共查询到20条相似文献，搜索用时 28 毫秒
1.
Determining the coronal electron density by the inversion of white-light polarized brightness (pB) measurements by coronagraphs is a classic problem in solar physics. An inversion technique based on the spherically symmetric geometry (spherically symmetric inversion, SSI) was developed in the 1950s and has been widely applied to interpret various observations. However, to date there is no study of the uncertainty estimation of this method. We here present the detailed assessment of this method using a three-dimensional (3D) electron density in the corona from 1.5 to 4 R ⊙ as a model, which is reconstructed by a tomography method from STEREO/COR1 observations during the solar minimum in February 2008 (Carrington Rotation, CR 2066). We first show in theory and observation that the spherically symmetric polynomial approximation (SSPA) method and the Van de Hulst inversion technique are equivalent. Then we assess the SSPA method using synthesized pB images from the 3D density model, and find that the SSPA density values are close to the model inputs for the streamer core near the plane of the sky (POS) with differences generally smaller than about a factor of two; the former has the lower peak but extends more in both longitudinal and latitudinal directions than the latter. We estimate that the SSPA method may resolve the coronal density structure near the POS with angular resolution in longitude of about 50°. Our results confirm the suggestion that the SSI method is applicable to the solar minimum streamer (belt), as stated in some previous studies. In addition, we demonstrate that the SSPA method can be used to reconstruct the 3D coronal density, roughly in agreement with the reconstruction by tomography for a period of low solar activity (CR 2066). We suggest that the SSI method is complementary to the 3D tomographic technique in some cases, given that the development of the latter is still an ongoing research effort. 相似文献
2.
William T. Thompson 《Solar physics》2018,293(3):49
Measurements of bright stars passing through the fields of view of the inner coronagraphs (COR1) on board the Solar Terrestrial Relations Observatory (STEREO) are used to monitor changes in the radiometric calibration over the course of the mission. Annual decline rates are found to be \(0.648 \pm 0.066\)%/year for COR1-A on STEREO Ahead and \(0.258 \pm 0.060\)%/year for COR1-B on STEREO Behind. These rates are consistent with decline rates found for other space-based coronagraphs in similar radiation environments. The theorized cause for the decline in sensitivity is darkening of the lenses and other optical elements due to exposure to high-energy solar particles and photons, although other causes are also possible. The total decline in the COR-B sensitivity when contact with Behind was lost on 1 October 2014 was 1.7%, while COR1-A was down by 4.4%. As of 1 November 2017, the COR1-A decline is estimated to be 6.4%. The SECCHI calibration routines will be updated to take these COR1 decline rates into account. 相似文献
3.
COR1 is the innermost coronagraph of the Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI) instrument suite
aboard the twin Solar Terrestrial Relations Observatory (STEREO) spacecraft. The paired COR1 telescopes observe the white-light K-corona from 1.4 to 4 solar radii in a waveband
22.5 nm wide centered on the Hα line at 656 nm. An internal polarizer allows the measurement of both total and polarized brightness.
The co-alignment of the two COR1 telescopes is derived from the star λ Aquarii for the Ahead spacecraft, and from an occultation
of the Sun by the Moon for Behind. Observations of the planet Jupiter are used to establish absolute photometric calibrations
for each telescope. The intercalibration of the two COR1 telescopes are compared using coronal mass ejection observations
made early in the mission, when the spacecraft were close together. Comparisons are also made with the Solar and Heliospheric
Observatory (SOHO) Large Angle and Spectrometric Coronagraph (LASCO) C2 and Mauna Loa Solar Observatory Mk4 coronagraphs. 相似文献
4.
