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1.
We demonstrate that a simple solar dynamo model, in the form of a Parker migratory dynamo with random fluctuations of the
dynamo governing parameters and algebraic saturation of dynamo action, can at least qualitatively reproduce all the basic
features of solar Grand Minima as they are known from direct and indirect data. In particular, the model successfully reproduces
such features as an abrupt transition into a Grand Minimum and the subsequent gradual recovery of solar activity, as well
as mixed-parity butterfly diagrams during the epoch of the Grand Minimum. The model predicts that the cycle survives in some
form during a Grand Minimum, as well as the relative stability of the cycle inside and outside of a Grand Minimum. The long-term
statistics of simulated Grand Minima appears compatible with the phenomenology of the Grand Minima inferred from the cosmogenic
isotope data. We demonstrate that such ability to reproduce the Grand Minima phenomenology is not a general feature of the
dynamo models but requires some specific assumption, such as random fluctuations in dynamo governing parameters. In general,
we conclude that a relatively simple and straightforward model is able to reproduce the Grand Minima phenomenology remarkably
well, in principle providing us with a possibility of studying the physical nature of Grand Minima. 相似文献
2.
The Heliospheric Imager (HI) instruments on the Solar TErrestrial RElations Observatory (STEREO) observe solar plasma as it streams out from the Sun and into the heliosphere. The telescopes point off-limb (from
about 4° to 90° elongation) and so the Sun is not in the field of view. Hence, the Sun cannot be used to confirm the instrument
pointing. Until now, the pointing of the instruments have been calculated using the nominal preflight instrument offsets from
the STEREO spacecraft together with the spacecraft attitude data. This paper develops a new method for deriving the instrument
pointing solutions, along with other optical parameters, by comparing the locations of stars identified in each HI image with
the known star positions predicted from a star catalogue. The pointing and optical parameters are varied in an autonomous
manner to minimise the discrepancy between the predicted and observed positions of the stars. This method is applied to all
HI observations from the beginning of the mission to the end of April 2008. For the vast majority of images a good attitude
solution has been obtained with a mean-squared deviation between the observed and predicted star positions of one image pixel
or less. Updated values have been obtained for the instrument offsets relative to the spacecraft, and for the optical parameters
of the HI cameras. With this method the HI images can be considered as “self-calibrating,” with the actual instrument offsets
calculated as a byproduct. The updated pointing results and their by-products have been implemented in SolarSoft. 相似文献
3.
Precursor techniques, in particular those using geomagnetic indices, often are used in the prediction of the maximum amplitude
for a sunspot cycle. Here, the year 2008 is taken as being the sunspot minimum year for cycle 24. Based on the average aa index value for the year of the sunspot minimum and the preceding four years, we estimate the expected annual maximum amplitude
for cycle 24 to be about 92.8±19.6 (1-sigma accuracy), indicating a somewhat weaker cycle 24 as compared to cycles 21 – 23.
Presuming a smoothed monthly mean sunspot number minimum in August 2008, a smoothed monthly mean sunspot number maximum is
expected about October 2012±4 months (1-sigma accuracy). 相似文献
4.
The Recovery of CME-Related Dimmings and the ICME’s Enduring Magnetic Connection to the Sun 总被引：1，自引：1，他引：0
G. D. R. Attrill L. van Driel-Gesztelyi P. Démoulin A. N. Zhukov K. Steed L. K. Harra C. H. Mandrini J. Linker 《Solar physics》2008,252(2):349-372
It is generally accepted that transient coronal holes (TCHs, dimmings) correspond to the magnetic footpoints of CMEs that
remain rooted in the Sun as the CME expands out into the interplanetary space. However, the observation that the average intensity
of the 12 May 1997 dimmings recover to their pre-eruption intensity in SOHO/EIT data within 48 hours, whilst suprathermal
unidirectional electron heat fluxes are observed at 1 AU in the related ICME more than 70 hours after the eruption, leads
us to question why and how the dimmings disappear whilst the magnetic connectivity is maintained. We also examine two other
CME-related dimming events: 13 May 2005 and 6 July 2006. We study the morphology of the dimmings and how they recover. We
find that, far from exhibiting a uniform intensity, dimmings observed in SOHO/EIT data have a deep central core and a more
shallow extended dimming area. The dimmings recover not only by shrinking of their outer boundaries but also by internal brightenings.
