Coronal Disturbances Research Articles

Prompt Solar Energetic Particles with Large-Scale Cross-Disk Coronal Disturbance

By using the observations of the Extreme-UV Imaging Telescope (EIT), we studied three major solar eruptions from the same super active region NOAA 10486 during the interval of October 26 to November 04, 2003. The three eruptions took place when the active region located on the eastern hemisphere, near the central meridian and on the western limb, respectively. In the first event (Oct 26 event), the coronal disturbance (indicated as an EIT wave) in EUV images was limited east to the central meridian, and there were no solar energetic particles (SEPs) detected. The second event (Oct 28 event) accompanied a nearly entire disk disturbance and very large and prompt SEP enhancements. For the last event (Nov 04 event), there was no obvious coronal disturbance on the disk, and the SEP enhancements were much more gradual. From these observational features, we suggest that different coronal disturbances correspond to different acceleration and propagation histories. A large-scale, cross-disk coronal disturbance may open quite a lot of magnetic field lines in the low corona, facilitating the direct access of flare accelerated SEPs to the Sun-Earth connected interplanetary magnetic field lines. Subsequently the SEP intensity will exhibit a very prompt enhancement.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Flare-induced coronal disturbances observed with Norikura “NOGIS” coronagraph

Flare-induced coronal disturbances observed with Norikura “NOGIS” coronagraph

Statistical Correlations between Solar Microwave Bursts and Coronal Mass Ejections

We compare listings of coronal mass ejections (CMEs) observed by LASCO on SOHO and solar microwave bursts (SMBs) recorded by the Radio Solar Telescope Network (RSTN) operated by the United States Air Force. These data sets are the product of stable and continuous observations of the whole Sun and provide suitable bases for robust statistical studies. In total, 3557 coronal ejections and nearly 1051 bursts above 50 sfu were observed from 1996 January through 2001 May. Correlated events are easily distinguished by time proximity. Correlations improve as CME launch heights are projected to the solar limb, when the rms scatter in CME-SMB delay was as little as 16 minutes, but because coronal disturbances are only visible when they emerge from behind occulting disks, timing associations depend on the assumed source and acceleration. The probability of correlation rises with burst flux, duration or temporal complexity, and ejection speed or width. For the 164 SMBs with intensities over 500 sfu, 70% ± 8% were associated with CMEs. For the 160 CMEs that were halo-like or have speeds over 1000 km s-1 (characteristics that have been associated with geoeffective events), 60% ± 8% and 84% ± 10% were associated with SMBs, respectively.

Origin of Helical Coronal Disturbances from the Sun

By combining data from the Nobeyama Radioheliograph and the LASCO coronagraph aboard the SoHO spacecraft, we report two helical coronal disturbances accompanying white-light coronal mass ejections (CMEs). These are activated prominences at the base, rotating around each vertical axis while moving on the solar surface with projected speeds of ≥50 km s-1. The activity continues in a CME core and in a neighboring streamer growing over 6 R☉. Neither flare activity nor radio bursts were observed during the two events. We suggest that the apparent presence or absence of a CME core depends on the density of the eruptive material associated with the CME.

Nonthermal Radio Signatures of Coronal Disturbances with and without Coronal Mass Ejections

This study presents data on two events from the Extreme-UV Imaging Telescope (EIT) and the Large Angle and Spectroscopic Coronagraph instruments (C1, C2, and C3), Geostationary Operational Environmental Satellite (GOES) soft X-ray data, and 40-800 MHz radio spectra of the Astrophysical Institute Potsdam. At first glance, the two events appear similar. However, one event decays after a flare-related ejection of cold and hot matter into the lower corona causing only brightness changes in EIT and C1, while the other event marks the onset of a coronal mass ejection (CME) that propagates with a leading-edge speed of ≈530 km s-1 between 2 and 30 R☉. The radio data reveal two differences between the CME and non-CME events: (1) a characteristic faint type III burst group in the time interval with the first clearly CME-related structural change in the coronagraph images and (2) a continuum emission with a frequency drift during the passage of the CME matter through the C1 field of view. Furthermore, we show that the radio spectral data can provide essential information on the timing of the early stages of CME formation and the initial mass motions associated with the ejection.

Recurrent solar wind streams

A new approach to investigating the statistical relationship between certain solar features and recurrent wind streams is presented. This approach is based, on a comparative analysis of the distributions of lifetimes of a set of solar features, recurrent geomagnetic disturbances, and geomagnetic “calms.” Correlation coefficients of 0.81, 0.85, 0.79, and 0.77 are found for the distributions of several solar features—filaments, large-scale magnetic fields, coronal features, and coronal holes, respectively—and recurrent geomagnetic disturbances. A correlation factor of 0.97 between the distributions of geomagnetic “calms” and active regions is found. The combined evidence indicates that no specific type of solar feature is responsible for the recurrent stream activity. Rather, the configuration of the large-scale magnetic field of the Sun appears to control the permanently existing corpuscular activity. Since prominences trace polarity division lines of the large-scale magnetic field structure of the Sun, they have been checked as a possible general predictor of recurrent corpuscular activity; their parameters could present the most reliable indices that relate closely with trends in geomagnetic disturbances. A comparative analysis of cyclic variations of sunspot numbers, the total number of prominences, the relative number of low-height (<-20″) prominences, and recurrent geomagnetic storms is made for solar cycle N16. The relative number of low-height prominences is found to correlate broadly (0.83) with recurrent wind streams.

