共查询到20条相似文献，搜索用时 31 毫秒
1.
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
2.
A set of smoothed temperature gradient profiles around overshooting layers at the solar convective zone bottom is considered. In classical local theories of convection the one point defined according to the Schwarzschild criterion is enough to describe a convective boundary. To get a sophisticated picture of the overshooting we use four points to compute the transition overshooting functions. Analyzing the transition gradient profiles we found that the overshooting convective flux may be either positive or negative. A negative overshooting flux appears in nonlocal convective theories and causes a steep temperature gradient profile. But we propose an evenly smoothed gradient which corresponds to a convective flux positive everywhere. To outline the effect of the temperature gradient on the solar oscillations the squared Brunt–Väisälä frequency N 2 is calculated. In local convective theories the N 2 profile shows the discontinuity of the first derivative at the convective boundary, while all smoothed profiles eliminate the break. 相似文献
3.
The direct propagation of acoustic waves, driven harmonically at the solar photosphere, into the three-dimensional solar atmosphere
is examined numerically in the framework of ideal magnetohydrodynamics. It is of particular interest to study the leakage
of 5-minute global solar acoustic oscillations into the upper, gravitationally stratified and magnetised atmosphere, where
the modelled solar atmosphere possesses realistic temperature and density stratification. This work aims to complement and
bring further into the 3D domain our previous efforts (by Erdélyi et al., 2007, Astron. Astrophys. 467, 1299) on the leakage of photospheric motions and running magnetic-field-aligned waves excited by these global oscillations.
The constructed model atmosphere, most suitable perhaps for quiet Sun regions, is a VAL IIIC derivative in which a uniform
magnetic field is embedded. The response of the atmosphere to a range of periodic velocity drivers is numerically investigated
in the hydrodynamic and magnetohydrodynamic approximations. Among others the following results are discussed in detail: i) High-frequency waves are shown to propagate from the lower atmosphere across the transition region, experiencing relatively
low reflection, and transmitting most of their energy into the corona; ii) the thin transition region becomes a wave guide for horizontally propagating surface waves for a wide range of driver periods,
and particularly at those periods that support chromospheric standing waves; iii) the magnetic field acts as a waveguide for both high- and low-frequency waves originating from the photosphere and propagating
through the transition region into the solar corona.
Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users. 相似文献
4.
Tilemahos J. Kalvouridis 《Astrophysics and Space Science》2009,319(2-4):105-114
We study the parametric evolution of the regions where three-dimensional motions of a charged particle are allowed in the combined electromagnetic field produced by two rotating magnetic stars. We discuss the changes in the topology of the zero-velocity surfaces, as well as in the trapping regions of the particle motion for various values of the dipoles’ magnetic moments. 相似文献
5.
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
6.
Hasmukh K. Tank 《Astrophysics and Space Science》2010,330(2):203-205
Keeping apart the problem, whether Modified Newtonian Dynamics [MOND] can replace ‘dark matter’, this letter considers seven different theoretical recurrences of ‘critical acceleration’ of MOND noticed by Sivaram in various physical situations; adds five more observational recurrences to the list; and arrives at a set of laws which seem to be followed by all the systems bound by different fundamental forces; suggesting a clue to unification of fundamental forces. This attempt proposes a general explanation for ‘flattening of galaxies’ rotation-curves’ as well as the ‘expansion of the universe’. 相似文献
7.
Moncy V. John 《Astrophysics and Space Science》2010,330(1):7-11
Marginal likelihoods for the cosmic expansion rates are evaluated using the ‘Constitution’ data of 397 supernovas, thereby
updating the results in some previous works. Even when beginning with a very strong prior probability that favors an accelerated
expansion, we obtain a marginal likelihood for the deceleration parameter q
0 peaked around zero in the spatially flat case. It is also found that the new data significantly constrains the cosmographic
expansion rates, when compared to the previous analyses. These results may strongly depend on the Gaussian prior probability
distribution chosen for the Hubble parameter represented by h, with h=0.68±0.06. This and similar priors for other expansion rates were deduced from previous data. Here again we perform the Bayesian
model-independent analysis in which the scale factor is expanded into a Taylor series in time about the present epoch. Unlike
such Taylor expansions in terms of redshift, this approach has no convergence problem. 相似文献
8.
Xin-Fa Deng Ji-Zhou He Jian-Ying Xu Ying-Ping Ding 《Astrophysics and Space Science》2009,323(3):273-279
From the approximately volume-limited Luminous Red Galaxy (LRG) sample of the Sloan Digital Sky Survey Data Release 6 (SDSS
DR6), we construct three LRG samples with different g-r color, which have the nearly same number density, to investigate the
color dependence of clustering properties of LRGs. It is found that the blue galaxies have a more filamentary distribution
than red galaxies, and that the bluest LRGs preferentially inhabit the dense groups and clusters. But in three LRG samples
with different u-g color, we do not observe the tendency for clustering properties of LRGs to significantly change with color.
We preferentially conclude that the clustering properties of LRGs are not strongly correlated with colors. 相似文献
9.
