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NASA NTRS1986

Coronal mass ejections and coronal structures

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.

Hildner, E.↗
NASA NTRS1996

Solar coronal structure: A comparison of NSO/SP ground-based coronal emission line intensities and temperatures with Yohkoh SXT and WSO magnetic data

The large-scale structure of the solar corona is investigated using synoptic maps produced from Fe XIV (530.3 nm), Fe X (637.4 nm) and Ca XV (569.4 nm) data obtained at National Solar Observatory (NSO/SP), Yohkoh/Soft X-ray Telescope (SXT) X-ray data and Wilcox Solar Observatory (WSO) 'source surface' maps. We find that the Fe XIV data are an excellent proxy for spatially-average Yohkoh/SXT data. Isolated emission features and large-scale structures are nearly identical in SXT and Fe XIV maps. In addition, coronal holes and other low-emission regions are very similar. Synoptic temperature maps, calculated from the Fe X/Fe XIV ratio, show a tendency for the highest temperatures to occur where the large-scale magnetic fields change polarity at high latitudes, while lower-latitude features, including active regions, have lower apparent tempertures. Regions of enhanced temperature generally follow the helisopheric current sheet (HCS) as defined by the WSO maps. Further, emission in Ca XV (formed at T is approximately equal to 3 MK), generally occurs only over low-latitude regions that are bright in both FE X (T approximately equal to 1 MK) and Fe XIV (T approximately equal to 2 MK). Thus, there is evidence for low (approximately equal to 1 MK), moderate (approximately equal to 2 MK) and high (approximately 3 MK) temperatures in close proximity in the low corona.

Altrock, R. C.↗
NASA NTRS2001

Combined Ulysses Solar Wind and SOHO Coronal Observations of Several West Limb Coronal Mass Ejections

From October 1996 to January 1997, Ulysses was situated roughly above the west limb of the Sun as observed from Earth at a heliocentric distance of about 4.6 AU and a latitude of about 25 deg. This presents the first opportunity to compare Solar and Heliospheric Observatory (SOHO) limb observations of coronal mass ejections (CMEs) directly with their solar wind counterparts far from the Sun using the Ulysses data. During this interval, large eruptive events were observed above the west limb of the Sun by the Large Angle Spectrometric Coronagraph (LASCO) on SOHO on October 5, November 28, and December 21-25, 1996. Using the combined plasma and magnetic field data from Ulysses, the October 5 event was clearly identified by several distinguishing signatures as a CME. The November 28 event was also identified as a CME that trailed fast ambient solar wind, although it was identified only by an extended interval of counterstreaming suprathermal electrons. The December 21 event was apparently characterized by a six-day interval of nearly radial field and a plasma rarefaction. For the numerous eruptive events observed by the LASCO coronagraph during December 23-25, Ulysses showed no distinct, CMEs, perhaps because of intermingling of two or more of the eruptive events. By mapping the Ulysses observations back in time to the Sun assuming a constant flow speed, we have identified intervals of plasma that were accelerated or decelerated between the LASCO and Ulysses observations.

Funsten, H. O.↗
NASA NTRS2003

Interactions of Dust Grains with Coronal Mass Ejections and Solar Cycle Variations of the F-Coronal Brightness

The density of interplanetary dust increases sunward to reach its maximum in the F corona, where its scattered white-light emission dominates that of the electron K corona above about 3 Solar Radius. The dust will interact with both the particles and fields of antisunward propagating coronal mass ejections (CMEs). To understand the effects of the CME/dust interactions we consider the dominant forces, with and without CMEs. acting on the dust in the 3-5 Solar Radius region. Dust grain orbits are then computed to compare the drift rates from 5 to 3 Solar Radius. for periods of minimum and maximum solar activity, where a simple CME model is adopted to distinguish between the two periods. The ion-drag force, even in the quiet solar wind, reduces the drift time by a significant factor from its value estimated with the Poynting-Robertson drag force alone. The ion-drag effects of CMEs result in even shorter drift times of the large (greater than or approx. 3 microns) dust grains. hence faster depletion rates and lower dust-pain densities, at solar maxima. If dominated by thermal emission, the near-infrared brightness will thus display solar cycle variations close to the dust plane of symmetry. While trapping the smallest of the grains, the CME magnetic fields also scatter the grains of intermediate size (0.1-3 microns) in latitude. If light scattering by small grains close to the Sun dominates the optical brightness. the scattering by the CME magnetic fields will result in a solar cycle variation of the optical brightness distribution not exceeding 100% at high latitudes, with a higher isotropy reached at solar maxima. A good degree of latitudinal isotropy is already reached at low solar activity since the magnetic fields of the quiet solar wind so close to the Sun are able to scatter the small (less than or approx. 3 microns) grains up to the polar regions in only a few days or less, producing strong perturbations of their trajectories in less than half their orbital periods. Finally, we consider possible observable consequences of individual CME/dust interactions. We show that the dust grains very likely have no observable effect on the dynamics of CMEs. The effect of an individual CME on the dust grains, however, might serve as a forecasting tool for the directions and amplitudes of the magnetic fields within the CME.

