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1.
The large loop or blob-like transient events viewed in the white-light corona are rimmed by broad regions where the density is slightly enhanced above the pre-transient corona. Every one of the Skylab events studied for which sufficiently good Skylab coronagraph coverage is available shows this effect. The upper boundaries of these forerunners blend gradually into the background corona 1 to 2R above the transients' leading edges. In any single event, the coronal mass enhancement represented by the forerunner comprises up to 25% of the total excess mass present in the coronagraph's field of view and includes a much larger volume of the corona than previously attributed to the underlying transient. We have not yet seen a forerunner without an accompanying transient. Clearly, forerunners must be reckoned with in any proposed models of discrete outward coronal mass motions, because they indicate the presence of disturbed corona far ahead of the denser portions of the event.Skylab Solar Workshop Postdoctoral Appointee 1975–78. The Skylab Solar Workshops are sponsored by NASA and NSF and managed by the High Altitude Observatory.The National Center for Atmospheric Research is sponsored by the National Science Foundation.  相似文献   

2.
We have compared sudden shifts in coronal hole boundaries observed by the S-054 X-ray telescope on Skylab between May and November, 1973, within 1 day of CMP of the holes, at latitudes 40 °, with the long-term evolution of coronal hole area. We find that large-scale shifts in boundary locations can account for most if not all of the evolution of coronal holes. The temporal and spatial scales of these large-scale changes imply that they are the results of a physical process occurring in the corona. We conclude that coronal holes evolve by magnetic field lines opening when the holes are growing, and by fields closing as the holes shrink.Skylab Solar Workshop post-doctoral appointee 1975–1976. The Skylab Solar Workshops are sponsored by NASA and NSF and managed by the High Altitude Observatory, National Center for Atmospheric Research.  相似文献   

3.
The fact that eruptive-prominence associated coronal mass ejection events may be accelerated over significant heights and times in the corona complicates the determination of possible surface or low coronal associations. A specific example of one such eruptive-prominence associated event, that observed in both the inner and outer solar corona on August 5, 1980, is used to illustrate the magnitude of the uncertainty of determining an onset time of the ejection. It is noted that such uncertainties may influence statistically-determined associations.The National Center for Atmospheric Research is sponsored by the National Science Foundation  相似文献   

4.
Sawyer  C. 《Solar physics》1985,98(2):369-378
Two thirds of the H flares associated in time and position with coronal mass ejections (CME) observed by the Coronagraph/Polarimeter (C/P) or by the coronagraph on Skylab lie within 30° of the solar limb. Among type II flares (those with type II radio spectral bursts) with C/P observations, 10 are within 10° of the limb and 8 of these are associated with CME. The high rate of CME association at the limb is interpreted here to imply: (1) Most type II flares (at least 80%) are physically associated with mass motion in the corona (although about half of CME flares lack type II bursts). (2) The longitude window, centered on the plane of the sky, within which C/P and Skylab coronagraphs detect CME has halfwidth of 20° to 30°. (3) CME observed at polar position angles are unlikely to be flare associated. (4) The total number of mass ejections must be considerably greater than the number detected. The ratio of total number to observed number is estimated to be between 2 and 3, and the total occurrence frequency of coronal mass ejections at solar-cycle maximum to be comparable to that of flares of importance 1. The clear dependence of CME detection on flare position implies that the location of the mass ejection must be well described by the location of the associated flare, and that the ejected mass must have limited longitudinal extent in the corona, comparable to the width of the detection window and to the directly observed latitudinal extent of 35° +- 15° for CME observed by C/P and the Skylab coronagraph.Much of the work reported here was done at the High Altitude Observatory, National Center for Atmospheric Research, Boulder, CO 80307, U.S.A. The National Center for Atmospheric Research is sponsored by the National Science Foundation.  相似文献   

5.
The apparent morphologies of the major coronal mass ejection transients observed during the Skylab mission with the High Altitude Observatory's white-light coronagraph are described and illustrated. The 77 major events are grouped into classes referred to as Loop, Filled Bottle, Material Injected into Streamer, Ray, Cloud, and Streamer Separation events, with 14 being Unclassifiable because of incomplete observations. One example of each class is shown, with references to others described in the literature. A chronological listing of all the events is given.The National Center for Atmospheric Research is sponsored by the National Science Foundation.  相似文献   