We quantitatively demonstrate that the model developed by Fisk and Schwadron (Astrophys. J.
560, 425, 2001) of interchange reconnections between “open” magnetic field and small coronal loops is a strong candidate for the mechanism
facilitating the recovery of the dimmings. This process disperses the concentration of “open” magnetic field (forming the
dimming) out into the surrounding quiet Sun, thus recovering the intensity of the dimmings whilst still maintaining the magnetic
connectivity to the Sun.
Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users. 相似文献
5.
Subdwarf B stars (sdBs) can significantly change the ultraviolet spectra of populations at age t～1 Gyr, and have been even included in the evolutionary population synthesis (EPS) models by Han et al. (Mon. Not. R. Astron. Soc. 380:1098, 2007). In this study we present the spectral energy distributions (SEDs) of binary stellar populations (BSPs) by combining the EPS models of Han et al. (Mon. Not. R. Astron. Soc. 380:1098, 2007) and those of the Yunnan group (Zhang et al. in Astron. Astrophys. 415:117, 2004; Mon. Not. R. Astron. Soc. 357:1088, 2005), which have included various binary interactions (except sdBs) in EPS models. This set of SEDs is available upon request from the authors. Using this set of SEDs of BSPs we build the spectra of Burst, E, S0–Sd and Irr types of galaxies by using the package of Bruzual and Charlot (Mon. Not. R. Astron. Soc. 344:1000, 2003). Combined with the photometric data (filters and magnitudes), we obtain the photometric redshifts and morphologies of 1502 galaxies by using the Hyperz code of Bolzonella et al. (Astron. Astrophys. 363:476, 2000). This sample of galaxies is obtained by removing those objects, mismatched with the SDSS/DR7 and GALEX/DR4, from the catalogue of Fukugita et al. (Astron. J. 134:579, 2007). By comparison the results with the SDSS spectroscopic redshifts and the morphological index of Fukugita et al. (Astron. J. 134:579, 2007), we find that the photo-z fluctuate with the SDSS spectroscopic redshifts, while the Sa–Sc galaxies in the catalogue of Fukugita et al. (Astron. J. 134:579, 2007) are classified earlier as Burst-E galaxies. 相似文献
6.
The high quality of the asteroseismic data provided by space missions such as CoRoT (Michel et al. in The CoRoT Mission, ESA Spec. Publ. vol. 1306, p. 39, 2006) or expected from new operating missions such as Kepler (Christensen-Dalsgaard et al. in Commun. Asteroseismol. 150:350, 2007) requires the capacity of stellar evolution codes to provide accurate models whose numerical precision is better than the expected observational errors (i.e. below 0.1 μHz on the frequencies in the case of CoRoT). We present a review of some thorough comparisons of stellar models produced by different evolution codes, involved in the CoRoT/ESTA activities (Monteiro in Evolution and Seismic Tools for Stellar Astrophysics, 2009). We examine the numerical aspects of the computations as well as the effects of different implementations of the same physics on the global quantities, physical structure and oscillations properties of the stellar models. We also discuss a few aspects of the input physics. 相似文献
7.