M. Mierla B. Inhester C. Marqué L. Rodriguez S. Gissot A. N. Zhukov D. Berghmans J. Davila 《Solar physics》2009,259(1-2):123-141
The data from SECCHI-COR1 and SECCHI-COR2 coronagraphs onboard the STEREO mission, which was launched in October 2006, provide us with the first-ever stereoscopic images of the Sun’s corona. These observations were found to be useful in inferring the three-dimensional structure of coronal mass ejections (CMEs) and their propagation direction in space. We apply four methods for reconstructing CMEs: i) Forward modeling technique; ii) Local correlation tracking (to identify the same feature in COR Ahead and COR Behind images) plus tie-point reconstruction technique; iii) Center of mass of the structures in a given epipolar plane plus tie-point reconstruction technique; iv) Polarization ratio technique. The four techniques are applied to three structured CMEs observed by COR1 and COR2 instruments, respectively, on 15 May 2007, 31 August 2007, and 25 March 2008. A comparison of the results obtained from the application of the four reconstruction algorithms is presented and discussed. 相似文献
5.
Richard A. Frazin Philippe Lamy Antoine Llebaria Alberto M. Vásquez 《Solar physics》2010,265(1-2):19-30
We present the first quantitative three-dimensional (3D) tomographic reconstructions of electron density from coronagraph measurements of the K-corona’s total brightness (B) made by LASCO-C2 on SOHO. This is possible because new calibrations of the LASCO-C2 images in both polarized brightness (pB) and B have now been made for the entire mission. The B and pB reconstructions are compared, and the differences are explained in terms of line of sight weighting functions in Thomson scattering. We conclude that the LASCO-C2 B archive, which is vastly larger than the pB archive, will be a very valuable resource for determining the 3D electron density throughout the SOHO mission which started taking data in 1996. 相似文献
6.
D. F. Webb T. A. Howard C. D. Fry T. A. Kuchar D. Odstrcil B. V. Jackson M. M. Bisi R. A. Harrison J. S. Morrill R. A. Howard J. C. Johnston 《Solar physics》2009,256(1-2):239-267
We are investigating the geometric and kinematic characteristics of interplanetary coronal mass ejections (ICMEs) using data obtained by the LASCO coronagraphs, the Solar Mass Ejection Imager (SMEI), and the SECCHI imaging experiments on the STEREO spacecraft. The early evolution of CMEs can be tracked by the LASCO C2 and C3 and SECCHI COR1 and COR2 coronagraphs, and the HI and SMEI instruments can track their ICME counterparts through the inner heliosphere. The HI fields of view (4?–?90°) overlap with the SMEI field of view (>?20° to all sky) and, thus, both instrument sets can observe the same ICME. In this paper we present results for ICMEs observed on 24?–?29 January 2007, when the STEREO spacecraft were still near Earth so that both the SMEI and STEREO views of large ICMEs in the inner heliosphere coincided. These results include measurements of the structural and kinematic evolution of two ICMEs and comparisons with drive/drag kinematic, 3D tomographic reconstruction, the HAFv2 kinematic, and the ENLIL MHD models. We find it encouraging that the four model runs generally were in agreement on both the kinematic evolution and appearance of the events. Because it is essential to understand the effects of projection across large distances, that are not generally crucial for events observed closer to the Sun, we discuss our analysis procedure in some detail. 相似文献
7.
E. Bosman V. Bothmer G. Nisticò A. Vourlidas R. A. Howard J. A. Davies 《Solar physics》2012,281(1):167-185
We identify 565 coronal mass ejections (CMEs) between January 2007 and December 2010 in observations from the twin STEREO/SECCHI/COR2 coronagraphs aboard the STEREO mission. Our list is in full agreement with the corresponding SOHO/LASCO CME Catalog ( http://cdaw.gsfc.nasa.gov/CME_list/ ) for events with angular widths of 45° and up. The monthly event rates behave similarly to sunspot rates showing a three- to fourfold rise between September 2009 and March 2010. We select 51 events with well-defined white-light structure and model them as three-dimensional (3D) flux ropes using a forward-modeling technique developed by Thernisien, Howard and Vourlidas (Astrophys. J. 652, 763??C?773, 2006). We derive their 3D properties and identify their source regions. We find that the majority of the CME flux ropes (82?%) lie within 30° of the solar equator. Also, 82?% of the events are displaced from their source region, to a lower latitude, by 25° or less. These findings provide strong support for the deflection of CMEs towards the solar equator reported in earlier observations, e.g. by Cremades and Bothmer (Astron. Astrophys. 422, 307??C?322, 2004). 相似文献
8.