6.
Coronal mass ejection transients observed with the white light coronagraph on Skylab are found to be associated with several other forms of solar activity. There is a strong correlation between such mass ejection transients and chromospheric H activity, with three-quarters of the transients apparently originating in or near active regions. We infer that 40% of transients are associated with flares, 50% are associated with eruptive prominences solely (without flares), and more than 70% are associated with eruptive prominences or filament disappearances (with or without flares). Nine of ten flares which displayed apparent mass ejections of H-emitting material from the flare site could be associated with coronal transients. Within each class of activity, the more energetic events are more likely to be associated with an observable mass ejection.Now at Los Alamos Scientific Laboratories, Los Alamos, NM., U.S.A.The National Center for Atmospheric Research is sponsored by the National Science Foundation.  相似文献   

7.
Using soft X-ray data from the S-054 X-ray spectrographic telescope aboard Skylab, we observed temporal changes in the emission structure of the X-ray corona associated with the birth of a small coronal hole. Designated as CH6, this coronal hole was born near the equator in a time interval less than 9 1/2 hr. By constructing a light curve for a point near the center of CH6, we observed a sudden 40% decrease in X-ray emission associated with the birth of this coronal hole. On a time scale of hours, the growth of CH6 in area proceeded faster than the average rate predicted by the diffusion of solar fields. The short term decay of CH6 followed the diffusive rate to within experimental uncertainty, On a time scale of one rotation, the subsequent development of CH6 was not consistent with steady growth at the average rate predicted by diffusion.Skylab Solar Workshop Post-Doctoral Appointee, 1975–1977. The Skylab Solar Workshops are sponsored by NASA and NSF and managed by the High Altitude Observatory, National Center for Atmospheric Research.  相似文献   

8.
A 90 s time resolution study of the soft X-ray emission from three active region loops shows the emission to be constant to about two percent over the half hour period of observation. Soft X-ray observations in two wavebands are used to deduce the temperature and density of these loops. The data unambiguously demonstrate that energy is supplied to each loop during the observations. If heating is due to discrete events, the time interval between events is shown to be less than 10 min, which is short relative to the radiative cooling time of the loops.Skylab Solar Workshop Post-Doctoral Appointee, 1975–1977. The Skylab Solar Workshops are sponsored by NASA and NSF and managed by the High Altitude Observatory, National Center for Atmospheric Research.  相似文献   

9.
For almost 20 years the physical nature of globally propagating waves in the solar corona (commonly called “EIT waves”) has been controversial and subject to debate. Additional theories have been proposed over the years to explain observations that did not agree with the originally proposed fast-mode wave interpretation. However, the incompatibility of observations made using the Extreme-ultraviolet Imaging Telescope (EIT) onboard the Solar and Heliospheric Observatory with the fast-mode wave interpretation was challenged by differing viewpoints from the twin Solar Terrestrial Relations Observatory spacecraft and data with higher spatial and temporal resolution from the Solar Dynamics Observatory. In this article, we reexamine the theories proposed to explain EIT waves to identify measurable properties and behaviours that can be compared to current and future observations. Most of us conclude that the so-called EIT waves are best described as fast-mode large-amplitude waves or shocks that are initially driven by the impulsive expansion of an erupting coronal mass ejection in the low corona.  相似文献   