We present a statistical analysis of the relationship between the kinematics of the leading edge and the eruptive prominence
in coronal mass ejections (CMEs). We study the acceleration phase of 18 CMEs in which kinematics was measured from the pre-eruption
stage up to the post-acceleration phase. In all CMEs, the three part structure (the leading edge, the cavity, and the prominence)
was clearly recognizable from early stages of the eruption. The data show a distinct correlation between the duration of the
leading edge (LE) acceleration and eruptive prominence (EP) acceleration. In the majority of events (78%) the acceleration
phase onset of the LE is very closely synchronized (within ± 20 min) with the acceleration of EP. However, in two events the
LE acceleration started significantly earlier than the EP acceleration (> 50 min), and in two events the EP acceleration started
earlier than the LE acceleration (> 40 min). The average peak acceleration of LEs (281 m s−2) is about two times larger than the average peak acceleration of EPs (136 m s−2). For the first time, our results quantitatively demonstrate the level of synchronization of the acceleration phase of LE
and EP in a rather large sample of events, i.e., we quantify how often the eruption develops in a “self-similar” manner. 相似文献
8.
S. Masson K.-L. Klein R. Bütikofer E. Flückiger V. Kurt B. Yushkov S. Krucker 《Solar physics》2009,257(2):305-322
The origin of relativistic solar protons during large flare/CME events has not been uniquely identified so far. We perform
a detailed comparative analysis of the time profiles of relativistic protons detected by the worldwide network of neutron
monitors at Earth with electromagnetic signatures of particle acceleration in the solar corona during the large particle event
of 20 January 2005. The intensity – time profile of the relativistic protons derived from the neutron monitor data indicates
two successive peaks. We show that microwave, hard X-ray, and γ-ray emissions display several episodes of particle acceleration within the impulsive flare phase. The first relativistic
protons detected at Earth are accelerated together with relativistic electrons and with protons that produce pion-decay γ rays during the second episode. The second peak in the relativistic proton profile at Earth is accompanied by new signatures
of particle acceleration in the corona within ≈1R
⊙ above the photosphere, revealed by hard X-ray and microwave emissions of low intensity and by the renewed radio emission
of electron beams and of a coronal shock wave. We discuss the observations in terms of different scenarios of particle acceleration
in the corona. 相似文献
9.
Donald C. Norquist 《Solar physics》2011,269(1):111-127
Designing a statistical solar flare forecasting technique can benefit greatly from knowledge of the flare frequency of occurrence
with respect to sunspot groups. This study analyzed sunspot groups and Hα and X-ray flares reported for the period 1997 – 2007.
Annual catalogs were constructed, listing the days that numbered sunspot groups were observed (designated sunspot group-days,
SSG-Ds) and for each day a record for each associated Hα flare of importance category one or greater and normal or bright
brightness and for each X-ray flare of intensity C 5 or higher. The catalogs were then analyzed to produce frequency distributions
of SSG-Ds by year, sunspot group class, likelihood of producing at least one flare overall and by sunspot group class, and
frequency of occurrence of numbers of flares per day and flare intensity category. Only 3% of SSG-Ds produced a substantial
Hα flare and 7% had a significant X-ray flare. We found that mature, complex sunspot groups were more likely than simple sunspot
groups to produce a flare, but the latter were more prevalent than the former. More than half of the SSG-Ds with flares had
a maximum intensity flare greater than the lowest category (C-class of intensity five and higher). The fact that certain sunspot
group classes had flaring probabilities significantly higher than the combined probabilities of the intensity categories when
all SSG-Ds were considered suggest that it might be best to first predict the flaring probability. For sunspot groups found
likely to flare, a separate diagnosis of maximum flare intensity category appears feasible. 相似文献
10.
Lorenzo Iorio 《Astrophysics and Space Science》2008,315(1-4):335-340
In this paper we explore the consequences of the recent determination of the mass m=(8.7±0.8)M ⊙ of Cygnus X-1, obtained from the Quasi-Periodic Oscillation (QPO)-photon index correlation scaling, on the orbital and physical properties of the binary system HDE 226868/Cygnus X-1. By using such a result and the latest spectroscopic optical data of the HDE 226868 supergiant star we get M=(24±5)M ⊙ for its mass. It turns out that deviations from the third Kepler law significant at more than 1-sigma level would occur if the inclination i of the system’s orbital plane to the plane of the sky falls outside the range ≈41–56 deg: such deviations cannot be due to the first post-Newtonian (1PN) correction to the orbital period because of its smallness; interpreted in the framework of the Newtonian theory of gravitation as due to the stellar quadrupole mass moment Q, they are unphysical because Q would take unreasonably large values. By conservatively assuming that the third Kepler law is an adequate model for the orbital period we obtain i=(48±7) deg which yields for the relative semimajor axis a=(42±9)R ⊙ (≈0.2 AU). 相似文献
11.
