共查询到20条相似文献，搜索用时 31 毫秒
1.
E. Tavabi 《Astrophysics and Space Science》2014,352(1):43-50
We present observations of a solar quiet region obtained using the Hinode Solar Optical telescope (SOT) in the Ca II H-line with broadband filter taken on November 2006. We study off-limb and on-disk spicules to find a counterpart of the limb spicule on the disk. This investigation shows a strong correspondence between the limb and near limb spicules (on-disk spicules that historically were called dark or bright mottles, especially when observed in Hα, being a rather cool line) from the dynamical behavior (e.g., periodicity). An excellent time sequence of images obtained near the equatorial region with a cadence of 8 s was selected for analysis. 1D Fourier power spectra made at different positions on the disk and above the limb are shown. We take advantage of the so-called mad-max operator to reduce the effects of overlapping and improve the visibility of these hair-like features. A definite signature with strong power in the 3-min (5.5 mHz) and 5-min (3.5 mHz) oscillations for both places exists. A full range of oscillations was found and the high frequency intensity fluctuation (greater than 10 mHz or less than 100 s) corresponding to the occurrence of the so-called type II spicules and, even more impressively, dominant peaks of Fourier power spectra are seen in a wide range of frequencies and for all places of “on” and “off” disk spicules, in rough agreement with what historical works report regarding disk mottles and limb spicules. Also, some statistically significant behavior, based on the power spectrum computed for different positions, is discussed. The power for all kinds of power spectra is decreasing with increasing distance from the limb, except for photospheric oscillations (5 min or p-mode), which show a dominant peak for on-disk power spectra. 相似文献
2.
The origin and the dynamical evolution of spicules and mottles continue to be a highly interesting research subject. Using high-resolution H observations obtained with the Dunn Solar Telescope of the Sacramento Peak Observatory and an image processing technique for the enhancement of near-limb solar images, we study the dynamics of spicules and mottles as well as their relation. Our image-processing technique is based on the correction for the limb darkening and the use of a directionally sensitive operator, the `MadMax'. The temporal evolution of characteristic cases of spicules, dark and bright mottles, indicates an association between them and supports the suggestion that the magnetic field and probably related forces play a fundamental role in their generation and dynamics. We present characteristic cases of fine bright mottles, observable in the H far wings, that appear in close juxtaposition to dark mottles. The phenomenon appears to be common, suggesting that the velocities derived from marginal resolution spectroscopic observations could be underestimated. Typical examples of individual mottles crossing the solar limb further support the association between spicules and mottles. Finally we show images of arch-shaped mottles above the limb and especially on the disk, confirming the existence of chromospheric small loops. Our image-processing method substantially enhances near-limb observations and permits an insight into the studies of the very fine chromospheric structures. 相似文献
3.
Zachariadis Th.G. Dara H.C. Alissandrakis C.E. Koutchmy S. Gontikakis C. 《Solar physics》2001,202(1):41-52
In this article we study chromospheric structures (spicules) crossing the solar limb in H images corrected for limb darkening. This correction enabled us to view structures both on the disk and beyond the limb in the same image. The observations were obtained at the Sacramento Peak Observatory at H±0.75 Å. The processed images reveal both bright and dark (relative to the local background) features crossing the limb. We also observed bushes (rosettes) crossing the limb, as well as structures indicating probably arch-shaped mottles beyond the limb. 相似文献
4.
We present an analysis of 2634 Ca II K‐line full‐disk filtergrams obtained with the 15‐cm aperture photometric full‐disk telescope at Big Bear Solar Observatory during the period from 1996 January 1 to 2005 October 24. Using limb darkening corrected and contrast enhanced filtergrams, solar activity indices were derived, which are sensitive to the 11‐year solar activity cycle and 27‐day rotational period of plages around active regions and the bright chromospheric network. The present work extends an earlier study (solar cycle 22), which was based on video data. The current digital data are of much improved quality with higher spatial resolution and a narrower passband ameliorating photometric accuracy. The time series of chromospheric activity indices cover most of solar cycle 23. One of the most conspicuous features of the Ca II K indices is the secondary maximum in late 2001/early 2002 after an initial decline of chromospheric activity during the first half of 2001. We conclude that a secular trend exists in the Ca II K indices, which has its origin in the bright chromospheric network and brightenings related to decaying active regions. Superposed on this secular trend are the signatures of recurring, long‐lived active regions, which are clusters of persistent and continuously emerging magnetic flux. Such features are less visible, when the activity belts on both side of the equator are devoid of the brightenings related to decaying active regions as was the case in October/November 2003 at a time when a superactivity complex including several naked‐eye sunspots emerged (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
5.
