma collisionality and hence the transition between the slow collisional Sweet-Parker and the fast collisionless reconnection regimes. In turn, coronal energy release leads to chromospheric evaporation, increasing the density and thus inhibiting subsequent reconnection of the newly reconnected loops. As a result, statistically, the density fluctuates around some critical level, comparable to that observed in the corona. In the long run, coronal heating can be represented by repeating cycles of fast reconnection events (nanoflares), evaporation episodes, and long periods of slow magnetic stress buildup and radiative cooling of the coronal plasma. PMID:18233563

  17. The Contribution of Jets to Coronal and Solar Wind Energetics: MHD Simulations

    NASA Astrophysics Data System (ADS)

    Lionello, Roberto; Torok, Tibor; Titov, Viacheslav; Linker, Jon A.; Mikic, Zoran; Leake, James E.; Linton, Mark

    2016-05-01

    Transient collimated plasma eruptions in the corona, commonly known as coronal jets, are among the most interesting manifestations of solar activity.We use the 3D MHD model with thermodynamics developed at PSI to investigate the origin, dynamics, and plasma properties of coronal jets.Our model is coupled with 3D MHD flux emergence simulations, i.e, we use boundary conditions provided by such simulations to drive a time-dependent coronal evolution. It includes parametric coronal heating, radiative losses, and thermal conduction in the energy equations.This enables us to simulate the energy transfer in coronal jets in a more realistic manner than done so far and to study the amount of energy and mass transported by these phenomena into the higher corona and inner heliosphere. We discuss our results and compare them with previous estimations obtained from observations.

  18. Coronal magnetic structure and the latitude and longitude distribution of energetic particles, 1-5 AU

    NASA Technical Reports Server (NTRS)

    Roelof, E. C.; Mitchell, D. G.

    1979-01-01

    The relation of the coronal magnetic field structure to the distribution of approximately 1 MeV protons in interplanetary space between 1 and 5 AU is discussed. After ordering the interplanetary data by its estimated coronal emission source location in heliographic coordinates, the multispacecraft measured proton fluxes are compared with coronal magnetic field structure infrared as observed in soft X-ray photographs and potential field calculations. Evidence for the propagation and possible acceleration of solar flare protons on high magnetic loop structure in the corona is presented. Further, it is shown that corotating proton flux enhancements are associated with regions of low coronal X-ray emission (including coronal holes), usually in association with solar wind stream structure.

  19. Unresolved fine-scale structure in solar coronal loop-tops

    SciTech Connect

    Scullion, E.; Van der Voort, L. Rouppe; Wedemeyer, S.; Antolin, P.

    2014-12-10

    New and advanced space-based observing facilities continue to lower the resolution limit and detect solar coronal loops in greater detail. We continue to discover even finer substructures within coronal loop cross-sections, in order to understand the nature of the solar corona. Here, we push this lower limit further to search for the finest coronal loop substructures, through taking advantage of the resolving power of the Swedish 1 m Solar Telescope/CRisp Imaging Spectro-Polarimeter (CRISP), together with co-observations from the Solar Dynamics Observatory/Atmospheric Image Assembly (AIA). High-resolution imaging of the chromospheric Hα 656.28 nm spectral line core and wings can, under certain circumstances, allow one to deduce the topology of the local magnetic environment of the solar atmosphere where its observed. Here, we study post-flare coronal loops, which become filled with evaporated chromosphere that rapidly condenses into chromospheric clumps of plasma (detectable in Hα) known as a coronal rain, to investigate their fine-scale structure. We identify, through analysis of three data sets, large-scale catastrophic cooling in coronal loop-tops and the existence of multi-thermal, multi-stranded substructures. Many cool strands even extend fully intact from loop-top to footpoint. We discover that coronal loop fine-scale strands can appear bunched with as many as eight parallel strands within an AIA coronal loop cross-section. The strand number density versus cross-sectional width distribution, as detected by CRISP within AIA-defined coronal loops, most likely peaks at well below 100 km, and currently, 69% of the substructure strands are statistically unresolved in AIA coronal loops.