In the paper by Kliem, Karlický, and Benz (Astron. Astrophys. 360, 715, 2000) it was suggested, that plasmoids formed during the bursty regime of solar flare reconnection can be “visualised” in the radio spectra as drifting pulsating structures via accelerated particles trapped inside the plasmoid. In the present paper we investigate this idea in detail. First, simple statistical analysis supporting this hypothesis is presented. Then, by using the 2.5-D MHD (including gravity) model solar flare reconnection in the inhomogeneous, stratified atmosphere is simulated and the formation and subsequent ejection of the plasmoid is demonstrated. The ejected plasmoid, which is considered to be a trap for accelerated electrons, is traced and its plasma parameters are computed. To estimate the associated plasma radio emission we need to know locations of accelerated electrons and corresponding plasma frequencies. General considerations predict that these electrons should be distributed mainly along the magnetic separatrix surfaces and this was confirmed by using a particle-in-cell simulation. Finally, under some simplifying assumptions the model dynamic radio spectrum is constructed. The relation between the global frequency drift and the plasmoid motion in the inhomogeneous ambient atmosphere is studied. The results are discussed with respect to the observed drifting pulsation structures and their possible utilisation for flare magnetic field diagnostics. 相似文献
12.
R. P. Kane 《Solar physics》2008,248(1):177-190
From the LASCO CME (Coronal Mass Ejection) catalog, the occurrence frequencies of all CMEs (all strong and weak CMEs, irrespective
of their widths) were calculated for 3-month intervals and their 12-month running means determined for cycle 23 (1996 – 2007)
and were compared with those of other solar parameters. The annual values of all-CME frequency were very well correlated (+ 0.97)
with sunspot numbers, but several other parameters also had similarly high correlations. Comparisons of 12-month running means
indicated that the sunspot numbers were very well correlated with solar electromagnetic radiations (Lyman-α, 2800-MHz flux,
coronal green line index, solar flare indices, and X-ray background); but for corpuscular radiations [proton fluxes, solar
energetic particles (SEP), CMEs, interplanetary CMEs (ICMEs), and stream interaction regions (SIR)] and solar open magnetic
fields, the correlations were lower. A notable feature was the appearance of two peaks during 2000 – 2002, and those double
peaks in different parameters matched approximately except for proton fluxes and SEP and SIR frequencies. When hemispheric
intensities were considered, north – south asymmetries appeared, more in some parameters than in others. When intensities
in smaller latitude belts (10°) were compared, sunspot group numbers (SGN) were found to be confined mostly to latitudes within
± 30° of the solar equator, showing two peaks in all latitude belts, and during the course of the 11-year cycle, the double peaks shifted from middle to equatorial
solar latitudes, just as seen in the Maunder butterfly diagrams. In contrast, CME frequency was comparable at all latitude
belts (including high, near-polar latitudes), having more than two peaks in almost all latitude belts, and the peaks were
almost simultaneous in all latitude belts. Thus, the matching of SGN peaks with those of CME peaks was poor. Incidentally,
the CME frequency data for all events (all widths) after 2003 are not comparable to earlier data, owing to inclusion of very
weak (narrow) CMEs in later years. The frequencies are comparable with earlier data only for widths exceeding about 70°. 相似文献
13.