A method for the full three-dimensional (3-D) reconstruction of the trajectories of coronal mass ejections (CMEs) using Solar TErrestrial RElations Observatory (STEREO) data is presented. Four CMEs that were simultaneously observed by the inner and outer coronagraphs (COR1 and 2) of the Ahead and Behind STEREO satellites were analysed. These observations were used to derive CME trajectories in 3-D out to ～?15?R ⊙. The reconstructions using COR1/2 data support a radial propagation model. Assuming pseudo-radial propagation at large distances from the Sun (15?–?240?R ⊙), the CME positions were extrapolated into the Heliospheric Imager (HI) field-of-view. We estimated the CME velocities in the different fields-of-view. It was found that CMEs slower than the solar wind were accelerated, while CMEs faster than the solar wind were decelerated, with both tending to the solar wind velocity. 相似文献
9.
We have estimated the speed and direction of propagation of a number of Coronal Mass Ejections (CMEs) using single-spacecraft data from the STEREO Heliospheric Imager (HI) wide-field cameras. In general, these values are in good agreement with those predicted by Thernisien, Vourlidas, and Howard in Solar Phys. 256, 111?–?130 (2009) using a forward modelling method to fit CMEs imaged by the STEREO COR2 coronagraphs. The directions of the CMEs predicted by both techniques are in good agreement despite the fact that many of the CMEs under study travel in directions that cause them to fade rapidly in the HI images. The velocities estimated from both techniques are in general agreement although there are some interesting differences that may provide evidence for the influence of the ambient solar wind on the speed of CMEs. The majority of CMEs with a velocity estimated to be below 400 km?s?1 in the COR2 field of view have higher estimated velocities in the HI field of view, while, conversely, those with COR2 velocities estimated to be above 400 km?s?1 have lower estimated HI velocities. We interpret this as evidence for the deceleration of fast CMEs and the acceleration of slower CMEs by interaction with the ambient solar wind beyond the COR2 field of view. We also show that the uncertainties in our derived parameters are influenced by the range of elongations over which each CME can be tracked. In order to reduce the uncertainty in the predicted arrival time of a CME at 1 Astronomical Unit (AU) to within six hours, the CME needs to be tracked out to at least 30 degrees elongation. This is in good agreement with predictions of the accuracy of our technique based on Monte Carlo simulations. Within the set of studied CMEs, there are two clear events that were predicted from the HI data to travel over another spacecraft; in-situ measurements at these other spacecraft confirm the accuracy of these predictions. The ability of the HI cameras to image Corotating Interaction Region (CIR)-entrained transients as well as CMEs can result in some ambiguity when trying to distinguishing individual signatures. 相似文献
10.
W.T. Thompson 《Icarus》2009,200(2):351-357
The bright Kreutz Comet C/2007 L3 (SOHO) entered the fields of view of the twin Solar Terrestrial Relations Observatory (STEREO) COR1 telescopes on 7–8 June 2007. The 12° separation between the two spacecraft at the time afforded the opportunity to derive the position of the comet's tail in three-dimensional space using direct triangulation. The track of the comet's orbit is compared against more traditional orbital calculations using observations from the STEREO COR2 telescopes, and from the Large Angle and Spectrometric Coronagraph (LASCO) aboard the Solar and Heliospheric Observatory (SOHO). The shape of the comet's tail shows that it is composed of dust particles released when the comet was between 18 and 22 solar radii, with no significant dust production after that. The comet did not survive perihelion passage, but a rare faint remnant of the comet tail persisted for several hours after the break-up, and was seen by both the SOHO and STEREO coronagraphs to drift slowly away from the Sun. This tail remnant was found to be composed of particles far back from the head of the comet. The motion of the tail remnant shows a loss of angular momentum during the passage through the solar corona. Atmospheric drag is estimated to account for a significant fraction of this change in angular momentum, but indications are that other mechanisms may be required to completely account for the total amount of change. 相似文献
11.
