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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Characteristics of flares producing metric type II bursts and coronal mass ejections

An attempt is made to study the origin of coronal shocks by comparing several flare characteristics for two groups of flares: those with associated metric type II bursts and coronal mass ejections (CMEs) and those with associated metric type II bursts but no CMEs. CMEs accompany about 60 percent of all flares with type II bursts for solar longitudes greater than 30 deg, where CMEs are well observed with the NRL Solwind coronagraph. H-alpha flare areas, 1-8 A X-ray fluxes, and impulsive 3-cm fluxes are all statistically smaller for events with no CMEs than for events with CMEs. It appears that both compact and large mass ejection flares are associated with type II bursts. The events with no CMEs imply that at least many type II shocks are not piston-driven, but the large number of events of both groups with small 3 cm bursts does not support the usual assumption that type II shocks are produced by large energy releases in flare impulsive phases. The poor correlation between 3 cm burst fluxes and the occurrence of type II bursts may be due to large variations in the coronal Alfven velocity.

Kahler, S.↗
NASA NTRS1985

Coronal mass ejections and interplanetary shocks

A comparison between Solwind observations of coronal mass ejections (CME's) and Helios 1 observations of interplanetary shocks during 1979-1982 indicates that 72 percent of the shocks were associated with large, low-latitude mass ejections on the nearby limb. Most of the associated CME's had speeds in excess of 500 km/s, but some of them had speeds in the range 200-400 km/s. An additional 26 percent of the shocks may have been associated with CME's, but we were less confident of these associations because the sizes and locations of the CME's did not seem appreciably different from those of the numerous CME's without Helios shocks. Only 2 percent of the shocks clearly lacked CME's. As the average level of sunspot activity declined during 1982, the shock frequency also declined, but the observed shocks and some of their associated CME's had unusually high speeds well in excess of 1000 km/s.

Sheeley, N. R., Jr.↗
NASA NTRS1984

Dynamic evolution of recurrent mass ejections observed in H-alpha and C IV lines

The mass ejections of 1 September, 1980 are studied from observations obtained with the MSDP spectrograph and with the Ultraviolet Spectrometer and Polarimeter aboard the Solar Maximum Mission satellite. The analysis is focused on observations in the chromospheric H-alpha line and the transition region C IV 1548 A line. It is noted that cold and hot material had the same projection, although the upward C IV velocity structure was more extended than the H-alpha one. It is shown that the observed contrast of the H-alpha absorbing structure can be interpreted in terms of a dynamic cloud model overlying the chromosphere. Radial velocities of 25-30 km/s and -40 km/s are estimated for the first and second phases of ejection, respectively.

Schmieder, B.↗
NASA NTRS1985

High-resolution X-ray spectra of solar flares. VII - A long-duration X-ray flare associated with a coronal mass ejection

It has been recognized that very long duration X-ray events (lasting several hours) are frequently associated with coronal mass ejection. Thus, Sheeley et al. (1983) found that the probability of the occurrence of a coronal mass ejection (CME) increases monotonically with the X-ray event duration time. It is pointed out that the association of long-duration, or long-decay, X-ray events (LDEs) with CMEs was first recognized from analysis of solar images obtained by the X-ray telescopes on Skylab and the Naval Research Laboratory (NRL) slitless spectroheliograph. Recently high-resolution Bragg crystal X-ray spectrometers have been flown on three spacecraft, including the Department of Defense P78-1 spacecraft, the NASA Solar Maximum Mission (SMM), and the Japanese Hinotori spacecraft. In the present paper, P78-1 X-ray spectra of an LDE which had its origin behind the solar west limb on November 14, 1980 is presented. The obtained data make it possible to estimate temperatures of the hottest portion of the magnetic loops in which the emission arises.

Kreplin, R. W.↗
NASA NTRS1985

Structural integrity of GAS ejection system

The following Get Away Special (GAS) ejection system components were analyzed: full diameter motorized door assembly (FDMDA); actuating assembly; gas ejection system; lower end plate; and the battery boxes. Special considerations and experiment constraints are also discussed.

Mark Cascia↗
NASA NTRS1986

Do we understand coronal mass ejections yet?

Though many more coronal mass ejections (CMEs) were observed, and though much more has been learned about them during the Solar Maximum Analysis period, they are not yet fully understood. A few recent observational results are reviewed; conclusions and implications drawn from these observations are presented. An emerging picture of the magnetic character of CMEs is sketched; the variations of CMEs' frequency and latitudes over most of a solar cycle are shown. A strong caution about the present lack of concensus on the definition of CMEs is illustrated with examples of the consequences of using different definitions. Finally, some remaining questions about coronal mass ejections are posed.

