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1.
A coronal hole was observed for three days of its passage near the central meridian of the Sun. Spectrograms containing strong lines of ionized calcium were obtained. The central intensities of the Ca II H, K, and λ849.8 nm lines in the region of the coronal hole and in the quiet-Sun region outside its boundaries were measured. Only the line profiles that were confidently identified as being undisturbed even by weak flocculi were selected. All profiles were averaged in each of the two chromospheric network components (network and cell), and the average profiles were calculated using all of the available data (network+cell). Small differences were found between the central intensities of the Ca II H and K lines inside and outside the coronal hole, with the hole being brighter than the quiet region. A detailed statistical analysis shows that these small differences are real at high confidence levels owing to the large sample sizes. A difference of the same sign is slightly noticeable in the infrared line, but its confidence level is less than 90%. The chromosphere in the coronal hole is brightened by the cell alone; in the network, the chromospheric foot of the coronal hole does not differ from the quiet region. Comparison with the results of other authors obtained from observations in higher atmospheric layers suggests that the network also contains a brightness peak that subsequently gives way to a characteristic depression, but it lies higher than that in the cell. 相似文献
2.
We investigate the regime of chromospheric oscillations at the bases of coronal holes and compare them with the oscillations
in the quiet chromosphere outside coronal holes using time series of spectrograms taken at different times in eight quiet
regions on the Sun. As the oscillation parameter being studied, we have chosen the central intensity of the chromospheric
Ca II K and H and 849.8-nm lines. The intensity measurements at all spatial points (along the spectrograph slit) have been
subjected to a standard Fourier analysis. For the identified areas of the networks, cells, and network boundaries, we have
calculated the integrated oscillation powers in several frequency bands. For all frequency bands, the powers of the intensity
oscillations at the formation level of the Ca II resonance doublet line cores have been found to be enhanced at the bases
of coronal holes approximately by a factor of 1.5. For the “three-minute” band, this enhancement is more pronounced in the
network than in the cell, while the opposite is true for the “five-minute” band. The power in the five-minute band is higher
than that in the three-minute one both at the bases of coronal holes and outside them, but this ratio in the network for a
coronal hole is higher (1.40 ± 0.25 and 1.30 ± 0.10). We interpret this fact and the fact that the power of the three-minute
oscillations for nonmagnetic regions changes with height differently at the base of a coronal hole and outside it as an increase
in the importance of magnetoacoustic portals at the chromospheric base of the coronal hole. 相似文献
3.
The profiles of the resonance lines of Caii have been studied in two large disk flares and in the surrounding plage. In the brightest portions of the flares no self-reversal in the central emission core was detected; self-reversed cores were present in the less bright portions of the flares. We find that as the intensity of the emission core increases the separation of the H2 and K2 peaks decreases monotonically, becoming unobservable at intensities near to 0.90 the local continuum. Possible reasons for the behavior of the H and K lines in flares are considered. It is suggested that the largest density enhancements in flares are found near the strongest magnetic field. 相似文献
4.
In order to investigate the high chromosphere and the low transition region in a coronal hole, we have analysed Ca ii, Mg ii and hydrogen resonance lines, recorded by the OSO-8 spectrometer in 1975. We present the comparison between average profiles observed in and out of the equatorial coronal hole which was at the center of the solar disk between 27 and 29 November, 1975. We separate internetwork and quiet-Sun (network+internetwork) profiles: for the internetwork, we observe that the hydrogen and Mg ii profiles recorded in the hole are stronger than the profiles recorded out of the hole; a similar result, but with a much lower contrast, is found for the quiet Sun. We discuss this surprising result. 相似文献
5.
The locations of coronal holes are usually based on equivalent-width images in the He i 1083 nm line. However, it is difficult to differentiate coronal holes from the centers of quiet chromospheric network without complementary data and the skill of an experienced observer. Analysis of imaging spectroscopy shows that line half-width and central intensity are correlated differently in coronal holes and a quiet Sun. This fact can be used to form linear combinations of these images in which coronal holes are better separated from the quiet Sun. Coronal hole borders agree well with SOHO/EIT data but can show significant differences from National Solar Observatory maps. 相似文献
6.
Observations of the central intensity of the Ca ii K and 849.8 nm lines are used to derive the ratios of the oscillation power in the frequency ranges of the “five-minute”
(W
5) and “three-minute” (W
3) oscillations. It is shown that at high significance level ratios, (W
5/W
3) >1 at coronal hole bases, and W
5/W
3 ≈1 in quiet chromospheric areas far from holes. 相似文献
7.