Ehab E. El-Houssieny Robert J. Nemiroff Timothy E. Pickering 《Astrophysics and Space Science》2010,330(1):19-22
The outburst and subsequent brightness evolution of comet 17P/Holmes has been observed using the MMT Observatory’s All-Sky
Camera (Pickering 2006) on Mt. Hopkins near Tucson, Arizona, USA. The comet was picked up at the limiting visual magnitude of 5.5 on October 24.38
and tracked by the camera continuously until sunrise four hours later. During this time the comet brightened to visual magnitude
3.5. Comet Holmes was next observed just after sunset on October 25.23 at visual magnitude 2.5, where it remained approximately
constant over the next three days. The comet then began to dim slowly and was followed into the early months of 2008 with
periods of dense time coverage. 相似文献
10.
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
11.
Starting with a large number (N=100) of Wind magnetic clouds (MCs) and applying necessary restrictions, we find a proper set of N=29 to investigate the average ecliptic plane projection of the upstream magnetosheath thickness as a function of the longitude
of the solar source of the MCs, for those cases of MCs having upstream shock waves. A few of the obvious restrictions on the
full set of MCs are the need for there to exist a driven upstream shock wave, knowledge of the MC’s solar source, and restriction
to only MCs of low axial latitudes. The analysis required splitting this set into two subsets according to average magnetosheath
speed: slow/average (300 – 500 km s−1) and fast (500 – 1100 km s−1) speeds. Only the fast set gives plausible results, where the estimated magnetosheath thickness (ΔS) goes from 0.042 to 0.079 AU (at 1 AU) over the longitude sector of 0° (adjusted source-center longitude of the average magnetic
cloud) to 40° off center (East or West), based on N=11 appropriate cases. These estimates are well determined with a sigma (σ) for the fit of 0.0055 AU, where σ is effectively the same as
(chi-squared) for the appropriate quadratic fit. The associated linear correlation coefficient for ΔS versus |Longitude| was very good (c.c.=0.93) for the fast range, and ΔS at 60° longitude is extrapolated to be 2.7 times the value at 0°. For the slower speeds we obtain the surprising result that
ΔS is typically more-or-less constant at 0.040±0.013 AU at all longitudes, indicating that the MC as a driver, when moving close
to the normal solar wind speed, has little influence on magnetosheath thickness. In some cases, the correct choice between
two candidate solar-source longitudes for a fast MC might be made by noting the value of the observed ΔS just upstream of the MC. Also, we point out that, for the 29 events, the average sheath speed was well correlated with the
quantity ΔV[=(〈V
MC〉−〈V
UPSTREAM〉)], and also with both 〈V
MC〉 and 〈V
MC,T〉, where 〈V
MC〉 is the first one-hour average of the MC speed, 〈V
MC,T〉 is the average MC speed across the full MC, and 〈V
UPSTREAM〉 is a five-hour average of the solar wind speed just upstream of the shock. 相似文献
12.
The Interplanetary Magnetic Field shows complex spatial and temporal variations. Single spacecraft measurements reveal only
a one-dimensional section of this rich four-dimensional phenomenon. Multi-point measurements of the four Cluster spacecraft provide a unique tool to study the spatiotemporal structure of the field. Using Cluster data we determined three-dimensional correlation functions of the fluctuations. By means of the correlation function one
can describe and measure field variations. Our results can be used to verify theoretical predictions, to understand the formation
and nature of solar wind turbulence. We found that the correlation length varies over almost six orders of magnitude. The
IMF turbulence shows significant anisotropy with two distinct populations. In certain time intervals the ratio of the three
axes of the correlation ellipse is 1/2.2/6 while in the remaining time we found extremely high correlation along one axis.
We found favored directions in the orientation of the correlation ellipsoids. 相似文献
13.
Jianpo Guo Fenghui Zhang Xianfei Zhang Zhanwen Han 《Astrophysics and Space Science》2010,329(1-2):15-18
Observations of metal elements in some halo or bulge globular clusters and in some elliptical galaxies have shown the α-enhancement phenomenon. Hot subdwarfs are important stars, e.g., they are important sources of far-ultraviolet light in the Galaxy and have successfully been used to explain the UV-upturn in elliptical galaxies. Therefore, we try to study the impacts of α-enhancement on hot subdwarfs. In our calculation, the value of the metallicity is 0.02, all the core masses of hot subdwarfs are 0.475 M ⊙, and the envelope masses of the hot subdwarfs are 0.001, 0.005 and 0.016 M ⊙, respectively. We find that the influences of α-enhancement on luminosity and evolutionary age of hot subdwarfs are not visible. But α-enhancement can make the effective temperatures of hot subdwarfs become higher, and the thicker their envelopes are, the more obvious this influence is. 相似文献
14.
15.
We study the simple periodic orbits of a particle that is subject to the gravitational action of the much bigger primary bodies
which form a regular polygonal configuration of (ν+1) bodies when ν=8. We investigate the distribution of the characteristic curves of the families and their evolution in the phase space of
the initial conditions, we describe various types of simple periodic orbits and we study their linear stability. Plots and
tables illustrate the obtained material and reveal many interesting aspects regarding particle dynamics in such a multi-body
system. 相似文献
16.
