Title: Quiet Sun EUV transient brightenings and turbulence. A panoramic view by EIT on board SOHO
Authors: BERGHMANS, D.; CLETTE, F.; MOSES, D.
Journal: Astronomy and Astrophysics, v.336, p.1039-1055 (1998)
Publication Date: 08/1998
Abstract: Since January 1996, the Extreme-Ultraviolet Imaging Telescope (EIT, onboard SOHO) has produced unique image sequences covering a wide field of view with a high temporal resolution, in the \ion{He}{ii} transition region line and in several Fe coronal emission lines. Using two sequences acquired with cadences of the order of one minute and with durations ranging from one hour to several hours, we analyse the dynamical properties of the transition region and corona. We find evidence of turbulence both in spatial and in temporal power spectra suggesting that the plasma of the quiet solar atmosphere is in a permanent state of turbulence.
As predicted by numerical simulations, this turbulence has an highly intermittent nature. We find an unexpectedly large number of small-scale brightenings. The coronal brightenings are identified as the low energy counterparts of ``X-ray network flares'' observed with SXT on board Yohkoh. The thousands of brightenings observed by EIT in the transition region include many that are similar to ``blinkers'' observed with CDS, though we find a larger variety.
Thanks to EIT's wide spatial coverage, we can perform a large scale statistical study, complementing spectroscopic studies which give access to only a very small subsample of events. We present occurrence distributions of duration, size and radiative output of the brightenings as well as various correlations between these parameters. The energy injected by the brightenings into the solar atmosphere is insufficient to be in itself responsible for coronal heating. We discuss the importance of the ubiquitous small brightenings as perhaps the most visible aspect of yet undetected heating events higher up in the quiet corona.
ARTICLE: Journal Article
Title: Multi-wavelength observations of post flare loops in two long duration solar flares
Authors: HARRA-MURNION, L. K.; SCHMIEDER, B.; VAN DRIEL-GESZTELYI, L.; SATO, J.; PLUNKETT, S. P.; RUDAWY, P.; ROMPOLT, B.; AKIOKA, M.; SAKAO, T.; ICHIMOTO, K.
Journal: Astronomy and Astrophysics, v.337, p.911-920 (1998)
Publication Date: 09/1998
Abstract: We have analysed two Long Duration solar Events (LDEs) which produced large systems of Post Flare Loops (PFLs) and which have been observed by Yohkoh and ground-based observatories. Using the Maximum Entropy Method (MEM) image synthesis technique with new modulation patterns we were able to make hard X-ray (HXR) images of the post flare loops recorded in the L Channel (13.9-22.7 keV) of the Yohkoh Hard X-ray Telescope. We obtained co-aligned 2-D maps in Halpha (10(4) K), in soft X-rays (5x 10(6) K) and in hard X-rays (20x 10(6) K). We conclude that the soft X-ray (SXR) loops lie higher than the Halpha loops and the former are overlaid by HXR emission. This is suggestive of the magnetic reconnection process. However some details are not consistent with the standard models. Firstly the separation between the HXR source and the SXR loop increases with time, with the HXR source being approximately a factor of five larger than the equivalent source in impulsive flares. Secondly the cooling times deduced from observations are longer than the theoretically expected ones and the discrepancy increases with time. We review the current models in view of these results.
ARTICLE: Journal Article
Title: Solar Cycle 22 UV Spectral Irradiance Variability: Current Measurements by SUSIM UARS
Authors: FLOYD, L. E.; REISER, P. A.; CRANE, P. C.; HERRING, L. C. ; PRINZ, D. K.; BRUECKNER, G. E.
Journal: Solar Physics, v. 177, Issue 1/2, p. 79-87.
Publication Date: 00/1998
Abstract: Not Available
Article: Not Available
Title: Magnetic Sources of the Solar Irradiance Cycle
Authors: LEAN, J. L.; COOK, J.; MARQUETTE, W.; JOHANNESSON, A.
