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Sample records for active regions coronal

  1. Active region coronal evolution

    NASA Technical Reports Server (NTRS)

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

    1982-01-01

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

  2. 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.

  3. OBSERVING CORONAL NANOFLARES IN ACTIVE REGION MOSS

    SciTech Connect

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

    2013-06-10

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

  4. The composition of a coronal active region

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

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

  5. 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.

  6. 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).

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

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

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

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

    NASA Astrophysics Data System (ADS)

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

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

  9. 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.

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

    NASA Astrophysics Data System (ADS)

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

    1994-08-01

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

  11. Breakout coronal mass ejections from solar active regions

    NASA Astrophysics Data System (ADS)

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

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

  12. 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.

  13. Electric currents and coronal heating in NOAA active region 6952

    NASA Technical Reports Server (NTRS)

    Metcalf, T. R.; Canfield, R. C.; Hudson, H. S.; Mickey, D. L.; Wulser, J. -P.; Martens, P. C. H.; Tsuneta, S.

    1994-01-01

    We examine the spatial and temporal relationship between coronal structures observed with the soft X-ray telescope (SXT) on board the Yohkoh spacecraft and the vertical electric current density derived from photospheric vector magnetograms obtained using the Stokes Polarimeter at the Mees Solar Observatory. We focus on a single active region: AR 6952 which we observed on 7 days during 1991 December. For 11 independent maps of the vertical electric current density co-aligned with non-flaring X-ray images, we search for a morphological relationship between sites of high vertical current density in the photosphere and enhanced X-ray emission in the overlying corona. We find no compelling spatial or temporal correlation between the sites of vertical current and the bright X-ray structures in this active region.

  14. A STATISTICAL STUDY OF CORONAL ACTIVE EVENTS IN THE NORTH POLAR REGION

    SciTech Connect

    Sako, Nobuharu; Shimojo, Masumi; Watanabe, Tetsuya; Sekii, Takashi

    2013-09-20

    In order to study the relationship between characteristics of polar coronal active events and the magnetic environment in which such events take place, we analyze 526 X-ray jets and 1256 transient brightenings in the polar regions and in regions around the equatorial limbs. We calculate the occurrence rates of these polar coronal active events as a function of distance from the boundary of coronal holes, and find that most events in the polar quiet regions occur adjacent to and equatorward of the coronal hole boundaries, while events in the polar coronal holes occur uniformly within them. Based primarily on the background intensity, we define three categories of regions that produce activity: polar coronal holes, coronal hole boundary regions, and polar quiet regions. We then investigate the properties of the events produced in these regions. We find no significant differences in their characteristics, for example, length and lifetime, but there are differences in the occurrence rates. The mean occurrence rate of X-ray jets around the boundaries of coronal holes is higher than that in the polar quiet regions, equatorial quiet regions, and polar coronal holes. Furthermore, the mean occurrence rate of transient brightenings is also higher in these regions. We make comparison with the occurrence rates of emerging and canceling magnetic fields in the photosphere reported in previous studies, and find that they do not agree with the occurrence rates of transient brightenings found in this study.

  15. FORMATION OF CORONAL HOLES ON THE ASHES OF ACTIVE REGIONS

    SciTech Connect

    Karachik, Nina V.; Pevtsov, Alexei A.; Abramenko, Valentyna I. E-mail: apevtsov@nso.ed

    2010-05-10

    We investigate the formation of isolated non-polar coronal holes (CHs) on the remnants of decaying active regions (ARs) at the minimum/early ascending phase of sunspot activity. We follow the evolution of four bipolar ARs and measure several parameters of their magnetic fields including total flux, imbalance, and compactness. As regions decay, their leading and following polarities exhibit different dissipation rates: loose polarity tends to dissipate faster than compact polarity. As a consequence, we see a gradual increase in flux imbalance inside a dissipating bipolar region, and later a formation of a CH in place of more compact magnetic flux. Out of four cases studied in detail, two CHs had formed at the following polarity of the decaying bipolar AR, and two CHs had developed in place of the leading polarity field. All four CHs contain a significant fraction of magnetic field of their corresponding AR. Using potential field extrapolation, we show that the magnetic field lines of these CHs were closed on the polar CH at the North, which at the time of the events was in imbalance with the polar CH at the South. This topology suggests that the observed phenomenon may play an important role in transformation of toroidal magnetic field to poloidal field, which is a key step in transitioning from an old solar cycle to a new one. The timing of this observed transition may indicate the end of solar cycle 23 and the beginning of cycle 24.

  16. The study of a spatial relationship between the Equatorial coronal hole and the Active region

    NASA Astrophysics Data System (ADS)

    Karna, Mahendra; Karna, Nishu

    2016-05-01

    The 11-year solar cycle is characterized by the periodic change in the solar activity like sunspot numbers, coronal holes, active regions, eruptions such as flares and coronal mass ejections. We study the relationship between equatorial coronal holes (ECH) and the active regions (AR) as coronal hole positions and sizes change with the solar cycle. We made a detailed study for two solar maximum: Solar Cycle 23 (1999, 2000, 2001 and 2002) and Solar Cycle 24 (2011, 2012 and 2013). We used publically available Heliophysics Feature Catalogue and NOAA Solar Geophysical data for. Moreover, we used daily Solar Region Summary (SRS) data from SWPC/NOAA website. We examined the position of ECH and AR and noted that during a maximum of 23, the majority of ECH were not near active regions. However, in cycle 24 coronal holes and equatorial holes were more close to each other. Moreover, we noticed the asymmetry in AR migrations towards the lower latitude in both Northern and Southern hemisphere in cycle 23. While, no such notable asymmetrical behavior was observed in a maximum of cycle 24. Our goal is to extend the study with cycle 21 and 22 and examine the correlation between equatorial holes, the active regions, and the flares. This combined study will shed light in determining the distribution of flares.

  17. Rendering Three-Dimensional Solar Coronal Structures of Active Region 8227

    NASA Technical Reports Server (NTRS)

    Gary, G. A.; Alexander, D. A.

    1999-01-01

    Coronal X-ray and EUV synthesized images are constructed of Active Region 8227 (May-June 1996) and are compared with Yohkoh/SXT, SOHO/EIT, and TRACE observations. Using the rendering technique of Gary (1997) and Alexander, Gary, and Thompson (1998), specific geometric and physical models are used to integrated the plasma emission along the line of sight to obtain a rendered image. The specific instrumental profiles are convolved in the integration process as well as specific heating functions. We analyze coronal X-ray and EUV structures by constructing synthesized image and comparison with observations provide test of specific physical models. We investigate how different pressure distributions within the active region loop system affect the emission characteristics and compare the various results with coronal observations. We investigate how the different heating functions in the active region are reflected in the effect of overall structure of the region. Specific heating rates are tested.

  18. Neutral-Line Magnetic Shear and Enhanced Coronal Heating in Solar Active Regions

    NASA Technical Reports Server (NTRS)

    Falconer, D. A.; Moore, R. L.; Porter, J. G.; Gary, G. A.; Shimizu, T.

    1997-01-01

    By examining the magnetic structure at sites in the bright coronal interiors of active regions that are not flaring but exhibit persistent strong coronal heating, we establish some new characteristics of the magnetic origins of this heating. We have examined the magnetic structure of these sites in five active regions, each of which was well observed by both the Yohkoh SXT and the Marshall Space Flight Center Vector Magnetograph and showed strong shear in its magnetic field along part of at least one neutral line (polarity inversion). Thus, we can assess whether this form of nonpotential field structure in active regions is a characteristic of the enhanced coronal heating and vice versa. From 27 orbits' worth of Yohkoh SXT images of the five active regions, we have obtained a sample of 94 persistently bright coronal features (bright in all images from a given orbit), 40 long (greater than or approximately equals 20,000 km) neutral-line segments having strong magnetic shear throughout (shear angle greater than 45 deg), and 39 long neutral-line segments having weak magnetic shear throughout (shear angle less than 45 deg). From this sample, we find that: (1) all of our persistently bright coronal features are rooted in magnetic fields that are stronger than 150 G; (2) nearly all (95%) of these enhanced coronal features are rooted near neutral lines (closer than 10,000 km); (3) a great majority (80%) of the bright features are rooted near strong-shear portions of neutral lines; (4) a great majority (85%) of long strong-shear segments of neutral lines have persistently bright coronal features rooted near them; (5) a large minority (40%) of long weak-shear segments of neutral lines have persistently bright coronal features rooted near them; and (6) the brightness of a persistently bright Coronal feature often changes greatly over a few hours. From these results, we conclude that most persistent enhanced heating of coronal loops in active regions: (1) requires the

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

    Solar coronal jets are common in both coronal holes and in active regions. 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, such as the hitherto popular ``emerging flux'' model for jets. We present observations of an on-disk active region 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.

  20. Coronal Magnetography of Solar Active Regions Using Coordinated SOHO/CDS and VLA Observations

    NASA Technical Reports Server (NTRS)

    Brosius, Jeffrey W.

    1999-01-01

    The purpose of this project is to apply the coronal magnetographic technique to SOHO (Solar Heliospheric Observatory) /CDS (Coronal Diagnostic Spectrometer) EUV (Extreme Ultraviolet Radiation) and coordinated VLA microwave observations of solar active regions to derive the strength and structure of the coronal magnetic field. A CDS observing plan was developed for obtaining spectra needed to derive active region differential emission measures (DEMs) required for coronal magnetography. VLA observations were proposed and obtained. SOHO JOP 100 was developed, tested, approved, and implemented to obtain coordinated CDS (Coronal Diagnostic Spectrometer)/EIT (Ultraviolet Imaging Telescope)/ VLA (Very Large Array)/ TRACE (Transition Region and Coronal Explorer)/ SXT (Solar X Ray Telescope) observations of active regions on April 12, May 9, May 13, and May 23. Analysis of all four data sets began, with heaviest concentration on COS data. It is found that 200-pixel (14 A in NIS1) wavelength windows are appropriate for extracting broadened Gaussian line profile fit parameters for lines including Fe XIV at 334.2, Fe XVI at 335.4, Fe XVI at 360.8, and Mg IX at 368.1 over the 4 arcmin by 4 arcmin CDS field of view. Extensive efforts were focused on learning and applying were focused on learning and applying CDS software, and including it in new IDL procedures to carry out calculations relating to coronal magnetography. An important step is to extract Gaussian profile fits to all the lines needed to derive the DEM in each spatial pixel of any given active region. The standard CDS absolute intensity calibration software was applied to derived intensity images, revealing that ratios between density-insensitive lines like Fe XVI 360.8/335.4 yield good agreement with theory. However, the resulting absolute intensities of those lines are very high, indicating that revisions to the CDS absolute intensity calibrations remain to be included in the CDS software, an essential step to

  1. THE ROLE OF MAGNETIC TOPOLOGY IN THE HEATING OF ACTIVE REGION CORONAL LOOPS

    SciTech Connect

    Lee, J.-Y.; Reeves, Katharine K.; Korreck, K. E.; Golub, L.; DeLuca, E. E.; Barnes, Graham; Leka, K. D.

    2010-11-10

    We investigate the evolution of coronal loop emission in the context of the coronal magnetic field topology. New modeling techniques allow us to investigate the magnetic field structure and energy release in active regions (ARs). Using these models and high-resolution multi-wavelength coronal observations from the Transition Region and Coronal Explorer and the X-ray Telescope on Hinode, we are able to establish a relationship between the light curves of coronal loops and their associated magnetic topologies for NOAA AR 10963. We examine loops that show both transient and steady emission, and we find that loops that show many transient brightenings are located in domains associated with a high number of separators. This topology provides an environment for continual impulsive heating events through magnetic reconnection at the separators. A loop with relatively constant X-ray and EUV emission, on the other hand, is located in domains that are not associated with separators. This result implies that larger-scale magnetic field reconnections are not involved in heating plasma in these regions, and the heating in these loops must come from another mechanism, such as small-scale reconnections (i.e., nanoflares) or wave heating. Additionally, we find that loops that undergo repeated transient brightenings are associated with separators that have enhanced free energy. In contrast, we find one case of an isolated transient brightening that seems to be associated with separators with a smaller free energy.

  2. Scaling laws of coronal loops compared to a 3D MHD model of an active region

    NASA Astrophysics Data System (ADS)

    Bourdin, Ph.-A.; Bingert, S.; Peter, H.

    2016-04-01

    Context. The structure and heating of coronal loops have been investigated for decades. Established scaling laws relate fundamental quantities like the loop apex temperature, pressure, length, and coronal heating. Aims: We test these scaling laws against a large-scale 3D magneto-hydrodynamics (MHD) model of the solar corona, which became feasible with current high-performance computing. Methods: We drove an active region simulation with photospheric observations and find strong similarities to the observed coronal loops in X-rays and extreme-ultraviolet (EUV) wavelength. A 3D reconstruction of stereoscopic observations shows that our model loops have a realistic spatial structure. We compared scaling laws to our model data extracted along an ensemble of field lines. Finally, we fit a new scaling law that represents hot loops and also cooler structures, which was not possible before based only on observations. Results: Our model data gives some support for scaling laws that were established for hot and EUV-emissive coronal loops. For the Rosner-Tucker-Vaiana (RTV) scaling law we find an offset to our model data, which can be explained by 1D considerations of a static loop with a constant heat input and conduction. With a fit to our model data we set up a new scaling law for the coronal heat input along magnetic field lines. Conclusions: RTV-like scaling laws were fitted to hot loops and therefore do not predict well the coronal heat input for cooler structures that are barely observable. The basic differences between 1D and self-consistent 3D modeling account for deviations between earlier scaling laws and ours. We also conclude that a heating mechanism by MHD-turbulent dissipation within a braided flux tube would heat the corona stronger than is consistent with our model corona.

  3. Model for the Coupled Evolution of Subsurface and Coronal Magnetic Fields in Solar Active Regions

    NASA Astrophysics Data System (ADS)

    van Ballegooijen, A. A.; Mackay, D. H.

    2007-04-01

    According to Babcock's theory of the solar dynamo, bipolar active regions are Ω-shaped loops emerging from a toroidal field located near the base of the convection zone. In this paper, a mean field model for the evolution of a twisted Ω-loop is developed. The model describes the coupled evolution of the magnetic field in the convection zone and the corona after the loop has fully emerged into the solar atmosphere. Such a coupled evolution is required to fully understand what happens to the coronal and subsurface fields as magnetic flux cancels at polarity inversion lines on the photosphere. The jump conditions for the magnetic field at the photosphere are derived from the magnetic stress balance between the convection zone and corona. The model reproduces the observed spreading of active region magnetic flux over the solar surface. At polarity inversion lines, magnetic flux submerges below the photosphere, but the component of magnetic field along the inversion line cannot submerge, because the field in the upper convection zone is nearly radial. Therefore, magnetic shear builds up in the corona above the inversion line, which eventually leads to a loss of equilibrium of the coronal fields and the ``lift-off'' of a coronal flux rope. Fields that submerge are transported back to the base of the convection zone, leading to the repair of the toroidal flux rope. Following Martens and Zwaan, interactions between bipoles are also considered.

  4. Coronal Mass Ejections from the Same Active Region Cluster: Two Different Perspectives

    NASA Astrophysics Data System (ADS)

    Cremades, H.; Mandrini, C. H.; Schmieder, B.; Crescitelli, A. M.

    2015-06-01

    The cluster formed by active regions (ARs) NOAA 11121 and 11123, approximately located on the solar central meridian on 11 November 2010, is of great scientific interest. This complex was the site of violent flux emergence and the source of a series of Earth-directed events on the same day. The onset of the events was nearly simultaneously observed by the Atmospheric Imaging Assembly (AIA) telescope onboard the Solar Dynamics Observatory (SDO) and the Extreme-Ultraviolet Imagers (EUVI) on the Sun-Earth Connection Coronal and Heliospheric Investigation (SECCHI) suite of telescopes onboard the Solar-Terrestrial Relations Observatory (STEREO) twin spacecraft. The progression of these events in the low corona was tracked by the Large Angle Spectroscopic Coronagraphs (LASCO) onboard the Solar and Heliospheric Observatory (SOHO) and the SECCHI/COR coronagraphs on STEREO. SDO and SOHO imagers provided data from the Earth's perspective, whilst the STEREO twin instruments procured images from the orthogonal directions. This spatial configuration of spacecraft allowed optimum simultaneous observations of the AR cluster and the coronal mass ejections that originated in it. Quadrature coronal observations provided by STEREO revealed many more ejective events than were detected from Earth. Furthermore, joint observations by SDO/AIA and STEREO/SECCHI EUVI of the source region indicate that all events classified by GOES as X-ray flares had an ejective coronal counterpart in quadrature observations. These results directly affect current space weather forecasting because alarms might be missed when there is a lack of solar observations in a view direction perpendicular to the Sun-Earth line.

  5. Relation between Thermal and Magnetic Properties of Active Regions as a Probe of Coronal Heating Mechanisms

    NASA Astrophysics Data System (ADS)

    Yashiro, Seiji; Shibata, Kazunari

    2001-03-01

    We study the relation between thermal and magnetic properties of active regions in the corona observed with the soft X-ray telescope aboard Yohkoh. We derive the mean temperature and pressure of 64 mature active regions using the filter ratio technique, and examine the relationship of region size with temperature and pressure. We find that the temperature T of active regions increases with increasing region size L as T~L0.28, while the pressure P slightly decreases with the region size as P~L-0.16. We confirm the scaling law T~(PL)1/3 for mature active regions found by R. Rosner, W. H. Tucker, & G. S. Vaiana. We examined the magnetic properties of active regions by analyzing 31 active regions observed with the Solar and Heliospheric Observatory/Michelson Doppler Imager and find the following empirical scaling law between thermal and magnetic properties,Uth~Φ1.33,P~B0.78,where Uth, Φ, and B are the total thermal energy content, total magnetic flux, and average magnetic flux density of active regions, respectively. The former is consistent with the results of L. Golub et al., but the latter is not. Implications of our findings for coronal heating mechanisms are discussed.

  6. TWO-DIMENSIONAL CELLULAR AUTOMATON MODEL FOR THE EVOLUTION OF ACTIVE REGION CORONAL PLASMAS

    SciTech Connect

    López Fuentes, Marcelo; Klimchuk, James A.

    2015-02-01

    We study a two-dimensional cellular automaton (CA) model for the evolution of coronal loop plasmas. The model is based on the idea that coronal loops are made of elementary magnetic strands that are tangled and stressed by the displacement of their footpoints by photospheric motions. The magnetic stress accumulated between neighbor strands is released in sudden reconnection events or nanoflares that heat the plasma. We combine the CA model with the Enthalpy Based Thermal Evolution of Loops model to compute the response of the plasma to the heating events. Using the known response of the X-Ray Telescope on board Hinode, we also obtain synthetic data. The model obeys easy-to-understand scaling laws relating the output (nanoflare energy, temperature, density, intensity) to the input parameters (field strength, strand length, critical misalignment angle). The nanoflares have a power-law distribution with a universal slope of –2.5, independent of the input parameters. The repetition frequency of nanoflares, expressed in terms of the plasma cooling time, increases with strand length. We discuss the implications of our results for the problem of heating and evolution of active region coronal plasmas.

  7. Two-dimensional Cellular Automaton Model for the Evolution of Active Region Coronal Plasmas

    NASA Astrophysics Data System (ADS)

    López Fuentes, Marcelo; Klimchuk, James A.

    2015-02-01

    We study a two-dimensional cellular automaton (CA) model for the evolution of coronal loop plasmas. The model is based on the idea that coronal loops are made of elementary magnetic strands that are tangled and stressed by the displacement of their footpoints by photospheric motions. The magnetic stress accumulated between neighbor strands is released in sudden reconnection events or nanoflares that heat the plasma. We combine the CA model with the Enthalpy Based Thermal Evolution of Loops model to compute the response of the plasma to the heating events. Using the known response of the X-Ray Telescope on board Hinode, we also obtain synthetic data. The model obeys easy-to-understand scaling laws relating the output (nanoflare energy, temperature, density, intensity) to the input parameters (field strength, strand length, critical misalignment angle). The nanoflares have a power-law distribution with a universal slope of -2.5, independent of the input parameters. The repetition frequency of nanoflares, expressed in terms of the plasma cooling time, increases with strand length. We discuss the implications of our results for the problem of heating and evolution of active region coronal plasmas.

  8. On the relationship between photospheric footpoint motions and coronal heating in solar active regions

    SciTech Connect

    Van Ballegooijen, A. A.; Asgari-Targhi, M.; Berger, M. A.

    2014-05-20

    Coronal heating theories can be classified as either direct current (DC) or alternating current (AC) mechanisms, depending on whether the coronal magnetic field responds quasi-statically or dynamically to the photospheric footpoint motions. In this paper we investigate whether photospheric footpoint motions with velocities of 1-2 km s{sup –1} can heat the corona in active regions, and whether the corona responds quasi-statically or dynamically to such motions (DC versus AC heating). We construct three-dimensional magnetohydrodynamic models for the Alfvén waves and quasi-static perturbations generated within a coronal loop. We find that in models where the effects of the lower atmosphere are neglected, the corona responds quasi-statically to the footpoint motions (DC heating), but the energy flux into the corona is too low compared to observational requirements. In more realistic models that include the lower atmosphere, the corona responds more dynamically to the footpoint motions (AC heating) and the predicted heating rates due to Alfvén wave turbulence are sufficient to explain the observed hot loops. The higher heating rates are due to the amplification of Alfvén waves in the lower atmosphere. We conclude that magnetic braiding is a highly dynamic process.

  9. THE ROLE OF ACTIVE REGION LOOP GEOMETRY. I. HOW CAN IT AFFECT CORONAL SEISMOLOGY?

    SciTech Connect

    Selwa, M.; Ofman, L.; Solanki, S. K. E-mail: leon.ofman@nasa.gov

    2011-01-01

    We present numerical results of coronal loop oscillation excitation using a three-dimensional (3D) MHD model of an idealized active region (AR) field. The AR is initialized as a potential dipole magnetic configuration with gravitationally stratified density and contains a loop with a higher density than its surroundings. We study different ways of excitation of vertical kink oscillations of this loop by velocity: as an initial condition, and as an impulsive excitation with a pulse of a given position, duration, and amplitude. We vary the geometry of the loop in the 3D MHD model and find that it affects both the period of oscillations and the synthetic observations (difference images) that we get from oscillations. Due to the overestimated effective length of the loop in the case of loops which have maximum separation between their legs above the footpoints (>50% of observed loops), the magnetic field obtained from coronal seismology can also be overestimated. The 3D MHD model shows how the accuracy of magnetic field strength determined from coronal seismology can be improved. We study the damping mechanism of the oscillations and find that vertical kink waves in 3D stratified geometry are damped mainly due to wave leakage in the horizontal direction.

  10. Realistic Modeling of SDO/AIA-discovered Coronal Fast MHD Wave Trains in Active Regions

    NASA Astrophysics Data System (ADS)

    Ofman, Leon; Liu, Wei

    2016-05-01

    High-resolution EUV observations by space telescopes have provided plenty of evidence for coronal MHD waves in active regions. In particular, SDO/AIA discovered quasi-periodic, fast-mode propagating MHD wave trains (QFPs), which can propagate at speeds of ~1000 km/s perpendicular to the magnetic field. Such waves can provide information on the energy release of their associated flares and the magnetized plasma structure of the active regions. Before we can use these waves as tools for coronal seismology, 3D MHD modeling is required for disentangling observational ambiguities and improving the diagnostic accuracy. We present new results of observationally contained models of QFPs using our recently upgraded radiative, thermally conductive, visco-resistive 3D MHD code. The waves are excited by time-depended boundary conditions constrained by the spatial (localized) and quasi-periodic temporal evolution of a C-class flare typically associated with QFPs. We investigate the excitation, propagation, and damping of the waves for a range of key model parameters, such as the background temperature, density, magnetic field structure, and the location of the flaring site within the active region. We synthesize EUV intensities in multiple AIA channels and then obtain the model parameters that best reproduce the properties of observed QFPs. We discuss the implications of our model results for the seismological application of QFPs and for understanding the dynamics of their associated flares.

  11. Time Evolution of Coronal Magnetic Helicity in the Flaring Active Region NOAA 10930

    NASA Astrophysics Data System (ADS)

    Park, Sung-Hong; Chae, Jongchul; Jing, Ju; Tan, Changyi; Wang, Haimin

    2010-09-01

    To study the three-dimensional (3D) magnetic field topology and its long-term evolution associated with the X3.4 flare of 2006 December 13, we investigate the coronal relative magnetic helicity in the flaring active region (AR) NOAA 10930 during the time period of December 8-14. The coronal helicity is calculated based on the 3D nonlinear force-free magnetic fields reconstructed by the weighted optimization method of Wiegelmann, and is compared with the amount of helicity injected through the photospheric surface of the AR. The helicity injection is determined from the magnetic helicity flux density proposed by Pariat et al. using Solar and Heliospheric Observatory/Michelson Doppler Imager magnetograms. The major findings of this study are the following. (1) The time profile of the coronal helicity shows a good correlation with that of the helicity accumulation by injection through the surface. (2) The coronal helicity of the AR is estimated to be -4.3 × 1043 Mx2 just before the X3.4 flare. (3) This flare is preceded not only by a large increase of negative helicity, -3.2 × 1043 Mx2, in the corona over ~1.5 days but also by noticeable injections of positive helicity through the photospheric surface around the flaring magnetic polarity inversion line during the time period of the channel structure development. We conjecture that the occurrence of the X3.4 flare is involved with the positive helicity injection into an existing system of negative helicity.

  12. TIME EVOLUTION OF CORONAL MAGNETIC HELICITY IN THE FLARING ACTIVE REGION NOAA 10930

    SciTech Connect

    Park, Sung-Hong; Jing, Ju; Wang Haimin; Chae, Jongchul; Tan, Changyi

    2010-09-10

    To study the three-dimensional (3D) magnetic field topology and its long-term evolution associated with the X3.4 flare of 2006 December 13, we investigate the coronal relative magnetic helicity in the flaring active region (AR) NOAA 10930 during the time period of December 8-14. The coronal helicity is calculated based on the 3D nonlinear force-free magnetic fields reconstructed by the weighted optimization method of Wiegelmann, and is compared with the amount of helicity injected through the photospheric surface of the AR. The helicity injection is determined from the magnetic helicity flux density proposed by Pariat et al. using Solar and Heliospheric Observatory/Michelson Doppler Imager magnetograms. The major findings of this study are the following. (1) The time profile of the coronal helicity shows a good correlation with that of the helicity accumulation by injection through the surface. (2) The coronal helicity of the AR is estimated to be -4.3 x 10{sup 43} Mx{sup 2} just before the X3.4 flare. (3) This flare is preceded not only by a large increase of negative helicity, -3.2 x 10{sup 43} Mx{sup 2}, in the corona over {approx}1.5 days but also by noticeable injections of positive helicity through the photospheric surface around the flaring magnetic polarity inversion line during the time period of the channel structure development. We conjecture that the occurrence of the X3.4 flare is involved with the positive helicity injection into an existing system of negative helicity.

  13. Time Evolution of Coronal Magnetic Helicity in the Flaring Active Region NOAA 10930

    NASA Astrophysics Data System (ADS)

    Park, Sung-Hong; Jing, J.; Wang, H.

    2010-05-01

    To study the three-dimensional (3D) magnetic field topology and its long-term (a few days) evolution associated with the X3.4 flare of 2006 December 13, we investigate the temporal evolution of the relative coronal magnetic helicity in NOAA active region (AR) 10930 during the time period of December 8, 21:20 UT through December 14, 5:00 UT. The coronal helicity is calculated based on the 3D nonlinear force-free (NLFF) magnetic fields reconstructed by the optimization method (Wheatland et al. 2000) as implemented by Wiegelmann (2004). As the boundary conditions for the force-free reconstruction, we use the preprocessed Hinode Spectropolarimeter (SP) vector magnetograms in which the net Lorentz force and the torque in the photosphere are minimized (see Wiegelmann et al. 2006 for the details). The major findings of this study are: (1) a negative (left-handed) helicity of -5×1043 Mx2 in the AR corona is estimated right before the X3.4 flare; (2) the major flare is preceded by a significantly and consistently large amount of negative helicity injection (-2×1043 Mx2) into the corona over 2 days; (3) the temporal variation of helicity is comparable to that of the rotational speed in the southern sunspot with positive polarity; (4) in general, the time profile of the coronal helicity is well-matched with that of the helicity accumulation by the time integration of the simplified helicity injection rate (Chae 2001) determined by using SOHO MDI magnetograms; (5) at the time period of the channel structure development (December 11, 4:00-8:00 UT) with newly emerging flux and just right before the C5.7 class flare, the time variation of the coronal helicity shows a rapid and huge increase of negative helicity, but that of the helicity accumulation by MDI magnetograms indicates a monotonous increase of negative helicity.

  14. Homologous Jet-driven Coronal Mass Ejections from Solar Active Region 12192

    NASA Astrophysics Data System (ADS)

    Panesar, Navdeep K.; Sterling, Alphonse C.; Moore, Ronald L.

    2016-05-01

    We report observations of homologous coronal jets and their coronal mass ejections (CMEs) observed by instruments onboard the Solar Dynamics Observatory (SDO) and the Solar and Heliospheric Observatory (SOHO) spacecraft. The homologous jets originated from a location with emerging and canceling magnetic field at the southeastern edge of the giant active region (AR) of 2014 October, NOAA 12192. This AR produced in its interior many non-jet major flare eruptions (X- and M- class) that made no CME. During October 20 to 27, in contrast to the major flare eruptions in the interior, six of the homologous jets from the edge resulted in CMEs. Each jet-driven CME (∼200–300 km s‑1) was slower-moving than most CMEs, with angular widths (20°–50°) comparable to that of the base of a coronal streamer straddling the AR and were of the “streamer-puff” variety, whereby the preexisting streamer was transiently inflated but not destroyed by the passage of the CME. Much of the transition-region-temperature plasma in the CME-producing jets escaped from the Sun, whereas relatively more of the transition-region plasma in non-CME-producing jets fell back to the solar surface. Also, the CME-producing jets tended to be faster and longer-lasting than the non-CME-producing jets. Our observations imply that each jet and CME resulted from reconnection opening of twisted field that erupted from the jet base and that the erupting field did not become a plasmoid as previously envisioned for streamer-puff CMEs, but instead the jet-guiding streamer-base loop was blown out by the loop’s twist from the reconnection.

  15. Photospheric and Coronal Observations of Abrupt Magnetic Restructuring in Two Flaring Active Regions

    NASA Astrophysics Data System (ADS)

    Petrie, Gordon

    2016-05-01

    For two major X-class flares observed by the Solar Dynamics Observatory (SDO) and the Solar TErrestrial RElations Observatory Ahead (STEREO-A) spacecraft when they were close to quadrature, we compare major, abrupt changes in the photospheric magnetic vector field to changes in the observed coronal magnetic structure during the two flares. The Lorentz force changes in strong photospheric fields within active regions are estimated from time series of SDO Helioseismic and Magnetic Imager (HMI) vector magnetograms. These show that the major changes occurred in each case near the main neutral line of the region and in two neighboring twisted opposite-polarity sunspots. In each case the horizontal parallel field strengthened significantly near the neutral line while the azimuthal field in the sunspots decreased, suggesting that a flux rope joining the two sunspots collapsed across the neutral line with reduced magnetic pressure because of a reduced field twist component. At the same time, the coronal extreme ultraviolet (EUV) loop structure was observed by the Atmospheric Imaging Assembly (AIA) onboard SDO and the Extreme Ultraviolet Imager (EUVI) on STEREO-A to decrease significantly in height during each eruption, discontinuous changes signifying ejection of magnetized plasma, and outward-propagating continuous but abrupt changes consistent with loop contraction. An asymmetry in the observed EUV loop changes during one of the flares matches an asymmetry in the photospheric magnetic changes associated with that flare. The observations are discussed in terms of the well-known tether-cutting and breakout flare initiation models.

  16. Photospheric and Coronal Observations of Abrupt Magnetic Restructuring in Two Flaring Active Regions

    NASA Astrophysics Data System (ADS)

    Petrie, G. J. D.

    2016-03-01

    For two major X-class flares observed by the Solar Dynamics Observatory (SDO) and the Solar TErrestrial RElations Observatory Ahead (STEREO-A) spacecraft when they were close to quadrature, we compare major, abrupt changes in the photospheric magnetic vector field to changes in the observed coronal magnetic structure during the two flares. The Lorentz force changes in strong photospheric fields within active regions are estimated from time series of SDO Helioseismic and Magnetic Imager (HMI) vector magnetograms. These show that the major changes occurred in each case near the main neutral line of the region and in two neighboring twisted opposite-polarity sunspots. In each case the horizontal parallel field strengthened significantly near the neutral line while the azimuthal field in the sunspots decreased, suggesting that a flux rope joining the two sunspots collapsed across the neutral line with reduced magnetic pressure because of a reduced field twist component. At the same time, the coronal extreme ultraviolet (EUV) loop structure was observed by the Atmospheric Imaging Assembly (AIA) onboard SDO and the Extreme Ultraviolet Imager (EUVI) on STEREO-A to decrease significantly in height during each eruption, discontinuous changes signifying ejection of magnetized plasma, and outward-propagating continuous but abrupt changes consistent with loop contraction. An asymmetry in the observed EUV loop changes during one of the flares matches an asymmetry in the photospheric magnetic changes associated with that flare. The observations are discussed in terms of the well-known tether-cutting and breakout flare initiation models.

  17. Doppler shift of hot coronal lines in a moss area of an active region

    NASA Astrophysics Data System (ADS)

    Dadashi, N.; Teriaca, L.; Tripathi, D.; Solanki, S. K.; Wiegelmann, T.

    2012-12-01

    The moss is the area at the footpoint of the hot (3 to 5 MK) loops forming the core of the active region where emission is believed to result from the heat flux conducted down to the transition region from the hot loops. Studying the variation of Doppler shift as a function of line formation temperatures over the moss area can give clues on the heating mechanism in the hot loops in the core of the active regions. We investigate the absolute Doppler shift of lines formed at temperatures between 1 MK and 2 MK in a moss area within active region NOAA 11243 using a novel technique that allows determining the absolute Doppler shift of EUV lines by combining observations from the SUMER and EIS spectrometers. The inner (brighter and denser) part of the moss area shows roughly constant blue shift (upward motions) of 5 km s-1 in the temperature range of 1 MK to 1.6 MK. For hotter lines the blue shift decreases and reaches 1 km s-1 for Fe xv 284 Å (~2 MK). The measurements are discussed in relation to models of the heating of hot loops. The results for the hot coronal lines seem to support the quasi-steady heating models for nonsymmetric hot loops in the core of active regions.

  18. Study of the Photospheric Magnetic Field and Coronal Emission from Solar Active Regions

    NASA Astrophysics Data System (ADS)

    Aguilera, Jordan Armando Guerra

    2016-01-01

    Solar explosive phenomena (flares and Coronal Mass Ejections, CMEs) are examples of how the most dynamical processes within the heliosphere are interconnected and powered by the Sun. Solar flares originate in active regions (AR) -- areas of strong magnetic field on the solar surface. The electromagnetic (EM) energy released during flares, along with the often-seen CMEs, propagate through the heliosphere. In the Earth's vicinity, EM radiation and charged particles have the potential to produce unfavorable conditions for humans and technology in space. From many points of view (scientific, operational, economical) it is thus important to understand and try to predict when solar flares and associated eruptive phenomena will occur. This dissertation explores how to best leverage the available observational data to provide predictive information about the future flaring activity. This dissertation consists of two main components: 1) investigation of the photosphere-corona coupling by analyzing photospheric magnetic field and coronal data in search for signals or behaviors that precede eruptions; and 2) the combination of existing flare prediction methods in order to develop a novel ensemble prediction. For the first part, the data employed correspond to line-of-sight (LOS) magnetograms from the Helioseismic and Magnetic Imager (HMI) and EUV intensity maps from the Atmospheric Imaging Assembly (AIA), both instruments onboard NASA's Solar Dynamics Observatory (SDO) satellite. Photospheric magnetic field and coronal EUV emissions were characterized by measuring the power-law decay of their spatio-temporal spectra and the data statistical associations (auto- and cross-correlations). These measures, calculated with high spatio-temporal resolution, appeared to characterize the AR evolution, provide information about the state of the photospheric plasma, reveal insights into the photospheric conditions for flares, and expose the potential of combining coronal and photospheric

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

    We present observations of eruptive events in an active region adjacent to an on-disk coronal hole on 2012 June 30, primarily using data from the Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA), SDO/Helioseismic and Magnetic Imager (HMI), and STEREO-B. One eruption is of a large-scale (∼100″) filament that is typical of other eruptions, showing slow-rise onset followed by a faster-rise motion starting as flare emissions begin. It also shows an “EUV crinkle” emission pattern, resulting from magnetic reconnections between the exploding filament-carrying field and surrounding field. Many EUV jets, some of which are surges, sprays and/or X-ray jets, also occur in localized areas of the active region. We examine in detail two relatively energetic ones, accompanied by GOES M1 and C1 flares, and a weaker one without a GOES signature. All three jets resulted from small-scale (∼20″) filament eruptions consistent with a slow rise followed by a fast rise occurring with flare-like jet-bright-point brightenings. The two more-energetic jets showed crinkle patters, but the third jet did not, perhaps due to its weakness. Thus all three jets were consistent with formation via erupting minifilaments, analogous to large-scale filament eruptions and to X-ray jets in polar coronal holes. Several other energetic jets occurred in a nearby portion of the active region; while their behavior was also consistent with their source being minifilament eruptions, we could not confirm this because their onsets were hidden from our view. Magnetic flux cancelation and emergence are candidates for having triggered the minifilament eruptions.

  20. Jets, Coronal “Puffs,” and a Slow Coronal Mass Ejection Caused by an Opposite-polarity Region within an Active Region Footpoint

    NASA Astrophysics Data System (ADS)

    Alzate, N.; Morgan, H.

    2016-06-01

    During a period of three days beginning 2013 January 17, twelve recurrent reconnection events occur within a small region of opposing flux embedded within one footpoint of an active region, accompanied by flares and jets observed in EUV and fast and faint structureless “puffs” observed by coronagraphs. During the same period a slow structured CME gradually erupts, with one end anchored close to, or within, the jetting region. Four of the jet events occur in pairs—a narrow, primary jet followed within a few tens of minutes by a wider, more massive, jet. All the jets are slow, with an apparent speed of ∼100 km s‑1. The speed of the wide puffs in the coronagraph data is ∼300 km s‑1, and the timing of their appearance rules out a direct association with the EUV jetting material. The jet material propagates along large-scale closed-field loops and does not escape to the extended corona. The rapid reconfiguration of the closed loops following reconnection causes an outwardly propagating disturbance, or wave front, which manifests as puffs in coronagraph data. Furthermore, the newly expanded closed flux tube forms a pressure imbalance, which can result in a secondary jet. The reconnection events, through recurrent field reconfiguration, also leads to the gradual eruption of the structured flux tube appearing as the slow CME. Faint propagating coronal disturbances resulting from flares/jets may be common, but are usually obscured by associated ejections. Occasionally, the associated material ejections are absent, and coronal puffs may be clearly observed.

  1. Characteristics of Anemone Active Regions Appearing in Coronal Holes Observed with the Yohkoh Soft X-Ray Telescope

    NASA Astrophysics Data System (ADS)

    Asai, Ayumi; Shibata, Kazunari; Hara, Hirohisa; Nitta, Nariaki V.

    2008-02-01

    Coronal structure of active regions appearing in coronal holes is studied, using data that were obtained with the Soft X-Ray Telescope (SXT) aboard Yohkoh between 1991 November and 1993 March. The following characteristics are found. Many of the active regions (ARs) appearing in coronal holes show a structure that looks like a sea anemone. Such active regions are called anemone ARs. About one-fourth of all active regions that were observed with SXT from their births showed the anemone structure. For almost all the anemone ARs, the order of the magnetic polarities is consistent with the Hale-Nicholson polarity law. These anemone ARs also showed, to a greater or lesser extent, an east-west asymmetry in the X-ray intensity distribution, such that the following (eastern) part of the AR was brighter than its preceding (western) part. This, as well as the anemone shape itself, is consistent with the magnetic polarity distribution around the anemone ARs. These observations also suggest that an active region appearing in coronal holes has a simpler (less sheared) and more preceding-spot-dominant magnetic structure than those appearing in other regions.

  2. Modelling nanoflares in active regions and implications for coronal heating mechanisms.

    PubMed

    Cargill, P J; Warren, H P; Bradshaw, S J

    2015-05-28

    Recent observations from the Hinode and Solar Dynamics Observatory spacecraft have provided major advances in understanding the heating of solar active regions (ARs). For ARs comprising many magnetic strands or sub-loops heated by small, impulsive events (nanoflares), it is suggested that (i) the time between individual nanoflares in a magnetic strand is 500-2000 s, (ii) a weak 'hot' component (more than 10(6.6) K) is present, and (iii) nanoflare energies may be as low as a few 10(23) ergs. These imply small heating events in a stressed coronal magnetic field, where the time between individual nanoflares on a strand is of order the cooling time. Modelling suggests that the observed properties are incompatible with nanoflare models that require long energy build-up (over 10 s of thousands of seconds) and with steady heating. PMID:25897093

  3. Modelling nanoflares in active regions and implications for coronal heating mechanisms

    PubMed Central

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

    2015-01-01

    Recent observations from the Hinode and Solar Dynamics Observatory spacecraft have provided major advances in understanding the heating of solar active regions (ARs). For ARs comprising many magnetic strands or sub-loops heated by small, impulsive events (nanoflares), it is suggested that (i) the time between individual nanoflares in a magnetic strand is 500–2000 s, (ii) a weak ‘hot’ component (more than 106.6 K) is present, and (iii) nanoflare energies may be as low as a few 1023 ergs. These imply small heating events in a stressed coronal magnetic field, where the time between individual nanoflares on a strand is of order the cooling time. Modelling suggests that the observed properties are incompatible with nanoflare models that require long energy build-up (over 10 s of thousands of seconds) and with steady heating. PMID:25897093

  4. Extraction of Active Regions and Coronal Holes from EUV Images Using the Unsupervised Segmentation Method in the Bayesian Framework

    NASA Astrophysics Data System (ADS)

    Arish, S.; Javaherian, M.; Safari, H.; Amiri, A.

    2016-04-01

    The solar corona is the origin of very dynamic events that are mostly produced in active regions (AR) and coronal holes (CH). The exact location of these large-scale features can be determined by applying image-processing approaches to extreme-ultraviolet (EUV) data.

  5. Correlation of Coronal Plasma Properties and Solar Magnetic Field in a Decaying Active Region

    NASA Astrophysics Data System (ADS)

    Ko, Yuan-Kuen; Young, Peter R.; Muglach, Karin; Warren, Harry P.; Ugarte-Urra, Ignacio

    2016-08-01

    We present the analysis of a decaying active region observed by the EUV Imaging Spectrometer on Hinode during 2009 December 7–11. We investigated the temporal evolution of its structure exhibited by plasma at temperatures from 300,000 to 2.8 million degrees, and derived the electron density, differential emission measure, effective electron temperature, and elemental abundance ratios of Si/S and Fe/S (as a measure of the First Ionization Potential (FIP) Effect). We compared these coronal properties to the temporal evolution of the photospheric magnetic field strength obtained from the Solar and Heliospheric Observatory Michelson Doppler Imager magnetograms. We find that, while these coronal properties all decreased with time during this decay phase, the largest change was at plasma above 1.5 million degrees. The photospheric magnetic field strength also decreased with time but mainly for field strengths lower than about 70 Gauss. The effective electron temperature and the FIP bias seem to reach a “basal” state (at 1.5 × 106 K and 1.5, respectively) into the quiet Sun when the mean photospheric magnetic field (excluding all areas <10 G) weakened to below 35 G, while the electron density continued to decrease with the weakening field. These physical properties are all positively correlated with each other and the correlation is the strongest in the high-temperature plasma. Such correlation properties should be considered in the quest for our understanding of how the corona is heated. The variations in the elemental abundance should especially be considered together with the electron temperature and density.

  6. Coronal Magnetography of a Simulated Solar Active Region from Microwave Imaging Spectropolarimetry

    NASA Astrophysics Data System (ADS)

    Wang, Zhitao; Gary, Dale E.; Fleishman, Gregory D.; White, Stephen M.

    2015-06-01

    We have simulated the Expanded Owens Valley Solar Array (EOVSA) radio images generated at multiple frequencies from a model solar active region, embedded in a realistic solar disk model, and explored the resulting data cube for different spectral analysis schemes to evaluate the potential for realizing one of EOVSA’s most important scientific goals—coronal magnetography. In this paper, we focus on modeling the gyroresonance and free-free emission from an on-disk solar active region model with realistic complexities in electron density, temperature and magnetic field distribution. We compare the magnetic field parameters extrapolated from the image data cube along each line of sight after folding through the EOVSA instrumental profile with the original (unfolded) parameters used in the model. We find that even the most easily automated, image-based analysis approach (Level-0) provides reasonable quantitative results, although they are affected by systematic effects due to finite sampling in the Fourier (UV) plane. Finally, we note the potential for errors due to misidentified harmonics of the gyrofrequency, and discuss the prospects for applying a more sophisticated spectrally based analysis scheme (Level-1) to resolve the issue in cases where improved UV coverage and spatial resolution are available.

  7. Photospheric and Coronal Observations of Abrupt Magnetic Restructuring in Flaring Active Regions

    NASA Astrophysics Data System (ADS)

    Petrie, G. J. D.

    2015-12-01

    The Lorentz force changes associated with strong photospheric fields in large structures within active regions can be estimated from time series of Solar Dynamics Observatory (SDO) Helioseismic and Magnetic Imager (HMI) vector magnetograms. The major, most organized changes tend to occur close to the centers of flaring regions, near the main neutral line and/or in twisted sunspots. Fields close to the neutral line tend to collapse downward and inward, consistent with compression rather than rotation of the vector field. In sunspots the twist (or azimuthal component around the sunspot axis) tends to decrease. In a limited number of cases particularly well-observed by the Atmospheric Imaging Assembly (AIA) on SDO and the Extreme Ultraviolet Imager (EUVI) on the Solar TErrestrial RElations Observatory (STEREO), the evolution of the photospheric magnetic vector field can be related to changes in coronal magnetic structure to provide a coherent description of the magnetic changes during the different phases of a flare. This work was supported by NASA grant NNX14AE05G.

  8. SERTS-95 Measurements of Wavelength Shifts in Coronal Emission Lines Across a Solar Active Region

    NASA Technical Reports Server (NTRS)

    Brosius, Jeffery W.; Thomas, Roger; Davila, Joseph

    1999-01-01

    We used slit spectra from the 1995 flight of Goddard Space Flight Center's Solar EUV Rocket Telescope and Spectrograph (SERTS-95) to measure wavelength shifts of coronal emission lines in the core of NOAA active region 7870 relative to its immediate surroundings (its "edge"). This method circumvents the unavailability of reliable laboratory rest wavelengths for the observed lines by using wavelengths from the edge spectrum as references. We derived the, SERTS-95 wavelength calibration from measurements of a post-flight laboratory spectrum containing 28 He II and Ne II EUV standard wavelengths known to high accuracy. Wavelength measurements for lines of He I, Ne III, and additional lines of Ne II in the laboratory calibration spectrum provide more accurate values than were previously available, enabling these lines also to serve as future calibration standards. Six solar lines were chosen for this study, namely, He II at 303.78 A, Fe XII at 193.51 A, Fe XIII at 202.05 A, Fe XIV at 211.33 A, Fe XV at 284.15 A, and Fe XVI at 335.41 A. Because these lines are free from known blends in the SERTS-95 spectra and are either intrinsically strong or near the SERTS-95 peak sensitivity, they are our most reliable lines for measuring relative wavelength shifts in the spatially resolved active region core spectra. The iron ions are the hottest ions ever used for this type of analysis. All six lines reveal statistically significant spatial variations in their measured relative wavelength shifts in the active region core, including mixtures of blueshifts and redshifts (each with maximum values corresponding to relative Doppler velocities approximately 15 km/s), indicating a dynamic, turbulent corona. For each of these lines we calculated weighted-average relative Doppler velocities from the wavelength shifts in the spatially resolved core spectra by weighting the shifts in the individual spatial pixels with their respective measurement uncertainties.

  9. WAITING TIMES OF QUASI-HOMOLOGOUS CORONAL MASS EJECTIONS FROM SUPER ACTIVE REGIONS

    SciTech Connect

    Wang Yuming; Liu Lijuan; Shen Chenglong; Liu Rui; Ye Pinzhong; Wang, S.

    2013-02-01

    Why and how do some active regions (ARs) frequently produce coronal mass ejections (CMEs)? These are key questions for deepening our understanding of the mechanisms and processes of energy accumulation and sudden release in ARs and for improving our space weather prediction capability. Although some case studies have been performed, these questions are still far from fully answered. These issues are now being addressed statistically through an investigation of the waiting times of quasi-homologous CMEs from super ARs in solar cycle 23. It is found that the waiting times of quasi-homologous CMEs have a two-component distribution with a separation at about 18 hr. The first component is a Gaussian-like distribution with a peak at about 7 hr, which indicates a tight physical connection between these quasi-homologous CMEs. The likelihood of two or more occurrences of CMEs faster than 1200 km s{sup -1} from the same AR within 18 hr is about 20%. Furthermore, the correlation analysis among CME waiting times, CME speeds, and CME occurrence rates reveals that these quantities are independent of each other, suggesting that the perturbation by preceding CMEs rather than free energy input is the direct cause of quasi-homologous CMEs. The peak waiting time of 7 hr probably characterizes the timescale of the growth of the instabilities triggered by preceding CMEs. This study uncovers some clues from a statistical perspective for us to understand quasi-homologous CMEs as well as CME-rich ARs.

  10. Reconstruction of the solar coronal magnetic field, from active region to large scale

    NASA Astrophysics Data System (ADS)

    Amari, T.; Canou, A.; Delyon, F.; Aly, J. J.; Frey, P.; Alauzet, F.

    2011-12-01

    The low solar corona is dominated by the magnetic field which is created inside the sun by a dynamo process and then emerges into the atmosphere. This magnetic field plays an important role in most structures and phenomena observed at various wavelengths such as prominences, small and large scale eruptive events, and continuous heating of the plasma, and therefore it is important to understand its three-dimensional properties in order to elaborate efficient theoretical models. Unfortunately, the magnetic field is difficult to measure locally in the hot and tenuous corona. But this can be done at the level of the cooler and denser photosphere, and several instruments with high resolution vector magnetographs are currently available (THEMIS, Imaging Vector Magnetograph (IVM), the Advanced Stokes Polarimeter (ASP), SOLIS, HINODE, Solar Dynamics Observatory (SDO), or will be shortly available by future telescopes such as EST and solar missions as SOLAR-ORBITER. This has lead solar physicists to develop an approach which consists in " reconstructing" the coronal magnetic field from boundary data given on the photosphere. We will discuss some of the issues encountered in solving this problem as well our recent progress and results at the scale of active region scales or the larger one such as full sun scale.

  11. Cluster of solar active regions and onset of coronal mass ejections

    NASA Astrophysics Data System (ADS)

    Wang, JingXiu; Zhang, YuZong; He, Han; Chen, AnQin; Jin, ChunLan; Zhou, GuiPing

    2015-09-01

    Abstract round-the-clock solar observations with full-disk coverage of vector magnetograms and multi-wavelength images demonstrate that solar active regions (ARs) are ultimately connected with magnetic field. Often two or more ARs are clustered, creating a favorable magnetic environment for the onset of coronal mass ejections (CMEs). In this work, we describe a new type of magnetic complex: cluster of solar ARs. An AR cluster is referred to as the close connection of two or more ARs which are located in nearly the same latitude and a narrow span of longitude. We illustrate three examples of AR clusters, each of which has two ARs connected and formed a common dome of magnetic flux system. They are clusters of NOAA (i.e., National Oceanic and Atmospheric Administration) ARs 11226 & 11227, 11429 & 11430, and 11525 & 11524. In these AR clusters, CME initiations were often tied to the instability of the magnetic structures connecting two partner ARs, in the form of inter-connecting loops and/or channeling filaments between the two ARs. We show the evidence that, at least, some of the flare/CMEs in an AR cluster are not a phenomenon of a single AR, but the result of magnetic interaction in the whole AR cluster. The observations shed new light on understanding the mechanism(s) of solar activity. Instead of the simple bipolar topology as suggested by the so-called standard flare model, a multi-bipolar magnetic topology is more common to host the violent solar activity in solar atmosphere.

  12. Study of Quasi-Homologous Coronal Mass Ejections from Super Active Regions in Solar Cycle 23

    NASA Astrophysics Data System (ADS)

    Liu, L.; Wang, Y.; Shen, C.; Liu, R.; Ye, P.; Wang, S.

    2014-12-01

    Coronal Mass Ejections are most severe eruptive phenomenon in the solar atmosphere and are believed as the major energy source of the Near-Earth Space Environment. The study of CMEs is very important for the Space Weather forecast. The active regions , especially super-active regions, containing lots of magnetic free energy, are considered as the most important source regions of CMEs. Knowing why and how may some active regions (ARs) frequently produce CMEs is one of the key questions to deepen our understanding of the mechanisms and processes of energy accumulation and sudden release in ARs as well as improving our capability of space weather prediction. Based on above, we have done two parts of work: the first one is selecting all 37 SARs in the entire 23 solar cycle, using data provided by SOHO/LASCO C2|EIT|MDI, manually determining 285 CMEs produced by those SARs; second, we use the term 'quasi-homologous'to refer to successive CMEs originating from the same ARs within a short interval, analyze the rules of quasi-homologous CMEs' generation. Finally, we got two conclusions. 1. The waiting times of quasi-homologous CMEs have a two-component distribution with a separation at about 18 hours. The first component is a Gaussian-like distribution with a peak at about 7 hours, which indicates a tight physical connection between these quasi-homologous CMEs. The likelihood of occurrences of two or more CMEs faster than 1200 km /s from the same AR within 18 hours is about 20%. 2. The correlation analysis among CME waiting times, CME speeds and CME occurrence rates reveals that these quantities are independent to each other, suggesting that the perturbation by preceding CMEs rather than free energy input be the direct cause of quasi-homologous CMEs. The peak waiting time of 7 hours probably characterize the time scale of the growth of instabilities triggered by preceding CMEs. This study uncovers more clues from a statistical perspective for us to understand quasi

  13. Ephemeral active regions and coronal bright points: A solar maximum Mission 2 guest investigator study

    NASA Technical Reports Server (NTRS)

    Harvey, K. L.; Tang, F. Y. C.; Gaizauskas, V.; Poland, A. I.