  20. TRANSVERSE OSCILLATIONS OF LOOPS WITH CORONAL RAIN OBSERVED BY HINODE/SOLAR OPTICAL TELESCOPE

    SciTech Connect

    Antolin, P.; Verwichte, E. E-mail: erwin.verwichte@warwick.ac.uk

    2011-08-01

    The condensations composing coronal rain, falling down along loop-like structures observed in cool chromospheric lines such as H{alpha} and Ca II H, have long been a spectacular phenomenon of the solar corona. However, considered a peculiar sporadic phenomenon, it has not received much attention. This picture is rapidly changing due to recent high-resolution observations with instruments such as the Hinode/Solar Optical Telescope (SOT), CRISP of the Swedish 1-m Solar Telescope, and the Solar Dynamics Observatory. Furthermore, numerical simulations have shown that coronal rain is the loss of thermal equilibrium of loops linked to footpoint heating. This result has highlighted the importance that coronal rain can play in the field of coronal heating. In this work, we further stress the importance of coronal rain by showing the role it can play in the understanding of the coronal magnetic field topology. We analyze Hinode/SOT observations in the Ca II H line of a loop in which coronal rain puts in evidence in-phase transverse oscillations of multiple strand-like structures. The periods, amplitudes, transverse velocities, and phase velocities are calculated, allowing an estimation of the energy flux of the wave and the coronal magnetic field inside the loop through means of coronal seismology. We discuss the possible interpretations of the wave as either standing or propagating torsional Alfven or fast kink waves. An estimate of the plasma beta parameter of the condensations indicates a condition that may allow the often observed separation and elongation processes of the condensations. We also show that the wave pressure from the transverse wave can be responsible for the observed low downward acceleration of coronal rain.

  1. Wing geometry of Culex coronator (Diptera: Culicidae) from South and Southeast Brazil

    PubMed Central

    2014-01-01

    Background The Coronator Group encompasses Culex coronator Dyar & Knab, Culex camposi Dyar, Culex covagarciai Forattini, Culex ousqua Dyar, Culex usquatissimus Dyar, Culex usquatus Dyar and Culex yojoae Strickman. Culex coronator has the largest geographic distribution, occurring in North, Central and South America. Moreover, it is a potential vector-borne mosquito species because females have been found naturally infected with several arboviruses, i.e., Saint Louis Encephalitis Virus, Venezuelan Equine Encephalitis Virus and West Nile Virus. Considering the epidemiological importance of Cx. coronator, we investigated the wing shape diversity of Cx. coronator from South and Southeast Brazil, a method to preliminarily estimate population diversity. Methods Field-collected immature stages of seven populations from a large geographical area in Brazil were maintained in the laboratory to obtain both females and males linked with pupal and/or larval exuviae. For each individual female, 18 landmarks of left wings were marked and digitalized. After Procrustes superimposition, discriminant analysis of shape was employed to quantify wing shape variation among populations. The isometric estimator centroid size was calculated to assess the overall wing size and allometry. Results Wing shape was polymorphic among populations of Cx. coronator. However, dissimilarities among populations were higher than those observed within each population, suggesting populational differentiation in Cx. coronator. Morphological distances between populations were not correlated to geographical distances, indicating that other factors may act on wing shape and thus, determining microevolutionary patterns in Cx. coronator. Despite the population differentiation, intrapopulational wing shape variability was equivalent among all seven populations. Conclusion The wing variability found in Cx. coronator populations brings to light a new biological problem to be investigated: the population genetics of

  2. An Estimate of the Coronal Magnetic Field near a Solar Coronal Mass Ejection from Low-frequency Radio Observations

    NASA Astrophysics Data System (ADS)

    Hariharan, K.; Ramesh, R.; Kishore, P.; Kathiravan, C.; Gopalswamy, N.

