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1.
We present in this paper a statistical study aimed at understanding the possible relationship between surface magnetic field
variation and CME initiation. The three samples studied comprise 189 CME-source regions, 46 active regions, and 15 newly emerging
active regions. Both large-scale and small-scale variations of longitudinal magnetic fields of these regions are studied.
To quantitatively study these variations, three physical quantities are calculated: the average total magnetic flux (ATF),
the flux variation rate (FVR), and the normalized flux variation rate (NFVR). Our results show that 60% of the CME-source
regions are found to have magnetic flux increases during 12 hours before CME eruptions and 40% are found to have magnetic
flux decreases. The NFVR of CME-source regions are found to be statistically identical to those of active regions, averaged
over 111 hours, and significantly smaller than those of newly emerging active regions. In addition 91% of the CME-source regions
are found to have small-scale flux emergence, whereas small-scale flux emergences are also easily identified in active regions
during periods with no solar surface activity. Our study suggests that the relationship between flux emergence and CME eruption
is complex and the appearance of flux emergence alone is not unique for the initiation of CME eruption. 相似文献
2.
V.A. Kovalenko 《Planetary and Space Science》1988,36(12):1343-1358
An analysis has been made of the origin of long-term variations in flux density of solar wind particles (nv) for different velocity regimes. The study revealed a relationship of these variations to the area of the polar coronal holes (CH). It is shown that within the framework of the model under development, the main longterm variations of nv are a result of the latitude redistribution of the solar wind mass flux in the heliosphere and are due to changes in the large-scale geometry of the solar plasma flow in the corona.
A study has been made of the variations of nv for high speed solar wind streams. It is found that nv in high speed streams which are formed in CH, decreases from minimum to maximum solar activity. The analysis indicates that this decrease is attributable to the magnetic field strength increase in coronal holes.
It has been found that periods of rapid global changes of background magnetic fields on the Sun are accompanied by a reconfiguration of coronal magnetic fields, rapid changes in the length of quiescent filaments, and by an increase in the density of the particle flux of a high speed solar wind. It has been established that these periods precede the formation of CH, corresponding to the increase in solar wind velocity near the Earth and to enhancement of the level of geomagnetic disturbance. 相似文献
3.
H.M. Antia S. Basu F. Hill R. Howe R.W. Komm J. Schou 《Monthly notices of the Royal Astronomical Society》2001,327(3):1029-1040
We study the variation of the frequency splitting coefficients describing the solar asphericity in both GONG and MDI data, and use these data to investigate temporal sound-speed variations as a function of both depth and latitude during the period 1995–2000 and a little beyond. The temporal variations in even splitting coefficients are found to be correlated to the corresponding component of magnetic flux at the solar surface. We confirm that the sound-speed variations associated with the surface magnetic field are superficial. Temporally averaged results show a significant excess in sound speed around and latitude of 60°. 相似文献
4.
Small-scale solar magnetic fields demonstrate features of fractal intermittent behavior, which requires quantification. For this purpose we investigate how the observational estimate of the solar magnetic flux density \(B\) depends on resolution \(D\) in order to obtain the scaling \(\ln B_{D} = - k \ln D +a\) in a reasonably wide range. The quantity \(k\) demonstrates cyclic variations typical of a solar activity cycle. In addition, \(k\) depends on the magnetic flux density, i.e. the ratio of the magnetic flux to the area over which the flux is calculated, at a given instant. The quantity \(a\) demonstrates some cyclic variation, but it is much weaker than in the case of \(k\). The scaling obtained generalizes previous scalings found for the particular cycle phases. The scaling is typical of fractal structures. In our opinion, the results obtained trace small-scale action in the solar convective zone and its coexistence with the conventional large-scale solar dynamo based on differential rotation and mirror-asymmetric convection. 相似文献
5.