    1986-01-01

    A dominate association of coronal bright points (as seen in He wavelength 10830) was confirmed with the approach and subsequent disappearance of opposite polarity magnetic network. While coronal bright points do occur with ephemeral regions, this association is a factor of 2 to 4 less than with sites of disappearing magnetic flux. The intensity variations seen in He I wavelength 10830 are intermittent and often rapid, varying over the 3 minute time resolution of the data; their bright point counterparts in the C IV wavelength 1548 and 20 cm wavelength show similar, though not always coincident time variations. Ejecta are associated with about 1/3 of the dark points and are evident in the C IV and H alpha data. These results support the idea that the anti-correlation of X-ray bright points with the solar cycle can be explained by the correlation of these coronal emission structures with sites of cancelling flux, indicating that, in some cases, the process of magnetic flux removal results in the release of energy. That the intensity variations are rapid and variable suggests that this process works intermittently.

  14. An investigation of coronal active region loop structures using AS&E rocket X-ray images

    NASA Technical Reports Server (NTRS)

    Webb, D. F.

    1983-01-01

    Simultaneous high spatial resolution observations at 6 cm in soft X-rays, in photospheric magnetograms, and in optical filtergrams were used to compare the most intense sources of centimetric emission in two active regions to coronal loops, sunspots, chromospheric structures, and photospheric magnetic fields. Results show that the majority of the bright microwave components are not associated with sunspots or X-ray emission. A nonthermal mechanism appears necessary to explain the brightest microwave components, discrete regions of continuous particle acceleration may be common in active regions. Studies of the plasma parameters of selected loops imply that the radio emission is consistent with gyro-resonance absorption at the third and fourth harmonic, at least from part of each loop. Results are presented for: (1) X-ray and microwave observations of active regions; (2) comparison of coronal holes observed in soft X-rays and Hel 10830 A spectrosheliograms; and (3) the reappearance of polar coronal holes and the evolution of the solar magnetic field.

  15. Coronal and transition-region Doppler shifts of an active region 3D-MHD model as indicator for the magnetic activity cycle of solar-like stars

    NASA Astrophysics Data System (ADS)

    Bourdin, Philippe A.

    2015-08-01

    For the Sun and solar-like stars, Doppler blueshifts are observed in the hot corona, while in average redshifts are seen in the cooler transition region layer below the corona. This clearly contradicts the idea of a continuous flow-equilibrium starting from a star's atmosphere and forming the stellar wind. To explain this, we implement a 3D-MHD model of the solar corona above an observed active region and use an atomic database to obtain the emission from the million Kelvin hot plasma. The generated EUV-bright loops system from the model compares well to the observed coronal loops. Therefore, we have access to realistic plasma parameters, including the flow dynamics within the active region core, and can derive total spectra as if we look the Sun as a star. We compare the model spectra to actual statistical observations of the Sun taken at different magnetic activity levels. We find characteristic Doppler-shift statistics that can be used to identify the magnetic activity state of the Sun and solar-like stars. This should help to model the variability of such stars by inferring their activity level from total spectra of coronal and transition-region emission lines.

  16. Determination of filling factors of Active Regions, Coronal Holes and Quiet Sun for the EIT archive 1997-2011

    NASA Astrophysics Data System (ADS)

    Verbeeck, Cis; Delouille, Veronique; De Visscher, Ruben; Mampaey, Benjamin; Haberreiter, Margit

    2013-04-01

    In previous work, we have proposed a multi-channel unsupervised spatially-constrained multichannel fuzzy clustering algorithm (SPoCA) that automatically segments EUV solar images into Active Regions (AR), Coronal Holes (CH), and Quiet Sun (QS). This algorithm has been running in near real time on AIA data as part of the SDO Feature Finding Team Project since 2010, populating the Heliophysics Events Knowledgebase (HEK) with Active Region and Coronal Hole events. After having corrected for the limb brightening effect, SPoCA computes an optimal clustering with respect to the regions of interest using fuzzy segmentation. The process is fast and automatic. Morphological dilation is employed to assemble neighboring bright AR cores into individual AR regions. Combining SPoCA's detection of AR, and CH on subsequent images allows automatic tracking and naming of any region of interest. We applied SPOCA on SOHO-EIT, SECCHI-EUVI, PROBA2-SWAP, and SDO-AIA, and show in particular the filling factors of AR/QS/CH as well as AR and CH mean intensity time series obtained from the full dataset of synoptic SOHO/EIT images taken between 1997 and 2011. Such segmentation can be used for several applications. Filling factors or AR, QS, and CH can be included into (semi-) empirical models of the solar atmosphere, which can in turn feed models of solar EUV irradiance. Another application is the investigation of active longitudes as well as long-term statistical studies of AR and CH parameters.

  17. Using coronal loops to reconstruct the magnetic field of an active region before and after a major flare

    SciTech Connect

    Malanushenko, A.; Schrijver, C. J.; DeRosa, M. L.; Wheatland, M. S.

    2014-03-10

    The shapes of solar coronal loops are sensitive to the presence of electrical currents that are the carriers of the non-potential energy available for impulsive activity. We use this information in a new method for modeling the coronal magnetic field of active region (AR) 11158 as a nonlinear force-free field (NLFFF). The observations used are coronal images around the time of major flare activity on 2011 February 15, together with the surface line-of-sight magnetic field measurements. The data are from the Helioseismic and Magnetic Imager and Atmospheric Imaging Assembly on board the Solar Dynamics Observatory. The model fields are constrained to approximate the coronal loop configurations as closely as possible, while also being subject to the force-free constraints. The method does not use transverse photospheric magnetic field components as input and is thereby distinct from methods for modeling NLFFFs based on photospheric vector magnetograms. We validate the method using observations of AR 11158 at a time well before major flaring and subsequently review the field evolution just prior to and following an X2.2 flare and associated eruption. The models indicate that the energy released during the instability is about 1 × 10{sup 32} erg, consistent with what is needed to power such a large eruptive flare. Immediately prior to the eruption, the model field contains a compact sigmoid bundle of twisted flux that is not present in the post-eruption models, which is consistent with the observations. The core of that model structure is twisted by ≈0.9 full turns about its axis.

  18. Coronal Loop Mapping to Infer the Best Magnetic Field Models for Active Region Prominences

    NASA Astrophysics Data System (ADS)

    Gary, G. Allen; Hu, Qiang; Lee, Jong Kwan

    2014-01-01

    This article comments on the results of a new, rapid, and flexible manual method to map on-disk individual coronal loops of a two-dimensional EUV image into the three-dimensional coronal loops. The method by Gary, Hu, and Lee (2013) employs cubic Bézier splines to map coronal loops using only four free parameters per loop. A set of 2D splines for coronal loops is transformed to the best 3D pseudo-magnetic field lines for a particular coronal model. The results restrict the magnetic field models derived from extrapolations of magnetograms to those admissible and inadmissible via a fitness parameter. This method uses the minimization of the misalignment angles between the magnetic field model and the best set of 3D field lines that match a set of closed coronal loops. We comment on the implication of the fitness parameter in connection with the magnetic free energy and comment on extensions of our earlier work by considering the issues of employing open coronal loops or employing partial coronal loop.

  19. The Fundamental Physical Processes Producing and Controlling Stellar Coronal/ Transition-Region/Chromospheric Activity and Structure

    NASA Technical Reports Server (NTRS)

    Ayres, Thomas R.; Brown, Alexander

    1998-01-01

    Our LTSA grant supports a long-term collaborative investigation of stellar activity. The project involves current NASA spacecraft and supporting ground-based telescopes, will make use of future missions, and utilizes the extensive archives of IUE, ROSAT, HST, and EUVE. Our interests include observational work (with a nonnegligible groundbased component); specialized processing techniques for imaging and spectral data; and semiempirical modeling, ranging from optically-thin emission measure studies to simulations of optically-thick resonance lines. Collaborations with our cool-star colleagues here in Boulder (at JILA and the High Altitude Observatory) provide access to even broader expertise, particularly on the solar corona, convection, and magnetohydrodynamic phenomena (including "dynamo" theories). The broad-brush of our investigation include the following: (1) where do coronae occur in the Hertzsprung-Russell diagram? (2) the winds of coronal stars: hot, cool, or both? (3) age, activity, rotation relations; (4) atmospheric inhomogeneities; and (5) heating mechanisms, subcoronal flows and flares. Our observation task has been to map the global properties of chromospheres and coronae in the H-R diagram and conduct detailed studies of key objects.

  20. 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).

  1. CORONAL HEATING BY THE INTERACTION BETWEEN EMERGING ACTIVE REGIONS AND THE QUIET SUN OBSERVED BY THE SOLAR DYNAMICS OBSERVATORY

    SciTech Connect

    Zhang, Jun; Zhang, Bin; Li, Ting; Yang, Shuhong; Zhang, Yuzong; Li, Leping; Chen, Feng; Peter, Hardi E-mail: liting@nao.cas.cn E-mail: yuzong@nao.cas.cn E-mail: chen@mps.mpg.de

    2015-02-01

    The question of what heats the solar corona remains one of the most important puzzles in solar physics and astrophysics. Here we report Solar Dynamics Observatory Atmospheric Imaging Assembly observations of coronal heating by the interaction between emerging active regions (EARs) and the surrounding quiet Sun (QS). The EARs continuously interact with the surrounding QS, resulting in dark ribbons which appear at the boundary of the EARs and the QS. The dark ribbons visible in extreme-ultraviolet wavelengths propagate away from the EARs with speeds of a few km s{sup −1}. The regions swept by the dark ribbons are brightening afterward, with the mean temperature increasing by one quarter. The observational findings demonstrate that uninterrupted magnetic reconnection between EARs and the QS occurs. When the EARs develop, the reconnection continues. The dark ribbons may be the track of the interface between the reconnected magnetic fields and the undisturbed QS’s fields. The propagating speed of the dark ribbons reflects the reconnection rate and is consistent with our numerical simulation. A long-term coronal heating which occurs in turn from nearby the EARs to far away from the EARs is proposed.

  2. Diagnostics of coronal heating and mechanisms of energy transport from IRIS and AIA observations of active region moss

    NASA Astrophysics Data System (ADS)

    Testa, Paola; Reale, Fabio; De Pontieu, Bart; Hansteen, Viggo; Carlsson, Mats; Allred, Joel; Daw, Adrian

    The variability of emission of the "moss", i.e., the upper transition region (TR) layer of high pressure loops in active regions provides stringent constraints on the characteristics of heating events. The Interface Region Imaging Spectrograph (IRIS), launched in June 2013, provides imaging and spectral observations at high spatial (0.166 arcsec/pix), and temporal (down to ~1s) resolution at FUV and NUV wavelengths, and together with the high spatial and temporal resolution observations of SDO/AIA, can provide important insights into the coronal heating mechanisms. We present here an analysis of the temporal variability properties of moss regions at the footpoints of hot active region core loops undergoing heating, as observed by IRIS and AIA, covering emission from the corona to the transition region and the chromosphere. We model the observations using dynamic loop models (the Palermo-Harvard code, and RADYN, which also includes the effects of non-thermal particles) and discuss the implications on energy transport mechanisms (thermal conduction vs beams of non-thermal particles).

  3. Diagnostics of coronal heating and mechanisms of energy transport from IRIS and AIA observations of active region moss

    NASA Astrophysics Data System (ADS)

    Testa, Paola; De Pontieu, Bart; Allred, Joel C.; Carlsson, Mats; Reale, Fabio; Daw, Adrian N.; Hansteen, Viggo

    2014-06-01

    The variability of emission of the "moss", i.e., the upper transition region (TR) layer of high pressure loops in active regions provides stringent constraints on the characteristics of heating events. The Interface Region Imaging Spectrograph (IRIS), launched in June 2013, provides imaging and spectral observations at high spatial (0.166 arcsec/pix), and temporal (down to ~1s) resolution at FUV and NUV wavelengths, and together with the high spatial and temporal resolution observations of SDO/AIA, can provide important insights into the coronal heating mechanisms. We present here an analysis of the temporal variability properties of moss regions at the footpoints of hot active region core loops undergoing heating, as observed by IRIS and AIA, covering emission from the corona to the transition region and the chromosphere. We model the observations using dynamic loop models (the Palermo-Harvard code, and RADYN, which also includes the effects of non-thermal particles) and discuss the implications on energy transport mechanisms (thermal conduction vs beams of non-thermal particles).

  4. Coronal Magnetic Structures Observing Campaign. II - Magnetic and plasma properties of a solar active region

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

    Simultaneous soft X-ray, microwave, and photospheric magnetic field observations were taken during the Coronal Magnetic Structures Observing Campaign. The plasma electron temperatures and emission measures determined from the X-ray data are used to predict the intensity and structure of the thermal bremsstrahlung emission at 20 and 6 cm. Comparing these predictions with the microwave observations, it is found that the 20 cm structure is very similar to that expected from the X-rays, but a substantial amount of the 6 cm emission was resolved out. The predicted 20 cm brightness temperatures are higher than the observed, requiring cool absorbing material (not greater than 500,000 K) between the hot X-ray plasma and the observer. The absorption mechanism in the cool plasma at 20 cm is most likely thermal bremsstrahlung, requiring coronal magnetic fields as high as 150 G. 'Coronal Magnetograms', made by extrapolating the photospheric longitudinal field using the Sakurai code, show that appropriate values of the total field are reached at heights of 6000-10,000 km above the photosphere (at many but not all locations).

  5. Properties of solar coronal active regions deduced from X-ray line spectra

    NASA Astrophysics Data System (ADS)

    McKenzie, D. L.

    1987-11-01

    Spectra from the SOLEX B RAP spectrometer have been used to analyze the temperature and density structure of over 100 nonflaring solar active regions. Density measurements that used the R ratio of O VII indicated that few regions have electron densities higher than ≡3×109cm-3. In a few cases, flare-productive regions had measured densities approximately twice this high. Temperature-sensitive line ratios in the helium-like ions O VII, Ne IX, and Mg XI were used to decude the general properties of the differential emission-measure function B(T) for nonflaring regions. B(T) falls off with increasing temperature above a peak temperature that is almost always lower than Tm(O VII) = 1.8×106K.

  6. Coronal Metallicities of Active Binaries

    NASA Astrophysics Data System (ADS)

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

    1998-09-01

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

  7. The Relationship Between Solar Coronal X-Ray Brightness and Active Region Magnetic Fields: A Study Using High-Resolution Hinode Observations

    NASA Astrophysics Data System (ADS)

    Hazra, Soumitra; Nandy, Dibyendu; Ravindra, B.

    2015-03-01

    By using high-resolution observations of nearly co-temporal and co-spatial Solar Optical Telescope spectropolarimeter and X-Ray Telescope coronal X-ray data onboard Hinode, we revisit the problematic relationship between global magnetic quantities and coronal X-ray brightness. Co-aligned vector magnetogram and X-ray data were used for this study. The total X-ray brightness over active regions is well correlated with integrated magnetic quantities such as the total unsigned magnetic flux, the total unsigned vertical current, and the area-integrated square of the vertical and horizontal magnetic fields. On accounting for the inter-dependence of the magnetic quantities, we inferred that the total magnetic flux is the primary determinant of the observed integrated X-ray brightness. Our observations indicate that a stronger coronal X-ray flux is not related to a higher non-potentiality of active-region magnetic fields. The data even suggest a slightly negative correlation between X-ray brightness and a proxy of active-region non-potentiality. Although there are small numerical differences in the established correlations, the main conclusions are qualitatively consistent over two different X-ray filters, the Al-poly and Ti-poly filters, which confirms the strength of our conclusions and validate and extend earlier studies that used low-resolution data. We discuss the implications of our results and the constraints they set on theories of solar coronal heating.

  8. The SPoCA-suite: Software for extraction, characterization, and tracking of active regions and coronal holes on EUV images

    NASA Astrophysics Data System (ADS)

    Verbeeck, C.; Delouille, V.; Mampaey, B.; De Visscher, R.

    2014-01-01

    Context. Precise localization and characterization of active regions (AR) and coronal holes (CH) as observed by extreme ultra violet (EUV) imagers are crucial for a wide range of solar and helio-physics studies. Aims: We introduce a set of segmentation procedures (known as the SPoCA-suite) that allows one to retrieve AR and CH properties on EUV images taken from SOHO-EIT, STEREO-EUVI, PROBA2-SWAP, and SDO-AIA. Methods: We build upon our previous work on the Spatial Possibilistic Clustering Algorithm (SPoCA), that we have improved substantially in several ways. Results: We apply our algorithm on the synoptic EIT archive from 1997 to 2011 and decompose this dataset into regions that can clearly be identified as AR, quiet Sun, and CH. An antiphase between AR and CH filling factor is observed, as expected. The SPoCA-suite is next applied to datasets from EUVI, SWAP, and AIA. The time series pertaining to ARs or CHs are presented. Conclusions: The SPoCA-suite enables the extraction of several long time series of AR and CH properties from the data files of EUV imagers and also allows tracking individual ARs or CHs over time. For AIA images, AR and CH catalogs are available in near-real time from the Heliophysics Events Knowledgebase. The full code, which allows processing any EUV images, is available upon request to the authors.

  9. An Assessment of Magnetic Conditions for Strong Coronal Heating in Solar Active Regions by Comparing Observed Loops with Computed Potential Field Lines

    NASA Technical Reports Server (NTRS)

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

    1999-01-01

    We report further results on the magnetic origins of coronal heating found from registering coronal images with photospheric vector magnetograms. For two complementary active regions, we use computed potential field lines to examine the global non-potentiality of bright extended coronal loops and the three-dimensional structure of the magnetic field at their feet, and assess the role of these magnetic conditions in the strong coronal heating in these loops. The two active regions are complementary, in that one is globally potential and the other is globally nonpotential, while each is predominantly bipolar, and each has an island of included polarity in its trailing polarity domain. We find the following: (1) The brightest main-arch loops of the globally potential active region are brighter than the brightest main- arch loops of the globally strongly nonpotential active region. (2) In each active region, only a few of the mainarch magnetic loops are strongly heated, and these are all rooted near the island. (3) The end of each main-arch bright loop apparently bifurcates above the island, so that it embraces the island and the magnetic null above the island. (4) At any one time, there are other main-arch magnetic loops that embrace the island in the same manner as do the bright loops but that are not selected for strong coronal heating. (5) There is continual microflaring in sheared core fields around the island, but the main-arch bright loops show little response to these microflares. From these observational and modeling results we draw the following conclusions: (1) The heating of the main-arch bright loops arises mainly from conditions at the island end of these loops and not from their global non-potentiality. (2) There is, at most, only a loose coupling between the coronal heating in the bright loops of the main arch and the coronal heating in the sheared core fields at their feet, although in both the heating is driven by conditions/events in and around the

  10. An Assessment of Magnetic Conditions for Strong Coronal Heating in Solar Active Regions by Comparing Observed Loops with Computed Potential Field Lines

    NASA Astrophysics Data System (ADS)

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

    2000-01-01

    We report further results on the magnetic origins of coronal heating found from registering coronal images with photospheric vector magnetograms. For two complementary active regions, we use computed potential field lines to examine the global nonpotentiality of bright extended coronal loops and the three-dimensional structure of the magnetic field at their feet, and assess the role of these magnetic conditions in the strong coronal heating in these loops. The two active regions are complementary, in that one is globally potential and the other is globally nonpotential, while each is predominantly bipolar, and each has an island of included polarity in its trailing polarity domain. We find the following: (1) The brightest main-arch loops of the globally potential active region are brighter than the brightest main-arch loops of the globally strongly nonpotential active region. (2) In each active region, only a few of the mainarch magnetic loops are strongly heated, and these are all rooted near the island. (3) The end of each main-arch bright loop apparently bifurcates above the island, so that it embraces the island and the magnetic null above the island. (4) At any one time, there are other main-arch magnetic loops that embrace the island in the same manner as do the bright loops but that are not selected for strong coronal heating. (5) There is continual microflaring in sheared core fields around the island, but the main-arch bright loops show little response to these microflares. From these observational and modeling results we draw the following conclusions: (1) The heating of the main-arch bright loops arises mainly from conditions at the island end of these loops and not from their global nonpotentiality. (2) There is, at most, only a loose coupling between the coronal heating in the bright loops of the main arch and the coronal heating in the sheared core fields at their feet, although in both the heating is driven by conditions/events in and around the

  11. Twisting solar coronal jet launched at the boundary of an active region

    NASA Astrophysics Data System (ADS)

    Schmieder, B.; Guo, Y.; Moreno-Insertis, F.; Aulanier, G.; Yelles Chaouche, L.; Nishizuka, N.; Harra, L. K.; Thalmann, J. K.; Vargas Dominguez, S.; Liu, Y.

    2013-11-01

    Aims: A broad jet was observed in a weak magnetic field area at the edge of active region NOAA 11106 that also produced other nearby recurring and narrow jets. The peculiar shape and magnetic environment of the broad jet raised the question of whether it was created by the same physical processes of previously studied jets with reconnection occurring high in the corona. Methods: We carried out a multi-wavelength analysis using the EUV images from the Atmospheric Imaging Assembly (AIA) and magnetic fields from the Helioseismic and Magnetic Imager (HMI) both on-board the Solar Dynamics Observatory, which we coupled to a high-resolution, nonlinear force-free field extrapolation. Local correlation tracking was used to identify the photospheric motions that triggered the jet, and time-slices were extracted along and across the jet to unveil its complex nature. A topological analysis of the extrapolated field was performed and was related to the observed features. Results: The jet consisted of many different threads that expanded in around 10 minutes to about 100 Mm in length, with the bright features in later threads moving faster than in the early ones, reaching a maximum speed of about 200 km s-1. Time-slice analysis revealed a striped pattern of dark and bright strands propagating along the jet, along with apparent damped oscillations across the jet. This is suggestive of a (un)twisting motion in the jet, possibly an Alfvén wave. Bald patches in field lines, low-altitude flux ropes, diverging flow patterns, and a null point were identified at the basis of the jet. Conclusions: Unlike classical λ or Eiffel-tower-shaped jets that appear to be caused by reconnection in current sheets containing null points, reconnection in regions containing bald patches seems to be crucial in triggering the present jet. There is no observational evidence that the flux ropes detected in the topological analysis were actually being ejected themselves, as occurs in the violent phase of

  12. Eunis Observation of Pervasive Faint Fe XIX Line Emission from a Solar Active Region: Evidence for Coronal Heating By Nanoflares

    NASA Astrophysics Data System (ADS)

    Brosius, J. W.; Daw, A. N.; Rabin, D. M.

    2014-12-01

    We present spatially resolved EUV spectroscopic measurements ofpervasive, faint Fe XIX 592.2 A line emission in an active regionobserved during the 2013 April 23 flight of the Extreme UltravioletNormal Incidence Spectrograph (EUNIS-13) sounding rocket instrument. With cooled detectors, high sensitivity, and high spectralresolution, EUNIS-13 resolves the lines of Fe XIX at 592.2 A (formedat temperature T around 8.9 MK) and Fe XII at 592.6 A (T around 1.6MK). The Fe XIX line emission, observed over an area in excess of4920 square arcsec (2.58x10^9 square km, more than 60% of the activeregion), provides strong evidence for the nanoflare heating model ofthe solar corona. No GOES events occurred in the region less than 2hours before the rocket flight, but a microflare was observed northand east of the region with RHESSI and EUNIS during the flight. Theabsence of significant upward velocities anywhere in the region,particularly the microflare, indicates that the pervasive Fe XIXemission is not propelled outward from the microflare site, but ismost likely attributed to localized heating (due to reconnection,wave dissipation, or some other mechanism) consistent with thenanoflare heating model of the solar corona. We measure average FeXIX/Fe XII intensity ratios of 0.070 outside the AR core, 0.22 inarea of bright coronal emission (the area in which the Fe XIIintensity exceeds half its maximum observed value), and 0.55 in theregion's hot core. Using the CHIANTI atomic physics database andassuming ionization equilibrium, we estimate corresponding Fe XIX/FeXII emission measure ratios of about 0.076, 0.23 and 0.59. Theemission measure ratios must be viewed with caution in light oflingering uncertainties in the Fe XII contribution functions.EUNIS-13 was supported by the NASA Heliophysics Division through itsLow Cost Access to Space program.

  13. The magnetic field of active region 11158 during the 2011 February 12-17 flares: Differences between photospheric extrapolation and coronal forward-fitting methods

    SciTech Connect

    Aschwanden, Markus J.; Sun, Xudong; Liu, Yang E-mail: xudongs@stanford.edu

    2014-04-10

    We developed a coronal nonlinear force-free field (COR-NLFFF) forward-fitting code that fits an approximate nonlinear force-free field (NLFFF) solution to the observed geometry of automatically traced coronal loops. In contrast to photospheric NLFFF codes, which calculate a magnetic field solution from the constraints of the transverse photospheric field, this new code uses coronal constraints instead, and this way provides important information on systematic errors of each magnetic field calculation method, as well as on the non-force-freeness in the lower chromosphere. In this study we applied the COR-NLFFF code to NOAA Active Region 11158, during the time interval of 2011 February 12-17, which includes an X2.2 GOES-class flare plus 35 M- and C-class flares. We calculated the free magnetic energy with a 6 minute cadence over 5 days. We find good agreement between the two types of codes for the total nonpotential E{sub N} and potential energy E{sub P} but find up to a factor of 4 discrepancy in the free energy E {sub free} = E{sub N} – E{sub P} and up to a factor of 10 discrepancy in the decrease of the free energy ΔE {sub free} during flares. The coronal NLFFF code exhibits a larger time variability and yields a decrease of free energy during the flare that is sufficient to satisfy the flare energy budget, while the photospheric NLFFF code shows much less time variability and an order of magnitude less free-energy decrease during flares. The discrepancy may partly be due to the preprocessing of photospheric vector data but more likely is due to the non-force-freeness in the lower chromosphere. We conclude that the coronal field cannot be correctly calculated on the basis of photospheric data alone and requires additional information on coronal loop geometries.

  14. 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

  15. The location and kinematics of the coronal-line emitting regions in active galactic nuclei

    NASA Astrophysics Data System (ADS)

    Mullaney, J. R.; Ward, M. J.; Done, C.; Ferland, G. J.; Schurch, N.

    2009-03-01

    We use the photoionization code CLOUDY to determine both the location and the kinematics of the optical forbidden, high-ionization line (hereafter, FHIL) emitting gas in the narrow line Seyfert 1 galaxy Ark 564. The results of our models are compared with the observed properties of these emission lines to produce a physical model that is used to explain both the kinematics and the source of this gas. The main features of this model are that the FHIL emitting gas is launched from the putative dusty torus and is quickly accelerated to its terminal velocity of a few hundred km s-1. Iron-carrying grains are destroyed during this initial acceleration. This velocity is maintained by a balance between radiative forces and gravity in this super-Eddington source. Eventually the outflow is slowed at large radii by the gravitational forces of and interactions with the host galaxy. In this model, FHIL emission traces the transition between the active galactic nucleus (AGN) and bulge zones of influence.

  16. Transition Region and Coronal Explorer

    NASA Technical Reports Server (NTRS)

    Wolfson, C. Jacob

    2001-01-01

    This contract is for the development and flight of an experiment to study the solar atmosphere with excellent spatial and temporal resolution; and reduction and analysis of the resultant data. After being launched into a near perfect orbit on 2 April 1998, the spacecraft and instrument remain in good condition and the resultant data are spectacular. Over 6.6 million images have now been taken. Observing highlights this month included several coordinations with CDS, studies of the quiet Sun with SUMER and NMI, coordinations with observers at the SPO Dunn Tower Telescope, and a variety of active region observations. Some of the latter were relatively unique in that they emphasized using the hottest (284A) channel of TRACE. We were informed of the results of the Senior Review Committee's evaluation of all Space Science on-orbit missions and the corresponding fiscal year budgets for TRACE. The budget for FY-02 is modestly less than is being spent in FY-01 and for the years beyond that it is much, much lower.

  17. A new view of solar wind origin near active regions and in polar coronal holes on the basis of Hinode observations

    NASA Astrophysics Data System (ADS)

    He, Jiansen; Marsch, Eckart; Tu, Chuanyi; Tian, Hui; Guo, Lijia; Curdt, Werner; Xia, Lidong; Kamio, Suguru

    The possibility of full-range solar observations from Hinode with high temporal and spatial resolution motivated us to revisit the solar wind origin in the solar atmosphere. For the solar wind origin near active regions, we reveal activity in the chromosphere to be responsible for the coronal outflow at the AR edge; meanwhile we also succeeded in finding the related solar wind stream in the heliosphere. Chromospheric spicule-like jets are found to occur intermittently, and to flow in similar direction than the intermittent coronal outflows. EIS observations reveal that there are blue-shifts at the edge of AR in both chromosphere and corona, and that the blue-shift increases with temperature. Therefore, we suggest that the nascent solar wind may probably originate in the chromosphere at the edge of ARs. The connection between the source regions and their respective solar wind streams is established through magnetic field lines, which are extrapolated to reach the solar ecliptic plane at 2.5 Rs. We find that the AR edge may be the source region of an intermediate-speed (400 km/s) solar wind stream. For the solar wind origin in polar coronal holes (CHs), we extend the blue-shift observations from the transition region up to the corona, investigate the magnetic characteristics in association with the polar coronal jets, and study in details the initial phase of meso-scale loop eruption in polar CHs. We find that the blue-shift becomes more and more dominant with increasing temperature from the transition region to the corona. The polar coronal jets are found to be elongated along the extrapolated open field lines, which appear in fanning-out shape. The cancellation between bipolar magnetic fields, or squeezing of monopolar magnetic fields, may be the driver for a jet launch. The meso-scale loop started its eruption with a sudden brightening at one footpoint, then expanded and moved upwardly with a speed of 20 km/s, causing the mass at the footpoint to flow outwardly

  18. Nonlinear Force-Free and Potential-Field Models of Active-Region and Global Coronal Fields during the Whole Heliosphere Interval

    NASA Astrophysics Data System (ADS)

    Petrie, G. J. D.; Canou, A.; Amari, T.

    2011-12-01

    Between 24 March 2008 and 2 April 2008, the three active regions (ARs) NOAA 10987, 10988 and 10989 were observed daily by the Synoptic Optical Long-term Investigations of the Sun (SOLIS) Vector Spectro-Magnetograph (VSM) while they traversed the solar disk. We use these measurements and the nonlinear force-free magnetic field code XTRAPOL to reconstruct the coronal magnetic field for each active region and compare model field lines with images from the Solar Terrestrial RElations Observatory (STEREO) and Hinode X-ray Telescope (XRT) telescopes. Synoptic maps made from continuous, round-the-clock Global Oscillations Network Group (GONG) magnetograms provide information on the global photospheric field and potential-field source-surface models based on these maps describe the global coronal field during the Whole Heliosphere Interval (WHI) and its neighboring rotations. Features of the modeled global field, such as the coronal holes and streamer-belt locations, are discussed in comparison with extreme ultra-violet and coronagraph observations from STEREO. The global field is found to be far from a minimum, dipolar state. From the nonlinear models we compute physical quantities for the active regions such as the photospheric magnetic and electric current fluxes, the free magnetic energy and the relative helicity for each region each day where observations permit. The interconnectivity of the three regions is addressed in the context of the potential-field source-surface model. Using local and global quantities derived from the models, we briefly discuss the different observed activity levels of the regions.

  19. Study of the 3D Coronal Magnetic Field of Active Region 11117 Around the Time of a Confined Flare Using a Data-Driven CESE-MHD Model

    NASA Astrophysics Data System (ADS)

    Jiang, C.; Feng, X.; Wu, S.; Hu, Q.

    2012-12-01

    Non-potentiality of the solar coronal magnetic field accounts for the solar explosion like flares and CMEs. We apply a data-driven CESE-MHD model to investigate the three-dimensional (3D) coronal magnetic field of NOAA active region (AR) 11117 around the time of a C-class confined flare occurred on 2010 October 25. The CESE-MHD model, based on the spacetime conservation-element and solution-element scheme, is designed to focus on the magnetic-field evolution and to consider a simplified solar atomsphere with finite plasma β. Magnetic vector-field data derived from the observations at the photoshpere is inputted directly to constrain the model. Assuming that the dynamic evolution of the coronal magnetic field can be approximated by successive equilibria, we solve a time sequence of MHD equilibria basing on a set of vector magnetograms for AR 11117 taken by the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamic Observatory (SDO) around the time of flare. The model qualitatively reproduces the basic structures of the 3D magnetic field, as supported by the visual similarity between the field lines and the coronal loops observed by the Atmospheric Imaging Assembly (AIA), which shows that the coronal field can indeed be well characterized by the MHD equilibrium in most time. The magnetic configuration changes very limited during the studied time interval of two hours. A topological analysis reveals that the small flare is correlated with a bald patch (BP, where the magnetic field is tangent to the photoshpere), suggesting that the energy release of the flare can be understood by magnetic reconnection associated with the BP separatrices. The total magnetic flux and energy keep increasing slightly in spite of the flare, while the magnetic free energy drops during the flare with an amount of 1.7 × 1030 erg, which can be interpreted as the energy budget released by the minor C-class flare.

  20. NUMERICAL INVESTIGATION OF A CORONAL MASS EJECTION FROM AN ANEMONE ACTIVE REGION: RECONNECTION AND DEFLECTION OF THE 2005 AUGUST 22 ERUPTION

    SciTech Connect

    Lugaz, N.; Shibata, K.; Downs, C.; Roussev, I. I.; Asai, A.; Gombosi, T. I.

    2011-09-10

    We present a numerical investigation of the coronal evolution of a coronal mass ejection (CME) on 2005 August 22 using a three-dimensional thermodynamic magnetohydrodynamic model, the space weather modeling framework. The source region of the eruption was anemone active region (AR) 10798, which emerged inside a coronal hole. We validate our modeled corona by producing synthetic extreme-ultraviolet (EUV) images, which we compare to EIT images. We initiate the CME with an out-of-equilibrium flux rope with an orientation and chirality chosen in agreement with observations of an H{alpha} filament. During the eruption, one footpoint of the flux rope reconnects with streamer magnetic field lines and with open field lines from the adjacent coronal hole. It yields an eruption which has a mix of closed and open twisted field lines due to interchange reconnection and only one footpoint line-tied to the source region. Even with the large-scale reconnection, we find no evidence of strong rotation of the CME as it propagates. We study the CME deflection and find that the effect of the Lorentz force is a deflection of the CME by about 3{sup 0} R{sup -1}{sub sun} toward the east during the first 30 minutes of the propagation. We also produce coronagraphic and EUV images of the CME, which we compare with real images, identifying a dimming region associated with the reconnection process. We discuss the implication of our results for the arrival at Earth of CMEs originating from the limb and for models to explain the presence of open field lines in magnetic clouds.

  1. Numerical Investigation of a Coronal Mass Ejection from an Anemone Active Region: Reconnection and Deflection of the 2005 August 22 Eruption

    NASA Astrophysics Data System (ADS)

    Lugaz, N.; Downs, C.; Shibata, K.; Roussev, I. I.; Asai, A.; Gombosi, T. I.

    2011-09-01

    We present a numerical investigation of the coronal evolution of a coronal mass ejection (CME) on 2005 August 22 using a three-dimensional thermodynamic magnetohydrodynamic model, the space weather modeling framework. The source region of the eruption was anemone active region (AR) 10798, which emerged inside a coronal hole. We validate our modeled corona by producing synthetic extreme-ultraviolet (EUV) images, which we compare to EIT images. We initiate the CME with an out-of-equilibrium flux rope with an orientation and chirality chosen in agreement with observations of an Hα filament. During the eruption, one footpoint of the flux rope reconnects with streamer magnetic field lines and with open field lines from the adjacent coronal hole. It yields an eruption which has a mix of closed and open twisted field lines due to interchange reconnection and only one footpoint line-tied to the source region. Even with the large-scale reconnection, we find no evidence of strong rotation of the CME as it propagates. We study the CME deflection and find that the effect of the Lorentz force is a deflection of the CME by about 3° R -1 sun toward the east during the first 30 minutes of the propagation. We also produce coronagraphic and EUV images of the CME, which we compare with real images, identifying a dimming region associated with the reconnection process. We discuss the implication of our results for the arrival at Earth of CMEs originating from the limb and for models to explain the presence of open field lines in magnetic clouds.

  2. Variability of a stellar corona on a time scale of days. Evidence for abundance fractionation in an emerging coronal active region

    NASA Astrophysics Data System (ADS)

    Nordon, R.; Behar, E.; Drake, S. A.

    2013-02-01

    Elemental abundance effects in active coronae have eluded our understanding for almost three decades, since the discovery of the first ionization potential (FIP) effect on the sun. The goal of this paper is to monitor the same coronal structures over a time interval of six days and resolve active regions on a stellar corona through rotational modulation. We report on four iso-phase X-ray spectroscopic observations of the RS CVn binary EI Eri with XMM-Newton, carried out approximately every two days, to match the rotation period of EI Eri. We present an analysis of the thermal and chemical structure of the EI Eri corona as it evolves over the six days. Although the corona is rather steady in its temperature distribution, the emission measure and FIP bias both vary and seem to be correlated. An active region, predating the beginning of the campaign, repeatedly enters into our view at the same phase as it rotates from beyond the stellar limb. As a result, the abundances tend slightly, but consistently, to increase for high FIP elements (an inverse FIP effect) with phase. We estimate the abundance increase of high FIP elements in the active region to be of about 75% over the coronal mean. This observed fractionation of elements in an active region on time scales of days provides circumstantial clues regarding the element enrichment mechanism of non-flaring stellar coronae.

  3. Variability of a Stellar Corona on a Time Scale of Days: Evidence for Abundance Fractionation in an Emerging Coronal Active Region

    NASA Technical Reports Server (NTRS)

    Nordon, R.; Behar, E.; Drake, S. A.

    2013-01-01

    Elemental abundance effects in active coronae have eluded our understanding for almost three decades, since the discovery of the first ionization potential (FIP) effect on the sun. The goal of this paper is to monitor the same coronal structures over a time interval of six days and resolve active regions on a stellar corona through rotational modulation. We report on four iso-phase X-ray spectroscopic observations of the RS CVn binary EI Eri with XMM-Newton, carried out approximately every two days, to match the rotation period of EI Eri. We present an analysis of the thermal and chemical structure of the EI Eri corona as it evolves over the six days. Although the corona is rather steady in its temperature distribution, the emission measure and FIP bias both vary and seem to be correlated. An active region, predating the beginning of the campaign, repeatedly enters into our view at the same phase as it rotates from beyond the stellar limb. As a result, the abundances tend slightly, but consistently, to increase for high FIP elements (an inverse FIP effect) with phase. We estimate the abundance increase of high FIP elements in the active region to be of about 75% over the coronal mean. This observed fractionation of elements in an active region on time scales of days provides circumstantial clues regarding the element enrichment mechanism of non-flaring stellar coronae.

  4. The transition region and coronal explorer (TRACE)

    NASA Technical Reports Server (NTRS)

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

    1995-01-01

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

  5. A Tool for Empirical Forecasting of Major Flares, Coronal Mass Ejections, and Solar Particle Events from a Proxy of Active-Region Free Magnetic Energy

    NASA Technical Reports Server (NTRS)

    Barghouty, A. F.; Falconer, D. A.; Adams, J. H., Jr.

    2010-01-01

    This presentation describes a new forecasting tool developed for and is currently being tested by NASA s Space Radiation Analysis Group (SRAG) at JSC, which is responsible for the monitoring and forecasting of radiation exposure levels of astronauts. The new software tool is designed for the empirical forecasting of M and X-class flares, coronal mass ejections, as well as solar energetic particle events. Its algorithm is based on an empirical relationship between the various types of events rates and a proxy of the active region s free magnetic energy, determined from a data set of approx.40,000 active-region magnetograms from approx.1,300 active regions observed by SOHO/MDI that have known histories of flare, coronal mass ejection, and solar energetic particle event production. The new tool automatically extracts each strong-field magnetic areas from an MDI full-disk magnetogram, identifies each as an NOAA active region, and measures a proxy of the active region s free magnetic energy from the extracted magnetogram. For each active region, the empirical relationship is then used to convert the free magnetic energy proxy into an expected event rate. The expected event rate in turn can be readily converted into the probability that the active region will produce such an event in a given forward time window. Descriptions of the datasets, algorithm, and software in addition to sample applications and a validation test are presented. Further development and transition of the new tool in anticipation of SDO/HMI is briefly discussed.

  6. Correlation of the Coronal Mass Ejection Productivity of Solar Active Regions with Measures of their Global Nonpotentiality from Vector Magnetograms: Baseline Results

    NASA Technical Reports Server (NTRS)

    Falconer, D. A.; Moore, R. L.; Gary, G. A.

    2002-01-01

    Conventional magnetograms and chromospheric and coronal images show qualitatively that the fastest coronal mass ejections (CMEs) are magnetic explosions from sunspot active regions where the magnetic field is globally strongly sheared and twisted from its minimum-energy potential configuration. We present measurements from active region vector magnetograms that start to quantify the dependence of an active region's CME productivity on the global nonpotentiality of its magnetic field. From each of 17 magnetograms of 12 bipolar active regions, we measured the size of the active region (the magnetic flux content, phi) and three separate measures of the global nonpotentiality (L(sub SS), the length of strong-shear, strong-field main neutral line: I(sub N), the net electric current connecting one polarity to the other; and alpha = (mu)I(sub N)/phi), a flux normalized measure of the field twist). From these measurements and the observed CME productivity of the active regions, we find that: (1) All three measures of global nonpotentiality are statistically correlated with the active region flux content and with each other; (2) All three measures of global nonpotentiality are significantly correlated with CME productivity. The flux content correlates with CME productivity, but at a lower statistically significant confidence level (less than 95%); (3) The net current is less closely correlated with CME productivity than alpha and the correlation of CME productivity with flux content is even weaker. If these differences in correlation strength, and a significant correlation of alpha with flux content, persist to larger active regions, this would imply that the size of active regions does not affect CME productivity except through global nonpotentiality; and (4) For each of the four global magnetic quantities, the correlation with CME productivity is stronger for a two-day time window for the CME production than for windows half as wide or twice as wide. This plausibly is a

  7. First Three-Dimensional Reconstructions of Coronal Loops with the STEREO A+B Spacecraft. III. Instant Stereoscopic Tomography of Active Regions

    NASA Astrophysics Data System (ADS)

    Aschwanden, Markus J.; Wuelser, Jean-Pierre; Nitta, Nariaki V.; Lemen, James R.; Sandman, Anne

    2009-04-01

    Here we develop a novel three-dimensional (3D) reconstruction method of the coronal plasma of an active region by combining stereoscopic triangulation of loops with density and temperature modeling of coronal loops with a filling factor equivalent to tomographic volume rendering. Because this method requires only a stereoscopic image pair in multiple temperature filters, which are sampled within ≈1 minute with the recent STEREO/EUVI instrument, this method is about four orders of magnitude faster than conventional solar rotation-based tomography. We reconstruct the 3D density and temperature distribution of active region NOAA 10955 by stereoscopic triangulation of 70 loops, which are used as a skeleton for a 3D field interpolation of some 7000 loop components, leading to a 3D model that reproduces the observed fluxes in each stereoscopic image pair with an accuracy of a few percents (of the average flux) in each pixel. With the stereoscopic tomography we infer also a differential emission measure distribution over the entire temperature range of T ≈ 104-107, with predictions for the transition region and hotter corona in soft X-rays. The tomographic 3D model provides also large statistics of physical parameters. We find that the extreme-ultraviolet loops with apex temperatures of Tm lsim 3.0 MK tend to be super-hydrostatic, while hotter loops with Tm ≈ 4-7 MK are near-hydrostatic. The new 3D reconstruction model is fully independent of any magnetic field data and is promising for future tests of theoretical magnetic field models and coronal heating models.

  8. FIRST THREE-DIMENSIONAL RECONSTRUCTIONS OF CORONAL LOOPS WITH THE STEREO A+B SPACECRAFT. III. INSTANT STEREOSCOPIC TOMOGRAPHY OF ACTIVE REGIONS

    SciTech Connect

    Aschwanden, Markus J.; Wuelser, Jean-Pierre; Nitta, Nariaki V.; Lemen, James R.; Sandman, Anne

    2009-04-10

    Here we develop a novel three-dimensional (3D) reconstruction method of the coronal plasma of an active region by combining stereoscopic triangulation of loops with density and temperature modeling of coronal loops with a filling factor equivalent to tomographic volume rendering. Because this method requires only a stereoscopic image pair in multiple temperature filters, which are sampled within {approx}1 minute with the recent STEREO/EUVI instrument, this method is about four orders of magnitude faster than conventional solar rotation-based tomography. We reconstruct the 3D density and temperature distribution of active region NOAA 10955 by stereoscopic triangulation of 70 loops, which are used as a skeleton for a 3D field interpolation of some 7000 loop components, leading to a 3D model that reproduces the observed fluxes in each stereoscopic image pair with an accuracy of a few percents (of the average flux) in each pixel. With the stereoscopic tomography we infer also a differential emission measure distribution over the entire temperature range of T {approx} 10{sup 4}-10{sup 7}, with predictions for the transition region and hotter corona in soft X-rays. The tomographic 3D model provides also large statistics of physical parameters. We find that the extreme-ultraviolet loops with apex temperatures of T{sub m} {approx}< 3.0 MK tend to be super-hydrostatic, while hotter loops with T{sub m} {approx} 4-7 MK are near-hydrostatic. The new 3D reconstruction model is fully independent of any magnetic field data and is promising for future tests of theoretical magnetic field models and coronal heating models.

  9. The Fundamental Physical Processes Producing and Controlling Stellar Coronal/Transition Region/Chromospheric Activity and Structure

    NASA Technical Reports Server (NTRS)

    Ayres, T. R.; Brown, A.

    2000-01-01

    Our LTSA (Long Term Space Astrophysics) research has utilized current NASA and ESA spacecraft, supporting ground-based IR, radio, and sub-mm telescopes, and the extensive archives of HST (Hubble Space Telescope), IUE (International Ultraviolet Explorer), ROSAT, EUVE (Extreme Ultraviolet Explorer), and other missions. Our research effort has included observational work (with a nonnegligible groundbased component), specialized processing techniques for imaging and spectral data, and semiempirical modelling, ranging from optically thin emission measure studies to simulations of optically thick resonance lines. In our previous LTSA efforts, we have had a number of major successes, including most recently: organizing and carrying out an extensive cool star UV survey in HST cycle eight; obtaining observing time with new instruments, such as Chandra and XMM (X-ray Multi-Mirror) in their first cycles; collaborating with the Chandra GTO program and participating with the Chandra Emission Line Project on multi-wavelength observations of HR 1099 and Capella. These are the main broad-brush themes of our previous investigation: a) Where do Coronae Occur in the Hertzsprung-Russell Diagram? b) Winds of Coronal and Noncoronal Stars; c) Activity, Age, Rotation Relations; d) Atmospheric Inhomogeneities; e) Heating Mechanisms, Subcoronal Flows, and Flares; f) Development of Analysis and Modelling Tools.

  10. Magnetic-field variations in the active region NOAA 10486 and their relationship to X-ray flares and coronal mass ejections

    NASA Astrophysics Data System (ADS)

    Chumak, O. V.; Zhang, H.-Q.; Guo, J.

    2008-10-01

    SOHO/MDI magnetograms are used to analyze the time variations in the magnetic parameters of the active region (AR) NOAA 10486, which was part of a large activity complex that passed over the solar disk from October 26 to 31, 2003, during solar cycle 23. The results are compared with X-ray flares in the AR and the parameters of coronal mass ejections associated with the AR. The time variations in the distributions of themagnetic-field strengths associated with the total magnetic flux (Fa), the flux imbalance between the northern and southern polarities (Im), the complexity of the field, as a measure of the mutual overlapping of the opposite polarities (Co), and the tilt angle of the magnetic axis (An) are considered. The time variations in the free energy accumulated in current sheets of ARs were traced using a parameter introduced for this purpose (Sh). The following results were obtained. First, the parameters Fa, Im, Co, An, and Sh quantitatively describe the current state of the AR and can be used to trace and analyze the dynamical evolution of its magnetic field. Second, variations in the magnetic-field-strength distributions and the mean values of Fa, Im, Co, An, and Sh are associated with flares and coronal mass ejections, and the variations have considerable amplitudes. Third, the parameter Sh characterizing the degree to which the magnetic field is non-potential in regions adjacent to the main neutral line increases before eruptive events, and is thus particular interest for monitoring the states of ARs in real time. Fourth, the magnetic field of the AR manifests a sort of quasi-elasticity, so that the field structure is restored after active events, on average, within 1 3 h.

  11. Coronal magnetic structures observing campaign. I - Simultaneous microwave and soft X-ray observations of active regions at the solar limb

    NASA Astrophysics Data System (ADS)

    Nitta, N.; White, S. M.; Kundu, M. R.; Gopalswamy, N.; Holman, G. D.; Brosius, J. W.; Schmelz, J. T.; Saba, J. L. R.; Strong, K. T.

    1991-06-01

    Using simultaneous microwave and soft X-ray measurements made with the Very Large Array (VLA) at 6 and 20 cm and the X-ray Polychromator (XRP) aboard the Solar Maximum Mission (SMM), we have studied two active regions near the solar limb. These observations were taken as part of the Coronal Magnetic Structures Observing Campaign (CoMStOC), a collaboration designed to study the magnetic field in the solar corona. The images in soft X-rays and at 20 cm wavelength are similar: both show peaks above the active regions and extended bridge of emission 200,000 km long connecting the two regions. The brightness temperature of the 20 cm emission is lower than that predicted from the X-ray emitting material, however; it can be attributed to free-free emission in cooler (<106 K) plasma not visible to XRP, with an optical depth ˜1. The 6 cm emission is concentrated at lower altitudes and in a ˜160,000 km long bundle of loops in the northern active region. Comparison of the 6 cm map with the potential magnetic field lines computed from photospheric magnetic fields (measured 2 days earlier) indicates that the 6 cm emission is associated with fields of less than ˜200 G. Such fields would be too weak to attribute the observed 6 cm emission to gyroresonance radiation. Analysis of the 6 cm loop bundle indicates that it is strongly asymmetric, with the magnetic field in the northern leg ˜2 times stronger than in the southern leg; the 6 cm emission most likely arises from a combination of hot ( ≥ 2 × 106 K) and cool plasmas, while the 20 cm emission becomes optically thick in the cooler (˜9 × 103 K) plasma. We estimate an Alfvén speed ˜7000 km s-1 and ratio of electron gyrofrequency to plasma frequency ˜1.0 in the northern leg of the 6 cm loop.

  12. Modified Coronal Index of the Solar Activity

    NASA Astrophysics Data System (ADS)

    Lukáč, B.; Rybanský, M.

    2010-05-01

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

  13. Coronal Activity and Extended Solar Cycles

    NASA Astrophysics Data System (ADS)

    Altrock, R. C.

    2012-12-01

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

  14. 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.

  15. 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.

  16. Solar activity during Skylab: Its distribution and relation to coronal holes

    NASA Technical Reports Server (NTRS)

    Speich, D. M.; Smith, J. B., Jr.; Wilson, R. M.; Mcintosh, P. S.

    1978-01-01

    Solar active regions observed during the period of Skylab observations (May 1973-February 1974) were examined for properties that varied systematically with location on the sun, particularly with respect to the location of coronal holes. Approximately 90 percent of the optical and X-ray flare activity occurred in one solar hemisphere (136-315 heliographic degrees longitude). Active regions within 20 heliographic degrees of coronal holes were below average in lifetimes, flare production, and magnetic complexity. Histograms of solar flares as a function of solar longitude were aligned with H alpha synoptic charts on which active region serial numbers and coronal hole boundaries were added.

  17. Low transition-region characteristics of equatorial coronal holes

    NASA Technical Reports Server (NTRS)

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

    1997-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Wheatley, Jonathan; Welsh, Barry

    2016-01-01

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

  19. Active Region Release Two CMEs

    NASA Video Gallery

    Solar material can be seen blowing off the sun in this video captured by NASA’s Solar Dynamics Observatory (SDO) on the night of Feb. 5, 2013. This active region on the sun sent out two coronal ...

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

    PubMed Central

    Tauro, David; Bagulkar, Bhupesh; Vyas, Anuj

    2015-01-01

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

  1. A Rapid, Manual Method to Map Coronal-Loop Structures of an Active Region Using Cubic Bézier Curves and Its Applications to Misalignment Angle Analysis

    NASA Astrophysics Data System (ADS)

    Gary, G. Allen; Hu, Qiang; Lee, Jong Kwan

    2014-03-01

    A rapid and flexible manual method is described that maps individual coronal loops of a 2D EUV image as Bézier curves using only four points per loop. Using the coronal loops as surrogates of magnetic-field lines, the mapping results restrict the magnetic-field models derived from extrapolations of magnetograms to those admissible and inadmissible via a fitness parameter. We outline explicitly how the coronal loops can be employed in constraining competing magnetic-field models by transforming 2D coronal-loop images into 3D field lines. The magnetic-field extrapolations must satisfy not only the lower boundary conditions of the vector field (the vector magnetogram) but also must have a set of field lines that satisfies the mapped coronal loops in the volume, analogous to an upper boundary condition. This method uses the minimization of the misalignment angles between the magnetic-field model and the best set of 3D field lines that match a set of closed coronal loops. The presented method is an important tool in determining the fitness of magnetic-field models for the solar atmosphere. The magnetic-field structure is crucial in determining the overall dynamics of the solar atmosphere.

  2. MHD Modeling of Coronal Loops: the Transition Region Throat

    NASA Technical Reports Server (NTRS)

    Guarrasi, M.; Reale, F.; Orlando, S.; Mignone, A.; Klimchuk, J. A.

    2014-01-01

    Context. The expansion of coronal loops in the transition region may considerably influence the diagnostics of the plasma emission measure. The cross-sectional area of the loops is expected to depend on the temperature and pressure, and might be sensitive to the heating rate. Aims. The approach here is to study the area response to slow changes in the coronal heating rate, and check the current interpretation in terms of steady heating models. Methods. We study the area response with a time-dependent 2D magnetohydrodynamic (MHD) loop model, including the description of the expanding magnetic field, coronal heating and losses by thermal conduction, and radiation from optically thin plasma. We run a simulation for a loop 50 Mm long and quasi-statically heated to about 4 millikelvin. Results. We find that the area can change substantially with the quasi-steady heating rate, e.g., by approx. 40% at 0.5 millikelvin as the loop temperature varies between 1 millikelvin and 4 millikelvin, and, therefore, affects the interpretation of the differential emission measure vs. temperature (DEM(T)) curves.

