排序方式： 共有13条查询结果，搜索用时 656 毫秒
1.
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
2.
The Heliospheric Imager (HI) instruments on the Solar TErrestrial RElations Observatory (STEREO) observe solar plasma as it streams out from the Sun and into the heliosphere. The telescopes point off-limb (from
about 4° to 90° elongation) and so the Sun is not in the field of view. Hence, the Sun cannot be used to confirm the instrument
pointing. Until now, the pointing of the instruments have been calculated using the nominal preflight instrument offsets from
the STEREO spacecraft together with the spacecraft attitude data. This paper develops a new method for deriving the instrument
pointing solutions, along with other optical parameters, by comparing the locations of stars identified in each HI image with
the known star positions predicted from a star catalogue. The pointing and optical parameters are varied in an autonomous
manner to minimise the discrepancy between the predicted and observed positions of the stars. This method is applied to all
HI observations from the beginning of the mission to the end of April 2008. For the vast majority of images a good attitude
solution has been obtained with a mean-squared deviation between the observed and predicted star positions of one image pixel
or less. Updated values have been obtained for the instrument offsets relative to the spacecraft, and for the optical parameters
of the HI cameras. With this method the HI images can be considered as “self-calibrating,” with the actual instrument offsets
calculated as a byproduct. The updated pointing results and their by-products have been implemented in SolarSoft. 相似文献
3.
The relative Doppler and non-thermal velocities of quiet-Sun and active-region blinkers identified in Ov with CDS are calculated. Relative velocities for the corresponding chromospheric plasma below are also determined using the Hei line. Ov blinkers and the chromosphere directly below, have a preference to be more red-shifted than the normal transition region and chromospheric plasma. The ranges of these enhanced velocities, however, are no larger than the typical spread of Doppler velocities in these regions. The anticipated ranges of Doppler velocities of blinkers are 10–15 km s–1 in the quiet Sun (10–20 km s–1 in active regions) for Hei and 25–30 km s–1 in the quiet Sun (20–40 km s–1 in active regions) for Ov. Blinkers and the chromosphere below also have preferentially larger non-thermal velocities than the typical background chromosphere and transition region. Again the increase in magnitude of these non-thermal velocities is no greater than the typical ranges of non-thermal velocities. The ranges of non-thermal velocities of blinkers in both the quiet Sun and active regions are estimated to be 15–25 km s–1 in Hei and 30–45 km s–1 in Ov. There are more blinkers with larger Doppler and non-thermal velocities than would be expected in the whole of the chromosphere and transition region. The recently suggested mechanisms for blinkers are revisited and discussed further in light of the new results. 相似文献
4.
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
5.
D. Bewsher D. S. Brown C. J. Eyles B. J. Kellett G. J. White B. Swinyard 《Solar physics》2010,264(2):433-460
The aim of this paper is to calculate an accurate large-scale flatfield for the STEREO HI-1 instruments. This is done by analysing
the variation in intensity of stars in the background starfield as they pass across the CCD. In order to use the background
starfield, a photometric calibration is performed which defines a HI magnitude scale and a conversion between this scale and
measured intensity. The photometric calibration uses stellar spectra folded through the instrument response to make initial
intensity predictions. However, a secondary prediction method based on the photometric calibration, which blends the R-, V-
and B-magnitudes of a star, is derived for stars with no spectral information. 相似文献
6.
Using standard instrument software and two independently developed data reduction and analysis procedures, we re-examine the accuracy of plasma velocity information derived from data obtained by the Solar and Heliospheric Observatory (SOHO)–Coronal Diagnostic Spectrometer (CDS). We discuss only the Ov 629 Å line data obtained by the Normal Incidence Spectrometer (NIS) and analyse a quiet Sun (QS) and active region (AR) dataset. Using the QS data, we demonstrate that the well-known North-South tilt in wavelength along the NIS slit varies significantly with time, which is not accounted for in the standard CDS correction procedures. In addition, when residual N – S trends exist in the data after processing, they may not be detected, nor removed, using the standard analysis software. This underscores the need for careful analysis of velocity results for individual datasets when using standard correction procedures. Furthermore, even when the results obtained by the two independent methods are well correlated (coefficients greater than 0.9), discrepancies in the values of the derived Doppler velocities can remain (95% within ±5 km s?1). Therefore, we apply the results to examine the velocities obtained for EUV blinkers by previous authors. It is found that a strong correlation exists in the patterns of variation of the blinker velocities (> 0.98), even though there may be differences in their magnitudes. That is, in a clear majority of cases, the methods agree that a blinker is red-shifted or blue-shifted, although the uncertainty in the absolute velocity may be large. 相似文献
7.