Journal: Astrophysical Journal v.492, p.390
Publication Date: 01/1998
Abstract: Using recently processed Ca K filtergrams, recorded with a 1 A filter at the Big Bear Solar Observatory (BBSO), we quantitatively assess the component of solar irradiance variability attributable to bright magnetic features on the Sun's disk. The Ca K filtergrams, "flattened" by removing instrumental effects and center-to-limb variations, provide information about bright sources of irradiance variability associated with magnetic activity in both active regions and dispersed active region remnants broadly distributed in the supergranule network (termed collectively "faculae"). Procedures are developed to construct both total and UV spectral solar irradiance variations explicitly from the processed Ca K filtergrams, independently of direct irradiance observations. The disk-integrated bolometric and UV facular brightness signals determined from the filtergrams between late 1991 and mid-1995 are compared with concurrent solar irradiance measurements made by high-precision solar radiometers on the Upper Atmosphere Research Satellite (UARS). The comparisons suggest that active-region and active-network changes can account for the measured variations. This good agreement during a period covering most of the decline in solar activity from the cycle 22 maximum to the impending solar minimum directly implicates magnetic features as the sources of the 11 yr irradiance cycle, apparently obviating the need for an additional component other than spots or faculae.
ARTICLE: Journal Article
Title: Origin of Streamer Material in the Outer Corona
Authors: WANG, Y.-M.; SHEELEY, N.R., JR.; WALTERS, J.H.; BRUECKNER, G.E.; HOWARD, R.A.; MICHELS, D.J.; LAMY, P.L.; SCHWENN, R.; SIMNETT, G.M.
Journal: Astrophysical Journal Letters v.498, p.L165
Publication Date: 05/1998
Abstract: We investigate the nature and origin of the outward-moving density inhomogeneities ("blobs") detected previously with the Large Angle and Spectrometric Coronagraph on the Solar and Heliospheric Observatory. The blobs are concentrated around the thin plasma layer that surrounds the heliospheric current sheet and that constitutes the outer streamer belt; they represent only a small, fluctuating component of the total density within the plasma sheet. As noted before in Sheeley et al., blobs are characterized by low speeds and are continually emitted from the elongated tips of helmet streamers at 3-4 Rsun from Sun center. We suggest that both the blobs and the plasma sheet itself represent closed-field material injected into the solar wind as a result of footpoint exchanges between the stretched helmet-streamer loops and neighboring open field lines. The plasma sheet is thus threaded by newly reconnected, open magnetic field lines, which lend the white-light streamer belt its filamentary appearance. Since in situ observations at 1 AU show that the slow wind (with speeds below 500 km/s) spreads over an angular extent much greater than the <~3 deg width of the plasma sheet, we deduce that a major component of this wind must originate outside the helmet streamers (i.e., from just inside coronal holes).
ARTICLE: Journal Article
Title: Search for Brightness Variations in Fe xiv Coronagraph Observations of the Quiescent Solar Corona
Authors: WOOD, B. E.; KAROVSKA, M.; COOK, J. W.; BRUECKNER, G. E.; HOWARD, R. A.; KORENDYKE, C. M.; SOCKER, D. G.
Journal: The Astrophysical Journal, Volume 505, Issue 1, pp. 432-442.
