共查询到20条相似文献，搜索用时 31 毫秒
1.
V. G. Fainshtein N. N. Stepanian Z. S. Akhtemov G. V. Rudenko E. V. Silakova 《Bulletin of the Crimean Astrophysical Observatory》2011,107(1):51-59
The radial component Br of magnetic field was calculated in the potential approximation and the synoptic maps of Br for several
heights in the Solar atmosphere were constructed based on observations of the photospheric magnetic field made on the old
magnetograph at the US Kitt Peak National Observatory and on the new SOLIS magnetograph at the US National Solar Observatory
for cycle 23 (the years 1997–2009). Parameters of large-scale structures of magnetic field with positive and negative polarities
were determined at seven heights in the Sun’s atmosphere—from the photosphere (H = Ro) to H = 2.5 Ro (Ro is the Solar radius). The processes of polar reversal for polar fields and changing of the sector structure
of the field at middle latitudes were observed. Characteristic lifespans and rotations were ascertained. The general picture
of variations of the large-scale solar magnetic field during cycle 23 was put forward. Two types of boundaries of large magnetic
structures at various heights were identified. 相似文献
2.
Thomas R. Metcalf Marc L. DeRosa Carolus J. Schrijver Graham Barnes Adriaan A. van Ballegooijen Thomas Wiegelmann Michael S. Wheatland Gherardo Valori James M. McTtiernan 《Solar physics》2008,247(2):269-299
We compare a variety of nonlinear force-free field (NLFFF) extrapolation algorithms, including optimization, magneto-frictional,
and Grad – Rubin-like codes, applied to a solar-like reference model. The model used to test the algorithms includes realistic
photospheric Lorentz forces and a complex field including a weakly twisted, right helical flux bundle. The codes were applied
to both forced “photospheric” and more force-free “chromospheric” vector magnetic field boundary data derived from the model.
When applied to the chromospheric boundary data, the codes are able to recover the presence of the flux bundle and the field’s
free energy, though some details of the field connectivity are lost. When the codes are applied to the forced photospheric
boundary data, the reference model field is not well recovered, indicating that the combination of Lorentz forces and small
spatial scale structure at the photosphere severely impact the extrapolation of the field. Preprocessing of the forced photospheric
boundary does improve the extrapolations considerably for the layers above the chromosphere, but the extrapolations are sensitive
to the details of the numerical codes and neither the field connectivity nor the free magnetic energy in the full volume are
well recovered. The magnetic virial theorem gives a rapid measure of the total magnetic energy without extrapolation though,
like the NLFFF codes, it is sensitive to the Lorentz forces in the coronal volume. Both the magnetic virial theorem and the
Wiegelmann extrapolation, when applied to the preprocessed photospheric boundary, give a magnetic energy which is nearly equivalent
to the value derived from the chromospheric boundary, but both underestimate the free energy above the photosphere by at least
a factor of two. We discuss the interpretation of the preprocessed field in this context. When applying the NLFFF codes to
solar data, the problems associated with Lorentz forces present in the low solar atmosphere must be recognized: the various
codes will not necessarily converge to the correct, or even the same, solution.
On 07/07/2007, the NLFFF team was saddened by the news that Tom Metcalf had died as the result of an accident. We remain grateful
for having had the opportunity to benefit from his unwavering dedication to the problems encountered in attempting to understand
the Sun’s magnetic field; Tom had completed this paper several months before his death, leading the team through the many
steps described above. 相似文献
3.
Longitudinal distributions of the photospheric magnetic field studied on the basis of National Solar Observatory (Kitt Peak)
data (1976 – 2003) displayed two opposite patterns during different parts of the 11-year solar cycle. Helio-longitudinal distributions
differed for the ascending phase and the maximum of the solar cycle on the one hand and for the descending phase and the minimum
on the other, depicting maxima around two diametrically opposite Carrington longitudes (180° and 0°/360°). Thus the maximum
of the distribution shifted its position by 180° with the transition from one characteristic period to the other. Two characteristic
periods correspond to different situations occurring in the 22-year magnetic cycle of the Sun, in the course of which both
global magnetic field and the magnetic field of the leading sunspot in a group change their sign. During the ascending phase
and the maximum (active longitude 180°) polarities of the global magnetic field and those of the leading sunspots coincide,
whereas for the descending phase and the minimum (active longitude 0°/360°) the polarities are opposite. Thus the observed
change of active longitudes may be connected with the polarity changes of Sun’s magnetic field in the course of 22-year magnetic
cycle. 相似文献
4.