10.
Activity associated with the solar origin of coronal mass ejections   总被引：2，自引：0，他引：2  
Solar coronal mass ejections (CMEs) observed in 1980 with the HAO Coronagraph/Polarimeter on the Solar Maximum Mission (SMM) satellite are compared with other forms of solar activity that might be physically related to the ejections. The solar phenomena checked and the method of association used were intentionally patterned after those of Munro et al.'s (1979) analysis of mass ejections observed with the Skylab coronagraph to facilitate comparison of the two epochs. Comparison of the results reveals that the types and degree of CME associations are similar near solar activity minimum and at maximum. For both epochs, most CMEs with associations had associated eruptive prominences and the proportions of association of all types of activity were similar. We also found a high percentage of association between SMM CMEs and X-ray long duration events (LDEs), in agreement with Skylab results. We conclude that most CMEs are the result of the destabilization and eruption of a prominence and its overlying coronal structure, or of a magnetic structure capable of supporting a prominence.Much of this work was performed as a Visiting Scientist at the High Altitude Observatory/NCAR.The National Center for Atmospheric Research is sponsored by the National Science Foundation.  相似文献   

11.
This study addresses the onset of coronal mass ejections. From examination of sensitive X-ray images from the Solar Maximum Mission around the projected onset time of coronal mass ejections we identify two important new features: (1) there is usually a weak, soft X-ray enhancement 15–30 min prior to the linearly extrapolated chromospheric departure time of the ejection; (2) this activity is generally from two widely separated ( 105 km) parts of the Sun. Possible physical mechanisms for these phenomena are examined and it is concluded that a plausible explanation is that the initial energy release is converted first into kinetic energy of suprathermal protons, 102–103 keV. The protons are trapped in a large magnetic loop which later breaks open as the mass ejection; Coulomb losses are the destabilizing agent but the mass ejection is probably magnetically driven. Protons that escape into the loss cone will impact the loop footpoints to heat the upper chromospheric material to a sufficiently high temperature to generate the weak soft X-ray emission. There will also be an H signature, and this is observed in a number of events. There is in general no radio emission or hard X-ray emission accompanying the soft X-ray precursor. When the coronal mass ejection is followed by a flare, then this is generally from a point close to, but not identical to, one of the points with the earlier soft X-ray enhancement.NCAR is sponsored by the National Science Foundation.  相似文献   

12.
R. M. MacQueen 《Solar physics》1993,145(1):169-188
We have measured the brightness and latitudinal extent of the depleted (cavity) region behind the leading edge of three coronal mass ejection (CME) events from the Skylab epoch. The events chosen are among those believed to be typical of non-impulsive, loop-like CMEs (Sime, MacQueen, and Hundhausen, 1984). The pre-event coronal brightness has been matched by a model corona, assuming both a background contribution and a contribution from a range of hypothetical streamer models, distinguished by differing longitudinal extent. Then, assuming that the cavities are voided regions in which the local electron density is negligible, we estimate their minimum line-of-sight extent and find them to be comparable to, or greater than, their measured latitudinal extent. As a result, we suggest this unambiguously demonstrates the three-dimensional nature of these — and likely, this class of — events.  相似文献   

13.
This paper describes Skylab/ATM observations of the events associated with a disappearing filament near the center of the solar disk on January 18, 1974. As the filament disappeared, the nearby coronal plasma was heated to a temperature in excess of 6 × 106K. A change in the pattern of coronal emission occurred during the 11/3 hr period that the soft X-ray flux was increasing. This change seemed to consist of the formation and apparent expansion of a loop-like coronal structure which remained visible until its passage around the west limb several days later. The time history of the X-ray and microwave radio flux displayed the well-known gradual-rise-and-fall (GRF) signature, suggesting that this January 18 event may have properties characteristic of a wide class of X-ray and radio events.In pursuit of this idea, we examined other spatially-resolved Skylab/ATM observations of long-duration X-ray events to see what characteristics they may have in common. Nineteen similar long-lived SOLRAD X-ray events having either the GRF or post-burst radio classification occurred during the nine-month Skylab mission. Sixteen of these occurred during HAO/ATM coronagraph observations, and 7 of these 16 events occurred during observations with both the NRL/ATM slitless spectrograph and the MSFC-A/ATM X-ray telescope. The tabulation of these events suggests that all long-lived SOLRAD X-ray bursts involve transients in the outer corona and that at least two-thirds of the bursts involve either the eruption or major activation of a prominence. Also, these observations indicate that long-lived SOLARD events are characterized by the appearance of new loops of emission in the lower corona during the declining phase of the X-ray emission. However, sometimes these loops disappear after the X-ray event (like the post-flare loops associated with a sporadic coronal condensation), and sometimes the loops remain indefinitely (like the emission from a permanent coronal condensation).Visiting Scientist, Kitt Peak National Observatory, Tucson, Ariz. 85726, U.S.A. operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation.Presently located at NASA/MSFC, Space Sciences Laboratory, Marshall Space Flight Center, Ala. 35812, U. S.A.  相似文献   