    2014-11-01

    We report ground-based, low-frequency (<100 MHz) radio imaging, spectral, and polarimeter observations of the type II radio burst associated with the solar coronal mass ejection (CME) that occurred on 2013 May 2. The spectral observations indicate that the burst has fundamental (F) and harmonic (H) emission components with split-band and herringbone structures. The imaging observations at 80 MHz indicate that the H component of the burst was located close to leading edge of the CME at a radial distance of r ≈ 2 R ⊙ in the solar atmosphere. The polarimeter observations of the type II burst, also at 80 MHz, indicate that the peak degree of circular polarization (dcp) corresponding to the emission generated in the corona ahead of and behind the associated MHD shock front are ≈0.05 ± 0.02 and ≈0.1 ± 0.01, respectively. We calculated the magnetic field B in the above two coronal regions by adopting the empirical relationship between the dcp and B for the harmonic plasma emission and the values are ≈(0.7-1.4) ± 0.2 G and ≈(1.4-2.8) ± 0.1 G, respectively.

  3. An estimate of the coronal magnetic field near a solar coronal mass ejection from low-frequency radio observations

    SciTech Connect

    Hariharan, K.; Ramesh, R.; Kishore, P.; Kathiravan, C.; Gopalswamy, N.

    2014-11-01

    We report ground-based, low-frequency (<100 MHz) radio imaging, spectral, and polarimeter observations of the type II radio burst associated with the solar coronal mass ejection (CME) that occurred on 2013 May 2. The spectral observations indicate that the burst has fundamental (F) and harmonic (H) emission components with split-band and herringbone structures. The imaging observations at 80 MHz indicate that the H component of the burst was located close to leading edge of the CME at a radial distance of r ≈ 2 R {sub ☉} in the solar atmosphere. The polarimeter observations of the type II burst, also at 80 MHz, indicate that the peak degree of circular polarization (dcp) corresponding to the emission generated in the corona ahead of and behind the associated MHD shock front are ≈0.05 ± 0.02 and ≈0.1 ± 0.01, respectively. We calculated the magnetic field B in the above two coronal regions by adopting the empirical relationship between the dcp and B for the harmonic plasma emission and the values are ≈(0.7-1.4) ± 0.2 G and ≈(1.4-2.8) ± 0.1 G, respectively.

  4. TRACKING CORONAL FEATURES FROM THE LOW CORONA TO EARTH: A QUANTITATIVE ANALYSIS OF THE 2008 DECEMBER 12 CORONAL MASS EJECTION

    SciTech Connect

    DeForest, C. E.; Howard, T. A.; McComas, D. J.

    2013-05-20

    We have tracked a slow magnetic cloud associated coronal mass ejection (CME) continuously from its origin as a flux rope structure in the low solar corona over a four-day passage to impact with spacecraft located near Earth. Combining measurements from the STEREO, ACE, and Wind space missions, we are able to follow major elements with enough specificity to relate pre-CME coronal structure in the low corona to the corresponding elements seen in the near-Earth in situ data. Combining extreme ultraviolet imaging, quantitative Thomson scattering data throughout the flight of the CME, and ''ground-truth'' in situ measurements, we: (1) identify the plasma observed by ACE and Wind with specific features in the solar corona (a segment of a long flux rope); (2) determine the onset mechanism of the CME (destabilization of a filament channel following flare reconnection, coupled with the mass draining instability) and demonstrate that it is consistent with the in situ measurements; (3) identify the origin of different layers of the sheath material around the central magnetic cloud (closed field lifted from the base of the corona, closed field entrained during passage through the corona, and solar wind entrained by the front of the CME); (4) measure mass accretion of the system via snowplow effects in the solar wind as the CME crossed the solar system; and (5) quantify the kinetic energy budget of the system in interplanetary space, and determine that it is consistent with no long-term driving force on the CME.