Large-scale distribution of the sunspot activity of the Sun has been analyzed by using a technique worked out previously (Erofeev, 1997) to study long-lived, non-axisymmetric magnetic structures with different periods of rotation. Results of the analysis have been compared with those obtained by analyzing both the solar large-scale magnetic field and large-scale magnetic field simulated by means of the well-known flux transport equation using the sunspot groups as a sole source of new magnetic flux in the photosphere. A 21-year period (1964–1985) has been examined.The rotation spectra calculated for the total time interval of two 11-year cycles indicate that sunspot activity consists of a series of discrete components (modes) with different periods of rotation. The largest-scale component of the sunspot activity reveals modes with 27-day and 28-day periods of rotation situated, correspondingly, in the northern and southern hemispheres of the Sun, and two modes with rotation periods of about 29.7 days situated in both hemispheres. Such a modal structure of the sunspot activity agrees well with that of the large-scale solar magnetic field. Moreover, the magnetic field distribution simulated with the flux transport equation also reveals the same modal structure. However, such an agreement between the large-scale solar magnetic field and both the sunspot activity and simulated magnetic field is unstable in time; so, it is absent in the northern hemisphere of the Sun during solar cycle No. 20. Thus the sources of magnetic flux responsible for formation of the large-scale, rigidly rotating magnetic patterns appear to be closely connected, but are not identical with the discrete modes of the sunspot activity. 相似文献
6.
We analyse data of magnetic flux emergence for solar cycles 21 and 22, Helios 1 interplanetary shocks for cycle 21, and sudden storm commencements (SSCs) for cycles 11–22. A dominant variation of 3-year periodicity was found for all three phenomena during cycles 21 and 22. This indicates a correlation and a possible influence of the rate of solar magnetic flux emergence to produce the interplanetary phenomena studied in this work; in particular, the suggested role of coronal mass ejections as a means by which magnetic flux and stresses are taken out of the corona seems to be plausible. When taking cycles 11–22 in SSCs, the main periodicity changes to around 4 years; this may be an indication of flux emergence rate variations over the cycles. 相似文献
7.
P. Ambro 《Journal of Astrophysics and Astronomy》2000,21(3-4):315-318
Horizontal large-scale velocity field describes horizontal displacement of the photospheric magnetic flux in zonal and meridian
directions. The flow systems of solar plasma, constructed according to the velocity field, create the large-scale cellular-like
patterns with up-flow in the center and the down-flow on the boundaries. Distribution of the largescale horizontal eddies
(with characteristic scale length from 350 to 490 Mm) was found in the broad equatorial zone, limited by 60‡ latitude
circles on both hemispheres. The zonal averages of the zonal and meridian velocities, and the total horizontal velocity for
each Carrington rotation during the activity cycles no. 21 and 22 varies during the 11-yr activity cycle. Plot of RMS values
of total horizontal velocity is shifted about 1.6 years before the similarly shaped variation of the magnetic flux. 相似文献
8.
U. M. Leiko 《Kinematics and Physics of Celestial Bodies》2012,28(3):142-148
The cyclicity of weak local and strong large-scale components of the low-latitude solar magnetic field during the last three cycles of solar activity is studied using the average monthly values for the total area of sunspots and general magnetic field of the sun as a star. A local decrease in the value of magnetic flux is found for both components of the magnetic field in the phase of growing solar activity. This decrease coincides in time with the intervals of monopolarity for the polar magnetic field of the sun. 相似文献
9.
Recent global magnetohydrodynamical simulations of solar convection producing a large-scale magnetic field undergoing regular, solar-like polarity reversals also present related cyclic modulations of large-scale flows developing in the convecting layers. Examination of these simulations reveal that the meridional flow, a crucial element in flux transport dynamos, is driven at least in part by the Lorentz force associated with the cycling large-scale magnetic field. This suggests that the backreaction of the field onto the flow may have a pronounced influence on the long-term evolution of the dynamo. We explore some of the associated dynamics using a low-order dynamo model that includes this Lorentz force feedback. We identify several characteristic solutions which include single period cycles, period doubling and chaos. To emulate the role of turbulence in the backreaction process we subject the model to stochastic fluctuations in the parameter that controls the Lorentz force amplitude. We find that short term fluctuations produce long-term modulations of the solar cycle and, in some cases, grand minima episodes where the amplitude of the magnetic field decays to near zero. The chain of events that triggers these quiescent phases is identified. A subsequent analysis of the energy transfer between large-scale fields and flows in the global magnetohydrodynamical simulation of solar convection shows that the magnetic field extracts energy from the solar differential rotation and deposits part of that energy into the meridional flow. The potential consequences of this marked departure from the kinematic regime are discussed in the context of current solar cycle modeling efforts based on flux transport dynamos. 相似文献
10.