14.
Loop-like white light coronal transients are generally believed to be nearly planar sheets which are thin compared to the loop extent; however, this picture may be questioned since virtually no observations (of the more than 100 transient events observed during 1973–74 Skylab period) show such loops edge-on. From the group of transient events studied by Munro etal. (1979) for which definite surface associations exist, we find loop transients are strongly correlated with filament regions where the filament axis was oriented north-south. From direct soft X-ray observations of an expanding arch, the possible identification of the soft X-ray signature of footpoints of transient loops, and monochramatic observations of low coronal loops, we infer that loop-like coronal transients have their origin in low-lying coronal loops nearly co-planar with the north-south aligned filament axis. The situation with respect to non-loop events is less clear; such events apparently often arise from more complex filament geometries. Possible reasons for the preference of transients to arise from north-south filament-oriented regions are discussed.The National Center for Atmospheric Research is sponsored by the National Science Foundation.  相似文献   

15.
In an examination of the evolution of coronal hole boundaries on a time scale of 1 day, we find that 38% of all the boundaries of coronal holes observed near central meridan passage during the Skylab period shifted in location by >1° heliocentric in 1 day. Of these boundary changes, 70% were on a scale 3 times the average supergranulation cell size. However, large-scale shifts in the boundary locations also occurred, which involved changes in the X-ray emission from these areas of the Sun. X-ray emitting structures on the borders of isolated and evolving holes were less clearly defined than those on the boundaries of well-established, elongated holes. There were generally more changes in the boundaries of the most rapidly evolving holes, but no simple relationship between the amount of change and the rate of hole growth or decay.Skylab Solar Workshop post-doctoral appointee 1975–1976. The Skylab Solar Workshops are sponsored by NASA and NSF and managed by the High Altitude Observatory, National Center for Atmosoheric Research.  相似文献   

16.
Three polar plumes were studied using Skylab Mg x and O vi data. The plumes lie within the boundaries of a polar coronal hole. We find that the mean temperature of the plumes is about 1.1 × 106 K and that they have a small vertical temperature gradient. Densities are determined and found consistent with white light analyses. The variation of density with height in the plumes is compared with that expected for hydrostatic equilibrium. As is the case for other coronal features, polar plumes will be a source of solar wind if the magnetic field lines are open. On the basis of the derived plume model and estimates of the numbers of plumes in polar coronal holes, it appears that polar plumes contain about 15% of the mass in a typical polar hole and occupy about 10% of the volume.Skylab Solar Workshop post-doc appointee 1975–1976. The Skylab Solar Workshops are sponsored by NASA and NSF and managed by the High Altitude Observatory, National Center for Atmospheric Research.  相似文献   

17.
Thompson  B.J.  Reynolds  B.  Aurass  H.  Gopalswamy  N.  Gurman  J.B.  Hudson  H.S.  Martin  S.F.  St. Cyr  O.C. 《Solar physics》2000,193(1-2):161-180
We report coincident observations of coronal and chromospheric flare wave transients in association with a flare, large-scale coronal dimming, metric radio activity and a coronal mass ejection. The two separate eruptions occurring on 24 September 1997 originate in the same active region and display similar morphological features. The first wave transient was observed in EUV and H data, corresponding to a wave disturbance in both the chromosphere and the solar corona, ranging from 250 to approaching 1000 km s–1 at different times and locations along the wavefront. The sharp wavefront had a similar extent and location in both the EUV and H data. The data did not show clear evidence of a driver, however. Both events display a coronal EUV dimming which is typically used as an indicator of a coronal mass ejection in the inner corona. White-light coronagraph observations indicate that the first event was accompanied by an observable coronal mass ejection while the second event did not have clear evidence of a CME. Both eruptions were accompanied by metric type II radio bursts propagating at speeds in the range of 500–750 km s–1, and neither had accompanying interplanetary type II activity. The timing and location of the flare waves appear to indicate an origin with the flaring region, but several signatures associated with coronal mass ejections indicate that the development of the CME may occur in concert with the development of the flare wave.  相似文献   