Tokio Tsubaki 《Solar physics》1975,43(1):147-175
A technique developed for analysing line profiles with both speed and high accuracy was used to study the physical conditions
of a coronal formation near a quiescent prominence. Detailed analyses of five coronal lines (Fe xiv λ 5303, Fe x λ 6374, Ni xv λ 6702, Fe xv λ 7059, and Fe xi λ 7892) provided total intensities, Doppler width temperatures, ionization temperatures, and velocities.
Dissimilar spatial fluctuations in intensity are obvious for ions grouped according to (low vs high) ionization potentials.
The intensity of the green line shows a local minimum around the observed quiescent prominence; a corresponding but much more
diffuse pattern is visible in the red line intensity.
Large differences are observed in temperatures derived by different means. In particular,
, while
, and
. The differences between
and
are taken as direct evidence of temperature inhomogeneity. One can thus put little significance in T
e
(xi/x). T
D(λ5303) and T
e
(xv/xiv) fluctuate nearly in parallel at each slit height, with a weak local minimum evident around the prominence. The discrepancy
between these two can be removed if a non-thermal turbulent motion of 6–16 km s−1 is assumed. Variations with height of both T
D(λ5303) and T
e
(xv/xiv) suggest that the coronal temperature maximum is located no more than 15000 km above the top of spicules. A negative gradient
of about 6 deg km−1 is found in the height variation of T
D(λ5303).
The height variation of the green line wavelength shows that the majority of coronal material in this region is flowing from
west to east on the Sun, with the highest velocity of 12 km s−1 found at the lowest heights. This motion is in the same sense as that of the nearby coronal rain, as determined both from
the spectra and wavelength-shifted Hα filtergrams. Superposed on the above flow is a systematic velocity field of up to ±5
km s−1. This field similarly reaches maximum amplitudes at lowest heights showing a local maximum around the prominence.
On leave from Institute of Earth Science and Astrophysics, Shiga University, Ohtsu 520, Japan, as 1973–75 National Academy
of Science/National Research Council Senior Post-Doctoral Research Associate at Sacramento Peak Observatory. 相似文献
8.
Imaging spectroscopic data of the He i 1083 nm limb emission were taken on several dates in October and November 1995 with the NASA/NSO spectromagnetograph at the NSO/Kitt Peak vacuum telescope and on 9 December, 1993 with the Michigan infrared camera at the NSO/Sacramento Peak vacuum tower telescope. Emission line profiles were observed in quiet-Sun and coronal hole locations on the northern and southern solar poles and on the east solar limb. The height of the He i 1083 nm shell above the continuum limb at 1083 nm was measured to be 2.11 ± 0.12 Mm with the Kitt Peak data, and 1.74 ± 0.05 Mm with the Sacramento Peak data. The Kitt Peak data show (1) within the measurement error there is no significant difference in the height or thickness of the emission shell in coronal holes compared with the quiet Sun, (2) the 1083 nm emission intensity drops by 50% in coronal holes, (3) the line width decreases by about 2 km s-1 in coronal holes (suggesting less inclined spicules), (4) the line width of the He i 1083 nm line jumps significantly as the line of sight crosses the solar limb (consistent with a higher temperature upper shell), (5) a quiescent prominence shows a smaller spectral line width (consistent with a cooler temperature or less velocity broadening), and (6) the entire emission shell and the prominence show a He i spectral component ratio of about 8 (suggesting optically thin emission).Operated by the Association of Universities for Research in Astronomy, Inc. (AURA), under cooperative agreement with the National Science Foundation. 相似文献
9.
Feature-to-feature identification is made on simultaneous Ca ii K-line spectrograms (SG) and K2v spectroheliograms (SHG). The line profiles in plages and in the network boundary nearly always have double-peaked reversal in the core, while those inside the cells present all possibilities: double-peaked, single-peaked on violet side, single-peaked on red side, and unreversed absorption. Statistics of the profiles in the quiet chromosphere show that 50% are K232 double-peaked, 20% are K2v single-peaked, 10% are K2r single-peaked, and 20% show only incipient reversal or even totally lack any reversal. We call attention to the nontrivial contribution of these absorption profiles which are formed in dark regions shown on SHG's.The physical conditions inferred from different kinds of profiles are briefly discussed.In part to be included in a dissertation to be submitted to the Graduate School, University of Maryland, by S. Y. Liu in partial fulfillment of the requirements for the Ph. D. degree in Astronomy.Visiting Graduate Student, Solar Division, Kitt Peak National Observatory.Visiting Astronomer, Solar Division, Kitt Peak National Observatory. 相似文献
10.
