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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.
The Large Angle Spectroscopic Coronagraph (LASCO) 总被引：12，自引：0，他引：12
G. E. Brueckner R. A. Howard M. J. Koomen C. M. Korendyke D. J. Michels J. D. Moses D. G. Socker K. P. Dere P. L. Lamy A. Llebaria M. V. Bout R. Schwenn G. M. Simnett D. K. Bedford C. J. Eyles 《Solar physics》1995,162(1-2):357-402
The Large Angle Spectroscopic Coronagraph (LASCO) is a three coronagraph package which has been jointly developed for the Solar and Heliospheric Observatory (SOHO) mission by the Naval Research Laboratory (USA), the Laboratoire d'Astronomie Spatiale (France), the Max-Planck-Institut für Aeronomie (Germany), and the University of Birmingham (UK). LASCO comprises three coronagraphs, C1, C2, and C3, that together image the solar corona from 1.1 to 30 R (C1: 1.1 – 3 R, C2: 1.5 – 6 R, and C3: 3.7 – 30 R). The C1 coronagraph is a newly developed mirror version of the classic internally-occulted Lyot coronagraph, while the C2 and C3 coronagraphs are externally occulted instruments. High-resolution imaging spectroscopy of the corona from 1.1 to 3 R can be performed with the Fabry-Perot interferometer in C1. High-volume memories and a high-speed microprocessor enable extensive on-board image processing. Image compression by a factor of about 10 will result in the transmission of 10 full images per hour. 相似文献
13.
The Heliospheric Imagers Onboard the STEREO Mission 总被引：1，自引：0，他引：1
C. J. Eyles R. A. Harrison C. J. Davis N. R. Waltham B. M. Shaughnessy H. C. A. Mapson-Menard D. Bewsher S. R. Crothers J. A. Davies G. M. Simnett R. A. Howard J. D. Moses J. S. Newmark D. G. Socker J.-P. Halain J.-M. Defise E. Mazy P. Rochus 《Solar physics》2009,254(2):387-445
Mounted on the sides of two widely separated spacecraft, the two Heliospheric Imager (HI) instruments onboard NASA’s STEREO mission view, for the first time, the space between the Sun and Earth. These instruments are wide-angle visible-light imagers that incorporate sufficient baffling to eliminate scattered light to the extent that the passage of solar coronal mass ejections (CMEs) through the heliosphere can be detected. Each HI instrument comprises two cameras, HI-1 and HI-2, which have 20° and 70° fields of view and are off-pointed from the Sun direction by 14.0° and 53.7°, respectively, with their optical axes aligned in the ecliptic plane. This arrangement provides coverage over solar elongation angles from 4.0° to 88.7° at the viewpoints of the two spacecraft, thereby allowing the observation of Earth-directed CMEs along the Sun?–?Earth line to the vicinity of the Earth and beyond. Given the two separated platforms, this also presents the first opportunity to view the structure and evolution of CMEs in three dimensions. The STEREO spacecraft were launched from Cape Canaveral Air Force Base in late October 2006, and the HI instruments have been performing scientific observations since early 2007. The design, development, manufacture, and calibration of these unique instruments are reviewed in this paper. Mission operations, including the initial commissioning phase and the science operations phase, are described. Data processing and analysis procedures are briefly discussed, and ground-test results and in-orbit observations are used to demonstrate that the performance of the instruments meets the original scientific requirements. 相似文献
14.
15.
During the impulsive phase of many solar flares, blueshifted emission wings are observed on the soft X-ray spectral lines of highly excited ions that are produced in the flare plasma. This emission has been commonly interpreted as chromospheric evaporation of material from the footpoints of coronal loops by non-thermal particle beams, although the question of whether the bulk of the energy is carried by electrons or ions (protons) has been the subject of much debate. The precise temporal relationship between the onsets of the blueshifted emission and the hard X-ray bursts is particularly important in resolving the mechanism of energy transfer to the hot plasma in the impulsive phase. A sample of flares observed with the Bragg Crystal Spectrometer (BCS) onYohkoh has been analysed for blueshifted emission and the results compared with hard X-ray light turves obtained with the Burst and Transient Source Experiment (BATSE) on the Compton Gamma Ray Observatory (CGRO). In some flares, the blueshifted emission precedes the onset of the hard X-rays by up to 100 s. There is no evidence for a temporal correlation between the maximum energy input to the hard X-ray bursts and the maximum blueshifted intensity. These results lend support to those models favouring protons as the dominant energy carrier in the impulsive phase of flares and are inconsistent with the hypothesis that the bulk of the energy resides in electron beatos, although some other energy input, while unlikely, cannot be completely eliminated. 相似文献
16.