Solar plasma that exists at around 105 K, which has traditionally been referred to as the solar transition region, is probably in a dynamic and fibril state with a small filling factor. Its origin is as yet unknown, but we suggest that it may be produced primarily by one of five different physical mechanisms, namely: the heating of cool spicular material; the containment of plasma in low-lying loops in the network; the thermal linking of cool and hot plasma at the feet of coronal loops; the heating and evaporating of chromospheric plasma in response to a coronal heating event; and the cooling and draining of hot coronal plasma when coronal heating is switched off. We suggest that, in each case, a blinker could be produced by the granular compression of a network junction, causing subtelescopic fibril flux tubes to spend more of their time at transition-region temperatures and so to increase the filling factor temporarily. 相似文献
8.
A. P. Rouillard N. P. Savani J. A. Davies B. Lavraud R. J. Forsyth S. K. Morley A. Opitz N. R. Sheeley L. F. Burlaga J.-A. Sauvaud K. D. C. Simunac J. G. Luhmann A. B. Galvin S. R. Crothers C. J. Davis R. A. Harrison M. Lockwood C. J. Eyles D. Bewsher D. S. Brown 《Solar physics》2009,256(1-2):307-326
The images taken by the Heliospheric Imagers (HIs), part of the SECCHI imaging package onboard the pair of STEREO spacecraft, provide information on the radial and latitudinal evolution of the plasma compressed inside corotating interaction regions (CIRs). A plasma density wave imaged by the HI instrument onboard STEREO-B was found to propagate towards STEREO-A, enabling a comparison between simultaneous remote-sensing and in situ observations of its structure to be performed. In situ measurements made by STEREO-A show that the plasma density wave is associated with the passage of a CIR. The magnetic field compressed after the CIR stream interface (SI) is found to have a planar distribution. Minimum variance analysis of the magnetic field vectors shows that the SI is inclined at 54° to the orbital plane of the STEREO-A spacecraft. This inclination of the CIR SI is comparable to the inclination of the associated plasma density wave observed by HI. A small-scale magnetic cloud with a flux rope topology and radial extent of 0.08 AU is also embedded prior to the SI. The pitch-angle distribution of suprathermal electrons measured by the STEREO-A SWEA instrument shows that an open magnetic field topology in the cloud replaced the heliospheric current sheet locally. These observations confirm that HI observes CIRs in difference images when a small-scale transient is caught up in the compression region. 相似文献
9.
Richard A. Harrison Jackie A. Davies Alexis P. Rouillard Christopher J. Davis Christopher J. Eyles Danielle Bewsher Steve R. Crothers Russell A. Howard Neil R. Sheeley Angelos Vourlidas David F. Webb Daniel S. Brown Gareth D. Dorrian 《Solar physics》2009,256(1-2):219-237
Imaging of the heliosphere is a burgeoning area of research. As a result, it is awash with new results, using novel applications, and is demonstrating great potential for future research in a wide range of topical areas. The STEREO (Solar TErrestrial RElations Observatory) Heliospheric Imager (HI) instruments are at the heart of this new development, building on the pioneering observations of the SMEI (Solar Mass Ejection Imager) instrument aboard the Coriolis spacecraft. Other earlier heliospheric imaging systems have included ground-based interplanetary scintillation (IPS) facilities and the photometers on the Helios spacecraft. With the HI instruments, we now have routine wide-angle imaging of the inner heliosphere, from vantage points outside the Sun-Earth line. HI has been used to investigate the development of coronal mass ejections (CMEs) as they pass through the heliosphere to 1 AU and beyond. Synoptic mapping has also allowed us to see graphic illustrations of the nature of mass outflow as a function of distance from the Sun – in particular, stressing the complexity of the near-Sun solar wind. The instruments have also been used to image co-rotating interaction regions (CIRs), to study the interaction of comets with the solar wind and CMEs, and to witness the impact of CMEs and CIRs on planets. The very nature of this area of research – which brings together aspects of solar physics, space-environment physics, and solar-terrestrial physics – means that the research papers are spread among a wide range of journals from different disciplines. Thus, in this special issue, it is timely and appropriate to provide a review of the results of the first two years of the HI investigations. 相似文献
10.
J.-P. Halain C. J. Eyles A. Mazzoli D. Bewsher J. A. Davies E. Mazy P. Rochus J. M. Defise C. J. Davis R. A. Harrison S. R. Crothers D. S. Brown C. Korendyke J. D. Moses D. G. Socker R. A. Howard J. S. Newmark 《Solar physics》2011,271(1-2):197-218
The SECCHI Heliospheric Imager (HI) instruments on-board the STEREO spacecraft have been collecting images of solar wind transients, including coronal mass ejections, as they propagate through the inner heliosphere since the beginning of 2007. The scientific use of the images depends critically on the performance of the instruments and its evolution over time. One of the most important factors affecting the performance of the instrument is the rejection of straylight from the Sun and from other bright objects located both within and outside the HI fields of view. This paper presents an analysis of the evolution of the straylight-rejection performance of the HI instrument on each of the two STEREO spacecraft over the three first years of the mission. The straylight level has been evaluated and expressed in mean solar brightness units, in which such scientific observations are usually quoted, using photometric conversion factors. 相似文献