共查询到20条相似文献，搜索用时 31 毫秒
1.
Using SOHO/MDI and SOHO/EIT data we study properties and dynamics of interconnected active regions, and the relations between
the photospheric magnetic fields and coronal structures in active longitudes during the beginning of solar cycle 23. The emergence
of new magnetic flux results in appearance of new interconnecting loops. The existence of stable coronal structures strongly
depends on the photospheric magnetic fluxes and their variations. We present some initial results for a complex of solar activity
observed in April 1997, and discuss the role of reconnection in the formation of the interconnected loops and coronal holes. 相似文献
2.
Margarita Karovska Brian Wood John W. Cook James Chen Russ Howard 《Astrophysics and Space Science》2000,273(1-4):7-15
Since January 1996, the Solar and Heliospheric Observatory (SOHO)has been providing unprecedented views of the extended solar coronato heliocentric distances of up to 32 solar radii. During the past threeyears we carried out studies of the morphology and dynamical evolutionof various structures in the solar corona using two instruments on boardSOHO: the Large Angle Spectrometric Coronagraph (LASCO) and the ExtremeUltraviolet Imaging Telescope (EIT). We have applied advanced image resolutionenhancement techniques to explore in detail the characteristics of thesmall-scale structures and/or the low contrast structures in the solarcorona. We describe here the results from these high-angular resolutionstudies, including of the kinematics of several Coronal Mass Ejections andpolar jets. 相似文献
3.
We present the main current issues concerning prominence studies. We recall the large range of plasma parameters found in prominences which makes the work of the MHD modeler more difficult. We also summarize the capabilities of the SOHO instrumentation. We present and discuss the most recent SOHO results concerning the determination of temperature, densities, and velocities. We put some emphasis on the different morphologies observed, the diagnostic capabilities of the Lyman lines profiles when accompanied by improved non-LTE modeling, and the information gathered from the first prominence oscillations measured from space. We also make an account of eruptive prominences. We finally discuss what could be done with present and future SOHO data to improve our understanding of prominences. 相似文献
4.
The large dynamic range provided by the SOHO/EIT CCD (1 : 5000) is needed to observe the large EUV zoom of coronal structures
from coronal homes up to flares. Histograms show that often a wide dynamic range is present in each image. Extracting hidden
structures in the background level requires specific techniques such as the use of the Multiscale Vision Model (MVM, Bijaoui
et al., 1998). This method, based on wavelet transformations optimizes detection of various size objects, however complex they may
be. Bijaoui et al. built the Multiscale Vision Model to extract small dynamical structures from noise, mainly for studying galaxies. In this
paper, we describe requirements for the use of this method with SOHO/EIT images (calibration, size of the image, dynamics
of the subimage, etc.). Two different areas were studied revealing hidden structures: (1) classical coronal mass ejection
(CME) formation and (2) a complex group of active regions with its evolution. The aim of this paper is to define carefully
the constraints for this new method of imaging the solar corona with SOHO/EIT. Physical analysis derived from multi-wavelength
observations will later complete these first results.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1017579625208
with J.P. Delaboudinière P.I. 相似文献
5.
The Solar TErrestrial RElations Observatory (STEREO) requires powerful tools for the three-dimensional (3D) reconstruction of the solar corona. Here we test such a program
with data from SOHO and TRACE. By taking advantage of solar rotation, a newly developed stereoscopy tool for the reconstruction
of coronal loops is applied to the solar active region NOAA 8891 observed from 1 March to 2 March 2000. The stereoscopic reconstruction
is composed of three steps. First, we identify loop structures in two TRACE images observed from two vantage viewpoints approximately
17 degrees apart, which corresponds to observations made about 30 hours apart. In the second step, we extrapolate the magnetic
field in the corona with the linear force-free field model from the photospheric line-of-sight SOHO/MDI data. Finally, combining
the extrapolated field lines and one-dimensional loop curves from two different viewpoints, we obtain the 3D loop structures
with the magnetic stereoscopy tool. We demonstrate that by including the magnetic modeling this tool is more powerful than
pure geometrical stereoscopy, especially in resolving the ambiguities generated by classical stereoscopy. This work will be
applied to the STEREO mission in the near future. 相似文献
6.