On the Solar Origins of Intense Geomagnetic Storms Observed During 6–11 March 1993

Intense geomagnetic storms with DST index ≤-100 nT were recorded on 9 March and 11 March 1993 associated with solar activity on 6 March and 9-10 March, respectively. In this paper, we discuss the characteristic features of the solar origins of the two events that gave rise to coronal and interplanetary disturbances and as a consequence produced strong geomagnetic activity at the Earth. The source of the activity in one case is attributed to a major 3M7.0 flare that occurred on 6 March 1993 and in the other case, to two large filament disruptions on the disk during 9-10 March, 1993. Both these sources were found to be located near changing or varying low-latitude coronal holes. They were also located close to the heliospheric currents sheets. Distinct X-ray activity was observed for both the events as observed by the Yohkoh SXT telescope. The detailed evolution and a comparison of these events on the basis of Yohkoh soft X-ray observations are presented here.

A Long-Duration Solar Flare with Mass Ejection and Global Consequences

view Abstract Citations (176) References (15) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Long-Duration Solar Flare with Mass Ejection and Global Consequences Hudson, H. S. ; Acton, L. W. ; Freeland, S. L. Abstract We report observations of a long-duration flare with mass ejection from the corona, using the Yohkoh soft X-ray telescope (SXT). This flare occurred 1994 November 13 near disk center during quiet solar conditions, with excellent temporal coverage of both the core activity in the active region itself and of the global corona. The initial X-ray images reveal two arcades of cusped magnetic loops, connected via a series of thin loops. These loops rise rapidly during the increasing phase of soft X-ray flare brightness. In its final state, the flare has the configuration of postflare loops with a cusp. Large regions of the X-ray corona appear to empty during the evolution of the event. We suggest that this corresponds a coronal mass ejection (CME) seen in soft X-rays. Its detection in the SXT images is consistent with the finding that material participating in a CME exists at elevated coronal temperatures (2.8 x 106 K in this case) before the ejection. We estimate a mass >4 x 1014 g for the ejected material. The X-ray morphology of the event has strong points of similarity with the classical reconnection picture of long-duration event (LDE) formation, but there are significant discrepancies: there is no observed inward flow during the rise phase, the expansions are multiple and appear to be nonradial, and none of the observed motions suggest a reconnection jet. We note the subsequent occurrence of very large scale coronal disturbances, including regions near the boundaries of coronal holes at both poles. We suggest that this global disturbance implies a perturbation reaching as far outward as the heliospheric neutral sheet. The exciter would require a horizontal velocity of approximately 200 km s-1 in such a case, consistent with the projected velocity of the plasma cloud that we identify with a CME in the process of launching. Publication: The Astrophysical Journal Pub Date: October 1996 DOI: 10.1086/177894 Bibcode: 1996ApJ...470..629H Keywords: SUN: FLARES; SUN: CORONA; SUN: MAGNETIC FIELDS; SUN: PARTICLE EMISSION full text sources ADS |

Large-Scale Interplanetary Magnetic Field Configuration Revealed by Solar Radio Bursts

An instantaneous view of the interplanetary extension of the solar magnetic field is provided here by measurements from a space platform at high ecliptic latitudes of the trajectories of individual type III solar radio bursts. The Ulysses spacecraft provides this unique vantage point with an orbit taking it far from the ecliptic plane. The Ulysses radio measurements illustrate the capability of detecting and tracking coronal disturbances as they propagate through the interplanetary medium.

Major flare effects on the intensity of the green corona and geomagnetic activity

The effects of the solar major flares indicated by the intensive radio bursts, high velocity streams or shock waves, coronal and ionospheric disturbances on the geomagnetic and coronal activities are investigated during the near the maximum phase of 21st solar cycle, in detail. The significant and the weak increases in the level of the geomagnetic and coronal activities indices were observed, respectively, after the occurrence of these events.

Simple tests for the ideal MHD stability of line-tied coronal magnetic fields

Methods for investigating the stability of line-tied, cylindrically-symmetric magnetic fields are presented. The energy method is used and the perturbed potential energy integral is manipulated to produce simple tests that predict either stability to general coronal disturbances or instability to localized modes, both satisfying photospheric line-tying. Using these tests the maximum amount of magnetic energy, that can be stored in the coronal magnetic field prior to an instability, can be estimated. The tests are applied to four different classes of equilibria and results are obtained for both arcade and loop geometries.