  3. Study of the Three-dimensional Coronal Magnetic Field of Active Region 11117 around the Time of a Confined Flare Using a Data-Driven CESE-MHD Model

    NASA Astrophysics Data System (ADS)

    Jiang, Chaowei; Feng, Xueshang; Wu, S. T.; Hu, Qiang

    2012-11-01

    We apply a data-driven magnetohydrodynamics (MHD) model to investigate the three-dimensional (3D) magnetic field of NOAA active region (AR) 11117 around the time of a C-class confined flare that occurred on 2010 October 25. The MHD model, based on the spacetime conservation-element and solution-element scheme, is designed to focus on the magnetic field evolution and to consider a simplified solar atomsphere with finite plasma β. Magnetic vector-field data derived from the observations at the photosphere is inputted directly to constrain the model. Assuming that the dynamic evolution of the coronal magnetic field can be approximated by successive equilibria, we solve a time sequence of MHD equilibria based on a set of vector magnetograms for AR 11117 taken by the Helioseismic and Magnetic Imager on board the Solar Dynamic Observatory around the time of the flare. The model qualitatively reproduces the basic structures of the 3D magnetic field, as supported by the visual similarity between the field lines and the coronal loops observed by the Atmospheric Imaging Assembly, which shows that the coronal field can indeed be well characterized by the MHD equilibrium in most cases. The magnetic configuration changes very little during the studied time interval of 2 hr. A topological analysis reveals that the small flare is correlated with a bald patch (BP, where the magnetic field is tangent to the photosphere), suggesting that the energy release of the flare can be understood by magnetic reconnection associated with the BP separatrices. The total magnetic flux and energy keep increasing slightly in spite of the flare, while the computed magnetic free energy drops during the flare by ~1030 erg, which seems to be adequate in providing the energy budget of a minor C-class confined flare.

  4. MICRO-SIGMOIDS AS PROGENITORS OF CORONAL JETS: IS ERUPTIVE ACTIVITY SELF-SIMILARLY MULTI-SCALED?

    SciTech Connect

    Raouafi, N.-E.; Rust, D. M.; Bernasconi, P. N.; Georgoulis, M. K.

    2010-08-01

    Observations from the X-ray telescope (XRT) on Hinode are used to study the nature of X-ray-bright points, sources of coronal jets. Several jet events in the coronal holes are found to erupt from small-scale, S-shaped bright regions. This finding suggests that coronal micro-sigmoids may well be progenitors of coronal jets. Moreover, the presence of these structures may explain numerous observed characteristics of jets such as helical structures, apparent transverse motions, and shapes. Analogous to large-scale sigmoids giving rise to coronal mass ejections (CMEs), a promising future task would perhaps be to investigate whether solar eruptive activity, from coronal jets to CMEs, is self-similar in terms of properties and instability mechanisms.

  5. THE TRANSITION REGION RESPONSE TO A CORONAL NANOFLARE: FORWARD MODELING AND OBSERVATIONS IN SDO/AIA

    SciTech Connect

    Viall, Nicholeen M.; Klimchuk, James A.

    2015-01-20

    The corona and transition region (TR) are fundamentally coupled through the processes of thermal conduction and mass exchange. It is not possible to understand one without the other. Yet the temperature-dependent emissions from the two locations behave quite differently in the aftermath of an impulsive heating event such as a coronal nanoflare. Whereas the corona cools sequentially, emitting first at higher temperatures and then at lower temperatures, the TR is multithermal and the emission at all temperatures responds in unison. We have previously applied the automated time lag technique of Viall and Klimchuk to disk observations of an active region (AR) made by the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory. Lines of sight passing through coronal plasma show clear evidence for post-nanoflare cooling, while lines of sight intersecting the TR footpoints of coronal strands show zero time lag. In this paper, we use the EBTEL hydrodynamics code to demonstrate that this is precisely the expected behavior when the corona is heated by nanoflares. We also apply the time lag technique for the first time to off-limb observations of an AR. Since TR emission is not present above the limb, the occurrence of zero time lags is greatly diminished, supporting the conclusion that zero time lags measured on the disk are due to TR plasma. Lastly, we show that the ''coronal'' channels in AIA can be dominated by bright TR emission. When defined in a physically meaningful way, the TR reaches a temperature of roughly 60% the peak temperature in a flux tube. The TR resulting from impulsive heating can extend to 3 MK and higher, well within the range of the ''coronal'' AIA channels.

  6. The Transition Region Response to a Coronal Nanoflare: Forward Modeling and Observations in SDO/AIA

    NASA Technical Reports Server (NTRS)

    Viall-Kepko, Nicholeen M.; Klimchuk, James A.

    2015-01-01

    The corona and transition region (TR) are fundamentally coupled through the processes of thermal conduction and mass exchange. It is not possible to understand one without the other. Yet the temperature-dependent emissions from the two locations behave quite differently in the aftermath of an impulsive heating event such as a coronal nanoflare. Whereas the corona cools sequentially, emitting first at higher temperatures and then at lower temperatures, the TR is multithermal and the emission at all temperatures responds in unison. We have previously applied the automated time lag technique of Viall & Klimchuk to disk observations of an active region (AR) made by the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory. Lines of sight passing through coronal plasma show clear evidence for post-nanoflare cooling, while lines of sight intersecting the TR footpoints of coronal strands show zero time lag. In this paper, we use the EBTEL hydrodynamics code to demonstrate that this is precisely the expected behavior when the corona is heated by nanoflares. We also apply the time lag technique for the first time to off-limb observations of an AR. Since TR emission is not present above the limb, the occurrence of zero time lags is greatly diminished, supporting the conclusion that zero time lags measured on the disk are due to TR plasma. Lastly, we show that the "coronal" channels in AIA can be dominated by bright TR emission. When defined in a physically meaningful way, the TR reaches a temperature of roughly 60% the peak temperature in a flux tube. The TR resulting from impulsive heating can extend to 3 MK and higher, well within the range of the "coronal" AIA channels.

  7. The Transition Region Response to a Coronal Nanoflare: Forward Modeling and Observations in SDO/AIA

    NASA Astrophysics Data System (ADS)

    Viall, Nicholeen M.; Klimchuk, James A.

    2015-01-01

    The corona and transition region (TR) are fundamentally coupled through the processes of thermal conduction and mass exchange. It is not possible to understand one without the other. Yet the temperature-dependent emissions from the two locations behave quite differently in the aftermath of an impulsive heating event such as a coronal nanoflare. Whereas the corona cools sequentially, emitting first at higher temperatures and then at lower temperatures, the TR is multithermal and the emission at all temperatures responds in unison. We have previously applied the automated time lag technique of Viall & Klimchuk to disk observations of an active region (AR) made by the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory. Lines of sight passing through coronal plasma show clear evidence for post-nanoflare cooling, while lines of sight intersecting the TR footpoints of coronal strands show zero time lag. In this paper, we use the EBTEL hydrodynamics code to demonstrate that this is precisely the expected behavior when the corona is heated by nanoflares. We also apply the time lag technique for the first time to off-limb observations of an AR. Since TR emission is not present above the limb, the occurrence of zero time lags is greatly diminished, supporting the conclusion that zero time lags measured on the disk are due to TR plasma. Lastly, we show that the ''coronal'' channels in AIA can be dominated by bright TR emission. When defined in a physically meaningful way, the TR reaches a temperature of roughly 60% the peak temperature in a flux tube. The TR resulting from impulsive heating can extend to 3 MK and higher, well within the range of the ''coronal'' AIA channels.

  8. 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.

  9. On the Correlation between Coronal and Lower Transition Region Structures at Arcsecond Scales

    NASA Astrophysics Data System (ADS)

    Vourlidas, A.; Klimchuk, J. A.; Korendyke, C. M.; Tarbell, T. D.; Handy, B. N.

    2001-12-01

    We compare the morphology of active region structures observed in the 171 Å (T~9×105 K) and Lyα (T~2×104 K) lines. The coronal data were obtained by the Transition Region and Coronal Explorer (TRACE) in support of the Very High Angular Resolution Ultraviolet Telescope (VAULT) sounding rocket launch, which acquired subarcsecond resolution images of an active region in the Lyα line, on 1999 May 7. Using a pair of calibrated, nearly simultaneous images, we find that: (i) a very good correlation exists between the Lyα and 171 Å intensities in the TRACE moss regions, (ii) we can identify several identical structures in some (but not all) moss areas, and (iii) the correlations are greatly reduced at the footpoints of the 171 Å large-scale loops. We derive a lower limit for the Lyα emission measure, under the assumption of effectively optically thin emission, and compare it to the 171 Å emission measure. As in previous studies, we find an excess of Lyα material compared to the amount expected for a thermal conduction-dominated corona-chromosphere transition region, even for structures that appear to be identical in the two wavelengths. This result implies that some other mechanism besides classical heat conduction from the corona must contribute to the observed Lyα intensities. The observations do not support the idea of a physically distinct cool loop component within active regions.

  10. Plasma Conditions in Polar Plumes and Interplume Regions in Polar Coronal Holes

    NASA Astrophysics Data System (ADS)

    Cranmer, S. R.; Kohl, J. L.; Miralles, M.; Panasyuk, A. V.

    2001-05-01

    During times of low solar activity, large polar coronal holes are observed to contain bright raylike polar plumes that appear to follow open magnetic field lines. Plumes are believed to be flux tubes that are heated impulsively at their base, which leads to a higher density, a lower outflow speed, and a lower overall temperature in the extended corona, compared to the surrounding interplume regions. Despite years of white light and spectroscopic observations, though, the differences in mass, momentum, and energy flux in plumes and between plumes are not known precisely. This poster presents an updated survey of data from the Ultraviolet Coronagraph Spectrometer (UVCS), aboard SOHO, that attempts to sort out the local plume and interplume conditions. These results will be compared with previous analyses that characterized the ``mean'' plume/interplume coronal hole, averaged over many lines of sight through varying concentrations of plumes. Limits on the relative contributions of plumes and interplume regions to the high-speed solar wind will be determined, with emphasis on the proton outflow speed in the corona and at 1 AU. Implications for theoretical models of coronal heating and solar wind acceleration will be discussed. This work is supported by the National Aeronautics and Space Administration under grant NAG5-10093 to the Smithsonian Astrophysical Observatory, by Agenzia Spaziale Italiana, and by the Swiss contribution to the ESA PRODEX program.

  11. Particle Acceleration at Low Coronal Compression Regions and Shocks

    NASA Astrophysics Data System (ADS)

    Schwadron, N. A.; Lee, M. A.; Gorby, M.; Lugaz, N.; Spence, H. E.; Desai, M.; Török, T.; Downs, C.; Linker, J.; Lionello, R.; Mikić, Z.; Riley, P.; Giacalone, J.; Jokipii, J. R.; Kota, J.; Kozarev, K.

    2015-09-01

    We present a study on particle acceleration in the low corona associated with the expansion and acceleration of coronal mass ejections (CMEs). Because CME expansion regions low in the corona are effective accelerators over a finite spatial region, we show that there is a rigidity regime where particles effectively diffuse away and escape from the acceleration sites using analytic solutions to the Parker transport equation. This leads to the formation of broken power-law distributions. Based on our analytic solutions, we find a natural ordering of the break energy and second power-law slope (above the break energy) as a function of the scattering characteristics. These relations provide testable predictions for the particle acceleration from low in the corona. Our initial analysis of solar energetic particle observations suggests a range of shock compression ratios and rigidity dependencies that give rise to the solar energetic particle (SEP) events studied. The wide range of characteristics inferred suggests competing mechanisms at work in SEP acceleration. Thus, CME expansion and acceleration in the low corona may naturally give rise to rapid particle acceleration and broken power-law distributions in large SEP events.

  12. Observations of an Emerging Flux Region Surge: Implications for Coronal Mass Ejections Triggered by Emerging Flux

    NASA Astrophysics Data System (ADS)

    Liu, Y.; Su, J. T.; Morimoto, T.; Kurokawa, H.; Shibata, K.

    2005-08-01

    It is well known that coronal mass ejections (CMEs) are often associated with flares and filament eruptions. Previous studies of CMEs, however, have not established any association between CMEs and surges. In this paper, we present a detailed analysis of a large emerging flux region (EFR) surge and a jetlike CME, both observed on 1998 April 16. Our analysis shows a close temporal and spatial relationship between the two. Using observations from the Large Angle and Spectrometric Coronagraph (LASCO) and Hida Flare Monitoring Telescope (Hα, Hα+/-0.8 Å), we found that the CME's onset time and central position angle were coincident with the surge features. Magnetograms and Hα filtergrams showed that the surge resulted from the successive emergence of a bipolar sunspot group, NOAA Active Region 8203, which was the only active region in the northern hemisphere. The surge was impulsively accelerated at around the peak time of the GOES SXR flux. The associated CME appeared in the field of view of LASCO C2 16 minutes after the surge disappeared. Importantly, observations from the EUV Imaging Telescope at λ195 Å clearly demonstrate topological changes in the coronal field due to its interaction with the EFR. An initially closed EFR-loop system opened up during the surge. There was no filament involved in this surge-CME event. We propose that the onset of the CME resulted from the significant restructuring of the large-scale coronal magnetic field as a result of flux emergence in the active region. This surge-CME event strongly suggests that emerging flux may not only trigger a surge but also simultaneously trigger a CME by means of small-scale reconnection in the lower atmosphere.

  13. 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

  14. 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

  15. MEASUREMENTS OF THE CORONAL ACCELERATION REGION OF A SOLAR FLARE

    SciTech Connect

    Krucker, Saem; Hudson, H. S.; Glesener, L.; Lin, R. P.; White, S. M.; Masuda, S.; Wuelser, J.-P.

    2010-05-10

    The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and the Nobeyama Radioheliograph (NoRH) are used to investigate coronal hard X-ray and microwave emissions in the partially disk-occulted solar flare of 2007 December 31. The STEREO mission provides EUV images of the flare site at different viewing angles, establishing a two-ribbon flare geometry and occultation heights of the RHESSI and NoRH observations of {approx}16 Mm and {approx}25 Mm, respectively. Despite the occultation, intense hard X-ray emission up to {approx}80 keV occurs during the impulsive phase from a coronal source that is also seen in microwaves. The hard X-ray and microwave source during the impulsive phase is located {approx}6 Mm above thermal flare loops seen later at the soft X-ray peak time, similar in location to the above-the-loop-top source in the Masuda flare. A single non-thermal electron population with a power-law distribution (with spectral index of {approx}3.7 from {approx}16 keV up to the MeV range) radiating in both bremsstrahlung and gyrosynchrotron emission can explain the observed hard X-ray and microwave spectrum, respectively. This clearly establishes the non-thermal nature of the above-the-loop-top source. The large hard X-ray intensity requires a very large number (>5 x 10{sup 35} above 16 keV for the derived upper limit of the ambient density of {approx}8 x 10{sup 9} cm{sup -3}) of suprathermal electrons to be present in this above-the-loop-top source. This is of the same order of magnitude as the number of ambient thermal electrons. We show that collisional losses of these accelerated electrons would heat all ambient electrons to superhot temperatures (tens of keV) within seconds. Hence, the standard scenario, with hard X-rays produced by a beam comprising the tail of a dominant thermal core plasma, does not work. Instead, all electrons in the above-the-loop-top source seem to be accelerated, suggesting that the above-the-loop-top source is itself the

  16. Three-dimensional magnetic field topology in a region of solar coronal heating.

    PubMed

    Solanki, S K; Lagg, A; Woch, J; Krupp, N; Collados, M

    2003-10-16

    Flares and X-ray jets on the Sun arise in active regions where magnetic flux emerges from the solar interior amd interacts with the ambient magnetic field. The interactions are believed to occur in electric current sheets separating regions of opposite magnetic polarity. The current sheets located in the corona or upper chromosphere have long been thought to act as an important source of coronal heating, requiring their location in the corona or upper chromosphere. The dynamics and energetics of these sheets are governed by a complex magnetic field structure that, until now, has been difficult to measure. Here we report the determination of the full magnetic vector in an interaction region near the base of the solar corona. The observations reveal two magnetic features that characterize young active regions on the Sun: a set of rising magnetic loops and a tangential discontinuity of the magnetic field direction, the latter being the observational signature of an electric current sheet. This provides strong support for coronal heating models based on the dissipation of magnetic energy at current sheets. PMID:14562096

  17. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  19. Recent perspectives in solar physics - Elemental composition, coronal structure and magnetic fields, solar activity

    NASA Technical Reports Server (NTRS)

    Newkirk, G., Jr.

    1975-01-01

    Elemental abundances in the solar corona are studied. Abundances in the corona, solar wind and solar cosmic rays are compared to those in the photosphere. The variation in silicon and iron abundance in the solar wind as compared to helium is studied. The coronal small and large scale structure is investigated, emphasizing magnetic field activity and examining cosmic ray generation mechanisms. The corona is observed in the X-ray and EUV regions. The nature of coronal transients is discussed with emphasis on solar-wind modulation of galactic cosmic rays. A schematic plan view of the interplanetary magnetic field during sunspot minimum is given showing the presence of magnetic bubbles and their concentration in the region around 4-5 AU by a fast solar wind stream.

  20. The Transition Region Response to a Coronal Nanoflare: Forward Modeling and Observations in SDO/AIA

    NASA Astrophysics Data System (ADS)

    Viall, Nicholeen; Klimchuk, James A.

    2016-05-01

    The corona and transition region (TR) are fundamentally coupled through the processes of thermal conduction and mass exchange. Yet the temperature-dependent emissions from the two locations behave quite differently in the aftermath of an impulsive heating event such as a coronal nanoflare. In this presentation, we use results from the EBTEL hydrodynamics code to demonstrate that after a coronal nanoflare, the TR is multithermal and the emission at all temperatures responds in unison. This is in contrast to the coronal plasma, which cools sequentially, emitting first at higher temperatures and then at lower temperatures. We apply the time lag technique of Viall & Klimchuk (2012) to the simulated Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory emission and show that coronal plasma light curves exhibit post-nanoflare cooling time lags, while TR light curves show time lags of zero, as observed. We further demonstrate that time lags of zero, regardless of physical cause, do not indicate a lack of variability. Rather, strong variability must be present, and it must occur in unison in the different channels. Lastly, we show that the 'coronal' channels in AIA can be dominated by bright TR emission. When defined in a physically meaningful way, the TR reaches a temperature of roughly 60% the peak temperature in a flux tube. The TR resulting from impulsive heating can extend to 3 MK and higher, well within the range of the 'coronal' AIA channels.

  1. Reexamination of the coronal index of solar activity

    NASA Astrophysics Data System (ADS)

    Rybanský, M.; Rušin, V.; Minarovjech, M.; Klocok, L.; Cliver, E. W.

    2005-08-01

    The coronal index (CI) of solar activity is the irradiance of the Sun as a star in the coronal green line (Fe XIV, 530.3 nm or 5303 Å). It is derived from ground-based observations of the green corona made by the network of coronal stations (currently Kislovodsk, Lomnický Štít, Norikura, and Sacramento Peak). The CI was introduced by Rybanský (1975) to facilitate comparison of ground-based green line measurements with satellite-based extreme ultraviolet and soft X-ray observations. The CI since 1965 is based on the Lomnický Štít photometric scale; the CI was extended to earlier years by Rybanský et al. (1994) based on cross-calibrations of Lomnický Štít data with measurements made at Pic du Midi and Arosa. The resultant 1939-1992 CI had the interesting property that its value at the peak of the 11-year cycle increased more or less monotonically from cycle 18 through cycle 22 even though the peak sunspot number of cycle 20 exhibited a significant local minimum between that of cycles 19 and 21. Rušin and Rybanský (2002) recently showed that the green line intensity and photospheric magnetic field strength were highly correlated from 1976 to 1999. Since the photospheric magnetic field strength is highly correlated with sunspot number, the lack of close correspondence between the sunspot number and the CI from 1939 to 2002 is puzzling. Here we show that the CI and sunspot number are highly correlated only after 1965, calling the previously-computed coronal index for earlier years (1939-1965) into question. We can use the correlation between the CI and sunspot number (also the 2800 MHz radio flux and the cosmic ray intensity) to recompute daily values of the CI for years before 1966. In fact, this method can be used to obtain CI values as far back as we have reliable sunspot observations (˜1850). The net result of this exercise is a CI that closely tracks the sunspot number at all times. We can use the sunspot-CI relationship (for 1966-2002) to identify

  2. Chromospheric and coronal variation across stellar activity cycles

    NASA Astrophysics Data System (ADS)

    Hagen, Cedric; Miller, Brendan P.; Gallo, Elena; Wright, Jason; Isaacson, Howard T.; Henry, Gregory W.

    2015-01-01

    We investigate cyclic chromospheric and coronal activity in main-sequence stars, using Ca II H and K core emission and X-ray luminosities, respectively. From a sample of 244 nearby stars with high-cadence Keck optical spectroscopy spanning up to 17 years (obtained for the California Planet Search program), we use automated sinusoid modeling and goodness-of-fit criteria to identify 33 stars with highly significant cyclic R'HK variability. The cycle periods are refined using mmag APT optical photometry. We also construct a comparison sample of 23 stars that show virtually no R'HK variability. The cyclic and flat stars have similar B-V and absolute magnitude distributions but the cyclic stars tend to be more active, with greater median R'HK values. We present new Swift/XRT observations of 10 cyclic stars and 1 flat star, totaling 32.6 ks; 5/11 are detected in this snapshot pilot survey. A comparison of their current-epoch X-ray luminosities to archival ROSAT values shows variation by a factor of 2-3 is common on decade-long timescales. Several stars also show suggestive evidence for X-ray variability on much shorter timescales, perhaps related to stellar rotation and coronal inhomogeneity or to small flares. We use the chromospheric activity cycles to calculate the phase of each X-ray observation. Additional Swift observations are ongoing and with this larger dataset we will measure the typical amplitude of cyclic X-ray variation. We discuss our initial results in the context of magnetic dynamo activity and consider the implications for exoplanet atmosphere heating and evaporation.

  3. 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.

  4. Polar Coronal Hole Ephemeral Regions, the Fast Solar Wind and the Global Magnetic Dynamo

    NASA Technical Reports Server (NTRS)

    Cirtain, Jonathan W.

    2010-01-01

    The X-Ray Telescope aboard Hinode has been regularly observing both the north and south solar polar coronal holes from November 2006 through March 2009. We use the observations of emerged flux regions within the coronal hole as evidenced by small x-ray bright points to study the physical properties of these regions. The width of the emerged flux region loop footpoints, the duration of the x-ray emission lifetime for the emerged flux region, the latitude of formation and whether an x-ray or EUV jet was observed were all recorded. In the present work we detail these observations and show a dependence on the width of the emerged flux region (bright point) to the number of x-ray jets observed. The distribution of base width is then related to a power law for number of emerged flux regions as a function of base width.

  5. Distribution and relative activity of matrix metalloproteinase-2 in human coronal dentin

    PubMed Central

    Boushell, Lee W; Kaku, Masaru; Mochida, Yoshiyuki; Yamauchi, Mitsuo

    2011-01-01

    The presence of matrix metalloproteinase-2 (MMP-2) in dentin has been reported, but its distribution and activity level in mature human coronal dentin are not well understood. The purpose of this study was to determine the MMP-2 distribution and relative activity in demineralized dentin. Crowns of twenty eight human molars were sectioned into inner (ID), middle (MD), and outer dentin (OD) regions and demineralized. MMP-2 was extracted with 0.33 mol·L−1 EDTA/2 mol·L−1 guanidine-HCl, pH 7.4, and MMP-2 concentration was estimated with enzyme-linked immunoabsorbant assay (ELISA). Further characterization was accomplished by Western blotting analysis and gelatin zymography. The mean concentrations of MMP-2 per mg dentin protein in the dentin regions were significantly different (P=0.043): 0.9 ng (ID), 0.4 ng (MD), and 2.2 ng (OD), respectively. The pattern of MMP-2 concentration was OD>ID>MD. Western blotting analysis detected ∼66 and ∼72 kDa immunopositive proteins corresponding to pro- and mature MMP-2, respectively, in the ID and MD, and a ∼66 kDa protein in the OD. Gelatinolytic activity consistent with MMP-2 was detected in all regions. Interestingly, the pattern of levels of Western blot immunodetection and gelatinolytic activity was MD>ID>OD. The concentration of MMP-2 in human coronal dentin was highest in the region of dentin that contains the dentinoenamel junction and least in the middle region of dentin. However, levels of Western blot immunodetection and gelatinolytic activity did not correlate with the estimated regional concentrations of MMP-2, potentially indicating region specific protein interactions. PMID:22010577

  6. Coronal extension of flaring region magnetic fields inferred from high-resolution microwave and type III burst observations

    NASA Technical Reports Server (NTRS)

    Lantos, P.; Pick, M.; Kundu, M. R.

    1984-01-01

    Observations of three solar radio bursts, obtained with the Very Large Array of the National Radio Astronomy Observatory at 6 cm wavelength, have been combined with meter observations from the Mark III Nancay Radioheliograph. There is a good correlation between solar activity observed at the two wavelength domains. A small change by about 10 sec in the centimetric burst location corresponds to a large change, by about 0.5 solar radius, in the related metric type III burst location. This indicates discrete injection/acceleration regions and the presence of very divergent magnetic fields. The bursts come from two distinct active regions. With two-dimensional spatial resolution, it is shown that, in this sample, each active region possesses a coronal extension that is separated from that of the neighboring active region.

  7. Coronal holes, large-scale magnetic field, and activity complexes in solar cycle 23

    NASA Astrophysics Data System (ADS)

    Tavastsherna, K. S.; Polyakow, E. V.

    2014-12-01

    A correlation among coronal holes (CH), a large-scale magnetic field (LMF), and activity complexes (AC) is studied in this work for 1997-2007 with the use of a coronal hole series obtained from observations at the Kitt Peak Observatory in the HeI 10830 Å line in 1975-2003 and SOHO/EIT-195 Å in 1996-2012 (Tlatov et al., 2014), synoptic Hα charts from Kislovodsk Mountain Astonomical Station, and the catalog of AC cores (Yazev, 2012). From the imposition of CH boundaries on Hα charts, which characterize the positions of neutral lines of the radial components of a large-scale solar magnetic field, it turns out that 70% of CH are located in unipolar regions of their sign during the above period, 10% are in the region of an opposite sign, and 20% are mainly very large CH, which are often crossed by the neutral lines of several unipolar regions. Data on mutual arrangement of CH and AC cores were obtained. It was shown that only some activity comples cores have genetic relationships with CH.

  8. The coronal field lines of an evolving bipolar magnetic region

    NASA Technical Reports Server (NTRS)

    Sheeley, N. R., Jr.

    1982-01-01

    A simple potential field model is presented to illustrate that loops of magnetic flux rise upward through the corona during the relatively short growth phase of a bipolar magnetic region but contract back to the sun's surface during the much longer decay phase of the photospheric region. To reconcile this behavior with the unidirectional, solar-wind-driven convection of flux outward from the sun, one must postulate the existence of an X-type neutral line in the middle corona where open field lines can be converted back to closed ones.

  9. Planar magnetic structures in coronal mass ejection-driven sheath regions

    NASA Astrophysics Data System (ADS)

    Palmerio, Erika; Kilpua, Emilia; Savani, Neel

    2016-04-01

    Coronal Mass Ejections (CMEs) often travel in the interplanetary space faster than the ambient solar wind. When their relative velocities exceed the local magnetosonic speed, a shock wave forms. The region between the shock front and the leading edge is known as sheath region. Sheaths are compressed regions characterized by turbulent magnetic field and plasma properties and they can cause significant space weather disturbances. Moreover, sheaths often exhibit a complex internal structure, which makes understanding their formation and predicting their geoeffectivity particularly difficult. Planar magnetic structures (PMSs) are frequently reported in CME-driven sheath regions. The magnetic field vectors in a PMS are characterized by abrupt changes in direction and magnitude, but they all remain for a time interval of several hours nearly parallel to a single plane that includes the interplanetary magnetic field (IMF) spiral direction but is inclined to the ecliptic plane. We present the study of PMSs in the sheath region of CMEs for a sample of 95 events observed in situ by the ACE and Wind spacecraft in the period 1997-2015. The presence of planar structures is detected with an automated method and evaluated through the minimum variance analysis (MVA), needed for determining the normal vector to the PMS-plane. We relate the occurrence and location of the PMSs to various shock, sheath and CME properties. We show in addition the dependence of the angle between the IP shock and PMS plane normals with respect to the PMS location within the sheath. Finally, we study the amount of strongly southward magnetic fields in planar and non-planar parts of the sheath, aiming at determining whether either feature is more likely to drive magnetospheric activity.

  10. OBSERVATIONAL ASPECTS OF THE THREE-DIMENSIONAL CORONAL STRUCTURE OVER A SOLAR ACTIVITY CYCLE

    SciTech Connect

    Morgan, Huw; Habbal, Shadia Rifai

    2010-02-10

    Solar rotational tomography is applied to almost eleven years of Large Angle Spectrometric Coronagraph C2/Solar and Heliospheric Observatory data, revealing for the first time the behavior of the large-scale coronal density structures, also known as streamers, over almost a full solar activity cycle. This study gives an overview of the main results of this project. (1) Streamers are most often shaped as extended, narrow plasma sheets. The sheets can be extremely narrow at times (<=0.14 x 10{sup 6} km at 4 R{sub sun}). This is over twice their heliocentric angular thickness at 1 AU. (2) At most times outside the height of solar maximum, there are two separate stable large helmet streamer belts extending from mid-latitudes (in both north and south). At solar minimum, the streamers converge and join near the equator, giving the impression of a single large helmet streamer. Outside of solar minimum, the two streamers do not join, forming separate high-density sheets in the extended corona (one in the north, another in the south). At solar maximum, streamers rise radially from their source regions, while during the ascending and descending activity phases, streamers are skewed toward the equator. (3) For most of the activity cycle, streamers share the same latitudinal extent as filaments on the disk, showing that large-scale stable streamers are closely linked to the same large-scale photospheric magnetic configuration, which give rise to large filaments. (4) The poleward footpoints of the streamers are often above crown polar filaments and the equatorial footpoints are above filaments or active regions (or above the photospheric neutral lines which underlie these structures). The high-density structures arising from the equatorial active regions either rise and form the equatorial footpoints of mid-latitude quiescent streamers, or form unstable streamers at the equator, not connected to the quiescent streamer structure at higher latitude (so there are often three

  11. 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.

  12. Study of the Source Regions of Coronal Mass Ejections Using Yohkoh SXT Data

    NASA Technical Reports Server (NTRS)

    Webb, David F.; Kahler, Stephen W.

    1997-01-01

    The scientific objective of the program was to better understand how CMEs (Coronal Mass Ejections) are initiated at the sun by examining structures on the disk which are related to the origins of CMEs. CMEs represent important disruptions of large-scale structures of closed magnetic fields in the corona, and result in significant disturbances of the interplanetary medium and near-Earth space. The program pertained to NASA's objectives of understanding the physics of solar activity and the structured and evolution of the corona, and the results are being applied to understanding CMEs currently being observed by SOHO near the sun and by WIND and Ulysses in the heliosphere. Three general areas of research were pursued in the program. One was to use Yohkoh soft X-ray telescope (SXT) images of eruptive events visible against the solar disk to examine the coronal structures and the boundaries of the large-scale magnetic fields considered to be involved in coronal mass ejections (CMEs). The second area involved a survey and study of SXT X-ray arcade events which exhibit dimming, or the possible depletion of coronal material above and possibly before onset of the bright long-duration event (LDE). Finally, we studied the SXT data during periods when white light CMEs were observed the HAO Mauna Loa K-coronameter and, conversely, we examined the white light data during periods when expanding X-ray loops were observed at the limb.

  13. ACTIVE LONGITUDES REVEALED BY LARGE-SCALE AND LONG-LIVED CORONAL STREAMERS

    SciTech Connect

    Li Jing

    2011-07-10

    We use time-series ultraviolet full sun images to construct limb-synoptic maps of the Sun. On these maps, large-scale, long-lived coronal streamers appear as repetitive sinusoid-like arcs projected over the polar regions. They are caused by high altitude plasma produced from sunspot-rich regions at latitudes generally far from the poles. The non-uniform longitudinal distribution of these streamers reveals four longitudinal zones at the surface of the Sun from which sunspots erupt preferentially over the 5 year observing interval (2006 January to 2011 April). Spots in these zones (or clusters) have individual lifetimes short compared to the lifetimes of the coronal features which they sustain, and they erupt at different times. The four sunspot clusters contain >75% of all numbered sunspots in this period. They occupy two distinct longitudinal zones separated by {approx}180{sup 0} and each spanning {approx}100{sup 0} in longitude. The rotation rates of the spot clusters are {approx}5% faster than the rates at both the surface and the bottom of the convection zone. While no convincing theoretical framework exists to interpret the sunspot clusters in the longitude-time space, their persistent and nonuniform distribution indicates long-lived, azimuthal structures beneath the surface, and are compatible with the existence of previously reported active longitudes on the Sun.

  14. Quiet-Sun Hα Transients and Corresponding Small-scale Transition Region and Coronal Heating

    NASA Astrophysics Data System (ADS)

    Henriques, V. M. J.; Kuridze, D.; Mathioudakis, M.; Keenan, F. P.

    2016-04-01

    Rapid blue- and redshifted excursions (RBEs and RREs) are likely to be the on-disk counterparts of Type II spicules. Recently, heating signatures from RBEs/RREs have been detected in IRIS slit-jaw images dominated by transition region (TR) lines around network patches. Additionally, signatures of Type II spicules have been observed in Atmospheric Imaging Assembly (AIA) diagnostics. The full-disk, ever-present nature of the AIA diagnostics should provide us with sufficient statistics to directly determine how important RBEs and RREs are to the heating of the TR and corona. We find, with high statistical significance, that at least 11% of the low coronal brightenings detected in a quiet-Sun region in He ii 304 Å can be attributed to either RBEs or RREs as observed in Hα, and a 6% match of Fe IX 171 Å detected events to RBEs or RREs with very similar statistics for both types of Hα features. We took a statistical approach that allows for noisy detections in the coronal channels and provides us with a lower, but statistical significant, bound. Further, we consider matches based on overlapping features in both time and space, and find strong visual indications of further correspondence between coronal events and co-evolving but non-overlapping, RBEs and RREs.

  15. FGFR2c-mediated ERK-MAPK activity regulates coronal suture development.

    PubMed

    Pfaff, Miles J; Xue, Ke; Li, Li; Horowitz, Mark C; Steinbacher, Derek M; Eswarakumar, Jacob V P

    2016-07-15

    Fibroblast growth factor receptor 2 (FGFR2) signaling is critical for proper craniofacial development. A gain-of-function mutation in the 2c splice variant of the receptor's gene is associated with Crouzon syndrome, which is characterized by craniosynostosis, the premature fusion of one or more of the cranial vault sutures, leading to craniofacial maldevelopment. Insight into the molecular mechanism of craniosynostosis has identified the ERK-MAPK signaling cascade as a critical regulator of suture patency. The aim of this study is to investigate the role of FGFR2c-induced ERK-MAPK activation in the regulation of coronal suture development. Loss-of-function and gain-of-function Fgfr2c mutant mice have overlapping phenotypes, including coronal synostosis and craniofacial dysmorphia. In vivo analysis of coronal sutures in loss-of-function and gain-of-function models demonstrated fundamentally different pathogenesis underlying coronal suture synostosis. Calvarial osteoblasts from gain-of-function mice demonstrated enhanced osteoblastic function and maturation with concomitant increase in ERK-MAPK activation. In vitro inhibition with the ERK protein inhibitor U0126 mitigated ERK protein activation levels with a concomitant reduction in alkaline phosphatase activity. This study identifies FGFR2c-mediated ERK-MAPK signaling as a key mediator of craniofacial growth and coronal suture development. Furthermore, our results solve the apparent paradox between loss-of-function and gain-of-function FGFR2c mutants with respect to coronal suture synostosis. PMID:27034231

  16. Multi-scale statistical analysis of coronal solar activity

    DOE PAGESBeta

    Gamborino, Diana; del-Castillo-Negrete, Diego; Martinell, Julio J.

    2016-07-08

    Multi-filter images from the solar corona are used to obtain temperature maps that are analyzed using techniques based on proper orthogonal decomposition (POD) in order to extract dynamical and structural information at various scales. Exploring active regions before and after a solar flare and comparing them with quiet regions, we show that the multi-scale behavior presents distinct statistical properties for each case that can be used to characterize the level of activity in a region. Information about the nature of heat transport is also to be extracted from the analysis.

  17. Multi-scale statistical analysis of coronal solar activity

    NASA Astrophysics Data System (ADS)

    Gamborino, Diana; del-Castillo-Negrete, Diego; Martinell, Julio J.

    2016-07-01

    Multi-filter images from the solar corona are used to obtain temperature maps that are analyzed using techniques based on proper orthogonal decomposition (POD) in order to extract dynamical and structural information at various scales. Exploring active regions before and after a solar flare and comparing them with quiet regions, we show that the multi-scale behavior presents distinct statistical properties for each case that can be used to characterize the level of activity in a region. Information about the nature of heat transport is also to be extracted from the analysis.

  18. Solar Magnetic Activity Cycles, Coronal Potential Field Models and Eruption Rates

    NASA Astrophysics Data System (ADS)

    Petrie, G. J. D.

    2013-05-01

    We study the evolution of the observed photospheric magnetic field and the modeled global coronal magnetic field during the past 3 1/2 solar activity cycles observed since the mid-1970s. We use synoptic magnetograms and extrapolated potential-field models based on longitudinal full-disk photospheric magnetograms from the National Solar Observatory's three magnetographs at Kitt Peak, the Synoptic Optical Long-term Investigations of the Sun vector spectro-magnetograph, the spectro-magnetograph and the 512-channel magnetograph instruments, and from Stanford University's Wilcox Solar Observatory. The associated multipole field components are used to study the dominant length scales and symmetries of the coronal field. Polar field changes are found to be well correlated with active fields over most of the period studied, except between 2003 and 2006 when the active fields did not produce significant polar field changes. Of the axisymmetric multipoles, only the dipole and octupole follow the poles whereas the higher orders follow the activity cycle. All non-axisymmetric multipole strengths are well correlated with the activity cycle. The tilt of the solar dipole is therefore almost entirely due to active-region fields. The axial dipole and octupole are the largest contributors to the global field except while the polar fields are reversing. This influence of the polar fields extends to modulating eruption rates. According to the Computer Aided CME Tracking, Solar Eruptive Event Detection System, and Nobeyama radioheliograph prominence eruption catalogs, the rate of solar eruptions is found to be systematically higher for active years between 2003 and 2012 than for those between 1997 and 2002. This behavior appears to be connected with the weakness of the late-cycle 23 polar fields as suggested by Luhmann. We see evidence that the process of cycle 24 field reversal is well advanced at both poles.

  19. Broken Power-law Distributions from Low Coronal Compression Regions or Shocks

    NASA Astrophysics Data System (ADS)

    Schwadron, N. A.; Lee, M. A.; Gorby, M.; Lugaz, N.; Spence, H. E.; Desai, M.; Török, T.; Downs, C.; Linker, J.; Lionello, R.; Mikić, Z.; Riley, P.; Giacalone, J.; Jokipii, J. R.; Kota, J.; Kozarev, K.

    2015-09-01

    Coronal Mass Ejection (CME) expansion regions low in the corona (< 2 - 3 Rs) are highly efficient for the acceleration of energetic particles. Because the acceleration occurs over a finite spatial region, there is a regime where particles diffuse away and escape from the acceleration sites, leading to the formation of broken power-law distributions. This paper highlights recent results indicating that CME expansion and acceleration in the low corona may cause rapid particle acceleration and create large solar energetic particle events with broken power-law distributions.

  20. The Magnetic Free Energy in Active Regions

    NASA Technical Reports Server (NTRS)

    Metcalf, Thomas R.; Mickey, Donald L.; LaBonte, Barry J.

    2001-01-01

    The magnetic field permeating the solar atmosphere governs much of the structure, morphology, brightness, and dynamics observed on the Sun. The magnetic field, especially in active regions, is thought to provide the power for energetic events in the solar corona, such as solar flares and Coronal Mass Ejections (CME) and is believed to energize the hot coronal plasma seen in extreme ultraviolet or X-rays. The question remains what specific aspect of the magnetic flux governs the observed variability. To directly understand the role of the magnetic field in energizing the solar corona, it is necessary to measure the free magnetic energy available in active regions. The grant now expiring has demonstrated a new and valuable technique for observing the magnetic free energy in active regions as a function of time.

  1. The Near-infrared Coronal Line Spectrum of 54 nearby Active Galactic Nuclei

    NASA Astrophysics Data System (ADS)

    Rodríguez-Ardila, A.; Prieto, M. A.; Portilla, J. G.; Tejeiro, J. M.

    2011-12-01

    The relationship between the emission of coronal lines (CLs) and nuclear activity in 36 Type 1 and 18 Type 2 active galactic nuclei (AGNs) is analyzed, for the first time, based on near-infrared (0.8-2.4 μm) spectra. The eight CLs studied, of Si, S, Fe, Al, and Ca elements and corresponding to ionization potentials (IPs) in the range 125-450 eV, are detected (3σ) in 67% (36 AGNs) of the sample. Our analysis shows that the four most frequent CLs [Si VI] 1.963 μm, [S VIII] 0.9913 μm, [S IX] 1.252 μm, and [Si X] 1.430 μm display a narrow range in luminosity, with most lines located in the interval log L 39-40 erg s-1. We found that the non-detection is largely associated with either loss of spatial resolution or increasing object distance: CLs are essentially nuclear and easily lose contrast in the continuum stellar light for nearby sources or get diluted by the strong AGN continuum as the redshift increases. Yet, there are AGNs where the lack of coronal emission, i.e., lines with IP >= 100 eV, may be genuine. The absence of these lines reflects a non-standard AGN ionizing continuum, namely, a very hard spectrum lacking photons below a few Kev. The analysis of the line profiles points out a trend of increasing FWHM with increasing IPs up to energies around 300 eV, where a maximum in the FWHM is reached. For higher IP lines, the FWHM remains nearly constant or decreases with increasing IPs. We ascribe this effect to an increasing density environment as we approach the innermost regions of these AGNs, where densities above the critical density of the CLs with IPs larger than 300 eV are reached. This sets a strict range limit for the density in the boundary region between the narrow and the broad region of 108-109 cm-3. A relationship between the luminosity of the CLs and that of the soft and hard X-ray emission and the soft X-ray photon index is observed: the coronal emission becomes stronger with both increasing X-ray emission (soft and hard) and steeper X

  2. 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.

  3. Statistical Study of Network Jets Observed in the Solar Transition Region: a Comparison Between Coronal Holes and Quiet-Sun Regions

    NASA Astrophysics Data System (ADS)

    Narang, Nancy; Arbacher, Rebecca T.; Tian, Hui; Banerjee, Dipankar; Cranmer, Steven R.; DeLuca, Ed E.; McKillop, Sean

    2016-04-01

    Recent IRIS observations have revealed a prevalence of intermittent small-scale jets with apparent speeds of 80 - 250 km s^{-1}, emanating from small-scale bright regions inside network boundaries of coronal holes. We find that these network jets appear not only in coronal holes but also in quiet-sun regions. Using IRIS 1330 Å (C II) slit-jaw images, we extracted several parameters of these network jets, e.g. apparent speed, length, lifetime, and increase in foot-point brightness. Using several observations, we find that some properties of the jets are very similar, but others are obviously different between the quiet Sun and coronal holes. For example, our study shows that the coronal-hole jets appear to be faster and longer than those in the quiet Sun. This can be directly attributed to a difference in the magnetic configuration of the two regions, with open magnetic field lines rooted in coronal holes and magnetic loops often present in the quiet Sun. We also detected compact bright loops that are most likely transition region loops and are mostly located in quiet-Sun regions. These small loop-like regions are generally devoid of network jets. In spite of different magnetic structures in the coronal hole and quiet Sun in the transition region, there appears to be no substantial difference for the increase in footpoint brightness of the jets, which suggests that the generation mechanism of these network jets is very likely the same in both regions.

  4. Coronal mass ejection-related particle acceleration regions during a simple eruptive event

    NASA Astrophysics Data System (ADS)

    Salas-Matamoros, Carolina; Klein, Karl-Ludwig; Rouillard, Alexis P.

    2016-05-01

    An intriguing feature of many solar energetic particle (SEP) events is the detection of particles over a very extended range of longitudes in the heliosphere. This may be due to peculiarities of the magnetic field in the corona, to a broad accelerator, to cross-field transport of the particles, or to a combination of these processes. The eruptive flare on 26 April 2008 provided an opportunity to study relevant processes under particularly favourable conditions since it occurred in a very quiet solar and interplanetary environment. This enabled us to investigate the physical link between a single well-identified coronal mass ejection (CME), electron acceleration as traced by radio emission, and the production of SEPs. We conduct a detailed analysis, which combines radio observations (Nançay Radio Heliograph and Nançay Decametre Array, Wind/Waves spectrograph) with remote-sensing observations of the corona in extreme ultraviolet (EUV) and white light, as well as in situ measurements of energetic particles near 1AU (SoHO and STEREO spacecraft). By combining images taken from multiple vantage points, we were able to derive the time-dependent evolution of the 3D pressure front that was developing around the erupting CME. Magnetic reconnection in the post-CME current sheet accelerated electrons, which remained confined in closed magnetic fields in the corona, while the acceleration of escaping particles can be attributed to the pressure front ahead of the expanding CME. The CME accelerated electrons remotely from the parent active region, owing to the interaction of its laterally expanding flank, which was traced by an EUV wave, with the ambient corona. SEPs detected at one STEREO spacecraft and SoHO were accelerated later, when the frontal shock of the CME intercepted the spacecraft-connected interplanetary magnetic field line. The injection regions into the heliosphere inferred from the radio and SEP observations are separated in longitude by about 140°. The

  5. The Main Sequence of Explosive Solar Active Regions: Comparison of Emerging and Mature Active Regions

    NASA Technical Reports Server (NTRS)

    Falconer, David; Moore, Ron

    2011-01-01

    For mature active regions, an active region s magnetic flux content determines the maximum free energy the active region can have. Most Large flares and CMEs occur in active regions that are near their free-energy limit. Active-region flare power radiated in the GOES 1-8 band increases steeply as the free-energy limit is approached. We infer that the free-energy limit is set by the rate of release of an active region s free magnetic energy by flares, CMEs and coronal heating balancing the maximum rate the Sun can put free energy into the active region s magnetic field. This balance of maximum power results in explosive active regions residing in a "mainsequence" in active-region (flux content, free energy content) phase space, which sequence is analogous to the main sequence of hydrogen-burning stars in (mass, luminosity) phase space.

  6. Active Region Emergence and Remote Flares

    NASA Astrophysics Data System (ADS)

    Fu, Yixing; Welsch, Brian T.

    2016-02-01

    We study the effect of new emerging solar active regions on the large-scale magnetic environment of existing regions. We first present a theoretical approach to quantify the "interaction energy" between new and pre-existing regions as the difference between i) the summed magnetic energies of their individual potential fields and ii) the energy of their superposed potential fields. We expect that this interaction energy can, depending upon the relative arrangements of newly emerged and pre-existing magnetic flux, indicate the existence of "topological" free magnetic energy in the global coronal field that is independent of any "internal" free magnetic energy due to coronal electric currents flowing within the newly emerged and pre-existing flux systems. We then examine the interaction energy in two well-studied cases of flux emergence, but find that the predicted energetic perturbation is relatively small compared to energies released in large solar flares. Next, we present an observational study of the influence of the emergence of new active regions on flare statistics in pre-existing active regions, using NOAA's Solar Region Summary and GOES flare databases. As part of an effort to precisely determine the emergence time of active regions in a large event sample, we find that emergence in about half of these regions exhibits a two-stage behavior, with an initial gradual phase followed by a more rapid phase. Regarding flaring, we find that the emergence of new regions is associated with a significant increase in the occurrence rate of X- and M-class flares in pre-existing regions. This effect tends to be more significant when pre-existing and new emerging active regions are closer. Given the relative weakness of the interaction energy, this effect suggests that perturbations in the large-scale magnetic field, such as topology changes invoked in the "breakout" model of coronal mass ejections, might play a significant role in the occurrence of some flares.

  7. 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.

  8. 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.

  9. 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.

  10. Coronal temperature, density, and magnetic field maps of a solar acitve region using the Owens Valley Solar Array

    NASA Technical Reports Server (NTRS)

    Gary, Dale E.; Hurford, G. J.

    1994-01-01

    We present the first results of solar active region observations with the recently completed five-element Owens Valley Solar Array. On 1991 October 24, maps of Active Region AR 6891 were obtained at 22 frequencies from 1.2-7.0 GHz to provide brightness temperature spectra at each point. This is the first time that both high spatial and frequency-resolution brightness temperature spectra have been available over such a broad radio-frequency range. We find that over most of the region the spectra fall into one of the two well-defined categories: thermal free-free or thermal gyroresonance. In these cases, we use the spectra to deduce the spatial variation of physical parameters-electron temperature, column emission measure (intergral n(sup 2)(sub e) dl), and the coronal magnetic field strength-in and around the active region. Over a limited area of the region, the spectra resemble neither of the simple types, and alternative interpretations are required. The possibilties include the presence of fine structure that is unresolved at low frequencies; the presence of a small number of nonthermal electrons; or the presence of overlying, cooler 10(exp 6) K material which at low frequencies absorbs the hot (3 x 10(exp 6) K) thermal emission generated below.

  11. Transition-region/Coronal Signatures and Magnetic Setting of Sunspot Penumbral Jets: Hinode (SOT/FG), Hi-C, and SDO/AIA Observations

    NASA Astrophysics Data System (ADS)

    Tiwari, Sanjiv K.; Moore, Ronald L.; Winebarger, Amy R.; Alpert, Shane E.

    2016-01-01

    Penumbral microjets (PJs) are transient narrow bright features in the chromosphere of sunspot penumbrae, first characterized by Katsukawa et al. using the Ca ii H-line filter on Hinode's Solar Optical Telescope (SOT). It was proposed that the PJs form as a result of reconnection between two magnetic components of penumbrae (spines and interspines), and that they could contribute to the transition region (TR) and coronal heating above sunspot penumbrae. We propose a modified picture of formation of PJs based on recent results on the internal structure of sunspot penumbral filaments. Using data of a sunspot from Hinode/SOT, High Resolution Coronal Imager, and different passbands of the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory, we examine whether PJs have signatures in the TR and corona. We find hardly any discernible signature of normal PJs in any AIA passbands, except for a few of them showing up in the 1600 Å images. However, we discovered exceptionally stronger jets with similar lifetimes but bigger sizes (up to 600 km wide) occurring repeatedly in a few locations in the penumbra, where evidence of patches of opposite-polarity fields in the tails of some penumbral filaments is seen in Stokes-V images. These tail PJs do display signatures in the TR. Whether they have any coronal-temperature plasma is unclear. We infer that none of the PJs, including the tail PJs, directly heat the corona in active regions significantly, but any penumbral jet might drive some coronal heating indirectly via the generation of Alfvén waves and/or braiding of the coronal field.

  12. 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.

  13. Membership and Coronal Activity in the NGC 2232 and Cr 140 Open Clusters

    NASA Technical Reports Server (NTRS)

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

    2001-01-01

    This is the second annual performance report for our grant "Membership and Coronal Activity in the NGC 2232 and Cr 140 Open Clusters." We propose to identify X-ray sources and extract net source counts in 8 archival ROSAT HRI images in the regions of the NGC 2232 and Cr 140 open clusters. These X-ray data will be combined with ground-based photometry and spectroscopy in order to identify G, K, and early-M type cluster members. At present, no members later than approximately F5 are currently known for either cluster. With ages of approximately 25 Myr and at a distance of just 320 - 360 pc, the combined late-type membership of the NGC 2232 and Cr 140 clusters will yield an almost unique sample of solar-type stars in the post-T Tauri/pre-main sequence phase of evolution. These stars will be used to assess the level and dispersion in coronal activity levels, as part of a probe of the importance of magnetic braking and the level of magnetic dynamo activity, for solar-type stars just before they reach the ZAMS. Over the past year we have successfully acquired all of the ground-based data necessary to support the analysis of the archival ROSAT X-ray data in the regions around both of these clusters. By the end of 2001 we expect to have completed the reduction and analysis of the ground-based photometry and spectroscopy and will begin the integration of these data with the ROSAT X-ray data. A certain amount of pressure to complete the work on NGC 2232 is coming from the SIRTF project, as this cluster may be a key component to a circumstellar disk evolution GTO program. We are only too happy to try to help and have worked to speed the analysis as much as possible. The primary activity to be undertaken in the next few months is the integration of the groundbased photometry and spectroscopy with the archival ROSAT X-ray data and then writing the paper summarizing our results. The most time consuming portion of this next phase is, of course, seeing the paper through

  14. SOLAR CYCLE VARIATIONS OF THE OCCURRENCE OF CORONAL TYPE III RADIO BURSTS AND A NEW SOLAR ACTIVITY INDEX

    SciTech Connect

    Lobzin, Vasili; Cairns, Iver H.; Robinson, Peter A.

    2011-07-20

    This Letter presents the results of studies of solar cycle variations of the occurrence rate of coronal type III radio bursts. The radio spectra are provided by the Learmonth Solar Radio Observatory (Western Australia), part of the USAF Radio Solar Telescope Network (RSTN). It is found that the occurrence rate of type III bursts strongly correlates with solar activity. However, the profiles for the smoothed type III burst occurrence rate differ considerably from those for the sunspot number, 10.7 cm solar radio flux, and solar flare index. The type III burst occurrence rate (T3BOR) is proposed as a new index of solar activity. T3BOR provides complementary information about solar activity and should be useful in different studies including solar cycle predictions and searches for different periodicities in solar activity. This index can be estimated from daily results of the Automated Radio Burst Identification System. Access to data from other RSTN sites will allow processing 24 hr radio spectra in near-real time and estimating true daily values of this index. It is also shown that coronal type III bursts can even occur when there are no visible sunspots on the Sun. However, no evidence is found that the bursts are not associated with active regions. It is also concluded that the type III burst productivity of active regions exhibits solar cycle variations.

  15. Size and physical conditions of the coronal line region in a nearby Seyfert 2: the Circinus galaxy

    NASA Astrophysics Data System (ADS)

    Oliva, E.; Salvati, M.; Moorwood, A. F. M.; Marconi, A.

    1994-08-01

    We present observations of visible ([FeVII], [FeX], [FeXI], [SVIII]) and near infrared ([SIX], [SiVI], [CaVIII], [SiVII], [SiIX]) coronal lines in the Circinus galaxy. The number of detected lines, their velocity profiles, and their spatial distribution pose tight constraints on models of the coronal line region (CLR), and lead to several important conclusions. We can exclude fast shocks and hot stars (warmers) as the origin of the coronal line emission, and find convincing (although not conclusive) evidence against a hot, collisionally ionized plasma. The CLR appears to be a dense (N_e_=~250cm^-3^), compact (diameter=~10pc), dustless region photoionized by the nuclear continuum which must be remarkably flat (Lnu_=~ν^-0.5^) around 300eV.

  16. Coronal mass ejections and major solar flares: The great active center of March 1989

    NASA Technical Reports Server (NTRS)

    Feynman, Joan; Hundhausen, Arthur J.