The north – south asymmetries (NSA) of three solar activity indices are derived and mutually compared over a period of more
than five solar cycles (1945 – 2001). A catalogue of the hemispheric sunspot numbers, the data set of the coronal green line
brightness developed by us, and the magnetic flux derived from the NSO/KP data (1975 – 2001) are treated separately within
the discrete low- and mid-latitude zones (5° – 30°, 35° – 60°). The calculated autocorrelations, cross-correlations, and regressions
between the long-term NSA data sets reveal regularities in the solar activity phenomenon. Namely, the appearance of a distinct
quasi-biennial oscillation (QBO) is evident in all selected activity indices. Nevertheless, a smooth behavior of QBO is derived
only when sufficient temporal averaging is performed over solar cycles. The variation in the significance and periodicity
of QBO allows us to conclude that the QBO is not persistent over the whole solar cycle. A similarity in the photospheric and
coronal manifestations of the NSA implies that their mutual relation will also show the QBO. A roughly two-year periodicity
is actually obtained, but again only after significant averaging over solar cycles. The derived cross-correlations are in
fact variable in degree of correlation as well as in changing periodicity. A clear and significant temporal shift of 1 – 2
months in the coronal manifestation of the magnetic flux asymmetry relative to the photospheric manifestation is revealed
as a main property of their mutual correlation. This shift can be explained by the delayed large-scale coronal manifestation
in responding to the emergence of the magnetic flux in the photosphere. The reliability of the derived results was confirmed
by numerical tests performed by selecting different numerical values of the used parameters. 相似文献
14.
We investigate coronal transients associated with a GOES M6.7 class flare and a coronal mass ejection (CME) on 13 July 2004. During the rising phase of the flare, a filament eruption, loop expansion, a Moreton wave, and an ejecta were observed. An EIT wave was detected later on. The main features in the radio dynamic spectrum were a frequency-drifting continuum and two type II bursts. Our analysis shows that if the first type II burst was formed in the low corona, the burst heights and speed are close to the projected distances and speed of the Moreton wave (a chromospheric shock wave signature). The frequency-drifting radio continuum, starting above 1 GHz, was formed almost two minutes prior to any shock features becoming visible, and a fast-expanding piston (visible as the continuum) could have launched another shock wave. A possible scenario is that a flare blast overtook the earlier transient and ignited the first type II burst. The second type II burst may have been formed by the same shock, but only if the shock was propagating at a constant speed. This interpretation also requires that the shock-producing regions were located at different parts of the propagating structure or that the shock was passing through regions with highly different atmospheric densities. This complex event, with a multitude of radio features and transients at other wavelengths, presents evidence for both blast-wave-related and CME-related radio emissions. 相似文献
15.
Michael A. Dopita Daniela Calzetti Jesús Maíz Apellániz William P. Blair Knox S. Long Max Mutchler Bradley C. Whitmore Howard E. Bond John MacKenty Bruce Balick Marcella Carollo Michael Disney Jay A. Frogel Robert O’Connell Donald Hall Jon A. Holtzman Randy A. Kimble Patrick McCarthy Francesco Paresce Abhijit Saha Alistair R. Walker Joe Silk Marco Sirianni John Trauger Rogier Windhorst Erick Young 《Astrophysics and Space Science》2010,330(1):123-131
We present narrow band, continuum subtracted Hα, [S ii], Hβ, [O iii] and [O ii] data taken with the Wide Field Camera 3 on the Hubble Space Telescope in the nearby dwarf starburst galaxy NGC 4214. From these images, we identify seventeen new planetary nebula candidates, and seven supernova remnant candidates. We use the observed emission line luminosity function of the planetary nebulae to establish a new velocity-independent distance to NGC 4214. We conclude that the PNLF technique gives a reddening independent distance to NGC 4214 of 3.19±0.36 Mpc, and that our current best-estimate of the distance to this galaxy ids 2.98±0.13 Mpc. 相似文献
16.
In a density-stratified turbulent medium, the cross helicity 〈u′⋅B′〉 is considered as a result of the interaction of the velocity fluctuations and a large-scale magnetic field. By means of
a quasilinear theory and by numerical simulations, we find the cross helicity and the mean vertical magnetic field to be anti-correlated.