  5. Presentación del estudio "Links" de hombres que tienes sexo con hombres en Buenos Aires, Argentina.

    PubMed

    Carballo-Diéguez, Alex; Avila, María M; Balán, Iván C; Marone, Rubén; Pando, María A; Barreda, Victoria

    2011-03-01

    Estudios previos en Buenos Aires reportaron altas prevalencias de HIV entre HSH, con valores que oscilan entre 9 y 14% durante casi 10 años de continuo testeo. El objetivo principal de este estudio fue la evaluación de factores relacionados al comportamiento de alto riesgo para transmisión del HIV entre HSH entre los que se incluyen el conocimiento y factores emocionales, socioculturales y ambientales. Por otro lado se realizó la estimación de prevalencia e incidencia de HIV utilizando RDS (Respondent Driven Sampling), así como la presencia de otras infecciones de transmisión sexual. Por último se evaluaron los hábitos de testeo para HIV indagando que factores facilitan o impiden su realización. El estudio constó de dos fases, en primer lugar una fase cualitativa y posteriormente una fase cuantitativa con una duración total de 4 años y medio. Durante la fase cualitativa se realizaron 44 entrevistas individuales en profundidad, 8 grupos focales y 10 observaciones etnográficas (hoteles, baños públicos ("teteras"), cines pornográficos, fiestas privadas, dark rooms y discotecas). Durante la fase cuantitativa del estudio se realizó el reclutamiento de 500 participantes que provinieron de la Ciudad Autónoma de Buenos Aires, así como del Gran Buenos Aires. El reclutamiento se comenzó con 16 participantes llamados semillas. Se realizó el diagnóstico de infección por HIV, hepatitis B y C (HBV y HCV), Treponema pallidum, Virus Papiloma Humano (HPV) y Chlamidias. La colaboración establecida entre los grupos de trabajo enfocados en áreas diversas posibilitó el abordaje conjunto de nuevas estrategias de investigación antes no exploradas en nuestro país. Los resultados más relevantes de esta investigación serán progresivamente publicados en sucesivos números de Actualizaciones en SIDA.

  6. Presentación del estudio “Links” de hombres que tienes sexo con hombres en Buenos Aires, Argentina

    PubMed Central

    Carballo-Diéguez, Alex; Ávila, María M; Balán, Iván C.; Marone, Rubén; Pando, María A.; Barreda, Victoria

    2011-01-01

    Resumen Estudios previos en Buenos Aires reportaron altas prevalencias de HIV entre HSH, con valores que oscilan entre 9 y 14% durante casi 10 años de continuo testeo. El objetivo principal de este estudio fue la evaluación de factores relacionados al comportamiento de alto riesgo para transmisión del HIV entre HSH entre los que se incluyen el conocimiento y factores emocionales, socioculturales y ambientales. Por otro lado se realizó la estimación de prevalencia e incidencia de HIV utilizando RDS (Respondent Driven Sampling), así como la presencia de otras infecciones de transmisión sexual. Por último se evaluaron los hábitos de testeo para HIV indagando que factores facilitan o impiden su realización. El estudio constó de dos fases, en primer lugar una fase cualitativa y posteriormente una fase cuantitativa con una duración total de 4 años y medio. Durante la fase cualitativa se realizaron 44 entrevistas individuales en profundidad, 8 grupos focales y 10 observaciones etnográficas (hoteles, baños públicos (“teteras”), cines pornográficos, fiestas privadas, dark rooms y discotecas). Durante la fase cuantitativa del estudio se realizó el reclutamiento de 500 participantes que provinieron de la Ciudad Autónoma de Buenos Aires, así como del Gran Buenos Aires. El reclutamiento se comenzó con 16 participantes llamados semillas. Se realizó el diagnóstico de infección por HIV, hepatitis B y C (HBV y HCV), Treponema pallidum, Virus Papiloma Humano (HPV) y Chlamidias. La colaboración establecida entre los grupos de trabajo enfocados en áreas diversas posibilitó el abordaje conjunto de nuevas estrategias de investigación antes no exploradas en nuestro país. Los resultados más relevantes de esta investigación serán progresivamente publicados en sucesivos números de Actualizaciones en SIDA. PMID:25264397

