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1.
Radio observations of some active regions (ARs) obtained with the Nobeyama radioheliograph at λ=1.76cm are used for estimating the magnetic field strength in the upper chromosphere, based on thermal bremsstrahlung. The results are compared with the magnetic field strength in the photosphere from observations with the Solar Magnetic Field Telescope (SMFT) at Huairou Solar Observing Station of Beijing Astronomical Observatory. The difference in the magnetic field strength between the two layers seems reasonable. The solar radio maps of active regions obtained with the Nobeyama radioheliograph, both in total intensity (I-map) and in circular polarizations (V-map), are compared with the optical magnetograms obtained with the SMFT. The comparison between the radio map in circular polarization and the longitudinal photospheric magnetogram of a plage region suggest that the radio map in circular polarization is a kind of magnetogram of the upper chromosphere. The comparison of the radio map in total intensity with the photospheric vector magnetogram of an AR shows that the radio map in total intensity gives indications of magnetic loops in the corona, thus we have a method of defining the coronal magnetic structure from the radio I-maps at λ=1.76 cm. Analysing the I-maps, we identified three components: (a) a compact bright source; (b) a narrow elongated structure connecting two main magnetic islands of opposite polarities (observed in both the optical and radio magnetograms); (c) a wide, diffuse, weak component that corresponds to a wide structure in the solar active region which shows in most cases an S or a reversed S contour, which is probably due to the differential rotation of the Sun. The last two components suggest coronal loops on different spatial scales above the neutral line of the longitudinal photospheric magnetic field. 相似文献
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To model and study local magnetic-field enhancements in a solar flux rope we consider the magnetic field in its interior as
a superposition of two linear (constant α) force-free magnetic-field distributions, viz. a global one, which is locally similar to a part of the cylinder, and a local torus-shaped magnetic distribution. The newly
derived solution for a toroid with an aspect ratio close to unity is applied. The symmetry axis of the toroid and that of
the cylinder may or may not coincide. Both the large and small radii of the toroid are set equal to the cylinder’s radius.
The total magnetic field distribution yields a flux tube which has a variable diameter with local minima and maxima. In principle,
this approach can be used for the interpretation and analysis of solar-limb observations of coronal loops. 相似文献
5.
The aim of this article is to investigate how the background magnetic field of the Sun behaves in different hemispheres. We used SOHO/MDI data obtained during a period of eight years from 2003 to 2011 to analyze the intensity distribution of the background magnetic field over the solar surface. We find that the background fields of both polarities (signs) are more intense in the southern than in the northern hemisphere. Mixed polarities are observed in the vicinity of the equator. In addition to the main field, a weaker field of opposite polarity is always present in the polar regions. In the declining phase of the cycle, the main field dominates, but at the minimum and in the rising phase of the cycle, it is gradually replaced by the growing stronger secondary field. 相似文献
6.
Yi Liao Shao-Lan BiNational Astronomical Observatories Yunnan Observatory Kunming 《中国天文和天体物理学报》2004,4(5):490-498
Correction of non-ideal effect due to a magnetic fluctuating tensor is derived from the ideal MHD equations. The inclusion of a magnetic turbulent field leads to modifications of the hydrostatic equilibrium equation and thermodynamical variables such as the temperature T, the adiabatic exponent γ, the adiabatic temperature gradient △↓ad and the temperature gradient △↓. In particular, the modifications in the adiabatic and radiative temperature gradients will result in a change in the Schwarzchild criterion, hence in the location of the base of the convective zone. Incorporating the modifications, we construct a modified thermodynamical equilibrium structure of the Sun. 相似文献
7.
We study the relationship between the brightness (I) and magnetic field (B) distributions of sunspots using 272 samples observed at the San Fernando Observatory and the National Solar Observatory,
Kitt Peak, whose characteristics varied widely. We find that the I – B relationship has a quadratic form for the spots with magnetic field less than about 2000 G. The slope of the linear part
of the I – B curve varies by about a factor of three for different types of spots. In general the slope increases as the spot approaches
disk center. The I – B slope does not have a clear dependency on the spot size but the lower limit appears to increase as a function of the ratio
of umbra and penumbra area. The I – B slope changes as a function of age of the sunspots. We discuss various sunspot models using these results. 相似文献
8.