High-resolution photographs of the photospheric network taken in the Caii K 3933 Å line and at 4308 Å are analysed in order to study the variation, in latitude and over the sunspot cycle, of its density (the density is defined as the number of network elements - also called facular points - per surface unity). It appears that the density of the photospheric network is not distributed uniformly at the surface of the Sun: on September 1983, during the declining phase of the current activity cycle, it was weakened at both the low (equatorial) and high (polar) active latitudes, while it was tremendously enhanced toward the pole. The density at the equator is varying in antiphase to the sunspot number: it increases by a factor 3 or more from maximum to minimum of activity. As a quantum of magnetic flux is associated to each network element, density variations of the photospheric network express in fact variations of the quiet Sun magnetic flux. It thus results that the quiet Sun magnetic flux is not uniformly distributed in latitude and not constant over the solar cycle: it probably varies in antiphase to the flux in active regions.The variation over the solar cycle and the latitude distribution of photospheric network density are compared to those of X-ray bright points and ephemeral active regions: there are no clear correlations between these three kinds of magnetic features. 相似文献
11.
A study of the upper-atmosphere variations induced by solar activity was made by using 29,574 densities derived from the drag of 10 satellites in the interval 1958–1971. In a comparison of the respective merits of the Ca II-plage index and the 10.7 cm solar flux to represent the erratic (‘27 day’) component of the variation, the latter is shown to give invariably better results. The ratio of the temperature variations to the variations of the decimetric flux is shown to vary considerably with solar activity, but little with height or with local solar time. The time lag of the atmospheric variations behind those of the decimetric flux varies from a minimum of 0.9 day at noon to 1.6 days at midnight. 相似文献
12.
L. Wallace 《Icarus》1984,59(3):367-375
Previous work on the atmosphere of Uranus is extended to Neptune. The variation of effective temperature with latitude and season is evaluated within the approximations that the redistribution of internal heat in the interior results in the temperature at fixed pressure near the top of the convective region being independent of latitude and time, and that the transport of heat in the atmosphere is by means of radiation and convection. Meridional heat transport in the atmosphere is neglected. It is found that as the absorbed solar flux varies with season the flux of internal heat varies in the opposite sense such that the variation in the sum of the two is much smaller than the variation in either. The resulting variation in the flux radiated out the top of the atmosphere, which responds to the sum of the internal and absorbed solar fluxes, is substantially smaller than for Uranus because of the much larger flux of internal heat. For Neptune, the time-averaged effective temperature at the pole is ≈0.2°K greater than at the equator and the seasonal variation in the polar effective temperature is ≈0.8°K. 相似文献
13.
Interplanetary observations from Helios 1, Helios 2, and IMP-8 spacecraft during 1976 and 1977, namely the early portion of solar cycle 21, have been used to investigate the latitudinal gradients of the solar wind parameters with respect to the angular displacement from the current sheet inferred from synoptic HAO white-light maps of the solar corona at 1.75 solar radii. A latitudinal belt of ±25 deg around the current sheet has been investigated. Large gradients for solar wind flow speed, proton density and temperature have been found. Smoother gradients were also found for particle flux, kinetic, gravitational and thermal energy density flux. All these gradients revealed to become smoother going towards the solar cycle's maximum. Neither latitudinal nor temporal variations were identified for magnetic and thermal energy density. A remarkable result of this study is that the momentum flux density and the total energy flux density which other authors found to be independent of any longitudinal stream structure were also found to be independent of any latitudinal structure. Moreover, these two parameters did not show any temporal variation during the period of interest. 相似文献
14.