Coronal disturbances

Etude de deux phenomenes dans la couronne solaire interne et externe: evenements transitoires coronaux de la raie verte Fe XIV et ejections de la masse coronale en lumiere blanche

Photospheric line-tying conditions for the MHD stability of coronal magnetic fields

Using the localised, ballooning ordering, the effect of a density stratification on the ideal MHD stability of magnetic fields is investigated. It is found that, when the photospheric density is very much greater than the coronal value, the line tying conditons are best simulated by assuming that all coronal disturbances vanish at the photospheric boundary. This is commonly known as the rigid wall conditions.

Coronal disturbances and their terrestrial effects

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

Direct correlations between coronal transients and interplanetary disturbances

Major interplanetary shock waves have often been successfully associated with major solar flares. The interplanetary response to weaker solar events, e. g., eruptive prominences (EP) and slow coronal transients, is far less pronounced. Recently, progress has been made by combining the newly-available data of white-light-coronagraph measurements from the earth-orbiting satellite P78/1 (these data show the development of coronal transients between 2.5 and 10 R ⊙), in-situ plasma measurements from the HELIOS solar probes positioned mostly above the Sun’s limb at solar distances between 60 and 200 R ⊙ (showing the reactions of the interplanetary plasma), ground based Hα-coronagraphs (showing in a few cases the evolution of EP’s from the Sun’s limb up to 1.5 R ⊙

Magneto-Atmospheric Waves

A theoretical treatment of magneto-atmospheric waves is presented and applied to the modelling of waves in the solar atmosphere. The waves arise in compressible, stratified, electrically conductive atmospheres within gravitational fields when permeated by a magnetic field. Compression, buoyancy, and distortion of the magnetic field all contribute to the existence of the waves. Basic linearized equations are introduced to describe the waves and attention is given to plane-stratified atmospheres and their stability. A dispersion relation is defined for wave propagation in a plane-stratified atmosphere when there are no plane-wave solutions. Solutions are found for the full wave equation in the presence of either a vertical or a horizontal magnetic field. The theory is applied to describing waves in sunspots, in penumbrae, and flare-induced coronal disturbances.

Helium abundance enhancements in the solar wind

Helium abundance (A(He)) enhancements observed with Los Alamos instruments on IMP 6, 7, and 8 during the 1972–1978 interval have been investigated. Statistical analysis of 73 large events with A(He) ≥ 10% (HAEs) provides evidence for a close link between helium enhancements at 1 A.U. and transient coronal mass ejections. HAE events are sporadic, sometimes clustered in time, and their frequency of occurrence is approximately in phase with the solar cycle. Nearly 50% of HAEs are associated with interplanetary shocks and/or geomagnetic activity sudden commencements, but the plasma pattern associated with A(He) enhancements is independent of shock occurrence. This pattern features high magnetic field strength, low alpha‐proton velocity difference, and low proton temperature. These plasma properties suggest that the enhancement is embedded in a ‘closed,’ magnetically dominated structure that expands adiabatically. In fact, HAEs are likely to be still evolving dynamically at 1 A.U. Evidence of a significant association between helium enhancements at 1 A.U. and type II and IV radio bursts in the corona is presented. We interpret these results to mean that most HAE events originate in transient coronal disturbances in which the magnetic field strength is enhanced.

A mechanism for a class of solar coronal disturbances

In this paper, a new ideal magnetohydrodynamic (MHD) model is used to examine the dynamical response of the upper solar atmosphere to injection of cold mass from the photosphere akin to a surge. A significant new physical phenomenon is revealed: the formation of an almost stationary loop prominence in the atmosphere as a consequence of the ejected material. Simultaneously with the formation of this new loop, the simulation exhibits MHD waves that propagate outward (i.e., away from the loop) to excite coronal material. It is conjectured that these waves may trigger a class of coronal disturbances.

Flare buildup in X-rays, UV, microwaves and white light

Coordinated observations using space and ground-based instruments were made of active region complex #2522/2530, 24–30 June, 1980. The 10 largest flares from these regions were of importance M1-M6 in X-rays, and all were observed from satellites, except for one observed from a balloon. Several kinds of buildup signature have been found in the tens of minutes before these flares. Among these signatures are the following: 1) Relative faintness in X-ray lines of the pre-flare pixels, 2) X-ray (5–15 keV) “flashes” at points displaced by 1′–2′ from the flare site, 3) Rising filaments seen in Hα and Ultraviolet 4) Microwave intensification, polarization increase and polarization flip 5) Coronal disturbances above limb flares at or before the impulsive phase.

Observations of coronal disturbances from 1 to 9 R ?

H alpha, white-light and radio observations of a coronal disturbance on Jan. 11, 1973, commencing at about 0036 hr UT show that a piston-driven shock wave propagated outward through the corona to heights of at least 9 solar radii. Probably most of the expelled coronal gas originated in a coronal enhancement in the lower corona. An estimate of the kinetic energy and the mass of the expelled gas is obtained which is compatible with observations of piston-driven shock waves near the earth. Shock-wave parameters are evaluated, and a model of the disturbance is outlined.