Since 4 December 2006, the SECCHI instrument suites onboard the two STEREO A and B probes have been imaging the solar corona
and the heliosphere on a wide range of angular scales. The EUVI telescopes have a plate scale of 1.7 arcseconds pixel−1, while that of the HI2 wide-angle cameras is 2.15 arcminutes pixel−1, i.e. 75 times larger, with the COR1 and COR2 coronagraphs having intermediate plate scales. These very different instruments,
aimed at studying Coronal Mass Ejections and their propagation in the heliosphere, create a data visualization challenge.
This paper presents FESTIVAL, a SolarSoftware package originally developed to be able to map the SECCHI data into dynamic
composite images of the sky as seen by the STEREO and SOHO probes. Data from other imaging instruments can also be displayed.
Using the mouse, the user can quickly and easily zoom in and out and pan through these composite images to explore all spatial
scales from EUVI to HI2 while keeping the native resolution of the original data. A large variety of numerical filters can
be applied, and additional data (i.e. coordinate grids, stars catalogs, etc.) can be overlaid on the images. The architecture of FESTIVAL is such that it is easy to add support for other instruments
and these new data immediately benefit from the already existing capabilities. Also, because its mapping engine is fully 3D,
FESTIVAL provides a convenient environment to display images from future out-of-the-Ecliptic solar missions, such as Solar Orbiter or Solar Probe. 相似文献
12.
A. R. Paraschiv D. A. Lacatus T. Badescu M. G. Lupu S. Simon S. G. Sandu M. Mierla M. V. Rusu 《Solar physics》2010,264(2):365-375
During the 2007 – 2008 minimum of solar activity, the internally occulted coronagraphs SECCHI-COR1 onboard the STEREO space
mission recorded numerous jet-like ejections over a great range of latitudes. We have found more than 10000 white-light jets
in the above-mentioned period. Sometimes they can be identified on the disk with bright points observed in ultraviolet images
by EUVI. In this study we present a catalog consisting of jets observed by the SECCHI-COR1 instrument and their association
with lower coronal activity (bright points, UV jets). Furthermore, their association with bright points in the context of
previously proposed models is discussed. From the complete catalog we have selected 106 jets observed in both STEREO-A and
STEREO-B images for which it is possible to derive their kinematics and point of origin. 相似文献
13.
Previous attempts to produce three-dimensional (3-D) reconstructions of coronal mass ejections (CMEs) have required either
modeling efforts or comparisons with secondary associated eruptions near the solar surface. This is because coronagraphs are
only able to produce sky-plane-projected images of CMEs and it has hence been impossible to overcome projection effects by
using coronagraphs alone. The SECCHI suite aboard the twin STEREO spacecraft allows us to provide the means for 3-D reconstruction
of CMEs directly from coronagraph measurements alone for the first time. We present these measurements from two CMEs observed
in November 2007. By identifying common features observed simultaneously with the LASCO coronagraphs aboard SOHO and the COR
coronagraphs aboard STEREO we have triangulated the source region of both CMEs. We present the geometrical analysis required
for this triangulation and identify the location of the CME in solar-meridional, ecliptic, and Carrington coordinates. None
of the two events were associated with an easily detectable solar surface eruption, so this triangulation technique is the
only means by which the source location of these CMEs could be identified. We present evidence that both CMEs originated from
the same magnetic structure on the Sun, but from a different magnetic field configuration. Our results reveal some insight
into the evolution of the high corona magnetic field, including its behavior over time scales of a few days and its reconfiguration
after a major eruption. 相似文献
14.
We present a hybrid combination of forward and inverse reconstruction methods using multiple observations of a coronal mass ejection (CME) to derive the three-dimensional (3D) “true” height?–?time plots for individual CME components. We apply this hybrid method to the components of the 31 December 2007 CME. This CME, observed clearly in both the STEREO A and STEREO B COR2 white-light coronagraphs, evolves asymmetrically across the 15-solar-radius field of view within a span of three hours. The method has two reconstruction steps. We fit a boundary envelope for the potential 3D CME shape using a flux-rope-type model oriented to best match the observations. Using this forward model as a constraining envelope, we then run an inverse reconstruction, solving for the simplest underlying 3D electron density distribution that can, when rendered, reproduce the observed coronagraph data frames. We produce plots for each segment to establish the 3D or “true” height?–?time plots for each center of mass as well as for the bulk CME motion, and we use these plots along with our derived density profiles to estimate the CME’s asymmetric expansion rate. 相似文献
15.