    1994-01-01

    The solar flare and coronal mass ejection (CME) events associated with the large and complex March 1989 active region are discussed. This active region gave us a chance to study the relation of CME with truly major solar flares. The work concentrates on questions of the relation of CMEs and flares to one another and to other types of activity on the Sun. As expected, some major (X-3B class) flares had associated CMEs. However, an unexpected finding is that others did not. In fact, there is strong evidence that the X4-4B flare of March 9th had no CME. This lack of a CME for such an outstanding flare event has important implications to theories of CME causation.Apparently, not all major flares cause CMEs or are caused by CMEs. The relations between CMEs and other types of solar activity are also discussed. No filament disappearances are reported for major CMEs studied here. Comparing these results with other studies, CMEs occur in association with flares and with erupting prominences, but neither are required for a CME. The relation between solar structures showing flaring without filament eruptions and structures showing filament eruptions without flares becomes important. The evolutionary relation between an active flaring sunspot region and extensive filaments without sunspots is reviewed, and the concept of an 'evolving magnetic structure' (EMS) is introduced. It is suggested that all CMEs arise in EMSs and that CMEs provide a major path through which azimuthal magnetic fields escape form the Sun during the solar cycle.

  17. Large-Scale Coronal Heating from "Cool" Activity in the Solar Magnetic Network

    NASA Technical Reports Server (NTRS)

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

    1999-01-01

    In Fe XII images from SOHO/EIT, the quiet solar corona shows structure on scales ranging from sub-supergranular (i.e., bright points and coronal network) to multi-supergranular (large-scale corona). In Falconer et al 1998 (Ap.J., 501, 386) we suppressed the large-scale background and found that the network-scale features are predominantly rooted in the magnetic network lanes at the boundaries of the supergranules. Taken together, the coronal network emission and bright point emission are only about 5% of the entire quiet solar coronal Fe XII emission. Here we investigate the relationship between the large-scale corona and the network as seen in three different EIT filters (He II, Fe IX-X, and Fe XII). Using the median-brightness contour, we divide the large-scale Fe XII corona into dim and bright halves, and find that the bright-half/dim half brightness ratio is about 1.5. We also find that the bright half relative to the dim half has 10 times greater total bright point Fe XII emission, 3 times greater Fe XII network emission, 2 times greater Fe IX-X network emission, 1.3 times greater He II network emission, and has 1.5 times more magnetic flux. Also, the cooler network (He II) radiates an order of magnitude more energy than the hotter coronal network (Fe IX-X, and Fe XII). From these results we infer that: 1) The heating of the network and the heating of the large-scale corona each increase roughly linearly with the underlying magnetic flux. 2) The production of network coronal bright points and heating of the coronal network each increase nonlinearly with the magnetic flux. 3) The heating of the large-scale corona is driven by widespread cooler network activity rather than by the exceptional network activity that produces the network coronal bright points and the coronal network. 4) The large-scale corona is heated by a nonthermal process since the driver of its heating is cooler than it is. This work was funded by the Solar Physics Branch of NASA's office of

  18. THE NEAR-INFRARED CORONAL LINE SPECTRUM OF 54 NEARBY ACTIVE GALACTIC NUCLEI

    SciTech Connect

    Rodriguez-Ardila, A.

    2011-12-20

    The relationship between the emission of coronal lines (CLs) and nuclear activity in 36 Type 1 and 18 Type 2 active galactic nuclei (AGNs) is analyzed, for the first time, based on near-infrared (0.8-2.4 {mu}m) spectra. The eight CLs studied, of Si, S, Fe, Al, and Ca elements and corresponding to ionization potentials (IPs) in the range 125-450 eV, are detected (3{sigma}) in 67% (36 AGNs) of the sample. Our analysis shows that the four most frequent CLs [Si VI] 1.963 {mu}m, [S VIII] 0.9913 {mu}m, [S IX] 1.252 {mu}m, and [Si X] 1.430 {mu}m display a narrow range in luminosity, with most lines located in the interval log L 39-40 erg s{sup -1}. We found that the non-detection is largely associated with either loss of spatial resolution or increasing object distance: CLs are essentially nuclear and easily lose contrast in the continuum stellar light for nearby sources or get diluted by the strong AGN continuum as the redshift increases. Yet, there are AGNs where the lack of coronal emission, i.e., lines with IP {>=} 100 eV, may be genuine. The absence of these lines reflects a non-standard AGN ionizing continuum, namely, a very hard spectrum lacking photons below a few Kev. The analysis of the line profiles points out a trend of increasing FWHM with increasing IPs up to energies around 300 eV, where a maximum in the FWHM is reached. For higher IP lines, the FWHM remains nearly constant or decreases with increasing IPs. We ascribe this effect to an increasing density environment as we approach the innermost regions of these AGNs, where densities above the critical density of the CLs with IPs larger than 300 eV are reached. This sets a strict range limit for the density in the boundary region between the narrow and the broad region of 10{sup 8}-10{sup 9} cm{sup -3}. A relationship between the luminosity of the CLs and that of the soft and hard X-ray emission and the soft X-ray photon index is observed: the coronal emission becomes stronger with both increasing X

  19. 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.

  20. Membership and Coronal Activity in the NGC 2232 and Cr 140 Open Clusters

    NASA Technical Reports Server (NTRS)

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

    2004-01-01

    Making use of eight archival ROSAT HRI images in the regions of the NGC 2232 and Cr 140, this project's primary focus is to identify X-ray sources and to extract net source counts for these sources in these two open clusters. These X-ray data would be combined with ground-based photometry and spectroscopy in order to identify G, K, and early-M type cluster members. Such membership data are important because, at present, no members later than spectral type approx. F5 are currently known for either cluster. With ages estimated to be approx. 25 Myr and at distances of just approx. 350 pc, the combined late-type membership of the NGC 2232 and Cr 140 clusters would yield an almost unique sample of solar-type stars in the post-T Tauri/pre-main sequence phase of evolution. These stars could be used to assess the level and dispersion of coronal activity levels, as a part of a probe of the importance of magnetic braking and the level of magnetic dynamo activity, for solar-type stars just before they reach the zero-age main sequence.

  1. Coronal Radio Sounding Experiments with Mars Express: Scintillation Spectra during Low Solar Activity

    SciTech Connect

    Efimov, A. I.; Lukanina, L. A.; Samoznaev, L. N.; Rudash, V. K.; Chashei, I. V.; Bird, M. K.; Paetzold, M.; Tellmann, S.

    2010-03-25

    Coronal radio sounding observations were carried out with the radio science experiment MaRS on the ESA spacecraft Mars Express during the period from 25 August to 22 October 2004. Differential frequency and log-amplitude fluctuations of the dual-frequency signals were recorded during a period of low solar activity. The data are applicable to low heliographic latitudes, i.e. to slow solar wind. The mean frequency fluctuation and power law index of the frequency fluctuation temporal spectra are determined as a function of heliocentric distance. The radial dependence of the frequency fluctuation spectral index alpha reflects the previously documented flattening of the scintillation power spectra in the solar wind acceleration region. Temporal spectra of S-band and X-band normalized log-amplitude fluctuations were investigated over the range of fluctuation frequencies 0.01 Hzactivity. Ranging measurements are presented and compared with frequency and log-amplitude scintillation data. Evidence for a weak increase in the fractional electron density turbulence level is obtained in the range 10-40 solar radii.

  2. Analysis of coronal H I Lyman-alpha measurements in a polar region of the sun observed in 1979

    NASA Technical Reports Server (NTRS)

    Withbroe, G. L.; Kohl, J. L.; Weiser, H.

    1986-01-01

    Measurements of the intensities and spectral line profiles of resonantly scattered hydrogen Ly-alpha radiation have been used to determine hydrogen kinetic temperatures and electron densities between r = 1.5 and 2.2 solar radii in a polar region of the corona observed in 1979 near solar maximum. The mean temperature, 1.8 x 10 to the 6th K, in this region is significantly higher, by about 60 percent, than that obtained in a similar region observed in a 1980 rocket flight. The densities in these two polar regions are similar and are a factor of about 4 larger than in polar coronal holes observed at solar minimum. The flow velocities in both regions are most likely subsonic for r less than about 4 solar radii. The results reported here support the hypothesis that polar coronal holes observed at different times during the solar cycle can have different temperatures, densities, and possibly flow velocities.

  3. FIP bias in a sigmoidal active region

    NASA Astrophysics Data System (ADS)

    Baker, D.; Brooks, D. H.; Démoulin, P.; van Driel-Gesztelyi, Lidia; Green, L. M.; Steed, K.; Carlyle, J.

    2014-01-01

    We investigate first ionization potential (FIP) bias levels in an anemone active region (AR) - coronal hole (CH) complex using an abundance map derived from Hinode/EIS spectra. The detailed, spatially resolved abundance map has a large field of view covering 359'' × 485''. Plasma with high FIP bias, or coronal abundances, is concentrated at the footpoints of the AR loops whereas the surrounding CH has a low FIP bias, ~1, i.e. photospheric abundances. A channel of low FIP bias is located along the AR's main polarity inversion line containing a filament where ongoing flux cancellation is observed, indicating a bald patch magnetic topology characteristic of a sigmoid/flux rope configuration.

  4. Quiet Sun mini-coronal mass ejections activated by supergranular flows

    NASA Astrophysics Data System (ADS)

    Innes, D. E.; Genetelli, A.; Attie, R.; Potts, H. E.

    2009-02-01

    Context: The atmosphere of the quiet Sun is controlled by photospheric flows sweeping up concentrations of mixed polarity magnetic field. Along supergranule boundaries and junctions, there is a strong correlation between magnetic flux and bright chromospheric and transition region emission. Aims: The aim is to investigate the relationship between photospheric flows and small flare-like brightenings seen in Extreme Ultraviolet images. Methods: We describe observations of small eruptions seen in quiet Sun images taken with the Extreme UltraViolet Imager (EUVI) on STEREO. The photospheric flows during the eruption build-up phase are investigated by tracking granules in high resolution MDI continuum images. Results: Eruptions with characteristics of small coronal mass ejections (CMEs) occur at the junctions of supergranular cells. The eruptions produce brightening at the onset site, dark cloud or small filament ejections, and faint waves moving with plane-of-sky speeds up to 100 km s-1. In the two examples studied, they appear to be activated by converging and rotating supergranular flows, twisting small concentrations of opposite polarity magnetic field. An estimate of the occurrence rate is about 1400 events per day over the whole Sun. One third of these events seem to be associated with waves. Typically, the waves last for about 30 min and travel a distance of 80 Mm, so at any one time they cover 1/50th of the lower corona. Movies are only available in electronic form at http://www.aanda.org

  5. Coronal and chromospheric physics

    NASA Technical Reports Server (NTRS)

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

    1983-01-01

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

  6. Identification of Super- and Subcritical Regions in Shocks Driven by Coronal Mass Ejections

    NASA Astrophysics Data System (ADS)

    Bemporad, A.; Mancuso, S.

    2011-10-01

    In this work, we focus on the analysis of a coronal mass ejection (CME) driven shock observed by the Solar and Heliospheric Observatory/Large Angle and Spectrometric Coronagraph Experiment. We show that white-light coronagraphic images can be employed to estimate the compression ratio X = ρ d /ρ u all along the front of CME-driven shocks. X increases from the shock flanks (where X ~= 1.2) to the shock center (where X ~= 3.0 is maximum). From the estimated X values, we infer the Alfvén Mach number for the general case of an oblique shock. It turns out that only a small region around the shock center is supercritical at earlier times, while higher up in the corona the whole shock becomes subcritical. This suggests that CME-driven shocks could be efficient particle accelerators at the initiation phases of the event, while at later times they progressively loose energy, also losing their capability to accelerate high-energy particles. This result has important implications on the localization of particle acceleration sites and in the context of predictive space weather studies.

  7. 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

  8. Coronal Diagnostics of Intermediate Activity Star XI Boo A

    NASA Technical Reports Server (NTRS)

    Drake, Jeremy

    2005-01-01

    The analysis of Xi Boo A proved difficult to adapt to our line-by-line approach because of the strong wings of the RGS instrumental profile, as has been detailed in earlier reports. While progress was also delayed because of problems in using SAS v4, we succeeded in the past year or so to bring the analysis to conclusion. Abundances have been derived using both EPIC and RGS data, confirming earlier EUVE findings of a mild solar-like FIP effect, though with some evidence of a turn-up in abundances of elements with higher FIP. Plasma densities appear normal for a moderately active stellar corona. Xi Boo A nicely bridges the gap between the very active stars and stars like the Sun, and it indeed does appear that these are the stars in which the solar-like FIP effects begins to change to the "inverse FIP" type of effect seen in the very active stars. Probing this divide was the main goal of the proposal. These results are in the process of being prepared for publication, though we have not decided the target journal as yet.

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

    NASA Technical Reports Server (NTRS)

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

    1978-01-01

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

  10. STUDY OF THE RECURRING DIMMING REGION DETECTED AT AR 11305 USING THE CORONAL DIMMING TRACKER (CoDiT)

    SciTech Connect

    Krista, Larisza D.; Reinard, Alysha

    2013-01-10

    We present a new approach to coronal dimming detection using the COronal DImming Tracker tool (CODIT), which was found to be successful in locating and tracking multiple dimming regions. This tool, an extension of a previously developed coronal hole tracking software, allows us to study the properties and the spatial evolution of dimming regions at high temporal and spatial cadence from the time of their appearance to their disappearance. We use Solar Dynamics Observatory/Atmospheric Imaging Assembly 193 A wavelength observations and Helioseismic and Magnetic Imager magnetograms to study dimmings. As a demonstration of the detection technique we analyzed six recurrences of a dimming observed near AR 11305 between 2011 September 29 and October 2. The dimming repeatedly appeared and formed in a similar way, first expanding then shrinking and occasionally stabilizing in the same location until the next eruption. The dimming areas were studied in conjunction with the corresponding flare magnitudes and coronal mass ejection (CME) masses. These properties were found to follow a similar trend during the observation period, which is consistent with the idea that the magnitude of the eruption and the CME mass affect the relative sizes of the consecutive dimmings. We also present a hypothesis to explain the evolution of the recurrent single dimming through interchange reconnection. This process would accommodate the relocation of quasi-open magnetic field lines and hence allow the CME flux rope footpoint (the dimming) to expand into quiet-Sun regions. By relating the properties of dimmings, flares, and CMEs we improve our understanding of the magnetic field reconfiguration caused by reconnection.

  11. Some features of active regions and bursts in millimetric range.

    NASA Astrophysics Data System (ADS)

    Yu, Xingfeng; Yao, Jinxing

    1995-09-01

    The characteristics of active regions and bursts at mm wavelengths, observed with the 13.7 m radio telescope at Quinghai from Nov 16 to Dec 1, 1993, are analyzed. It appears that the active region collapsed and vanished while there occurred a coronal loop with two polarities. GRE bursts at mm wavelength may be interpreted by thermal gyro-resonance radiation and are part of the chromospheric eruption. There is no indication of FFS in 10 ms recordings.

  12. Resolving the coronal line region of NGC 1068 with near-infrared integral field spectroscopy

    NASA Astrophysics Data System (ADS)

    Mazzalay, X.; Rodríguez-Ardila, A.; Komossa, S.; McGregor, Peter J.

    2013-04-01

    We present adaptive optics-assisted J- and K-band integral field spectroscopy of the inner 300 × 300 pc of the Seyfert 2 galaxy NGC 1068. The data were obtained with the Gemini Near-infrared Integral-Field Spectrograph integral field unit spectrometer, which provided us with high-spatial and high-spectral resolution sampling. The wavelength range covered by the observations allowed us to study the [Ca VIII], [Si VI], [Si VII], [Al IX] and [S IX] coronal line (CL) emission, covering ionization potentials up to 328 eV. The observations reveal very rich and complex structures, both in terms of velocity fields and emission-line ratios. The CL emission is elongated along the NE-SW direction, with the stronger emission preferentially localized to the NE of the nucleus. CLs are emitted by gas covering a wide range of velocities, with maximum blueshifts/redshifts of ˜ -1600/1000 km s-1. There is a trend for the gas located on the NE side of the nucleus to be blueshifted while the gas located towards the SW is redshifted. The morphology and the kinematics of the near-infrared CLs are in very good agreement with the ones displayed by low-ionization lines and optical CLs, suggesting a common origin. The line flux distributions, velocity maps, ionization structure (traced by the [Si VII]/[Si VI] emission-line ratio) and low-ionization emission-line ratios (i.e. [Fe II]/Paβ and [Fe II]/[P II]) suggest that the radio jet plays an important role in the structure of the CL region of this object, and possibly in its kinematics.

  13. High Angular Resolution Radio Observations of a Coronal Mass Ejection Source Region at Low Frequencies during a Solar Eclipse

    NASA Astrophysics Data System (ADS)

    Ramesh, R.; Kathiravan, C.; Barve, Indrajit V.; Rajalingam, M.

    2012-01-01

    We carried out radio observations of the solar corona in the frequency range 109-50 MHz during the annular eclipse of 2010 January 15 from the Gauribidanur Observatory, located about 100 km north of Bangalore in India. The radio emission in the above frequency range originates typically in the radial distance range ≈1.2-1.5 R ⊙ in the "undisturbed" solar atmosphere. Our analysis indicates that (1) the angular size of the smallest observable radio source (associated with a coronal mass ejection in the present case) is ≈1' ± 0farcm3, (2) the source size does not vary with radial distance, (3) the peak brightness temperature of the source corresponding to the above size at a typical frequency like 77 MHz is ≈3 × 109 K, and (4) the coronal magnetic field near the source region is ≈70 mG.

  14. Activity associated with coronal mass ejections at solar minimum - SMM observations from 1984-1986

    NASA Technical Reports Server (NTRS)

    St. Cyr, O. C.; Webb, D. F.

    1991-01-01

    Seventy-three coronal mass ejections (CMEs) observed by the coronagraph aboard SMM between 1984 and 1986 were examined in order to determine the distribution of various forms of solar activity that were spatially and temporally associated with mass ejections during solar minimum phase. For each coronal mass ejection a speed was measured, and the departure time of the transient from the lower corona estimated. Other forms of solar activity that appeared within 45 deg longitude and 30 deg latitude of the mass ejection and within +/-90 min of its extrapolated departure time were explored. The statistical results of the analysis of these 73 CMEs are presented, and it is found that slightly less than half of them were infrequently associated with other forms of solar activity. It is suggested that the distribution of the various forms of activity related to CMEs does not change at different phases of the solar cycle. For those CMEs with associations, it is found that eruptive prominences and soft X-rays were the most likely forms of activity to accompany the appearance of mass ejections.

  15. Solar Energetic Particle Production by Coronal Mass Ejection-driven Shocks in Solar Fast-Wind Regions

    NASA Astrophysics Data System (ADS)

    Kahler, S. W.; Reames, D. V.

    2003-02-01

    Gradual solar energetic particle (SEP) events at 1 AU are produced by coronal/interplanetary shocks driven by coronal mass ejections (CMEs). Fast (vCME>~900 km s-1) CMEs might produce stronger shocks in solar slow-wind regions, where the flow and fast-mode MHD wave speeds are low, than in fast-wind regions, where those speeds are much higher. At 1 AU the O+7/O+6 ratios distinguish between those two kinds of wind streams. We use the 20 MeV proton event intensities from the EPACT instrument on Wind, the associated CMEs observed with the LASCO coronagraph on SOHO, and the ACE SWICS solar wind values of O+7/O+6 to look for variations of peak SEP intensities as a function of O+7/O+6. No significant dependence of the SEP intensities on O+7/O+6 is found for either poorly connected or well-connected CME source regions or for different CME speed ranges. However, in the 3 yr study period we find only five cases of SEP events in fast wind, defined by regions of O+7/O+6<0.15. We suggest that in coronal holes SEP acceleration may take place only in the plume regions, where the flow and Alfvén speeds are low. A broad range of angular widths are associated with fast (vCME>=900 km s-1) CMEs, but we find that no fast CMEs with widths less than 60° are associated with SEP events. On the other hand, nearly all fast halo CMEs are associated with SEP events. Thus, the CME widths are more important in SEP production than previously thought, but the speed of the solar wind source regions in which SEPs are produced may not be a factor.

  16. Solar cycle variations of coronal structures

    NASA Astrophysics Data System (ADS)

    Loucif, M. L.; Koutchmy, S.

    1989-01-01

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

  17. Coronal holes, solar wind streams, and geomagnetic activity during the new sunspot cycle

    NASA Technical Reports Server (NTRS)

    Sheeley, N. R., Jr.; Harvey, J. W.

    1978-01-01

    The paper presents results obtained for 1976-1977 using daily He I 10830 A spectroheliograms and photospheric magnetograms. It was found that as the magnetic field patterns changed, the solar atmosphere evolved from a structure with a few large long-lived low-latitude coronal holes to one with numerous small short-lived high-latitude holes. High-latitude holes recurred with a synodic rotation period of 28-29 days instead of the 27-day period already known to be characteristic of low-latitude holes. A Bartels display of the occurrence of holes, wind speed, and geomagnetic activity is considered.

  18. 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.

  19. Dating the Stars Next Door: Ages and Coronal X-Ray Activities of Local K-Type Stars

    NASA Astrophysics Data System (ADS)

    Katynski, Marcus; Guinan, Edward F.; Engle, Scott G.

    2016-01-01

    Age is one of the most difficult (but important) basic stellar physical property to determine. One possible means to estimate stellar age is from rotational period; it is known that as cool stars age, they lose angular momentum from magnetic braking and slow-down. Thus, good Rotation-Age relationships exist, which are calibrated with stars possessing reliable ages from: evolutionary tracks and/or memberships in clusters/moving groups or binary star systems. Further, ages of older stars can be estimated from (low) metal abundances and kinematics (high space motions). More recently, age determinations from asteroseismology are also becoming more reliable. Except for the many G, K, M stars in the Kepler/K2 fields, rotational periods are difficult to measure photometrically for older, less active stars since star spots and active regions are smaller & less prominent. Thus measuring the coronal X-ray activity of a star is an appealing alternative. Coronal X-ray emission is generated by the stellar dynamo, and so is directly related to the stars' rotation (and age). Measurement of X-ray fluxes (or upper limits) have been made for most of the nearby stars (within ~20 pc) with data available in the HEASARC archives. During the 1990's the ROSAT X-Ray Satellite carried out an all-sky survey of thousands of X-ray sources, including hundreds of nearby stars, producing a large archival database. Using these and other available X-ray data from XMM-Newton & Chandra, we explore the relation between coronal X-ray activity and stellar age of all stars within 10 pc (32.6 LY), with special emphasis on dK and early dM stars that make up ~85% of the sample. Here we report the progress made in determination the ages these nearby stars. We focused on nearby dK-stars, due to their long lifetimes (>20 Gyr) and habitable zones that lie ~0.5 -1.5 AU from their host stars. They appear to be ideal candidates for hosting potentially habitable planets, making them interesting targets. We present

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

    NASA Technical Reports Server (NTRS)

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

    2001-01-01

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

  1. Patterns of Activity Revealed by a Time Lag Analysis of a Model Active Region

    NASA Astrophysics Data System (ADS)

    Bradshaw, Stephen; Viall, Nicholeen

    2016-05-01

    We investigate the global activity patterns predicted from a model active region heated by distributions of nanoflares that have a range of average frequencies. The activity patterns are manifested in time lag maps of narrow-band instrument channel pairs. We combine an extrapolated magnetic skeleton with hydrodynamic and forward modeling codes to create a model active region, and apply the time lag method to synthetic observations. Our aim is to recover some typical properties and patterns of activity observed in active regions. Our key findings are: 1. Cooling dominates the time lag signature and the time lags between the channel pairs are generally consistent with observed values. 2. Shorter coronal loops in the core cool more quickly than longer loops at the periphery. 3. All channel pairs show zero time lag when the line-of-sight passes through coronal loop foot-points. 4. There is strong evidence that plasma must be re-energized on a time scale comparable to the cooling timescale to reproduce the observed coronal activity, but it is likely that a relatively broad spectrum of heating frequencies operates across active regions. 5. Due to their highly dynamic nature, we find nanoflare trains produce zero time lags along entire flux tubes in our model active region that are seen between the same channel pairs in observed active regions.

  2. 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.

  3. 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.

  4. Transition-Region/Coronal Signatures of Penumbral Microjets: Hi-C, SDO/AIA and Hinode (SOT/FG) Observations

    NASA Technical Reports Server (NTRS)

    Tiwari, Sanjiv K.; Alpert, Shane E.; Moore, Ronald L.; Winebarger, Amy R.

    2014-01-01

    Penumbral microjets are bright, transient features seen in the chromosphere of sunspot penumbrae. Katsuaka et al. (2007) noted their ubiquity and characterized them using the Ca II H-line filter on Hinode's Solar Optical Telescope (SOT). The jets are 1000{4000 km in length, 300{400 km in width, and last less than one minute. It was proposed that these penumbral microjets could contribute to the transition-region and coronal heating above sunspots. We examine whether these microjets appear in the transition-region (TR) and/or corona or are related{ temporally and spatially{ to similar brightenings in the TR and/or corona. First, we identify penumbral microjets with the SOT's Ca II H-line filter. The chosen sunspot is observed on July 11, 2012 from 18:50:00 UT to 20:00:00 UT at approx. 14 inches, -30 inches. We then examine the sunspot in the same field of view and at the same time in other wavelengths. We use the High Resolution Coronal Imager Telescope (Hi-C) at 193A and the 1600A, 304A, 171A, 193A, and 94A passbands of the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamic Observatory. We include examples of these jets and where they should appear in the other passbands, but find no signifcant association, except for a few jets with longer lifetimes and bigger sizes seen at locations in the penumbra with repeated stronger brightenings. We conclude that the normal microjets are not heated to transition-region/coronal temperatures, but the larger jets are.

  5. Patterns of Activity in a Global Model of a Solar Active Region

    NASA Astrophysics Data System (ADS)

    Bradshaw, S. J.; Viall, N. M.

    2016-04-01

    In this work we investigate the global activity patterns predicted from a model active region heated by distributions of nanoflares that have a range of frequencies. What differs is the average frequency of the distributions. The activity patterns are manifested in time lag maps of narrow-band instrument channel pairs. We combine hydrodynamic and forward modeling codes with a magnetic field extrapolation to create a model active region and apply the time lag method to synthetic observations. Our aim is not to reproduce a particular set of observations in detail, but to recover some typical properties and patterns observed in active regions. Our key findings are the following. (1) Cooling dominates the time lag signature and the time lags between the channel pairs are generally consistent with observed values. (2) Shorter coronal loops in the core cool more quickly than longer loops at the periphery. (3) All channel pairs show zero time lag when the line of sight passes through coronal loop footpoints. (4) There is strong evidence that plasma must be re-energized on a timescale comparable to the cooling timescale to reproduce the observed coronal activity, but it is likely that a relatively broad spectrum of heating frequencies are operating across active regions. (5) Due to their highly dynamic nature, we find nanoflare trains produce zero time lags along entire flux tubes in our model active region that are seen between the same channel pairs in observed active regions.

  6. Determination of coronal magnetic fields from vector magnetograms

    NASA Technical Reports Server (NTRS)

    Mikic, Zoran

    1993-01-01

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

  7. Linking Stellar Coronal Activity and Rotation at 500 Myr: A Deep Chandra Observation of M37

    NASA Astrophysics Data System (ADS)

    Núñez, Alejandro; Agüeros, Marcel A.; Covey, Kevin R.; Hartman, Joel D.; Kraus, Adam L.; Bowsher, Emily C.; Douglas, Stephanie T.; López-Morales, Mercedes; Pooley, David A.; Posselt, Bettina; Saar, Steven H.; West, Andrew A.

    2015-08-01

    Empirical calibrations of the stellar age-rotation-activity relation (ARAR) rely on observations of the co-eval populations of stars in open clusters. We used the Chandra X-ray Observatory to study M37, a 500-Myr-old open cluster that has been extensively surveyed for rotation periods ({P}{rot}). M37 was observed almost continuously for five days, for a total of 440.5 ks, to measure stellar X-ray luminosities ({L}{{X}}), a proxy for coronal activity, across a wide range of masses. The cluster’s membership catalog was revisited to calculate updated membership probabilities from photometric data and each star’s distance to the cluster center. The result is a comprehensive sample of 1699 M37 members: 426 with {P}{rot}, 278 with X-ray detections, and 76 with both. We calculate Rossby numbers, {R}o= {P}{rot}/τ , where τ is the convective turnover time, and ratios of the X-ray-to-bolometric luminosity, {L}{{X}}/{L}{bol}, to minimize mass dependencies in our characterization of the rotation-coronal activity relation at 500 Myr. We find that fast rotators, for which {R}o\\lt 0.09+/- 0.01, show saturated levels of activity, with log({L}{{X}}/{L}{bol})=\\-3.06+/- 0.04. For {R}o≥slant 0.09+/- 0.01, activity is unsaturated and follows a power law of the form {R}oβ , where β = -{2.03}-0.14+0.17. This is the largest sample available for analyzing the dependence of coronal emission on rotation for a single-aged population, covering stellar masses in the range 0.4-1.3 {M}⊙ , {P}{rot} in the range 0.4-12.8 days, and {L}{{X}} in the range {10}28.4-30.5 {erg} {{{s}}}-1. Our results make M37 a new benchmark open cluster for calibrating the ARAR at ages of ≈ 500 Myr.

  8. Coordinated Observations of X-ray and High-resolution EUV Active Region Dynamics

    NASA Technical Reports Server (NTRS)

    Savage, Sabrina

    2013-01-01

    The recently-launched High-resolution Coronal imager (Hi-C) sounding rocket provided the highest resolution images of coronal loops and other small-scale structures in the 193 Angstrom passband to date. With just 5 minutes of observations, the instrument recorded a variety of dynamic coronal events -- including even a small B-class flare. We will present our results comparing these extreme-ultraviolet (EUV) observations with X-ray imaging from Hinode/XRT as well as EUV AIA data to identify sources of hot plasma rooted in the photosphere and track their affect on the overall topology and dynamics of the active region.

  9. Coordinated Observations of X-ray and High-Resolution EUV Active Region Dynamics

    NASA Technical Reports Server (NTRS)

    Savage, Sabrina; Cirtain, Jonathan; Winebarger, Amy; Kobayashi, Ken; Golub, Leon; Korreck, Kelly

    2013-01-01

    The recently-launched High-resolution Coronal imager (Hi-C) sounding rocket provided the highest resolution images of coronal loops and other small-scale structures in the 193 Angstrom passband to date. With just 5 minutes of observations, the instrument recorded a variety of dynamic coronal events -- including even a small B-class flare. We will present our results comparing these extreme-ultraviolet (EUV) observations with X-ray imaging from Hinode/XRT as well as EUV AIA data to identify sources of hot plasma rooted in the photosphere and track their affect on the overall topology and dynamics of the active region.

  10. Solar magnetic activity cycles, coronal potential field models and eruption rates

    NASA Astrophysics Data System (ADS)

    Petrie, Gordon

    2013-07-01

    We study the evolution of the observed photospheric magnetic field and the modeled global coronal magnetic field during the past 3 1/2 solar activity cycles observed since the mid-1970s. We use synoptic magnetograms and extrapolated potential-field models based on longitudinal full-disk photospheric magnetograms from the NSO's three magnetographs at Kitt Peak, the Synoptic Optical Long-term Investigations of the Sun (SOLIS) vector spectro-magnetograph (VSM), the spectro-magnetograph and the 512-channel magnetograph instruments, and from the U. Stanford's Wilcox Solar Observatory. The associated multipole field components are used to study the dominant length scales and symmetries of the coronal field. Of the axisymmetric multipoles, only the dipole and octupole follow the poles whereas the higher orders follow the activity cycle. All non-axisymmetric multipole strengths are well correlated with the activity cycle. The axial dipole and octupole are the largest contributors to the global field except while the polar fields are reversing. This influence of the polar fields extends to modulating eruption rates. According to the Computer Aided CME Tracking (CACTus), Solar Eruptive Event Detection System (SEEDS), and Nobeyama radioheliograph prominence eruption catalogs, the rate of solar eruptions is found to be systematically higher for active years between 2003-2012 than for those between 1997-2002. This behavior appears to be connected with the weakness of the late-cycle 23 polar fields as suggested by Luhmann. We see evidence that the process of cycle 24 field reversal is well advanced at both poles.

  11. 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

  12. 3D MHD Models of Active Region Loops

    NASA Technical Reports Server (NTRS)

    Ofman, Leon

    2004-01-01

    Present imaging and spectroscopic observations of active region loops allow to determine many physical parameters of the coronal loops, such as the density, temperature, velocity of flows in loops, and the magnetic field. However, due to projection effects many of these parameters remain ambiguous. Three dimensional imaging in EUV by the STEREO spacecraft will help to resolve the projection ambiguities, and the observations could be used to setup 3D MHD models of active region loops to study the dynamics and stability of active regions. Here the results of 3D MHD models of active region loops are presented, and the progress towards more realistic 3D MHD models of active regions. In particular the effects of impulsive events on the excitation of active region loop oscillations, and the generation, propagations and reflection of EIT waves are shown. It is shown how 3D MHD models together with 3D EUV observations can be used as a diagnostic tool for active region loop physical parameters, and to advance the science of the sources of solar coronal activity.

  13. A Search for Coronal Activity Among Two Metal-poor Subdwarfs and One Subgiant

    NASA Astrophysics Data System (ADS)

    Smith, Graeme H.; Dupree, Andrea K.; Günther, Hans Moritz

    2016-08-01

    A search has been made using the XMM-Newton satellite for coronal soft X-ray emission from HD 19445, HD 25329, and HD 140283, three Population II stars in the Galactic halo having metallicities of {{[Fe/H]}}˜ -2. The program stars, consisting of two subdwarfs and one metal-poor subgiant, were pre-selected from ground-based observations to have He i λ10830 absorption lines with an equivalent width (EW) of 30 mÅ or more. If such stars follow a relation between He i EW and soft X-ray flux applicable to Population I dwarf stars, then they would be expected to have X-ray luminosities ˜ 5× {10}-7 times their bolometric luminosity, and as such would yield detectable sources in 20 ks exposures with the XMM-Newton EPIC-PN and MOS cameras. No detections were found in such exposures made with XMM-Newton. Upper limits to soft X-ray emission from the two program stars that have effective temperatures most similar to that of the Sun, namely HD 19445 and HD 140283, are comparable to the level of the quiet Sun. The star HD 25329, a cooler subdwarf, exhibits an upper limit similar to the Sun at maximum activity. These measurements suggest that coronal activity appears to decrease with age among the oldest G dwarfs, but K-M subdwarfs possibly have maintained a solar-like level of activity. Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA.

  14. A Search for Coronal Activity Among Two Metal-poor Subdwarfs and One Subgiant

    NASA Astrophysics Data System (ADS)

    Smith, Graeme H.; Dupree, Andrea K.; Günther, Hans Moritz

    2016-08-01

    A search has been made using the XMM-Newton satellite for coronal soft X-ray emission from HD 19445, HD 25329, and HD 140283, three Population II stars in the Galactic halo having metallicities of {{[Fe/H]}}∼ -2. The program stars, consisting of two subdwarfs and one metal-poor subgiant, were pre-selected from ground-based observations to have He i λ10830 absorption lines with an equivalent width (EW) of 30 mÅ or more. If such stars follow a relation between He i EW and soft X-ray flux applicable to Population I dwarf stars, then they would be expected to have X-ray luminosities ∼ 5× {10}-7 times their bolometric luminosity, and as such would yield detectable sources in 20 ks exposures with the XMM-Newton EPIC-PN and MOS cameras. No detections were found in such exposures made with XMM-Newton. Upper limits to soft X-ray emission from the two program stars that have effective temperatures most similar to that of the Sun, namely HD 19445 and HD 140283, are comparable to the level of the quiet Sun. The star HD 25329, a cooler subdwarf, exhibits an upper limit similar to the Sun at maximum activity. These measurements suggest that coronal activity appears to decrease with age among the oldest G dwarfs, but K-M subdwarfs possibly have maintained a solar-like level of activity. Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA.

  15. The heliospheric sheet configuration according to the coronal ray synoptic maps in solar activity cycles 23 and 24

    NASA Astrophysics Data System (ADS)

    Guseva, S. A.; Fat'yanov, M. P.; Shramko, A. D.

    2015-05-01

    Two catalogs of coronal ray synoptic maps for different altitudes (1.5-5 R ⊙) for solar activity cycles 23 and 24 (1996-2013) were compiled based on a proposed technique with the data from the SOHO space observatory LASCO C2 coronograph and the Mauna-Loa observatory Mark-IV K coronometer. The constructed synoptic maps of coronal rays represent an image of three-dimensional spherical sections of the heliospheric neutral sheet expanded along the heliographic longitude. The evolution of different heliospheric sheet spatial parameters during the analyzed period was studied based on the obtained maps.

  16. Active-Region Twist Derived from Magnetic Tongues and Linear Force-Free Extrapolations

    NASA Astrophysics Data System (ADS)

    Poisson, Mariano; López Fuentes, Marcelo; Mandrini, Cristina H.; Démoulin, Pascal

    2015-11-01

    The main aim of this study is to compare the amount of twist present in emerging active regions (ARs) from photospheric and coronal data. We use linear force-free field models of the observed coronal structure of ARs to determine the global twist. The coronal twist is derived, on one hand, from the force-free parameter [α] of the model and, on the other, from the computed coronal magnetic helicity normalized by the magnetic flux squared. We compare our results, for the same set of ARs, with those of Poisson et al. ( Solar Phys. 290, 727, 2015), in which the twist was estimated using the so-called magnetic tongues observed in line-of-sight magnetograms during AR emergence. We corroborate the agreement between the photospheric and coronal twist-sign and the presence of magnetic tongues as an early proxy of the AR non-potentiality. We find a globally linear relationship between the coronal twist and the one previously deduced for the emerging AR flux rope at the photospheric level. The coronal-twist value is typically lower by a factor of six than the one deduced for the emerging flux rope. We interpret this result as due to the partial emergence of the flux rope that forms the region.

  17. Evidence for Widespread Cooling in an Active Region Observed with the SDO Atmospheric Imaging Assembly

    NASA Technical Reports Server (NTRS)

    Viall, Nicholeen M.; Klimchuk, James A.

    2012-01-01

    A well known behavior of EUV light curves of discrete coronal loops is that the peak intensities of cooler channels or spectral lines are reached at progressively later times. This time lag is understood to be the result of hot coronal loop plasma cooling through these lower respective temperatures. However, loops typically comprise only a minority of the total emission in active regions. Is this cooling pattern a common property of active region coronal plasma, or does it only occur in unique circumstances, locations, and times? The new SDO/AIA data provide a wonderful opportunity to answer this question systematically for an entire active region. We measure the time lag between pairs of SDO/AIA EUV channels using 24 hours of images of AR 11082 observed on 19 June 2010. We find that there is a time-lag signal consistent with cooling plasma, just as is usually found for loops, throughout the active region including the diffuse emission between loops for the entire 24 hour duration. The pattern persists consistently for all channel pairs and choice of window length within the 24 hour time period, giving us confidence that the plasma is cooling from temperatures of greater than 3 MK, and sometimes exceeding 7 MK, down to temperatures lower than approx. 0.8 MK. This suggests that the bulk of the emitting coronal plasma in this active region is not steady; rather, it is dynamic and constantly evolving. These measurements provide crucial constraints on any model which seeks to describe coronal heating.

  18. Formation of active region and quiescent prominence magnetic field configurations

    NASA Technical Reports Server (NTRS)

    An, C.-H.; Bao, J. J.; Wu, S. T.

    1986-01-01

    To investigate the formation of prominences, researchers studied chromospheric mass injection into an overlying coronal dipole magnetic field using a 2-D ideal magnetohydrodynamic (MHD) numerical model. Researchers propose that active region prominences are formed by chromospheric plasmas injected directly into the overlying coronal magnetic field and that quiescent prominences are formed by plasmas evaporated at the interface between spicules and corona. Hence, for the simulation of an active region prominence magnetic field we inject the mass from one side, but use a symmetric mass injection to form a quiescent prominence field configuration. Researchers try to find optimum conditions for the formation of Kippenhahn-Schuluter(K-S)type field configuration for stable support of the injection plasmas. They find that the formation of K-S type field configuration by mass injection requires a delicate balance between injection velocity, density, and overlying magnetic fields. These results may explain why a prominence does not form on every neutral line.

  19. IMPLICATIONS OF MASS AND ENERGY LOSS DUE TO CORONAL MASS EJECTIONS ON MAGNETICALLY ACTIVE STARS

    SciTech Connect

    Drake, Jeremy J.; Cohen, Ofer; Yashiro, Seiji; Gopalswamy, Nat

    2013-02-20

    Analysis of a database of solar coronal mass ejections (CMEs) and associated flares over the period 1996-2007 finds well-behaved power-law relationships between the 1-8 A flare X-ray fluence and CME mass and kinetic energy. We extrapolate these relationships to lower and higher flare energies to estimate the mass and energy loss due to CMEs from stellar coronae, assuming that the observed X-ray emission of the latter is dominated by flares with a frequency as a function of energy dn/dE = kE {sup -{alpha}}. For solar-like stars at saturated levels of X-ray activity, the implied losses depend fairly weakly on the assumed value of {alpha} and are very large: M-dot {approx}5 Multiplication-Sign 10{sup -10} M{sub sun} yr{sup -1} and E-dot {approx}0.1 L{sub sun}. In order to avoid such large energy requirements, either the relationships between CME mass and speed and flare energy must flatten for X-ray fluence {approx}> 10{sup 31} erg, or the flare-CME association must drop significantly below 1 for more energetic events. If active coronae are dominated by flares, then the total coronal energy budget is likely to be up to an order of magnitude larger than the canonical 10{sup -3} L {sub bol} X-ray saturation threshold. This raises the question of what is the maximum energy a magnetic dynamo can extract from a star? For an energy budget of 1% of L {sub bol}, the CME mass loss rate is about 5 Multiplication-Sign 10{sup -11} M {sub Sun} yr{sup -1}.

  20. Solar wind and coronal structure

    NASA Technical Reports Server (NTRS)

    Withbroe, G. L.

    1983-01-01

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

  1. Signatures of Slow Solar Wind Streams from Active Regions in the Inner Corona

    NASA Astrophysics Data System (ADS)

    Slemzin, V.; Harra, L.; Urnov, A.; Kuzin, S.; Goryaev, F.; Berghmans, D.

    2013-08-01

    The identification of solar-wind sources is an important question in solar physics. The existing solar-wind models ( e.g., the Wang-Sheeley-Arge model) provide the approximate locations of the solar wind sources based on magnetic field extrapolations. It has been suggested recently that plasma outflows observed at the edges of active regions may be a source of the slow solar wind. To explore this we analyze an isolated active region (AR) adjacent to small coronal hole (CH) in July/August 2009. On 1 August, Hinode/EUV Imaging Spectrometer observations showed two compact outflow regions in the corona. Coronal rays were observed above the active-region coronal hole (ARCH) region on the eastern limb on 31 July by STEREO-A/EUVI and at the western limb on 7 August by CORONAS- Photon/TESIS telescopes. In both cases the coronal rays were co-aligned with open magnetic-field lines given by the potential field source surface model, which expanded into the streamer. The solar-wind parameters measured by STEREO-B, ACE, Wind, and STEREO-A confirmed the identification of the ARCH as a source region of the slow solar wind. The results of the study support the suggestion that coronal rays can represent signatures of outflows from ARs propagating in the inner corona along open field lines into the heliosphere.

  2. HIGH ANGULAR RESOLUTION RADIO OBSERVATIONS OF A CORONAL MASS EJECTION SOURCE REGION AT LOW FREQUENCIES DURING A SOLAR ECLIPSE

    SciTech Connect

    Ramesh, R.; Kathiravan, C.; Barve, Indrajit V.; Rajalingam, M. E-mail: kathir@iiap.res.in E-mail: rajalingam@iiap.res.in

    2012-01-10

    We carried out radio observations of the solar corona in the frequency range 109-50 MHz during the annular eclipse of 2010 January 15 from the Gauribidanur Observatory, located about 100 km north of Bangalore in India. The radio emission in the above frequency range originates typically in the radial distance range Almost-Equal-To 1.2-1.5 R{sub Sun} in the 'undisturbed' solar atmosphere. Our analysis indicates that (1) the angular size of the smallest observable radio source (associated with a coronal mass ejection in the present case) is Almost-Equal-To 1' {+-} 0.'3, (2) the source size does not vary with radial distance, (3) the peak brightness temperature of the source corresponding to the above size at a typical frequency like 77 MHz is Almost-Equal-To 3 Multiplication-Sign 10{sup 9} K, and (4) the coronal magnetic field near the source region is Almost-Equal-To 70 mG.

  3. Radio magnetography of the solar active regions

    NASA Astrophysics Data System (ADS)

    Gelfreikh, G. B.; Shibasaki, K.

    The observations of the solar magnetic fields is one of the most important basics for study of all important processes in structuring the solar atmosphere and most kinds of the release of the energy. The radio methods are of the special interest here because they gain the information on the magnetic field strength in the solar corona and upper chromosphere where traditional optical methods do not work. The construction of the Nobeyama radio heliograph opens a new era in usage radio methods for solar radio magnetography due to some unique property of the instrument: - The 2D mapping of the whole disk of the sun both in I and V Stokes parameters with resolution of 10 arcsec. - Regular observations (without breaks due to weather conditions), eight hours a day, already for seven years. The most effective and representative radio method of measuring the solar magnetic fields is to use polarization measurements of the thermal bremsstrahlung (free-free emission). It is applicable both to analysis of chromospheric and coronal magnetic fields and presents information on longitude component of the magnetic field strength in solar active regions. Three problems are met, however: (i) One needs to measure very low degree of polarization (small fraction of a percent); (ii) To get the real value of the field the spectral data are necessary. (iii) While observing an active region on the disk we have got the overlapping effects on polarized signal of the chromospheric and coronal magnetic fields. To get higher sensitivity the averaging of the radio maps over periods of about ten minutes were used with the results of sensitivity on V-maps of the order 0.1%. Observations for a number of dates have been analysed (August 22, 1992, October 31, 1992; June 30, 1993, July 22,1994, June 15, 1995 and some more). In all cases a very good similarity was found of the polarized regions (V-maps) with the Ca^ + plages in form and total coincidence with the direction of the magnetic fields on the

  4. 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

  5. Software Displays Data on Active Regions of the Sun

    NASA Technical Reports Server (NTRS)

    Golightly, Mike; Weyland, Mark; Raben, Vern

    2011-01-01

    The Solar Active Region Display System is a computer program that generates, in near real time, a graphical display of parameters indicative of the spatial and temporal variations of activity on the Sun. These parameters include histories and distributions of solar flares, active region growth, coronal mass ejections, size, and magnetic configuration. By presenting solar-activity data in graphical form, this program accelerates, facilitates, and partly automates what had previously been a time-consuming mental process of interpretation of solar-activity data presented in tabular and textual formats. Intended for original use in predicting space weather in order to minimize the exposure of astronauts to ionizing radiation, the program might also be useful on Earth for predicting solar-wind-induced ionospheric effects, electric currents, and potentials that could affect radio-communication systems, navigation systems, pipelines, and long electric-power lines. Raw data for the display are obtained automatically from the Space Environment Center (SEC) of the National Oceanic and Atmospheric Administration (NOAA). Other data must be obtained from the NOAA SEC by verbal communication and entered manually. The Solar Active Region Display System automatically accounts for the latitude dependence of the rate of rotation of the Sun, by use of a mathematical model that is corrected with NOAA SEC active-region position data once every 24 hours. The display includes the date, time, and an image of the Sun in H light overlaid with latitude and longitude coordinate lines, dots that mark locations of active regions identified by NOAA, identifying numbers assigned by NOAA to such regions, and solar-region visual summary (SRVS) indicators associated with some of the active regions. Each SRVS indicator is a small pie chart containing five equal sectors, each of which is color-coded to provide a semiquantitative indication of the degree of hazard posed by one aspect of the activity at

  6. MAXIMUM CORONAL MASS EJECTION SPEED AS AN INDICATOR OF SOLAR AND GEOMAGNETIC ACTIVITIES

    SciTech Connect

    Kilcik, A.; Yurchyshyn, V. B.; Abramenko, V.; Goode, P. R.; Gopalswamy, N.; Ozguc, A.; Rozelot, J. P.

    2011-01-20

    We investigate the relationship between the monthly averaged maximal speeds of coronal mass ejections (CMEs), international sunspot number (ISSN), and the geomagnetic Dst and Ap indices covering the 1996-2008 time interval (solar cycle 23). Our new findings are as follows. (1) There is a noteworthy relationship between monthly averaged maximum CME speeds and sunspot numbers, Ap and Dst indices. Various peculiarities in the monthly Dst index are correlated better with the fine structures in the CME speed profile than that in the ISSN data. (2) Unlike the sunspot numbers, the CME speed index does not exhibit a double peak maximum. Instead, the CME speed profile peaks during the declining phase of solar cycle 23. Similar to the Ap index, both CME speed and the Dst indices lag behind the sunspot numbers by several months. (3) The CME number shows a double peak similar to that seen in the sunspot numbers. The CME occurrence rate remained very high even near the minimum of the solar cycle 23, when both the sunspot number and the CME average maximum speed were reaching their minimum values. (4) A well-defined peak of the Ap index between 2002 May and 2004 August was co-temporal with the excess of the mid-latitude coronal holes during solar cycle 23. The above findings suggest that the CME speed index may be a useful indicator of both solar and geomagnetic activities. It may have advantages over the sunspot numbers, because it better reflects the intensity of Earth-directed solar eruptions.

  7. Maximum Coronal Mass Ejection Speed as an Indicator of Solar and Geomagnetic Activities

    NASA Astrophysics Data System (ADS)

    Kilcik, A.; Yurchyshyn, V. B.; Abramenko, V.; Goode, P. R.; Gopalswamy, N.; Ozguc, A.; Rozelot, J. P.

    2011-01-01

    We investigate the relationship between the monthly averaged maximal speeds of coronal mass ejections (CMEs), international sunspot number (ISSN), and the geomagnetic Dst and Ap indices covering the 1996-2008 time interval (solar cycle 23). Our new findings are as follows. (1) There is a noteworthy relationship between monthly averaged maximum CME speeds and sunspot numbers, Ap and Dst indices. Various peculiarities in the monthly Dst index are correlated better with the fine structures in the CME speed profile than that in the ISSN data. (2) Unlike the sunspot numbers, the CME speed index does not exhibit a double peak maximum. Instead, the CME speed profile peaks during the declining phase of solar cycle 23. Similar to the Ap index, both CME speed and the Dst indices lag behind the sunspot numbers by several months. (3) The CME number shows a double peak similar to that seen in the sunspot numbers. The CME occurrence rate remained very high even near the minimum of the solar cycle 23, when both the sunspot number and the CME average maximum speed were reaching their minimum values. (4) A well-defined peak of the Ap index between 2002 May and 2004 August was co-temporal with the excess of the mid-latitude coronal holes during solar cycle 23. The above findings suggest that the CME speed index may be a useful indicator of both solar and geomagnetic activities. It may have advantages over the sunspot numbers, because it better reflects the intensity of Earth-directed solar eruptions.

  8. Active region seismology

    NASA Technical Reports Server (NTRS)

    Bogdan, Tom; Braun, D. C.

    1995-01-01

    Active region seismology is concerned with the determination and interpretation of the interaction of the solar acoustic oscillations with near-surface target structures, such as magnetic flux concentration, sunspots, and plage. Recent observations made with a high spatial resolution and a long temporal duration enabled measurements of the scattering matrix for sunspots and solar active regions to be carried out as a function of the mode properties. Based on this information, the amount of p-mode absorption, partial-wave phase shift, and mode mixing introduced by the sunspot, could be determined. In addition, the possibility of detecting the presence of completely submerged magnetic fields was raised, and new procedures for performing acoustic holography of the solar interior are being developed. The accumulating evidence points to the mode conversion of p-modes to various magneto-atmospheric waves within the magnetic flux concentration as being the unifying physical mechanism responsible for these diverse phenomena.

  9. DISTRIBUTION OF ELECTRIC CURRENTS IN SOLAR ACTIVE REGIONS

    SciTech Connect

    Török, T.; Titov, V. S.; Mikić, Z.; Leake, J. E.; Archontis, V.; Linton, M. G.; Dalmasse, K.; Aulanier, G.; Kliem, B.

    2014-02-10

    There has been a long-standing debate on the question of whether or not electric currents in solar active regions are neutralized. That is, whether or not the main (or direct) coronal currents connecting the active region polarities are surrounded by shielding (or return) currents of equal total value and opposite direction. Both theory and observations are not yet fully conclusive regarding this question, and numerical simulations have, surprisingly, barely been used to address it. Here we quantify the evolution of electric currents during the formation of a bipolar active region by considering a three-dimensional magnetohydrodynamic simulation of the emergence of a sub-photospheric, current-neutralized magnetic flux rope into the solar atmosphere. We find that a strong deviation from current neutralization develops simultaneously with the onset of significant flux emergence into the corona, accompanied by the development of substantial magnetic shear along the active region's polarity inversion line. After the region has formed and flux emergence has ceased, the strong magnetic fields in the region's center are connected solely by direct currents, and the total direct current is several times larger than the total return current. These results suggest that active regions, the main sources of coronal mass ejections and flares, are born with substantial net currents, in agreement with recent observations. Furthermore, they support eruption models that employ pre-eruption magnetic fields containing such currents.

  10. Multi-wavelength Observations of Solar Active Region NOAA 7154

    NASA Technical Reports Server (NTRS)

    Bruner, M. E.; Nitta, N. V.; Frank. Z. A.; Dame, L.; Suematsu, Y.

    2000-01-01

    We report on observations of a solar active region in May 1992 by the Solar Plasma Diagnostic Experiment (SPDE) in coordination with the Yohkoh satellite (producing soft X-ray images) and ground-based observatories (producing photospheric magnetograms and various filtergrams including those at the CN 3883 A line). The main focus is a study of the physical conditions of hot (T is approximately greater than 3 MK) coronal loops at their foot-points. The coronal part of the loops is fuzzy but what appear to be their footpoints in the transition region down to the photosphere are compact. Despite the morphological similarities, the footpoint emission at 10(exp 5) K is not quantitatively correlated with that at approximately 300 km above the tau (sub 5000) = 1 level, suggesting that the heat transport and therefore magnetic field topology in the intermediate layer is complicated. High resolution imaging observations with continuous temperature coverage are crucially needed.

  11. Anemone structure of Active Region NOAA 10798 and related geo-effective flares/ CMEs

    NASA Astrophysics Data System (ADS)

    Asai, A.; Ishii, T. T.; Shibata, K.; Gopalswamy, N.

    2006-08-01

    Introduction: We report the evolution and the coronal features of an active region NOAA 10798, and the related magnetic storms. Method: We examined in detail the photospheric and coronal features of the active region by using observational data in soft X-rays, in extreme ultraviolet images, and in magnetogram obtained with GOES, SOHO satellites. We also examined the interplanetary disturbances from the ACE data. Results: This active region was located in the middle of a small coronal hole, and generated 3 M-class flares. The flares are associated with high speed CMEs up to 2000 km/s. The interplanetary disturbances also show a structure with southward strong magnetic field. These produced a magnetic storm on 2005 August 24. Conclusions: The anemone structure may play a role for producing the high-speed and geo-effective CMEs even the near limb locations.

  12. DN Tauri - coronal activity and accretion in a young low-mass CTTS

    NASA Astrophysics Data System (ADS)

    Robrade, J.; Güdel, M.; Günther, H. M.; Schmitt, J. H. M. M.