Explosive events appear as broad non-Gaussian wings in the line profiles of small transition-region phenomena. Images from the Solar Dynamics Observatory (SDO) give a first view of the plasma dynamics at the sites of explosive events seen simultaneously in O?vi spectra of a region of quiet Sun, taken with the ultraviolet spectrometer Solar Ultraviolet Measurements of Emitted Radiation (SUMER) onboard the Solar and Heliospheric Observatory (SOHO). Distinct event bursts were seen either at the junction of supergranular network cells or near emerging flux. Three are described in the context of their surrounding transition region (304 Å) and coronal (171 Å) activity. One showed plasma ejections from an isolated pair of sites, with a time lag of 50 seconds between events. At the site where the later explosive event was seen, the extreme ultraviolet (EUV) images show a hot core surrounded by a small, expanding ring of chromospheric emission, which we interpret as a “splash.” The second explosive-event burst was related to flux cancellation, inferred from Helioseismic and Magnetic Imager (HMI) magnetograms, and a coronal dimming surrounded by a ring of bright EUV emission with explosive events at positions where the spectrometer slit crossed the bright ring. The third series of events occurred at the base of a slow, small coronal mass ejection (mini-CME). All events studied here imply jet-like flows probably triggered by magnetic reconnection at supergranular junctions. Events come from sites close to the footpoints of jets seen in Atmospheric Imaging Assembly (AIA) images, and possibly from the landing site of high-velocity flows. They are not caused by rapid rotation in spicules. 相似文献
6.
A statistical analysis of the SOT-Hinode observations of solar spicules and their wave-like behavior
Spicules are an important very dynamical and rather cool structure extending between the solar surface and the corona. They are partly filling the space inside the chromosphere and they are surrounded by a transition thin layer. New space observations taken with the SOT of the Hinode mission shed some light on their still mysterious formation and dynamics. Here we restrict the analysis to the most radial and the most interesting polar spicules situated at the base of the fast solar wind of coronal holes.We consider a first important parameter of spicules as observed above the solar visible limb: their apparent diameter as a function of the height above the limb which determines their aspect ratio and leads to the discussion of their magnetic origin using the flux tube approximation. We found that indeed spicules show a whole range of diameters, including unresolved “interacting spicules” (I-S), depending of the definition chosen to characterize this ubiquitous dynamical phenomenon occurring into a low coronal surrounding. Superposition effects along the line of sight have to be taken into account in order to correctly measure individual spicules and look at I-S. We take advantage of the so-called mad-max operator to reduce these effects and improve the visibility of these hair-like features. An excellent time sequence of images obtained above a polar region with the Hinode SOT through the HCaII filter with a cadence of 8 s was selected for analysis. 1-D Fourier amplitude spectra (AS) made at different heights above the limb are shown for the first time. A definite signature in the 0.18–0.25 Mm range exists, corresponding to the occurrence of the newly discovered type II spicules and, even more impressively, large Fourier amplitudes are observed in the 0.3–1.2 Mm range of diameters and spacing, in rough agreement with what historical works were reporting. Additionally, some statistically significant behavior, based on AS computed for different heights above the limb, is discussed.“Time slice or x–t diagrams” revealing the dynamical behavior of spicules are also analyzed. They show that most of spicules have multiple structures (similarly to the doublet spicules) and they show impressive transverse periodic fluctuations which were interpreted as upward kink or Alfven waves. Evidence of the helical motion in spicules is now well evidenced, the typical periods of the apparent oscillation being around 120 s. A fine analysis of the time-slice diagram as a function of the effective heights shows an interesting new feature near the 2 Mm height. We speculate on the interpretation of this feature as being a result of the dynamical specificities of the spicule helical motion as seen in these unprecedented high resolution HCaII line emission time series. 相似文献
7.