L. Gy?ri 《Solar physics》2012,280(2):365-378
Sunspot and white light facular areas are important data for solar activity and are used, for example, in the study of the evolution of sunspots and their effect on solar irradiance. Solar Dynamic Observatory??s Helioseismic and Magnetic Imager (SDO/HMI) solar images have much higher resolution (??0.5????pixel?1) than Solar and Heliospheric Observatory??s Michelson Doppler Imager (SOHO/MDI) solar images (??2????pixel?1). This difference in image resolution has a significant impact on the sunspot and white light facular areas measured in the two datasets. We compare the area of sunspots and white light faculae derived from SDO/HMI and SOHO/MDI observations. This comparison helps the calibration of the SOHO sunspot and facular area to those in SDO observations. We also find a 0.22 degree difference between the North direction in SDO/HMI and SOHO/MDI images. 相似文献
7.
Fletcher Lyndsay López Fuentes Marcelo C. Mandrini Cristina H. Schmieder Brigitte Démoulin Pascal Mason Helen E. Young Peter R. Nitta Nariaki 《Solar physics》2001,203(2):255-287
We present multi-instrument observations of active region (AR) 8048, made between 3 June and 5 June 1997, as part of the SOHO
Joint Observing Program 33. This AR has a sigmoid-like global shape and undergoes transient brightenings in both soft X-rays
and transition region (TR) lines. We compute a magneto-hydrostatic model of the AR magnetic field, using as boundary condition
the photospheric observations of SOHO/MDI. The computed large-scale magnetic field lines show that the large-scale sigmoid
is formed by two sets of coronal loops. Shorter loops, associated with the core of the SXT emission, coincide with the loops
observed in the hotter CDS lines. These loops reveal a gradient of temperature, from 2 MK at the top to 1 MK at the ends.
The field lines most closely matching these hot loops extend along the quasi-separatrix layers (QSLs) of the computed coronal
field. The TR brightenings observed with SOHO/CDS can also be associated with the magnetic field topology, both QSL intersections
with the photosphere, and places where separatrices issuing from bald patches (sites where field lines coming from the corona
are tangent to the photosphere) intersect the photosphere. There are, furthermore, suggestions that the element abundances
measured in the TR may depend on the type of topological structure present. Typically, the TR brightenings associated with
QSLs have coronal abundances, while those associated with BP separatrices have abundances closer to photospheric values. We
suggest that this difference is due to the location and manner in which magnetic reconnection occurs in two different topological
structures.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1013302317042 相似文献
8.
Bocchialini K. Costa A. Domenech G. Rovira M. Vial J.C. Wingfield K. 《Solar physics》2001,199(1):133-143
We present the results obtained from analyzing SUMER/SOHO observational data of a quiescent solar prominence. The studied prominence is made of complex structures. From the 1-hr data set, we derive characteristic frequencies in terms of intensity and velocity oscillations, as measured in 4 transition-region lines. The presence of different types of frequencies is detected: chromospheric oscillations and intermediate periods (6 min to 12 min). This result suggests that these oscillations are transmitted by the magnetic fields from the chromosphere to the transition region. 相似文献
9.
O. C. St. Cyr L. Sánchez-Duarte P. C. H. Martens J. B. Gurman E. Larduinat 《Solar physics》1995,162(1-2):39-59
We describe the ground segment, pre-launch operations concepts, and data products supporting the SOHO mission. Our goal is threefold: first, we provide a historical view of the design and development of the systems described here, as a background perspective to those who will use the system and those who may build such systems for future missions. Second, because we hope that many researchers from the solar and space physics communities will visit these facilities during the mission, we provide an overview for the benefit of the end-user. We anticipate that visitors to GSFC may plan observations for one or more of SOHO's complement of instruments, and such researchers may use the facilities to analyze data gathered by the SOHO instruments. Third, we present the working plan for investigators with groundbased or other spacebased instruments to collaborate with SOHO. 相似文献
10.
We show that under certain conditions, subsurface structures in the solar interior can alter the average acoustic power observed
at the photosphere above them. By using numerical simulations of wave propagation, we show that this effect is large enough
for it to be potentially used for detecting emerging active regions before they appear on the surface. In our simulations,
simplified subsurface structures are modeled as regions with enhanced or reduced acoustic wave speed. We investigate the dependence
of the acoustic power above a subsurface region on the sign, depth, and strength of the wave-speed perturbation. Observations
from the Solar and Heliospheric Observatory/Michelson Doppler Imager (SOHO/MDI) prior and during the emergence of NOAA active region 10488 are used to test the use of acoustic power as a potential
precursor of the emergence of magnetic flux. 相似文献
11.