18.
The origin of the material which is ejected during a white light coronal transient has not been determined heretofore. Study of a disturbance on 26 and 27 August 1973, during which a slowly ascending prominence and a more rapid accompanying coronal transient were simultaneously observed, helps to resolve this question. Prominence images obtained in Hα 6563 Å and in He II 304 Å are nearly identical. The mass ejection transient observed in white light (3700–7000 Å) appeared to be a loop about 1 R⊙ higher than the top of the ascending prominence; it accelerated away from the prominence below it. These observations imply: (1) the bulk of the ejected material did not originate in the ascending prominence; (2) therefore, most of the material must have come from the low corona above the prominence, (and was at coronal temperatures during its outward passage); and (3) the total event - ascending prominence accompanied by coronal mass ejection - was far larger, more energetic, and longer lasting than would be inferred from the prominence observations alone. The transient of 26–27 August was slow and of atypical shape compared to other mass ejection transients, but we believe that these three conclusions apply to most, if not all, of the more than 60 loop-shaped coronal transients observed by the High Altitude Observatory's coronagraph during the nine-month flight of Skylab.  相似文献   

19.
An eruptive prominence and coronal transient of 19 December, 1973 comprised one of the best-observed coronal mass ejection events during the skylab period (May, 1973–January, 1974). EUV observations show that the pre-eruptive quiescent prominence was (at 8000 K) not appreciably hotter than other quiescent prominences, but EUV radiation from it and its prominence-corona interface was unusually faint. The prominence material was distributed in helical threads which decreased in pitch angle during the early phases of eruption. No region of the prominence was markedly different from any other just prior to and during the eruption. For the first time, the temperature and density of rising prominence material were determined at great heights in the corona. At 3R , the prominence material was still confined in threads whose temperature and total hydrogen density were 2 × 104 K and 1.5 × 109 cm–3, respectively. Shortly after this observation ( 7hr after the start of the eruption), the prominence material expanded dramatically. A small portion (1%) of the prominence material was observed draining downward near the solar surface late in the event, and we infer that only a small fraction (10%) of the pre-eruptive prominence mass was expelled from the Sun. The remainder of the prominence apparently lay outside the instruments' fields of view. The bulk of the material expelled did not originate in the prominence. Both coronal and prominence material accelerated outward during the period of observations. A pre-existing streamer was disrupted by the outflowing material.The National Center for Atmospheric Research is sponsored by the National Science Foundation.  相似文献   

20.
A coronal streamer was observed by the white light coronagraph on Skylab during 5 successive limb passages between 1 June, 1973 and 6 August, 1973. The Skylab data give independent measures of coronal brightness and polarization, as functions of time. These permit the distinction between changes in the coronal streamer's appearance due to solar rotation and actual structural changes. The streamer's visual appearance changed slightly between successive limb passages indicating that it was not a steady state feature. Measurements of the streamer's latitude, brightness, and polarization during 3 east limb passages show that: (1) the streamer's axis migrated southward from 25° N at first east limb passage to 11° N at second east limb passage to 8° N latitude at third east limb passage; (2) the streamer's mass (and mass gradient with height), varied by between 20 and 50% from one east limb passage to the next; (3) the streamer's longitudinal extent was also observed to be less on successive east limb passages; and (4) mass changes (distinct from coronal transients) occurring over hours were detected during at least two limb passages. Comparison of the outer coronal observations with observations from lower in the solar atmosphere indicate that the streamer was associated with a complex of solar activity consisting of active regions and filaments. This complex of activity shifted southward by the same amount as the streamer. The variations detected in the streamer preclude the detailed determination of its three-dimensional structure.The National Center for Atmospheric Research is sponsored by the National Science Foundation.  相似文献   

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