Based on Hinode SOT/NFI observations with greatly improved spatial and temporal resolution and polarization sensitivity, the lifestory of
the intranetwork (IN) magnetic elements are explored in a solar quiet region. A total of 2282 IN elements are followed from
their appearance to disappearance and their fluxes measured. By tracing individual IN elements their lifetimes are obtained,
which fall in the range from 1 to 20 min. The average lifetime is 2.9±2.0 min. The observed lifetime distribution is well
represented by an exponential function. Therefore, the e-fold characteristic lifetime is determined by a least-square fitting
to the observations, which is 2.1±0.3 min. The lifetime of IN elements is correlated closely with their flux. The evolution
of IN elements is described according to the forms of their birth and disappearance. Based on the lifetime and flux obtained
from the new observations, it is estimated that the IN elements have the capacity of heating the corona with a power of 2.1×1028 erg s−1 for the whole Sun. 相似文献
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K. D. Leka Graham Barnes A. D. Crouch Thomas R. Metcalf G. Allen Gary Ju Jing Y. Liu 《Solar physics》2009,260(1):83-108
The objective testing of algorithms for performing ambiguity resolution in vector magnetic field data is continued, with an
examination of the effects of noise in the data. Through the use of analytic magnetic field models, two types of noise are
“added” prior to resolving: noise to simulate Poisson photon noise in the observed polarization spectra, and a spatial binning
to simulate the effects of unresolved structure. The results are compared through the use of quantitative metrics and performance
maps. We find that while no algorithm severely propagates the effects of Poisson noise beyond very local influences, some
algorithms are more robust against high photon-noise levels than others. In the case of limited spatial resolution, loss of
information regarding fine-scale structure can easily result in erroneous solutions. Our tests imply that photon noise and
limited spatial resolution can act so as to make assumptions used in some ambiguity resolution algorithms no longer consistent
with the observed magnetogram. We confirm a finding of the earlier comparison study that results can be very sensitive to
the details of the treatment of the observed boundary and the assumptions governing that treatment. We discuss the implications
of these findings, given the relative sensitivities of the algorithms to the two sources of noise tested here. We also touch
on further implications for interpreting observational vector magnetic field data for general solar physics research. 相似文献
11.
The good quality of the observing sequence of about 60 photographs of the white-light corona taken during the total solar
eclipse observations on 29 March 2006, in Al Sallum, Egypt, enable us to use a new method of image processing for enhancement
of the fine structure of coronal phenomena. We present selected magnetic-field lines derived for different parameters of the
extrapolation model. The coincidence of the observed coronal white-light fine structures and the computed field-line positions
provides a 3D causal relationship between coronal structures and the coronal magnetic field. 相似文献
12.
The photospheric vector magnetic fields, H and soft X-ray images of AR 7321 were simultaneously observed with the Solar Flare Telescope at Mitaka and the Soft X-ray Telescope of Yohkoh on October 26, 1992, when there was no important activity in this region. Taking the observed photospheric vector magnetic fields as the boundary condition, 3D magnetic fields above the photosphere were computed with a new numerical technique. Then quasi-separatrix layers (QSLs), i.e., regions where 3D magnetic reconnection takes place, were determined in the computed 3D magnetic fields. Since Yohkoh data and Mitaka data were obtained in well-arranged time sequences during the day, the evolution of 3D fields, H features and soft X-ray features in this region can be studied in detail. Through a comparison among the 3D magnetic fields, H features and soft X-ray features, the following results have been obtained: (a) H plages are associated with the portions of QSLs in the chromosphere; (b) diffuse coronal features (DCFs) and bright coronal features (BCFs) are morphologically confined by the coronal linkage of the field lines related to the QSLs; (c) BCFs are associated with a part of the magnetic field lines related to the QSLs. These results suggest that as the likely places where energy release may occur by 3D magnetic reconnection, QSLs play an important role in the chromospheric and coronal heating in this active region. 相似文献
13.
STEREO A and B observations of the radial magnetic field between 1 January 2007 and 31 October 2008 show significant evidence
that in the heliosphere, the ambient radial magnetic field component with any dynamic effects removed is uniformly distributed.
Based on this monopolar nature of the ambient heliospheric field we find that the surface beyond which the magnetic fields
are in the monopolar configuration must be spherical, and this spherical surface can be defined as the inner boundary of the
heliosphere that separates the monopole-dominated heliospheric magnetic field from the multipole-dominated coronal magnetic
field. By using the radial variation of the coronal helmet streamers belts and the horizontal current – current sheet – source
surface model we find that the spherical inner boundary of the heliosphere should be located around 14 solar radii near solar
minimum phase. 相似文献
14.
L. K. Harra T. Magara H. Hara S. Tsuneta T. J. Okamoto A. J. Wallace 《Solar physics》2010,263(1-2):105-119
Active region magnetic flux that emerges to the photosphere from below will show complexity in the structure, with many small-scale fragmented features appearing in between the main bipole and then disappearing. Some fragments seen will be absorbed into the main polarities and others seem to cancel with opposite magnetic field. In this paper we investigate the response of the corona to the behaviour of these small fragments and whether energy through reconnection will be transported into the corona. In order to investigate this we analyse data from the Hinode space mission during flux emergence on 1?–?2 December 2006. At the initial stages of flux emergence several small-scale enhancements (of only a few pixels size) are seen in the coronal line widths and diffuse coronal emission exists. The magnetic flux emerges as a fragmented structure, and coronal loops appear above these structures or close to them. These loops are large-scale structures – most small-scale features predominantly stay within the chromosphere or at the edges of the flux emergence. The most distinctive feature in the Doppler velocity is a strong ring of coronal outflows around the edge of the emerging flux region on the eastern side which is either due to reconnection or compression of the structure. This feature lasts for many hours and is seen in many wavelengths. We discuss the implications of this feature in terms of the onset of persistent outflows from an active region that could contribute to the slow solar wind. 相似文献
15.