Mitsuo Kanno 《Solar physics》1983,89(2):253-259
The weakening of the EUV line emission near the Sun's limb is studied to acquire information about the absorbers causing the weakening. The equivalent optical thickness of the absorbers for the Lyman continuum is determined as a function of the distance from the center of the solar disk by use of Skylab spectroheliograms in Oiv λ554 and Ovi λ1032. It is found that (1) the weakening cannot be explained by shielding of EUV emitting sources in terms of completely opaque spicules and (2) the distribution of the equivalent optical thickness on the solar disk is extremely flat with a maximum at a position of ～ 5″ above the white-light limb. The results imply that the absorbers are a number of mass blobs consisting of cool chromospheric material which overlies the EUV emitting sources. It is suggested that both the EUV emitting sources and the absorbers are the remnants of Hα-emitting spicules which are diffused into the corona. 相似文献
8.
Polar crown prominences, that partially circle the Sun’s poles between 60° and 70° latitude, are made of chromospheric plasma. We aim to diagnose the 3D dynamics of a polar crown prominence using high-cadence EUV images from the Solar Dynamics Observatory (SDO)/AIA at 304, 171, and 193 Å and the Ahead spacecraft of the Solar Terrestrial Relations Observatory (STEREO-A)/EUVI at 195 Å. Using time series across specific structures, we compare flows across the disk in 195 Å with the prominence dynamics seen on the limb. The densest prominence material forms vertical columns that are separated by many tens of Mm and connected by dynamic bridges of plasma that are clearly visible in 304/171 Å two-colour images. We also observe intermittent but repetitious flows with velocity 15 km?s?1 in the prominence that appear to be associated with EUV bright points on the solar disk. The boundary between the prominence and the overlying cavity appears as a sharp edge. We discuss the structure of the coronal cavity seen both above and around the prominence. SDO/HMI and GONG magnetograms are used to infer the underlying magnetic topology. The evolution and structure of the prominence with respect to the magnetic field seems to agree with the filament-linkage model. 相似文献
9.
Rawi Bhavilai 《Solar physics》1968,5(4):471-488
Evidence is presented demonstrating the existence of a type of chromospheric structure in the form of bright streaks. These are extensions across the solar disk of elongated bright mottles which originate in the central regions of clusters of mottles. They are best observed on good filtergrams at H ± 0.5 Å through comparison with filtergrams at other positions on the line profile. Their length can be as much as 200 sec of arc. The bright streaks appear to be predominantly horizontal loop structures, while the well-known spicules are mainly vertical structures. A bright streak may be well defined or rather diffuse along its length, and many of them are accompanied by darker boundaries or envelopes. It is usual to find a loop of bright streak bridging the central areas of two mottle clusters. It seems that the observed pattern in the space between the chromospheric network at H ± 0.5 Å results partly from the interactions of the bright streaks of different stages of evolution traversing the area in different directions. 相似文献
10.
Monte Carlo radiative transfer techniques are used to develop a height-dependent spicule model based upon a more realistic configuration than has hitherto been considered. The spicule is represented by a uniform cylinder, of finite length, standing vertically upon a plane chromosphere. The observed, limb-darkened, anisotropic chromospheric flux incident upon the cylinder is incorporated into the transfer calculations.The resulting model is characterized by a random, line broadening velocity of 20 km/sec, with electron temperature increasing from 6 × 103 K at the base to about 1.5 × 104 K at 11500 km above the solar surface. The corresponding values of electron density are 8 × 1011 cm-3 and 4 × 1010 cm-3. Contrast curves of the spicule model against the chromospheric background are computed and indicate that spicules should appear both bright and dark on the disk, depending upon their position with respect to the limb, the spectral frequency of observation and the viewing height.This work is based on a Ph.D. thesis submitted to the Department of Astro-Geophysics, University of Colorado.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
11.
V. Gaizauskas 《Solar physics》1984,93(2):257-268
The progressive rotation from the limb onto the disk of a long-lived cluster of coaligned Hα spicules was observed at high spatial resolution on the fringe of a large complex of activity. Although individual spicules were steadily changing, the organized cluster appeared consistently suspended above the photospheric limb when viewed in the wings of Hα (|Δλ| ≈ 0.9 Å). The phenomenon is the counterpart near an active region of the dark band discovered in the quiet low chromosphere by Loughhead (1969). But in the present circumstances the effect is perceived as a weakening of emission, i.e. as a gap rather than an obscuration. The initial gap between the off-band spicules and the photospheric limb narrowed and closed in about 4 h. A day later, the cluster of spicules could be identified at the same wavelength with a cluster of elongated dark mottles, similarly coaligned; they were adjacent to, but not in contact with, a foreshortened patch of faculae. The persistence of the gap in this cluster, and its occurrence in isolated spicules reported here in quiet regions, imply that the phenomenon is an inherent property of spicules. It is proposed that the gap results from a spicule-generating process initiated above the temperature minimum. 相似文献
12.
