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1.
We present the results of a statistical study of the solar cycle based on the analysis of the superficial toroidal magnetic
field component phase space. The magnetic field component used to create the embedded phase space was constructed from monthly
sunspot number observations since 1750. The phase space was split into 32 sections (or time instants) and the average values
of the orbits on this phase space were calculated (giving the most probable cycle). In this phase space it is shown that the
magnetic field on the Sun’s surface evolves through a set of orbits that go around a mean orbit (i.e., the most probable magnetic cycle that we interpret as the equilibrium solution). It follows that the most probable cycle
is well represented by a van der Pol oscillator limit curve (equilibrium solution), as can be derived from mean-field dynamo
theory. This analysis also retrieves the empirical Gnevyshev – Ohl’s rule between the first and second parts of the solar
magnetic cycle. The sunspot number evolution corresponding to the most probable cycle (in phase space) is presented. 相似文献
2.
Historically, our understanding of the solar magnetic field has been shaped by an interplay between theoretical ideas about the subsurface dynamo and precise measurements of magnetic flux at the level of the photosphere. Today we have an unprecedented ability to measure, or to infer from measurements, properties of the magnetic field at every level from the solar interior to interplanetary space, although photospheric observations still lead the way in completeness and precision. I review the state of our capabilities to measure or calculate the magnetic field and suggest that the next major goal should be to follow specific magnetic structures in space and time from before they emerge until they can no longer be detected at any level. 相似文献
3.
S.-I. Akasofu 《Planetary and Space Science》1984,32(11):1469-1496
The presently prevailing theories of sunspots and solar flares rely on the hypothetical presence of magnetic flux tubes beneath the photosphere and the two subsequent hypotheses, their emergence above the photosphere and explosive magnetic reconnection, converting magnetic energy carried by the flux tubes for solar flare energy.In this paper, we pay attention to the fact that there are large-scale magnetic fields which divide the photosphere into positive and negative (line-of-sight) polarity regions and that they are likely to be more fundamental than sunspot fields, as emphasized most recently by McIntosh (1981). A new phenomenological model of the sunspot pair formation is then constructed by considering an amplification process of these largescale fields near their boundaries by shear flows, including localized vortex motions. The amplification results from a dynamo process associated with such vortex flows and the associated convergence flow in the largescale fields.This dynamo process generates also some of the familiar “force-free” fields or the “sheared” magnetic fields in which the magnetic field-aligned currents are essential. Upward field-aligned currents generated by the dynamo process are carried by downward streaming electrons which are expected to be accelerated by an electric potential structure; a similar structure is responsible for accelerating auroral electrons in the magnetosphere. Depending on the magnetic field configuration and the shear flows, the current-carrying electrons precipitate into different geometrical patterns, causing circular flares, umbral flares, two-ribbon flares, etc. Thus, it is suggested that “low temperature flares” are directly driven by the photospheric dynamo process. 相似文献
4.
We present a straightforward comparison of model calculations for the α-effect, helicities, and magnetic field line twist
in the solar convection zone with magnetic field observations at atmospheric levels. The model calculations are carried out
in a mixing-length approximation for the turbulence with a profile of the solar internal rotation rate obtained from helioseismic
inversions. The magnetic field data consist of photospheric vector magnetograms of 422 active regions for which spatially-averaged
values of the force-free twist parameter and of the current helicity density are calculated, which are then used to determine
latitudinal profiles of these quantities. The comparison of the model calculations with the observations suggests that the
observed twist and helicity are generated in the bulk of the convection zone, rather than in a layer close to the bottom.
This supports two-layer dynamo models where the large-scale toroidal field is generated by differential rotation in a thin
layer at the bottom while the α-effect is operating in the bulk of the convection zone. Our previous observational finding
was that the moduli of the twist factor and of the current helicity density increase rather steeply from zero at the equator
towards higher latitudes and attain a certain saturation at about 12 – 15∘. In our dynamo model with algebraic nonlinearity, the increase continues, however, to higher latitudes and is more gradual.
This could be due to the neglect of the coupling between small-scale and large-scale current and magnetic helicities and of
the latitudinal drift of the activity belts in the model. 相似文献
5.