U. M. Leiko 《Kinematics and Physics of Celestial Bodies》2016,32(6):299-306
The results of an analysis of the north–south asymmetry in solar activity and solar magnetic fields are reported. The analysis is based on solar mean magnetic field and solar polar magnetic field time series, 1975–2015 (http://wso.stanford.edu), and the Greenwich sunspot data, 1875–2015 (http://solarscience.msfc.nasa.gov/greenwch.shtml). A long-term cycle (small-scale magnetic fields, toroidal component) of ~140 years is identified in the north–south asymmetry in solar activity by analyzing the cumulative sum of the time series for the north–south asymmetry in the area of sunspots. A comparative analysis of the variations in the cumulative sums of the time series composed of the daily values of the sun’s global magnetic field and in the asymmetry of the daily sunspot data over the time interval 1975–2015 shows that the photospheric large-scale magnetic fields may also have a similar long-term cycle. The variations in the asymmetry of large-scale and small-scale solar magnetic fields (sunspot area) are in sync until 2005.5 and in antiphase since then. 相似文献
15.
Based on SOHO/MDI data (an archive of magnetic maps with a resolution of ～2″), we have investigated the dynamics of the small-scale background magnetic field on the Sun in solar cycle 23. The cyclic variations and surface structure of the background magnetic field have been analyzed using the mean estimates of 〈B〉 and 〈B 2〉 of the observed magnetic field strength B for various solar surface areas and at various B levels. We have established that the cyclic variations of 〈2〉 at latitudes below 30° are essentially similar to those of the total radio flux F 10.7. A significant difference between the background magnetic fields in the northern and southern solar hemispheres persisting throughout the solar cycle has been detected. We have found the effect of background magnetic field growth toward the solar limb and concluded that the transversal component in the background magnetic field is significant. The relatively weak small-scale background magnetic fields are shown to form a special population with its own special laws of cyclic variation. 相似文献
16.
D. V. Erofeev 《Solar physics》1996,167(1-2):25-45
Discrete rigidly rotating components (modes) of the large-scale solar magnetic field have been investigated. We have used a specially calculated basic set of functions to resolve the observed magnetic field into discrete components. This adaptive set of functions, as well as the expansion coefficients, have been found by processing a series of digitized synoptic maps of the background magnetic field over a 20-year period. As a result, dependences have been obtained which describe the spatial structure and the temporal evolution of the 27-day and 28-day rigidly rotating modes of the Sun's magnetic field.The spatial structure of the modes has been compared with simulations based on the known flux-transport equation. In the simulations, the rigidly rotating modes were regarded as stationary states of the magnetic field whose rigid rotation and stability were maintained by a balance between the emergence of magnetic flux from stationary sources located at low latitudes and the horizontal transport of flux by turbulent diffusion and poleward directed meridional flow. Under these assumptions, the structure of the modes is determined solely by the horizontal velocity field of the plasma, except for the low-latitude zone where sources of magnetic flux concentrate. We have found a detailed agreement between the simulations and the results of the data analysis, provided that the amplitude of the meridional flow velocity and the diffusion constant are equal to 9.5 m s–1 and 600 km2 s–1, respectively.The analysis of the expansion coefficients has shown that the rigidly rotating modes undergo rapid step-like variations which occur quasi-periodically with a period of about two years. These variations are caused by separate surges of magnetic flux in the photosphere, so that each new surge gives rise to a rapid replacement of old large-scale magnetic structures by newly arisen ones. 相似文献
17.