Previous models of microwave limb brightening have omitted the alignment of spicules along supergranule boundaries, have neglected the high temperature sheath around spicules, and have assumed an interspicular medium which was averaged over chromospheric network and non-network regions. We present a model which includes these factors. By constraining the model to conform to results from earlier UV and optical studies we are effectively left with two free parameters: the temperature at the core of the spicules, T
core, and (at solar minimum), the interspicular chromospheric network density model of the lower transition zone. The absence of limb brightening at the short millimeter wavelengths implies T
core 6000 k. Differences between the model and certain deconvolved observations near 9 mm are expected as a consequence of an extension of emission beyond the optical limb, predicted by the model, which affects the accuracy of the deconvolution technique. Unlike models which assume homogeneous spicules in a random distribution, ours does not require an abnormally high spicule area. 相似文献
13.
H spectra and effectively simultaneous filtergrams were taken at the Fraunhofer Observatory on Capri with the 35 cm domeless Coudé. The spatial resolution of the 19 best spectra selected for analysis was estimated to be 1–2 arc sec. The comparison of several hundred H line profiles emitted by typical chromospheric structure elements with theoretical prediction yielded strong evidence to suggest that the chromosphere consists of two parts: A lower, rather uniform layer at rest superposed by clouds (condensations of great spatial variability) which constitute the well-known structure pattern of H filtergrams. For most image points the line-of-sight velocity, optical thickness, source function and Doppler broadening of these clouds could be determined. While the values of the latter three quantities were found to be similar to what Beckers (1968) has found for limb spicules the velocity of the bright and of the dark mottles is considerably smaller than to be expected if these features were the spicules as seen on the disk. However, our results do not rule out the possibility that the spicules rise at the centers of rosettes where they are difficult to detect.Mitteilung aus dem Fraunhofer Institut No. 105. 相似文献
14.
I. S. Kim I. V. Alexeeva O. I. Bugaenko V. V. Popov E. Z. Suyunova 《Solar physics》2013,288(2):651-661
“Weak” magnetic-field diagnostics in faint objects near the bright solar disk are discussed in terms of the level of non-object signatures, in particular, of the stray light in telescopes. Calculated dependencies of the stray light caused by diffraction at the 0.5-, 1.6-, and 4-meter entrance aperture are presented. The requirements for micro-roughness of refractive and reflective primary optics are compared. Several methods for reducing the stray light (the Lyot coronagraphic technique, multiple stages of apodizing in the focal and exit pupil planes, apodizing in the entrance aperture plane with a special mask), and reducing the random and systematic errors are noted. An acceptable level of stray light in telescopes is estimated for the V-profile recording with a signal-to-noise ratio greater than three. Prospects for the limb chromosphere magnetic measurements are indicated. 相似文献
15.
E. I. Kryuchkov O. K. Cheremnykh A. K. Fedorenko 《Kinematics and Physics of Celestial Bodies》2017,33(3):122-129
The properties of acoustic-gravity waves in the polar regions of the Earth’s thermosphere have been studied. It has been shown that the change in AGW amplitudes occurs against the background of large-scale rotational movements of the medium in the polar thermosphere. The amplitudes of waves increase with AGW propagation against the motion of the medium and decrease when AGW propagate along rotation. An analytical expression for the gain coefficient of AGW perturbations is obtained; the wave’s amplification effect in the opposite wind given the characteristic parameters of the thermosphere is estimated. The results are consistent with the measurements of AGW parameters in the polar regions from the “Dynamic Explorer 2” satellite.) 相似文献
16.
