共查询到20条相似文献，搜索用时 46 毫秒
1.
Since the 1970s, the Solar-Terrestrial Environment Laboratory, Japan, has been publishing synoptic maps of solar wind velocity prepared using the technique of interplanetary scintillation. These maps, known as V-maps, are useful to study the global distribution of solar wind in the heliosphere. As the Earth-orbiting satellites are unable to probe regions outside the ecliptic, it is important to exploit the scope of interplanetary scintillation to study the solar wind properties at these regions and their relation with coronal features. It has been shown by Wang and Sheeley that there exists an inverse correlation between rate of magnetic flux expansion and the solar wind velocity. The NOAA/Space Environment Center daily updated version of the Wang and Sheeley model has been used to produce synoptic maps of solar wind velocity and magnetic field polarity for individual Carrington rotations. The predictions of the model at 1 AU have been found to be in good agreement with the observed values of the same. The present work is a comparison of the synoptic maps on the source surface using the interplanetary scintillation measurements from Japan and the NOAA/SEC version of the Wang and Sheeley model. The two results agree near the equatorial regions and the slow solar wind locations are consistent most of the times. However, at higher latitudes within ±60°, the wind velocities differ considerably. In the Wang and Sheeley model the highest speed obtained is 600 km s–1 whereas in the IPS results velocities as high as 800 km s–1 have been detected. The paper discusses the possible causes for this discrepancy and suggestion to improve the agreement between the two results. 相似文献
2.
David H. Hathaway 《Solar physics》1992,137(1):15-32
The use of the spherical harmonic functions to analyse the nearly steady flows in the solar photosphere is extended to situations in which B
0, the latitude at disk center, is nonzero and spurious velocities are present. The procedures for extracting the rotation profile and meridional circulation are altered to account for the seasonal tilt of the Sun's rotation axis toward and away from the observer. A more robust and accurate method for separating the limb shift and meridional circulation signals is described. The analysis procedures include the ability to mask out areas containing spurious velocities (velocity-like signals that do not represent true flow velocities in the photosphere). The procedures are shown to work well in extracting the various flow components from realistic artificial data with a broad, continuous spectrum for the supergranulation. The presence of this supergranulation signal introduces errors of a few m s -1 in the measurements of the rotation profile, meridional circulation, and limb shift from a single Doppler image. While averaging the results of 24 hourly measurements has little effect in reducing these errors, an average of 27 daily measurements reduces the errors to well under 1 m s -1. 相似文献
3.
The purpose of this work is to image solar far-side active regions using acoustic signals with three skips and improve the
quality of existing images. The mapping of far-side active regions was first made possible using the helioseismic holography
technique by use of four-skip acoustic signals. The quality of far-side images was later improved with the combination of
four- and five-skip signals using the time – distance helioseismology technique. In this work, we explore the possibility
of making three-skip far-side images of active regions, and improving the image quality by combining the three-skip images
with the images obtained from existing techniques. A new method of combining images is proposed that increases the signal-to-noise
ratio and reduces the appearance of spurious features. 相似文献
4.
An observational program at the Sacramento Peak Observatory in 1965 provided high-dispersion spectra of the solar chromosphere in several spectral regions simultaneously. These regions included various combinations of the spectral lines Hα, Hβ and H?, the D3-line of Hei, the infrared triplet of Oi, and the H- and K-lines and the infrared triplet of Caii. With the use of an image slicer the observations were made simultaneously at two heights in the solar chromosphere separated by several thousand kilometers. From these data we draw the following conclusions:
- Emission of different lines arises in the same chromospheric features. The intensity ratio of lines of different elements varies significantly from spicule to spicule. For the H- and K-lines of ionized calcium, this ratio remains constant, independent of wavelength throughout the line, overall intensity, and height in the chromosphere. Two rare-earth lines in the wing of the H-line show no spicular structure at all.
- The line-of-sight velocities of many features reverse as a function of time, although most spicules show velocities in only one direction. The simultaneous spectra at two heights show most spicules to have the same line-of-sight velocity at both. There may be an additional class of features, mostly rapidly moving, whose members have line-of-sight velocities that increase with height. These features comprise perhaps 10% of the total. Velocity changes occur simultaneously, to within 20 sec, at two heights separated by 1800 km, indicating velocities of propagation of hundreds of km/sec. The velocity field of individual features is often quite complicated; many spectral features are inclined to the direction of dispersion, implying that differential mass motions are present.