Publication Date: 09/1998
Abstract: We use Fe xiv 5303 Å green line images obtained by the Large Angle Spectrometric Coronagraph (LASCO) on board SOHO to search for variability in the quiescent solar corona in the shortest observable time scales. The observing program obtained Fe xiv images of a small area of the inner corona every 2 minutes over a period of 1 hr. We present results from two executions of this program taken several months apart. The most obvious variability observed in the two sequences is in the form of quasi-steady brightening on time scales of at least an hour. Of particular interest are two compact loops that are observed to vary significantly during the course of the observations. Superposed on the long-term brightening in these loops are statistically significant variations on time scales of about 30 minutes. In both loops, the overall brightening is greatest at the apparent loop tops, where the intensity increases by at least 25%. In one loop there appears to be a flow up one of the legs of the loop. We place these observations in context with earlier observations of coronal variability, and we discuss the energy requirements for the observed brightening. Emission measures computed from Fe xiv intensities measured within the two brightening loops are over an order of magnitude lower than those typically found for active regions on the solar disk, which suggests significantly lower average densities. For one of the loops, we measure densities in the range Ne = (5.0-7.4) x 10^8 cm^-3. Lower than average densities are expected for the two loops, given that they reach more than 1 pressure scale height above the solar limb.
ARTICLE: Journal Article
Title: Observations of Correlated White-Light and Extreme-Ultraviolet Jets from Polar Coronal Holes
Authors: WANG, Y.-M.; SHEELEY, N.R. JR.; SOCKER, D.G.; HOWARD, R.A.; BRUECKNER, G.E.; MICHELS, D.J.; MOSES, D.; ST. CYR, O.C.; LLEBARIA, A.; DELABOUDINIÈRE, J.-P.
Journal: The Astrophysical Journal, Volume 508, Issue 2, pp. 899-907.
Publication Date: 12/1998
Abstract: Time-lapse sequences of white-light images recorded with the Large Angle Spectrometric Coronagraph (LASCO) on the Solar and Heliospheric Observatory (SOHO) frequently show long, narrow structures moving outward over the Sun's polar regions at high apparent speeds. By comparing the LASCO observations with Fe XII 19.5 nm spectroheliograms made with the Extreme-ultraviolet Imaging Telescope (EIT) on SOHO between 1997 April and 1998 February, we have identified 27 correlated white-light and extreme-ultraviolet (EUV) jet events. In each case, the EUV jet was observed near the limb of the polar coronal hole 20-60 minutes before the corresponding white-light jet was registered in the coronagraph's 2-6 Rsun; field of view. The jets originate near flaring EUV bright points and are presumably triggered by field line reconnection between magnetic bipoles and neighboring unipolar flux. The leading edges of the white-light jets propagate outward at speeds of 400-1100 km s^-1, whereas the bulk of their material travels at much lower velocities averaging around 250 km s^-1 at heliocentric distances of 2.9-3.7 Rsun;. These lower velocities may reflect the actual outflow speeds of the background polar wind.
ARTICLE: Journal Article
Title: SOHO/EIT observations of an Earth-directed coronal mass ejection on May 12, 1997
Authors: THOMPSON, B.J.; PLUNKETT, S.P.; GURMAN, J.B.; NEWMARK, J.S.; ST. CYR, O.C.; MICHELS, D.J.
Journal: Geophysical Research Letters, v. 25, No. 14, p. 2465 (1998).
Publication Date: 07/1998
Abstract: An earth-directed coronal mass ejection (CME) was observed on May 12, 1997 by the SOHO Extreme ultraviolet Imaging Telescope (EIT). The CME, originating north of the central solar meridian, was later observed by the Large Angle Spectrometric Coronagraph (LASCO) as a "halo" CME: a bright expanding ring centered about the occulting disk. Beginning at about 04:35 UT, EIT recorded several CME signatures, including dimming regions close to the eruption, post-eruption arcade formation, and a bright wavefront propagating quasi-radially from the source region. Each of these phenomena appear to be associated with the same eruption, and the onset time of these features corresponds with the estimated onset time observed in LASCO. We discuss the correspondence of these features as observed by EIT with the structure of the CME in the LASCO data.
ARTICLE: Journal Article
Title: Evidence for multiple ejecta: April 7-11, 1997, ISTP Sun-Earth connection event
Authors: BERDICHEVSKY, D.; BOUGERET, J.-L.; DELABOUDINIÈRE, J.-P.; FOX, N.; KAISER, M.; LEPPING, R.; MICHELS, D.; PLUNKETT, S.; REAMES, D.; REINER, M.; RICHARDSON, I.; ROSTOKER, G.; STEINBERG, J.; THOMPSON, B.; VON ROSENVINGE, T.