  7. Presentación del estudio "Links" de hombres que tienes sexo con hombres en Buenos Aires, Argentina.

    PubMed

    Carballo-Diéguez, Alex; Avila, María M; Balán, Iván C; Marone, Rubén; Pando, María A; Barreda, Victoria

    2011-03-01

    Estudios previos en Buenos Aires reportaron altas prevalencias de HIV entre HSH, con valores que oscilan entre 9 y 14% durante casi 10 años de continuo testeo. El objetivo principal de este estudio fue la evaluación de factores relacionados al comportamiento de alto riesgo para transmisión del HIV entre HSH entre los que se incluyen el conocimiento y factores emocionales, socioculturales y ambientales. Por otro lado se realizó la estimación de prevalencia e incidencia de HIV utilizando RDS (Respondent Driven Sampling), así como la presencia de otras infecciones de transmisión sexual. Por último se evaluaron los hábitos de testeo para HIV indagando que factores facilitan o impiden su realización. El estudio constó de dos fases, en primer lugar una fase cualitativa y posteriormente una fase cuantitativa con una duración total de 4 años y medio. Durante la fase cualitativa se realizaron 44 entrevistas individuales en profundidad, 8 grupos focales y 10 observaciones etnográficas (hoteles, baños públicos ("teteras"), cines pornográficos, fiestas privadas, dark rooms y discotecas). Durante la fase cuantitativa del estudio se realizó el reclutamiento de 500 participantes que provinieron de la Ciudad Autónoma de Buenos Aires, así como del Gran Buenos Aires. El reclutamiento se comenzó con 16 participantes llamados semillas. Se realizó el diagnóstico de infección por HIV, hepatitis B y C (HBV y HCV), Treponema pallidum, Virus Papiloma Humano (HPV) y Chlamidias. La colaboración establecida entre los grupos de trabajo enfocados en áreas diversas posibilitó el abordaje conjunto de nuevas estrategias de investigación antes no exploradas en nuestro país. Los resultados más relevantes de esta investigación serán progresivamente publicados en sucesivos números de Actualizaciones en SIDA. PMID:25264397

  8. Coronal magnetic fields from multiple type II bursts

    NASA Astrophysics Data System (ADS)

    Honnappa, Vijayakumar; Raveesha, K. H.; Subramanian, K. R.

    Coronal magnetic fields from multiple type II bursts Vijayakumar H Doddamani1*, Raveesha K H2 and Subramanian3 1Bangalore University, Bangalore, Karnataka state, India 2CMR Institute of Technology, Bangalore, Karnataka state, India 3 Retd, Indian Institute of Astrophysics, Bangalore, Karnataka state, India Abstract Magnetic fields play an important role in the astrophysical processes occurring in solar corona. In the solar atmosphere, magnetic field interacts with the plasma, producing abundant eruptive activities. They are considered to be the main factors for coronal heating, particle acceleration and the formation of structures like prominences, flares and Coronal Mass Ejections. The magnetic field in solar atmosphere in the range of 1.1-3 Rsun is especially important as an interface between the photospheric magnetic field and the solar wind. Its structure and time dependent change affects space weather by modifying solar wind conditions, Cho (2000). Type II doublet bursts can be used for the estimation of the strength of the magnetic field at two different heights. Two type II bursts occur sometimes in sequence. By relating the speed of the type II radio burst to Alfven Mach Number, the Alfven speed of the shock wave generating type II radio burst can be calculated. Using the relation between the Alfven speed and the mean frequency of emission, the magnetic field strength can be determined at a particular height. We have used the relative bandwidth and drift rate properties of multiple type II radio bursts to derive magnetic field strengths at two different heights and also the gradient of the magnetic field in the outer corona. The magnetic field strength has been derived for different density factors. It varied from 1.2 to 2.5 gauss at a solar height of 1.4 Rsun. The empirical relation of the variation of the magnetic field with height is found to be of the form B(R) = In the present case the power law index ‘γ’ varied from -3 to -2 for variation of

  9. Physical Properties of a Coronal Hole from a Coronal Diagnostics Spectrometer, Mauna Loa Coronagraph, and LASCO Observations during the Whole Sun Month

    NASA Technical Reports Server (NTRS)

    Guhathakurta, M.; Fludra, A.; Gibson, S. E.; Biesecker, D.; Fisher, R.