- The existence of anomalously broad H and K profiles is real. Even with high dispersion and the best seeing, such profiles are not resolved into smaller features. The central reversal in K, H and Hα appears to remain unshifted when the wings are displaced in wavelength, indicating that the reversal is non-spicular.
5.
Automatic Sunspots Detection on Full-Disk Solar Images using Mathematical Morphology 总被引：1，自引：0，他引：1
Sunspots are solar features located in active regions of the Sun, whose number is an indicator of the Sun’s magnetic activity.
Therefore accurate detection and classification of sunspots are fundamental for the elaboration of solar activity indices
such as the Wolf number. However, irregularities in the shape of the sunspots and their variable intensity and contrast with
the surroundings, make their automated detection from digital images difficult. Here, we present a morphological tool that
has allowed us to construct a simple and automatic procedure to treat digital photographs obtained from a solar telescope,
and to extract the main features of sunspots. Comparing the solar indices computed with our algorithm against those obtained
with the previous method exhibit an obvious improvement. A favorable comparison of the Wolf sunspot number time series obtained
with our methodology and from other reference observatories is also presented. Finally, we compare our sunspot and group detection
to that of other observatories. 相似文献
6.
A distribution map of the large-scale chromospheric Doppler velocities on the solar disk for 5 June 2002 is presented. The map was obtained using a 2D-spectroscopy technique within the He?i 10830 Å line. The spatial resolution of the map is about 30 arc sec. The map demonstrates a downflow in the chromosphere over active regions, especially significant around the spots and inside the plages. Positive Doppler velocities correspond to strong magnetic field areas, regardless of the field sign. Three major chromospheric outflow zones are observed: an equatorial and two polar ones. Each area of substantial negative Doppler velocities matches a zone of weak intensity of inner corona observed within the Fe?ix-x 171 Å line by the SOHO spacecraft. A Doppler velocity histogram and the dependence of the Doppler velocities on the cosine of the heliocentric angle for the solar disk are calculated. The total mass outflow from the upper chromosphere is estimated as 2×1013 g s?1. Four percent of this amount is sufficient to produce the fast solar wind.
相似文献7.
Synoptic maps of white-light coronal brightness from SOHO/LASCO C2 and distributions of solar wind velocity obtained from
interplanetary scintillation are studied. Regions with velocity V≈300 – 450 km s−1 and increased density N>10 cm−3, typical of the “slow” solar wind originating from the belt and chains of streamers, are shown to exist at Earth’s orbit,
between the fast solar wind flows (with a maximum velocity V
max ≈450 – 800 km s−1). The belt and chains of streamers are the main sources of the “slow” solar wind. As the sources of “slow” solar wind, the
contribution from the chains of streamers may be comparable to that from the streamer belt. 相似文献
8.
R. I. Kostyk 《Kinematics and Physics of Celestial Bodies》2011,27(4):175-182
Using a three-dimensional hydrodynamical model of the solar atmosphere, we calculated profiles of the Fe I λ 639.361 nm and
Fe II λ 523.462 nm lines with consideration for deviations from the local thermodynamic equilibrium. We determined heights
for intensity contrast reversal and for velocity sign reversal of convective elements. Both of these parameters depend strongly
on the convective velocity and intensity measured in the continuum. The larger the parameters, the greater is the atmosphere
altitude where the reversal takes place. We compared all the calculated relations with the observations obtained at the German
Vacuum Tower Telescope in Izana (Tenerife, Spain). In our opinion, the 3D hydrodynamical model of the solar atmosphere satisfactorily
describes all the main features of observed convective velocities and intensities. 相似文献
9.
J. A. Yates E. M. L. Humphreys A. M. S. Richards 《Astrophysics and Space Science》1997,251(1-2):285-288
The combination of a time-dependent spherically symmetric hydrodynamic model of stellar atmosphere pulsation and a radiation
transport code, which incorporates maser saturation theory, enabled us to synthesise maps and spectra of H2O maser emission from the circumstellar envelopes of long period variable stars.