Large-scale solar eruptions, known as coronal mass ejections (CMEs), are regarded as the main drivers of space weather. The exact trigger mechanism of these violent events is still not completely clear; however, the solar magnetic field indisputably plays a crucial role in the onset of CMEs. The strength and morphology of the solar magnetic field are expected to have a decisive effect on CME properties, such as size and speed. This study aims to investigate the evolution of a magnetic configuration when driven by the emergence of new magnetic flux in order to get a better insight into the onset of CMEs and their magnetic structure. The three-dimensional, time-dependent equations for ideal magnetohydrodynamics are numerically solved on a spherical mesh. New flux emergence in a bipolar active region causes destabilisation of the initial stationary structure, finally resulting in an eruption. The initial magnetic topology is suitable for the ??breakout?? CME scenario to work. Although no magnetic flux rope structure is present in the initial condition, highly twisted magnetic field lines are formed during the evolution of the system as a result of internal reconnection due to the interaction of the active region magnetic field with the ambient field. The magnetic energy built up in the system and the final speed of the CME depend on the strength of the overlying magnetic field, the flux emergence rate, and the total amount of emerged flux. The interaction with the global coronal field makes the eruption a large-scale event, involving distant parts of the solar surface. 相似文献
18.
From late October to the beginning of November 2003, a series of intense solar eruptive events took place on the Sun. More
than six active regions (ARs), including three large ARs (NOAA numbers AR 10484, AR 10486, and AR 10488), were involved in
the activity. Among the six ARs, four of them bear obviously quasi-simultaneous emergence of magnetic flux. Based on the global
Hα and SOHO/EIT EUV observations, we found that a very long filament channel went through the six ARs. This implies that there
is a magnetic connection among these ARs. The idea of large-scale magnetic connectivity among the ARs is supported by the
consistency of the same chirality in the three major ARs and in their associated magnetic clouds. Although the detailed mechanisms
for the quasi-simultaneous flux emergence and the large-scale flux system formation need to be extensively investigated, the
observations provide new clues in studying the global solar activity. 相似文献
19.
The structure of electric current and magnetic helicity in the solar corona is closely linked to solar activity over the 11-year cycle, yet is poorly understood. As an alternative to traditional current-free “potential-field” extrapolations, we investigate a model for the global coronal magnetic field which is non-potential and time-dependent, following the build-up and transport of magnetic helicity due to flux emergence and large-scale photospheric motions. This helicity concentrates into twisted magnetic flux ropes, which may lose equilibrium and be ejected. Here, we consider how the magnetic structure predicted by this model – in particular the flux ropes – varies over the solar activity cycle, based on photospheric input data from six periods of cycle 23. The number of flux ropes doubles from minimum to maximum, following the total length of photospheric polarity inversion lines. However, the number of flux rope ejections increases by a factor of eight, following the emergence rate of active regions. This is broadly consistent with the observed cycle modulation of coronal mass ejections, although the actual rate of ejections in the simulation is about a fifth of the rate of observed events. The model predicts that, even at minimum, differential rotation will produce sheared, non-potential, magnetic structure at all latitudes. 相似文献
20.
Surface magnetic fields during the solar activity cycle 总被引：1，自引：0，他引：1
We examine magnetic field measurements from Mount Wilson that cover the solar surface over a 13 1/2 year interval, from 1967 to mid-1980. Seen in long-term averages, the sunspot latitudes are characterized by fields of preceding polarity, while the polar fields are built up by a few discrete flows of following polarity fields. These drift speeds average about 10 m s-1 in latitude - slower early in the cycle and faster later in the cycle - and result from a large-scale poleward displacement of field lines, not diffusion. Weak field plots show essentially the same pattern as the stronger fields, and both data indicate that the large-scale field patterns result only from fields emerging at active region latitudes. The total magnetic flux over the solar surface varies only by a factor of about 3 from minimum to a very strong maximum (1979). Magnetic flux is highly concentrated toward the solar equator; only about 1% of the flux is at the poles. Magnetic flux appears at the solar surface at a rate which is sufficient to create all the flux that is seen at the solar surface within a period of only 10 days. Flux can spread relatively rapidly over the solar surface from outbreaks of activity. This is presumably caused by diffusion. In general, magnetic field lines at the photospheric level are nearly radial.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands. 相似文献