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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.
Qixiu Li 《Solar physics》2008,249(1):135-145
The counts of the monthly averaged polar faculae, from observations of the National Astronomical Observatory of Japan (NAOJ),
are examined by using linear and nonlinear approaches to find the periodicity characteristics of the polar faculae in the
northern and southern hemispheres and the phase relationship between them. Both the cross-wavelet transform (XWT) and wavelet
coherence (WTC) indicate the prominent period with 95% confidence level, namely the Schwabe cycle of about 11 years. The Schwabe
cycle is in phase in the two hemispheres. Within the 11-year frequency band, there is a small phase difference during the
period of 1966 – 1975 when the activity of polar faculae in the northern hemisphere slightly leads the one in the southern
hemisphere. A cross-recurrence plot analysis and the line of synchronization (LOS) extracted from the cross-recurrence plot
show further the phase difference between the two hemispheres. The LOS deviates significantly from the main diagonal during
the period of 1965 – 1970 and LOS >0, showing that the activity of polar faculae in the northern hemisphere leads in phase,
which is in accordance with XWT and WTC analyses. Moreover, asynchronization is highest (about 30 months) during this period. 相似文献
3.
H. Kiliç 《Solar physics》2009,255(1):155-162
The short-term periodicities in sunspot numbers, sunspot areas, and flare index data are investigated in detail using the
Date Compensated Discrete Fourier Transform (DCDFT) for the full disk of the Sun separately over the rising, the maximum,
and the declining portions of solar cycle 23 (1996 – 2006). While sunspot numbers and areas show several significant periodicities
in a wide range between 23.1 and 36.4 days, the flare index data do not exhibit any significant periodicity. The earlier conclusion
of Pap, Tobiska, and Bouwer (1990, Solar Phys.
129, 165) and Kane (2003, J. Atmos. Solar-Terr. Phys.
65, 1169), that the 27-day periodicity is more pronounced in the declining portion of a solar cycle than in the rising and maximum
ones, seems to be true for sunspot numbers and sunspot area data analyzed here during solar cycle 23. 相似文献
4.
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
5.
Mohammadmahdi Rezaei Yousefi Babak Salehi Kasmaei Abdolhossein Vahabie Caro Lucas Babak Nadjar Araabi 《Solar physics》2009,258(2):297-318
Various phenomena with solar origin and their mutual dependence must be studied in order to predict behaviors in solar – terrestrial
system. Linear statistical methods prevalent in analyzing natural systems may not be able to detect nonlinear dependencies
among solar and geomagnetic processes. When relations, whether linear or nonlinear, between indices and their changes over
time are revealed, better predictions can be made through appropriate modeling techniques. Selection of nonredundant input
variables to build suitable models for prediction of solar and geomagnetic activity is of utmost importance. Mutual information
is a tool that is capable of capturing all dependencies for detecting nonlinear relations and selecting the best subset of
input variables by means of an applicable algorithm that maximizes information about the output and minimizes the shared information
between inputs. High generalization power and improved interpretability of the selected inputs are the consequences of this
analysis. 相似文献
6.
We study the evolution of the longitudinal asymmetry in solar activity through the wave packet technique applied to the period
domain of 25 – 31 days (centered at the 27-day solar rotation period) for the sunspot number and geomagnetic aa index. We observe the occurrence of alternating smaller and larger amplitudes of the 11-year cycle, resulting in a 22-year
periodicity in the 27-day signal. The evolution of the 22-year cycle shows a change of regime around the year 1912 when the
22-year period disappears from the sunspot number series and appears in the aa index. Other changes, such as a change in the correlation between solar and geomagnetic activity, took place at the same
time. Splitting the 27-day frequency domain of aa index shows an 11-year cycle for higher frequencies and a pure22-year cycle for lower frequencies, which we attribute to
higher latitude coronal holes. This evidence is particularly clear after 1940, which is another benchmark in the evolution
of the aa index. We discuss briefly the mechanisms that could account for the observed features of the 22-year cycle evolution. 相似文献
7.
Long-term changes in the magnetic activity of the Sun were studied in terms of the empirical mode decomposition that revealed
their essential modes. The occurrence of grand minima was also studied in their relation to long-term changes in sunspot activity
throughout the past 11 000 yr. Characteristic timescales of long-term changes in solar activity manifest themselves in the
occurrence of grand minima. A quantitative criterion has been defined to identify epochs of grand minima. This criterion reveals
the important role of secular and bicentennial activity variations in the occurrence of grand minima and relates their amplitudes
with the current activity level, which is variable on a millennial timescale. We have revealed specific patterns in the magnetic
activity between successive grand minima which tend to recur approximately every 2300 yr but occasionally alternate with irregular
changes. Such intermittent activity behavior indicates low dimensional chaos in the solar dynamo due to the interplay of its
dominant modes. The analysis showed that in order to forecast activity level in forthcoming cycles, one should take into account
long-term changes in sunspot activity on a ≈2300-yr timescale. The regularities revealed suggest solar activity to decrease
in the foreseeable future. 相似文献
8.