The synthetic maps and spectra compare favourably with observed 22, 321 and 325 GHz H2O maser emission. As is observed in H2O maser regions the peak emission occurs between 3–8 stellar radii from the star. The calculated H2O maser regions are in conditions of nH2 = 106 − 108 cm−3, assuming a fractional abundance of 10−4; kinetic temperatures of 550–3000 K; dust ensemble temperatures of 500–1200 K and an accelerating velocity field. The IR
radiation field is explicitly included in the radiation transport model, incorporating the latest absorption efficiency data
for silicates from Draine. We reproduce the features seen in high angular resolution MERLIN spectral line datacubes. This
shows that a mass outflow model which extends the photosphere using pulsations and incorporates radiation pressure on silicate
based dust particles can produce the observed data on small (10-mas) angular scales.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
10.
A. Khlystova 《Solar physics》2013,284(2):343-361
The dynamics of horizontal plasma flows during the first hours of the emergence of active region magnetic flux in the solar photosphere have been analyzed using SOHO/MDI data. Four active regions emerging near the solar limb have been considered. It has been found that extended regions of Doppler velocities with different signs are formed in the first hours of the magnetic flux emergence in the horizontal velocity field. The flows observed are directly connected with the emerging magnetic flux; they form at the beginning of the emergence of active regions and are present for a few hours. The Doppler velocities of flows observed increase gradually and reach their peak values 4?–?12 hours after the start of the magnetic flux emergence. The peak values of the mean (inside the ±?500 m?s?1 isolines) and maximum Doppler velocities are 800?–?970 m?s?1 and 1410?–?1700 m?s?1, respectively. The Doppler velocities observed substantially exceed the separation velocities of the photospheric magnetic flux outer boundaries. The asymmetry was detected between velocity structures of leading and following polarities. Doppler velocity structures located in a region of leading magnetic polarity are more powerful and exist longer than those in regions of following polarity. The Doppler velocity asymmetry between the velocity structures of opposite sign reaches its peak values soon after the emergence begins and then gradually drops within 7?–?12 hours. The peak values of asymmetry for the mean and maximal Doppler velocities reach 240?–?460 m?s?1 and 710?–?940 m?s?1, respectively. An interpretation of the observable flow of photospheric plasma is given. 相似文献
11.
E. Margaret Burbidge 《Astrophysics and Space Science》1999,265(1-4):99-101
Absorption features in the UV spectra in about 10–15% of quasars show very broad profiles, indicating outflow velocities from
the quasars of one or even two tenths the speed of light. Determinations of the abundances of some elements, particularly
phosphorus, have yielded apparent large overabundances relative to solar. However, it has recently been shown that the absorbing
gas which does not completely cover the continuum source of the emission-line clouds may have large optical depth so that
the absorption lines are heavily saturated, leading to spurious overabundances of some elements, including phosphorus.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
12.
We present a method for calibrating every instrument working with magneto-optical filter (MOF) technology, in order to take
into account the effect in the observations due to the aging of the vapour cells. The method allows the evaluation of some
characteristics of the transmission profile by modelling the blue and/or the red line intensity images acquired with the MOF
system. In particular, it reveals the presence of unwanted spurious transmissions and prevents cross-talk between the intensity
and velocity fluctuations. The method also gives information about the position of the “working point” of the instrument,
i.e. the average wavelength position of its transmission profile, which is necessary for estimating the right solar atmospheric
layer observed by the MOF. This analysis is powerful and fast: applied before every observing campaign, it enables setting
Q the most suitable value for the cell temperature, which is one of the parameters that controls the MOF transmission profile. 相似文献
13.
Properties of the surfaces of Jupiter’s satellites—Ganymede and Callisto—are shortly described. Their images acquired in space
missions are shown. Causes of the discrepancy between orbital lightcurves of the satellites obtained from the earth and spaceborne
maps of the satellites are considered. The groundbased observations were carried out under phase angles of solar illumination
ranging from 0° to 12°, and the maps were built from images acquired from spacecraft in a wide interval of solar phase angles.
We suggest that the main cause of the discrepancies between the lightcurves is the coherent backscattering effect observed
only at small phase angles of the sun. 相似文献
14.