    2014-01-01

    Context. Classical T Tauri stars (CTTSs) are young, accreting low-mass stars; their X-ray emission differs from that of their main-sequence counterparts in a number of aspects. Aims: We study the specific case of DN Tau, a young M0-type accreting CTTS, to extend the range of young CTTSs studied with high-resolution X-ray spectroscopy at lower masses and to compare its high-energy properties with those of similar objects. Methods: We use a deep XMM-Newton observation of DN Tau to investigate its X-ray properties and X-ray generating mechanisms. Specifically, we examine the presence of X-ray emission from magnetic activity and accretion shocks. We also compare our new X-ray data with UV data taken simultaneously and with X-ray/UV observations performed before. Results: We find that the X-ray emission from DN Tau is dominated by coronal plasma generated via magnetic activity, but also clearly detect a contribution of the accretion shocks to the cool plasma component at ≲2 MK as consistently inferred from density and temperature analysis. Typical phenomena of active coronae, such as flaring, the presence of very hot plasma at 30 MK, and an abundance pattern showing the inverse FIP effect, are seen on DN Tau. Strong variations in the emission measure of the cooler plasma components between the 2005 and 2010 data point to accretion related changes; in contrast, the hotter coronal plasma component is virtually unchanged. The UV light curve taken simultaneously is in general not related to the X-ray brightness, but exhibits clear counterparts during the observed X-ray flares. Conclusions: The X-ray properties of DN Tau are similar to those of more massive CTTSs, but its low mass and large radius associated with its youth shift the accretion shocks to lower temperatures, reducing their imprint in the X-ray regime. DN Tau's overall X-ray properties are dominated by strong magnetic activity.

  13. Detection and activity assessment of primary coronal caries lesions: a methodologic study.

    PubMed

    Ekstrand, Kim Rud; Martignon, Stefania; Ricketts, David James Nigel; Qvist, Vibeke

    2007-01-01

    This study has three main objectives: Study (1) test the reproducibility and accuracy of the ICDAS I and ICDAS II caries detection systems; Study (2) validate a new impression material (Clinpro, 3M ESPE), which is said to detect lactic acid in plaque fermenting sucrose; Study (3) devise and test a scoring system for the assessment of caries activity of coronal lesions. Study (1): 141 extracted teeth were examined by two examiners using the ICDAS I and ICDAS II caries detection systems and validated against a histological classification system. Study (2): The accuracy of the impression material in predicting plaque with pH lower/higher than 5.5 was determined in an in situ study of 45 root dentin specimens by comparing the color change in the impression with the actual pH of the plaque, determined with a pH meter. Study (3): A scoring system to assess lesion activity was devised based on the predictive power of the visual appearance of the lesion (ICDAS II system), location of the lesion in a plaque stagnation area and, finally, the tactile feeling, rough/soft or smooth/hard, when running a perio-probe over the lesion. The accuracy was tested in a clinical study of 35 children with 225 lesions/sound surfaces and was validated using the Clinpro impression material for construct validity. Study (1): Intra- and inter-examiner reproducibility was found to be excellent (Kappa-values > 0.82) and the associations strong (Spearmans correlation coefficients > 0.90). Study (2): The Clinpro impression material was found to be acceptable as compared to the results of a pH meter, the combined sensitivity and specificity was 1.63. Study (3): ROC analysis showed that the devised classification system for determining lesion activity had acceptable accuracy (area under curve = 0.84 and the highest combined sum of specificity and sensitivity was 1.67). Thus, it is possible to predict lesion depth and assess the activity of primary coronal caries lesions accurately by using the

  14. The solar extreme ultra-violet corona: Resolved loops and the unresolved active region corona

    NASA Astrophysics Data System (ADS)

    Cirtain, Jonathan Wesley

    In this work, physical characteristics of the solar corona as observed in the Extreme Ultra-Violet (EUV) regime are investigated. The focus will be the regions of intense EUV radiation generally found near the locations of sunspots. These regions are commonly called active regions. Multiple space- based observing platforms have been deployed in the last decade; it is possible to use several of these observatories in combination to develop a more complete picture of the solar corona. Joint Observing Program 146 was created to collect spectroscopic intensities using the Coronal Diagnostic Spectrometer on Solar and Heliospheric Observatory and EUV images using NASA's Transition Region and Coronal Explorer. The emission line intensities are analyzed to develop an understanding of the temperature and density of the active region coronal plasma. However, the performance of the CDS instrument in the spatial and temporal domains is limited and to compensate for these limitations, data collected by the TRACE instrument provide a high spatial and temporal resolution set of observations. One of the most exciting unsolved problems in solar astrophysics is to understand why the corona maintains a temperature roughly two orders of magnitude higher than the underlying material. A detailed investigation of the coronal emission has provided constraints on models of the heating mechanism, since the temperature, density and evolution of emission rates for multiple ionic species are indicative of the mechanism(s) working to heat the corona. The corona appears to consist of multiple unresolved structures as well as resolved active region structures, called coronal loops. The purpose of the present work is to determine the characteristics of the unresolved background corona. Using the characterizations of the coronal unresolved background, results for loops after background subtraction are also presented. This work demonstrates the magnitude of the unresolved coronal emission with

  15. Magnetic cycles of Sun-like stars with different levels of coronal and chromospheric activity — comparison with the Sun

    NASA Astrophysics Data System (ADS)

    Shimanovskaya, Elena; Bruevich, Vasiliy; Bruevich, Elena

    2016-09-01

    The atmospheric activity of the Sun and Sun-like stars is analyzed involving observations from the HK-project at the Mount Wilson Observatory, the California and Carnegie Planet Search Program at the Keck and Lick Observatories and the Magellan Planet Search Program at the Las Campanas Observatory. We show that for stars of F, G and K spectral classes, the cyclic activity, similar to the 11-yr solar cycle, is different: it becomes more prominent in K-stars. Comparative study of Sun-like stars with different levels of chromospheric and coronal activity confirms that the Sun belongs to stars with a low level of chromospheric activity and stands apart among these stars by its minimum level of coronal radiation and minimum level of variations in photospheric flux.

  16. Sunspots and Coronal Bright Points Tracking using a Hybrid Algorithm of PSO and Active Contour Model

    NASA Astrophysics Data System (ADS)

    Dorotovic, I.; Shahamatnia, E.; Lorenc, M.; Rybansky, M.; Ribeiro, R. A.; Fonseca, J. M.

    2014-02-01

    In the last decades there has been a steady increase of high-resolution data, from ground-based and space-borne solar instruments, and also of solar data volume. These huge image archives require efficient automatic image processing software tools capable of detecting and tracking various features in the solar atmosphere. Results of application of such tools are essential for studies of solar activity evolution, climate change understanding and space weather prediction. The follow up of interplanetary and near-Earth phenomena requires, among others, automatic tracking algorithms that can determine where a feature is located, on successive images taken along the period of observation. Full-disc solar images, obtained both with the ground-based solar telescopes and the instruments onboard the satellites, provide essential observational material for solar physicists and space weather researchers for better understanding the Sun, studying the evolution of various features in the solar atmosphere, and also investigating solar differential rotation by tracking such features along time. Here we demonstrate and discuss the suitability of applying a hybrid Particle Swarm Optimization (PSO) algorithm and Active Contour model for tracking and determining the differential rotation of sunspots and coronal bright points (CBPs) on a set of selected solar images. The results obtained confirm that the proposed approach constitutes a promising tool for investigating the evolution of solar activity and also for automating tracking features on massive solar image archives.

  17. A Study of the Coronal Non-thermal Velocity in Polar Regions During the Rise from Solar Minimum to Solar Maximum in Cycle 24

    NASA Astrophysics Data System (ADS)

    Harra, L.; Baker, D.; Edwards, S. J.; Hara, H.; Howe, R.; van Driel-Gesztelyi, L.

    2015-11-01

    We explore the changes in coronal non-thermal velocity ( V nt) measurements at the poles from solar minimum to solar maximum using Hinode EUV Imaging Spectrometer data. We find that although the intensity in the corona at the poles does tend to increase with the cycle, there are no significant changes in the V nt values. The locations of enhanced V nt values measured do not always have a counterpart in intensity, and they are sometimes located in weak emission regions. Unipolar magnetic streams, created through diffusion of the following polarity of the decaying active regions, slowly progress towards the poles. These streams are expected to be related to magnetic nulls as locations that indicate an increased likelihood for magnetic reconnection to occur. Through global potential field source-surface modelling, we determine how the number of nulls varied during the cycle and find that those that lie at < 1.1 solar radii vary significantly. We search for a correlation between the variation of the magnetic nulls and the V nt values, as it may be expected that with an increasing number of nulls, the V nt values in the corona increase as well. There is no correlation with the V nt values, however. This indicates that the magnetic structures that create the enhanced V nt behaviour are small-scale features and hence not easily measurable at the poles. Because they do not change during the solar cycle, they are likely to be created by a local dynamo. The variation of the upper range of V nt is reduced, which highlights that strongly dynamic behaviour is reduced as the solar maximum approaches. This is likely to be due to the reduced area of the polar coronal hole, which allows fewer opportunities for reconnection to occur between open and closed magnetic fields.

  18. Modeling Active Region Evolution - A New LWS TR and T Strategic Capability Model Suite

    NASA Technical Reports Server (NTRS)

    MacNeice, Peter

    2012-01-01

    In 2006 the LWS TR&T Program funded us to develop a strategic capability model of slowly evolving coronal active regions. In this poster we report on the overall design, and status of our new modeling suite. Our design features two coronal field models, a non-linear force free field model and a global 3D MHD code. The suite includes supporting tools and a user friendly GUI which will enable users to query the web for relevant magnetograms, download them, process them to synthesize a sequence of photospheric magnetograms and associated photospheric flow field which can then be applied to drive the coronal model innner boundary, run the coronal models and finally visualize the results.

  19. Models of Impulsively Heated Solar Active Regions

    NASA Astrophysics Data System (ADS)

    Airapetian, Vladimir; Klimchuk, J.

    2009-05-01

    A number of attempts to model solar active regions with steady coronal heating have been modestly successful at reproducing the observed soft X-ray emission, but they fail dramatically at explaining EUV observations. Since impulsive heating (nanoflare) models can reproduce individual EUV loops, it seems reasonable to consider that entire active regions are impulsively heated. However, nanoflares are characterized by many parameters, such as magnitude, duration, and time delay between successive events, and these parameters may depend on the strength of the magnetic field or the length of field lines, for example, so a wide range of active region models must be examined. We have recently begun such a study. Each model begins with a magnetic "skeleton” obtained by extrapolating an observed photospheric magnetogram into the corona. Field lines are populated with plasma using our highly efficient hydro code called Enthalpy Based Thermal Evolution of Loops (EBTEL). We then produce synthetic images corresponding to emission line or broad-band observations. By determining which set of nanoflare parameters best reproduces actual observations, we hope to constrain the properties of the heating and ultimately to reveal the physical mechanism. We here report on the initial progress of our study.

  20. Investigating Alfvénic wave propagation in coronal open-field regions.

    PubMed

    Morton, R J; Tomczyk, S; Pinto, R

    2015-01-01

    The physical mechanisms behind accelerating solar and stellar winds are a long-standing astrophysical mystery, although recent breakthroughs have come from models invoking the turbulent dissipation of Alfvén waves. The existence of Alfvén waves far from the Sun has been known since the 1970s, and recently the presence of ubiquitous Alfvénic waves throughout the solar atmosphere has been confirmed. However, the presence of atmospheric Alfvénic waves does not, alone, provide sufficient support for wave-based models; the existence of counter-propagating Alfvénic waves is crucial for the development of turbulence. Here, we demonstrate that counter-propagating Alfvénic waves exist in open coronal magnetic fields and reveal key observational insights into the details of their generation, reflection in the upper atmosphere and outward propagation into the solar wind. The results enhance our knowledge of Alfvénic wave propagation in the solar atmosphere, providing support and constraints for some of the recent Alfvén wave turbulence models. PMID:26213234

  1. Investigating Alfvénic wave propagation in coronal open-field regions

    PubMed Central

    Morton, R. J.; Tomczyk, S.; Pinto, R.

    2015-01-01

    The physical mechanisms behind accelerating solar and stellar winds are a long-standing astrophysical mystery, although recent breakthroughs have come from models invoking the turbulent dissipation of Alfvén waves. The existence of Alfvén waves far from the Sun has been known since the 1970s, and recently the presence of ubiquitous Alfvénic waves throughout the solar atmosphere has been confirmed. However, the presence of atmospheric Alfvénic waves does not, alone, provide sufficient support for wave-based models; the existence of counter-propagating Alfvénic waves is crucial for the development of turbulence. Here, we demonstrate that counter-propagating Alfvénic waves exist in open coronal magnetic fields and reveal key observational insights into the details of their generation, reflection in the upper atmosphere and outward propagation into the solar wind. The results enhance our knowledge of Alfvénic wave propagation in the solar atmosphere, providing support and constraints for some of the recent Alfvén wave turbulence models. PMID:26213234

  2. The Three-Dimensional Velocity Fields Of Solar Disappearing Filaments And Their Relations To Coronal Activities

    NASA Astrophysics Data System (ADS)

    Morimoto, T.; Kurokawa, H.

    2003-12-01

    Solar filament disappearance (Disparition Brusque: DB) is often accompanied by a great magnetic activities such as flares and transient shock waves on and near the solar surface as well as enormous disturbances in interplanetary space due to the associated coronal mass ejection (CMEs). Thus, DBs are of great interest not only to solar physics research, but also to space science, and solar-terrestrial study. Since it is impossible to measure the velocity field of DBs with ordinal observations in the Hα line center alone, most previous studies have focused on the morphological signatures of DBs. In order to obtain the physical characteristics of DBs and relate them to other active phenomena, much effort is put into the calculation of their three-dimensional (3-D) velocity fields. Using the Hα line center, blue and red wing (Hα +/- 0.8 Å ) images obtained by the Flare Monitoring Telescope (FMT) at Hida Observatory, Kyoto University, and based on the Beckers' cloud model, we developed a new method to obtain the line-of-sight velocity of disappearing solar filaments. The line-of-sight velocity is obtained (i) by calculating the Hα line profile of the filament, and (ii) by measuring the Doppler shift which best fits the observed temporal variations of contrasts of the filament. The tangential velocity is obtained by tracing the motions of internal structures on successive images, and both line-of-sight and tangential velocities are combined to yield the 3-D velcoty field of DBs. In this method, corrections for the effective filter bandwidths of the instrument, stray light and Doppler brightening effect, are performed. Using the 3-D velocity field of DBs, we also developed a method to judge whether the DB was ejected into interplanetary space (eruptive) or remained in the corona (quasi-eruptive). The type of DBs are compared with the type of the associated coronal activites such as arcade formations observed in soft X-rays and EUV, CMEs and we conclude that the

  3. THE MAGNETIC ENERGY-HELICITY DIAGRAM OF SOLAR ACTIVE REGIONS

    SciTech Connect

    Tziotziou, Kostas; Georgoulis, Manolis K.; Raouafi, Nour-Eddine

    2012-11-01

    Using a recently proposed nonlinear force-free method designed for single-vector magnetograms of solar active regions, we calculate the instantaneous free magnetic energy and relative magnetic helicity budgets in 162 vector magnetograms corresponding to 42 different active regions. We find a statistically robust, monotonic correlation between the free magnetic energy and the relative magnetic helicity in the studied regions. This correlation implies that magnetic helicity, in addition to free magnetic energy, may be an essential ingredient for major solar eruptions. Eruptive active regions appear well segregated from non-eruptive ones in both free energy and relative helicity with major (at least M-class) flares occurring in active regions with free energy and relative helicity exceeding 4 Multiplication-Sign 10{sup 31} erg and 2 Multiplication-Sign 10{sup 42} Mx{sup 2}, respectively. The helicity threshold agrees well with estimates of the helicity contents of typical coronal mass ejections.

  4. 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

  5. Evolution of Active Regions

    NASA Astrophysics Data System (ADS)

    van Driel-Gesztelyi, Lidia; Green, Lucie May

    2015-09-01

    The evolution of active regions (AR) from their emergence through their long decay process is of fundamental importance in solar physics. Since large-scale flux is generated by the deep-seated dynamo, the observed characteristics of flux emergence and that of the subsequent decay provide vital clues as well as boundary conditions for dynamo models. Throughout their evolution, ARs are centres of magnetic activity, with the level and type of activity phenomena being dependent on the evolutionary stage of the AR. As new flux emerges into a pre-existing magnetic environment, its evolution leads to re-configuration of small-and large-scale magnetic connectivities. The decay process of ARs spreads the once-concentrated magnetic flux over an ever-increasing area. Though most of the flux disappears through small-scale cancellation processes, it is the remnant of large-scale AR fields that is able to reverse the polarity of the poles and build up new polar fields. In this Living Review the emphasis is put on what we have learned from observations, which is put in the context of modelling and simulation efforts when interpreting them. For another, modelling-focused Living Review on the sub-surface evolution and emergence of magnetic flux see Fan (2009). In this first version we focus on the evolution of dominantly bipolar ARs.

  6. Plasma Beta Above a Solar Active Region: Rethinking the Paradigm

    NASA Technical Reports Server (NTRS)

    Gary, G. Allen; Whitaker, Ann F. (Technical Monitor)

    2001-01-01

    In this paper, we present a model of the plasma beta above an active region and discuss its consequences in terms of coronal magnetic field modeling. The beta-plasma model is representative and derived from a collection of sources. The resulting beta variation with height is used to emphasize the assumption that the magnetic pressure dominates over the plasma pressure must be carefully considered depending on what part of the solar atmosphere is being considered. This paper points out (1) that the paradigm that the coronal magnetic field can be constructed from a force-free magnetic field must be used in the correct context, since the forcefree region is sandwiched between two regions which have beta greater than 1, (2) that the chromospheric MgIICIV magnetic measurements occur near the beta-minimum, and (3) that, moving from the photosphere upwards, beta can return to 1 at relatively low coronal heights, e.g. R approximately 1.2R(sub)s.

  7. Evolution and Activity in the Solar Corona: A Comparison of Coronal and Chromospheric Structures Seen in Soft X-Rays, White Light and H-Alpha Emission

    NASA Technical Reports Server (NTRS)

    Bagenal, Fran

    2001-01-01

    The work completed under this project, 'Evolution and Activity in the Solar Corona: A Comparison of Coronal and Chromospheric Structures Seen in Soft X-Rays, White Light and H-Alpha Emission', includes the following presentations: (1) Analysis of H-alpha Observations of High-altitude Coronal Condensations; (2) Multi-spectral Imaging of Coronal Activity; (3) Measurement and Modeling of Soft X-ray Loop Arcades; (4) A Study of the Origin and Dynamics of CMEs; and various poster presentations and thesis dissertations.

  8. Active region studies with coordinated SOHO, microwave, and magnetograph observations

    NASA Technical Reports Server (NTRS)

    Holman, Gordon D.

    1992-01-01

    The scientific justification for an observing campaign to study the quantitative magnetic and plasma properties of coronal loops in active regions is presented. The SOHO (Solar and Heliospheric Observatory) instruments of primary relevance are CDS (Coronal Diagnostic Spectrometer), EIT, SUMER (Solar Ultraviolet Measurement of Emitted Radiation), and MDI. The primary ground based instruments would be the VLA (Very Large Array), the Owens Valley Radio Observatory, and vector and longitudinal field magnetographs. Similar campaigns have successfully been carried out with the Solar Maximum Mission x-ray polychromator and the Soft X-ray Imaging Sounding Rocket Payload (CoMStOC '87), the Goddard Solar EUV Rocket Telescope and Spectrograph, the Lockheed Solar Plasma Diagnostics Experiment rocket payload, and the Soft X-ray Telescope in Yohkoh (CoMStoc '92). The scientific payoff from such a campaign is discussed in light of the results from these previous campaigns.

  9. The evolution and orientation of early cycle 22 active regions

    NASA Technical Reports Server (NTRS)

    Cannon, Anne T.; Marquette, William H.

    1991-01-01

    The evolution of six major active regions which appeared during the first phase of the present solar cycle (cycle 22) has been studied. It was found that the northern hemisphere regions exhibited a broad range of evolutionary behavior in which the commonly accepted 'normal pattern' (whereby the follower flux moves preferentially polewards ahead of the leader flux) is represented at one end of the range. At the other end of the range, the leader flux is displaced polewards of the follower flux. In the latter cases equatorward extensions of the polar coronal hole are noted.

  10. Observation of coronal loop torsional oscillation

    NASA Astrophysics Data System (ADS)

    Zaqarashvili, T. V.

    2003-02-01

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

  11. 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

  12. A flare observed in coronal, transition region, and helium I 10830 Å emissions

    SciTech Connect

    Zeng, Zhicheng; Cao, Wenda; Qiu, Jiong; Judge, Philip G.

    2014-10-01

    On 2012 June 17, we observed the evolution of a C-class flare associated with the eruption of a filament near a large sunspot in the active region NOAA 11504. We obtained high spatial resolution filtergrams using the 1.6 m New Solar Telescope at the Big Bear Solar Observatory in broadband TiO at 706 nm (bandpass: 10 Å) and He I 10830 Å narrow band (bandpass: 0.5 Å, centered 0.25 Å to the blue). We analyze the spatio-temporal behavior of the He I 10830 Å data, which were obtained over a 90''×90'' field of view with a cadence of 10 s. We also analyze simultaneous data from the Atmospheric Imaging Assembly and Extreme Ultraviolet Variability Experiment instruments on board the Solar Dynamics Observatory spacecraft, and data from the Reuven Ramaty High Energy Solar Spectroscopic Imager and GOES spacecrafts. Non-thermal effects are ignored in this analysis. Several quantitative aspects of the data, as well as models derived using the '0D' enthalpy-based thermal evolution of loops model code, indicate that the triplet states of the 10830 Å multiplet are populated by photoionization of chromospheric plasma followed by radiative recombination. Surprisingly, the He II 304 Å line is reasonably well matched by standard emission measure calculations, along with the C IV emission which dominates the Atmosphere Imaging Assembly 1600 Å channel during flares. This work lends support to some of our previous work combining X-ray, EUV, and UV data of flares to build models of energy transport from corona to chromosphere.

  13. 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.

  14. Can coronal hole spicules reach coronal temperatures?

    NASA Astrophysics Data System (ADS)

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

    2011-08-01

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

  15. A unified theory of coronal heating

    NASA Technical Reports Server (NTRS)

    Ionson, J. A.

    1985-01-01

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

  16. Coronal Magnetic Fields Derived from Simultaneous Microwave and EUV Observations and Comparison with the Potential Field Model

    NASA Astrophysics Data System (ADS)

    Miyawaki, Shun; iwai, Kazumasa; Shibasaki, Kiyoto; Shiota, Daikou; Nozawa, Satoshi

    2016-02-01

    We estimated the accuracy of coronal magnetic fields derived from radio observations by comparing them to potential field calculations and the differential emission measure measurements using EUV observations. We derived line-of-sight components of the coronal magnetic field from polarization observations of the thermal bremsstrahlung in the NOAA active region 11150, observed around 3:00 UT on 2011 February 3 using the Nobeyama Radioheliograph at 17 GHz. Because the thermal bremsstrahlung intensity at 17 GHz includes both chromospheric and coronal components, we extracted only the coronal component by measuring the coronal emission measure in EUV observations. In addition, we derived only the radio polarization component of the corona by selecting the region of coronal loops and weak magnetic field strength in the chromosphere along the line of sight. The upper limits of the coronal longitudinal magnetic fields were determined as 100-210 G. We also calculated the coronal longitudinal magnetic fields from the potential field extrapolation using the photospheric magnetic field obtained from the Helioseismic and Magnetic Imager. However, the calculated potential fields were certainly smaller than the observed coronal longitudinal magnetic field. This discrepancy between the potential and the observed magnetic field strengths can be explained consistently by two reasons: (1) the underestimation of the coronal emission measure resulting from the limitation of the temperature range of the EUV observations, and (2) the underestimation of the coronal magnetic field resulting from the potential field assumption.

  17. Study of the geoeffectiveness of coronal mass ejections, corotating interaction regions and their associated structures observed during Solar Cycle 23

    NASA Astrophysics Data System (ADS)

    Badruddin, A.; Falak, Z.

    2016-08-01

    The interplanetary coronal mass ejections (ICMEs) and the corotating interaction regions (CIRs) are the two most important structures of the interplanetary medium affecting the Earth and the near-Earth space environment. We study the solar wind-magnetosphere coupling during the passage of ICMEs and CIRs, in the Solar Cycle 23 (Jan. 1995-Dec. 2009), and their relative geoeffectiveness. We utilize the timings of different features of these structures, their arrival and duration. As geomagnetic parameter, we utilize high time resolution data of Dst and AE indices. In addition to these geomagnetic indices, we utilize the simultaneous and similar time resolution data of interplanetary plasma and field, namely, solar wind velocity, interplanetary magnetic field, its north-south component and dawn-dusk electric field. We apply the method of superposed epoch analysis. Utilizing the properties of various structures during the passage of ICMEs and CIRs, and variations observed in plasma and field parameters during their passage along with the simultaneous changes observed in geomagnetic parameters, we identify the interplanetary conditions, plasma/field parameters and their relative importance in solar wind-magnetosphere coupling. Geospace consequences of ICMEs and CIRs, and the implications of these results for solar wind-magnetosphere coupling are discussed.

  18. 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.

  19. 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

  20. Coronal behavior before the large flare onset

    NASA Astrophysics Data System (ADS)

    Imada, Shinsuke; Bamba, Yumi; Kusano, Kanya

    2014-12-01

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

  1. Active region emission measure distributions and implications for nanoflare heating

    SciTech Connect

    Cargill, P. J.

    2014-03-20

    The temperature dependence of the emission measure (EM) in the core of active regions coronal loops is an important diagnostic of heating processes. Observations indicate that EM(T) ∼ T{sup a} below approximately 4 MK, with 2 < a < 5. Zero-dimensional hydrodynamic simulations of nanoflare trains are used to demonstrate the dependence of a on the time between individual nanoflares (T{sub N} ) and the distribution of nanoflare energies. If T{sub N} is greater than a few thousand seconds, a < 3. For smaller values, trains of equally spaced nanoflares cannot account for the observed range of a if the distribution of nanoflare energies is either constant, randomly distributed, or a power law. Power law distributions where there is a delay between consecutive nanoflares proportional to the energy of the second nanoflare do lead to the observed range of a. However, T{sub N} must then be of the order of hundreds to no more than a few thousand seconds. If a nanoflare leads to the relaxation of a stressed coronal field to a near-potential state, the time taken to build up the required magnetic energy is thus too long to account for the EM measurements. Instead, it is suggested that a nanoflare involves the relaxation from one stressed coronal state to another, dissipating only a small fraction of the available magnetic energy. A consequence is that nanoflare energies may be smaller than previously envisioned.

  2. Plasma Composition in a Sigmoidal Anemone Active Region

    NASA Astrophysics Data System (ADS)

    Baker, D.; Brooks, D. H.; Démoulin, P.; van Driel-Gesztelyi, L.; Green, L. M.; Steed, K.; Carlyle, J.

    2013-11-01

    Using spectra obtained by the EUV Imaging Spectrometer (EIS) instrument onboard Hinode, we present a detailed spatially resolved abundance map of an active region (AR)-coronal hole (CH) complex that covers an area of 359'' × 485''. The abundance map provides first ionization potential (FIP) bias levels in various coronal structures within the large EIS field of view. Overall, FIP bias in the small, relatively young AR is 2-3. This modest FIP bias is a consequence of the age of the AR, its weak heating, and its partial reconnection with the surrounding CH. Plasma with a coronal composition is concentrated at AR loop footpoints, close to where fractionation is believed to take place in the chromosphere. In the AR, we found a moderate positive correlation of FIP bias with nonthermal velocity and magnetic flux density, both of which are also strongest at the AR loop footpoints. Pathways of slightly enhanced FIP bias are traced along some of the loops connecting opposite polarities within the AR. We interpret the traces of enhanced FIP bias along these loops to be the beginning of fractionated plasma mixing in the loops. Low FIP bias in a sigmoidal channel above the AR's main polarity inversion line, where ongoing flux cancellation is taking place, provides new evidence of a bald patch magnetic topology of a sigmoid/flux rope configuration.

  3. Plasma composition in a sigmoidal anemone active region

    SciTech Connect

    Baker, D.; Van Driel-Gesztelyi, L.; Green, L. M.; Carlyle, J.; Brooks, D. H.; Démoulin, P.; Steed, K.

    2013-11-20

    Using spectra obtained by the EUV Imaging Spectrometer (EIS) instrument onboard Hinode, we present a detailed spatially resolved abundance map of an active region (AR)-coronal hole (CH) complex that covers an area of 359'' × 485''. The abundance map provides first ionization potential (FIP) bias levels in various coronal structures within the large EIS field of view. Overall, FIP bias in the small, relatively young AR is 2-3. This modest FIP bias is a consequence of the age of the AR, its weak heating, and its partial reconnection with the surrounding CH. Plasma with a coronal composition is concentrated at AR loop footpoints, close to where fractionation is believed to take place in the chromosphere. In the AR, we found a moderate positive correlation of FIP bias with nonthermal velocity and magnetic flux density, both of which are also strongest at the AR loop footpoints. Pathways of slightly enhanced FIP bias are traced along some of the loops connecting opposite polarities within the AR. We interpret the traces of enhanced FIP bias along these loops to be the beginning of fractionated plasma mixing in the loops. Low FIP bias in a sigmoidal channel above the AR's main polarity inversion line, where ongoing flux cancellation is taking place, provides new evidence of a bald patch magnetic topology of a sigmoid/flux rope configuration.

  4. The response of the equatorial ionosphere to fast stream solar coronal holes during 2008 deep solar minimum over Indian region

    NASA Astrophysics Data System (ADS)

    Sripathi, S.; Singh, Ram; Banola, S.; Singh, Dupinder; Sathish, S.

    2016-01-01

    In this paper, we report ionospheric response to fast stream solar coronal holes during 2008 deep solar minimum year using ground-based multi-instruments over Indian region. To examine this, we analyzed foF2 (MHz) and hpF2(km) from Canadian Advanced Digital Ionosonde and total electron content (TEC) from GPS receiver over Tirunelveli (8.73°N, 77.70°E; dip 0.5°N) along with equatorial electrojet (EEJ) strength. Our analysis shows good correlation between solar wind and foF2/TEC, while hpF2 is poorly correlated. However, moderate correlation exists between solar wind and EEJ strength. When we performed periodogram analysis, we observed 9 and 13 day periods as dominant periods in foF2 and TEC. Interestingly, the occurrence pattern of plasma irregularities also resembles these periodic oscillations. Since it is believed that lower atmospheric waves are dominant forces for ionospheric variabilities during deep solar minimum, we examined the mesosphere/lower thermosphere region temperature using Thermosphere Ionosphere Mesosphere Energetics and Dynamics Sounding of the Atmosphere using Broadband Emission Radiometry and winds using medium frequency radar along with outgoing longwave radiation in the troposphere altitudes to rule out the sources for these periodic oscillations in the lower atmosphere. Using cross-wavelet and cross-coherence spectra of both solar wind and ionospheric/atmospheric parameters, we suggest that ionospheric periodicities are similar to that of solar wind. Based on these results, we suggest that while the periodic oscillations are associated with the disturbance dynamo winds/electric fields that are propagated to equatorial latitudes, the differences in their temporal/seasonal variations are attributed to the variations in the composition/recombination changes.

  5. 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.

  6. 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

  7. An Empirical Model of Coronal Heating Deduced from SOHO Observations of Transition Region Dynamics

    NASA Technical Reports Server (NTRS)

    Emslie, A. Gordon

    2002-01-01

    The research carried out under the above award was concerned with the analysis of "explosive events" in the solar atmosphere. Explosive events are small energy releases that reveal themselves as skewed, broadened line profiles in the 10(exp 5) K degree material of the solar transition region. Using a data set of such events from the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) instrument on the NASA SoHo satellite, with unprecedented temporal, spatial and spectral resolution, we have evaluated (Winebarger, Emslie, Mariska, & Warren 1999, Ap. J., 526, 471) the energetics of these events through application of the Velocity Differential Emission Measure (VDEM) analysis technique introduced by Newton, Emslie & Mariska, (1995, Ap. J, 447, 915). This work has allowed us to evaluate the contribution of various terms (such as enthalpy flux, free-streaming of high-energy electrons, etc.) to the energy budget of these events.

  8. Emission Measure Distribution and Heating of Two Active Region Cores

    NASA Technical Reports Server (NTRS)

    Tripathi, Durgesh; Klimchuk, James A.; Mason, Helen E.

    2011-01-01

    Using data from the Extreme-ultraviolet Imaging Spectrometer aboard Hinode, we have studied the coronal plasma in the core of two active regions. Concentrating on the area between opposite polarity moss, we found emission measure distributions having an approximate power-law form EM/T(exp 2.4) from log T = 5.55 up to a peak at log T = 6.57. The observations are explained extremely well by a simple nanoflare model. However, in the absence of additional constraints, the observations could possibly also be explained by steady heating.

  9. High-resolution laboratory measurements of coronal lines in the 198-218 å region

    SciTech Connect

    Beiersdorfer, Peter; Träbert, Elmar; Lepson, Jaan K.; Brickhouse, Nancy S.; Golub, Leon

    2014-06-10

    We present high-resolution laboratory measurements of the emission from various ions of C, N, O, F, Ne, S, Ar, Fe, and Ni in the extreme ultraviolet wavelength band centered around the λ211 Fe XIV channel of the Atmospheric Imaging Assembly on the Solar Dynamics Observatory. While all of the strong iron lines in this region are well known, we note many weaker lines of iron that are not yet identified. The high resolution of our measurements also allows us to resolve several lines in Fe XI, Fe XII, and Fe XIII between 200 and 205 Å, whose identities were in question based on a disagreement between different databases. The spectra of the elements other than iron are much less known, and we find a multitude of lines that are not yet in the databases. For example, the CHIANTI database clearly disagrees with the NIST data listings on several of the argon lines we observe and also it contains only about half of the observed sulfur lines.

  10. Determination of Differential Emission Measure Distribution of Coronal Structures Observed by SphinX During Recent Minimum of Solar Activity

    NASA Astrophysics Data System (ADS)

    Kepa, Anna; Gburek, Szymon; Siarkowski, Marek; Sylwester, Barbara; Sylwester, Janusz; Kowalinski, Miroslaw

    SphinX is a high-sensitivity soft X-ray spectrophotometer which measures soft X-ray spectra in the energy range between 0.8 keV and 15 keV. From February to November 2009 the instrument has observed unusually quiet solar coronal emission as well as a number of weak solar flares. Based on SphinX spectra it is possible to study the differential emission measure distributions (DEM) in the temperature range roughly between 1 MK and 10 MK. The aim of the present study is to unveil DEM plasma distributions for selected activity conditions and analyze their variability.

  11. Instant Stereoscopic Tomography of Active Regions with STEREO/EUVI

    NASA Astrophysics Data System (ADS)

    Aschwanden, M. J.; Wuelser, J.; Nitta, N.; Lemen, J.; Sandman, A.

    2008-12-01

    We develop a novel 3D reconstruction method of the coronal plasma of an active region by combining stereoscopic triangulation of loops with density and temperature modeling of coronal loops with a filling factor equivalent to tomographic volume rendering. Because this method requires only a stereoscopic image pair in multiple temperature filters, which are sampled within ~1 minute with the recent STEREO/EUVI instrument, this method is about 4 orders of magnitude faster than conventional solar rotation-based tomography. We reconstruct the 3D density and temperature distribution of active region NOAA 10955 by stereoscopic triangulation of 70 loops, which are used as a skeleton for a 3D field interpolation of some 7000 loop components, leading to a 3D model that reproduces the observed fluxes in each stereosocpic image pair with an accuracy of a few percent (of the average flux) in each pixel. With the stereoscopic tomography we infer also a differential emission measure (DEM) distribution over the entire temperature range of T~0.01-10 MK, with predictions for the transition region and hotter corona in soft X-rays. The tomographic 3D model provides also large statistics of physical parameters. We find that the EUV loops with apex temperatures of T = 1- 3 MK tend to be super-hydrostatic, while hotter loops with T = 4-7 MK are near-hydrostatic. The new 3D reconstruction model is fully independent of any magnetic field data and is promising for future tests of theoretical magnetic field models and coronal heating models.

  12. Regional Activities Division. Papers.

    ERIC Educational Resources Information Center

    International Federation of Library Associations, The Hague (Netherlands).

    Papers on library network activities in Canada, the Third World, Japan, Malaysia, Brazil, and Sweden which were presented at the 1982 International Federation of Library Associations (IFLA) conference include: (1) "Canada: A Voluntary and Flexible Network," a review by Guy Sylvestre of the political, social, and economic structures affecting…

  13. Commission 10: Solar Activity

    NASA Astrophysics Data System (ADS)

    Klimchuk, James A.; van Driel-Gesztelyi, Lidia; Schrijver, Carolus J.; Melrose, Donald B.; Fletcher, Lyndsay; Gopalswamy, Natchimuthuk; Harrison, Richard A.; Mandrini, Cristina H.; Peter, Hardi; Tsuneta, Saku; Vršnak, Bojan; Wang, Jing-Xiu

    Commission 10 deals with solar activity in all of its forms, ranging from the smallest nanoflares to the largest coronal mass ejections. This report reviews scientific progress over the roughly two-year period ending in the middle of 2008. This has been an exciting time in solar physics, highlighted by the launches of the Hinode and STEREO missions late in 2006. The report is reasonably comprehensive, though it is far from exhaustive. Limited space prevents the inclusion of many significant results. The report is divided into the following sections: Photosphere and chromosphere; Transition region; Corona and coronal heating; Coronal jets; flares; Coronal mass ejection initiation; Global coronal waves and shocks; Coronal dimming; The link between low coronal CME signatures and magnetic clouds; Coronal mass ejections in the heliosphere; and Coronal mass ejections and space weather. Primary authorship is indicated at the beginning of each section.

  14. Evolution of two Flaring Active Regions With CME Association

    NASA Astrophysics Data System (ADS)

    Thalmann, J. K.; Wiegelmann, T.

    2008-12-01

    We study the coronal magnetic field structure of two active regions, one during solar activity minimum (June 2007) and another one during a more active time (January 2004). The temporal evolution was explored with the help of nonlinear force-free coronal magnetic field extrapolations of SOLIS/VSM and NAOJ/SFT photospheric vector magnetograms. We study the active region NOAA 10960 observed on 2007 June 7 with three SOLIS/VSM snapshots taken during a small C1.0 flare of time cadence 10 minutes and six snapshots during a quiet period. The total magnetic energy in the active region was approximately 3 × 1025 J. Before the flare the free magnetic energy was about 5~% of the potential field energy. A part of this excess energy was released during the flare, producing almost a potential configuration at the beginning of the quiet period. The return to an almost potential structure can be assigned to a CME as recorded by the SoHO/LASCO instrument on 2007 June 07 around 10 minutes after the flare peaked, so that whatever magnetic helicity was bodily removed from the structure. This was compared with active region 10540 observed on 2004 January 18 -- 21, which was analyzed with the help of vector magnetograph data from the Solar Flare Telescope in Japan of time cadence of about 1 day. The free energy was Efree≈ 66~% of the total energy which was sufficiently high to power a M6.1 flare on January 20, which was associated with a CME 20 minutes later. The activity of AR 10540 was significantly higher than for AR 10960, as was the total magnetic energy. Furthermore, we found the common feature that magnetic energy accumulates before the flare/CME and a significant part of the excess energy is released during the eruption.

  15. Doppler Shifts in Active Region Moss Using SOHO/SUMER

    NASA Astrophysics Data System (ADS)

    Winebarger, Amy; Tripathi, Durgesh; Mason, Helen E.; Del Zanna, Giulio

    2013-04-01

    The velocity of the plasma at the footpoint of hot loops in active region cores can be used to discriminate between different heating frequencies. Velocities on the order of a few kilometers per second would indicate low-frequency heating on sub-resolution strands, while velocities close to zero would indicate high-frequency (steady) heating. To discriminate between these two values requires accurate velocity measurements; previous velocity measurements suffer from large uncertainties, mainly due to the lack of an absolute wavelength reference scale. In this paper, we determine the velocity in the loop footpoints using observations from Solar Ultraviolet Measurements of Emitted Radiation (SUMER) on Solar and Heliospheric Observatory. We use neutral spectral lines to determine the wavelength scale of the observations with an uncertainty in the absolute velocity of <3.5 km s-1 and co-aligned Transition Region and Coronal Explorer (TRACE) images to identify footpoint regions. We studied three different active regions and found average redshifts in the Ne VIII 770 Å emission line (formed at 6 × 105 K) of 5.17 ± 5.37 km s-1 and average redshifts in the C IV 1548 and 1550 Å emission lines (formed at 1 × 105 K) of 13.94 ± 4.93 km s-1 and 14.91 ± 6.09 km s-1, respectively. We find no correlation between the brightness in the spectral line and the measured velocity, nor do we find correlation between the Ne VIII and C IV velocities measured co-spatially and co-temporally. SUMER scanned two of the active regions twice; in those active regions we find positive correlation between the co-spatial velocities measured during the first and second scans. These results provide definitive and quantitative measurements for comparisons with simulations of different coronal heating mechanisms.

  16. MAGNETIC FIELD TOPOLOGY AND THE THERMAL STRUCTURE OF THE CORONA OVER SOLAR ACTIVE REGIONS

    SciTech Connect

    Schrijver, Carolus J.; DeRosa, Marc L.; Title, Alan M.

    2010-08-20

    Solar extreme ultraviolet (EUV) images of quiescent active-region coronae are characterized by ensembles of bright 1-2 MK loops that fan out from select locations. We investigate the conditions associated with the formation of these persistent, relatively cool, loop fans within and surrounding the otherwise 3-5 MK coronal environment by combining EUV observations of active regions made with TRACE with global source-surface potential-field models based on the full-sphere photospheric field from the assimilation of magnetograms that are obtained by the Michelson Doppler Imager (MDI) on SOHO. We find that in the selected active regions with largely potential-field configurations these fans are associated with (quasi-)separatrix layers (QSLs) within the strong-field regions of magnetic plage. Based on the empirical evidence, we argue that persistent active-region cool-loop fans are primarily related to the pronounced change in connectivity across a QSL to widely separated clusters of magnetic flux, and confirm earlier work that suggested that neither a change in loop length nor in base field strengths across such topological features are of prime importance to the formation of the cool-loop fans. We discuss the hypothesis that a change in the distribution of coronal heating with height may be involved in the phenomenon of relatively cool coronal loop fans in quiescent active regions.

  17. Solar Sources of Coronal Mass Ejections

    NASA Astrophysics Data System (ADS)

    Li, Y.

    2014-12-01

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

  18. 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.

  19. 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.

  20. THE COLD SHOULDER: EMISSION MEASURE DISTRIBUTIONS OF ACTIVE REGION CORES

    SciTech Connect

    Schmelz, J. T.; Pathak, S.

    2012-09-10

    The coronal heating mechanism for active region core loops is difficult to determine because these loops are often not resolved and cannot be studied individually. Rather, we concentrate on the 'inter-moss' areas between loop footpoints. We use observations from the Hinode EUV Imaging Spectrometer and the X-Ray Telescope to calculate the emission measure distributions of eight inter-moss areas in five different active regions. The combined data sets provide both high- and low-temperature constraints and ensure complete coverage in the temperature range appropriate for active regions. For AR 11113, the emission can be modeled with heating events that occur on timescales less than the cooling time. The loops in the core regions appear to be close to equilibrium and are consistent with steady heating. The other regions studied, however, appear to be dominated by nanoflare heating. Our results are consistent with the idea that active region age is an important parameter in determining whether steady or nanoflare heating is primarily responsible for the core emission, that is, older regions are more likely to be dominated by steady heating, while younger regions show more evidence of nanoflares.

  1. Three-dimensional MHD modeling of vertical kink oscillations in an active region plasma curtain

    NASA Astrophysics Data System (ADS)

    Ofman, L.; Parisi, M.; Srivastava, A. K.

    2015-10-01

    Context. Observations on 2011 August 9 of an X 6.9-class flare in active region (AR) 11263 by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO), were followed by a rare detection of vertical kink oscillations in a large-scale coronal active region plasma curtain in extreme UV coronal lines with periods in the range 8.8-14.9 min. Aims: Our aim is to study the generation and propagation of the magnetohydrodynamic (MHD) oscillations in the plasma curtain taking the realistic 3D magnetic and the density structure of the curtain into account. We also aim to test and improve coronal seismology for a more accurate determination of the magnetic field than with the standard method. Methods: We use the observed morphological and dynamical conditions, as well as plasma properties of the coronal curtain, to initialize a 3D MHD model of the observed vertical and transverse oscillations. To accomplish this, we implemented the impulsively excited velocity pulse mimicking the flare-generated nonlinear fast magnetosonic propagating disturbance interacting obliquely with the curtain. The model is simplified by utilizing an initial dipole magnetic field, isothermal energy equation, and gravitationally stratified density guided by observational parameters. Results: Using the 3D MHD model, we are able to reproduce the details of the vertical oscillations and study the process of their excitation by a nonlinear fast magnetosonic pulse, propagation, and damping, finding agreement with the observations. Conclusions: We estimate the accuracy of simplified slab-based coronal seismology by comparing the determined magnetic field strength to actual values from the 3D MHD modeling results, and demonstrate the importance of taking more realistic magnetic geometry and density for improving coronal seismology into account. A movie associated to Fig. 1 is available in electronic form at http://www.aanda.org

  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.

    1997-01-01

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

  3. Long-term variations of the coronal rotation and solar activity

    NASA Astrophysics Data System (ADS)

    Li, K. J.; Shi, X. J.; Feng, W.; Xie, J. L.; Gao, P. X.; Zhan, L. S.; Liang, H. F.

    2012-07-01

    Recently, Chandra and Vats have obtained the yearly period length of the solar coronal rotation cycle by analysing the daily adjusted solar radio flux at the 10.7-cm wavelength for the years 1947-2009. In this paper, we use the time series (series I) of the yearly period length to investigate the long-term variation of the rotation of radio emission corona, and we find a weak decreasing trend in the time series. We use the empirical mode decomposition to decompose both the yearly mean value (series II) of the solar radio flux at the 10.7-cm wavelength and series I into different periodical components. There is a secular trend for each of the two series, and we find a negative correlation in the two trends. The decomposed 11-yr-cycle components of the two series show different and complicated periods and there is a phase relation between them. We investigate the cycle-related variation of the coronal rotation length, and we find that there is no Schwable cycle of statistical significance for the long-term variation of the rotation cycle length.

  4. 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.

  5. Plasma outflows at the border of active regions and the solar wind

    NASA Astrophysics Data System (ADS)

    Nuevo, F. A.; Mandrini, C. H.; Vásquez, A. M.; Deumoulin, P.; Van Driel-Gesztely, L.; Baker, D.; Cristiani, G. D.; Pick, M.; Culhane, J. L.

    We present a detailed topological analysis of active region (AR) 10978; based on a Potential Field Source Surface (PFSS) model. AR 10978 is a standard bipolar region which appears fully covered by the magnetic field lines of a coronal streamer. Despite this simple magnetic configuration; our analysis shows that it is possible for the AR plasma; contained in the outflows observed at the AR borders; to be released into the solar wind via magnetic reconnection.

  6. THE 'MAIN SEQUENCE' OF EXPLOSIVE SOLAR ACTIVE REGIONS: DISCOVERY AND INTERPRETATION

    SciTech Connect

    Falconer, David A.; Moore, Ronald L.; Adams, Mitzi; Gary, G. Allen

    2009-08-01

    We examine the location and distribution of the production of coronal mass ejections (CMEs) and major flares by sunspot active regions in the phase space of two whole-active-region magnetic quantities measured from 1897 SOHO/MDI magnetograms. These magnetograms track the evolution of 44 active regions across the central disk of radius 0.5 R {sub Sun}. The two quantities are {sup L}WL{sub SG}, a gauge of the total free energy in an active region's magnetic field, and {sup L}{phi}, a measure of the active region's total magnetic flux. From these data and each active region's history of production of CMEs, X flares, and M flares, we find (1) that CME/flare-productive active regions are concentrated in a straight-line 'main sequence' in (log {sup L}WL{sub SG}, log {sup L}{phi}) space, (2) that main-sequence active regions have nearly their maximum attainable free magnetic energy, and (3) evidence that this arrangement plausibly results from equilibrium between input of free energy to an explosive active region's magnetic field in the chromosphere and corona by contortion of the field via convection in and below the photosphere and loss of free energy via CMEs, flares, and coronal heating, an equilibrium between energy gain and loss that is analogous to that of the main sequence of hydrogen-burning stars in (mass, luminosity) space.

  7. Fine structure of the magnetic field in active regions

    NASA Astrophysics Data System (ADS)

    Pustilnik, Lev; Beskrovnaya, Nina; Ikhsanov, Nazar

    High-resolution observations with SOHO, SDO, TRACE, HINODE suggest that the solar magnetic field in active regions has a complicated fine structure. There is a large number of thin magnetic arcs extended from the photosphere to corona with almost constant cross-section. We explore a possibility to model the complex of interacting arcs in terms of a dynamical percolating network. A transition of the system into flaring can be triggered by the flute instability of prominences and/or coronal condensations. We speculate around an assumption that the energy release in active regions is governed by the same scenario as dynamical current percolation through a random resistors network in which the saltatory conduction is controlled by a local current level.

  8. Differential Magnetic Field Shear in an Active Region

    NASA Technical Reports Server (NTRS)

    Schmeider, B.; DeMoulin, P.; Aulanier, G.; Golub, Leon

    1997-01-01

    The three-dimensional extrapolation of magnetic field lines from a magnetogram obtained at Kitt Peak allows us to understand the global structure of the NOAA active region 6718, as observed in X-rays with the Normal Incidence X-ray Telescope (NIXT) and in Ha with the Multichannel Subtractive Double Pass spectrograph (MSDP) in Meudon on 1991 July 11. This active region was in a quiet stage. Bright X-ray loops connect plages having field strengths of approx. 300 G, while H-alpha fibriles connect penumbrae having strong spot fields to the surrounding network. Small, intense X-ray features in the moat region around a large spot, which could be called X-ray-bright points, are due mainly to the emergence of magnetic flux and merging of these fields with surrounding ones. A set of large-scale, sheared X-ray loops is observed in the central part of the active region. Based on the fit between the observed coronal structure and the field configurations (and assuming a linear force-free field), we propose a differential magnetic field shear model for this active region. The decreasing shear in outer portions of the active region may indicate a continual relaxation of the magnetic field to a lower energy state in the progressively older portions of the AR.

  9. A study of the physical mechanisms for filament eruption and coronal mass ejection via numerical simulation

    NASA Technical Reports Server (NTRS)

    Wu, S. T.

    1992-01-01

    During this period of performance (1 Jan. 1992 - 31 Dec. 1992), the investigation of the following tasks was accomplished: (1) application of the Non-linear Force-free Field (NLFF) Model to study the active region evolution; (2) coronal dynamical responses due to emerging flux including the transition region; (3) loss of MHD equilibrium due to footpoint motions; and (4) two-dimensional MHD global coronal model: steady-state streamers. The detailed description of these studies are included.

  10. On the coronae of rapidly rotating stars. I - The relation between rotation and coronal activity in RS CVn systems

    NASA Technical Reports Server (NTRS)

    Walter, F. M.; Bowyer, S.

    1981-01-01

    Soft X-ray observations are presented of a nearly complete sample of RS Canum Venaticorum systems taken with the Einstein X-ray Observatory. It is shown that the quiescent coronal activity, as measured by the ratio of the X-ray to bolometric flux, is directly proportional to the angular velocity of the star with the active chromosphere in these systems. This relation is found to hold over two decades in angular velocity. It is also found that the stellar surface gravity has no obvious influence on the ratio of the X-ray luminosity to the bolometric luminosity over two decades in surface gravity. It is pointed out that the linear relation between the ratio of the X-ray luminosity to the bolometric luminosity on the one hand, and the angular velocity, on the other, holds important implications for dynamo theories of the generation of stellar magnetic fields.

  11. 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

  12. FIP Bias Evolution in a Decaying Active Region

    NASA Astrophysics Data System (ADS)

    Baker, D.; Brooks, D. H.; Démoulin, P.; Yardley, S. L.; van Driel-Gesztelyi, L.; Long, D. M.; Green, L. M.

    2015-04-01

    Solar coronal plasma composition is typically characterized by first ionization potential (FIP) bias. Using spectra obtained by Hinode’s EUV Imaging Spectrometer instrument, we present a series of large-scale, spatially resolved composition maps of active region (AR)11389. The composition maps show how FIP bias evolves within the decaying AR during the period 2012 January 4-6. Globally, FIP bias decreases throughout the AR. We analyzed areas of significant plasma composition changes within the decaying AR and found that small-scale evolution in the photospheric magnetic field is closely linked to the FIP bias evolution observed in the corona. During the AR’s decay phase, small bipoles emerging within supergranular cells reconnect with the pre-existing AR field, creating a pathway along which photospheric and coronal plasmas can mix. The mixing timescales are shorter than those of plasma enrichment processes. Eruptive activity also results in shifting the FIP bias closer to photospheric in the affected areas. Finally, the FIP bias still remains dominantly coronal only in a part of the AR’s high-flux density core. We conclude that in the decay phase of an AR’s lifetime, the FIP bias is becoming increasingly modulated by episodes of small-scale flux emergence, i.e., decreasing the AR’s overall FIP bias. Our results show that magnetic field evolution plays an important role in compositional changes during AR development, revealing a more complex relationship than expected from previous well-known Skylab results showing that FIP bias increases almost linearly with age in young ARs.

  13. Relating magnetic reconnection to coronal heating.

    PubMed

    Longcope, D W; Tarr, L A

    2015-05-28

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

  14. 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.

  15. CAN THERMAL NONEQUILIBRIUM EXPLAIN CORONAL LOOPS?

    SciTech Connect

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

    2010-05-10

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

  16. 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.

  17. Simultaneous Solar Maximum Mission (SMM) and Very Large Array (VLA) observations of solar active regions

    NASA Technical Reports Server (NTRS)

    Willson, Robert F.

    1991-01-01

    Very Large Array observations at 20 cm wavelength can detect the hot coronal plasma previously observed at soft x ray wavelengths. Thermal cyclotron line emission was detected at the apex of coronal loops where the magnetic field strength is relatively constant. Detailed comparison of simultaneous Solar Maximum Mission (SMM) Satellite and VLA data indicate that physical parameters such as electron temperature, electron density, and magnetic field strength can be obtained, but that some coronal loops remain invisible in either spectral domain. The unprecedent spatial resolution of the VLA at 20 cm wavelength showed that the precursor, impulsive, and post-flare components of solar bursts originate in nearby, but separate loops or systems of loops.. In some cases preburst heating and magnetic changes are observed from loops tens of minutes prior to the impulsive phase. Comparisons with soft x ray images and spectra and with hard x ray data specify the magnetic field strength and emission mechanism of flaring coronal loops. At the longer 91 cm wavelength, the VLA detected extensive emission interpreted as a hot 10(exp 5) K interface between cool, dense H alpha filaments and the surrounding hotter, rarefield corona. Observations at 91 cm also provide evidence for time-correlated bursts in active regions on opposite sides of the solar equator; they are attributed to flare triggering by relativistic particles that move along large-scale, otherwise-invisible, magnetic conduits that link active regions in opposite hemispheres of the Sun.