Solar Wind Forecasting with Coronal Holes 总被引：1，自引：0，他引：1
An empirical model for forecasting solar wind speed related geomagnetic events is presented here. The model is based on the
estimated location and size of solar coronal holes. This method differs from models that are based on photospheric magnetograms
(e.g., Wang–Sheeley model) to estimate the open field line configuration. Rather than requiring the use of a full magnetic
synoptic map, the method presented here can be used to forecast solar wind velocities and magnetic polarity from a single
coronal hole image, along with a single magnetic full-disk image. The coronal hole parameters used in this study are estimated
with Kitt Peak Vacuum Telescope He I 1083 nm spectrograms and photospheric magnetograms. Solar wind and coronal hole data for the period between May 1992 and
September 2003 are investigated. The new model is found to be accurate to within 10% of observed solar wind measurements for
its best 1-month period, and it has a linear correlation coefficient of ∼0.38 for the full 11 years studied. Using a single
estimated coronal hole map, the model can forecast the Earth directed solar wind velocity up to 8.5 days in advance. In addition,
this method can be used with any source of coronal hole area and location data. 相似文献
11.
The rotational behaviour of the chromosphere, observed in the Ca ii K3 line, is studied during 1972–1973, years of decreasing solar activity. Daily chromospheric filtergrams, detected at the Anacapri Observatory, are digitized by means of a flying-spot photometer, controlled by computer. The time series of the daily chromospheric data detected at central meridian, relative to 30 consecutive latitude zones, are analyzed to determine the recurrence tendency due to the rotation of long-lived chromospheric features. The computed rotation rate is independent of latitude, in agreement with the results obtained for the green corona during the years before sunspot minimum. Namely both chromospheric and coronal features, with lifetime exceeding one solar rotation, are almost not affected by differential rotation before sunspot minimum. 相似文献
12.
We present our results of high temporal resolution spectroscopic observation and study in Hα, Ca II, and He I lines for the 2B/M1.9 confined disk flare on September 9, 2001, combining with GOES soft X-ray (SXR) and Yohkoh hard X-ray (HXR) observations. Apparent redshifted and red-asymmetric profiles were observed in the initial phase. The redshift
lasted until the late phase. The derived velocity depends on both the spectral line and the used method. The redshift velocities
computed from the line centers of the observed emission profiles (υ0) are of the order of 10 km s−1 both inside and outside the streak area. However, the velocities determined from the excess profiles by the bisector method
(υ) are larger in the streak (18–50 km s−1). Both υ and the red full widths (RFWs) derived from the excess profiles show temporal variations similar to the HXR light-curve
in the streak area. Moreover, the Hα line wings of nonthermal characteristics, the redshift velocities, and the lifetime of
impulsive broadening suggest that the streak is related to nonthermal electron bombardment. Spectral simulations reveal that
we cannot reproduce the observed profiles in the three lines simultaneously with a set of parameters, indicating that the
flare atmosphere was not homogeneous along the line-of-sight. Most of the observed Hα profiles showed a ‘flat-top’ structure,
implying the flare plasma was optically thick for this line. The electron temperatures (Te) deduced from the line-center intensity of the three lines are similar and estimated to be higher than 7200 K. The obvious
central reversal of the Hα profiles due to absorption of materials in the impulsive phase lasted more than 2 min. However,
the far blue wings of the Ca II profiles in the impulsive phase showed low-intensity emission, which is suggestive of the
existence of large turbulence or macroscopic motion (> 50 km s−1), which is inconsistent with the current flare model. 相似文献
13.
Nine coronal emission lines representing five stages of Fe ionization and one stage of Ni were observed in an enhanced coronal region. The data from these observations are presented along with a density model of the enhanced region obtained from the FeXIII and NiXV emission line ratios as a function of position angle. The electron densities obtained from FeXIII lines range from N
e = 108 to 109 cm–3, and are slightly lower for NiXV line data. Estimates of the variation of temperature over the enhanced region are inferred from the observed line intensities. 相似文献
14.
Airborne eclipse observations of the [Six] 1430.5 nm coronal emission line are reviewed, and new ground-based out-of-eclipse coronagraph observations obtained at NSO/Sacramento
Peak are reported. We find that the [Six] 1430.5 nm coronal emission line brightness is less than 8 × 10−6
B⊙ in small active region corona which showed [Fexiii] 1074.7 nm emission (corrected for sky background) of about 20 × 10−6
B⊙.
Operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under cooperative agreement with the National
Science Foundation. 相似文献
15.
We investigate the velocity field of the solar chromosphere at the location of 65 He i 10830 dark points (DP's). We have obtained spectra of such points in the vicinity of the Ca II K line. As a measure of differential chromospheric velocity, we use the shift of the K line center relative to a nearby photospheric Fe i line. We find that in He i DP's, the distribution of K line shifts is skewed towards the blue: the blueward skewing is more pronounced in He i DP's located in coronal holes. To the extent that He i DP's are proxies of coronal bright points, our study is relevant to previous reports of outflows from such bright points. 相似文献
16.