    2004-01-01

    Until recently, inference of electron density distribution in the solar corona was limited by the field of view of white-light coronagraphs (typically out to 6 Rs). Now, for the first time we have a series of white- light coronagraphs (SOHO/LASCO) whose combined field of view extends from 1.1 - 30 Rs. Quantitative information on electron density distribution of coronal hole and coronal plumes/rays are estimated by using white-light, polarized brightness (pB) observations from the SOHO/LASCO/C2 and C3 and HAO/Mauna Loa Mark III coronagraphs from 1.15 to 8.0 Rs. Morphological information on the boundary of the polar coronal hole and streamer interface is determined from the white-light observations in a manner similar to the Skylab polar coronal hole boundary estimate. The average coronal hole electron density in the region 1 - 1.15 Rs is estimated from the density-sensitive EUV line ratios of Si IX 3501342 A observed by the SOHO/coronal diagnostic spectrometer (CDS). We combine these numbers with the estimate from white-light (WL) observations to obtain a density profile from 1 to 8 Rs for the plumes and the polar coronal hole. We find that white light and spectral analysis produce consistent density information. Extrapolated densities inferred from SOHO observations are compared to Ulysses in situ observations of density. Like the density inferred from the Spartan 201-03 coronagraph, the current SOHO density profiles suggest that the acceleration of the fast solar wind takes place very close to the Sun, within 10-15 Rs. The density information is used to put constraints on solar wind flow velocities and effective temperatures. Finally, these results are compared to the recent analysis of the Spartan 201-03 white-light observations.

  10. Nonlinear twist-kink instability of a coronal loop

    SciTech Connect

    Zaidman, E.G.; Tajima, T.

    1989-03-01

    Three-dimensional magnetoinductive particle simulations are used to demonstrate that the mechanical twisting motion applied to a magnetized plasma column induces a current aligned to the external magnetic field direction, pinches the plasma and magnetic fields, and stores the energy in poloidal magnetic fields. As the twist motion continues, the field lines locally begin to wrap around the plasma more than one revolution. A strong MHD instability sets in that is a mixture of kink and ballooning modes, releasing the magnetic energy and causing destruction of coherent column structure and flows of turbulent plasma. A similar episode ensues, exhibiting relaxation oscillations. The buildup of poloidal fields and structure and its sudden release driven by the twist motion may be a model for the solar coronal loop dynamics which exhibits a slow energy buildup with some photospheric motion and a sudden energy release by flares. 16 references.

  11. Asymmetric Magnetic Reconnection in Coronal Mass Ejection Current Sheets

    NASA Astrophysics Data System (ADS)

    Pope, Crystal; Miralles, M. P.; Murphy, N. A.

    2012-01-01

    Flux rope models of coronal mass ejections (CMEs) predict the formation ofan elongated current sheet in the wake behind the rising plasmoid. These current sheets have been seen to drift or tilt over time by instruments including SOHO/LASCO and Hinode/XRT. We measure this in multiple observations including the 2008 April 9 "Cartwheel CME" and find an average drift that is far more than can be accounted for via the effects of solar rotation. The observed drift could be due to different parts of the current sheet actively reconnecting at different times (e.g., Savage et al. 2010), macroscopic effects from the rising flux rope pulling the plasma sheet along with it, or asymmetry in the magnetic reconnection process itself. These drift rates are compared with resistive magnetohydrodynamic (MHD) simulations of line-tied reconnection between magnetic fields of different strengths. The observed drift rates are comparable to predictions made by the simulations.

  12. FLOWS AND WAVES IN BRAIDED SOLAR CORONAL MAGNETIC STRUCTURES

    SciTech Connect

    Pant, V.; Datta, A.; Banerjee, D.