Y.-M. Wang 《Solar physics》2004,224(1-2):21-35
The Sun’s large-scale external field is formed through the emergence of magnetic flux in active regions and its subsequent
dispersal over the solar surface by differential rotation, supergranular convection, and meridional flow. The observed evolution
of the polar fields and open flux (or interplanetary field) during recent solar cycles can be reproduced by assuming a supergranular
diffusion rate of 500 – 600 km2 s−1 and a poleward flow speed of 10 –20 m s−1. The nonaxisymmetric component of the large-scale field decays on the flow timescale of ∼1 yr and must be continually regenerated
by new sunspot activity. Stochastic fluctuations in the longitudinal distribution of active regions can produce large peaks
in the Sun’s equatorial dipole moment and in the interplanetary field strength during the declining phase of the cycle; by
the same token, they can lead to sudden weakenings of the large-scale field near sunspot maximum (Gnevyshev gaps). Flux transport
simulations over many solar cycles suggest that the meridional flow speed is correlated with cycle amplitude, with the flow
being slower during less active cycles. 相似文献
5.
6.
We outline a method to determine the direction of solar open flux transport that results from the opening of magnetic clouds
(MCs) by interchange reconnection at the Sun based solely on in-situ observations. This method uses established findings about i) the locations and magnetic polarities of emerging MC footpoints, ii) the hemispheric dependence of the helicity of MCs, and iii) the occurrence of interchange reconnection at the Sun being signaled by uni-directional suprathermal electrons inside MCs.
Combining those observational facts in a statistical analysis of MCs during solar cycle 23 (period 1995 – 2007), we show that
the time of disappearance of the northern polar coronal hole (1998 – 1999), permeated by an outward-pointing magnetic field,
is associated with a peak in the number of MCs originating from the northern hemisphere and connected to the Sun by outward-pointing
magnetic field lines. A similar peak is observed in the number of MCs originating from the southern hemisphere and connected
to the Sun by inward-pointing magnetic field lines. This pattern is interpreted as the result of interchange reconnection
occurring between MCs and the open field lines of nearby polar coronal holes. This reconnection process closes down polar
coronal hole open field lines and transports these open field lines equatorward, thus contributing to the global coronal magnetic
field reversal process. These results will be further constrainable with the rising phase of solar cycle 24. 相似文献
7.
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
8.
This paper describes a new 2D model for the photospheric evolution of the magnetic carpet. It is the first in a series of
papers working towards constructing a realistic 3D non-potential model for the interaction of small-scale solar magnetic fields.
In the model, the basic evolution of the magnetic elements is governed by a supergranular flow profile. In addition, magnetic
elements may evolve through the processes of emergence, cancellation, coalescence and fragmentation. Model parameters for
the emergence of bipoles are based upon the results of observational studies. Using this model, several simulations are considered,
where the range of flux with which bipoles may emerge is varied. In all cases the model quickly reaches a steady state where
the rates of emergence and cancellation balance. Analysis of the resulting magnetic field shows that we reproduce observed
quantities such as the flux distribution, mean field, cancellation rates, photospheric recycle time and a magnetic network.
As expected, the simulation matches observations more closely when a larger, and consequently more realistic, range of emerging
flux values is allowed (4×1016 – 1019 Mx). The model best reproduces the current observed properties of the magnetic carpet when we take the minimum absolute flux
for emerging bipoles to be 4×1016 Mx. In future, this 2D model will be used as an evolving photospheric boundary condition for 3D non-potential modeling. 相似文献
9.
Kenneth H. Schatten 《Solar physics》2009,255(1):3-38
Photospheric ephemeral regions (EPRs) cover the Sun like a magnetic carpet. From this, we update the Babcock – Leighton solar
dynamo. Rather than sunspot fields appearing in the photosphere de novo from eruptions originating in the deep interior, we consider that sunspots form directly in the photosphere by a rapid accumulation
of like-sign field from EPRs. This would only occur during special circumstances: locations and times when the temperature
structure is highly superadiabatic and contains a large subsurface horizontal magnetic field (only present in the Sun’s lower
latitudes). When these conditions are met, superadiabatic percolation occurs, wherein an inflow and downflow of gas scours
the surface of EPRs to form active regions. When these conditions are not met, magnetic elements undergo normal percolation,
wherein magnetic elements move about the photosphere in Brownian-type motions. Cellular automata (CA) models are developed
that allow these processes to be calculated and thereby both small-scale and large-scale models of magnetic motions can be
obtained. The small-scale model is compared with active region development and Hinode observations. The large-scale CA model offers a solar dynamo, which suggests that fields from decaying bipolar magnetic regions
(BMRs) drift on the photosphere driven by subsurface magnetic forces. These models are related to observations and are shown
to support Waldmeier’s findings of an inverse relationship between solar cycle length and cycle size. Evidence for significant
amounts of deep magnetic activity could disprove the model presented here, but recent helioseismic observations of “butterfly
patterns” at depth are likely just a reflection of surface activity. Their existence seems to support the contention made
here that the field and flow separate, allowing cool, relatively field-free downdrafts to descend with little field into the
nether worlds of the solar interior. There they heat by compression to form a hot solar-type Santa Ana wind deep below active
regions. 相似文献
10.