  18. Slow Magnetosonic Waves and Fast Flows in Active Region Loops

    NASA Technical Reports Server (NTRS)

    Ofman, L.; Wang, T. J.; Davila, J. M.

    2012-01-01

    Recent extreme ultraviolet spectroscopic observations indicate that slow magnetosonic waves are present in active region (AR) loops. Some of the spectral data were also interpreted as evidence of fast (approx 100-300 km/s) quasiperiodic flows. We have performed three-dimensional magnetohydrodynamic (3D MHD) modeling of a bipolar AR that contains impulsively generated waves and flows in coronal loops. The model AR is initiated with a dipole magnetic field and gravitationally stratified density, with an upflow-driven steadily or periodically in localized regions at the footpoints of magnetic loops. The resulting flows along the magnetic field lines of the AR produce higher density loops compared to the surrounding plasma by injection of material into the flux tubes and the establishment of siphon flow.We find that the impulsive onset of flows with subsonic speeds result in the excitation of damped slow magnetosonic waves that propagate along the loops and coupled nonlinearly driven fast-mode waves. The phase speed of the slow magnetosonic waves is close to the coronal sound speed. When the amplitude of the driving pulses is increased we find that slow shock-like wave trains are produced. When the upflows are driven periodically, undamped oscillations are produced with periods determined by the periodicity of the upflows. Based on the results of the 3D MHD model we suggest that the observed slow magnetosonic waves and persistent upflows may be produced by the same impulsive events at the bases of ARs.

  19. SLOW MAGNETOSONIC WAVES AND FAST FLOWS IN ACTIVE REGION LOOPS

    SciTech Connect

    Ofman, L.; Wang, T. J.; Davila, J. M.

    2012-08-01

    Recent extreme ultraviolet spectroscopic observations indicate that slow magnetosonic waves are present in active region (AR) loops. Some of the spectral data were also interpreted as evidence of fast ({approx}100-300 km s{sup -1}) quasi-periodic flows. We have performed three-dimensional magnetohydrodynamic (3D MHD) modeling of a bipolar AR that contains impulsively generated waves and flows in coronal loops. The model AR is initiated with a dipole magnetic field and gravitationally stratified density, with an upflow-driven steadily or periodically in localized regions at the footpoints of magnetic loops. The resulting flows along the magnetic field lines of the AR produce higher density loops compared to the surrounding plasma by injection of material into the flux tubes and the establishment of siphon flow. We find that the impulsive onset of flows with subsonic speeds result in the excitation of damped slow magnetosonic waves that propagate along the loops and coupled nonlinearly driven fast-mode waves. The phase speed of the slow magnetosonic waves is close to the coronal sound speed. When the amplitude of the driving pulses is increased we find that slow shock-like wave trains are produced. When the upflows are driven periodically, undamped oscillations are produced with periods determined by the periodicity of the upflows. Based on the results of the 3D MHD model we suggest that the observed slow magnetosonic waves and persistent upflows may be produced by the same impulsive events at the bases of ARs.

  20. Correlation of the CME Productivity of Solar Active Regions with Measures of their Global Nonpotentiality from Vector Magnetograms: Baseline Results

    NASA Technical Reports Server (NTRS)

    Falconer, David A.; Moore, Ron L.; Gary, G. Allen; Six, N. Frank (Technical Monitor)

    2001-01-01

    From conventional magnetograms and chromospheric and coronal images, it is known qualitatively that the fastest coronal mass ejections (CMEs) are magnetic explosions from sunspot active regions in which the magnetic field is globally strongly sheared and twisted from its minimum-energy potential configuration. In this paper, we present measurements from active-region vector magnetograms that begin to quantify the dependence of the CME productivity of an active region on the global nonpotentiality of its magnetic field. From each of 17 magnetograms of 12 bipolar active regions, we obtain a measure of the size of the active region (the magnetic flux content, phi) and three different measures of the global nonpotentiality (L(sub SS), the length of strong-shear, strong-field main neutral line; I(sub N), the net electric current arching from one polarity to the other; and alpha = muI(subN/phi), a flux-normalized measure of the field twist).

  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. EVIDENCE OF IMPULSIVE HEATING IN ACTIVE REGION CORE LOOPS

    SciTech Connect

    Tripathi, Durgesh; Mason, Helen E.; Klimchuk, James A.

    2010-11-01

    Using a full spectral scan of an active region from the Extreme-Ultraviolet Imaging Spectrometer (EIS) we have obtained emission measure EM(T) distributions in two different moss regions within the same active region. We have compared these with theoretical transition region EMs derived for three limiting cases, namely, static equilibrium, strong condensation, and strong evaporation from Klimchuk et al. The EM distributions in both the moss regions are strikingly similar and show a monotonically increasing trend from log T[K] = 5.15-6.3. Using photospheric abundances, we obtain a consistent EM distribution for all ions. Comparing the observed and theoretical EM distributions, we find that the observed EM distribution is best explained by the strong condensation case (EM{sub con}), suggesting that a downward enthalpy flux plays an important and possibly dominant role in powering the transition region moss emission. The downflows could be due to unresolved coronal plasma that is cooling and draining after having been impulsively heated. This supports the idea that the hot loops (with temperatures of 3-5 MK) seen in the core of active regions are heated by nanoflares.

  3. 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

  4. 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.

  5. Ultraviolet observations of the structure and dynamics of an active region at the limb

    NASA Technical Reports Server (NTRS)

    Korendyke, C. M.; Dere, K. P.; Socker, D. G.; Brueckner, G. E.; Schmieder, B.

    1995-01-01

    The structure and dynamics of active region NOAA 7260 at the limb have been studied using ultraviolet spectra and spectroheliograms obtained during the eighth rocket flight of the Naval Research Laboratory's High Resolution Telescope an Spectrograph (HRTS). The instrument configuration included a narrow-bandpass spectroheliograph to observe the Sun in the lines of C IV lambda 550 and a tandem-Wadsworth mount spectrograph to record the profiles of chromospheric transition region and coronal lines in the 1850-2670 A region. The combination of high spatial resolution and high spectral purity C IV slit jaw images with ultraviolet emission-line spectra corresponding allows examination of a variety of active region phenomena. A time series of spectroheliograms shows large-scale loop systems composed of fine-scale threads with some extending up to 100 Mm above the limb. The proper motion of several supersonic features, including a surge were measured. The accelerated plasmas appear in several different geometries and environments. Spectrograph exposures were taken with the slit positioned at a range of altitudes above the limb and provide a direct comparison between coronal, transition region and chromospheric emission line profiles. The spectral profiles of chromospheric and transition region emission lines show line-of-sight velocities up to 70 km/s. These lower temperature, emission-line spectra show small-scale spatial and velocity variations which are correlated with the threadlike structures seen in C IV. Coronal lines of Fe XII show much lower velocities and no fine structure.

  6. Multithermal emission in active regions

    NASA Astrophysics Data System (ADS)

    Del Zanna, Giulio

    High-resolution EUV observations from SDO/AIA, Hi-C and Hinode/EIS are used, together with updated new atomic data, to study the multi-thermal emission in active region structures. Previous observations are largely confirmed, with most structures being not co-spatial and having nearly isothermal cross-sections. Those at temperatures below 1 MK appear as nearly resolved but those at 1-3 MK are still largely unresolved even at the Hi-C resolution. Very little emission above 3 MK is present in quiescent active regions. Elemental abundances vary in different structures. The active region cores show FIP enhancements of about a factor of three. X-ray spectroscopy confirms the results of the EUV observations for the hot cores.

  7. How Much Energy Can Be Stored in Solar Active Region Magnetic Fields?

    NASA Astrophysics Data System (ADS)

    Linker, J.; Downs, C.; Torok, T.; Titov, V. S.; Lionello, R.; Mikic, Z.; Riley, P.

    2015-12-01

    Major solar eruptions such as X-class flares and very fast coronal mass ejections usually originate in active regions on the Sun. The energy that powers these events is believed to be stored as free magnetic energy (energy above the potential field state) prior to eruption. While coronal magnetic fields are not in general force-free, active regions have very strong magnetic fields and at low coronal heights the plasma beta is therefore very small, making the field (in equilibrium) essentially force-free. The Aly-Sturrock theorem shows that the energy of a fully force-free field cannot exceed the energy of the so-called open field. If the theorem holds, this places an upper limit on the amount of free energy that can be stored: the maximum free energy (MFE) is the difference between the open field energy and the potential field energy of the active region. In thermodynamic MHD simulations of a major eruption (the July 14, 2000 'Bastille' day event) and a modest event (February 13, 2009, we have found that the MFE indeed bounds the energy stored prior to eruption. We compute the MFE for major eruptive events in cycles 23 and 24 to investigate the maximum amount of energy that can be stored in solar active regions.Research supported by AFOSR, NASA, and NSF.

  8. Recurrent flares in active region NOAA 11283

    NASA Astrophysics Data System (ADS)

    Romano, P.; Zuccarello, F.; Guglielmino, S. L.; Berrilli, F.; Bruno, R.; Carbone, V.; Consolini, G.; de Lauretis, M.; Del Moro, D.; Elmhamdi, A.; Ermolli, I.; Fineschi, S.; Francia, P.; Kordi, A. S.; Landi Degl'Innocenti, E.; Laurenza, M.; Lepreti, F.; Marcucci, M. F.; Pallocchia, G.; Pietropaolo, E.; Romoli, M.; Vecchio, A.; Vellante, M.; Villante, U.

    2015-10-01

    Context. Flares and coronal mass ejections (CMEs) are solar phenomena that are not yet fully understood. Several investigations have been performed to single out their related physical parameters that can be used as indices of the magnetic complexity leading to their occurrence. Aims: In order to shed light on the occurrence of recurrent flares and subsequent associated CMEs, we studied the active region NOAA 11283 where recurrent M and X GOES-class flares and CMEs occurred. Methods: We use vector magnetograms taken by HMI/SDO to calculate the horizontal velocity fields of the photospheric magnetic structures, the shear and the dip angles of the magnetic field, the magnetic helicity flux distribution, and the Poynting fluxes across the photosphere due to the emergence and the shearing of the magnetic field. Results: Although we do not observe consistent emerging magnetic flux through the photosphere during the observation time interval, we detected a monotonic increase of the magnetic helicity accumulated in the corona. We found that both the shear and the dip angles have high values along the main polarity inversion line (PIL) before and after all the events. We also note that before the main flare of X2.1 GOES class, the shearing motions seem to inject a more significant energy than the energy injected by the emergence of the magnetic field. Conclusions: We conclude that the very long duration (about 4 days) of the horizontal displacement of the main photospheric magnetic structures along the PIL has a primary role in the energy release during the recurrent flares. This peculiar horizontal velocity field also contributes to the monotonic injection of magnetic helicity into the corona. This process, coupled with the high shear and dip angles along the main PIL, appears to be responsible for the consecutive events of loss of equilibrium leading to the recurrent flares and CMEs. A movie associated to Fig. 4 is available in electronic form at http://www.aanda.org

  9. Comparison of Solar Active Region Complexity Andgeomagnetic Activity from 1996 TO 2014

    NASA Astrophysics Data System (ADS)

    Tanskanen, E. I.; Nikbakhsh, S.; Perez-Suarez, D.; Hackman, T.

    2015-12-01

    We have studied the influence of magnetic complexity of solar Active Regions (ARs)on geomagnetic activity from 1996 to 2014. Sunspots are visual indicators of ARswhere the solar magnetic field is disturbed. We have used International, American,Space Environment Service Center (SESC) and Space Weather Prediction Center(SWPC) sunspot numbers to examine ARs. Major manifestations of solar magneticactivity, such as flares and Coronal Mass Ejections (CMEs), are associated withARs. For this study we chose the Mount Wilson scheme. It classifies ARs in terms oftheir magnetic topology from the least complex (?) to the most complex one ( ?).Several cases have been found where the more complex structures produce strongerflares and CMEs than the less complex ones. We have a list of identified substormsavailable with different phases and their durations. This will be compared to ourmagnetic complexity data to analyse the effects of active region magnetic complexityto the magnetic activity on the vicinity of the Earth.

  10. Active Region Moss: Doppler Shifts from Hinode/EIS Observations

    NASA Technical Reports Server (NTRS)

    Tripathi, Durgesh; Mason, Helen E.; Klimchuk, James A.

    2012-01-01

    Studying the Doppler shifts and the temperature dependence of Doppler shifts in moss regions can help us understand the heating processes in the core of the active regions. In this paper we have used an active region observation recorded by the Extreme-ultraviolet Imaging Spectrometer (EIS) onboard Hinode on 12-Dec- 2007 to measure the Doppler shifts in the moss regions. We have distinguished the moss regions from the rest of the active region by defining a low density cut-off as derived by Tripathi et al. (2010). We have carried out a very careful analysis of the EIS wavelength calibration based on the method described in Young, O Dwyer and Mason (2012). For spectral lines having maximum sensitivity between log T = 5.85 and log T = 6.25 K, we find that the velocity distribution peaks at around 0 km/s with an estimated error of 4 km/s. The width of the distribution decreases with temperature. The mean of the distribution shows a blue shift which increases with increasing temperature and the distribution also shows asymmetries towards blue-shift. Comparing these results with observables predicted from different coronal heating models, we find that these results are consistent with both steady and impulsive heating scenarios. Further observational constraints are needed to distinguish between these two heating scenarios.

  11. 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.

  12. Radiative and magnetic properties of solar active regions. I. Global magnetic field and EUV line intensities

    NASA Astrophysics Data System (ADS)

    Fludra, A.; Ireland, J.

    2008-05-01

    Context: The relationships between the photospheric magnetic flux and either the X-ray or extreme ultraviolet emission from the solar atmosphere have been studied by several authors. Power-law relations have been found between the total magnetic flux and X-ray flux or intensities of the chromospheric, transition region, and coronal emission lines in solar active regions. These relations were then used to infer the mechanism of the coronal heating. Aims: We derive accurate power laws between EUV line intensities and the total magnetic flux in solar active regions and discuss their applications. We examine whether these global power laws are capable of providing the diagnostics of the coronal heating mechanism. Methods: This analysis is based on EUV lines recorded by the Coronal Diagnostic Spectrometer (CDS) on SOHO for 48 solar active regions, as they crossed the central meridian in years 1996-1998. Four spectral lines are used: He I 584.3 Å (3×104 K), O V 629.7 Å (2.2×105 K), Mg IX 368.06 Å (9.5×105 K), and Fe XVI 360.76 Å (2.0×106 K). In particular, the Fe XVI 360.76 Å line, seen only in areas of enhanced heating in active regions or bright points, has not been used before for this analysis. Results: Empirical power laws are established between the total active region intensity in the lines listed above and the total magnetic flux. We demonstrate the usefulness of some spatially integrated EUV line intensities, I_T, as a proxy for the total magnetic flux, Φ, in active regions. We point out the approximate, empirical nature of the I_T-Φ relationships and discuss the interpretation of the global power index. Different power index values for transition region and coronal lines are explained by their different dependence on pressure under the assumption of hydrostatic loop models. However, the global power laws are dominated by the size of the active regions, and we demonstrate for the first time the difficulties in uniquely relating the power index in the

  13. MODELING SUPER-FAST MAGNETOSONIC WAVES OBSERVED BY SDO IN ACTIVE REGION FUNNELS

    SciTech Connect

    Ofman, L.; Liu, W.; Title, A.; Aschwanden, M.

    2011-10-20

    Recently, quasi-periodic, rapidly propagating waves have been observed in extreme ultraviolet by the Solar Dynamics Observatory/Atmospheric Imaging Assembly (AIA) instrument in about 10 flare/coronal mass ejection (CME) events thus far. A typical example is the 2010 August 1 C3.2 flare/CME event that exhibited arc-shaped wave trains propagating in an active region (AR) magnetic funnel with {approx}5% intensity variations at speeds in the range of 1000-2000 km s{sup -1}. The fast temporal cadence and high sensitivity of AIA enabled the detection of these waves. We identify them as fast magnetosonic waves driven quasi-periodically at the base of the flaring region and develop a three-dimensional MHD model of the event. For the initial state we utilize the dipole magnetic field to model the AR and include gravitationally stratified density at coronal temperature. At the coronal base of the AR, we excite the fast magnetosonic wave by periodic velocity pulsations in the photospheric plane confined to a funnel of magnetic field lines. The excited fast magnetosonic waves have similar amplitude, wavelength, and propagation speeds as the observed wave trains. Based on the simulation results, we discuss the possible excitation mechanism of the waves, their dynamical properties, and the use of the observations for coronal MHD seismology.

  14. THE EXPANSION OF ACTIVE REGIONS INTO THE EXTENDED SOLAR CORONA

    SciTech Connect

    Morgan, Huw; Jeska, Lauren; Leonard, Drew

    2013-06-01

    Advanced image processing of Large Angle and Spectrometric Coronagraph Experiment (LASCO) C2 observations reveals the expansion of the active region closed field into the extended corona. The nested closed-loop systems are large, with an apparent latitudinal extent of 50 Degree-Sign , and expanding to heights of at least 12 R{sub Sun }. The expansion speeds are {approx}10 km s{sup -1} in the AIA/SDO field of view, below {approx}20 km s{sup -1} at 2.3 R{sub Sun }, and accelerate linearly to {approx}60 km s{sup -1} at 5 R{sub Sun }. They appear with a frequency of one every {approx}3 hr over a time period of around three days. They are not coronal mass ejections (CMEs) since their gradual expansion is continuous and steady. They are also faint, with an upper limit of 3% of the brightness of background streamers. Extreme ultraviolet images reveal continuous birth and expansion of hot, bright loops from a new active region at the base of the system. The LASCO images show that the loops span a radial fan-like system of streamers, suggesting that they are not propagating within the main coronal streamer structure. The expanding loops brighten at low heights a few hours prior to a CME eruption, and the expansion process is temporarily halted as the closed field system is swept away. Closed magnetic structures from some active regions are not isolated from the extended corona and solar wind, but can expand to large heights in the form of quiescent expanding loops.

  15. Time Evolution of Force-Free Parameter and Free Magnetic Energy in Active Region NOAA 10365

    NASA Astrophysics Data System (ADS)

    Valori, G.; Romano, P.; Malanushenko, A.; Ermolli, I.; Giorgi, F.; Steed, K.; van Driel-Gesztelyi, L.; Zuccarello, F.; Malherbe, J.-M.

    2015-02-01

    We describe the variation of the accumulated coronal helicity derived from the magnetic helicity flux through the photosphere in active region (AR) NOAA 10365, where several large flares and coronal mass ejections (CMEs) occurred. We used SOHO/MDI full-disk line-of-sight magnetograms to measure the helicity flux, and the integral of GOES X-ray flux as a proxy of the coronal energy variations due to flares or CMEs. Using the linear force-free field model, we transformed the accumulated helicity flux into a time sequence of the force-free parameter α accounting for flares or CMEs via the proxy derived from GOES observations. This method can be used to derive the value of α at different times during the AR evolution, and is a partial alternative to the commonly used match of field lines with EUV loops. By combining the accumulated helicity obtained from the observations with the linear force-free theory, we describe the main phases of the emergence process of the AR, and relate them temporally with the occurrence of flares or CMEs. Additionally, a comparison with the loop-matching method of fixing alpha at each time independently shows that the proposed method may be helpful in avoiding unrealistic or undetermined values of alpha that may originate from an insufficient quality of the image used to identify coronal loops at a given time. For the relative intensity of the considered events, the linear force-free field theory implies that there is a direct correlation between the released energy on the one hand and the product of the coronal helicity with the variation of α due to the event on the other. Therefore, the higher the value of the accumulated coronal helicity, the smaller the force-free parameter variation required to produce the same decrease in the free energy during the CMEs.

  16. SPECTROSCOPIC ANALYSIS OF INTERACTION BETWEEN AN EXTREME-ULTRAVIOLET IMAGING TELESCOPE WAVE AND A CORONAL UPFLOW REGION

    SciTech Connect

    Chen, F.; Ding, M. D.; Chen, P. F.; Harra, L. K.

    2011-10-20

    We report a spectroscopic analysis of an EUV Imaging Telescope (EIT) wave event that occurred in active region 11081 on 2010 June 12 and was associated with an M2.0 class flare. The wave propagated nearly circularly. The southeastern part of the wave front passed over an upflow region near a magnetic bipole. Using EUV Imaging Spectrometer raster observations for this region, we studied the properties of plasma dynamics in the wave front, as well as the interaction between the wave and the upflow region. We found a weak blueshift for the Fe XII {lambda}195.12 and Fe XIII {lambda}202.04 lines in the wave front. The local velocity along the solar surface, which is deduced from the line-of-sight velocity in the wave front and the projection effect, is much lower than the typical propagation speed of the wave. A more interesting finding is that the upflow and non-thermal velocities in the upflow region are suddenly diminished after the transit of the wave front. This implies a significant change of magnetic field orientation when the wave passed. As the lines in the upflow region are redirected, the velocity along the line of sight is diminished as a result. We suggest that this scenario is more in accordance with what was proposed in the field-line stretching model of EIT waves.

  17. The morphology of flare phenomena, magnetic fields, and electric currents in active regions. II - NOAA active region 5747 (1989 October)

    NASA Technical Reports Server (NTRS)

    Leka, K. D.; Canfield, Richard C.; Mcclymont, A. N.; De La Beaujardiere, J.-F.; Fan, Yuhong; Tang, F.

    1993-01-01

    The paper describes October 1989 observations in NOAA Active Region 5747 of the morphology of energetic electron precipitation and high-pressure coronal flare plasmas of three flares and their relation to the vector magnetic field and vertical electric currents. The H-alpha spectroheliograms were coaligned with the vector magnetograms using continuum images of sunspots, enabling positional accuracy of a few arcsec. It was found that, during the gradual phase, the regions of the H-alpha flare that show the effects of enhanced pressure in the overlying corona often encompass extrema of the vertical current density, consistent with earlier work showing a close relationship between H-alpha emission and line-of-sight currents. The data are also consistent with the overall morphology and evolution described by erupting-filament models such as those of Kopp and Pneuman (1976) and Sturrock (1989).

  18. SDO Sees Active Region Outbursts

    NASA Video Gallery

    This close up video by NASA’s Solar Dynamics Observatory shows an active region near the right-hand edge of the sun’s disk, which erupted with at least a dozen minor events over a 30-hour period fr...

  19. ON MAGNETIC ACTIVITY BAND OVERLAP, INTERACTION, AND THE FORMATION OF COMPLEX SOLAR ACTIVE REGIONS

    SciTech Connect

    McIntosh, Scott W.; Leamon, Robert J.

    2014-11-20

    Recent work has revealed a phenomenological picture of the how the ∼11 yr sunspot cycle of the Sun arises. The production and destruction of sunspots is a consequence of the latitudinal-temporal overlap and interaction of the toroidal magnetic flux systems that belong to the 22 yr magnetic activity cycle and are rooted deep in the Sun's convective interior. We present a conceptually simple extension of this work, presenting a hypothesis on how complex active regions can form as a direct consequence of the intra- and extra-hemispheric interaction taking place in the solar interior. Furthermore, during specific portions of the sunspot cycle, we anticipate that those complex active regions may be particularly susceptible to profoundly catastrophic breakdown, producing flares and coronal mass ejections of the most severe magnitude.

  20. Hi-C Observations of an Active Region Corona, and Investigation of the Underlying Magnetic Structure

    NASA Technical Reports Server (NTRS)

    Tiwari, S. K.; Alexander, C. E.; Winebarger, A.; Moore, R. L.

    2014-01-01

    The solar corona is much hotter (>=10(exp 6) K) than its surface (approx 6000 K), puzzling astrophysicists for several decades. Active region (AR) corona is again hotter than the quiet Sun (QS) corona by a factor of 4-10. The most widely accepted mechanism that could heat the active region corona is the energy release by current dissipation via reconnection of braided magnetic field structure, first proposed by E. N. Parker three decades ago. The first observational evidence for this mechanism has only recently been presented by Cirtain et al. by using High-resolution Coronal Imager (Hi-C) observations of an AR corona at a spatial resolution of 0.2 arcsec, which is required to resolve the coronal loops, and was not available before the rocket flight of Hi-C in July 2012. The Hi-C project is led by NASA/MSFC. In the case of the QS, work done by convection/granulation on the inter-granular feet of the coronal field lines translates into the heat observed in the corona. In the case of the AR, as here, there could be flux emergence, cancellation/submergence, or shear flows generating large stress and tension in coronal field loops which is released as heat in the corona. We are currently investigating the changes taking place in photospheric feet of the magnetic field involved with brightenings in the Hi-C AR corona. For this purpose, we are also using SDO/AIA data of +/- 2 hours around the 5 minutes Hi-C flight. In the present talk, I will first summarize some of the results of the Hi-C observations and then present some results from our recent analysis on what photospheric processes feed the magnetic energy that dissipates into heat in coronal loops.

  1. Active region upflows. I. Multi-instrument observations

    NASA Astrophysics Data System (ADS)

    Vanninathan, K.; Madjarska, M. S.; Galsgaard, K.; Huang, Z.; Doyle, J. G.

    2015-12-01

    Context. We study upflows at the edges of active regions, called AR outflows, using multi-instrument observations. Aims: This study intends to provide the first direct observational evidence of whether chromospheric jets play an important role in furnishing mass that could sustain coronal upflows. The evolution of the photospheric magnetic field, associated with the footpoints of the upflow region and the plasma properties of active region upflows is investigated with the aim of providing information for benchmarking data-driven modelling of this solar feature. Methods: We spatially and temporally combine multi-instrument observations obtained with the Extreme-ultraviolet Imaging Spectrometer on board the Hinode, the Atmospheric Imaging Assembly and the Helioseismic Magnetic Imager instruments on board the Solar Dynamics Observatory and the Interferometric BI-dimensional Spectro-polarimeter installed at the National Solar Observatory, Sac Peak, to study the plasma parameters of the upflows and the impact of the chromosphere on active region upflows. Results: Our analysis shows that the studied active region upflow presents similarly to those studied previously, i.e. it displays blueshifted emission of 5-20 kms-1 in Fe xii and Fe xiii and its average electron density is 1.8 × 109 cm-3 at 1 MK. The time variation of the density is obtained showing no significant change (in a 3σ error). The plasma density along a single loop is calculated revealing a drop of 50% over a distance of ~20 000 km along the loop. We find a second velocity component in the blue wing of the Fe xii and Fe xiii lines at 105 kms-1 reported only once before. For the first time we study the time evolution of this component at high cadence and find that it is persistent during the whole observing period of 3.5 h with variations of only ±15 kms-1. We also, for the first time, study the evolution of the photospheric magnetic field at high cadence and find that magnetic flux diffusion is

  2. 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.

  3. THE EFFECT OF HOT CORONAL ELECTRONS ON EXTREME-ULTRAVIOLET SPECTRAL LINES OF He II EMITTED BY SOLAR TRANSITION REGION PLASMAS

    SciTech Connect

    Feldman, U.; Ralchenko, Yu.; Doschek, G. A.

    2010-01-01

    The cause of the lower intensities of extreme-ultraviolet (EUV) He II lines emitted by coronal hole (CH) plasmas compared with quiet Sun (QS) plasmas has been the subject of many studies dating back over half a century. In this paper, we study the effect of small amounts of 'hot' electrons at coronal temperatures (T{sub e} = 1.4 x 10{sup 6} K) on the intensities of EUV He II lines, as well as on the intensities of EUV lines of C III, C IV, O III, and O IV emitted by 1.5 x 10{sup 4} K-1.5 x 10{sup 5} K (4.2 <= log T{sub e} <= 5.2) plasmas in the QS. We show that although the influence of a fraction as small as 10{sup -4}-10{sup -3} of hot electrons on the intensities of the C and O lines is noticeable, the effect on the intensities of the He lines is much larger, to the extent that it could explain the excess brightness of He II lines emitted by QS regions relative to CH plasmas.

  4. 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.

  5. Global oscillations and active regions

    NASA Astrophysics Data System (ADS)

    Durrant, C. J.

    The author presents further estimates of the amplitude of the modulation of the solar global velocity signal caused by the passage of active regions across the solar disc. Using measurements of the profile of the K I λ769.9 nm line in the quiet sun and in plages he finds a global velocity variation of ≡2 m s-1 during the transit of a typical active region of area 3300 millionths of the hemisphere. However, during the period in which a velocity amplitude of 6 m s-1 was reported by Claverie et al. (1982), the sunspot areas were exceptionally large and the author confirms Schröter's (1984) result that the combination of spot and plage contributions is sufficient to account for the observed signal. The velocity modulation is thus attributable to surface inhomogeneities, not to the structure of the solar core.

  6. 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

  7. Simulations of Solar Jets Confined by Coronal Loops

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

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

  8. The relationship between coronal streamers and CMEs.

    NASA Astrophysics Data System (ADS)

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

    1999-06-01

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

  9. A Three-dimensional Model of Active Region 7986: Comparison of Simulations with Observations

    NASA Astrophysics Data System (ADS)

    Mok, Yung; Mikić, Zoran; Lionello, Roberto; Downs, Cooper; Linker, Jon A.

    2016-01-01

    In the present study, we use a forward modeling method to construct a 3D thermal structure encompassing active region 7986 of 1996 August. The extreme ultraviolet (EUV) emissions are then computed and compared with observations. The heating mechanism is inspired by a theory on Alfvén wave turbulence dissipation. The magnetic structure is built from a Solar and Heliospheric Observatory (SOHO)/MDI magnetogram and an estimated torsion parameter deduced from observations. We found that the solution to the equations in some locations is in a thermal nonequilibrium state. The time variation of the density and temperature profiles leads to time dependent emissions, which appear as thin, loop-like structures with uniform cross-section. Their timescale is consistent with the lifetime of observed coronal loops. The dynamic nature of the solution also leads to plasma flows that resemble observed coronal rain. The computed EUV emissions from the coronal part of the fan loops and the high loops compare favorably with SOHO/EIT observations in a quantitative comparison. However, the computed emission from the lower atmosphere is excessive compared to observations, a symptom common to many models. Some factors for this discrepancy are suggested, including the use of coronal abundances to compute the emissions and the neglect of atmospheric opacity effects.

  10. The solar atmosphere and the structure of active regions

    NASA Technical Reports Server (NTRS)

    Sturrock, P. A.

    1974-01-01

    The existence of 'holes' in the corona is reported characterized by abnormally low densities and temperatures. It was found that such coronal holes appear to be the source of high-velocity, enhanced-density streams in the solar wind as observed at the earth's orbit. It was further noted that coronal holes appear to be associated with regions of diverging magnetic fields in the corona. Models were developed to accomplish the objective for the principal energy flows in the transition region and corona.

  11. 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...

  12. Studies on Three-Dimensional Dynamic Evolution of Filaments and Coronal EUV Waves

    NASA Astrophysics Data System (ADS)

    Li, T.

    2014-01-01

    . The successful launch of the SDO provides us the third viewpoint to reconstruct filaments. We firstly reconstruct an eruptive filament by applying the three-viewpoint observations from STEREO A, STEREO B, and SDO, and focus on the three-dimensional evolution of a polar crown filament. We find that its eruption is anisotropic, with the latitudinal variation greater than the longitudinal one. The filament moves toward the low-latitude region with a change in inclination of about 48°. SDO observations show that part of the filament material separates from the eastern leg during the late phase of the eruption, and moves along the filament channel with a constant velocity of 140 km\\cdots^{-1}. When the flare in the nearby active region starts, the filament is accelerated simultaneously. The extrapolated coronal magnetic field shows that there are two groups of magnetic structures above the filament; the larger magnetic structures link the filament and the nearby active region; the smaller ones stretch across the polar crown filament. This indicates that the solar activities have a global characteristic. The study on the interaction of coronal EUV wave with coronal structures is an important means to understand the nature of coronal EUV wave. If the coronal EUV wave is a fast-mode magnetosonic wave, it should reflect and deflect from the areas with a large gradient of magnetosonic speed, such as in the boundaries of coronal holes and active regions. If the coronal EUV wave is not a real wave, it should stop at the boundaries of coronal holes and active regions. Using the full-disk, multi-wavelength, high spatial and temporal resolution, and continuous observations of the SDO, we investigate the interaction of the coronal EUV wave with coronal holes, active regions, and coronal bright structures. The results are as follows: (1) the coronal EUV wave has a three-dimensional dome shape, with propagation speeds ranging from 430 to 780 km\\cdots^{-1} in different directions; (2

  13. Treatment of Viscosity in the Shock Waves Observed After Two Consecutive Coronal Mass Ejection Activities CME08/03/2012 and CME15/03/2012

    NASA Astrophysics Data System (ADS)

    Cavus, Huseyin

    2016-07-01

    A coronal mass ejection (CME) is one of the most the powerful activities of the Sun. There is a possibility to produce shocks in the interplanetary medium after CMEs. Shock waves can be observed when the solar wind changes its velocity from being supersonic nature to being subsonic nature. The investigations of such activities have a central place in space weather purposes, since; the interaction of shocks with viscosity is one of the most important problems in the supersonic and compressible gas flow regime (Blazek in Computational fluid dynamics: principles and applications. Elsevier, Amsterdam 2001). The main aim of present work is to achieve a search for the viscosity effects in the shocks occurred after two consecutive coronal mass ejection activities in 2012 (i.e. CME08/03/2012 and CME15/03/2012).

  14. Flux Rope Formation Preceding Coronal Mass Ejection Onset

    NASA Astrophysics Data System (ADS)

    Kliem, Bernhard; Green, L. M.

    2009-12-01

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

  15. Flux Rope Formation Preceding Coronal Mass Ejection Onset

    NASA Astrophysics Data System (ADS)

    Green, L. M.; Kliem, B.

    2009-08-01

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

  16. 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.

  17. White Light Coronograph (WLC) and Ultra-Violet Coronal Spectrometer (UVCS)

    NASA Technical Reports Server (NTRS)

    Moore, R. L.

    1985-01-01

    The white light coronagraph (WLC) and ultraviolet coronal spectrometer (UVCS) together reveal the corona and the roots of the solar wind from 1.5 to 6 solar radii from Sun center. The WLC measures the plasma density and spatial structure of the corona and coronal mass ejections at a resolution of about 20 arcseconds. The UVCS, in combination with the WLC, measures the temperature and radial outflow speed of the coronal plasma. These instruments will detect mass ejections from active regions and high speed solar wind streams from coronal holes a few days before the source regions rotate onto the face of the Sun, thus giving a week or more of advanced warning for disturbed geomagnetic conditions at Earth.

  18. White Light Coronagraph (WLC) and Ultra-Violet Coronal Spectrometer (UVCS)

    NASA Technical Reports Server (NTRS)

    Moore, R.

    1986-01-01

    The WLC and UVS together reveal the corona and the roots of the solar wind from 1.5 to 6 solar radii from sun center. The WLC measures the plasma density and spatial structure of the corona and coronal mass ejections at a plasma density and spatial structure of the corona and coronal mass ejections at a resolution of about 20 arcsec. The UVCS in combination with the WLC measures the temperature and radial outflow speed of the coronal plasma. These instruments will detect mass ejections from active regions and high speed solar wind streams from coronal holes a few days before the source regions rotate onto the face of the Sun, thus giving a week or more of advanced warning for disturbed geomagnetic conditions at Earth.

  19. 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.

  20. 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.

  1. On the Active Region Bright Grains Observed in the Transition Region Imaging Channels of IRIS

    NASA Astrophysics Data System (ADS)

    Skogsrud, H.; Rouppe van der Voort, L.; De Pontieu, B.

    2016-02-01

    The Interface Region Imaging Spectrograph (IRIS) provides spectroscopy and narrow band slit-jaw (SJI) imaging of the solar chromosphere and transition region at unprecedented spatial and temporal resolutions. Combined with high-resolution context spectral imaging of the photosphere and chromosphere as provided by the Swedish 1 m Solar Telescope (SST), we can now effectively trace dynamic phenomena through large parts of the solar atmosphere in both space and time. IRIS SJI 1400 images from active regions, which primarily sample the transition region with the Si iv 1394 and 1403 Å lines, reveal ubiquitous bright “grains” which are short-lived (two to five minute) bright roundish small patches of sizes 0.″5-1.″7 that generally move limbward with velocities up to about 30 km s-1. In this paper, we show that many bright grains are the result of chromospheric shocks impacting the transition region. These shocks are associated with dynamic fibrils (DFs), most commonly observed in Hα. We find that the grains show the strongest emission in the ascending phase of the DF, that the emission is strongest toward the top of the DF, and that the grains correspond to a blueshift and broadening of the Si iv lines. We note that the SJI 1400 grains can also be observed in the SJI 1330 channel which is dominated by C ii lines. Our observations show that a significant part of the active region transition region dynamics is driven from the chromosphere below rather than from coronal activity above. We conclude that the shocks that drive DFs also play an important role in the heating of the upper chromosphere and lower transition region.

  2. 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.

  3. Simulation of Active-Region-Scale Flux Emergence

    NASA Astrophysics Data System (ADS)

    Manchester, W.; van der Holst, B.

    2015-12-01

    Shear flows long observed in solar active regions are now understood to be a consequence of the Lorentz force that develops from a complex interaction between magnetic fields and the thermal pressure of the Sun's gravitationally stratified atmosphere. The shearing motions transport magnetic flux and energy from the submerged portion of the field to the corona providing the necessary energy for flares, filament eruptions and CMEs. To further examine this shearing process, we simulate flux emergence on the scale of active regions with a large-scale model of the near surface convection zone constructed on an adaptive spherical grid. This model is designed to simulate flux emerging on the scale of active regions from a depth of 30 Mm. Here, we show results of a twisted flux rope emerging through the hierarchy of granular convection, and examine the flow patterns that arise as the flux approaches the photosphere. We show how these organized flows driven by the Lorentz force cause the coronal field evolve to a highly non-potential configuration capable of driving solar eruptions such as CMEs and flares.

  4. Living With A Red Dwarf: Rotation, Starspots, Activity Cycles, Coronal X-ray Activity And X-uv Irradiances Of Proxima Centauri

    NASA Astrophysics Data System (ADS)

    Jason, Merritt; Guinan, E.; Engle, S.; Pojmanski, G.

    2007-12-01

    As part of our Living with a Red Dwarf Program, we have carried out a detailed study of the radiative and plasma properties of the nearby dM5.5e star Proxima Centauri. Proxima Cen is noteworthy as the nearest star to the Sun. Because of its proximity ( 4.3 L.Y.) and membership in the α Cen system, Proxima Cen is an important star to use as a surrogate for solar-aged mid-dM stars. It is relatively bright (V = 11-mag) and has well determined observational and physical properties (MV, Teff, [Fe/H], angular diameter, mass and age). Importantly for our purposes, Proxima Cen has a reliable age of 5.5-6.0 Gyr from its association with the α Cen system in which α Cen A (G2 V) has a reliable isochronal age determination. We have analyzed 5 years of ASAS-3, V-band photometry to search for evidence of short- and long-term variations in brightness that could arise from magnetically related phenomenon (star spots, faculae, and possible UV flares). We also examine its coronal X-ray emission and variations as well as the stars chromospheric and transition regions in the UV from IUE and FUSE observations. The X-UV/optical data are combined and irradiances are calculated for use in extrasolar planet studies. From the photometry we find a rotational modulation of Prot = 83.5 days, in excellent agreement with the earlier HST/FGS study of Benedict et al. (1998). The character of its light variations indicates possible differential rotation as well as a probable long-term activity cycle of 6.9 +/- 0.5 yrs. Although Proxima Cen should be a fully convective star with a different magnetic dynamo (α2) than our Sun (αΩ), its overall magnetic behavior appears to be solar-like. This research is supported by grants from NSF/RUI AST-507536 and NASA Grants NNX06AD386 and NNG04G038G. We are grateful for this support.

  5. Cometary nucleus and active regions

    NASA Technical Reports Server (NTRS)

    Whipple, F. L.

    1984-01-01

    On the basis of the icy conglomerate model of cometary nuclei, various observations demonstrate the spotted nature of many or most nuclei, i.e., regions of unusual activity, either high or low. Rotation periods, spin axes and even precession of the axes are determined. The observational evidence for variations in activity over the surfaces of cometary nuclei are listed and discussed. On June 11 the comet IRAS-ARAKI-ALCOCK approached the Earth to a distance of 0.031 AU, the nearest since C/Lexell, 1770 I, providing a unique opportunity for near-nucleus observations. Preliminary analysis of these images establishes the spin axis of the nucleus, with an oblioquity to the orbit plane of approximately 50 deg, and a lag angle of sublimation approximately 35 deg from the solar meridian on the nucleus. Asymmetries of the inner coma suggests a crazy-quilt distribution of ices with differing volatility over the surface of the nucleus. The observations of Comet P/Homes 1892 III, exhibiting two 8-10 magnitude bursts, are carefully analyzed. The grazing encounter produced, besides the first great burst, an active area on the nucleus, which was rotating retrograde with a period of 16.3hr and inclination nearly 180 deg. After the first burst the total magnitude fell less than two magnitudes from November 7 to November 30 (barely naked eye) while the nuclear region remained diffuse or complex, rarely if ever showing a stellar appearance. The fading was much more rapid after the second burst. The grazing encounter distributed a volume of large chunks in the neighborhood of the nucleus, maintaining activity for weeks.

  6. Variations of solar EUV radiation and coronal index of solar activity. (Slovak Title: Variácie EUV žiarenia Slnka a koronálny index slnečnej aktivity)

    NASA Astrophysics Data System (ADS)

    Lorenc, M.; Pastorek, L.; Rybanský, M.

    2010-12-01

    This is a follow-up contribution of the work Lukáč and Rybanský "Modified coronal index of solar activity (MCI) - presented during the last workshop. While MCI has been derived from measurements of the CELIAS/SEM spectrometer onboard the SOHO satellite, in this paper we have focused on the application of the measurements from satellites SORCE and TIMED SEE to the same goal, i.e. for compiling the coronal index of solar activity replacing the ground based coronal measurements.

  7. 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).

  8. Coronal Heating, Spicules, and Solar-B

    NASA Technical Reports Server (NTRS)

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

    2003-01-01

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

  9. VLA observations of solar active regions at 6 and 20 cm

    NASA Technical Reports Server (NTRS)

    Alissandrakis, C. E.; Kundu, M. R.; Shevgaonkar, K. R.

    1991-01-01

    High-resolution observations are presented of two active regions at 6 and 20 cm over a period of 5 days, together with H-alpha and photospheric magnetic fields. The large-scale emission at 20 cm is associated with the H-alpha plage. In one region the strongest source was over the neutral line, near the tip of an active-region filament, which indicates that the emission probably originated in small-scale coronal loops. In the second region the peak of the emission was near a well-developed sunspot. Neither region showed evidence of large-scale loops joining their preceding and following parts. Several other sources were observed at 20 cm; a source associated with an H-alpha plage region crossed by a filament and one associated with a small bipolar region are briefly discussed. The 6-cm emission from a well-developed spot showed clearly the characteristics expected from gyroresonance model computations.

  10. Coronal Activity in Low-Mass Pre-Main Sequence Stars: NGC 2264

    NASA Technical Reports Server (NTRS)

    Tebbe, H. J.; Patten, B. M.

    2000-01-01

    We present the preliminary results of an analysis of ROSAT images in the region of the populous young (age approx. 3 Myr) star-forming region NGC 2264. The cluster was imaged with the ROSAT HRI in two sets of pointings -- one set near the central region of the cluster, centered on the star LW Mon, and the other set in the southern part of the cluster, centered near the star V428 Mon, just south of the Cone Nebula. In total 113 unique X-ray sources have been identified in the ROSAT images with signal-to-noise ratios greater than 3. The limiting luminosities (log Lx(ergs/sec)) for 3-sigma detections are estimated to be 30.18, 30.23, and 30.08 for the northern field, southern field, and overlap region between the two fields respectively. Extensive optical photometry, classification spectroscopy, and proper motions, obtained from recent ground-based surveys of this region, were used to identify the most likely optical counterpart to each X-ray source. Although most of our X-ray selected sample appears to be associated with NGC 2264 members, we find that the vast majority of the cluster membership was undetected in the ROSAT HRI survey. The X-ray cumulative luminosity function for solar-mass stars in NGC 2264 shows that most of the low-mass members probably have X-ray luminosities similar to those seen for the X-ray brightest members of older clusters such as IC 2391/IC 2602 (age approx. 50 Myr) and the Pleiades (age approx. 100 Myr). This research was funded in part by the SAO Summer Intern Program and NASA grant NAG5-8120.

  11. 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.

  12. EVIDENCE FOR WIDESPREAD COOLING IN AN ACTIVE REGION OBSERVED WITH THE SDO ATMOSPHERIC IMAGING ASSEMBLY

    SciTech Connect

    Viall, Nicholeen M.; Klimchuk, James A.

    2012-07-01

    A well-known behavior of EUV light curves of discrete coronal loops is that the peak intensities of cooler channels or spectral lines are reached at progressively later times than hotter channels. This time lag is understood to be the result of hot coronal loop plasma cooling through these lower respective temperatures. However, loops typically comprise only a minority of the total emission in active regions (ARs). Is this cooling pattern a common property of AR coronal plasma, or does it only occur in unique circumstances, locations, and times? The new Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA) data provide a wonderful opportunity to answer this question systematically for an entire AR. We measure the time lag between pairs of SDO/AIA EUV channels using 24 hr of images of AR 11082 observed on 2010 June 19. We find that there is a time-lag signal consistent with cooling plasma, just as is usually found for loops, throughout the AR including the diffuse emission between loops for the entire 24 hr duration. The pattern persists consistently for all channel pairs and choice of window length within the 24 hr time period, giving us confidence that the plasma is cooling from temperatures of greater than 3 MK, and sometimes exceeding 7 MK, down to temperatures lower than {approx}0.8 MK. This suggests that the bulk of the emitting coronal plasma in this AR is not steady; rather, it is dynamic and constantly evolving. These measurements provide crucial constraints on any model which seeks to describe coronal heating.

  13. Triennial Report 2006-2009. Commission 10: Solar Activity

    NASA Technical Reports Server (NTRS)

    Klimchuk, James A.

    2008-01-01

    Commission 10 deals with solar activity in all of its forms, ranging from the smallest nanoflares to the largest coronal mass ejections. This report reviews scientific progress over the roughly two-year period ending in the middle of 2008. This has been an exciting time in solar physics, highlighted by the launches of the Hinode and STEREO missions late in 2006. The report is reasonably comprehensive, though it is far from exhaustive. Limited space prevents the inclusion of many significant results. The report is divided into following sections: Photosphere and Chromosphere; Transition Region; Corona and Coronal Heating; Coronal Jets; Flares; Coronal Mass Ejection Initiation; Global Coronal Waves and Shocks; Coronal Dimming; The Link Between Low Coronal CME signatures and Magnetic Clouds; Coronal Mass Ejections in the Heliosphere; and Coronal Mass Ejections and Space Weather. Primary authorship is indicated at the beginning of each section.

  14. 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.

  15. OBSERVING THE FINE STRUCTURE OF LOOPS THROUGH HIGH-RESOLUTION SPECTROSCOPIC OBSERVATIONS OF CORONAL RAIN WITH THE CRISP INSTRUMENT AT THE SWEDISH SOLAR TELESCOPE

    SciTech Connect

    Antolin, P.; Rouppe van der Voort, L. E-mail: v.d.v.l.rouppe@astro.uio.no

    2012-02-01

    Observed in cool chromospheric lines, such as H{alpha} or Ca II H, coronal rain corresponds to cool and dense plasma falling from coronal heights. Considered as a peculiar sporadic phenomenon of active regions, it has not received much attention since its discovery more than 40 years ago. Yet, it has been shown recently that a close relationship exists between this phenomenon and the coronal heating mechanism. Indeed, numerical simulations have shown that this phenomenon is most likely due to a loss of thermal equilibrium ensuing from a heating mechanism acting mostly toward the footpoints of loops. We present here one of the first high-resolution spectroscopic observations of coronal rain, performed with the CRisp Imaging Spectro Polarimeter (CRISP) instrument at the Swedish Solar Telescope. This work constitutes the first attempt to assess the importance of coronal rain in the understanding of the coronal magnetic field in active regions. With the present resolution, coronal rain is observed to literally invade the entire field of view. A large statistical set is obtained in which dynamics (total velocities and accelerations), shapes (lengths and widths), trajectories (angles of fall of the blobs), and thermodynamic properties (temperatures) of the condensations are derived. Specifically, we find that coronal rain is composed of small and dense chromospheric cores with average widths and lengths of {approx}310 km and {approx}710 km, respectively, average temperatures below 7000 K, displaying a broad distribution of falling speeds with an average of {approx}70 km s{sup -1}, and accelerations largely below the effective gravity along loops. Through estimates of the ion-neutral coupling in the blobs we show that coronal rain acts as a tracer of the coronal magnetic field, thus supporting the multi-strand loop scenario, and acts as a probe of the local thermodynamic conditions in loops. We further elucidate its potential in coronal heating. We find that the cooling

  16. A METHOD FOR DATA-DRIVEN SIMULATIONS OF EVOLVING SOLAR ACTIVE REGIONS

    SciTech Connect

    Cheung, Mark C. M.; DeRosa, Marc L.

    2012-10-01

    We present a method for performing data-driven simulations of solar active region formation and evolution. The approach is based on magnetofriction, which evolves the induction equation assuming that the plasma velocity is proportional to the Lorentz force. The simulations of active region (AR) coronal field are driven by temporal sequences of photospheric magnetograms from the Helioseismic Magnetic Imager instrument on board the Solar Dynamics Observatory (SDO). Under certain conditions, the data-driven simulations produce flux ropes that are ejected from the modeled AR due to loss of equilibrium. Following the ejection of flux ropes, we find an enhancement of the photospheric horizontal field near the polarity inversion line. We also present a method for the synthesis of mock coronal images based on a proxy emissivity calculated from the current density distribution in the model. This method yields mock coronal images that are somewhat reminiscent of images of ARs taken by instruments such as SDO's Atmospheric Imaging Assembly at extreme ultraviolet wavelengths.

  17. Automated Detection and Extraction of Coronal Dimmings from SDO/AIA Data

    NASA Astrophysics Data System (ADS)

    Davey, Alisdair R.; Attrill, G. D. R.; Wills-Davey, M. J.

    2010-05-01

    The sheer volume of data anticipated from the Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA) highlights the necessity for the development of automatic detection methods for various types of solar activity. Initially recognised in the 1970s, it is now well established that coronal dimmings are closely associated with coronal mass ejections (CMEs), and are particularly recognised as an indicator of front-side (halo) CMEs, which can be difficult to detect in white-light coronagraph data. An automated coronal dimming region detection and extraction algorithm removes visual observer bias from determination of physical quantities such as spatial location, area and volume. This allows reproducible, quantifiable results to be mined from very large datasets. The information derived may facilitate more reliable early space weather detection, as well as offering the potential for conducting large-sample studies focused on determining the geoeffectiveness of CMEs, coupled with analysis of their associated coronal dimmings. We present examples of dimming events extracted using our algorithm from existing EUV data, demonstrating the potential for the anticipated application to SDO/AIA data. Metadata returned by our algorithm include: location, area, volume, mass and dynamics of coronal dimmings. As well as running on historic datasets, this algorithm is capable of detecting and extracting coronal dimmings in near real-time. The coronal dimming detection and extraction algorithm described in this poster is part of the SDO/Computer Vision Center effort hosted at SAO (Martens et al., 2009). We acknowledge NASA grant NNH07AB97C.

  18. Prediction of Active-Region CME Productivity from Magnetograms

    NASA Technical Reports Server (NTRS)

    Falconer, D. A.; Moore, R. L.; Gary, G. A.

    2004-01-01

    We report results of an expanded evaluation of whole-active-region magnetic measures as predictors of active-region coronal mass ejection (CME) productivity. Previously, in a sample of 17 vector magnetograms of 12 bipolar active regions observed by the Marshall Space Flight Center (MSFC) vector magnetograph, from each magnetogram we extracted a measure of the size of the active region (the active region s total magnetic flux a) and four measures of the nonpotentiality of the active region: the strong-shear length L(sub SS), the strong-gradient length L(sub SG), the net vertical electric current I(sub N), and the net-current magnetic twist parameter alpha (sub IN). This sample size allowed us to show that each of the four nonpotentiality measures was statistically significantly correlated with active-region CME productivity in time windows of a few days centered on the day of the magnetogram. We have now added a fifth measure of active-region nonpotentiality (the best-constant-alpha magnetic twist parameter (alpha sub BC)), and have expanded the sample to 36 MSFC vector magnetograms of 31 bipolar active regions. This larger sample allows us to demonstrate statistically significant correlations of each of the five nonpotentiality measures with future CME productivity, in time windows of a few days starting from the day of the magnetogram. The two magnetic twist parameters (alpha (sub 1N) and alpha (sub BC)) are normalized measures of an active region s nonpotentially in that they do not depend directly on the size of the active region, while the other three nonpotentiality measures (L(sub SS), L(sub SG), and I(sub N)) are non-normalized measures in that they do depend directly on active-region size. We find (1) Each of the five nonpotentiality measures is statistically significantly correlated (correlation confidence level greater than 95%) with future CME productivity and has a CME prediction success rate of approximately 80%. (2) None of the nonpotentiality

  19. Coronal Hole Boundaries as Source Regions of a Steady Slow Solar Wind: Global Modeling of Charge State Composition and Sun-to-Earth Observations

    NASA Astrophysics Data System (ADS)

    Oran, R.; Landi, E.; van der Holst, B.; Lepri, S. T.; Manchester, W.; Frazin, R. A.; Nuevo, F.; Vásquez, A. M.; Sokolov, I.; Gombosi, T. I.

    2014-12-01

    We combine the results from a global MHD model of the solar atmosphere with a charge state evolution code in order to predict the large-scale variation of charge state composition in the fast and slow solar wind during solar minimum. The model captures the well-known increase in charge state ratios C+6/ C+5 and O+7/O+6 in the slow wind, inline with Ulysses observations. We present a theoretical picture explaining the formation of these increases, which are related to regions of higher electron density and temperature near the boundaries of coronal holes. We verify the existence of these regions using a 3D tomographic reconstruction of the lower corona. This work establishes that a steady slow wind flowing along open magnetic field lines can carry high charge states without invoking reconnection with closed field regions. This subset of slow wind can play a role explaining the properties of the non-steady slow wind, and complement dynamic models of slow solar wind formation.