We analyse data from Hinode spacecraft taken over two 54-minute periods during the emergence of AR 11024. We focus on small-scale portions within the
observed solar active region and discover the appearance of very distinctive small-scale and short-lived dark features in
Ca ii H chromospheric filtergrams and Stokes I images. The features appear in regions with close-to-zero longitudinal magnetic field, and are observed to increase in length
before they eventually disappear. Energy release in the low chromospheric line is detected while the dark features are fading.
Three complete series of these events are detected with remarkably similar properties, i.e. lifetime of ≈ 12 min, maximum length and area of 2 – 4 Mm and 1.6 – 4 Mm2, respectively, and all with associated brightenings. In time series of magnetograms a diverging bipolar configuration is
observed accompanying the appearance of the dark features and the brightenings. The observed phenomena are explained as evidencing
elementary flux emergence in the solar atmosphere, i.e. small-scale arch filament systems rising up from the photosphere to the lower chromosphere with a length scale of a few solar
granules. Brightenings are explained as being the signatures of chromospheric heating triggered by reconnection of the rising
loops (once they have reached chromospheric heights) with pre-existing magnetic fields, as well as being due to reconnection/cancellation
events in U-loop segments of emerging serpentine fields. The characteristic length scale, area and lifetime of these elementary
flux emergence events agree well with those of the serpentine field observed in emerging active regions. We study the temporal
evolution and dynamics of the events and compare them with the emergence of magnetic loops detected in quiet Sun regions and
serpentine flux emergence signatures in active regions. The physical processes of the emergence of granular-scale magnetic
loops seem to be the same in the quiet Sun and active regions. The difference is the reduced chromospheric emission in the
quiet Sun attributed to the fact that loops are emerging in a region of lower ambient magnetic field density, making interactions
and reconnection less likely to occur. Incorporating the novel features of granular-scale flux emergence presented in this
study, we advance the scenario for serpentine flux emergence. 相似文献
6.
D. Sokoloff H. Zhang K. M. Kuzanyan V. N. Obridko D. N. Tomin V. N. Tutubalin 《Solar physics》2008,248(1):17-28
A comparison between the two tracers of magnetic field mirror asymmetry in solar active regions – twist and current helicity
– is presented. It is shown that for individual active regions these tracers do not possess visible similarity but averaging
by time over the solar cycle, or by latitude, reveals similarities in their behavior. The main property of the data set is
antisymmetry over the solar equator. Considering the evolution of helical properties over the solar cycle we find signatures
of a possible sign change at the beginning of the cycle, though more systematic observational data are required for a definite
confirmation. We discuss the role of both tracers in the context of solar dynamo theory. 相似文献
7.
J. K. Lawrence 《Solar physics》1991,135(2):249-259
Recent observations have indicated that magnetic field elements are distributed on the Sun in fractal patterns with dimension D < 2. We suggest that the transport of magnetic field elements across the solar surface should be treated as diffusion on a fractal geometry. We review a semi-analytical, theoretical treatment of fractal diffusion. Comparison with observations of small-scale motions of solar magnetic flux concentrations indicates that fractal diffusion may be taking place with dimension in the range 1.3 to 1.8. It is shown that, compared to the predictions that would be made for two-dimensional diffusion, fractal diffusion in this range would lead to an increased level of in situ flux cancellation in decaying active regions by 7% to 35%. Other work in specialities outside of solar physics may be useful in explaining solar magnetic phenomena. 相似文献
8.
We study the relationship between full-disk solar radiative flux at different wavelengths and average solar photospheric magnetic-flux
density, using daily measurements from the Kitt Peak magnetograph and other instruments extending over one or more solar cycles.