We use an innovative research technique to analyze combined images from the Coronal Diagnostic Spectrometer (CDS) on the Solar and Heliospheric Observatory (SOHO) and the Transition Region and Coronal Explorer (TRACE). We produce a high spatial and temporal resolution simulated CDS raster or “composite” map from TRACE data and use
this composite map to jointly analyze data from both instruments. We show some of the advantages of using the “composite”
map method for coronal loop studies. We investigate two postflare loop structures. We find cool material (250 000 K) concentrated
at the tips or apex of the loops. This material is found to be above its scale height and therefore not in hydrostatic equilibrium.
The exposure times of the composite map and TRACE images are used to give an estimate of another loop’s cooling time. The
contribution to the emission in the TRACE images for the spectral lines present in its narrow passband is estimated by using
the CDS spectral data and CHIANTI to derive synthetic spectra. We obtain cospatial and cotemporal data collected by both instruments
in SOHO Joint Observations Program (JOP) 146 and show how the combination of these data can be utilized to obtain more accurate
measurements of coronal plasmas than if analyzed individually.
Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users. 相似文献
12.
A new algorithm for automatic detection of prominences on the solar limb in 304 Å EUV images is presented, and results of its application to SOHO/EIT data discussed. The detection is based on the method of moments combined with a classifier analysis aimed at discriminating between limb prominences, active regions, and the quiet corona. This classifier analysis is based on a Support Vector Machine (SVM). Using a set of 12 moments of the radial intensity profiles, the algorithm performs well in discriminating between the above three categories of limb structures, with a misclassification rate of 7%. Pixels detected as belonging to a prominence are then used as the starting point to reconstruct the whole prominence by morphological image-processing techniques. It is planned that a catalogue of limb prominences identified in SOHO and STEREO data using this method will be made publicly available to the scientific community. 相似文献
13.
Bogdan Valcu Peter L. Smith Larry D. Gardner John C. Raymond Mari-Paz Miralles John L. Kohl 《Solar physics》2007,243(1):93-104
We have tracked the spectral responsivity of the ultraviolet channels of the UVCS (Ultraviolet Coronagraph Spectrometer) instrument
on SOHO by repeated observations of a stable hot star. We demonstrate first that the ultraviolet spectral irradiance of the
Be star ζ Tau (HD 37202) for the 100- to 125-nm wavelength range has been sufficiently constant for our purposes when measured periodically
over the course of the SOHO mission. We then use ζ Tau as a radiometric transfer standard to determine an average decrease beginning in November of 1998 of 13.0% per year in
the responsivity of the UVCS O vi channel for wavelengths near H i Ly α and for a particular UVCS unvignetted aperture used for science observations. The calibration tracking method involves
separating two ζ Tau spectral regions that are overlapped on part of the detector. The change in the responsivity of UVCS/SOHO began in late
1998 as determined by comparison of simultaneous observations of the corona carried out with UVCS/SOHO and the freshly-calibrated
UVCS instrument on the Spartan 201 satellite in early November of 1998.
B. Valcu now at BrainLAB, Inc, 3 Westbrook Corporate Ctr., Tower 3, Suite 400, Westchester, IL 60154, USA, e-mail: bogdan.valcu@brainlab.com
or Bogdan_valcu@hotmail.com 相似文献
14.
Recent space missions have changed our view of the solar transition region. In particular the ESA/NASA Solar and Heliospheric
Observatory (SOHO) and NASA's TRACE satellite have provided a unique opportunity to explore the solar atmosphere in detail.
The combination of high spatial, spectral and temporal observations has made it possible to derive three dimensional images
of the emission and velocity structures of solar features. Active region loop structures at transition region temperatures
appear to be extremely time variable and dynamic, a result with profound implications for our understanding and modeling of
the upper solar atmosphere. Large Dopplershifts have also been observed in these structures. A 3-minute transition region
oscillation has been observed above sunspots suggesting upward-propagating acoustic waves. Clear evidence of velocity oscillations
in the internetwork regions has also been observed in both the chromosphere and the transition region. The longstanding and
puzzling problem of the apparent net red shift of emission lines from the transition region has been revisited. The extensive
wavelength coverage of the SOHO spectrometers has made it possible to extend the measurements to much higher temperatures
compared to previous instruments. The combination of magnetograms, EUV spectral imaging and the high resolution broad-band
images from TRACE has also given us new insight concerning the structure of the transition region and its relation with the
photospheric magnetic field.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1005224709046 相似文献
15.