  20. Volcanically Active Regions on Io

    NASA Technical Reports Server (NTRS)

    1997-01-01

    Shown here is a portion of one of the highest-resolution images of Io (Latitude: +10 to +60 degrees, Longitude: 180 to 225 degrees) acquired by the Galileo spacecraft, revealing immense lava flows and other volcanic landforms. Several high-temperature volcanic hot spots have been detected in this region by both the Near Infrared Mapping Spectrometer and the imaging system of Galileo. The temperatures are consistent with active silicate volcanism in lava flows or lava lakes (which reside inside irregular depressions called calderas). The large dark lava flow in the upper left region of the image is more than 400 km long, similar to ancient flood basalts on Earth and mare lavas on the Moon.

    North is to the top of the picture and the sun illuminates the surface from the left. The image covers an area 1230 kilometers wide and the smallest features that can be discerned are 2.5 kilometers in size. This image was taken on November 6th, 1996, at a range of 245,719 kilometers by the Solid State Imaging (CCD) system on the Galileo Spacecraft.

    Launched in October 1989, Galileo entered orbit around Jupiter on December 7, 1995. The spacecraft's mission is to conduct detailed studies of the giant planet, its largest moons and the Jovian magnetic environment. The Jet Propulsion Laboratory, Pasadena, CA manages the mission for NASA's Office of Space Science, Washington, DC.

    This image and other images and data received from Galileo are posted on the Galileo mission home page on the World Wide Web at http://galileo.jpl.nasa.gov. Background information and educational context for the images can be found at URL http://www.jpl.nasa.gov/galileo/sepo

  1. 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.

  2. Case study of a complex active-region filament eruption

    NASA Astrophysics Data System (ADS)

    Yan, X. L.; Qu, Z. Q.; Kong, D. F.; Deng, L. H.; Xue, Z. K.

    2013-09-01

    Context. We investigated a solar active-region filament eruption associated with a C6.6 class flare and a coronal mass ejection (CME) in NOAA active region 08858 on 2000 February 9. Aims: We aim to better understand the relationship between filament eruptions and the associated flares and CMEs. Methods: Using BBSO, SOHO/EIT, and TRACE observational data, we analyzed the process of the active-region filament eruption in the chromosphere and the corona. Using the SOHO/MDI magnetograms, we investigated the change of the magnetic fields in the photosphere. Using the GOES soft X-ray flux and the SOHO/LASCO images, we identified the flare and CME, which were associated with this active-region filament eruption. Results: The brightenings in the chromosphere are a precursor of the filament expansion. The eruption itself can be divided into four phases: In the initial phase, the intertwined bright and dark strands of the filament expand. Then, the bright strands are divided into three parts with different expansion velocity. Next, the erupting filament-carrying flux rope expands rapidly and combines with the lower part of the expanding bright strands. Finally, the filament erupts accompanied by other dark strands overlying the filament.The overlying magnetic loops and the expansion of the filament strands can change the direction of the eruption. Conclusions: The time delay between the velocity peaks of the filament and that of the two parts of the bright strands clearly demonstrates that the breakup of the bright loops tying on the filament into individual strands is important for its eruption. The eruption is a collection of multiple processes that are physically coupled rather than a single process.

  3. Feel the Burn: What accounts for spatial variations in coronal heating?

    NASA Astrophysics Data System (ADS)

    Atwood, Shane; Kankelborg, Charles C.

    2016-05-01

    The coronal volume is filled with magnetic field, yet only part of that volume has sufficient heating to exhibit hot x-ray loops. How does the Sun decide where the heat goes? Using XRT and AIA images and HMI magnetograms, we identify footpoints of hot coronal loops, and magnetically similar regions underlying relatively unheated corona. We then use IRIS rasters and sit-and-stare observations to compare the spatial, temporal, and spectral structure of these relatively ``heated’’ and ``unheated’’ regions. We seek a signature of upward propagating energy that could be associated with hot active region loops.

  4. Behaviour of oscillations in loop structures above active regions

    NASA Astrophysics Data System (ADS)

    Kolobov, D. Y.; Kobanov, N. I.; Chelpanov, A. A.; Kochanov, A. A.; Anfinogentov, S. A.; Chupin, S. A.; Myshyakov, I. I.; Tomin, V. E.

    2015-12-01

    In this study we combine the multiwavelength ultraviolet-optical (Solar Dynamics Observatory, SDO) and radio (Nobeyama Radioheliograph, NoRH) observations to get further insight into space-frequency distribution of oscillations at different atmospheric levels of the Sun. We processed the observational data on NOAA 11711 active region and found oscillations propagating from the photospheric level through the transition region upward into the corona. The power maps of low-frequency (1-2 mHz) oscillations reproduce well the fan-like coronal structures visible in the Fe IX 171 Å line. High frequency oscillations (5-7 mHz) propagate along the vertical magnetic field lines and concentrate inside small-scale elements in the umbra and at the umbra-penumbra boundary. We investigated the dependence of the dominant oscillation frequency upon the distance from the sunspot barycentre to estimate inclination of magnetic tubes in higher levels of sunspots where it cannot be measured directly, and found that this angle is close to 40° above the umbra boundaries in the transition region.

  5. 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.

  6. Magnetic field measurements in and above a limb active region

    NASA Astrophysics Data System (ADS)

    Philip, Judge

    2013-07-01

    We analyze spectropolarimetric data of a limb active region (NOAA 11302) obtained on September 22nd 2011 using the Facility Infrared Spectrometer (FIRS) at the Dunn Solar Telescope (DST). Stokes profiles including lines of Si I 1028.7 nm and He I 1083 nm were obtained in three scans over a 45"x75" area. Simultaneous narrow band Ca II K and G-band intensity data were acquired with a cadence of 5s at the DST. The He I data show not only typical active region polarization signatures, but also signatures in plumes -- cool post flare loops -- which extend many Mm into the corona across the visible limb. The plumes have remarkably uniform brightness, and the plume plasma is significantly Doppler shifted as it drains from the corona. Using carefully constructed observing and calibration sequences and applying Principal Component Analysis to remove instrumental artifacts, we achieved a polarization sensitivity approaching 0.02%. With this sensitivity we attempt to diagnose the vector magnetic fields and plasma properties of chromospheric and cool coronal material in and above NOAA 11302. Inversions using various radiative transfer models in the HAZEL code are remarkably consistent with the idea that plume spectra are formed in a simple, slab-like geometry, but that the ``disk'' spectra are formed under more traditional models (Milne-Eddington). The inverted magnetic data of He I lines are compared with photospheric inversions of DST Si I and Fe I data from the Solar Dynamics Observatory.

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

    NASA Technical Reports Server (NTRS)

    Guhathakurta, Madhulika

    1998-01-01

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

  8. Emerging flux in active regions. [of sun

    NASA Technical Reports Server (NTRS)

    Liggett, M.; Zirin, H.

    1985-01-01

    The rates at which flux emerges in active and quiet solar regions within the sunspot belts are compared. The emerging flux regions (EFRs) were identified by the appearance of arch filament structures in H-alpha. All EFRs in high resolution films of active regions made at Big Bear in 1978 were counted. The comparable rate of flux emergence in quiet regions was obtained from SGD data and independently from EFRs detected outside the active region perimeter on the same films. The rate of flux emergence is 10 times higher in active regions than in quiet regions. A sample of all active regions in 31 days of 1983 gave a ratio of 7.5. Possible mechanisms which might funnel new magnetic flux to regions of strong magnetic field are discussed.

  9. Emission measure distribution for diffuse regions in solar active regions

    SciTech Connect

    Subramanian, Srividya; Tripathi, Durgesh; Klimchuk, James A.; Mason, Helen E.

    2014-11-01

    Our knowledge of the diffuse emission that encompasses active regions is very limited. In this paper we investigate two off-limb active regions, namely, AR 10939 and AR 10961, to probe the underlying heating mechanisms. For this purpose, we have used spectral observations from Hinode/EIS and employed the emission measure (EM) technique to obtain the thermal structure of these diffuse regions. Our results show that the characteristic EM distributions of the diffuse emission regions peak at log T = 6.25 and the coolward slopes are in the range 1.4-3.3. This suggests that both low- as well as high-frequency nanoflare heating events are at work. Our results provide additional constraints on the properties of these diffuse emission regions and their contribution to the background/foreground when active region cores are observed on-disk.

  10. Coronal Structures in Cool Stars

    NASA Technical Reports Server (NTRS)

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

    2004-01-01

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

  11. High Spatial Resolution Fe XII Observations of Solar Active Regions

    NASA Astrophysics Data System (ADS)

    Testa, Paola; De Pontieu, Bart; Hansteen, Viggo

    2016-08-01

    We use UV spectral observations of active regions with the Interface Region Imaging Spectrograph (IRIS) to investigate the properties of the coronal Fe xii 1349.4 Å emission at unprecedented high spatial resolution (∼0.33″). We find that by using appropriate observational strategies (i.e., long exposures, lossless compression), Fe xii emission can be studied with IRIS at high spatial and spectral resolution, at least for high-density plasma (e.g., post-flare loops and active region moss). We find that upper transition region (TR; moss) Fe xii emission shows very small average Doppler redshifts ({v}{{D}} ∼ 3 km s‑1) as well as modest non-thermal velocities (with an average of ∼24 km s‑1 and the peak of the distribution at ∼15 km s‑1). The observed distribution of Doppler shifts appears to be compatible with advanced three-dimensional radiative MHD simulations in which impulsive heating is concentrated at the TR footpoints of a hot corona. While the non-thermal broadening of Fe xii 1349.4 Å peaks at similar values as lower resolution simultaneous Hinode Extreme Ultraviolet Imaging Spectrometer (EIS) measurements of Fe xii 195 Å, IRIS observations show a previously undetected tail of increased non-thermal broadening that might be suggestive of the presence of subarcsecond heating events. We find that IRIS and EIS non-thermal line broadening measurements are affected by instrumental effects that can only be removed through careful analysis. Our results also reveal an unexplained discrepancy between observed 195.1/1349.4 Å Fe xii intensity ratios and those predicted by the CHIANTI atomic database.

  12. High Spatial Resolution Fe XII Observations of Solar Active Regions

    NASA Astrophysics Data System (ADS)

    Testa, Paola; De Pontieu, Bart; Hansteen, Viggo

    2016-08-01

    We use UV spectral observations of active regions with the Interface Region Imaging Spectrograph (IRIS) to investigate the properties of the coronal Fe xii 1349.4 Å emission at unprecedented high spatial resolution (˜0.33″). We find that by using appropriate observational strategies (i.e., long exposures, lossless compression), Fe xii emission can be studied with IRIS at high spatial and spectral resolution, at least for high-density plasma (e.g., post-flare loops and active region moss). We find that upper transition region (TR; moss) Fe xii emission shows very small average Doppler redshifts ({v}{{D}} ˜ 3 km s‑1) as well as modest non-thermal velocities (with an average of ˜24 km s‑1 and the peak of the distribution at ˜15 km s‑1). The observed distribution of Doppler shifts appears to be compatible with advanced three-dimensional radiative MHD simulations in which impulsive heating is concentrated at the TR footpoints of a hot corona. While the non-thermal broadening of Fe xii 1349.4 Å peaks at similar values as lower resolution simultaneous Hinode Extreme Ultraviolet Imaging Spectrometer (EIS) measurements of Fe xii 195 Å, IRIS observations show a previously undetected tail of increased non-thermal broadening that might be suggestive of the presence of subarcsecond heating events. We find that IRIS and EIS non-thermal line broadening measurements are affected by instrumental effects that can only be removed through careful analysis. Our results also reveal an unexplained discrepancy between observed 195.1/1349.4 Å Fe xii intensity ratios and those predicted by the CHIANTI atomic database.

  13. THE LIMIT OF MAGNETIC-SHEAR ENERGY IN SOLAR ACTIVE REGIONS

    SciTech Connect

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

    2012-05-01

    It has been found previously, by measuring from active-region magnetograms a proxy of the free energy in the active region's magnetic field, (1) that there is a sharp upper limit to the free energy the field can hold that increases with the amount of magnetic field in the active region, the active region's magnetic flux content, and (2) that most active regions are near this limit when their field explodes in a coronal mass ejection/flare eruption. That is, explosive active regions are concentrated in a main-sequence path bordering the free-energy-limit line in (flux content, free-energy proxy) phase space. Here, we present evidence that specifies the underlying magnetic condition that gives rise to the free-energy limit and the accompanying main sequence of explosive active regions. Using a suitable free-energy proxy measured from vector magnetograms of 44 active regions, we find evidence that (1) in active regions at and near their free-energy limit, the ratio of magnetic-shear free energy to the non-free magnetic energy the potential field would have is of the order of one in the core field, the field rooted along the neutral line, and (2) this ratio is progressively less in active regions progressively farther below their free-energy limit. Evidently, most active regions in which this core-field energy ratio is much less than one cannot be triggered to explode; as this ratio approaches one, most active regions become capable of exploding; and when this ratio is one, most active regions are compelled to explode.

  14. The Limit of Magnetic-Shear Energy in Solar Active Regions

    NASA Technical Reports Server (NTRS)

    Moore, Ronald; Falconer, David; Sterling, Alphonse

    2012-01-01

    It has been found previously, by measuring from active-region magnetograms a proxy of the free energy in the active region's magnetic field, (1) that there is a sharp upper limit to the free energy the field can hold that increases with the amount of magnetic field in the active region, the active region's magnetic flux content, and (2) that most active regions are near this limit when their field explodes in a coronal mass ejection/flare eruption. That is, explosive active regions are concentrated in a main-sequence path bordering the free-energy-limit line in (flux content, free-energy proxy) phase space. Here, we present evidence that specifies the underlying magnetic condition that gives rise to the free-energy limit and the accompanying main sequence of explosive active regions. Using a suitable free-energy proxy measured from vector magnetograms of 44 active regions, we find evidence that (1) in active regions at and near their free-energy limit, the ratio of magnetic-shear free energy to the non-free magnetic energy the potential field would have is of the order of one in the core field, the field rooted along the neutral line, and (2) this ratio is progressively less in active regions progressively farther below their free-energy limit. Evidently, most active regions in which this core-field energy ratio is much less than one cannot be triggered to explode; as this ratio approaches one, most active regions become capable of exploding; and when this ratio is one, most active regions are compelled to explode.

  15. Coronal Loops: New Insights from EIS Observations

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

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

  16. How Did a Major Confined Flare Occur in Super Solar Active Region 12192?

    NASA Astrophysics Data System (ADS)

    Jiang, Chaowei; Wu, S. T.; Yurchyshyn, Vasyl; Wang, Haiming; Feng, Xueshang; Hu, Qiang

    2016-09-01

    We study the physical mechanism of a major X-class solar flare that occurred in the super NOAA active region (AR) 12192 using data-driven numerical magnetohydrodynamic (MHD) modeling complemented with observations. With the evolving magnetic fields observed at the solar surface as bottom boundary input, we drive an MHD system to evolve self-consistently in correspondence with the realistic coronal evolution. During a two-day time interval, the modeled coronal field has been slowly stressed by the photospheric field evolution, which gradually created a large-scale coronal current sheet, i.e., a narrow layer with intense current, in the core of the AR. The current layer was successively enhanced until it became so thin that a tether-cutting reconnection between the sheared magnetic arcades was set in, which led to a flare. The modeled reconnecting field lines and their footpoints match well the observed hot flaring loops and the flare ribbons, respectively, suggesting that the model has successfully “reproduced” the macroscopic magnetic process of the flare. In particular, with simulation, we explained why this event is a confined eruption—the consequence of the reconnection is a shared arcade instead of a newly formed flux rope. We also found a much weaker magnetic implosion effect compared to many other X-class flares.

  17. Photospheric Vector Magnetic Field Evolution of NOAA Active Region 11504 and the Ensuing CME

    NASA Astrophysics Data System (ADS)

    James, Alexander; Green, Lucie; Valori, Gherardo; van Driel-Gesztelyi, Lidia; Baker, Deborah; Brooks, David; Palmerio, Erika

    2016-05-01

    Coronal mass ejections (CMEs) are eruptions of billions of tonnes of plasma from the Sun that drive the most severe space weather effects we observe. In order to be able to produce forecasts of space weather with lead times of the order of days, accurate predictions of the occurrence of CMEs must be developed. The eruptive active-region studied in this work (NOAA 11504) is complex, featuring fragmentation of penumbral magnetic field in the days prior to eruption, as well as rotation of the leading sunspot. SDO/HMI vector photospheric magnetic field measurements are utilised alongside SDO/AIA multi-wavelength extreme ultra-violet (EUV) observations to study the dynamics of the photospheric and coronal structures, as well as Hinode/EIS spectroscopic measurements, including elemental composition data. The EUV data show flare ribbons as well as coronal dimmings, which are used to infer the orientation of the erupting flux rope. This flux rope orientation is then compared to in situ measurements of the flux rope. The vector magnetic field data is used to determine the possible contributions the field fragmentation and sunspot rotation may have made to the formation of the flux rope and the triggering of the CME.

  18. A Series of Jets that Drove Streamer-Puff CMEs from Giant Active Region of 2014

    NASA Technical Reports Server (NTRS)

    Panesar, Navdeep K.; Sterling, Alphonse C.; Moore, Ronald L.

    2016-01-01

    We investigate characteristics of solar coronal jets that originated from active region NOAA 12192 and produced coronal mass ejections (CMEs). This active region produced many non-jet major flare eruptions (X and M class) that made no CME. A multiitude of jets occurred from the southeast edge of the active region, and in contrast to the major-flare eruptions in the core, six of these jets resulted in CMEs. Our jet observations are from multiple SDO/AIA EUV channels, including 304, 171 and 193 Angstrom, and CME observations are taken from SOHO/LASCO C2 coronograph. Each jet-driven CME was relatively slow-moving (approximately 200 - 300 km s(sup-1) compared to most CMEs; had angular width (20deg - 50deg) comparable to that of the streamer base; and was of the "streamer-puff" variety, whereby a preexisting streamer was transiently inflated but not removed (blown out) by the passage of the CME. Much of the chromospheric-temperature plasma of the jets producing the CMEs escaped from the Sun, whereas relatively more of the chromospheric plasma in the non-CME-producing jets fell back to the solar surface. We also found that the CME-producing jets tended to be faster in speed and longer in duration than the non-CME-producing jets. We expect that the jets result from eruptions of mini-filaments. We further propose that the CMEs are driven by magnetic twist injected into streamer-base coronal loops when erupting twisted mini-filament field reconnects with the ambient field at the foot of those loops.

  19. A Series of Jets that Drove Streamer-Puff CMEs from Giant Active Region of 2014

    NASA Technical Reports Server (NTRS)

    Panesar, Navdeep K.; Sterling, Alphonse C.; Moore, Ronald L.

    2016-01-01

    We investigate characteristics of solar coronal jets that originated from active region NOAA 12192 and produced coronal mass ejections (CMEs). This active region produced many non­-jet major flare eruptions (X and M class) that made no CME. A multitude of jets occurred from the southeast edge of the active region, and in contrast to the major-­flare eruptions in the core, six of these jets resulted in CMEs. Our jet observations are from SDO/AIA EUV channels and from Hinode/XRT, and CME observations are from the SOHO/LASCO C2 coronograph. Each jet-­driven CME was relatively slow-­moving (approx. 200 - 300 km/s) compared to most CMEs; had angular width (20deg - 50deg) comparable to that of the streamer base; and was of the "streamer­-puff" variety, whereby a pre-existing streamer was transiently inflated but not removed (blown out) by the passage of the CME. Much of the chromospheric-­temperature plasma of the jets producing the CMEs escaped from the Sun, whereas relatively more of the chromospheric plasma in the non-CME-producing jets fell back to the solar surface. We also found that the CME-producing jets tended to be faster in speed and longer in duration than the non-CME-­producing jets. We expect that the jets result from eruptions of mini-filaments. We further propose that the CMEs are driven by magnetic twist injected into streamer-­base coronal loops when erupting twisted mini-filament field reconnects with the ambient field at the foot of those loops.

  20. A Series of Streamer-Puff CMEs Driven by Solar Homologous Jets from Active Region 12192

    NASA Astrophysics Data System (ADS)

    Panesar, Navdeep K.; Sterling, Alphonse C.; Moore, Ronald L.

    2016-05-01

    We investigate characteristics of solar coronal jets that originated from active region NOAA 12192 and produced coronal mass ejections (CMEs). This active region produced many non-jet major flare eruptions (X and M class) that made no CME. A multitude of jets occurred from the southeast edge of the active region, and in contrast to the major-flare eruptions in the core, six of these jets resulted in CMEs. Our jet observations are from multiple SDO/AIA EUV channels, including 304, 171 and 193Å, and CME observations are taken from SOHO/LASCO C2 coronograph. Each jet-driven CME was relatively slow-moving (~200 - 300 km s-1) compared to most CMEs; had angular width (20° – 50°) comparable to that of the streamer base; and was of the “streamer-puff” variety, whereby a preexisting streamer was transiently inflated but not removed (blown out) by the passage of the CME. Much of the chromospheric-temperature plasma of the jets producing the CMEs escaped from the Sun, whereas relatively more of the chromospheric plasma in the non-CME-producing jets fell back to the solar surface. We also found that the CME-producing jets tended to be faster in speed and longer in duration than the non-CME-producing jets. We expect that the jets result from eruptions of minifilaments (Sterling et al. 2015). We further propose that the CMEs are driven by magnetic twist injected into streamer-base coronal loops when erupting-twisted-minifilament field reconnects with the ambient field at the foot of those loops. This research was supported by funding from NASA's LWS program.

  1. The morphology of flare phenomena, magnetic fields, and electric currents in active regions. III - NOAA active region 6233 (1990 August)

    NASA Technical Reports Server (NTRS)

    De La Beaujardiere, J.-F.; Canfield, Richard C.; Leka, K. D.

    1993-01-01

    We investigate the spatial relationship between vertical electric currents and flare phenomena in NOAA Active Region 6233, which was observed 1990, August 28-31 at Mees Solar Observatory. The two flares studied are the 1N/M1.8 flare on August 28, 22:30 UT and the 1N/M1.6 flare on August 29, 20:35 UT. Using Stokes polarimetry we make magnetograms of the region and compute the vertical current density. Using H-alpha imaging spectroscopy we identify sites of intense nonthermal electron precipitation or of high coronal pressure. The precipitation in these flares is barely strong enough to be detectable. We find that both precipitation and high pressure tend to occur near vertical currents, but that neither phenomenon is cospatial with current maxima. In contrast with the conclusion of other authors, we argue that these observations do not support a current-interruption model for flares, unless the relevant currents are primarily horizontal. The magnetic morphology and temporal evolution of these flares suggest that an erupting filament model may be relevant, but this model does not explicitly predict the relationship between precipitation, high pressure, and vertical currents.

  2. 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.

  3. 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.

  4. Measurements of Non-thermal Line Widths in Solar Active Regions

    NASA Astrophysics Data System (ADS)

    Brooks, David H.; Warren, Harry P.

    2016-03-01

    Spectral line widths are often observed to be larger than can be accounted for by thermal and instrumental broadening alone. This excess broadening is a key observational constraint for both nanoflare and wave dissipation models of coronal heating. Here we present a survey of non-thermal velocities measured in the high temperature loops (1-4 MK) often found in the cores of solar active regions. This survey of Hinode Extreme Ultraviolet Imaging Spectrometer (EIS) observations covers 15 non-flaring active regions that span a wide range of solar conditions. We find relatively small non-thermal velocities, with a mean value of 17.6 ± 5.3 km s-1, and no significant trend with temperature or active region magnetic flux. These measurements appear to be inconsistent with those expected from reconnection jets in the corona, chromospheric evaporation induced by coronal nanoflares, and Alfvén wave turbulence models. Furthermore, because the observed non-thermal widths are generally small, such measurements are difficult and susceptible to systematic effects.

  5. 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.

  6. Out-of-ecliptic studies of coronal holes and their relation to the solar wind. [project planning for solar probes to study solar activity

    NASA Technical Reports Server (NTRS)

    Noyes, R. W.

    1976-01-01

    The advantages of observing coronal holes of the sun above the solar ecliptic plane by a solar probe are discussed. Also discussed are the size of coronal holes, their temperature, and magnetic fields associated with the holes. The role of coronal holes in contributing to the solar wind is examined. Data and observations on coronal holes from Skylab and OSO are treated. It is concluded that an out-of-the-ecliptic solar probe mission would greatly add to the understanding of coronal holes (at high latitudes) thus adding a new perspective to the observation of these phenomena. (Photographs of the sun taken by Skylab are shown).

  7. The Twist Limit for Bipolar Active Regions

    NASA Technical Reports Server (NTRS)

    Moore, Ron; Falconer, David; Gary, Allen

    2008-01-01

    We present new evidence that further supports the standard idea that active regions are emerged magnetic-flux-rope omega loops. When the axial magnetic twist of a cylindrical flux rope exceeds a critical amount, the flux rope becomes unstable to kinking, and the excess axial twist is converted into writhe twist by the kinking. This suggests that, if active regions are emerged omega loops, then (1) no active region should have magnetic twist much above the limit set by kinking, (2) active regions having twist near the limit should often arise from kinked omega loops, and (3) since active regions having large delta sunspots are outstandingly twisted, these arise from kinked omega loops and should have twist near the limit for kinking. From each of 36 vector magnetograms of bipolar active regions, we have measured (1) the total flux of the vertical field above 100 G, (2) the area covered by this flux, and (3) the net electric current that arches over the polarity inversion line. These three quantities yield an estimate of the axial magnetic twist in a simple model cylindrical flux rope that corresponds to the top of the active region s hypothetical omega loop prior to emergence. In all 36 cases, the estimated twist is below the critical limit for kinking. The 11 most twisted active regions (1) have estimated twist within a factor of approx.3 of the limit, and (2) include all of our 6 active regions having large delta sunspots. Thus, our observed twist limit for bipolar active regions is in good accord with active regions being emerged omega loops.

  8. Coronal structures deduced from photospheric magnetic field and He I lambda 10830 observations

    NASA Technical Reports Server (NTRS)

    Harvey, Karen L.

    1995-01-01

    The National Solar Observatory synoptic program provides an extensive and unique data base of high-resolution full-disk observations of the line-of-sight photospheric magnetic fields and of the He I lambda 10830 equivalent width. These data have been taken nearly daily for more than 21 years since 1974 and provide the opportunity to investigate the behavior of the magnetic fields in the photosphere and those inferred for the corona spanning on the time scales of a day to that of a solar cycle. The intensity of structures observed in He I lambda 10830 are strongly modulated by overlying coronal radiation; areas with low coronal emission are generally brighter in He I lambda 10830, while areas with high coronal emission are darker. For this reason, He I lambda 10830 was selected in the mid-1970's as way to identify and monitor coronal holes, magnetic fields with an open configuration, and the sources of high-speed solar wind streams. The He I lambda 10830 spectroheliograms also show a wide variety of other structures from small-scale, short-lived dark points (less than 30 arc-sec, hours) to the large-scale, long-lived two 'ribbon' flare events that follow the filament eruptions (1000 arc-sec, days). Such structures provide clues about the connections and changes in the large-scale coronal magnetic fields that are rooted in concentrations of magnetic network and active regions in the photosphere. In this paper, what observations of the photospheric magnetic field and He I lambda 10830 can tell us about the short- and long-term evolution of the coronal magnetic fields will be discussed, focussing on the quiet Sun and coronal holes. These data and what we infer from them will be compared with direct observations of the coronal structure from the Yohkoh Soft X-ray Telescope.

  9. TRIGGER MECHANISM OF SOLAR SUBFLARES IN A BRAIDED CORONAL MAGNETIC STRUCTURE

    SciTech Connect

    Tiwari, Sanjiv K.; Alexander, Caroline E.; Winebarger, Amy R.; Moore, Ronald L.

    2014-11-01

    Fine-scale braiding of coronal magnetic loops by continuous footpoint motions may power coronal heating via nanoflares, which are spontaneous fine-scale bursts of internal reconnection. An initial nanoflare may trigger an avalanche of reconnection of the braids, making a microflare or larger subflare. In contrast to this internal triggering of subflares, we observe external triggering of subflares in a braided coronal magnetic field observed by the High-resolution Coronal Imager (Hi-C). We track the development of these subflares using 12 s cadence images acquired by SDO/AIA in 1600, 193, 94 Å, and registered magnetograms of SDO/HMI, over four hours centered on the Hi-C observing time. These data show numerous recurring small-scale brightenings in transition-region emission happening on polarity inversion lines where flux cancellation is occurring. We present in detail an example of an apparent burst of reconnection of two loops in the transition region under the braided coronal field which is appropriate for releasing a short reconnected loop downward and a longer reconnected loop upward. The short loop presumably submerges into the photosphere, participating in observed flux cancellation. A subflare in the overlying braided magnetic field is apparently triggered by the disturbance of the braided field by the reconnection-released upward loop. At least 10 subflares observed in this braided structure appear to be triggered this way. How common this external trigger mechanism for coronal subflares is in other active regions, and how important it is for coronal heating in general, remain to be seen.

  10. 3D reconstruction methods of coronal structures by radio observations

    NASA Astrophysics Data System (ADS)

    Aschwanden, Markus J.; Bastian, T. S.; White, Stephen M.

    1992-11-01

    The ability to carry out the three dimensional (3D) reconstruction of structures in the solar corona would represent a major advance in the study of the physical properties in active regions and in flares. Methods which allow a geometric reconstruction of quasistationary coronal structures (for example active region loops) or dynamic structures (for example flaring loops) are described: stereoscopy of multi-day imaging observations by the VLA (Very Large Array); tomography of optically thin emission (in radio or soft x-rays); multifrequency band imaging by the VLA; and tracing of magnetic field lines by propagating electron beams.

  11. 3D reconstruction methods of coronal structures by radio observations

    NASA Technical Reports Server (NTRS)

    Aschwanden, Markus J.; Bastian, T. S.; White, Stephen M.

    1992-01-01

    The ability to carry out the three dimensional (3D) reconstruction of structures in the solar corona would represent a major advance in the study of the physical properties in active regions and in flares. Methods which allow a geometric reconstruction of quasistationary coronal structures (for example active region loops) or dynamic structures (for example flaring loops) are described: stereoscopy of multi-day imaging observations by the VLA (Very Large Array); tomography of optically thin emission (in radio or soft x-rays); multifrequency band imaging by the VLA; and tracing of magnetic field lines by propagating electron beams.

  12. Eddy viscosity and flow properties of the solar wind: Co-rotating interaction regions, coronal-mass-ejection sheaths, and solar-wind/magnetosphere coupling

    SciTech Connect

    Borovsky, Joseph E.

    2006-05-15

    The coefficient of magnetohydrodynamic (MHD) eddy viscosity of the turbulent solar wind is calculated to be {nu}{sub eddy}{approx_equal}1.3x10{sup 17} cm{sup 2}/s: this coefficient is appropriate for velocity shears with scale thicknesses larger than the {approx}10{sup 6} km correlation length of the solar-wind turbulence. The coefficient of MHD eddy viscosity is calculated again accounting for the action of smaller-scale turbulent eddies on smaller scale velocity shears in the solar wind. This eddy viscosity is quantitatively tested with spacecraft observations of shear flows in co-rotating interaction regions (CIRs) and in coronal-mass-ejection (CME) sheaths and ejecta. It is found that the large-scale ({approx}10{sup 7} km) shear of the CIR fractures into intense narrow ({approx}10{sup 5} km) slip zones between slabs of differently magnetized plasma. Similarly, it is found that the large-scale shear of CME sheaths also fracture into intense narrow slip zones between parcels of differently magnetized plasma. Using the solar-wind eddy-viscosity coefficient to calculate vorticity-diffusion time scales and comparing those time scales with the {approx}100-h age of the solar-wind plasma at 1 AU, it is found that the slip zones are much narrower than eddy-viscosity theory says they should be. Thus, our concept of MHD eddy viscosity fails testing. For the freestream turbulence effect in solar-wind magnetosphere coupling, the eddy-viscous force of the solar wind on the Earth's magnetosphere is rederived accounting for the action of turbulent eddies smaller than the correlation length, along with other corrections. The improved derivation of the solar-wind driver function for the turbulence effect fails to yield higher correlation coefficients between measurements of the solar-wind driver and measurements of the response of the Earth's magnetosphere.

  13. Analysis of a coronal mass ejection and corotating interaction region as they travel from the Sun passing Venus, Earth, Mars, and Saturn

    NASA Astrophysics Data System (ADS)

    Prise, A. J.; Harra, L. K.; Matthews, S. A.; Arridge, C. S.; Achilleos, N.

    2015-03-01

    During June 2010 a good alignment in the solar system between Venus, STEREO-B, Mars, and Saturn provided an excellent opportunity to study the propagation of a coronal mass ejection (CME) and closely occurring corotating interaction region (CIR) from the Sun to Saturn. The CME erupted from the Sun at 01:30 UT on 20 June 2010,with v≈ 600 km s-1, as observed by STEREO-B, Solar Dynamics Observatory, and SOHO/Large Angle and Spectrometric Coronagraph. It arrived at Venus over 2 days later, some 3.5 days after a CIR is also detected here. The CIR was also observed at STEREO-B and Mars, prior to the arrival of the CME. The CME is not directed earthward, but the CIR is detected here less than 2 days after its arrival at Mars. Around a month later, a strong compression of the Saturn magnetosphere is observed by Cassini, consistent with the scenario that the CME and CIR have merged into a single solar transient. The arrival times of both the CME and the CIR at different locations were predicted using the ENLIL solar wind model. The arrival time of the CME at Venus, STEREO-B, and Mars is predicted to within 20 h of its actual detection, but the predictions for the CIR showed greater differences from observations, all over 1.5 days early. More accurate predictions for the CIR were found by extrapolating the travel time between different locations using the arrival times and speeds detected by STEREO-B and ACE. We discuss the implications of these results for understanding the propagation of solar transients.

  14. Simultaneous Solar Maximum Mission (SMM) and very large array observations of solar active regions

    NASA Technical Reports Server (NTRS)

    Lang, K. R.

    1986-01-01

    The research deals mainly with Very Large Array and Solar Maximum Mission observations of the ubiquitous coronal loops that dominate the structure of the low corona. As illustrated, the observations of thermal cyclotron lines at microwave wavelengths provide a powerful new method of accurately specifying the coronal magnetic field strength. Processes are delineated that trigger solar eruptions from coronal loops, including preburst heating and the magnetic interaction of coronal loops. Evidence for coherent burst mechanisms is provided for both the Sun and nearby stars, while other observations suggest the presence of currents that may amplify the coronal magnetic field to unexpectedly high levels. The existence is reported of a new class of compact, variable moving sources in regions of apparently weak photospheric field.

  15. Turbulence and Heating in the Side and Wake Regions of Coronal Mass Ejection in the Low Corona

    NASA Astrophysics Data System (ADS)

    Fan, S.; He, J.; Yan, L.; Zhang, L.; Tomczyk, S.

    2014-12-01

    Ahead of CMEs usually exist the shocked sheaths, in which the background solar corona / solar wind is heated due to the compression of the driving CME. The other regions around the CME, e.g., the side and wake, which may also be influenced by the CME, are the objects of this work. Various instruments including LASCO, AIA, and CoMP observed a CME close to the east limb on October 26th, 2013. The CME core is very hot (~10 MK) (appearing only in the 131 channel of AIA), and ejects away at a high speed (~330 km/s). Magnetic structures (low-lying loops and large loop legs) on both sides and in the wake of the CME are strongly disturbed, showing turbulent signatures with enhanced Doppler-shift oscillations (~±15km/s) and effective thermal velocities (~60 km/s) from the CoMP observations in the Fe XIII line. As recognized from the CoMP Doppler-shift maps, the turbulent vortices behave differently at various heights, illustrating torsional oscillations back and forth around the leg axis at lower altitude and continuous rotation with the same handedness at higher altitude. This difference may be due to the lower part being more likely to be line-tied with the motionless footpoint than the upper part. The turbulence of loop legs is also revealed in the AIA animations in the Fe 171 Å and Fe 193 Å channels with some differences between each other. The turbulence in Fe 171 Å seems to be weaker than that in Fe 193 Å, with the former behaving more wave-like and the latter involving more whirling vortices. The difference in turbulence level might come from the difference in turnover time of the vortices: ~1000s for Fe 171 Å and ~500s for Fe 193 Å. Moreover, in the wake of the CME, the eddies turning over up and down as well as the eddies rotating horizontally are also presented in the Fe 193 Å. The leg-like straps in Fe 171 Å seem to be braided by the turbulent vortices, and disappear afterwards probably due to heating by coherent current sheet formed between braided

  16. A Space Weather mission concept: Observatories of the Solar Corona and Active Regions (OSCAR)

    NASA Astrophysics Data System (ADS)

    Strugarek, Antoine; Janitzek, Nils; Lee, Arrow; Löschl, Philipp; Seifert, Bernhard; Hoilijoki, Sanni; Kraaikamp, Emil; Isha Mrigakshi, Alankrita; Philippe, Thomas; Spina, Sheila; Bröse, Malte; Massahi, Sonny; O'Halloran, Liam; Pereira Blanco, Victor; Stausland, Christoffer; Escoubet, Philippe; Kargl, Günter

    2015-02-01

    Coronal Mass Ejections (CMEs) and Corotating Interaction Regions (CIRs) are major sources of magnetic storms on Earth and are therefore considered to be the most dangerous space weather events. The Observatories of Solar Corona and Active Regions (OSCAR) mission is designed to identify the 3D structure of coronal loops and to study the trigger mechanisms of CMEs in solar Active Regions (ARs) as well as their evolution and propagation processes in the inner heliosphere. It also aims to provide monitoring and forecasting of geo-effective CMEs and CIRs. OSCAR would contribute to significant advancements in the field of solar physics, improvements of the current CME prediction models, and provide data for reliable space weather forecasting. These objectives are achieved by utilising two spacecraft with identical instrumentation, located at a heliocentric orbital distance of 1 AU from the Sun. The spacecraft will be separated by an angle of 68° to provide optimum stereoscopic view of the solar corona. We study the feasibility of such a mission and propose a preliminary design for OSCAR.

  17. Static and Impulsive Models of Solar Active Regions

    NASA Technical Reports Server (NTRS)

    Patsourakos, S.; Klimchuk, James A.

    2008-01-01

    The physical modeling of active regions (ARs) and of the global coronal is receiving increasing interest lately. Recent attempts to model ARs using static equilibrium models were quite successful in reproducing AR images of hot soft X-ray (SXR) loops. They however failed to predict the bright EUV warm loops permeating ARs: the synthetic images were dominated by intense footpoint emission. We demonstrate that this failure is due to the very weak dependence of loop temperature on loop length which cannot simultaneously account for both hot and warm loops in the same AR. We then consider time-dependent AR models based on nanoflare heating. We demonstrate that such models can simultaneously reproduce EUV and SXR loops in ARs. Moreover, they predict radial intensity variations consistent with the localized core and extended emissions in SXR and EUV AR observations respectively. We finally show how the AR morphology can be used as a gauge of the properties (duration, energy, spatial dependence, repetition time) of the impulsive heating.

  18. The temperature structure and pressure balance of magnetic loops in active regions. [in solar atmosphere

    NASA Technical Reports Server (NTRS)

    Foukal, P.

    1975-01-01

    EUV observations show many active region loops in lines formed at temperatures between 10,000 and 2,000,000 K. The brightest loops are associated with flux tubes leading to the umbrae of sunspots. It is shown that the high visibility of certain loops in transition region lines is due principally to a sharp radial decrease of temperature to chromospheric values toward the loop axis. The plasma density of these cool loops is not significantly greater than in the hot gas immediately surrounding it. Consequently, the internal gas pressure of the cool material is clearly lower. The hot material immediately surrounding the cool loops is generally denser than the external corona by a factor 3-4. When the active region is examined in coronal lines, this hot high pressure plasma shows up as loops that are generally parallel to the cool loops but significantly displaced laterally.

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

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

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

  20. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2010-06-01

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

  2. Coronal magnetic fields and the solar wind

    NASA Technical Reports Server (NTRS)

    Newkirk, G., Jr.

    1972-01-01

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

  3. 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.

  4. Too big to fail: The role of magnetic structure and dynamics in super active regions, on the Sun and Sun-like stars

    NASA Astrophysics Data System (ADS)

    McAteer, R. T. James

    2015-08-01

    Accurate and timely solar activity forecasting has proved to be illusive. Despite many decades of research, we are not much further advanced in our forecasting efforts of the occurrence of solar activity than we were two decades ago. However, one aspect has become clear - big, complex magnetic active regions on the Sun inevitably produce big, complex solar flares and coronal mass ejections. Here, I present observations and models that show why these super active regions are too big to fail.First I focus on studies of the largest active regions of solar cycle 23 and 24, comparing proxies of non-potential magnetic structure in these regions with similar proxies in less active regions of the Sun. This shows that the necessary and sufficient conditions exist in these super active regions to provide both the largest solar flares and large, fast, coronal mass ejections.Second I show why these conditions in super active regions differ so dramatically from the conditions in smaller, less active, regions of the Sun. This uses magnetic feature tracking to infer the Poynting flux injected into the corona, and DEM analysis to provide radiative and conductive loss estimates from the corona. The difference between energy injected, and energy lost, is stored in the coronal magnetic field structure in the super active regions.Finally, I apply this this research to Kepler starspots , showing why these regions must differ in a fundamental way in order to overcome the limitations that super granular flow places on solar active regions formation and energy storage.

  5. 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.

  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. Magnetic Structure of Sites of Braiding in Hi-C Active Region

    NASA Technical Reports Server (NTRS)

    Tiwari, S. K.; Alexander, C. E.; Winebarger, A.; Moore, R. L.

    2014-01-01

    High-resolution Coronal Imager (Hi-C) observations of an active region (AR) corona, at a spatial resolution of 0.2 arcsec, have offered the first direct evidence of field lines braiding, which could deliver sufficient energy to heat the AR corona by current dissipation via magnetic reconnection, a proposal given by Parker three decades ago. The energy required to heat the corona must be transported from the photosphere along the field lines. The mechanism that drives the energy transport to the corona is not yet fully understood. To investigate simultaneous magnetic and intensity structure in and around the AR in detail, we use SDO/HMI+AIA data of + / - 2 hours around the 5 minute Hi-C flight. In the case of the QS, work done by convection/granulation on the inter-granular feet of the coronal field lines probably translates into the heat observed in the corona. In the case of the AR, as here, there could be flux emergence, cancellation/submergence, or shear flows generating large stress and tension in coronal field loops which is released as heat in the corona. However, to the best of our knowledge, there is no observational evidence available to these processes. We investigate the changes taking place in the photospheric feet of the magnetic field involved with brightenings in the Hi-C AR corona. Using HMI 45s magnetograms of four hours we find that, out of the two Hi-C sub-regions where the braiding of field lines were recently detected, flux emergence takes place in one region and flux cancellation in the other. The field in these sub-regions are highly sheared and have apparent high speed plasma flows at their feet. Therefore, shearing flows plausibly power much of the coronal and transition region heating in these areas of the AR. In addition, the presence of large flux emergence/cancellation strongly suggests that the work done by these processes on the pre-existing field also drives much of the observed heating.

  8. 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.

  9. Large-scale coronal structures in EUV and soft X-rays in solar cycle 23

    NASA Astrophysics Data System (ADS)

    Benevolenskaya, E. E.; Kosovichev, A. G.; Scherrer, P. H.; Lemen, J. R.; Slater, G. L.

    2002-06-01

    We have analyzed the EIT/SOHO data in four EUV lines (171 Å, 195 Å, 284 Å and 304 Å) and soft X-ray YOHKOH data in two filters (AlMg and Al) in the form of coronal synoptic maps for the period 1996 - 2001 yrs. Two types of the bright structures have been detected in EUV in the axisymmetrically averaged synoptic maps. The structures of the first type migrate equatorward as the solar cycle progresses. They are related to complexes of sunspot activity and display the "butterfly"-type distribution. The structures of the second type migrate polarward and are associated with footpoints of giant coronal loops, which connect the polar regions and the following parts of the active complexes. These structures of coronal activity are also pronounced in the soft X-ray maps. However, the whole structure of the giant polar loops is visible in X-rays, and reveals connections to the low-latitude coronal structures. The relationship between the soft X-rays emission and the photospheric magnetic flux obtained from SOHO/MDI and Kitt Peak Solar Observatory has been investigated. It has been found that the relationship depends on the phase of the solar cycle. We discuss the role of the magnetic flux in the formation and evolution of the stable coronal structures during the rising phase of cycle 23.

  10. Why Is the Great Solar Active Region 12192 Flare-rich but CME-poor?

    NASA Astrophysics Data System (ADS)

    Sun, Xudong; Bobra, Monica G.; Hoeksema, J. Todd; Liu, Yang; Li, Yan; Shen, Chenglong; Couvidat, Sebastien; Norton, Aimee A.; Fisher, George H.

    2015-05-01

    Solar active region (AR) 12192 of 2014 October hosts the largest sunspot group in 24 years. It is the most prolific flaring site of Cycle 24 so far, but surprisingly produced no coronal mass ejection (CME) from the core region during its disk passage. Here, we study the magnetic conditions that prevented eruption and the consequences that ensued. We find AR 12192 to be “big but mild” its core region exhibits weaker non-potentiality, stronger overlying field, and smaller flare-related field changes compared to two other major flare-CME-productive ARs (11429 and 11158). These differences are present in the intensive-type indices (e.g., means) but generally not the extensive ones (e.g., totals). AR 12192's large amount of magnetic free energy does not translate into CME productivity. The unexpected behavior suggests that AR eruptiveness is limited by some relative measure of magnetic non-potentiality over the restriction of background field, and that confined flares may leave weaker photospheric and coronal imprints compared to their eruptive counterparts.

  11. Why Is the Great Solar Active Region 12192 CME-Poor?

    NASA Astrophysics Data System (ADS)

    Sun, Xudong; Bobra, Monica G.; Hoeksema, Todd; Liu, Yang; Li, Yan; Shen, Chenglong; Couvidat, Sebastien; Norton, Aimee A.; Fisher, George H.

    2015-04-01

    Solar active region (AR) 12192 of October 2014 hosts the largest sunspot group in 24 years. It is the most prolific flaring site of Cycle 24, but surprisingly produced no coronal mass ejection (CME) from the core region during its disk passage. Here, we study the magnetic conditions that prevented eruption and the consequences that ensued. We find AR 12192 to be "big but mild"; its core region exhibits weaker non-potentiality, stronger overlying field, and smaller flare-related field changes compared to two other major flare-CME-productive ARs (11429 and 11158). These differences are present in the intensive-type indices (e.g., means) but generally not the extensive ones (e.g., totals). AR 12192's large amount of magnetic free energy does not translate into CME productivity. The unexpected behavior suggests that AR eruptiveness is limited by some relative measure of magnetic non-potentiality over the restriction of background field, and that confined flares may leave weaker photospheric and coronal imprints compared to their eruptive counterparts.

  12. Normal incidence X-ray telescope power spectra of X-ray emission from solar active regions. I - Observations. II - Theory

    NASA Technical Reports Server (NTRS)

    Gomez, Daniel O.; Martens, Petrus C. H.; Golub, Leon

    1993-01-01

    Fourier analysis is applied to very high resolution image of coronal active regions obtained by the Normal Incidence X-Ray Telescope is used to find a broad isotropic power-law spectrum of the spatial distribution of soft X-ray intensities. Magnetic structures of all sizes are present down to the resolution limit of the instrument. Power spectra for the X-ray intensities of a sample of topologically different active regions are found which fall off with increasing wavenumber as 1/k-cubed. A model is presented that relates the basic features of coronal magnetic fluctuations to the subphotospheric hydrodynamic turbulence that generates them. The model is used to find a theoretical power spectrum for the X-ray intensity which falls off with increasing wavenumber as 1/k-cubed. The implications of a turbulent regime in active regions are discussed.

  13. 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

    -vanishing magnetic forces, and (3) provides a global magnetic field solution, which contains high- and low-beta regimes and maximizes the similarity between the field lines structure and all the coronal images of the region. The coronal image analysis is crucial to the investigation and for the first time these images can be exploited to derive the coronal magnetic field in a well-posed mathematical formulation. This program is an outgrowth of an investigation in which an extrapolated potential field was required to be "inflated" in order to have the field lines match the Yohkoh/SXT images. The field lines were radially stretched resulting in a better match to the coronal loops of an active region. The PTA method of radial and non-radial deformations of field lines to provide a match to the EUV/SXR images will be presented.

  14. 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.

  15. ON THE ROLE OF ROTATING SUNSPOTS IN THE ACTIVITY OF SOLAR ACTIVE REGION NOAA 11158

    SciTech Connect

    Vemareddy, P.; Ambastha, A.; Maurya, R. A. E-mail: ambastha@prl.res.in

    2012-12-10

    We study the role of rotating sunspots in relation to the evolution of various physical parameters characterizing the non-potentiality of the active region (AR) NOAA 11158 and its eruptive events using the magnetic field data from the Helioseismic and Magnetic Imager (HMI) and multi-wavelength observations from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory. From the evolutionary study of HMI intensity and AIA channels, it is observed that the AR consists of two major rotating sunspots, one connected to a flare-prone region and another with coronal mass ejection (CME). The constructed space-time intensity maps reveal that the sunspots exhibited peak rotation rates coinciding with the occurrence of major eruptive events. Further, temporal profiles of twist parameters, namely, average shear angle, {alpha}{sub av}, {alpha}{sub best}, derived from HMI vector magnetograms, and the rate of helicity injection, obtained from the horizontal flux motions of HMI line-of-sight magnetograms, correspond well with the rotational profile of the sunspot in the CME-prone region, giving predominant evidence of rotational motion causing magnetic non-potentiality. Moreover, the mean value of free energy from the virial theorem calculated at the photospheric level shows a clear step-down decrease at the onset time of the flares revealing unambiguous evidence of energy release intermittently that is stored by flux emergence and/or motions in pre-flare phases. Additionally, distribution of helicity injection is homogeneous in the CME-prone region while in the flare-prone region it is not and often changes sign. This study provides a clear picture that both proper and rotational motions of the observed fluxes played significant roles in enhancing the magnetic non-potentiality of the AR by injecting helicity, twisting the magnetic fields and thereby increasing the free energy, leading to favorable conditions for the observed transient activity.

  16. 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.

  17. Hinode Captures Images of Solar Active Region

    NASA Video Gallery

    In these images, Hinode's Solar Optical Telescope (SOT) zoomed in on AR 11263 on August 4, 2011, five days before the active region produced the largest flare of this cycle, an X6.9. We show images...

  18. Functional photoacoustic imaging to observe regional brain activation induced by cocaine hydrochloride

    NASA Astrophysics Data System (ADS)

    Jo, Janggun; Yang, Xinmai

    2011-09-01

    Photoacoustic microscopy (PAM) was used to detect small animal brain activation in response to drug abuse. Cocaine hydrochloride in saline solution was injected into the blood stream of Sprague Dawley rats through tail veins. The rat brain functional change in response to the injection of drug was then monitored by the PAM technique. Images in the coronal view of the rat brain at the locations of 1.2 and 3.4 mm posterior to bregma were obtained. The resulted photoacoustic (PA) images showed the regional changes in the blood volume. Additionally, the regional changes in blood oxygenation were also presented. The results demonstrated that PA imaging is capable of monitoring regional hemodynamic changes induced by drug abuse.

  19. 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.

  20. 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.

  1. 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.

  2. TRACE and SVST Observations of an Active-Region Filament

    NASA Astrophysics Data System (ADS)

    van Ballegooijen, A. A.; Deluca, E. E.

    1999-05-01

    In June 1998 the Transition Region and Coronal Explorer (TRACE) observed filaments and prominences in coordination with various ground-based solar observatories, including the Swedish Vacuum Solar Telescope (SVST) on La Palma. Here we present results for an active-region filament observed on June 21-22. This horse-shoe shaped filament had a "barb" that reached down from the filament spine to the chomosphere below. We use high-resolution images obtained at the SVST on June 21 from 18:03 to 19:04 UT to study the fine structure and dynamics of plasmas in the barb and other parts of the filament. The data consist of narrowband Hα images taken with the Lockheed Tunable Filtergraph operating at a cadence of 20 s. We present Doppler maps derived from these images. The filament erupted six hours after the SVST observations. The eruption was observed with TRACE, which obtained images in Fe IX/X 171, Fe XII 195, Fe XV 284 and H I Lyalpha . At the start of the event, a thin bright loop appears high above the filament at the location of the barb. We interpret this feature as the outline of a magnetic "bubble" which forms as a result of kink instability in the magnetic field that supports the filament. The bright loop appears to be due to particle acceleration and impulsive heating along certain field lines on the periphery of this magnetic structure. A few minutes later, the dark filament threads turn into emission and move outward, exhibiting a helical structure. We discuss the magnetic structure of the barb and its possible role in the filament eruption.

  3. The effect of solar flares, coronal mass ejections, and co-rotating interaction regions on the Venusian 557.7 nm oxygen green line

    NASA Astrophysics Data System (ADS)

    Gray, Candace L.; Chanover, Nancy; Slanger, Tom; Molaverdikhani, Karan; Peter, Kerstin; Häusler, Bernd; Tellmann, Silvia; Pätzold, Martin; Witasse, Olivier; Blelly, Pierre-Louis; Collinson, Glyn

    2015-11-01

    The Venusian 557.7nm OI (1S - 1D) (oxygen green line) nightglow emission is known to be highly temporally variable. The reason for this variability is unknown. We propose that the emission is due to electron precipitation from intense solar storms. For my dissertation, I observed the Venusian green line after solar flares, coronal mass ejections (CMEs), and co-rotating interaction regions from December 2010 to April 2015 using the high resolution Astrophysical Research Consortium Echelle Spectrograph on the Apache Point Observatory 3.5-m telescope. Combining these observation with all other published observations, we find that the strongest detections occur after CME impacts and we conclude electron precipitation is required to produce green line emission. We do not detect emission from the 630.0nm OI (1D - 3P) oxygen red line for any observation.In an effort to determine the emitting altitude, thereby constraining the possible emission processes responsible for green line emission, and quantify the electron energy and flux entering the Venusian nightside, we conducted analyses of space-based observations of the Venusian nightglow and ionosphere collected by the Venus Express (VEX) spacecraft. We were unable to detect the green line but confirmed that electron energy and flux increases after CME impacts.In order to determine the effect of storm condition electron precipitation on the Venusian green line, we modeled the Venusian ionosphere using the TRANSCAR model (a 1-D magnetohydrodynamic ionospheric model that simulates auroral emission from electron precipitation) by applying observed electron energies and fluxes. We found that electron energy plays a primary role in producing increased green line emission in the Venusian ionosphere.Based on observation and modeling results, we conclude that the Venusian green line is an auroral-type emission that occurs after solar storms with the largest intensities observed after CMEs. Post-CME electron fluxes and energies

  4. 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.