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
11.
The north – south asymmetries (NSA) of three solar activity indices are derived and mutually compared over a period of more
than five solar cycles (1945 – 2001). A catalogue of the hemispheric sunspot numbers, the data set of the coronal green line
brightness developed by us, and the magnetic flux derived from the NSO/KP data (1975 – 2001) are treated separately within
the discrete low- and mid-latitude zones (5° – 30°, 35° – 60°). The calculated autocorrelations, cross-correlations, and regressions
between the long-term NSA data sets reveal regularities in the solar activity phenomenon. Namely, the appearance of a distinct
quasi-biennial oscillation (QBO) is evident in all selected activity indices. Nevertheless, a smooth behavior of QBO is derived
only when sufficient temporal averaging is performed over solar cycles. The variation in the significance and periodicity
of QBO allows us to conclude that the QBO is not persistent over the whole solar cycle. A similarity in the photospheric and
coronal manifestations of the NSA implies that their mutual relation will also show the QBO. A roughly two-year periodicity
is actually obtained, but again only after significant averaging over solar cycles. The derived cross-correlations are in
fact variable in degree of correlation as well as in changing periodicity. A clear and significant temporal shift of 1 – 2
months in the coronal manifestation of the magnetic flux asymmetry relative to the photospheric manifestation is revealed
as a main property of their mutual correlation. This shift can be explained by the delayed large-scale coronal manifestation
in responding to the emergence of the magnetic flux in the photosphere. The reliability of the derived results was confirmed
by numerical tests performed by selecting different numerical values of the used parameters. 相似文献
12.
V. A. Kotov 《Solar physics》2006,239(1-2):461-474
The mean magnetic field (MMF) of the Sun-as-a-star was measured over the last 38 years by six observatories (about 17 000
MMF daily records, 1968 – 2005). The MMF power spectrum reveals the presence of an enigmatic 1.029(7) year periodicity whose
origin requires explanation. We show that this quasi-annual variation is not produced by modulation of the MMF signal due
to the annual change of the Earth’s helio-latitude (one-year change of visibility of the Sun’s polar regions) as commonly
accepted. The nature of this new solar phenomenon is open for discussion. 相似文献
13.
R. P. Kane 《Solar physics》2007,245(2):415-421
The occurrence of double peaks near the maximum of sunspot activity was first emphasized by Gnevyshev (Solar Phys.
1, 107, 1967) for the peak years of solar cycle 19 (1954 – 1964). In the present analysis, it is shown that double peaks in sunspot numbers
were clearly visible in solar latitudes 10 – 30° N but almost absent in the southern latitudes, where some single peaks were
observed out of phase by several months from any of the peaks in the northern latitudes. The spacing between the double peaks
increased from higher to lower northern latitudes, hinting at latitudinal migration. In the next cycle 20 (1965 – 1976), which
was of about half the strength of cycle 19, no clear-cut double peaks were seen, and the prominent peak in the early part
of 1967 in the northern latitudes was seen a few months later in the southern latitudes. A direct relationship of Gnevyshev
peaks with changes in the solar polar magnetic fields seems to be dubious. The commencements do not match. 相似文献
14.
C. O. Lee J. G. Luhmann J. T. Hoeksema X. Sun C. N. Arge I. de Pater 《Solar physics》2011,269(2):367-388
The solar cycle 23 minimum period has been characterized by a weaker solar and interplanetary magnetic field. This provides
an ideal time to study how the strength of the photospheric field affects the interplanetary magnetic flux and, in particular,
how much the observed interplanetary fields of different cycle minima can be understood simply from differences in the areas
of the coronal holes, as opposed to differences in the surface fields within them. In this study, we invoke smaller source
surface radii in the potential-field source-surface (PFSS) model to construct a consistent picture of the observed coronal
holes and the near-Earth interplanetary field strength as well as polarity measurements for the cycles 23 and 22 minimum periods.
Although the source surface value of 2.5 R
⊙ is typically used in PFSS applications, earlier studies have shown that using smaller source surface heights generates results
that better match observations during low solar activity periods. We use photospheric field synoptic maps from Mount Wilson
Observatory (MWO) and find that the values of ≈ 1.9 R
⊙ and ≈ 1.8 R
⊙ for the cycles 22 and 23 minimum periods, respectively, produce the best results. The larger coronal holes obtained for the
smaller source surface radius of cycle 23 somewhat offsets the interplanetary consequences of the lower magnetic field at
their photospheric footpoints. For comparison, we also use observations from the Michelson Doppler Imager (MDI) and find that
the source surface radius of ≈ 1.5 R
⊙ produces better results for cycle 23, rather than ≈ 1.8 R
⊙ as suggested from MWO observations. Despite this difference, our results obtained from MWO and MDI observations show a qualitative
consistency regarding the origins of the interplanetary field and suggest that users of PFSS models may want to consider using
these smaller values for their source surface heights as long as the solar activity is low. 相似文献
15.