We use two different statistical methods to determine the underlying nature of these flux – flux relationships. First, we
use statistical correlation and regression analysis and show that the relationships are not monotonic for total solar irradiance
and for continuum radiation from the photosphere, but are approximately linear for chromospheric and coronal radiation. Second,
we use signal theory to examine the flux – flux relationships for a temporal component. We find that a well-defined temporal
component exists and accounts for some of the variance in the data. This temporal component arises because active regions
with high magnetic-field strength evolve, breaking up into small-scale magnetic elements with low field strength, and radiative
and magnetic fluxes are sensitive to different active-region components. We generate empirical models that relate radiative
flux to magnetic flux, allowing us to predict spectral-irradiance variations from observations of disk-averaged magnetic-flux
density. In most cases, the model reconstructions can account for 85 – 90% of the variability of the radiative flux from the
chromosphere and corona. Our results are important for understanding the relationship between magnetic and radiative measures
of solar and stellar variability. 相似文献
9.
我们在文[1]的启发下,计算了磁中性线附近异极性磁区相互入侵(或挤压)引起的等离子体动力学问题。气体初态取用流行的宁静太阳光球色球大气模型,即非等温的密度指数变化的重力分层大气。采用Lagrangian格式数值求解自洽的MHD方程,这可使入侵力学变得直观明显——磁场随流体而运动。我们的新结果是入侵流动在光球低层产生出强的水平磁场(即强的横向场),但光球高层和色球低层的磁结构却变化不大,有力地支持了文[13]提出的光球色球里可能出现磁流体力学间断面的概念。入侵确实在磁中性线附近建立了电流片,但这电流片主要在光球低层,其量级和观测一致。另外还显示垂直下降运动也可能导致异极磁区的入侵。尽管在MHD~1方程里包含了电阻耗散和热传导流,但计算证明它们对入侵力学影响不大,热传导的作用只是使气体温度分布逐渐趋于宁静太阳分布(尽管高度变了)。 相似文献
10.
首先是对太阳光球亮点近年来研究工作的总结。光球亮点是一种发生在太阳光球上宁静区域的的小尺度和短寿命增亮现象,平均直径在100～300knm之间,平均寿命约为几分钟。光球亮点的研究对于光球辐射和磁场性质的认识具有重要意义。过去的观测显示,绝大多数光球亮点的产生和演化与磁场,特别是光球上的小尺度磁场的演化密切相关,比如,两个同极性磁场的合并,或者反极性磁场的对消,或者一个同极性磁场的分裂,均可以促使光球亮点产生或消失。基于这样的观测结果,统计研究了2722个光球亮点(1600A)与光球上偶极磁元的关系,发现大约有1/3的光球亮点出现在偶极磁元中心附近。 相似文献
11.
Dibyendu Nandy 《Astrophysics and Space Science》2002,282(1):209-219
We report here results from a dynamo model developed on the lines of the Babcock-Leighton idea that the poloidal field is
generated at the surface of the Sun from the decay of active regions. In this model magnetic buoyancy is handled with a realistic
recipe – wherein toroidal flux is made to erupt from the overshoot layer wherever it exceeds a specified critical field B
c (105 G). The erupted toroidal field is then acted upon by the α-effect near the surface to give rise to the poloidal field. In
this paper we study the effect of buoyancy on the dynamo generated magnetic fields. Specifically, we show that the mechanism
of buoyant eruption and the subsequent depletion of the toroidal field inside the overshoot layer, is capable of constraining
the magnitude and distribution of the magnetic field there. We also believe that a critical study of this mechanism may give
us new information regarding the solar interior and end with an example, where we propose a method for estimating an upper
limit of the difusivity within the overshoot layer.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
12.
J. H. Piddington 《Astrophysics and Space Science》1982,87(1-2):477-478
This paper is largely a reply to Cowling's review of the present status of cosmic dynamo theory and its alternatives of primordial or fossil field models. Central is the question of turbulent diffusion, without which plasma dynamos will not work but primordial magnetic fields are retained. Turbulence does not shred or divide fields into small-scale elements as claimed; instead it creates these elements in addition to the large-scale field which remains after Ohmic diffusion has destroyed the small fields. The significance of the existence of a terrestrial dynamo is stressed and various objections to the existence of a solar-type dynamo are discussed, including the steady divergence of theory and observational evidence over a quarter century. Cowling's criticisms of the primordial field theory are discussed; these include turbulent diffusion, the timing of the solar magnetic cycle, and the importance attached to observations in active and quiet magnetic regions.Since this paper was communicated, a personal communication from Professor Cowling has partially resolved the difference of opinion about turbulent diffusion and its effects. This is discussed in a letter to the Editor, at the end of this volume, p. 477. 相似文献
13.