Hong-Qi Zhang National Astronomical Observatories Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2006,6(1):96-112
We present the evolution of magnetic field and its relationship with mag- netic(current)helicity in solar active regions from a series of photospheric vector magnetograms obtained by Huairou Solar Observing Station,longitudinal magne- tograms by MDI of SOHO and white light images of TRACE.The photospheric current helicity density is a quantity reflecting the local twisted magnetic field and is related to the remaining magnetic helicity in the photosphere,even if the mean current helicity density brings the general chiral property in a layer of solar active regions.As new magnetic flux emerges in active regions,changes of photospheric cur- rent helicity density with the injection of magnetic helicity into the corona from the subatmosphere can be detected,including changes in sign caused by the injection of magnetic helicity of opposite sign.Because the injection rate of magnetic helicity and photospheric current helicity density have different means in the solar atmosphere, the injected magnetic helicity is probably not proportional to the current helicity den- sity remaining in the photosphere.The evidence is that rotation of sunspots does not synchronize exactly with the twist of photospheric transverse magnetic field in some active regions(such as,delta active regions).They represent different aspects of mag- netic chirality.A combined analysis of the observational magnetic helicity parameters actually provides a relative complete picture of magnetic helicity and its transfer in the solar atmosphere. 相似文献
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We present a catalog of high-speed streams, along with their solar sources for solar cycle 23. We study their distribution
during different years and different phases of solar cycle after classifying them into different groups based on their source(s),
duration, and speed. We also study the average plasma/field properties of streams after dividing them into suitable groups
on the basis of their source(s), duration and speed. It is expected that the catalog and statistical results presented in
this work will further stimulate the space weather and solar-terrestrial studies involving high-speed streams. 相似文献
18.
Using one-minute cadence time-series full disk magnetograms taken by the SOHO/MDI, we have studied the magnetic field elements
at high latitude (poleward of 65° in latitude). It is found that an average lifetime of the magnetic field elements is 16.5
h during solar minimum, much longer than that during solar maximum (7.3 h). During solar minimum, number of the magnetic field
elements with the dominant polarity is about 3 times as that of the opposite polarity elements. Their lifetime is 21.0 h on
average, longer than that of the opposite polarity elements (2.3 h). It is also found that the lifetime of the magnetic field
elements is related with their size, consistent with the magnetic field elements in the quiet sun at low latitude found by
Hagenaar et al. (Astrophys. J. 511:932, 1999). During solar maximum, the polar regions are equally occupied by magnetic field elements with both polarities, and their
lifetimes are roughly the same on average. No evidence shows there is a correlation between the lifetime and size of the magnetic
field elements. Using an image cross-correlation method, we also measure the solar rotation rate at high latitude, up to 85°
in latitude. The rate is ω=2.914−0.342sin 2
φ−0.482sin 4
φ μrad s−1 sidereal. It agrees with previous studies using the spectroscopic and image cross-correlation methods, and also agrees with
the results using the element tracking method when the sample of the tracked magnetic field elements is large. The consistency
of those results strongly suggests that this rate at high latitude is reliable. 相似文献
19.
Ellerman bombs and type Ⅱ white-light flares share many common features despite the large energy gap between them.Both are considered to result from local heation in the solar lower atmosphere.This paper presents numerical simulations of magnetic reconnection occurring in such a deep atmosphere,with the aim to account for the common features of the two phenomena.Our numerical results manifest the following two typical characteristics of the assumed reconnection process:(1)magnetic reconnection saturates in-600-900s,which is just the lifetime of the two phenomens;(2)ionization in the upper chromosphere consumes quite a large part of the energy released through reconnection,making the heation effect most significant in the lower chromosphere.The applicationof the reconnection model to the two phenomena is discussed in detail. 相似文献
20.
In a density-stratified turbulent medium, the cross helicity 〈u′⋅B′〉 is considered as a result of the interaction of the velocity fluctuations and a large-scale magnetic field. By means of
a quasilinear theory and by numerical simulations, we find the cross helicity and the mean vertical magnetic field to be anti-correlated.
In the high-conductivity limit the ratio of the helicity and the mean magnetic field equals the ratio of the magnetic eddy
diffusivity and the (known) density scale height. The result can be used to predict that the cross helicity at the solar surface
will exceed the value of 1 gauss km s−1. Its sign is anti-correlated to that of the radial mean magnetic field. Alternatively, we can use our result to determine
the value of the turbulent magnetic diffusivity from observations of the cross helicity. 相似文献