Large-scale solar activity is considered as a manifestation of 3 types of magnetic field activity which is demonstrated in the 22-year cycle (a) of small-scale flux emergence (polar faculae at latitudes > 40°), (b) of somewhat larger scale flux emergence (sunspots at latitudes < 40°), and (c) of the global magnetic neutral lines at all latitudes. The migration (poleward or equatorward) of the place of birth and/or of the phenomena themselves of these three types of manifestation of magnetic field is discussed. The poleward migration of the global field is explained in a phenomenological way. 相似文献
16.
Gordon Petrie 《Solar physics》2017,292(1):13
The Sun’s polar fields play a leading role in structuring the large-scale solar atmosphere and in determining the interplanetary magnetic field. They are also believed to supply the seed field for the subsequent solar activity cycle. However, present-day synoptic observations do not have sufficient spatial resolution or sensitivity to diagnose accurately the high-latitude magnetic vector field. The high spatial resolution and sensitivity of the full-Stokes observations from the Hinode Solar Optical Telescope Spectro-Polarimeter, observing the poles long-term, allows us to build up a detailed picture of the Cycle 24 polar field reversal, including the changing latitude distribution of the high-latitude flux, and to study the effect on global coronal field models. The Hinode observations provide detailed information on the dominant facular-scale magnetic structure of the polar fields, and their field inclination and flux distribution. Hybrid synoptic magnetograms are constructed from Hinode polar measurements and full-disk magnetograms from the Synoptic Optical Long-term Investigations of the Sun (SOLIS) Vector Spectro-Magnetograph (VSM), and coronal potential field models are calculated. Loss of effective spatial resolution at the highest latitudes presents complications. Possible improvements to synoptic polar data are discussed. 相似文献
17.
The exact nonlinear cylindrical solution for incompressible Hall – magnetohydrodynamic (HMHD) waves, including dissipation,
essentially from electron – neutral collisions, is obtained in a uniformly rotating, weakly ionized plasma such as exists
in photospheric flux tubes. The ω – k relation of the waves, called here Hall – MHD waves, demonstrates the dispersive nature of the waves, introduced by the Hall
effect, at large axial and radial wavenumbers. The Hall – MHD waves are in general elliptically polarized. The partially ionized
plasma supports lower frequency modes, lowered by the factor δ≡ratio of the ion mass density to the neutral particle mass density, as compared to the fully ionized plasma (δ=1). The relation between the velocity and the magnetic field fluctuations departs significantly from the equipartition found
in Alfvén waves. These short-wavelength and arbitrarily large amplitude waves could contribute toward the heating of the solar
atmosphere. 相似文献
18.
The presence of the red flash at total solar eclipses requires the existence of an extended chromosphere and therefore of
a photospheric magnetic network that gives rise to spicules. We draw attention to the earliest historical reports of a red
flash at the 1706 and 1715 eclipses, which therefore imply a substantial, widespread photospheric field during at least the
last decade of the Maunder Minimum. Our finding is consistent with reports of a persistent photospheric field throughout the
Maunder Minimum from analyses of 10Be radioisotope evidence. We note, however, that the last decade may not be representative of conditions throughout the roughly
1645 – 1715 extent of that prolonged activity minimum. 相似文献
19.
Solar filaments show the position of large-scale polarity-inversion lines and are used for the reconstruction of large-scale
solar magnetic field structure on the basis of Hα synoptic charts for the periods that magnetographic measurements are not
available. Sometimes crossing filaments are seen in Hα filtergrams. We analyze daily Hα filtergrams from the archive of Big
Bear Solar Observatory for the period of 1999 – 2003 to find crossing and interacting filaments. A number of examples are
presented and filament patterns are compared with photospheric magnetic field distributions. We have found that all crossing
filaments reveal quadrupolar magnetic configurations of the photospheric field and presume the presence of null points in
the corona. 相似文献
20.
Time-latitudinal distributions of the solar-surface magnetic fields and the green corona (530.3 nm, Fe XIV) intensities in
the period 1975 – 2004 are analyzed. Meridional migration maps show that time-varying components consist of both the poleward
and equatorward belts over a solar cycle. The green-corona maps are, for the first time, directly compared with magnetic flux
charts, yielding a good association between the green corona and magnetic fields; this is most reliably seen at high latitudes. 相似文献