T. Dudok De Wit 《Solar physics》2006,239(1-2):519-530
A segmentation scheme for identifying large-scale structures (coronal holes, active regions, etc.) in solar extreme ultraviolet images, is presented. Unlike standard approaches, both the image intensity and the relative
contribution of different wavelengths are used. Spectral information is important for compensating luminosity changes. The
approach is illustrated with images taken in the extreme ultraviolet by the EIT telescope onboard SOHO. This supervised segmentation
scheme, which incorporates a Bayesian classifier, is computationally simple, and can easily be used to track in near-real
time structures, such as coronal holes. 相似文献
16.
The Mercury transit of 15 November 1999 has been observed from space by the SOHO and TRACE spacecraft. We exploited the data
recorded by EIT/SOHO to determine the stray-light level and the plate-scale of the instrument. The asymmetric distribution
of stray light across the images is confirmed, but the absolute amount was found to be higher than previously estimated. The
plate scale averaged over wavelengths was found to be 2.627±0.001 arc sec pixel−1, in excellent agreement with two previous and independent determinations. 相似文献
17.
The structure of the solar corona is dominated by the magnetic field because the magnetic pressure is about four orders of
magnitude higher than the plasma pressure. Due to the high conductivity the emitting coronal plasma (visible, e.g., in SOHO/EIT)
outlines the magnetic field lines. The gradient of the emitting plasma structures is significantly lower parallel to the magnetic
field lines than in the perpendicular direction. Consequently information regarding the coronal magnetic field can be used
for the interpretation of coronal plasma structures. We extrapolate the coronal magnetic field from photospheric magnetic
field measurements into the corona. The extrapolation method depends on assumptions regarding coronal currents, e.g., potential
fields (current-free) or force-free fields (current parallel to magnetic field). As a next step we project the reconstructed
3D magnetic field lines on an EIT-image and compare with the emitting plasma structures. Coronal loops are identified as closed
magnetic field lines with a high emissivity in EIT and a small gradient of the emissivity along the magnetic field. 相似文献
18.
Shibu K. Mathew 《Solar physics》2008,251(1-2):515-522
We investigate p-mode absorption in a sunspot using SOHO/MDI high-resolution Doppler images. The Doppler power computed from a 3.5-hour data set is used for studying the absorption in a sunspot. The result shows an enhancement in absorption near the umbral?–?penumbral boundary of the sunspot. We attempt to relate the observed absorption with the magnetic-field structure of the sunspot. The transverse component of the potential field is computed by using the observed SOHO/MDI line-of-sight magnetograms. A comparison of the power map and the computed potential field shows enhanced absorption near the umbral?–?penumbral boundary where the computed transverse field strength is higher. 相似文献
19.
G. D. R. Attrill L. K. Harra L. van Driel-Gesztelyi M. J. Wills-Davey 《Solar physics》2010,264(1):119-147
We study two CME events on 13 and 14 December 2006 that were associated with large-scale dimmings. We study the eruptions
from pre-event on 11 December through the recovery on 15 December, using a combination of Hinode/EIS, SOHO/EIT, SOHO/MDI, and MLSO Hα data. The GOES X-class flares obscured the core dimmings, but secondary dimmings developed
remote from the active region (AR) in both events. The secondary dimmings are found to be formed by a removal of bright coronal
material from loops in the plage region to the East of the AR. Using Hinode/EIS data, we find that the outflows associated with the coronal-dimming regions are highly structured. The concentrated outflows
are located at the footpoints of coronal loops (which exist before, and are re-established after, the eruptions), and these
are correlated with regions of positive magnetic elements. Comparative study of the Hinode/EIS and SOHO/EIT data shows that the reduction in outflow velocity is consistent with the recovery in intensity of the studied
regions. We find that concentrated downflows develop during the recovery phase of the dimmings and are also correlated with
the same positive magnetic elements that were previously related to outflows. 相似文献
20.
In this paper we discuss the two mechanisms by which solar prominences on the limb can manifest themselves when observed in
coronal UV – EUV lines and in the soft X-ray continuum. These mechanisms are the absorption in the resonance continua of hydrogen
and helium on one hand and the reduction of the emissivity in a part of the coronal volume occupied by a prominence on the
other one. We briefly describe earlier observations made with SOHO/SUMER, EIT and Yohkoh/SXT. We then discuss how the instruments on the new Japanese satellite Hinode can be used for more detailed studies of prominences. We also propose some combined observations between the Hinode satellite and the SOHO/SUMER instrument. 相似文献