Ragot, B. R.↗
NASA NTRS2003

Coronal Structure of a Flaring Region and Associated Coronal Mass Ejection

We report the multiwavelength investigations of an eruptive flare event that occurred on 2001 April 2 at about 11 UT. The manifestations associated with this flare event have been studied from the near-Sun region to about 0.5 AU. The H-alpha images from the Meudon Spectroheliograph reveal a fast spectacular eruption of plasmoids from the flare site to the west and a Moreton wave disturbance propagating toward the south, A bright, fast, wide coronal mass ejection (CME) associated with this eruptive event was imaged by SOHO/LASCO and the remote-sensing interplanetary scintillation technique. The timings and positions of the Type II radio bursts, H-alpha eruption, and CME onset as well as the magnetic field configuration suggest a release of energy at the null point. The results seem to support the "breakout" scenario proposed by Antiochos and coworkers, and they are also suggestive that the energy release is followed by magnetic reconnection between the low-lying loops near the separatrix and the loop system above them.

Kundu, Mukul R.↗
NASA NTRS1974

Solar wind model predictions for the sources of streams observed at 1 AU - Coronal enhancements or coronal holes

The present paper discusses attempts which have been made to locate the solar sources of the solar wind streams observed at or near 1 AU. Solar-wind data collected by the Mariner 2, Mariner 5, and IMP-1 spacecraft are considered. It is concluded that the type of solar feature considered as the source of solar-wind velocity enhancements depends upon the solar-wind model used. All single-fluid models predict the source to have a significantly higher temperature and lower density than the surrounding region, while the two-fluid model predicts a change in temperature that is much smaller than the predicted change in density.

Jones, D. E.↗
NASA NTRS1989

Coronal activity in F-, G-, and K-type stars. III - The coronal differential emission measure distribution of Capella, Sigma-squared CrB, and Procyon

EXOSAT soft X-ray spectra of three binary systems of cool stars are analyzed: Capella (G6 III + F9 III), Sigma-squared CrB (F8 V + G1 V), and Procyon (F5 IV-V + DF). The EXOSAT transmission grating spectrometer permits the study of individual spectral lines and line complexes between 10 and 200 A with approximately 3 A resolution. First it is demonstrated that the spectra can be described reasonably well by a two-temperature model corona. Then the assumption that only two temperatures exist in the stellar coronas is relaxed and differential emission measure distributions are derived from the three spectra. The results from the multithermal modeling are consistent with those of the two-temperature models: emission from the coronas of each of the three stars is dominated by plasma in two relative narrow temperature intervals. These intervals are centered on 5 MK and 25 MK in the cases of Capella and Sigma-squared CrB, and 0.6 MK and 3 MK in the case of Procyon. The implications of the results for the structure of stellar coronas are briefly discussed.

Lemen, J. R.↗
NASA NTRS1992

Coronal magnetic structures observing campaign. IV - Multiwaveband observations of sunspot and plage-associated coronal emission

Results of simultaneous observations of an active region located near the central meridian obtained on December 18, 1987, are presented. An asymmetric looplike structure connects the strong leading sunspot with a nearby region of opposite polarity. Both 6- and 20-cm emission lie along this structure, rather than over the sunspot, with higher frequency emission originating closer to the footpoint inside the sunspot. The 20-cm emission is due to a superposition of second- and third-harmonic gyroemission, where the field strength is 160-300 G, while the 6-cm emission is due to third-harmonic gyroemission from a region where the magnetic field strength ranges from 547 to 583 G. X-ray data associated with an area of trailing plage are used to predict the brightness temperature structure due to thermal bremsstrahlung emission in the 6- and 20-cm wavebands.

Brosius, Jeffrey W.↗
NASA NTRS2007

The Coronal-Dimming Footprint of a Streamer-Puff Coronal Mass Ejection: Confirmation of the Magnetic-Arch-Blowout Scenario

In this paper, for a CME of the particular variety recently identified by Bemporad et al (2005), we present new evidence that strengthens the conclusion of Bemporad et al that for these CMEs the pre-eruption magnetic field that explodes to drive the CME is laterally far offset from the radial path of the full-blown CME in the outer corona. In CMEs of the particular variety of those found by Bemporad et al, the flare-site field that explodes is much more compact than the flare-site fields that explode in most major flares and large CMEs, and is located in a flank of the base of a streamer. After presenting our new evidence for how CMEs of this variety are produced, we cite and discuss examples of larger flare-producing magnetic explosions that are not necessarily in a flank of a streamer but occur together with a large CME that in the outer corona is laterally far offset from the flare. We conclude that there is a broad class of CMEs that come from flare-producing magnetic explosions of various sizes and that are laterally far offset from the flare. We propose that all CMEs of this broad class are produced in basically the same way as those of the particular variety of the one that we present in this paper. In this paper, it is therefore convenient and useful to refer to this broad class of CMEs (regardless of the pre-eruption size of the offset field that explodes and whether or not this field is in the flank of a streamer), as "over-and-out" CMEs. Because the lack of recognition of this class of CMEs has contributed to the confusion and controversy regarding the relation between flares and CMEs (e.g., Kahler 1992; Gosling 1993; Hudson et al 1995), it is important that this class of CME have an explicit name. We adopt the name over-and-out CME because it is a needed descriptive term, especially for the purpose of this paper.

Moore, Ronald L.↗