Eyles C.J. Simnett G.M. Cooke M.P. Jackson B.V. Buffington A. Hick P.P. Waltham N.R. King J.M. Anderson P.A. Holladay P.E. 《Solar physics》2003,217(2):319-347
We describe an instrument (SMEI) which has been specifically designed to detect and forecast the arrival of solar mass ejections and other heliospheric structures which are moving towards the Earth. Such events may cause geomagnetic storms, with resulting radiation hazards and disruption to military and commercial communications; damage to Earth-orbiting spacecraft; and also terrestrial effects such as surges in transcontinental power transmission lines. The detectors are sensitive over the optical wave-band, which is measured using CCD cameras. SMEI was launched on 6 January 2003 on the Coriolis spacecraft into a Sun-synchronous polar orbit as part of the US DoD Space Test Programme. The instrument contains three cameras, each with a field of view of 60°×3°, which are mounted onto the spacecraft such that they scan most of the sky every 102-min orbit. The sensitivity is such that changes in sky brightness equivalent to a tenth magnitude star in one square degree of sky may be detected. Each camera takes an image every 4 s. The normal telemetry rate is 128 kbits s–1. In order to extract the emission from a typical large coronal mass ejection, stellar images and the signal from the zodiacal dust cloud must be subtracted. This requires accurate relative photometry to 0.1%. One consequence is that images of stars and the zodiacal cloud will be measured to this photometric accuracy once per orbit. This will enable studies of transient zodiacal cloud phenomena, flare stars, supernovae, comets, and other varying point-like objects. 相似文献
17.
L.J. Lanzerotti T.P. Armstrong C.G. Maclennan G.M. Simnett A.F. Cheng R.E. Gold D.J. Thomson S.M. Krimigis K.A. Anderson S.E. Hawkins III M. Pick E.C. Roelof E.T. Sarris S.J. Tappin 《Planetary and Space Science》1993,41(11-12)
This paper presents an overview of a number of the principal findings regarding the hot plasmas (E 50 keV) in Jupiter's magnetosphere by the HISCALE instrument during the encounter of the Ulysses spacecraft with the planet in February 1992. The hot plasma ion fluxes measured by HI-SCALE in the dayside magnetosphere are similar to those measured in the same energy range in this region by the Voyager spacecraft in 1979. Within the dayside plasma sheet, the hot-ion energy densities are comparable with, or larger than, the magnetic field energy densities; these hot ions are found to corotate at about one-half the planetary corotational speed. For ions of energies 500 keV/nucleon, the protons contributed from 50–60% to as much as 80% of the energy content of these plasmas. Strong, magnetic-field-aligned streaming was found for both the ions and electrons in the high-latitude duskside magnetosphere. The ion and electron pitch-angle distributions could be characterized by cos25 α throughout many of the high anisotropy intervals of the outbound pass. There is some evidence in the ion pitch-angle distributions for a corotational component in the hot plasmas at high Jovian latitudes. While there are limitations owing to the finite geometries of the detector telescope systems on the determination of the angular spreads of the ion and electron beams, the measurements show that there are intervals when the particle distributions are not bidirectional. At such times, locally the hot plasmas could be carrying currents of 10−4μAm−2. The temporal variations in the streaming electron fluxes are substantially larger than the variations measured for the fluxes that are more locally mirroring. The temporal variations contain periodicities that may correspond to hydromagnetic wave frequencies in the magnetosphere as well as to larger scale motions of magnetospheric plasmas. On nearly half of the days for about a 130 day interval around the time of the Ulysses encounter with the planet, particles of Jovian origin were measured in the interplanetary medium. An event discussed herein shows evidence of an energy dependence of the particle release process from the planetary magnetosphere into the interplanetary medium. 相似文献
18.