Journal: Geophysical Research Letters, v. 25, No. 14, p. 2473 (1998).
Publication Date: 07/1998
Abstract:Evidence is presented that the enhanced geomagnetic activity, on April 10-11, 1997, was caused by one of two ejecta that left the Sun at 14 UT on April 7. This ejecta was not directly detected at the Earth. The evidence for this interpretation is based on WIND spacecraft observations in the solar wind (SW). It is consistent with: (i) measured velocities of the coronal mass ejections from the SOHO coronagraph; (ii) the initial propagation speed of the shock generated in this event, estimation from type II radio burst observations from the WAVES instrument on WIND, and (iii) the time profile of energetic ions observed by EPACT on WIND. This locally unobserved ejecta (moving at 600 to 700 kms-1) generated a fast shock which accelerated ions to several tens of MeV/amu. The inferred passage of the first ejecta close to Earth (on April 10 to 11) is based on the observation of an interplanetary shock (IS) ahead of a field and plasma compressional region where the draping of the SW flow and possibly the changes in the direction of the IMF are consistent with a location northward of a faster ejecta. This ejecta was responsible for disturbed SW conditions including approximately ten hours of southward orientation of the interplanetary magnetic field (IMF) and a ram pressure many times above normal. The slower moving ejecta was directed toward Earth and was observed with WIND from about 0550 until 1500 UT on April 11. It had a strong northward IMF and produced density enhancements which elevated the ram pressure to more than four times above normal.
ARTICLE: Journal Article
Title: LASCO observations of an Earth-directed coronal mass ejection on May 12, 1997
Authors: PLUNKETT, S.P.; THOMPSON, B.J.; HOWARD, R.A.; MICHELS, D.J.; ST. CYR, O.C.; TAPPIN, S.J.; SCHWENN, R.; LAMY, P.L.
Journal: Geophysical Research Letters, v. 25, No. 14, p. 2477 (1998).
Publication Date: 07/1998
Abstract: Coronal mass ejections (CMEs) that occur near the center of the solar disk are most likely to impact Earth. Detection of such events as `halos' in white-light coronagraphs has been somewhat controversial in recent years. We present observations from the LASCO coronagraphs on SOHO that provide convincing evidence of the detection of an Earth-directed CME on May 12, 1997. The event began at about 04:35 UT and propagated outwards from the Sun with a projected speed of around 250 km s. Using some reasonable assumptions about the geometry of the CME, we estimate the true speed to be around 600 km s. The onset of the event in LASCO is coincident (to within measurement uncertainties) with an eruptive event detected in extreme ultraviolet observations of the solar disk by the SOHO EIT. This is the first reported observation of a halo CME at projected distances greater than 10 , with a clearly identifiable solar origin. We discuss the possibility that at least some of the enhanced brightness observed by LASCO may be due to a compressional wave propagating in the corona.
ABSTRACT: Journal Article
Title: On the relationship between coronal mass ejections and magnetic clouds
Authors: GOPALSWAMY, N.; HANAOKA, Y.; KOSUGI, T.; LEPPING, R.P.; STEINBERG, J.T.; PLUNKETT, S.; HOWARD, R.A.; THOMPSON, B.J.; GURMAN, J.; HO, G.; NITTA, N.; HUDSON, H.S.
Journal: Geophysical Research Letters, v. 25, No. 14, p. 2485 (1998).