Hildner, Ernest↗
NASA NTRS1987

On the association of erupting magnetic fields with eruptive prominences and coronal mass ejections

A number of space and ground-based observations give evidence that the eruptive prominences, coronal mass ejections (CMEs) and associated shocks are generated by a common cause, i.e., the eruption of the magnetic field on the Sun. Some 60% of the observed CMEs are associated with the eruptive prominences. It is believed that in reality a much better correlation should be between these events because of observational limitations and of the effect of partial eruption. Some recent results on the formation and evolution of the quiescent and the active region prominences give an idea on the early phase of eruption of the magnetic field with the prominence plasma frozen in. In the latter phase of eruption the magnetic field lifted high into the corona and is seen (as manifested by the cold plasma frozen in) as a system of huge loops - evidently the result of some reconnections at lower heights. The legs of these erupting loops interact sometimes with the local magnetic field, i.e., it often appears to be an active region. In consequence of this interaction the activation of prominences and generation of flares can take place on some occasions as well as ejection of surges and sprays.

Rompolt, Bogdan↗
NASA NTRS1988

Ejection of sodium from sodium sulfide by the sputtering of the surface of Io

The mechanism by which Na is removed from the surface of Io prior to its injection into the plasma torus is investigated experimentally. Na2S films of thickness 3-8 microns were produced by spray coating an Ni substrate in a dry N2 atmosphere and subjected to sputtering by 34-keV Ar(+), Ne(+), Kr(+), or Xe(+) ions up to total doses of about 5 x 10 to the 18th ions/sq cm. The sputtering yields and mass spectra are found to be consistent with ejection of only small amounts of atomic Na and somewhat larger amounts of Na-containing molecules. It is concluded that the amount of Na ejected by magnetospheric-ion sputtering of Na2S would be insufficient to account for the amounts observed in the Io neutral cloud. A scenario involving sputtering of larger polysulfide molecules is considered.

Chrisey, D. B.↗
NASA NTRS1988

Density and white light brightness in looplike coronal mass ejections - Importance of the preevent atmosphere

Following studies of Sime et al. (1984), in which some models that simulate coronal mass ejections were found to be inaccurate simulators, two of these models (a model of a static corona in a current-free magnetic field, and a model of a polytropic corona with a coronal streamer) were reexamined, along with a new model, which differed from the second model in that it contained an atmospheric heating term. It is shown that the inclusion of a realistic preevent atmosphere can improve agreement with observations. The essential improvement in the heated atmosphere is that the fast-mode speed is increased to the extent that shocks may not form for typical ejection velocities.

Steinolfson, R. S.↗
NASA NTRS1990

MHD simulations of coronal mass ejections - Importance of the driving mechanism

The importance of the form of the driving mechanism in MHD simulations of coronal mass ejections is investigated. A model simulation problem is devised, and it is found that the use of a simple form for the initial corona, with an upward moving parcel of cold, dense plasma as the driving mechanism, can produce results that are consistent with many of the features observed by coronagraphs. The results imply that the nature of the driving mechanism may play an important role in determining the dynamical evolution of mass ejections.

Linker, J. A.↗
NASA NTRS1990

MHD intermediate shocks in coronal mass ejections

A simplified model of coronal mass ejections is considered in which at least a portion of the interaction with the background corona involves a shock wave, and the allowable shock solutions and their compressive signatures are examined. The MHD shock-jump equations have a maximum of three possible types of solutions with an entropy rise for fixed values of the physical variables (slow, intermediate, and fast shocks). However, one of the three solution classes (the intermediate shock) is widely believed to not occur in nature and is regarded as nonevolutionary or extraneous. Without the intermediate shock, there is no multiplicity of solutions in that only one shock (or none) can occur for given physical values. All three potential shock types are considered, and it is shown solely on the basis of the shock-jump equations, that intermediate shocks must exist along some segment of the shock front for certain parametric regimes and for conditions that probably occur in some coronal mass ejections.