S. Liu 《Astrophysics and Space Science》2014,351(2):409-416
Magnetic fields dominate most solar activities, there exist direct relations between solar flare and the distributions of magnetic field, and also its corresponding magnetic energy. In this paper, the statistical results about the relationships between the spatial magnetic field and solar flare are given basing on vector magnetic field observed by the Solar Magnetic Field Telescope (SMFT) at Huairou Solar Observing Station (HSOS). The spatial magnetic fields are obtained by extrapolated photosphere vector magnetic field observed by SMFT. There are 23 active regions with flare eruption are chosen as data samples, which were observed from 1997 to 2007. The results are as follows: 1. Magnetic field lines become lower after flare for 16 (69 %) active regions; 2. The free energy are decreased after flare for 17 (74 %) active regions. It can conclude that for most active regions the changes of magnetic field after solar flare re coincident with the previous observations and studies. 相似文献
14.
Recent helioseismic observations have found strong fluctuations at a period of about 1.3 years in the rotation speed around
the tachocline in the deep solar convection layer. Similar mid-term quasi-periodicities (MTQP; periods between 1–2 years)
are known to occur in various solar atmospheric and heliospheric parameters for centuries. Since the deep convection layer
is the expected location of the solar magnetic dynamo, its fluctuations could modulate magnetic flux generation and cause
related MTQP fluctuations at the solar surface and beyond. Accordingly, it is likely that the heliospheric MTQP periodicities
reflect similar changes in solar dynamo activity. Here we study the occurrence of the MTQP periodicities in the near and distant
heliosphere in the solar wind speed and interplanetary magnetic field observed by several satellites at 1 AU and by four interplanetary
probes (Pioneer 10 and 11 and Voyager 1 and 2) in the outer heliosphere. The overall structure of MTQP fluctuations in the different locations of the heliosphere
is very consistent, verifying the solar (not heliospheric) origin of these periodicities. We find that the mid-term periodicities
were particularly strong during solar cycle 22 and were observed at two different periods of 1.3 and 1.7 years simultaneously.
These periodicities were latitudinally organized so that the 1.3-year periodicity was found in solar wind speed at low latitudes
and the 1.7-year periodicity in IMF intensity at mid-latitudes. While all heliospheric results on the 1.3-year periodicity
are in a good agreement with helioseismic observations, the 1.7-year periodicity has so far not been detected in helioseismic
observations. This may be due to temporal changes or due to the helioseismic method where hemispherically antisymmetric fluctuations
would so far have remained hidden. In fact, there is evidence that MTQP fluctuations may occur antisymmetrically in the northern
and southern solar hemisphere. Moreover, we note that the MTQP pattern was quite different during solar cycles 21 and 22,
implying fundamental differences in solar dynamo action between the two halves of the magnetic cycle. 相似文献
15.
H. Q. Zhang 《Astrophysics and Space Science》2006,305(3):211-224
We discuss the study of solar magnetic fields based on the photospheric vector magnetograms of solar active regions which were obtained at Huairou Solar Observing Station near Beijing in the period of 22nd and 23th solar cycles. The measurements of the chromospheric magnetic field and the spatial configuration of the field at the lower solar atmosphere inferred by the distribution of the solar photospheric and chromospheric magnetic field. After the analysis on the formation process of delta configuration in some super active regions based on the photospheric vector magnetogram observations, some results are obtained: (1) The analysis of magnetic writhe of whole active regions cannot be limited in the strong field of sunspots, because the contribution of the fraction of decayed magnetic field is non-negligible. (2) The magnetic model of kink magnetic ropes, proposed to be generated in the subatmosphere, is not consistent with the evolution of large-scale twisted photospheric transverse magnetic field and the relationship with magnetic shear in some delta active regions completely. (3) The proposition is that the large-scale delta active regions are formed from contribution by highly sheared non-potential magnetic flux bundles generated in the subatmosphere. We present some results of a study of the magnetic helicity. We also compare these results with other data sets obtained by magnetographs (or Stokes polarimeters) at different observatories, and analyze the basic chirality of the magnetic field in the solar atmosphere. 相似文献
16.