Publication Date: 07/1998
Abstract: We compare the substructures of the 1997 February 07 coronal mass ejection (CME) observed near the Sun with a corresponding event in the interplanetary medium to determine the origin of magnetic clouds (MCs). We find that the eruptive prominence core of the CME observed near the Sun may not directly become a magnetic cloud as suggested by some authors and that it might instead become the ''pressure pulse'' following the magnetic cloud. We substantiate our conclusions using time of arrival, size and composition estimates of the CME-MC substructures obtained from ground based, SOHO and WIND observations.
ARTICLE: Journal Article
Title: Type II radio emissions in the frequency range from 1 to 14 MHz associated with the April 7, 1997, solar event
Authors: KAISER, M.L.; REINER, M.J.; GOPALSWAMY, N.; HOWARD, R.A.; ST. CYR, O.C.; THOMPSON, B.J.; BOUGERET, J.-L.
Journal: Geophysical Research Letters, v. 25, No. 14, p. 2501 (1998).
Publication Date: 07/1998
Abstract: We present an analysis of radio emissions associated with the April 7, 1997 solar eruptive event. The event consisted of a filament disappearance, a complex two-phase coronal mass ejection (CME) , and a C6.9, 2N flare. At the same time, intermittent type II radio emissions in the frequency range 1-10 MHz, corresponding to an altitude range of 2-15 R , were observed by the Wind/WAVES radio receiver. Using the onset times and inferred heights and speeds of the radio bursts, we considered both a CME-driven shock and a flare-associated blast wave shock as possible causes of the type II radio emissions. We conclude that some of the radio emissions in the WAVES data are associated with each shock. The type II radio emissions associated with the blast wave shock were farther from the sun than any emission of this type that has been reported previously.
ARTICLE: Journal Article
Title: The interplanetary events of January-May, 1997, as inferred from energetic particle data, and their relationship with solar events
Authors: Cane, H. V. ; Richardson, I. G. ; St. Cyr, O. C. 1998
Journal: Geophysical Research Letters, v. 25 , No. 14 , p. 2517 (1998)
Publication Date: 08/1998
Abstract: Not Available
Article: Not Available
Title: X ray coronal changes during halo CMEs
Authors: Hudson, H. S. ; Lemen, J. R. ; St. Cyr, O. C. ; Sterling, A. C. ; Webb, D. F.
Journal: Geophysical Research Letters, v. 25 , No. 14 , p. 2481 (1998)
Publication Date: 08/1998
Abstract: Not Available
Article: Not Available
Title: Geomagnetic storms caused by coronal mass ejections (CMEs): March 1996 through June 1997
Authors: BRUECKNER, G.E.; DELABOUDINIERE, J.-P.; HOWARD, R.A.; PASWATERS, S.E.; ST. CYR, O.C.; SCHWENN, R.; LAMY, P.; SIMNETT, G.M.; THOMPSON, B.; WANG, D.
Journal: Geophysical Research Letters, v. 25, No. 15, p. 3019 (1998).
Publication Date: 08/1998
Abstract: (1) All but two geomagnetic storms with Kp6 during the operating period (March
1996 through June 1997) of the Large Angle Spectroscopic Coronagraph (LASCO) experiment
on the Solar and Heliospheric Observatory (SOHO) spacecraft can be traced to Coronal Mass
Ejections (CMEs). (2) These geomagnetic storms are not related to high speed solar wind
streams. (3) The CMEs which cause geomagnetic effects, can be classified into two categories:
Halo events and toroidal CMEs. (4) The CMEs are accompanied by Coronal Shock Waves as
seen in the Extreme Ultraviolet Imaging Telescope (EIT) Fe XII images. (5) Some CMEs are
related to flares, others are not. (6) In many cases, the travel time between the explosion on the
Sun and the maximum geomagnetic activity is about 80 hours.
Article: Not Available
Title: A magnetic cloud containing prominence material - January 1997
Authors: BURLAGA, L.; FITZENREITER, R.; LEPPING, R.; OGILVIE, K.; SZABO, A.; LAZARUS, A.; STEINBERG, J.; GLOECKLER, G.; HOWARD, R.; MICHELS, D.