K. P. Raju 《Solar physics》2010,262(1):61-69
Intensity distributions of the EUV network and the cell interior in the solar atmosphere have been obtained in fourteen emission
lines from Solar and Heliospheric Observatory (SOHO)/Coronal Diagnostic Spectrometer (CDS) observations. The formation temperature of the observed lines is in the range
log T=4.90 – 6.06 (T in Kelvin), and hence they represent increasing heights in the solar atmosphere from the upper chromosphere and the transition
region to the low corona. Intensity distributions of the cell interior have been found to be different in the quiet Sun and
the coronal hole even at the lower transition region, which is at variance with some earlier results. The intensity contrast
of the network with respect to the cell interior has been obtained for each line, and differences in the quiet Sun and the
coronal hole have been examined. The network contrast, in general, is lower for the coronal hole as compared to the quiet
Sun, but becomes equal to it in the upper transition region. The maximum contrast for both the regions is at about log T=5.3. Also obtained are the relative contributions of the network and the cell interior to the total intensity. The implications
of the results for models of the transition region are briefly mentioned. 相似文献
17.
A semi-empirical model of a penumbral chromosphere is presented which represents a specific region of the penumbra located approximately one-fourth the distance outward from the umbra-penumbra interface. The model is based on simultaneous observations of high-resolution spectra of Caii K, H, and 8498 made over a sunspot penumbra (SPO 5007) with the Echelle Spectrograph at the Vacuum Tower Telescope at Sacramento Peak Observatory on 18 December, 1979.Spectral profiles were calculated using a non-LTE line formation procedure with various chromospheric models where the optimum model is determined by matching the synthesized profiles with the observational features. The best fit yields a model with overlying column mass m
0 of 8 × 10–6 g cm–2 which also agrees with the observed K3/H3 intensity ratio of 1.22.This work was supported by the US-Republic of Korea Cooperative Science Program (K-53). 相似文献
18.
O vi ( = 1032 Å) profiles have been measured in and above a filament at the limb, previously analyzed in H i, Mg ii, Ca ii resonance lines (Vial et al., 1979). They are compared to profiles measured at the quiet Sun center and at the quiet Sun limb.Absolute intensities are found to be about 1.55 times larger than above the quiet limb at the same height (3); at the top of the prominence (15 above the limb) one finds a maximum blue shift and a minimum line width. The inferred non-thermal velocity (29 km s–1) is about the same as in cooler lines while the approaching line-of-sight velocity (8 km s–1) is lower than in Ca ii lines.The O vi profile recorded 30 above the limb outside the filament is wider (FWHM = 0.33 Å). It can be interpreted as a coronal emission of O vi ions with a temperature of about 106 K, and a non-thermal velocity (NTV) of 49 km s–1. This NTV is twice the NTV of quiet Sun center O vi profiles. Lower NTV require higher temperatures and densities (as suggested by K-coronameter measurements). Computed emission measures for this high temperature regime agree with determinations from disk intensities of euv lines. 相似文献
19.
Using Fe ix/x 17.1 nm observations from the Extreme-Ultraviolet Imaging Telescope (EIT) on the Solar and Heliospheric Observatory (SOHO), we have identified many coronal plumes inside low-latitude coronal holes as they transited the solar limb during the late
declining phase of cycle 23. These diffuse, linear features appear to be completely analogous to the familiar polar plumes.
By tracking them as they rotate from the limb onto the disk (or vice versa), we confirm that EUV plumes seen against the disk appear as faint, diffuse blobs of emission surrounding a brighter core.
When the EIT images are compared with near-simultaneous magnetograms from the SOHO Michelson Doppler Imager (MDI), the low-latitude, on-disk plumes are found to overlie regions of mixed polarity, where small
bipoles are in contact with unipolar flux concentrations inside the coronal hole. The birth and decay of the plumes are shown
to be closely related to the emergence of ephemeral regions, their dispersal in the supergranular flow field, and the cancellation
of the minority-polarity flux against the dominant-polarity network elements. In addition to the faint polar and nonpolar
plumes associated with ephemeral regions, we note the existence of two topologically similar coronal structures: the giant
plume-like features that occur above active regions inside coronal holes, and the even larger scale “pseudostreamers” that
separate coronal holes of the same polarity. In all three cases, the basic structure consists of open field lines of a given
polarity overlying a photospheric region of the opposite polarity; ongoing interchange reconnection at the X-point separating
the open field domains from the underlying double-arcade system appears to result in the steady evaporation of material from
the closed into the open region. 相似文献