We present a summary of results from ten years of interplanetary scintillation (IPS) observations of stream interaction regions
(SIRs) in the solar wind. Previous studies had shown that SIRs were characterized by intermediate-velocity solar wind and
– in the case of compressive interactions – higher levels of scintillation. In this study we considered all cases of intermediate
velocities in IPS observations from the European Incoherent SCATter (EISCAT) radar facility made at low- and mid-heliographic latitudes between 1994 and 2003. After dismissing intermediate-velocity
observations which were associated with solar-wind transients (such as coronal mass ejections) we found that the remaining
cases of intermediate velocities lay above coronal structures where stream interaction would be expected. An improved ballistic
mapping method (compared to that used in earlier EISCAT studies of interaction regions) was used to identify the regions of
raypath in IPS observations which might be expected to include interaction regions and to project these regions out to the
distances of in-situ observations. The early stages of developing compression regions, consistent with their development on the leading edges
of compressive stream interaction regions, were clearly detected as close to the Sun as 30 R
⊙, and further ballistic projection out to the distances of in-situ observations clearly associated these developing structures with density and velocity features characteristic of developed
interaction regions in in-situ data in the cases when such data were available. The same approach was applied to study non-compressive interaction regions
(shear layers) between solar-wind streams of different velocities where the stream interface lay at near-constant latitude
and the results compared with those from compressive interaction regions. The results confirm that intermediate velocities
seen in IPS observations above stream boundaries may arise from either detection of intermediate-velocity flow in compression
regions, or from non-compressive shear layers. The variation in velocity about the mean determined from IPS measurements (representing
the spread in velocity across that part of the raypath associated with the interaction region in the analysis) was comparable
in compressive and non-compressive regions – a potentially interesting result which may contain important information on the
geometry of developing SIRs. It is clear from these results that compressive and non-compressive interaction regions belong
to the same class of stream – stream interaction, with the dominant mode determined by the latitudinal gradient of the stream
interface. Finally, we discuss the results from this survey in the light of new data from the Heliospheric Imagers (HI) on the Solar TErrestrial RElations Observatory (STEREO) spacecraft and other instruments, and suggest possible directions for further work. 相似文献
15.
We analyzed two sequences of quiet-Sun magnetograms obtained on June 4, 1992 and July 28, 1994. Both were observed during excellent seeing conditions such that the weak intranetwork (IN) fields are observed clearly during the entire periods. Using the local correlation tracking technique, we derived the horizontal velocity fields of IN and network magnetic fields. They consist of two components: (1) radial divergence flows which move IN fields from the network interior to the boundaries, and (2) lateral flows which move along the network boundaries and converge toward stronger magnetic elements. Furthermore, we constructed divergence maps based on horizonal velocities, which are a good representation of the vertical velocities of supergranules. For the June 4, 1992 data, the enhanced network area in the field of view has twice the flux density, 10% higher supergranular velocity and 20% larger cell sizes than the quiet, unenhanced network area. Based on the number densities and flow velocities of IN fields derived in this paper and a previous paper (Wang et al., 1995), we estimate that the lower limit of total energy released from the recycling of IN fields is 1.2 × 1028 erg s–1, which is comparable to the energy required for coronal heating. 相似文献
16.
The Coronal Diagnostic Spectrometer (CDS) aboard the Solar and Heliospheric Observatory (SOHO) carries out a regular program of measuring the full-disk irradiance using the Normal Incidence Spectrograph (NIS). The full-disk solar spectrum is returned in the wavelength bands 308–379 Å and 513–633 Å, with a spectral resolution between 0.3 and 0.6 Å. A recent modification to the CDS on-board software allows simultaneous moderate resolution monochromatic images to be made of the stronger lines in these wavelength ranges. We report on observations made 23 April 1998, 21 May 1998, and 22 June 1998. A total of 69 monochromatic full-Sun images are extracted from the spectral line data. For the first time, spectrally resolved images of the full Sun in Heii 303.8 Å and Sixi 303.3 Å are presented and compared. Velocity maps of the Sun in singly ionized helium are presented. Correlations of intensity to velocity over a wide range of transition region and coronal temperatures are shown. Lines from Hei to Fexiv show statistical red shifts of 1–7 km s–1 between active regions and quiet Sun areas. Velocity maps of Mgix andx are presented, showing strong upflow and downflow regions associated with active regions, but not correlated with the brightest emission. Changes in line width are also presented in Hei, with discussion of similar features in other lines of comparable temperature. Corrections which need to be applied to CDS/NIS data to extract meaningful velocities and line widths are presented and discussed. The identifications of the lines in the CDS spectrum are examined. The spatial and spectral variation of the background component of the CDS spectrum is examined. 相似文献
17.