Journal: Journal of Geophysical Research, vol. 10, p. 277
Publication Date: 01/1998
Abstract: This work discusses the relations among (1) an interplanetary force-free magnetic cloud containing a plug of cold high-density material with unusual composition, (2) a coronal mass ejection (CME), (3) an eruptive prominence, and (4) a model of prominence material supported by a force-free magnetic flux rope in a coronal streamer. The magnetic cloud moved past the Wind spacecraft located in the solar wind upstream of Earth on January 10 and 11, 1997. The magnetic field configuration in the magnetic cloud was approximately a constant-alpha, force-free flux rope. The He-4(2+)/H(+) abundance in the most of the magnetic cloud was similar to that of the streamer belt material, suggesting an association between the magnetic cloud and a helmet streamer. A very cold region of exceptionally high density was detected at the rear of the magnetic cloud. This dense region had an unusual composition, including (1) a relatively high (10 percent) He-4(2+)/He(+) abundance and (2) He-4(+), with an abundance relative to He-4(2+) of about 1 percent, and the unusual charge states of O(5+) and Fe(5+). Thus we suggest that the high-density region might be prominence material. The CME was seen in the solar corona on January 6, 1997, by the large angle and spectrometric coronagraph (LASCO) instrument on SOHO shortly after an eruptive prominence. A helmet streamer was observed near the latitude of the eruptive prominence a quarter of a solar rotation before and after the eruptive prominence.
Article: Not Available
Title: Missions to the Sun II
Authors: KORENDYKE, C.M.
Journal: Proc. SPIE Vol. 3442
Publication Date: 11/1998
Abstract: Not Available
Article: Not Available
Title: Stereographic image potential of a STEREO mission
Authors: SOCKER, D.G.
Journal: Proc. SPIE Vol. 3442, p. 44-52, Missions to the Sun II, Clarence M. Korendyke; Ed.
Publication Date: 11/1998
Abstract: The potential quality increase of the scientific results obtainable with stereographic observations on a Solar- Terrestrial Relations Observatory (STEREO) mission are examined in terms of the science objectives, observables, instrument performance, spacecraft vantage points and stereographic image reconstruction.
Article: Not Available
Title: Corrals, hubcaps, and crystal balls: some new designs for very-wide-angle visible-light heliospheric imagers
Authors: BUFFINGTON, A.; HICK, P.P.; JACKSON, B.V.; KORENDYKE, C.M.
Journal: Proc. SPIE Vol. 3442, p. 77-86, Missions to the Sun II, Clarence M. Korendyke; Ed.
Publication Date: 11/1998
Abstract: Emerging techniques allow instruments to view very large sky areas, a hemisphere or more, in visible light. In space, such wide-angle coverage enables observation of heliospheric features form close to the Sun to well beyond Earth. Observations from deep-space missions such as Solar Probe, Stereo, and Solar Polar Sail, coupled with observations near Earth, permit 3D reconstruction of solar mass ejections and co-rotating structures, discovery and study of new comets and asteroids, and detailed measurements of brightness variations in the zodiacal cloud. Typical heliospheric features have 1 percent or less of ambient brightness, so visible-light cameras must deliver < 0.1 percent photometry and be well protected from stray background light. When more than a hemisphere of viewing area is free of bright background-light sources, we have shown that corral-like structures with several vane-like walls reduces background light illuminating to wide-angle optical system by up to ten orders of magnitude. The optical system itself typically provides another five orders of surface-brightness reduction. With CCDs as the light-detection device, images of point-like sources must cover typically 100 pixels to average down sub-pixel response gradients and provide the above 0.1 percent photometry. With present-day CCDs this requires images of order 1 degree in angular size. Tolerating such large images in turn enables wide-angle sky coverage using simple reflecting and refracting optical systems such as convex spherical reflectors, toroids and thick lenses. We show that combining these with light- reducing corrals yields practical, light-weight instruments suitable for inclusion on deep-space probes.