COR1 is an internally occulted Lyot coronagraph, part of the Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI)
instrument suite aboard the twin Solar Terrestrial Relations Observatory (STEREO) spacecraft. Because the front objective lens is subjected to a full solar flux, the images are dominated by instrumental
scattered light which has to be removed to uncover the underlying K corona data. We describe a procedure for removing the
instrumental background from COR1 images. F coronal emission is subtracted at the same time. The resulting images are compared
with simultaneous data from the Mauna Loa Solar Observatory Mk4 coronagraph. We find that the background subtraction technique
is successful in coronal streamers, while the baseline emission in coronal holes (i.e. between plumes) is suppressed. This is an expected behavior of the background subtraction technique. The COR1 radiometric
calibration is found to be either 10 – 15% lower, or 5 – 10% higher than that of the Mk4, depending on what value is used
for the Mk4 plate scale, while an earlier study found the COR1 radiometric response to be ∼ 20% higher than that of the Large
Angle Spectroscopic Coronagraph (LASCO) C2 telescope. Thus, the COR1 calibration is solidly within the range of other operating
coronagraphs. The background levels in both COR1 telescopes have been quite steady in time, with the exception of a single
contamination event on 30 January 2009. Barring too many additional events of this kind, there is every reason to believe
that both COR1 telescopes will maintain usable levels of scattered light for the remainder of the STEREO mission. 相似文献
16.
We present for the first time a three-dimensional reconstruction of the electron density in the corona at distances from 1.5R ⊙ to 4R ⊙ using COR1 STEREO observations. The reconstruction is performed using a regularized tomography inversion method for two biweekly periods corresponding to Carrington Rotations 2058 and 2066. Images from the two STEREO spacecraft are used to compare the reconstructed density structures with coronal features located by triangulation. We find that the location of a bright tip of a helmet streamer obtained from the tomographic reconstruction is in good agreement with the location obtained by triangulation. The reconstructed density structure of the equatorial streamer belt is largely consistent with the variation of the current sheet derived from a potential magnetic field extrapolation for most of the equatorial region and for an MHD model of the corona. A zero-value density region in the reconstruction is identified with a low-density region seen in an EUVI image below the reconstruction domain. 相似文献
17.
Richard Woo 《Solar physics》2007,241(2):251-261
In the absence of magnetic field measurements of the solar corona, the density structure of white-light images has provided
important insight into the coronal magnetic field. Recent work sparked by highly sensitive radio occultation measurements
of path-integrated density has elucidated the density structure of unprocessed solar eclipse pictures. This paper does the
same for processed images that reveal low-contrast small-scale structures, specifically Koutchmy’s edge-enhanced white-light
image of the 11 August 1999 solar eclipse. This processed image provides visual evidence for two important results deduced
from radio occultation measurements of small-scale density variations. First, in addition to the closed loops readily seen
at the base of the corona in high-resolution EUV and soft X-ray images, open filamentary structures permeate the corona including
active regions generally thought to be magnetically closed. Observed at the image resolution, the filamentary structures are
1° wide in latitude and an order of magnitude smaller than polar plumes. Second, although inhomogeneities that are convected
along with the solar wind are also present, filamentary structures dominate the image because of their steeper density gradients.
The quantitative profile of polarized brightness (pB) at the base of the corona shows that the filamentary structures have transverse density gradients that are proportional
to their density. This explains why edge-enhanced images, limited in sensitivity to density gradients, tend to detect filamentary
structures more readily in high-density regions (e.g., active regions, streamer stalks, and prominences) than in low-density polar coronal holes, and why filamentary structures
seem more prevalent in solar eclipse pictures during solar maximum. The pB profile at the base of the corona also fills the gap in Doppler measurements there, reinforcing that open ultra-fine-scale
filamentary structures observed by the radio measurements are predominantly radial and that they are an integral part of the
radial expansion of the solar wind. 相似文献
18.