In the high-conductivity limit the ratio of the helicity and the mean magnetic field equals the ratio of the magnetic eddy
diffusivity and the (known) density scale height. The result can be used to predict that the cross helicity at the solar surface
will exceed the value of 1 gauss km s−1. Its sign is anti-correlated to that of the radial mean magnetic field. Alternatively, we can use our result to determine
the value of the turbulent magnetic diffusivity from observations of the cross helicity. 相似文献
17.
The Murchison Widefield Array (MWA) is one of the new technology low frequency radio interferometers currently under construction at an extremely radio-quiet location in Western Australia. The MWA design brings to bear the recent availability of powerful high-speed computational and digital signal processing capabilities on the problem of low frequency high-fidelity imaging with a rapid cadence and high spectral resolution. Solar and heliosphere science are among the key science objectives of the MWA and have guided the array design from its very conception. We present here a brief overview of the design and capabilities of the MWA with emphasis on its suitability for solar physics and remote-sensing of the heliosphere. We discuss the solar imaging and interplanetary scintillation (IPS) science capabilities of the MWA and also describe a new software framework. This software, referred to as Haystack InterPlanetary Software System (HIPSS), aims to provide a common data repository, interface, and analysis tools for IPS data from all observatories across the world. 相似文献
18.
Cyclic variations of the mean semi-annual intensities I
of the coronal green line 530.3 nm are compared with the mean semi-annual variations of the Wolf numbers W during the period of 1943–1999 (activity cycles 18–23). The values of I
in the equatorial zone proved to correlate much better with the Wolf numbers in a following cycle than in a given one (the correlation coefficient r is 0.86 and 0.755, respectively). Such increase of the correlation coefficient with a shift by one cycle differs in different phases of the cycle, being the largest at the ascending branch. The regularities revealed make it possible to predict the behaviour of W in the following cycle on the basis of intensities of the coronal green line in the preceding cycle. We predict the maximum semi-annual W in cycle 23 to be 110–122 and the epoch of minimum between cycles 23 and 24 to take place at 2006–2007. A slow increase of I
in the current cycle 23 permits us to forecast a low-Wolf-number cycle 24 with the maximum W50 at 2010–2011. A scheme is proposed on the permanent transformation of the coronal magnetic fields of different scales explaining the found phenomenon. 相似文献
19.
20.
Resonant absorption of fast magnetoacoustic (FMA) waves in an inhomogeneous, weakly dissipative, one-dimensional planar, strongly
anisotropic and dispersive plasma is investigated. The magnetic configuration consists of an inhomogeneous magnetic slab sandwiched
between two regions of semi-infinite homogeneous magnetic plasmas. Laterally driven FMA waves penetrate the inhomogeneous
slab interacting with the localised slow or Alfvén waves present in the inhomogeneous layer and are partly reflected, dissipated
and transmitted by this region. The presented research aims to find the coefficient of wave energy absorption under solar
chromospheric and coronal conditions. Numerical results are analysed to find the coefficient of wave energy absorption at
both the slow and Alfvén resonance positions. The mathematical derivations are based on the two simplifying assumptions that
i) nonlinearity is weak, and ii) the thickness of the inhomogeneous layer is small in comparison to the wavelength of the wave, i.e. we employ the so-called long wavelength approximation. Slow resonance is found to be described by the nonlinear theory, while
the dynamics at the Alvén resonance can be described within the linear framework. We introduce a new concept of coupled resonances,
which occurs when two different resonances are in close proximity to each other, causing the incoming wave to act as though it has been influenced by the two resonances simultaneously. Our results show that the wave energy absorption is heavily
dependent on the angle of the incident wave in combination with the inclination angle of the equilibrium magnetic field. In
addition, it is found that FMA waves are very efficiently absorbed at the Alvén resonance under coronal conditions. Under
chromospheric conditions the FMA waves are far less efficiently absorbed, despite an increase in efficiency due to the coupled
resonances. 相似文献