Title: In-orbit performances of the EIT instrument on board SOHO and intercalibration with the EIT Calroc Sounding Rocket program
Authors: DEFISE, J.-M; MOSES, J.D.; CLETTE, F.
Journal: Proc. SPIE Vol. 3442, p. 126-139, Missions to the Sun II, Clarence M. Korendyke; Ed.
Publication Date: 11/1998
Abstract: The Extreme UV Imaging Telescope (EIT) instrument is operating on-board the SOHO spacecraft since January 1996. EIT is providing EUV observations of the solar corona in four narrow channels: 171, 195, 284 and 304 angstrom. Due to continuous exposure to the EUV solar irradiation, the instrument performance is continuously evolving. The backside thinned detector is showing important changes in its overall response and local damage of EUV highly exposed areas. These performance modifications can be characterized through several observation analyses that are discussed in this paper. Two major effects are identified: contamination on the detector surface and charge mobility changes in the CCD produced by the EUV irradiation. To restore the instrument response, bakeouts are regularly planned as well as specific observation sequences that are used to characterize the detector damages. An overview of the instrument response behavior is presented in this paper.
Article: Not Available
Title: Wavelet image compression aboard the LASCO/SOHO coronagraph
Authors: WANG, D.; HOWARD, R.A.; PASWATERS, S.E.
Journal: Proc. SPIE Vol. 3442, p. 150-156, Missions to the Sun II, Clarence M. Korendyke; Ed.
Publication Date: 11/1998
Abstract: The LASCO coronagraph consists of three CCD equipped telescopes taking images of up to 1024 X 1024 pixels in size. For approximately the last year a wavelet image compression has been in use for images from LASCO. The testing and performance of this compression will be discussed within the constraints of the spacecraft computer, hardware and telemetry. Effects of the image compression on the data taking, data analysis and reduction will be discussed.
Title: The Shape of the Outer Corona during Cycle 21
Authors: KOOMEN, M.J.; HOWARD, R.A.; MICHELS, D.J.
Journal: Solar Physics, v. 180, Issue 1/2, p. 247-263.
Publication Date: 06/1998
Abstract: Not Available
Article: Not Available
Title: Joint Nançay Radioheliograph and Lasco Observations of Coronal Mass Ejections - I. The 1 July 1996 Event
Authors: MAIA, D.; PICK, M.; KERDRAON, A.; HOWARD, R.; BRUECKNER, G.E.; MICHELS, D.J.; PASWATERS, S.; SCHWENN, R.; LAMY, P.; LLEBARIA, A.; SIMNETT, G.; AURASS, H.
Journal: Solar Physics, v. 181, Issue 1, p. 121-132 (1998).
Publication Date: 07/1998
Abstract: The development of a coronal mass ejection on 1 July 1996 has been analyzed by comparing the observations of the LASCO/SOHO coronagraph with those of the Nançay radioheliograph. This comparison brings new insight and very useful diagnosis for the study of CME events. It is shown that the initial instability took place in a small volume located above an active region and that the occurrence of short radio type III bursts implies a triggering process due to magnetic field interactions. The subsequent spatial and temporal evolution of the radio emission strongly suggests that the large scale structure becomes unstable within the first minute of the event.
Article: Not Available
Title: The Solar Minimum Active Region 7978, Its X2.6/1B Flare, CME, and
Interplanetary Shock Propagation of 9 July 1996
Authors: DRYER, M.; ANDREWS, M.D.; AURASS, H.; DEFOREST, C.; GALVIN, A.B.; GARCIA, H.; IPAVICH, F.M.; KARLICKY, M.; KIPLINGER, A.; KLASSEN, A.; MEISNER, R.; PASWATERS, S.E.; SMITH, Z.; TAPPIN, S.J.; THOMPSON, B.J.; WATARI, S.I.; MICHELS, D.J.; BRUECKNER, G.E.; HOWARD, R.A.; KOOMEN, M.J.; LAMY, P.; MANN, G.; ARZNER, K.; SCHWENN, R.