The Soft X-ray Telescope (SXT) onboard Yohkoh often observed large-scale coronal loops connecting two active regions situated in opposite hemispheres. These are the trans-equatorial
loop systems (TLSs). The formation mechanism of TLSs is not yet known. We analyzed a TLS observed simultaneously with Yohkoh/SXT and a coronagraph (SOHO/LASCO-C1). SOHO/LASCO-C1 observed loop expansion and eruption at the west solar limb. Yohkoh/SXT observed a rising motion (chromospheric evaporation) of hot and dense plasmas from the active regions located at the
footpoints of the loop. Important results of our analyses are that (1) the loop eruption and the rising motion of the plasmas
were simultaneous, (2) the TLS had a cusp-like appearance, and (3) the highest temperature region of the TLS was located above
the bright loop seen in soft X rays. These observational results (loop expansion, eruption, and chromospheric evaporation)
suggest that this bright (high-density) TLS was created by the same mechanism by which a solar flare occurs, namely, magnetic
reconnection. In this paper, we propose a formation mechanism of the TLS that forms between two independent active regions. 相似文献
17.
Keiji Ohtsuki 《Icarus》2006,183(2):373-383
We derive an equation for the evolution of rotational energy of Keplerian particles in a dilute disk due to mutual collisions. Three-dimensional Keplerian motion of particles is taken into account precisely, on the basis of Hill's approximation. The Rayleigh distribution of particles' orbital eccentricities and inclinations, and the Gaussian distribution of their rotation rates are also taken into account. Performing appropriate variable transformation, we show that the equation can be expressed with two terms. The first term, which we call collisional stirring term, represents energy exchange between rotation and random motion via collisions. The second term, which we call rotational friction term, tends to equalize the mean rotational energy of particles with different sizes. The equation can describe the evolution of rotational energy of Keplerian particles with an arbitrary size distribution. We analytically evaluate the rates of stirring and friction for the random kinetic energy and rotational energy due to inelastic collisions, for non-gravitating particles in a dilute disk. Using these results, we discuss equilibrium states in a disk of spinning, non-gravitating Keplerian particles. 相似文献
18.
We present a technique for automatic determination of flare ribbon separation and the energy released during the course of two-ribbon flares. We have used chromospheric Hα filtergrams and photospheric line-of-sight magnetograms to analyse flare ribbon separation and magnetic field structures, respectively. Flare ribbons were first enhanced and then extracted by the technique of “region growing”, i.e., a morphological operator to help resolve the flare ribbons. Separation of flare ribbons was then estimated from the magnetic-polarity reversal line using an automatic technique implemented into an Interactive Data Language (IDLTM) platform. Finally, the rate of flare-energy release was calculated using photospheric magnetic field data and the corresponding separation of the chromospheric Hα flare ribbons. This method could be applied to measure the motion of any feature of interest (e.g., intensity, magnetic, Doppler) from a given point of reference. 相似文献
19.
The model of a protoplanetary disk around a star with a low-mass companion (M 2: M 1 ≤ 0.1) moving in a circular orbit inclined at a small angle to the disk plane (≤10°) is considered. The SPH method is used to calculate the hydrodynamic flows. The orbital motion of the companion leads to a nonuniform distribution of matter in the disk: a matter-free gap, density waves, and gas flows are formed in it. As a result of perturbations, the inner part of the disk is inclined relative to its periphery and does not coincide with the orbital plane of the companion either. This leads to an anisotropic illumination of the disk by the star and, as a consequence, to the appearance of a large-scale inhomogeneity in the disk image: it has a bright horseshoe-shaped region and a small shadow zone located asymmetrically relative to the line of nodes. An asymmetry of the disk image is clearly seen even when it is viewed pole-on. The orbital motion of the companion does not lead to any synchronous motion of the dark (shadow) and bright regions: they only execute small oscillations relative to some preferential direction. The asymmetric image of the disk around the star LkHα 101 seen nearly pole-on can be reproduced rather accurately within the proposed model. A study of such asymmetric disks opens up new opportunities for the search of massive bodies in the neighborhoods of young stars. 相似文献
20.
K. A. Marsh 《Solar physics》1978,57(1):37-48
High resolution filtergrams of the solar limb in D3 and off-band H have been used to investigate the spatial structure of the D3 chromosphere. It was found that spicules provide the major contribution to the intensity of the D3 emission band observed above the limb, with the remainder of the emission coming from a semi-homogeneous background component at low heights.The observations can be understood on the basis of the photoionization model, whereby it is found that helium is only slightly ionized at the height of peak intensity in the D3 emission band, and that spicules are at least 3 times denser than their surroundings at this height.In coronal holes, the D3 emission is confined to isolated emission patches, and these patches contain a fine structure resembling normal chromospheric spicules. 相似文献