    2015-03-01

    We study the high frequency dynamics in the braided magnetic structure of an active region (AR 11520) moss as observed by the High-Resolution Coronal Imager (Hi-C). We detect quasi-periodic flows and waves in these structures. We search for high frequency dynamics while looking at power maps of the observed region. We find that shorter periodicities (30–60 s) are associated with small spatial scales which can be resolved by Hi-C only. We detect quasi-periodic flows with a wide range of velocities, from 13–185 km s{sup −1}, associated with braided regions. This can be interpreted as plasma outflows from reconnection sites. We also find short period and large amplitude transverse oscillations associated with the braided magnetic region. Such oscillations could be triggered by reconnection or such oscillations may trigger reconnection.

  13. An ice-cream cone model for coronal mass ejections

    NASA Astrophysics Data System (ADS)

    Xue, X. H.; Wang, C. B.; Dou, X. K.

    2005-08-01

    In this study, we use an ice-cream cone model to analyze the geometrical and kinematical properties of the coronal mass ejections (CMEs). Assuming that in the early phase CMEs propagate with near-constant speed and angular width, some useful properties of CMEs, namely the radial speed (v), the angular width (α), and the location at the heliosphere, can be obtained considering the geometrical shapes of a CME as an ice-cream cone. This model is improved by (1) using an ice-cream cone to show the near real configuration of a CME, (2) determining the radial speed via fitting the projected speeds calculated from the height-time relation in different azimuthal angles, (3) not only applying to halo CMEs but also applying to nonhalo CMEs.

  14. Prominence condensation and magnetic levitation in a coronal loop

    NASA Technical Reports Server (NTRS)

    Van Hoven, G.; Mok, Y.; Drake, J. F.

    1992-01-01

    The results of a model dynamic simulation of the formation and support of a narrow prominence at the apex of a coronal magnetic loop or arcade are described. The condensation process proceeds via an initial radiative cooling and pressure drop, and a secondary siphon flow from the dense chromospheric ends. The antibuoyancy effect as the prominence forms causes a bending of the confining magnetic field, which propagates toward the semirigid ends of the magnetic loop. Thus, a wide magnetic 'hammock' or well (of the normal-polarity Kippenhahn-Schlueter-type) is formed, which supports the prominence at or near the field apex. The simplicity of this 1.5-dimensional model, with its accompanying diagnostics, elucidates the various contributions to the nonlinear dynamics of prominence condensation and levitation.

  15. What Preparatory Science is Needed in Coronal Structure and Activity

    NASA Technical Reports Server (NTRS)

    Antiochos, S. K.

    2011-01-01

    Solar Orbiter and Solar Probe Plus will launch in six short years! Before then, we need to accomplish a great deal of science in order to be able to maximize the return of these missions. Preparatory science is especially important for exploratory missions such as SO and SPP, because they truly will be going "where no mission has gone before". Such preparatory science may include all types of research: theory, modeling, data exploitation, and supporting observations. This meeting provides an opportunity for the community to define and begin this critical preparatory work. In this talk I will provide an overview of our state of knowledge in coronal structure and activity, describe what I believe are the most promising opportunities for advances by SO and SPP, and lead a discussion on what programs need to be implemented now in order to achieve these science advances by the time SO and SPP launch.

  16. Aspects of Coronal Mass Ejections Related to Space Weather

    NASA Astrophysics Data System (ADS)

    Gopalswamy, N.

    2010-12-01

    Solar cycle 23 witnessed an unprecedented array of space- and ground-based instruments observing the violent eruptions from the Sun that had huge impact on the heliosphere. It was possible to characterize coronal mass ejections (CMEs) that cause extreme solar energetic particle events and geomagnetic storms, the two aspects that concern the space weather community. In this paper I discuss the special populations of CMEs that have significant interplanetary consequences: shock-driving CMEs identified based on their association with type II radio bursts and in-situ shocks, SEP-producing CMEs, and geoeffective CMEs (those that produce geomagnetic storms). I discuss the kinematic and solar-source properties of these populations and how they vary with the solar activity cycle. I also compare their properties with the general population of CMEs, so one can recognize when and where these events occur on the Sun.