We present an implementation of the extended Knox-Thompson (EKT) speckle reconstruction algorithm dedicated to solar observations.
EKT speckle imaging yields nearly diffraction-limited images from bursts of short exposure solar observations under a wide
range of seeing conditions. Our implementation supports field dependent amplitude calibration to permit analyzing data obtained
with a partially compensating adaptive optics systems. The principles of the method and some technical details of our implementation
are discussed. We have performed various tests using simulated data of representative solar scenes. The simulations include
the effects of seeing and noise with the exception of anisoplanatism. The expected photometric error of a reconstructed image
amounts to a few percent of the mean intensity under seeing conditions ranging from poor to excellent. We also present sample
reconstructions of real data and discuss issues arising from anisoplanatism. 相似文献
18.
P. R. Wilson 《Solar physics》1972,22(2):434-442
Savage has suggested that an energy flux of 2 × 1010 erg cm–2 s–1 passes through the umbra of a sunspot in the form of hydromagnetic waves. In this paper some of the consequences of this flux are considered. It is first shown that it is not inconsistent with the energy requirements for the heating of umbral dots and for solar wind storms, assuming in the latter case that the flux tubes emerging from about one tenth of the area of a large spot are open-ended.However, the hypothesis also requires that Alfvén waves travel along the closed flux tubes linking the umbra either with the umbra of another spot or with the surrounding faculae and passing through regions of variable field strength and density. It is shown that, for a very simplified model, standing waves are possible in a symmetrical field configuration. For velocities of 3 km/s in the umbra, the maximum particle velocity in the loop is of order 80 km/s which strains the perturbation assumption severely. However, it is pointed out that periodic velocities of this order are observed in the chromosphere near sunspots.It is further shown that mechanical dissipation of these waves in local regions of the flux tube may contribute to the heating of faculae. 相似文献
19.
The structure of the large-scale background magnetic field evolves in time and space. The large-scale horizontal transport
velocity field of the magnetic flux patterns was inferred over the whole solar photosphere in the course of two solar activity
cycles from year 1976 to 1999. The method of velocity determination and the testing procedures of the velocity accuracy are
presented. The non-axially symmetric component of the horizontal velocity was found and both zonal and meridional velocity
regions were described. The horizontal large-scale transport velocity regions vary in shape and the intensity during different
phases of the 11-year solar activity cycle. The total horizontal transport velocity is characterized by the presence of variable
amounts of the vector field vortices with symmetric orientation relative to the solar equator. The zonal velocity regions,
distributed inside of the zonal belt limited by latitudes ± 35°, are persistent for about 4 Carrington rotations. Recurrent
structures of similar velocity distributions are not coherent over the whole solar photosphere. 相似文献
20.
We developed a method to automatically detect and trace solar filaments in Hα full-disk images. The program is able not only to recognize filaments and determine their properties, such as the position, the area, the spine, and other relevant parameters, but also to trace the daily evolution of the filaments. The program consists of three steps: First, preprocessing is applied to correct the original images; second, the Canny edge-detection method is used to detect filaments; third, filament properties are recognized through morphological operators. To test the algorithm, we successfully applied it to observations from the Mauna Loa Solar Observatory (MLSO). We analyzed Hα images obtained by the MLSO from 1998 to 2009 and obtained a butterfly diagram of filaments. This shows that the latitudinal migration of solar filaments has three trends in Solar Cycle 23: The drift velocity was fast from 1998 to the solar maximum, after which it became relatively slow. After 2006, the migration became divergent, signifying the solar minimum. About 60 % of the filaments with latitudes higher than 50° migrate toward the polar regions with relatively high velocities, and the latitudinal migrating speeds in the northern and the southern hemispheres do not differ significantly in Solar Cycle 23. 相似文献