In this study we present the new R and I light curve solutions for the eclipsing binary systems RW CrB and VZ Leo, which for
VZ Leo is the first one in the literature. Our new observations have been analyzed using the Wilson-Devinney code from which
new geometric and photometric elements are derived. The geometry of both stars is that of a semi-detached binary system where
the secondary component fills its Roche lobe while the primary component is well inside. In the case of RW CrB, asymmetry
in the light curve was explained by a spot model. The orbital period changes of both systems were studied and the results
indicated a period decrease which can be explained by angular momentum loss. We also investigated the possibility of pulsations
of the primary components since these systems are mentioned as candidates of δ Sct type pulsation. However, a time-series analysis of the residual curves in the filter I does not indicate any evidence
of periodic light variation for both systems. Finally, we compared the results obtained for both binary stars to those of
similar systems. 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.
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
12.
We analyze a special kind of temporal fine structure in microwave radio emission for the 25 August 1999 solar flare observed
by the PMO spectrometer over the range of 4.5 – 7.5 GHz. This flare displays continuum emission after a group of reverse-slope
type III bursts around 6 GHz. High-resolution dynamic spectra reveal three evolving emission lines (EELs) following the type
III group. They are characterized by isolated, narrow, and continuous emission strips, which display frequency fluctuations
with time. Their frequency-drift rates are between −2 and 3 GHz s−1. Distinct from the EELs at lower frequencies, three EELs have a very short duration of a few seconds. They show an average
bandwidth of Δf≈330 MHz and a relative bandwidth of Δf/f≈0.057. This is the first time that this kind of fine structure has been observed around 6 GHz. 相似文献
13.
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
14.
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
15.
E. N. Parker 《中国天文和天体物理学报》2001,1(2):99-124
1 INTRODUCTION
The Sun is close enough to observe in some detail, and it shows that a star is more than
the traditional stable self-gravitating thermonuclear body established half a celltury ago. For
the fact is that out of sight beneath the visible surface the outward flow of heat from the
thermonuclear core drives hydrodynamics that generates magnetic fields. It is the complicated
dynamics of those magnetic fields that produces the modern mysteries of the active Sun. The… 相似文献
16.
As part of a program to estimate the solar spectrum back to the early twentieth century, we have generated fits to UV spectral
irradiance measurements from 1 – 410 nm. The longer wavelength spectra (150 – 410 nm) were fit as a function of two solar
activity proxies, the Mg ii core-to-wing ratio, or Mg ii index, and the total Ca ii K disk activity derived from ground based observations. Irradiance spectra at shorter wavelengths (1 – 150 nm) where used
to generate fits to the Mg ii core-to-wing ratio alone. Two sets of spectra were used in these fitting procedures. The fits at longer wavelengths (150
to 410 nm) were derived from the high-resolution spectra taken by the Solar Ultraviolet Spectral Irradiance Monitor (SUSIM)
on the Upper Atmospheric Research Satellite (UARS). Spectra measured by the Solar EUV Experiment (SEE) instrument on the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite were used for the fits at wavelengths from 1 to 150 nm. To generate fits between solar irradiance and solar
proxies, this study uses the above irradiance data, the NOAA composite Mg ii index, and daily Ca ii K disk activity determined from images measured by Big Bear Solar Observatory (BBSO). In addition to the fitting coefficients
between irradiance and solar proxies, other results from this study include an estimated relationship between the fraction
of the disk with enhanced Ca ii K activity and the Mg ii index, an upper bound of the average solar UV spectral irradiance during periods where the solar disk contains only regions
of the quiet Sun, as was believed to be present during the Maunder Minimum, as well as results indicating that slightly more
than 60% of the total solar irradiance (TSI) variability occurs between 150 and 400 nm. 相似文献
17.
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
18.
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
19.
The interpretation of multi-spacecraft heliospheric observations and three-dimensional reconstruction of structured and evolving solar wind is challenging. This is especially true for the interpretation of white-light structures observed by the Heliospheric Imagers (HI) onboard STEREO spacecraft since their appearance depends on three-dimensional geometric factors. Numerical simulations can provide global context and suggest what may and may not be observed. We use the heliospheric code ENLIL to simulate various scenarios of well-defined corotating solar wind streams and ejected transient density structures, and we generate from the solutions synthetic white-light images at various locations. We illustrate that corotating interaction regions (CIRs) show up differently in HI-2A and HI-2B and that they may appear as transient structures in HI-2A but not in HI-2B. This asymmetry is caused by differing Thomson scattering responses. Further, we illustrate that a given interplanetary coronal mass ejection (ICME) may exhibit drastically different white-light brightness depending on the observing position and that some ICMEs can eventually reach Earth without being detected by the imagers. Finally, we demonstrate application of the modeling system through simulation of the 24?–?25 January 2007, 31 December 2007 and 26 April 2008 CMEs. 相似文献