  17. FAST DIFFERENTIAL EMISSION MEASURE INVERSION OF SOLAR CORONAL DATA

    SciTech Connect

    Plowman, Joseph; Kankelborg, Charles; Martens, Petrus

    2013-07-01

    We present a fast method for reconstructing differential emission measures (DEMs) using solar coronal data. The method consists of a fast, simple regularized inversion in conjunction with an iteration scheme for removal of residual negative emission measure. On average, it computes over 1000 DEMs s{sup -1} for a sample active region observed by the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory, and achieves reduced chi-squared of order unity with no negative emission in all but a few test cases. The high performance of this method is especially relevant in the context of AIA, which images of order one million solar pixels per second. This paper describes the method, analyzes its fidelity, compares its performance and results with other DEM methods, and applies it to an active region and loop observed by AIA and by the Extreme-ultraviolet Imaging Spectrometer on Hinode.

  18. Einstein Observatory coronal temperatures of late-type stars

    NASA Technical Reports Server (NTRS)

    Schmitt, J. H. M. M.; Collura, A.; Sciortino, S.; Vaiana, G. S.; Harnden, F. R., Jr.

    1990-01-01

    The results are presented of a survey of the coronal temperatures of late-type stars using the Einstein Observatory IPC. The spectral analysis shows that the frequently found one- and two-temperature descriptions are mainly influenced by the SNR of the data and that models using continuous emission measure distributions can provide equally adequate and physically more meaningful and more plausible descriptions. Intrinsic differences in differential emission measure distributions are found for four groups of stars. M dwarfs generally show evidence for high-temperature gas in conjunction with lower-temperature material, while main-sequence stars of types F and G have the high-temperature component either absent or very weak. Very hot coronae without the lower-temperature component appearing in dwarf stars are evident in most of the giant stars studied. RS CVn systems show evidence for extremely hot coronae, sometimes with no accompanying lower-temperature material.

  19. Magnetohydrodynamic turbulent cascade of coronal loop magnetic fields.

    PubMed

    Rappazzo, A F; Velli, M

    2011-06-01

    The Parker model for coronal heating is investigated through a high resolution simulation. An inertial range is resolved where fluctuating magnetic energy EMk[Please see symbol]) [Please see symbol] k[Please see symbol](-2.7) exceeds kinetic energy EK(k[Please see symbol])[Please see symbol]k[Please see symbol](-0.6). Increments scale as δbℓ ~/= ℓ(-0.85) and δuℓ ~/= ℓ(+0.2) with velocity increasing at small scales, indicating that magnetic reconnection plays a prime role in this turbulent system. We show that spectral energy transport is akin to standard magnetohydrodynamic (MHD) turbulence even for a system of reconnecting current sheets sustained by the boundary. In this new MHD turbulent cascade, kinetic energy flows are negligible while cross-field flows are enhanced, and through a series of "reflections" between the two fields, cascade more than half of the total spectral energy flow.

  20. A NEW VIEW OF CORONAL WAVES FROM STEREO

    SciTech Connect

    Ma, S.; Lin, J.; Zhao, S.; Li, Q.; Chen, P. F.; Chen, H.

    2009-12-10

    On 2007 December 7, there was an eruption from AR 10977, which also hosted a sigmoid. An EUV Imaging Telescope (EIT) wave associated with this eruption was observed by EUVI on board the Solar Terrestrial Relations Observatory (STEREO). Using EUVI images in the 171 A and the 195 A passbands from both STEREO A and B, we study the morphology and kinematics of this EIT wave. In the early stages, images of the EIT wave from the two STEREO spacecrafts differ markedly. We determine that the EUV fronts observed at the very beginning of the eruption likely include some intensity contribution from the associated coronal mass ejection (CME). Additionally, our velocity measurements suggest that the EIT wave front may propagate at nearly constant velocity. Both results offer constraints on current models and understanding of EIT waves.