  5. Three-dimensional MHD modeling of flare-induced waves in coronal loops: thermal effects

    NASA Astrophysics Data System (ADS)

    Provornikova, Elena; Ofman, Leon; Wang, Tongjiang

    EUV imaging and spectroscopic observations from several space missions (SOHO, TRACE, Hinode/EIS, SDO/AIA) have revealed the presence of MHD waves in solar coronal loops. Past analysis of SOHO/SUMER data suggested that slow magnetosonic waves in hot coronal loops are excited by flares at the loop`s footpoint. Recent Hinode/EIS observed propagating disturbances in active region loops were interpreted as flows as well as waves most likely generated by plasma outflows or jets. In order to understand dynamics of plasma in coronal loops due to flares or jets at the lower corona boundary, we perform full 3D MHD modeling of an active region and consider different mechanisms of wave excitation. We assume an initial equilibrium of the model active region with dipole magnetic field structure, gravitationally stratified density and temperature obtained from polytropic equation of state of the background coronal plasma. We extend previous isothermal studies by including full energy equation with empirical heating and radiative losses terms in the model. We study waves in both, short and long loops, and consider two excitation mechanisms in the model: impulsive plasma injection into the steady plasma upflow along the magnetic field lines, and impulsive heating at the footpoint of the loop. We show initiation and evolution of flows, excitation and damping of waves and flow-wave interaction in the loops. We compare our new results with previous models and observations.

  6. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2003-05-01

    We investigate the heating of the quiet corona by measuring the increase of coronal luminosity with the amount of magnetic flux in the underlying network at solar minimum when there were no active regions on the face of the Sun. The coronal luminosity is measured from Fe IX/X-Fe XII pairs of coronal images from SOHO/EIT. The network magnetic flux content is measured from SOHO/MDI magnetograms. We find that the luminosity of the corona in our quiet regions increases roughly in proportion to the square root of the magnetic flux content of the network and roughly in proportion to the length of the perimeter of the network magnetic flux clumps. From (1) this result, (2) other observations of many fine-scale explosive events at the edges of network flux clumps, and (3) a demonstration that it is energetically feasible for the heating of the corona in quiet regions to be driven by explosions of granule-sized sheared-core magnetic bipoles embedded in the edges of network flux clumps, we infer that in quiet regions that are not influenced by active regions the corona is mainly heated by such magnetic activity in the edges of the network flux clumps. Our observational results together with our feasibility analysis allow us to predict that (1) at the edges of the network flux clumps there are many transient sheared-core bipoles of the size and lifetime of granules and having transverse field strengths > 100 G, (2) 30 of these bipoles are present per supergranule, and (3) most spicules are produced by explosions of these bipoles. This work was supported by NASA's Office of Space Science through its Solar and Heliospheric Physics Supporting Research and Technology Program and its Sun-Earth Connection Guest Investigator Program.

  8. The flare productivity of active regions

    NASA Astrophysics Data System (ADS)

    Kuroda, N.; Christe, S.

    2012-12-01

    Previous studies have shown that the flare frequency distribution is consistent with a power-law. Furthermore, studies have shown that regions of higher magnetic complexity produce more large flares. This may imply that the flare frequency distribution is harder for magnetically complex active regions. However, the relationship between source active regions' magnetic complexity and the flare size distribution has not been extensively studied. We present a new study of 25,000 microflares detected by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) from March 2002 to February 2007. For each flare, we have obtained the two classifications of magnetic complexity, the Mount Wilson Magnetic Classification and the Zurich/McIntosh Sunspot Classification, from the Solar Region Summary prepared by the National Oceanic and Atmospheric Administration (NOAA)/ Space Weather Prediction Center (SWPC), and compared them with the RHESSI flare size distribution as observed in the 12 to 25 keV energy range. We investigate the relationship between the slope of the microflare size distribution and the magnetic properties of source active regions. For each flare we obtain the relevant MDI magnetogram to determine properties such as the area of the source active region and total unsigned magnetic flux. These properties are then compared to properties of the associated microflares such as peak flux and microflare size distribution. We find that, for both the Mount Wilson Magnetic Classification and the Zurich/McIntosh Sunspot Classification, the slopes of the microflare size distribution tend to get harder as a function of magnetic complexity. For example, in Mount Wilson Magnetic Classification the slope for α regions was 1.66 and the slope for βγδ region was 1.51.This suggests that βγδ regions are 50 % more likely to produce X class flares than α regions.

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

    SciTech Connect

    Reinard, A. A.

    2009-11-01

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

  10. Suppression of heating of coronal loops rooted in opposite polarity sunspot umbrae

    NASA Astrophysics Data System (ADS)

    Tiwari, Sanjiv K.; Thalmann, Julia K.; Moore, Ronald L.; Panesar, Navdeep; Winebarger, Amy R.

    2016-05-01

    EUV observations of active region (AR) coronae reveal the presence of loops at different temperatures. To understand the mechanisms that result in hotter or cooler loops, we study a typical bipolar AR, near solar disk center, which has moderate overall magnetic twist and at least one fully developed sunspot of each polarity. From AIA 193 and 94 A images we identify many clearly discernible coronal loops that connect plage or a sunspot of one polarity to an opposite-polarity plage region. The AIA 94 A images show dim regions in the umbrae of the spots. To see which coronal loops are rooted in a dim umbral area, we performed a non-linear force-free field (NLFFF) modeling using photospheric vector magnetic field measurements obtained with the HMI onboard SDO. After validation of the NLFFF model by comparison of calculated model field lines and observed loops in AIA 193 and 94, we specify the photospheric roots of the model field lines. The model field then shows the coronal magnetic loops that arch from the dim umbral areas of the opposite polarity sunspots. Because these coronal loops are not visible in any of the coronal EUV and X-ray images of the AR, we conclude they are the coolest loops in the AR. This result suggests that the loops connecting opposite polarity umbrae are the least heated because the field in umbrae is so strong that the convective braiding of the field is strongly suppressed.We hypothesize that the convective freedom at the feet of a coronal loop, together with the strength of the field in the body of the loop, determines the strength of the heating. In particular, we expect the hottest coronal loops to have one foot in an umbra and the other foot in opposite-polarity penumbra or plage (coronal moss), the areas of strong field in which convection is not as strongly suppressed as in umbra. Many transient, outstandingly bright, loops in the AIA 94 movie of the AR do have this expected rooting pattern. We will also present another example of AR in

  11. EVOLUTION OF MAGNETIC FIELD AND ENERGY IN A MAJOR ERUPTIVE ACTIVE REGION BASED ON SDO/HMI OBSERVATION

    SciTech Connect

    Sun Xudong; Hoeksema, J. Todd; Liu, Yang; Hayashi, Keiji; Wiegelmann, Thomas; Thalmann, Julia; Chen Qingrong

    2012-04-01

    We report the evolution of the magnetic field and its energy in NOAA active region 11158 over five days based on a vector magnetogram series from the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamic Observatory (SDO). Fast flux emergence and strong shearing motion led to a quadrupolar sunspot complex that produced several major eruptions, including the first X-class flare of Solar Cycle 24. Extrapolated nonlinear force-free coronal fields show substantial electric current and free energy increase during early flux emergence near a low-lying sigmoidal filament with a sheared kilogauss field in the filament channel. The computed magnetic free energy reaches a maximum of {approx}2.6 Multiplication-Sign 10{sup 32} erg, about 50% of which is stored below 6 Mm. It decreases by {approx}0.3 Multiplication-Sign 10{sup 32} erg within 1 hr of the X-class flare, which is likely an underestimation of the actual energy loss. During the flare, the photospheric field changed rapidly: the horizontal field was enhanced by 28% in the core region, becoming more inclined and more parallel to the polarity inversion line. Such change is consistent with the conjectured coronal field 'implosion' and is supported by the coronal loop retraction observed by the Atmospheric Imaging Assembly (AIA). The extrapolated field becomes more 'compact' after the flare, with shorter loops in the core region, probably because of reconnection. The coronal field becomes slightly more sheared in the lowest layer, relaxes faster with height, and is overall less energetic.

  12. 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.

  13. Coronal magnetic reconnection driven by CME expansion—the 2011 June 7 event

    SciTech Connect

    Van Driel-Gesztelyi, L.; Baker, D.; Green, L. M.; Williams, D. R.; Carlyle, J.; Kliem, B.; Long, D. M.; Matthews, S. A.; Török, T.; Pariat, E.; Valori, G.; Démoulin, P.; Malherbe, J.-M.

    2014-06-10

    Coronal mass ejections (CMEs) erupt and expand in a magnetically structured solar corona. Various indirect observational pieces of evidence have shown that the magnetic field of CMEs reconnects with surrounding magnetic fields, forming, e.g., dimming regions distant from the CME source regions. Analyzing Solar Dynamics Observatory (SDO) observations of the eruption from AR 11226 on 2011 June 7, we present the first direct evidence of coronal magnetic reconnection between the fields of two adjacent active regions during a CME. The observations are presented jointly with a data-constrained numerical simulation, demonstrating the formation/intensification of current sheets along a hyperbolic flux tube at the interface between the CME and the neighboring AR 11227. Reconnection resulted in the formation of new magnetic connections between the erupting magnetic structure from AR 11226 and the neighboring active region AR 11227 about 200 Mm from the eruption site. The onset of reconnection first becomes apparent in the SDO/AIA images when filament plasma, originally contained within the erupting flux rope, is redirected toward remote areas in AR 11227, tracing the change of large-scale magnetic connectivity. The location of the coronal reconnection region becomes bright and directly observable at SDO/AIA wavelengths, owing to the presence of down-flowing cool, dense (10{sup 10} cm{sup –3}) filament plasma in its vicinity. The high-density plasma around the reconnection region is heated to coronal temperatures, presumably by slow-mode shocks and Coulomb collisions. These results provide the first direct observational evidence that CMEs reconnect with surrounding magnetic structures, leading to a large-scale reconfiguration of the coronal magnetic field.

  14. 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

  15. Chromospheric Acoustic Oscillations in Active Flaring Regions

    NASA Astrophysics Data System (ADS)

    Monsue, T.; Hill, F.; Stassun, K.

    2014-12-01

    Chromospheric p-mode oscillations are studied in Hα to obtain helioseismic information regarding the local structural conditions around highly magnetic regions such as sunspots. Solar flares commonly occur in active regions where these sunspots exist therefore boosting the p-mode power. In our current study of analyzing p-modes in the chromosphere we study the time evolution of acoustic p-mode oscillation data taken from the Global Oscillation Network Group (GONG) Hα, and investigate the p-modes across the frequency band (1 < ν < 8.33 mHz). This study entails three active regions directly over sunspots, with accompanying flaring activity from two solar flares, occurring on June 13th and July 12th, 2012. Our analysis utilizes time series data to create Fourier power spectra of individual pixels spatially resolved around the flare region, to study the frequency bands. We then study how the frequency distribution evolves temporally by constructing a Power Map Movie (PMM) of the regions. From these PMMs we can take a survey of the chromospheric oscillations for each frequency band. We found that the intensity of the flare has an effect on the behavior of the p-modes within different frequency bands. The suppression of power was observed in dark anomalous structures within the PMMs and in other regions there was an observed boost in power due to flaring activity.

  16. Growth and Decay of Solar Active Regions

    NASA Astrophysics Data System (ADS)

    Dobias, J. J.; Chapman, G. A.; Cookson, A. M.; Preminger, D. G.; Walton, S. R.

    2002-05-01

    We report here on a study of growth and decay rates of sunspot and facular areas of solar active regions. The data used in this project come from an ongoing program of daily photometric observations of the sun with the Cartesian Full Disk Telescope No. 1 (CFDT1) at the San Fernando Observatory (SFO). Sunspot regions are determined from images taken with a red filter centered at 672.3 nm with a bandpass of 9.7 nm, while images taken with a Ca II K line filter, centered at 393.4 nm and with a bandpass of only 1nm, are used to find facular areas. Before any areas can be found on any observed images, they have to be calibrated then flattened by removing limb darkening thus producing contrast images. Sunspot areas are then determined from any pixel with contrast of -8.5% or less, while any pixel on a K line contrast image with a contrast of +4.8%/μ or higher, where μ is the cosine of the heliocentric angle, is considered to be a facular pixel. To identify the areas as clearly as possible, studied active regions were usually observed on the sun with relatively low activity; that means that each region is either alone on the sun's disk or with only very few other active regions present. Furthermore, to obtain growth and decay patterns of the areas as reliably as possible, only such active regions must be chosen for which there is as complete observational coverage as possible. At the present time studies have been finished for only a few active regions, but analysis of several others is on going. Obtained results will be presented at the meeting. This work is supported by NSF grant ATM-9912132 and NASA grants NAG5-7191 and NAG5-7778.

  17. PATTERNS OF NANOFLARE STORM HEATING EXHIBITED BY AN ACTIVE REGION OBSERVED WITH SOLAR DYNAMICS OBSERVATORY/ATMOSPHERIC IMAGING ASSEMBLY

    SciTech Connect

    Viall, Nicholeen M.; Klimchuk, James A.

    2011-09-01

    It is largely agreed that many coronal loops-those observed at a temperature of about 1 MK-are bundles of unresolved strands that are heated by storms of impulsive nanoflares. The nature of coronal heating in hotter loops and in the very important but largely ignored diffuse component of active regions is much less clear. Are these regions also heated impulsively, or is the heating quasi-steady? The spectacular new data from the Atmospheric Imaging Assembly (AIA) telescopes on the Solar Dynamics Observatory offer an excellent opportunity to address this question. We analyze the light curves of coronal loops and the diffuse corona in six different AIA channels and compare them with the predicted light curves from theoretical models. Light curves in the different AIA channels reach their peak intensities with predictable orderings as a function the nanoflare storm properties. We show that while some sets of light curves exhibit clear evidence of cooling after nanoflare storms, other cases are less straightforward to interpret. Complications arise because of line-of-sight integration through many different structures, the broadband nature of the AIA channels, and because physical properties can change substantially depending on the magnitude of the energy release. Nevertheless, the light curves exhibit predictable and understandable patterns consistent with impulsive nanoflare heating.

  18. The 17 GHz active region number

    SciTech Connect

    Selhorst, C. L.; Pacini, A. A.; Costa, J. E. R.; Giménez de Castro, C. G.; Valio, A.; Shibasaki, K.

    2014-08-01

    We report the statistics of the number of active regions (NAR) observed at 17 GHz with the Nobeyama Radioheliograph between 1992, near the maximum of cycle 22, and 2013, which also includes the maximum of cycle 24, and we compare with other activity indexes. We find that NAR minima are shorter than those of the sunspot number (SSN) and radio flux at 10.7 cm (F10.7). This shorter NAR minima could reflect the presence of active regions generated by faint magnetic fields or spotless regions, which were a considerable fraction of the counted active regions. The ratio between the solar radio indexes F10.7/NAR shows a similar reduction during the two minima analyzed, which contrasts with the increase of the ratio of both radio indexes in relation to the SSN during the minimum of cycle 23-24. These results indicate that the radio indexes are more sensitive to weaker magnetic fields than those necessary to form sunspots, of the order of 1500 G. The analysis of the monthly averages of the active region brightness temperatures shows that its long-term variation mimics the solar cycle; however, due to the gyro-resonance emission, a great number of intense spikes are observed in the maximum temperature study. The decrease in the number of these spikes is also evident during the current cycle 24, a consequence of the sunspot magnetic field weakening in the last few years.

  19. 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.

  20. Ultra-Hot Plasma in Active Regions Observed by the Extreme-ultraviolet Imaging Spectrometer on Hinode

    NASA Astrophysics Data System (ADS)

    Doschek, G. A.; Warren, H. P.; Feldman, U.

    2008-05-01

    The Extreme-ultraviolet Imaging Spectrometer (EIS) on the Hinode spacecraft obtains high resolution spectra of the solar atmosphere in two wavelength ranges: 170 - 210 and 250 — 290 Angstroms. These wavelength regions contain a wealth of emission lines covering temperature regions from the chromosphere/transition region (e.g., He II, Si VII) up to soft X-ray flare temperatures (Fe XXIII, Fe XXIV). EIS can obtain line profiles and intensities for the spectral lines in these wavelength regions. Of particular interest for understanding coronal heating is a line of Ca XVII, formed near a temperature of 6 MK. This line is blended with lines of Fe XI and O V. However, by using unblended lines of these ions, the Ca XVII line can be deconvolved from the blended emission. EIS has obtained many raster observations of active regions by stepping the slit in small increments across the active region, producing monochromatic images of the active region. The Ca XVII blend has been included in many of these rasters. In this paper we discuss the appearance and frequency of 6 MK plasma in active regions in the absence of strong flaring activity. This temperature region is not well-observed by normal incidence imaging spectrometers and therefore the EIS data shed light on higher temperature areas of active regions than normally available from imaging instruments alone. We discuss how to deconvolve the blend and show examples of 6 MK plasma emission in several active regions.

  1. Fast Magnetosonic Waves and Global Coronal Seismology in the Extended Solar Corona

    NASA Astrophysics Data System (ADS)

    Kwon, Ryun Young; Zhang, J.; Kramar, M.; Wang, T.; Ofman, L.; Davila, J. M.

    2013-07-01

    We present global coronal seismology, for the first time, that allows us to determine inhomogeneous magnetic field strengths in a wide range of the extended solar corona. We use observations of propagating disturbance associated with a coronal mass ejection observed on 2011 August 4 by the COR1 inner coronagraphs on board the STEREO spacecraft. We establish that the disturbance is in fact a fast magnetosonic wave as the upper coronal counterpart of the EIT wave observed by STEREO EUVI and travels across magnetic field lines with inhomogeneous speeds, passing through various coronal regions such as quiet/active corona, coronal holes, and streamers. We derive magnetic field strengths along the azimuthal trajectories of the fronts at heliocentric distances 2.0, 2.5, and 3.0 Rs, using the varying speeds and electron densities. The derived magnetic field strengths are consistent with values determined with a potential field source surface model and reported in previous works. The ranges of the magnetic field strengths at these heliocentric distances are 0.44 ± 0.29, 0.23 ± 0.15, and 0.26 ± 0.14 G, respectively. The uncertainty in determining magnetic field strengths is about 40 %. This work demonstrates that observations of fast magnetosonic waves by white-light coronagraphs can provide us with a unique way to diagnose magnetic field strength of an inhomogeneous medium in a wide spatial range of the extended solar corona.

  2. Fluxon Modeling of Active Region Evolution

    NASA Astrophysics Data System (ADS)

    Deforest, C. E.; Kankelborg, C. C.; Davey, A. R.; Rachmeler, L.

    2006-12-01

    We present current results and status on fluxon modeling of free energy buildup and release in active regions. Our publicly available code, FLUX, has the unique ability to track magnetic energy buildup with a truly constrained topology in evolving, nonlinear force-free conditions. Recent work includes validation of the model against Low &Lou force-free field solutions, initial evolution studies of idealized active regions, and inclusion of locally parameterized reconnection into the model. FLUX is uniquely able to simulate complete active regions in 3-D on a single workstation; we estimate that a parallelized fluxon model, together with computer vision code to ingest solar data, could run faster than real time on a cluster of \\textasciitilde 30 CPUs and hence provide a true predictive space weather model in the style of predictive simulations of terrestrial weather.

  3. Spectroscopic Observations of Fe XVIII in Solar Active Regions

    NASA Astrophysics Data System (ADS)

    Teriaca, Luca; Warren, Harry P.; Curdt, Werner

    2012-08-01

    The large uncertainties associated with measuring the amount of high temperature emission in solar active regions (ARs) represents a significant impediment to making progress on the coronal heating problem. Most current observations at temperatures of 3 MK and above are taken with broadband soft X-ray instruments. Such measurements have proven difficult to interpret unambiguously. Here, we present the first spectroscopic observations of the Fe XVIII 974.86 Å emission line in an on-disk AR taken with the SUMER instrument on SOHO. Fe XVIII has a peak formation temperature of 7.1 MK and provides important constraints on the amount of impulsive heating in the corona. Detailed evaluation of the spectra and comparison of the SUMER data with soft X-ray images from the X-Ray Telescope on Hinode confirm that this line is unblended. We also compare the spectroscopic data with observations from the Atmospheric Imaging Assembly (AIA) 94 Å channel on the Solar Dynamics Observatory. The AIA 94 Å channel also contains Fe XVIII, but is blended with emission formed at lower temperatures. We find that it is possible to remove the contaminating blends and form relatively pure Fe XVIII images that are consistent with the spectroscopic observations from SUMER. The observed spectra also contain the Ca XIV 943.63 Å line that, although a factor 2-6 weaker than the Fe XVIII 974.86 Å line, allows us to probe the plasma around 3.5 MK. The observed ratio between the two lines indicates (isothermal approximation) that most of the plasma in the brighter Fe XVIII AR loops is at temperatures between 3.5 and 4 MK.

  4. Quantifying the Complexity of Flaring Active Regions

    NASA Astrophysics Data System (ADS)

    Stark, B.; Hagyard, M. J.

    1997-05-01

    While solar physicists have a better understanding of the importance magnetic fields play in the solar heating mechanism, it is still not possible to predict whether or when an active region will flare. In recent decades, qualitative studies of the changes in active region morphology have shown that there is generally an increase in the complexity of the spatial configuration of a solar active region leading up to a flare event. In this study, we quantify the spatial structure of the region using the Differential Box-Counting Method (DBC)of fractal analysis. We analyze data from NASA/Marshall Space Flight Center's vector magnetograph from two flaring active regions: AR 6089 from June 10, 1990, which produced one M1.7 flare, and AR 6659 from June 8, 9 and 10, 1991, this data set including one C5.7 and two M(6.4 and 3.2) flares. (AR 6659 produced several other flares). Several magnetic parameters are studied, including the transverse and longitudinal magnetic field components (Bt and Bl), the total field (Bmag), and the magnetic shear, which describes the non-potentiality of the field. Results are presented for the time series of magnetograms in relation to the timing of flare events.

  5. Quantifying the Complexity of Flaring Active Regions

    NASA Technical Reports Server (NTRS)

    Stark, B.; Hagyard, M. J.

    1997-01-01

    While solar physicists have a better understanding of the importance magnetic fields play in the solar heating mechanism, it is still not possible to predict whether or when an active region will flare. In recent decades, qualitative studies of the changes in active region morphology have shown that there is generally an increase in the complexity of the spatial configuration of a solar active region leading up to a flare event. In this study, we quantify the spatial structure of the region using the differential Box-Counting Method (DBC) of fractal analysis. We analyze data from NASA/Marshall Space Flight Centr's vector magnetograph from two flaring active regions: AR 6089 from June 10, 1990, which produced one M1.7 flare, and AR 6659 from June 8, 9 and 10, 1991, this data set including one C5.7 and two M(6.4 and 3.2) flare. (AR 6659 produced several other flares). Several magnetic parameters are studied, including the transverse and longitudinal magnetic field components (Bt and B1), the total field (Bmag), and the magnetic shear, which describes the non-potentiality of the field. Results are presented for the time series of magnetograms in relation to the timing of flare events.

  6. ON THE FORMATION OF ACTIVE REGIONS

    SciTech Connect

    Stein, Robert F.; Nordlund, Ake E-mail: aake@nbi.dk

    2012-07-01

    Magnetoconvection can produce an active region without an initial coherent flux tube. A simulation was performed where a uniform, untwisted, horizontal magnetic field of 1 kG strength was advected into the bottom of a computational domain 48 Mm wide by 20 Mm deep. The up and down convective motions produce a hierarchy of magnetic loops with a wide range of scales, with smaller loops riding 'piggy-back' in a serpentine fashion on larger loops. When a large loop approaches the surface, it produces a small active region with a compact leading spot and more diffuse following spots.

  7. On the Formation of Active Regions

    NASA Astrophysics Data System (ADS)

    Stein, Robert F.; Nordlund, Åke

    2012-07-01

    Magnetoconvection can produce an active region without an initial coherent flux tube. A simulation was performed where a uniform, untwisted, horizontal magnetic field of 1 kG strength was advected into the bottom of a computational domain 48 Mm wide by 20 Mm deep. The up and down convective motions produce a hierarchy of magnetic loops with a wide range of scales, with smaller loops riding "piggy-back" in a serpentine fashion on larger loops. When a large loop approaches the surface, it produces a small active region with a compact leading spot and more diffuse following spots.

  8. Nonlinear force-free field extrapolation of the coronal magnetic field using the data obtained by the Hinode satellite

    NASA Astrophysics Data System (ADS)

    He, Han; Wang, Huaning; Yan, Yihua

    2011-01-01

    The Hinode satellite can obtain high-quality photospheric vector magnetograms of solar active regions and the simultaneous coronal loop images in soft X-ray and extreme ultraviolet (EUV) bands. In this paper, we continue the work of He and Wang (2008) and apply the newly developed upward boundary integration computational scheme for the nonlinear force-free field (NLFFF) extrapolation of the coronal magnetic field to the photospheric vector magnetograms acquired by the Spectro-Polarimeter of the Solar Optical Telescope aboard Hinode. Three time series vector magnetograms of the same solar active region, NOAA 10930, are selected for the NLFFF extrapolations, which were observed within the time interval of 26 h during 10-11 December 2006 when the active region crossed the central area of the Sun's disk. Parallel computation of the NLFFF extrapolation code was realized through OpenMP multithreaded, shared memory parallelism and Fortran 95 programming language for the extrapolation calculations. The comparison between the extrapolated field lines and the coronal loop images obtained by the X-Ray Telescope and the EUV Imaging Spectrometer of Hinode shows that, in the central area of the active region, the field line configurations generally agree with the coronal images, and the orientations of the field lines basically coincide with the coronal loop observations for all three successive magnetograms. This result supports the NLFFF model being used for tracing the time series evolution of the 3-D coronal magnetic structures as the responses of the quasi-equilibrium solar atmosphere to the vector magnetic field changes in the photosphere.

  9. 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.

  10. 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.

  11. Microflaring in Low-Lying Core Fields and Extended Coronal Heating in the Quiet Sun

    NASA Technical Reports Server (NTRS)

    Porter, Jason G.; Falconer, D. A.; Moore, Ronald L.

    1999-01-01

    We have previously reported analyses of Yohkoh SXT data examining the relationship between the heating of extended coronal loops (both within and stemming from active regions) and microflaring in core fields lying along neutral lines near their footpoints (J. G. Porter, D. A. Falconer, and R. L. Moore 1998, in Solar Jets and Coronal Plumes, ed. T. Guyenne, ESA SP-421, and references therein). We found a surprisingly poor correlation of intensity variations in the extended loops with individual microflares in the compact heated areas at their feet, despite considerable circumstancial evidence linking the heating processes in these regions. Now, a study of Fe XII image sequences from SOHO EIT show that similar associations of core field structures with the footpoints of very extended coronal features can be found in the quiet Sun. The morphology is consistent with the finding of Wang et al. (1997, ApJ 484, L75) that polar plumes are rooted at sites of mixed polarity in the magnetic network. We find that the upstairs/downstairs intensity variations often follow the trend, identified in the active region observations, of a weak correspondence. Apparently much of the coronal heating in the extended loops is driven by a type of core field magnetic activity that is "cooler" than the events having the coronal signature of microflares, i.e., activity that results in little heating within the core fields themselves. This work was funded by the Solar Physics Branch of NASA's Office of Space Science through the SR&T Program and the SEC Guest Investigator Program.

  12. Solar Eruptions Initiated in Sigmoidal Active Regions

    NASA Astrophysics Data System (ADS)

    Savcheva, Antonia

    2016-07-01

    active regions that have been shown to possess high probability for eruption. They present a direct evidence of the existence of flux ropes in the corona prior to the impulsive phase of eruptions. In order to gain insight into their eruptive behavior and how they get destabilized we need to know their 3D magnetic field structure. First, we review some recent observations and modeling of sigmoidal active regions as the primary hosts of solar eruptions, which can also be used as useful laboratories for studying these phenomena. Then, we concentrate on the analysis of observations and highly data-constrained non-linear force-free field (NLFFF) models over the lifetime of several sigmoidal active regions, where we have captured their magnetic field structure around the times of major flares. We present the topology analysis of a couple of sigmoidal regions pointing us to the probable sites of reconnection. A scenario for eruption is put forward by this analysis. We demonstrate the use of this topology analysis to reconcile the observed eruption features with the standard flare model. Finally, we show a glimpse of how such a NLFFF model of an erupting region can be used to initiate a CME in a global MHD code in an unprecedented realistic manner. Such simulations can show the effects of solar transients on the near-Earth environment and solar system space weather.

  13. 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.

  14. 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.

  15. 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.

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

    PubMed Central

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

    2012-01-01

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

  17. Forward Modeling Transient Brightenings and Microflares around an Active Region Observed with Hi-C

    NASA Astrophysics Data System (ADS)

    Kobelski, Adam R.; McKenzie, David E.

    2014-10-01

    Small-scale flare-like brightenings around active regions are among the smallest and most fundamental of energetic transient events in the corona, providing a testbed for models of heating and active region dynamics. In a previous study, we modeled a large collection of these microflares observed with Hinode/X-Ray Telescope (XRT) using EBTEL and found that they required multiple heating events, but could not distinguish between multiple heating events on a single strand, or multiple strands each experiencing a single heating event. We present here a similar study, but with extreme-ultraviolet data of Active Region 11520 from the High Resolution Coronal Imager (Hi-C) sounding rocket. Hi-C provides an order of magnitude improvement to the spatial resolution of XRT, and a cooler temperature sensitivity, which combine to provide significant improvements to our ability to detect and model microflare activity around active regions. We have found that at the spatial resolution of Hi-C (≈0.''3), the events occur much more frequently than expected (57 events detected, only 1 or 2 expected), and are most likely made from strands of the order of 100 km wide, each of which is impulsively heated with multiple heating events. These findings tend to support bursty reconnection as the cause of the energy release responsible for the brightenings.

  18. Forward modeling transient brightenings and microflares around an active region observed with Hi-C

    SciTech Connect

    Kobelski, Adam R.; McKenzie, David E.

    2014-10-20

    Small-scale flare-like brightenings around active regions are among the smallest and most fundamental of energetic transient events in the corona, providing a testbed for models of heating and active region dynamics. In a previous study, we modeled a large collection of these microflares observed with Hinode/X-Ray Telescope (XRT) using EBTEL and found that they required multiple heating events, but could not distinguish between multiple heating events on a single strand, or multiple strands each experiencing a single heating event. We present here a similar study, but with extreme-ultraviolet data of Active Region 11520 from the High Resolution Coronal Imager (Hi-C) sounding rocket. Hi-C provides an order of magnitude improvement to the spatial resolution of XRT, and a cooler temperature sensitivity, which combine to provide significant improvements to our ability to detect and model microflare activity around active regions. We have found that at the spatial resolution of Hi-C (≈0.''3), the events occur much more frequently than expected (57 events detected, only 1 or 2 expected), and are most likely made from strands of the order of 100 km wide, each of which is impulsively heated with multiple heating events. These findings tend to support bursty reconnection as the cause of the energy release responsible for the brightenings.

  19. Asia Section. Regional Activities Division. Paper.

    ERIC Educational Resources Information Center

    International Federation of Library Associations, The Hague (Netherlands).

    Two papers on library and information activities in developing nations, particularly in India and other Asian countries, were presented at the 1983 International Federation of Library Associations (IFLA) conference. In "IFLA in Asia: A Review of the Work of the Regional Section for Asia," Edward Lim Huck Tee (Malaysia) describes the low level of…

  20. Active region upflow plasma: its relation to small activity and the solar wind

    NASA Astrophysics Data System (ADS)

    Mandrini, Cristina H.; Culhane, J. Leonard; Cristiani, Germán; Vásquez, Alberto; Van Driel-Gesztelyi, Lidia; Baker, Deborah; Pick, Monique; Demoulin, Pascal; Nuevo, Federico

    Recent studies show that active region (AR) upflowing plasma, observed by the Hinode EUV Imaging Spectrometer (EIS), can gain access to open field lines and be released into the solar wind via magnetic interchange reconnection occurring below the source surface at magnetic null-points in pseudo-streamer configurations. When only one simple bipolar AR is present on the Sun and it is fully covered by the separatrix of a streamer, like AR 10978 on December 2007, it seems unlikely that the upflowing AR plasma could find its way into the slow solar wind. However, signatures of plasma with AR composition at 1 AU that appears to originate from the West of AR 10978 were recently found by Culhane and coworkers. We present a detailed topology analysis of AR 10978 based on a linear force-free magnetic field model at the AR scale, combined with a global PFSS model. This allows us, on one hand, to explain the variations observed in the upflows to the West of the AR as the result of magnetic reconnection at quasi-separatrix layers (QSLs). While at a global scale, we show that reconnection, occurring in at least two main steps, first at QSLs and later at a high-altitude coronal null-point, allows the AR plasma to get around the topological obstacle of the streamer separatrix and be released into the solar wind.

  1. High resolution studies of complex solar active regions

    NASA Astrophysics Data System (ADS)

    Deng, Na

    Flares and Coronal Mass Ejections (CMEs) are energetic events, which can even impact the near-Earth environment and are the principal source of space weather. Most of them originate in solar active regions. The most violent events are produced in sunspots with a complex magnetic field topology. Studying their morphology and dynamics is helpful in understanding the energy accumulation and release mechanisms for flares and CMEs, which are intriguing problems in solar physics. The study of complex active regions is based on high-resolution observations from space missions and new instruments at the Big Bear Solar Observatory (BBSO). Adaptive optics (AO) in combination with image restoration techniques (speckle masking imaging) can achieve improved image quality and a spatial resolution (about 100 km on the solar surface) close to the diffraction limit of BBSO's 65 cm vacuum telescope. Dopplergrams obtained with a two-dimensional imaging spectrometer combined with horizontal flow maps derived with Local Correlation Tracking (LCT) provide precise measurements of the three-dimensional velocity field in sunspots. Magnetic field measurements from ground- and space-based instruments complement these data. At the outset of this study, the evolution and morphology of a typical round sunspot are described in some detail. The sunspot was followed from disk center to the limb, thus providing some insight into the geometry of the magnetic flux system. Having established a benchmark for a stable sunspot, the attention is turned to changes of the sunspot structure associated with flares and CMEs. Rapid penumbral decay and the strengthening of sunspot umbrae are manifestations of photospheric magnetic field changes after a flare. These sudden intensity changes are interpreted as a result of magnetic reconnection during the flare, which causes the magnetic field lines to be turned from more inclined to more vertical. Strong photospheric shear flows along the flaring magnetic

  2. Initiation and Evolution of Global Coronal Waves

    NASA Astrophysics Data System (ADS)

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

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

  3. 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.

  4. 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.

  5. Modeling active region transient brightenings observed with X-ray telescope as multi-stranded loops

    SciTech Connect

    Kobelski, Adam R.; McKenzie, David E.; Donachie, Martin

    2014-05-10

    Strong evidence exists that coronal loops as observed in extreme ultraviolet and soft X-rays may not be monolithic isotropic structures, but can often be more accurately modeled as bundles of independent strands. Modeling the observed active region transient brightenings (ARTBs) within this framework allows for the exploration of the energetic ramifications and characteristics of these stratified structures. Here we present a simple method of detecting and modeling ARTBs observed with the Hinode X-Ray Telescope (XRT) as groups of zero-dimensional strands, which allows us to probe parameter space to better understand the spatial and temporal dependence of strand heating in impulsively heated loops. This partially automated method can be used to analyze a large number of observations to gain a statistical insight into the parameters of coronal structures, including the number of heating events required in a given model to fit the observations. In this article, we present the methodology and demonstrate its use in detecting and modeling ARTBs in a sample data set from Hinode/XRT. These initial results show that, in general, multiple heating events are necessary to reproduce observed ARTBs, but the spatial dependence of these heating events cannot yet be established.

  6. SUMER Observations of Coronal-Hole Temperatures

    NASA Astrophysics Data System (ADS)

    Wilhelm, Klaus

    2012-11-01

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

  7. 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

    constraints on Alfven wave heating as a coronal heating mechanism, especially for active region loops.

  8. Episodic coronal heating

    NASA Astrophysics Data System (ADS)

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

    1990-06-01

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

  9. 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.

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

    PubMed Central

    2007-01-01

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

  11. Magnetic helicity in emerging solar active regions

    SciTech Connect

    Liu, Y.; Hoeksema, J. T.; Bobra, M.; Hayashi, K.; Sun, X.; Schuck, P. W.

    2014-04-10

    Using vector magnetic field data from the Helioseismic and Magnetic Imager instrument aboard the Solar Dynamics Observatory, we study magnetic helicity injection into the corona in emerging active regions (ARs) and examine the hemispheric helicity rule. In every region studied, photospheric shearing motion contributes most of the helicity accumulated in the corona. In a sample of 28 emerging ARs, 17 follow the hemisphere rule (61% ± 18% at a 95% confidence interval). Magnetic helicity and twist in 25 ARs (89% ± 11%) have the same sign. The maximum magnetic twist, which depends on the size of an AR, is inferred in a sample of 23 emerging ARs with a bipolar magnetic field configuration.

  12. Silicon on insulator with active buried regions

    DOEpatents

    McCarthy, Anthony M.

    1998-06-02

    A method for forming patterned buried components, such as collectors, sources and drains, in silicon-on-insulator (SOI) devices. The method is carried out by epitaxially growing a suitable sequence of single or multiple etch stop layers ending with a thin silicon layer on a silicon substrate, masking the silicon such that the desired pattern is exposed, introducing dopant and activating in the thin silicon layer to form doped regions. Then, bonding the silicon layer to an insulator substrate, and removing the silicon substrate. The method additionally involves forming electrical contact regions in the thin silicon layer for the buried collectors.

  13. Silicon on insulator with active buried regions

    DOEpatents

    McCarthy, Anthony M.

    1996-01-01

    A method for forming patterned buried components, such as collectors, sources and drains, in silicon-on-insulator (SOI) devices. The method is carried out by epitaxially growing a suitable sequence of single or multiple etch stop layers ending with a thin silicon layer on a silicon substrate, masking the silicon such that the desired pattern is exposed, introducing dopant and activating in the thin silicon layer to form doped regions. Then, bonding the silicon layer to an insulator substrate, and removing the silicon substrate. The method additionally involves forming electrical contact regions in the thin silicon layer for the buried collectors.

  14. Silicon on insulator with active buried regions

    DOEpatents

    McCarthy, A.M.

    1998-06-02

    A method is disclosed for forming patterned buried components, such as collectors, sources and drains, in silicon-on-insulator (SOI) devices. The method is carried out by epitaxially growing a suitable sequence of single or multiple etch stop layers ending with a thin silicon layer on a silicon substrate, masking the silicon such that the desired pattern is exposed, introducing dopant and activating in the thin silicon layer to form doped regions. Then, bonding the silicon layer to an insulator substrate, and removing the silicon substrate. The method additionally involves forming electrical contact regions in the thin silicon layer for the buried collectors. 10 figs.

  15. Silicon on insulator with active buried regions

    DOEpatents

    McCarthy, A.M.

    1996-01-30

    A method is disclosed for forming patterned buried components, such as collectors, sources and drains, in silicon-on-insulator (SOI) devices. The method is carried out by epitaxially growing a suitable sequence of single or multiple etch stop layers ending with a thin silicon layer on a silicon substrate, masking the silicon such that the desired pattern is exposed, introducing dopant and activating in the thin silicon layer to form doped regions. Then, bonding the silicon layer to an insulator substrate, and removing the silicon substrate. The method additionally involves forming electrical contact regions in the thin silicon layer for the buried collectors. 10 figs.

  16. Active region plasma outflows as sources of slow/intermediate solar wind

    NASA Astrophysics Data System (ADS)

    van Driel-Gesztelyi, Lidia M.

    2015-08-01

    L. van Driel-Gesztelyi (1,2,3), D. Baker (1), P. Démoulin (2), Culhane, J.L. (1), M.L. DeRosa (4) C.H. Mandrini (5,6), D.H. Brooks (7), A.N. Fazakerley (1), L.K. Harra (1), L. Zhao (7), T.H. Zurbuchen (7), F.A. Nuevo (5,6), A.M. Vásquez (5,6), G.D. Cristiani (5,6) M. Pick (2)1) UCL/MSSL, UK, (2) Paris Observatory, LESIA, CNRS, France, (3) Konkoly Observatory, Hungary, (4) Lockheed Martin Solar and Astrophysics Laboratory, USA, (5) IAFE, CONICET-UBA, Argentina (6) FCEN, UBA, Argentina (7) Dept. of Atmospheric, Oceanic and Earth Sciences, Univ. of Michigan, USAWe analyse plasma upflows of tens of km/s from the edges of solar active regions discovered by Hinode/EIS and investigate whether or not they become outflows, i.e. find their way into the solar wind. We analyse two magnetic configurations: bipolar and quadrupolar and find that the active region plasma may be directly channeled into the solar wind via interchange reconnection at a high-altitude null point above the active region especially when active regions are located besides coronal holes or in a more complex way via multiple reconnections even from under a closed helmet streamer. We relate the solar observations to in-situ slow/intermediate solar wind streams.

  17. Magnetic Characteristics of Active Region Heating Observed with TRACE, SOHO/EIT, and Yohkoh/SXT

    NASA Technical Reports Server (NTRS)

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

    2001-01-01

    Over the past several years, we have reported results from studies that have compared the magnetic structure and heating of the transition region and corona (both in active regions and in the quiet Sun) by combining X-ray and EUV images from Yohkoh and Solar and Heliospheric Observatory (SOHO) with photospheric magnetograms from ground-based observatories. Our findings have led us to the hypothesis that most heating throughout the corona is driven from near and below the base of the corona by eruptive microflares occurring in compact low-lying "core magnetic fields (i.e., fields rooted along and closely enveloping polarity inversion lines in the photospheric magnetic flux). We now extend these studies, comparing sequences of UV images from Transition Region and Coronal Explorer (TRACE) with longitudinal magnetograms from Kitt Peak and vector magnetograms from MUSIC. These comparisons confirm the previous results regarding the importance of core-field activity to active region heating. Activity in fields associated with satellite polarity inclusions and/or magnetically sheared configurations is especially prominent. This work is funded by NASA's Office of Space Science through the Sun-Earth Connection Guest Investigator Program and the Solar Physics Supporting Research and Technology Program.

  18. Synthetic 3D modeling of active regions and simulation of their multi-wavelength emission

    NASA Astrophysics Data System (ADS)

    Nita, Gelu M.; Fleishman, Gregory; Kuznetsov, Alexey A.; Loukitcheva, Maria A.; Viall, Nicholeen M.; Klimchuk, James A.; Gary, Dale E.

    2015-04-01

    To facilitate the study of solar active regions, we have created a synthetic modeling framework that combines 3D magnetic structures obtained from magnetic extrapolations with simplified 1D thermal models of the chromosphere, transition region, and corona. To handle, visualize, and use such synthetic data cubes to compute multi-wavelength emission maps and compare them with observations, we have undertaken a major enhancement of our simulation tools, GX_Simulator (ftp://sohoftp.nascom.nasa.gov/solarsoft/packages/gx_simulator/), developed earlier for modeling emission from flaring loops. The greatly enhanced, object-based architecture, which now runs on Windows, Mac, and UNIX platform, offers important new capabilities that include the ability to either import 3D density and temperature distribution models, or to assign to each individual voxel numerically defined coronal or chromospheric temperature and densities, or coronal Differential Emission Measure distributions. Due to these new capabilities, the GX_Simulator can now apply parametric heating models involving average properties of the magnetic field lines crossing a given voxel volume, as well as compute and investigate the spatial and spectral properties of radio (to be compared with VLA or EOVSA data), (sub-)millimeter (ALMA), EUV (AIA/SDO), and X-ray (RHESSI) emission calculated from the model. The application integrates shared-object libraries containing fast free-free, gyrosynchrotron, and gyroresonance emission codes developed in FORTRAN and C++, and soft and hard X-ray and EUV codes developed in IDL. We use this tool to model and analyze an active region and compare the synthetic emission maps obtained in different wavelengths with observations.This work was partially supported by NSF grants AGS-1250374, AGS-1262772, NASA grant NNX14AC87G, the Marie Curie International Research Staff Exchange Scheme "Radiosun" (PEOPLE-2011-IRSES-295272), RFBR grants 14-02-91157, 15-02-01089, 15-02-03717, 15

  19. High Resolution Simulations of Tearing and Flux-Rope Formation in Active Region Jets

    NASA Astrophysics Data System (ADS)

    Wyper, P. F.; DeVore, C. R.; Karpen, J. T.

    2015-12-01

    Observations of coronal jets increasingly suggest that local fragmentation and the generation of small-scale structure plays an important role in the dynamics of these events. In the magnetically closed corona, jets most often occur near active regions and are associated with an embedded-bipole topology consisting of a 3D magnetic null point atop a domed fan separatrix surface at the base of a coronal loop. Impulsive reconnection in the vicinity of the null point between the magnetic fluxes inside and outside the dome launches the jet along the loop. Wyper & Pontin 2014 showed that the 3D current layers that facilitate such reconnection are explosively unstable to tearing, generating complex flux-rope structures. Utilizing the adaptive mesh capabilities of the Adaptively Refined Magnetohydrodynamics Solver, we investigate the generation of such fine-scale structure in high-resolution simulations of active-region jets. We observe the formation of multiple flux-rope structures forming across the fan separatrix surface and discuss the photospheric signatures of these flux ropes and the associated local topology change. We also introduce a new way of identifying such flux ropes in the magnetic field, based on structures observed in the magnetic squashing factor calculated on the photosphere. By tracking the position and number of new null points produced by the fragmentation, we also show that the formation of flux ropes can occur away from the main null region on the flanks of the separatrix dome and that the jet curtain has a highly complex magnetic structure. This work was funded through an appointment to the NASA Postdoctoral Program and by NASA's Living With a Star TR&T program.

  20. Observations of photospheric magnetic fields and shear flows in flaring active regions

    NASA Technical Reports Server (NTRS)

    Tarbell, T.; Ferguson, S.; Frank, Z.; Title, A.; Topka, K.

    1988-01-01

    Horizontal flows in the photosphere and subsurface convection zone move the footpoints of coronal magnetic field lines. Magnetic energy to power flares can be stored in the corona if the flows drive the fields far from the potential configuration. Videodisk movies were shown with 0.5 to 1 arcsecond resolution of the following simultaneous observations: green continuum, longitudinal magnetogram, Fe I 5576 A line center (mid-photosphere), H alpha wings, and H alpha line center. The movies show a 90 x 90 arcsecond field of view of an active region at S29, W11. When viewed at speeds of a few thousand times real-time, the photospheric movies clearly show the active region fields being distorted by a remarkable combination of systematic flows and small eruptions of new flux. Magnetic bipoles are emerging over a large area, and the polarities are systematically flowing apart. The horizontal flows were mapped in detail from the continuum movies, and these may be used to predict the future evolution of the region. The horizontal flows are not discernable in H alpha. The H alpha movies strongly suggest reconnection processes in the fibrils joining opposite polarities. When viewed in combination with the magnetic movies, the cause for this evolution is apparent: opposite polarity fields collide and partially cancel, and the fibrils reconnect above the surface. This type of reconnection, driven by subphotospheric flows, complicates the chromospheric and coronal fields, causing visible braiding and twisting of the fibrils. Some of the transient emission events in the fibrils and adjacent plage may also be related.

  1. CALCULATING SEPARATE MAGNETIC FREE ENERGY ESTIMATES FOR ACTIVE REGIONS PRODUCING MULTIPLE FLARES: NOAA AR11158

    SciTech Connect

    Tarr, Lucas; Longcope, Dana; Millhouse, Margaret

    2013-06-10

    It is well known that photospheric flux emergence is an important process for stressing coronal fields and storing magnetic free energy, which may then be released during a flare. The Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) captured the entire emergence of NOAA AR 11158. This region emerged as two distinct bipoles, possibly connected underneath the photosphere, yet characterized by different photospheric field evolutions and fluxes. The combined active region complex produced 15 GOES C-class, two M-class, and the X2.2 Valentine's Day Flare during the four days after initial emergence on 2011 February 12. The M and X class flares are of particular interest because they are nonhomologous, involving different subregions of the active region. We use a Magnetic Charge Topology together with the Minimum Current Corona model of the coronal field to model field evolution of the complex. Combining this with observations of flare ribbons in the 1600 A channel of the Atmospheric Imaging Assembly on board SDO, we propose a minimization algorithm for estimating the amount of reconnected flux and resulting drop in magnetic free energy during a flare. For the M6.6, M2.2, and X2.2 flares, we find a flux exchange of 4.2 Multiplication-Sign 10{sup 20} Mx, 2.0 Multiplication-Sign 10{sup 20} Mx, and 21.0 Multiplication-Sign 10{sup 20} Mx, respectively, resulting in free energy drops of 3.89 Multiplication-Sign 10{sup 30} erg, 2.62 Multiplication-Sign 10{sup 30} erg, and 1.68 Multiplication-Sign 10{sup 32} erg.

  2. Supergranule Diffusion and Active Region Decay

    NASA Technical Reports Server (NTRS)

    Hathaway, David H.; Choudhary, Debi Prasad

    2004-01-01

    Models of the Sun's magnetic dynamo include turbulent diffusion to parameterize the effects of convective motions on the evolution of the Sun's magnetic field. Supergranules are known to dominate the evolution of the surface magnetic field structure as evidenced by the structure of both the active and quiet magnetic network. However, estimates for the dif hivity attributed to su perymules differ by an order of magnitude from about 100 km sup2/s to more than 1000 km sup2/s. We examine this question of the e i v i t y using three merent approaches. 1) We study the decay of more than 30,000 active regions by determining the rate of change in the sunspot area of each active region from day-to-day. 2) We study the decay of a single isolated active region near the time of solar minimum by examining the magnetic field evolution over five solar rotations fiom SOHOMDI magnetograms obtained at 96-minute intervals. 3) We study the characteristics of supergranules that influence the estimates of their diffusive properties - flow speeds and lifetimes as functions of size - fiom SOHO/MDI Dopplergrams.

  3. The Inconvenient Truth About Coronal Dimmings

    NASA Astrophysics Data System (ADS)

    McIntosh, Scott W.

    2009-03-01

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

  4. Simulating coronal condensation dynamics in 3D

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  5. Radio-derived three-dimensional structure of a solar active region

    NASA Astrophysics Data System (ADS)

    Tun, Samuel D.

    Solar active regions are the source of the most violent events observed on the Sun, some of which have a direct impact to modern civilization. Efforts to understand and predict such events require determination of the three-dimensional distributions of density, temperature, and magnetic fields above such active regions. This thesis presents the structure of the solar atmosphere above active region AR 10923, observed on 2006 Nov 10, as deduced from multi-wavelength studies including combined microwave observations from the Very Large Array (VLA) and the Owens Valley Solar Array (OVSA). The VLA observations provide excellent image quality at a few widely spaced frequencies while the OVSA data provide information at many intermediate frequencies to fill in the spectral coverage. In order to optimize the OVSA data for spectroscopic studies, the L1 method of self-calibration was implemented at this observatory, producing the best single frequency maps produced to date. Images at the 25 distinct, available frequencies are used to provide spatially resolved spectra along many lines of sight in the active region, from which microwave spectral diagnostics are obtained for deducing two-dimensional maps of temperature, magnetic field strength, and column density. The derived quantities are compared with multi-wavelength observations from SoHO and Hinode spacecraft, and with a standard potential magnetic field extrapolation. It is found that a two component temperature model is required to fit the data, in which a hot (> 2 MK) lower corona above the strong-field plage and sunspot regions (emitting via the gyroresonance process) is overlaid with somewhat cooler (˜ 1 MK) coronal loops that partially absorb the gyroresonance emission through the free-free (Bremsstrahlung) process. It is also found that the potential magnetic field extrapolation model can quantitatively account for the observed gyroresonance emission over most of the active region, but in a few areas a higher

  6. Global Coronal Waves

    NASA Astrophysics Data System (ADS)

    Chen, P. F.

    2016-02-01

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

  7. Proper Motion Of Emerging Active Regions

    NASA Astrophysics Data System (ADS)

    Tian, Lirong

    2009-05-01

    Observational and modeling results indicate that typically the leading magnetic field of bipolar active regions is often spatially more compact, while more dispersed and fragmented in following polarity. Tian & Alexander (2009, ApJ, 695) studied 15 emerging active regions and find that magnetic helicity flux injected into the corona by the leading polarity is generally several times larger than that injected by the following polarity. They argue that the asymmetry of the magnetic helicity should be responsible for the asymmetry of the magnetic morphology. This argument is supported by two resent model results that magnetic flux tubes with higher degree of twist (and therefor greater magnetic tension) have higher rates of emergence (Murray & Hood 2008, A&A, 479; Cheung et al. 2008, ApJ, 687). These results are consistent because the proper motion (related to the emergence) of the leading polarity was found to be faster than that of the following polarity (van Driel-Gesztelyi & Petrovay 1990, Solar Phys., 126). In this paper, we will reinvestigate the proper motion of leading and following polarities of the emerging active regions, and study possible relationship between the proper motion and magnetic helicity.

  8. Forward Models of Solar Soft X-ray Emissions: What Can They Tell Us About Coronal Heating?

    NASA Astrophysics Data System (ADS)

    Lundquist, Loraine L.

    2006-06-01

    Forward modeling can yield a lot of insight about processes in the solar corona. For the purposes of constraining proposed coronal heating mechanisms, I have developed a forward modeling approach to predict active region coronal emissions, using magnetic field observations at the photosphere as input. First, I calculate a coronal magnetic field and a set of a few thousand magnetic field lines representing it. Next, I treat each field line as a steadily heated coronal loop, with the heating term approximated as a simple parameterized function based on magnetic field properties. Then I use a 1-D energy balance calculation with steady-state flows to solve for loop temperature and density profiles, using different heating parameterizations to simulate different proposed coronal heating mechanisms. After interpolating these thermodynamic variables to a 3-D grid, I then simulate the image expected from a coronal imaging instrument viewing the simulated active region. I compare the observed image to simulated images using different heating mechanisms to see which heating theories best match the observations.I have performed this forward modeling exercise for 10 active regions using four different heating parameterizations. I find significant differences in the predictive accuracy of the four mechanisms, with the best match from a volumetric heating rate that scales proportionally to average loop magnetic field strength and inversely proportional to field line loop length. However, none of the predicted emissions match well with the observed emissions. The mismatch implies that the corona is likely not heated in a steady-state fashion. I gratefully acknowledge funding support from the NASA GSRP program and the DOD solar MURI project at UC Berkeley for completion of this dissertation.

  9. 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.

  10. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2003-08-01

    We investigate the heating of the quiet corona by measuring the increase of coronal luminosity with the amount of magnetic flux in the underlying network at solar minimum when there were no active regions on the face of the Sun. The coronal luminosity is measured from Fe IX/X-Fe XII pairs of coronal images from SOHO/EIT, under the assumption that practically all of the coronal luminosity in our quiet regions comes from plasma in the temperature range 0.9×106K<=T<=1.3×106 K. The network magnetic flux content is measured from SOHO/MDI magnetograms. We find that the luminosity of the corona in our quiet regions increases roughly in proportion to the square root of the magnetic flux content of the network and roughly in proportion to the length of the perimeter of the network magnetic flux clumps. From (1) this result, (2) other observations of many fine-scale explosive events at the edges of network flux clumps, and (3) a demonstration that it is energetically feasible for the heating of the corona in quiet