M. M. Bisi B. V. Jackson A. R. Breen G. D. Dorrian R. A. Fallows J. M. Clover P. P. Hick 《Solar physics》2010,265(1-2):233-244
The European Incoherent SCATter (EISCAT) radar has been used for remote-sensing observations of interplanetary scintillation (IPS) for a quarter of a century. During the April/May 2007 observing campaign, a large number of observations of IPS using EISCAT took place to give a reasonable spatial and temporal coverage of solar wind velocity structure throughout this time during the declining phase of Solar Cycle 23. Many co-rotating and transient features were observed during this period. Using the University of California, San Diego three-dimensional (3-D) time-dependent computer assisted tomography (C.A.T.) solar-wind reconstruction analysis, we show the velocity structure of the inner heliosphere in three dimensions throughout the time interval of 20 April through 20 May 2007. We also compare to white-light remote-sensing observations of an interplanetary coronal mass ejection (ICME) seen by the STEREO Ahead spacecraft inner Heliospheric Imager on 16 May 2007, as well as to in-situ solar-wind measurements taken with near-Earth spacebourne instrumentation throughout this interval. The reconstructions show clear co-rotating regions during this period, and the time-series extraction at spacecraft locations compares well with measurements made by the STEREO, Wind, and ACE spacecraft. This is the first time such clear structures have been revealed using this 3-D technique with EISCAT IPS data as input. 相似文献
19.
Solar tomography has progressed rapidly in recent years thanks to the development of robust algorithms and the availability of more powerful computers. It can today provide crucial insights in solving issues related to the line-of-sight integration present in the data of solar imagers and coronagraphs. However, there remain challenges such as the increase of the available volume of data, the handling of the temporal evolution of the observed structures, and the heterogeneity of the data in multi-spacecraft studies. We present a generic software package that can perform fast tomographic inversions that scales linearly with the number of measurements, linearly with the length of the reconstruction cube (and not the number of voxels), and linearly with the number of cores and can use data from different sources and with a variety of physical models: TomograPy ( http://nbarbey.github.com/TomograPy/ ), an open-source software freely available on the Python Package Index. For performance, TomograPy uses a parallelized-projection algorithm. It relies on the World Coordinate System standard to manage various data sources. A variety of inversion algorithms are provided to perform the tomographic-map estimation. A test suite is provided along with the code to ensure software quality. Since it makes use of the Siddon algorithm it is restricted to rectangular parallelepiped voxels but the spherical geometry of the corona can be handled through proper use of priors. We describe the main features of the code and show three practical examples of multi-spacecraft tomographic inversions using STEREO/EUVI and STEREO/COR1 data. Static and smoothly varying temporal evolution models are presented. 相似文献
20.
N. Lugaz P. Kintner C. M?stl L. K. Jian C. J. Davis C. J. Farrugia 《Solar physics》2012,279(2):497-515
We present a study of coronal mass ejections (CMEs) which impacted one of the STEREO spacecraft between January 2008 and early 2010. We focus our study on 20 CMEs which were observed remotely by the Heliospheric Imagers (HIs) onboard the other STEREO spacecraft up to large heliocentric distances. We compare the predictions of the Fixed-?? and Harmonic Mean (HM) fitting methods, which only differ by the assumed geometry of the CME. It is possible to use these techniques to determine from remote-sensing observations the CME direction of propagation, arrival time and final speed which are compared to in-situ measurements. We find evidence that for large viewing angles, the HM fitting method predicts the CME direction better. However, this may be due to the fact that only wide CMEs can be successfully observed when the CME propagates more than 100° from the observing spacecraft. Overall eight CMEs, originating from behind the limb as seen by one of the STEREO spacecraft can be tracked and their arrival time at the other STEREO spacecraft can be successfully predicted. This includes CMEs, such as the events on 4 December 2009 and 9 April 2010, which were viewed 130° away from their direction of propagation. Therefore, we predict that some Earth-directed CMEs will be observed by the HIs until early 2013, when the separation between Earth and one of the STEREO spacecraft will be similar to the separation of the two STEREO spacecraft in 2009??C?2010. 相似文献