Recently observed oscillations in the solar atmosphere have been interpreted and modeled as magnetohydrodynamic wave modes.
This has allowed for the estimation of parameters that are otherwise hard to derive, such as the coronal magnetic-field strength.
This work crucially relies on the initial detection of the oscillations, which is commonly done manually. The volume of Solar Dynamics Observatory (SDO) data will make manual detection inefficient for detecting all of the oscillating regions. An algorithm is presented
that automates the detection of areas of the solar atmosphere that support spatially extended oscillations. The algorithm
identifies areas in the solar atmosphere whose oscillation content is described by a single, dominant oscillation within a
user-defined frequency range. The method is based on Bayesian spectral analysis of time series and image filtering. A Bayesian
approach sidesteps the need for an a-priori noise estimate to calculate rejection criteria for the observed signal, and it also provides estimates of oscillation frequency,
amplitude, and noise, and the error in all of these quantities, in a self-consistent way. The algorithm also introduces the
notion of quality measures to those regions for which a positive detection is claimed, allowing for simple post-detection discrimination by the user.
The algorithm is demonstrated on two Transition Region and Coronal Explorer (TRACE) datasets, and comments regarding its suitability for oscillation detection in SDO are made. 相似文献
17.
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
18.
Dengkai Jiang Zhanwen Han Cheng Liu Jiancheng Wang Lifang Li 《Astrophysics and Space Science》2010,329(1-2):283-286
According to the prevenient theoretical study, the minimum mass ratio for tidal stability of W Ursae Majoris (W UMa) systems is q min?=(M 2/M 1)～0.071–0.078. However, the mass ratios of some observed W UMa binaries are smaller than the theoretical minimum mass ratio. Using Eggleton’s stellar evolution code, we study the effects of metallicity and evolution on the minimum mass ratio of W UMa systems (M 1=1.2M ⊙). We assume that $k_{1}^{2}=k_{2}^{2}$ for the component’s dimensionless gyration radii and that the contact degree is about 70 per cent. We find that the dynamical stability of W UMa binaries depends on the metallicity of W UMa systems. For the W UMa systems at age = 0 Gyr, the distribution of the minimum mass ratio has a fairly wide range, from 0.083 to 0.064, with the metallicity range from Z=0.0001 to 0.03. W UMa systems with Z=0.01 have the smallest value of the minimum mass ratio, which is about 0.064. The existence of low-q systems can be explained partly by the dependence of the dimensionless gyration radius on the metallicity. In addition, the dependence of the minimum mass ratio on the evolution, as suggested by previously work, is confirmed. 相似文献
19.
A. Papaioannou O. Malandraki A. Belov R. Skoug H. Mavromichalaki E. Eroshenko A. Abunin S. Lepri 《Solar physics》2010,266(1):181-193
In this work an analysis of a series of complex cosmic ray events that occurred between 17 January 2005 and 23 January 2005
using solar, interplanetary and ground based cosmic ray data is being performed. The investigated period was characterized
both by significant galactic cosmic ray (GCR) and solar cosmic ray (SCR) variations with highlighted cases such as the noticeable
series of Forbush effects (FEs) from 17 January 2005 to 20 January 2005, the Forbush decrease (FD) on 21 January 2005 and
the ground level enhancement (GLE) of the cosmic ray counter measurements on 20 January 2005. The analysis is focusing on
the aforementioned FE cases, with special attention drawn on the 21 January 2005, FD event, which demonstrated several exceptional
features testifying its uniqueness. Data from the ACE spacecraft, together with GOES X-ray recordings and LASCO CME coronagraph
images were used in conjunction to the ground based recordings of the Worldwide Neutron Monitor Network, the interplanetary
data of OMNI database and the geomagnetic activity manifestations denoted by K
p and D
st indices. More than that, cosmic ray characteristics as density, anisotropy and density gradients were also calculated. The
results illustrate the state of the interplanetary space that cosmic rays crossed and their corresponding modulation with
respect to the multiple extreme solar events of this period. In addition, the western location of the 21 January 2005 solar
source indicates a new cosmic ray feature, which connects the position of the solar source to the cosmic ray anisotropy variations.
In the future, this feature could serve as an indicator of the solar source and can prove to be a valuable asset, especially
when satellite data are unavailable. 相似文献
20.
We investigate the M1.8 solar flare of 20 October 2002. The flare was accompanied by quasi-periodic pulsations (QPP) of both thermal and nonthermal hard X-ray emissions (HXR) observed by RHESSI in the 3?–?50 keV energy range. Analysis of the HXR time profiles in different energy channels made with the Lomb periodogram has indicated two statistically significant time periods of about 16 and 36 s. The 36 s QPP were observed only in the nonthermal HXR emission in the impulsive phase of the flare. The 16 s QPP were found in thermal and nonthermal HXR emission both in the impulsive and in the decay phases of the flare. Imaging analysis of the flare region, the determined time periods of the QPP, and the estimated physical parameters of the flare loops allowed us to interpret the observed QPP in terms of MHD oscillations excited in two spatially separated, but interacting systems of flaring loops. 相似文献