Journal: Solar Physics, v. 181, Issue 1, p. 159-183.
Publication Date: 07/1998
Abstract: Not Available
Article: Not Available
Title: Joint NANCAY RADIOHELIOGRAPH AND LASCO OBSERVATIONS OF
CORONAL MASS EJECTIONS - II. The 9 July 1996 Event
Authors: PICK, M.; MAIA, D.; KERDRAON, A.; HOWARD, R.; BRUECKNER, G.E.; MICHELS, D.J.; PASWATERS, S.; SCHWENN, R.; LAMY, P.; LLEBARIA, A.; SIMNETT, G.; LANZEROTTI, L.J.; AURASS, H.
Journal: Solar Physics, v. 181, Issue 2, p. 455-468 (1998).
Publication Date: 08/1998
Abstract: The development of a coronal mass ejection on 9 July 1996 has been analyzed by comparing the observations of the LASCO/SOHO coronagraphs with those of the Nancay radioheliograph. The spatial and temporal evolution of the associated radioburst is complex and involves a long-duration continuum. The analysis of the time sequence of the radio continuum reveals the existence of distinct phases associated with distinct reconnection processes and magnetic restructuring of the corona. Electrons are accelerated in association with these reconnection processes. An excellent spatial association is found between the position and extension of the radio source and the CME seen by LASCO. Furthermore, it is shown that the topology and evolution of the source of the radio continuum involve successive interactions between two systems of loops. These successive interactions lead to magnetic reconnection, then to a large scale coronal restructuring. Thus electrons of coronal origin may have access to the interplanetary medium in a large range of heliographic latitudes as revealed by the Ulysses observations.
Article: Not Available
Title: Observations of Coronal Structures Above an Active Region by Eit and Implications for Coronal Energy Deposition
Authors: NEUPERT, W.M.; NEWMARK, J.; DELABOUDINIÈRE, J.-P.; THOMPSON, B.J.; CATURA, R.C.; MOSES, J.D.; GURMAN, J.B.; PORTIER-FOZZANI, F.; GABRIEL, A.H.; ARTZNER, G.; CLETTE, F.; CUGNON, P.; MAUCHERAT, A.J.; DEFISE, J.M.; JAMAR, C.; ROCHUS, P.; DERE, K.P.; HOWARD, R.A.; MICHELS, D.J.; FREELAND, S.; LEMEN, J.R.; STERN, R.A.
Journal: Solar Physics, v. 183, Issue 2, p. 305-321 (1998).
Publication Date: 12/1998
Abstract: Solar EUV images recorded by the EUV Imaging Telescope (EIT) on SOHO have been used to evaluate temperature and density as a function of position in two largescale features in the corona observed in the temperature range of 1.0-2.0MK. Such observations permit estimates of longitudinal temperature gradients (if present) in the corona and, consequently, estimates of thermal conduction and radiative losses as a function of position in the features. We examine two relatively cool features as recorded in EIT's Fe IX/X (171Å) and Fe XII (195Å) bands in a decaying active region. The first is a long-lived loop-like feature with one leg, ending in the active region, much more prominent than one or more distant footpoints assumed to be rooted in regions of weakly enhanced field. The other is a near-radial feature, observed at the West limb, which may be either the base of a very high loop or the base of a helmet streamer. We evaluate energy requirements to support a steady-state energy balance in these features and find in both instances that downward thermal conductive losses (at heights above the transition region) are inadequate to support local radiative losses, which are the predominant loss mechanism. The requirement that a coronal energy deposition rate proportional to the square of the ambient electron density (or pressure) is present in these cool coronal features provides an additional constraint on coronal heating mechanisms.
Article: Not Available