We present data obtained from the Large Angle Spectrometric Coronagraph (LASCO) aboard the Solar and Heliospheric Observatory spacecraft (SOHO). We compare the rotation of the white-light corona as seen during a period approaching the maximum of the solar 11-year activity cycle with that observed in a previous study made at solar minimum (Lewis et al., 1999). We find no fundamental difference in the rotation characteristics and again find the white-light corona to be radially rigid. The rotation has been observed at altitudes from 2.5 R ⊙ to beyond 15 R ⊙ and as predicted in the previous study, the greater level of complexity in the coronal structures and their relatively rapid evolution has not allowed periods to be determined as accurately as at solar minimum. Our best estimate of the mean synodic rotation period during the period of study (7 March 1999 to 6 March 2000) is 27.5±0.3 days. This is consistent with the relatively small scale structures associated with the surface activity imposing their rotation signature on an otherwise axisymmetric background corona. The short-lived nature of the small scale coronal morphologies at this epoch has made a thorough analysis of the latitudinal variation difficult, although we again find some evidence for the white light corona's increased latitudinal rigidity when compared to the underlying photosphere. However, we again note how projection effects create difficulties in confirming the exact degree of rigidity in the corona at these altitudes and a very simple coronal model is used to highlight how the appearance of lower latitude features in projection can contaminate the coronal signal observed at other latitudes. We also note evidence for a sudden and apparently fundamental change to the global coronal morphology on the approach to solar maximum and suggest this may represent the time beyond which the classical solar dipole ceases to dominate the coronal field. 相似文献
19.
Richard A. Harrison Christopher J. Davis Christopher J. Eyles Danielle Bewsher Steve R. Crothers Jackie A. Davies Russell A. Howard Daniel J. Moses Dennis G. Socker Jeffrey S. Newmark Jean-Philippe Halain Jean-Marc Defise Emmanuel Mazy Pierre Rochus David F. Webb George M. Simnett 《Solar physics》2008,247(1):171-193
We show for the first time images of solar coronal mass ejections (CMEs) viewed using the Heliospheric Imager (HI) instrument
aboard the NASA STEREO spacecraft. The HI instruments are wide-angle imaging systems designed to detect CMEs in the heliosphere,
in particular, for the first time, observing the propagation of such events along the Sun – Earth line, that is, those directed
towards Earth. At the time of writing the STEREO spacecraft are still close to the Earth and the full advantage of the HI
dual-imaging has yet to be realised. However, even these early results show that despite severe technical challenges in their
design and implementation, the HI instruments can successfully detect CMEs in the heliosphere, and this is an extremely important
milestone for CME research. For the principal event being analysed here we demonstrate an ability to track a CME from the
corona to over 40 degrees. The time – altitude history shows a constant speed of ascent over at least the first 50 solar radii
and some evidence for deceleration at distances of over 20 degrees. Comparisons of associated coronagraph data and the HI
images show that the basic structure of the CME remains clearly intact as it propagates from the corona into the heliosphere.
Extracting the CME signal requires a consideration of the F-coronal intensity distribution, which can be identified from the
HI data. Thus we present the preliminary results on this measured F-coronal intensity and compare these to the modelled F-corona
of Koutchmy and Lamy (IAU Colloq.
85, 63, 1985). This analysis demonstrates that CME material some two orders of magnitude weaker than the F-corona can be detected; a specific
example at 40 solar radii revealed CME intensities as low as 1.7×10−14 of the solar brightness. These observations herald a new era in CME research as we extend our capability for tracking, in
particular, Earth-directed CMEs into the heliosphere. 相似文献
20.
Z. Švestka R. T. Stewart P. Hoyng W. Van Tend L. W. Acton A. H. Gabriel C. G. Rapley A. Boelee E. C. Bruner C. De Jager H. Lafleur G. Nelson G. M. Simnett H. F. Van Beek W. J. Wagner 《Solar physics》1982,75(1-2):305-329
More than six hours after the two-ribbon flare of 21 May 1980, the hard X-ray spectrometer aboard the SMM imaged an extensive arch above the flare region which proved to be the lowest part of a stationary post-flare noise storm recorded at the same time at Culgoora. The X-ray arch extended over 3 or more arc minutes to a projected distance of 95 000 km, and its real altitude was most probably between 110 000 and 180 000 km. The mean electron density in the cloud was close to 109 cm–3 and its temperature stayed for many hours at a fairly constant value of about 6.5 × 106 K. The bent crystal spectrometer aboard the SMM confirms that the arch emission was basically thermal. Variations in brightness and energy spectrum at one of the supposed footpoints of the arch seem to correlate in time with radio brightness suggesting that suprathermal particles from the radio noise regions dumped in variable quantities into the low corona and transition layer; these particles may have contributed to the population of the arch, after being trapped and thermalized. The arch extended along the H
= 0 line thus apparently hindering any upward movement of the upper loops reconnected in the flare process. There is evidence from Culgoora that this obstacle may have been present above the flare since 15–30 min after its onset. 相似文献