Steinolfson, R. S.↗
NASA NTRS1992

Focused transport of energetic particles along magnetic field lines draped around a coronal mass ejection

Evidence is presented for focused transport of energetic particles along magnetic field lines draped around a coronal mass ejection. This evidence was obtained with the University of Maryland/Max-Planck-Institute experiment on the ISEE-3 spacecraft during the decay phase of the June 6, 1979, solar particle event. During the early portion of the decay phase of this event, interplanetary magnetic field lines were apparently draped around a coronal mass ejection, leading to a small focusing length on the western flank where ISEE 3 was located. A period of very slow decrease of particle intensity was observed, along with large sunward anisotropy in the solar wind frame, which is inconsistent with predictions of the standard Fokker-Planck equation models for diffusive transport. It was found possible to fit the observations, assuming that focused transport dominates and that the particle pitch angle scattering is isotropic.

Tan, L. C.↗
NASA NTRS1992

Martens-Kuin models of normal and inverse polarity filament eruptions and coronal mass ejections

An analysis is made of the Martens-Kuin filament eruption model in relation to observations of coronal mass ejections (CMEs). The field lines of this model are plotted in the vacuum or infinite resistivity approximation with two background fields. The first is the dipole background field of the model and the second is the potential streamer model of Low. The Martens-Kuin model predicts that, as the filament erupts, the overlying coronal magnetic field lines rise in a manner inconsistent with observations of CMEs associated with eruptive filaments. This model and, by generalization the whole class of so-called Kuperus-Raadu configurations in which a neutral point occurs below the filament, are of questionable utility for CME modeling. An alternate case is considered in which the directions of currents in the Martens-Kuin model are reversed resulting in a so-called normal polarity configuration of the filament magnetic field. The background field lines now distort to support the filament and help eject it. While the vacuum field results make this configuration appear very promising, a full two- or more-dimensional MHD simulations is required to properly analyze the dynamics resulting from this configuration.

Smith, D. F.↗
NASA NTRS1990

Coronal mass ejections and magnetic flux ropes in interplanetary space

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

Gosling, J. T.↗
NASA NTRS1990

A bubblelike coronal mass ejection flux rope in the solar wind

A resolution to the question of whether coronal mass ejections are loops or bubbles is proposed and applied to the geometrical analysis of a solar wind event detected at 1 AU by ISEE 1 and 3. The discontinuity orientations, the size determined by time of passage, and the magnetic cloud signature are fit into the topology of a flux rope loop distorted by expansion into a thick rope with comparable dimensions in both the ecliptic and meridional planes. The looped rope fills a bubblelike cavity, thus preserving both types of proposed coronal mass ejection geometries. Other interesting features of the data include an apparent separation by the rope core of bidirectionally streaming protons in the leading section from electrons in the trailing section, possible vortical flow within the magnetic cloud, and a well-defined filamentary structure behind the shock.

Crooker, N. U.↗
NASA NTRS1993

Thermal and nonthermal emissions during a coronal mass ejection

Observations were made of thermal and nonthermal radio emissions from a coronal mass ejection (CME) at meter-decameter wavelengths. The speed of the CME was found to be approximately 450 km/sec. It was possible to observe the thermal structure of the CME in radio due to the absence of nonthermal radio emission in the beginning of the event, and the weakness of the following event. Several minutes after the onset of the CME, type III bursts and a nonthermal continuum began. Radio and optical observations are used to show that the CME was not driven by the flare. The thermal structure and geometry of the mass ejection in radio is investigated and compared with the optical evidence. Lastly, a schematic model of the event is developed to show that particle acceleration high in the corona is possible.

Gopalswamy, N.↗
NASA NTRS1993

Coronal mass ejections - The link between solar and geomagnetic activity

The phenomenon of coronal mass ejections (CME) is examined with reference to recent work in this field. In particular, attention is given to CMEs close to the sun, CMEs in interplanetary space, solar cycle variations of CMEs, and magnetic field topology and the problem of magnetic flux balance in interplanetary space. It is demonstrated that transient ejections of material from the sun are the cause of almost all large nonrecurrent geomagnetic substorms, as originally suggested by Chapman and his colleagues.

Gosling, J. T.↗
NASA NTRS1990

Models of material ejection

Some recently developed models related to the formation of a coronal mass ejection (CME) are reviewed. The models individually consider the stability of a prominence, the eruption of a coupled prominence and CME configuration with driven reconnection below the prominence, magnetic arcade equilibrium, and coronal evolution due to shear motion. No effort is made to critique the various models. Their relevance to actual observed material ejections will ultimately be determined by detailed comparison with present and future observations.

Steinolfson, R. S.↗