K. F. Tapping D. Boteler P. Charbonneau A. Crouch A. Manson H. Paquette 《Solar physics》2007,246(2):309-326
We develop a model for estimating solar total irradiance since 1600 AD using the sunspot number record as input, since this
is the only intrinsic record of solar activity extending back far enough in time. Sunspot number is strongly correlated, albeit
nonlinearly with the 10.7-cm radio flux (F
10.7), which forms a continuous record back to 1947. This enables the nonlinear relationship to be estimated with usable accuracy
and shows that relationship to be consistent over multiple solar activity cycles. From the sunspot number record we estimate
F
10.7 values back to 1600 AD. F
10.7 is linearly correlated with the total amount of magnetic flux in active regions, and we use it as input to a simple cascade
model for the other magnetic flux components. The irradiance record is estimated by using these magnetic flux components plus
a very rudimentary model for the modulation of energy flow to the photosphere by the subphotospheric magnetic flux reservoir
feeding the photospheric magnetic structures. Including a Monte Carlo analysis of the consequences of measurement and fitting
errors, the model indicates the mean irradiance during the Maunder Minimum was about 1 ± 0.4 W m−2 lower than the mean irradiance over the last solar activity cycle. 相似文献
17.
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
18.
The availability of vector-magnetogram sequences with sufficient accuracy and cadence to estimate the temporal derivative
of the magnetic field allows us to use Faraday’s law to find an approximate solution for the electric field in the photosphere,
using a Poloidal–Toroidal Decomposition (PTD) of the magnetic field and its partial time derivative. Without additional information,
however, the electric field found from this technique is under-determined – Faraday’s law provides no information about the
electric field that can be derived from the gradient of a scalar potential. Here, we show how additional information in the
form of line-of-sight Doppler-flow measurements, and motions transverse to the line-of-sight determined with ad-hoc methods such as local correlation tracking, can be combined with the PTD solutions to provide much more accurate solutions
for the solar electric field, and therefore the Poynting flux of electromagnetic energy in the solar photosphere. Reliable,
accurate maps of the Poynting flux are essential for quantitative studies of the buildup of magnetic energy before flares
and coronal mass ejections. 相似文献
19.
Given the complexity involved in a flux-transport-type dynamo driven by both Babcock – Leighton and tachocline α effects, we present here a step-by-step procedure for building a flux-transport dynamo model calibrated to the Sun as a guide
for anyone who wishes to build this kind of model. We show that a plausible sequence of steps to reach a converged solution
in such a dynamo consists of (i) numerical integration of a classical α – ω dynamo driven by a tachocline α effect, (ii) continued integration with inclusion of meridional circulation to convert the model into a flux-transport dynamo
driven by only a tachocline α effect, (iii) final integration with inclusion of a Babcock – Leighton surface α effect, resulting in a flux-transport dynamo that can be calibrated to obtain a close fit of model output with solar observations. 相似文献
20.
Guided by the recent observational result that the meridional circulation of the Sun becomes weaker at the time of the sunspot
maximum, we have included a parametric quenching of the meridional circulation in solar dynamo models such that the meridional
circulation becomes weaker when the magnetic field at the base of the convection zone is stronger. We find that a flux transport
solar dynamo tends to become unstable on including this quenching of meridional circulation if the diffusivity in the convection
zone is less than about 2×1011 cm2 s−1. The quenching of α, however, has a stabilizing effect and it is possible to stabilize a dynamo with low diffusivity with sufficiently strong
α-quenching. For dynamo models with high diffusivity, the quenching of meridional circulation does not produce a large effect
and the dynamo remains stable. We present a solar-like solution from a dynamo model with diffusivity 2.8×1012 cm2 s−1 in which the quenching of meridional circulation makes the meridional circulation vary periodically with solar cycle as observed
and does not have any other significant effect on the dynamo. 相似文献