共查询到20条相似文献，搜索用时 23 毫秒
1.
F. K. Lamb 《Solar physics》1970,12(2):186-201
Hyder (1968) has suggested that longitudinal magnetograph measurements of weak magnetic fields in prominences have underestimated field strengths as the result of zero-field levelcrossing interference (the Hanle effect). Hyder (1968) also suggested that resonance polarization effects have sometimes led to errors in measurements of the transverse component of magnetic fields. Stenflo (1969) has pointed out some errors in Hyder's paper, while contending that the Hanle effect is implicitly included in current theories of line formation in the presence of Zeeman splitting.In the present Note these questions are re-examined using the results of a density matrix treatment of absorption, emission, and scattering processes. The basic conclusions are as follows: (1) Longitudinal magnetograph measurements using optically thin lines are not influenced by the Hanle effect. (2) Although present theories of line formation in magnetic fields do not include the Hanle effect, this omission is generally unimportant for lines formed in the photosphere and lower chromosphere due to rapid collisional depolarization of atomic levels. (3) For the same reason, other resonance polarization effects are probably too small to cause significant errors in magnetograph measurements of all but the very weakest magnetic fields, when photospheric and lower chromospheric lines are used. (4) By contrast, the general phenomenon of atomic level polarization is quite important in most prominences. As emphasized by Hyder, extreme care must be used in selecting lines for magnetograph studies of solar magnetic fields. 相似文献
2.
J. O. Stenflo 《Solar physics》1982,80(2):209-226
The theory of the Hanle effect is used to interpret the linear polarization measured in a number of spectral lines on the solar disk near the heliographic north and south poles, in search for a turbulent magnetic field in the solar atmosphere. The Hanle depolarization is separated from a number of other effects, including collisional depolarization and scattering geometry. Although the main aim of the paper is to elucidate the physics of the Hanle effect as applied to the Sun, our results indicate the existence of hidden or turbulent magnetic flux near the temperature minimum of the solar atmosphere, with a field strength between 10 and 100 G. This field is hidden in the sense that it is not seen in measurements of the longitudinal Zeeman effect (solar magnetograms). It carries more total magnetic flux than the kG network fields. 相似文献
3.
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
4.
In this paper we evaluate the possibility of detecting, for the first time, the surface magnetic field of Jupiter (∼1 bar level) by observing the change of linear polarization induced by the Hanle effect on the H Lyman-alpha (Lyα) emission line of the planet. We find that, indeed, the Hanle effect, which results from the interaction between a local magnetic field and the atomic polarization induced by absorption of anisotropic radiation, is sensitive to relatively weak values of the strength of the magnetic fields expected on planets. First, we show that for the Lyα emission backscattered by atomic H in the presence of a magnetic field, the Hanle effect is polarizing. This new result is in total contrast to the depolarizing effect predicted and observed for emission lines scattered at right angles in solar prominences. Additionally, to estimate the polarization rate for the case of Jupiter, we have considered three magnetic field models: a dipole field for reference, an O4 based model [Connerney, J.E.P., 1981. The magnetic field of Jupiter—A generalized inverse approach. J. Geophys. Res. 86, 7679-7693], and finally, an O6 based model [Khurana, K.K., 1997. Euler potential models of Jupiter's magnetospheric field. J. Geophys. Res. 102, 11295-11306]. In all models, we show that for the jovian backscattered Lyα line, the Hanle effect does enhance the Lyα linear polarization; the polarization rate may exceed 2% at specific regions of the jovian disc, making detection possible either remotely or from an orbiter around Jupiter. In general, depending on the instrumental sensitivity and the observing strategy used, we show that accurate mapping of the linear polarization rate at the planetary surface (thermosphere) or off-disc (corona) may provide a rather accurate estimate of the jovian total magnetic field strength on large area scales. 相似文献
5.
J. O. Stenflo 《Solar physics》1985,100(1-2):189-208
Recent advances in polarimetry allowing the recording of polarized line profiles with high spectral resolution and signal-to-noise ratio over large portions of the solar spectrum offer rich new diagnostic possibilities. Thus we can now in a systematic way build models of the height variation of the magnetic field, temperature, density, and mass motions in the spatially unresolved subarcsecond magnetic structures. The analysis of the Stokes spectra also allows us to build a foundation for proper diagnostics of vector magnetic fields, a goal that cannot be achieved before the intrinsic properties of the spatially unresolved magnetic fields have been determined. Another new diagnostic tool is the Hanle effect. A recent exploratory survey of coherence effects through the recording of the linear polarization with high spectral resolution throughout the whole visible solar spectrum aims at establishing a foundation for the exploitation of the Hanle effect on the solar disk.This review describes these developments, most of which have taken place in the 1980s, and summarizes the results obtained so far. 相似文献
6.
Yun-Tung Lau 《Solar physics》1993,148(2):301-324
We study the magnetic field-line topology in a class of solar flare models with four magnetic dipoles. By introducing a series of symmetry-breaking perturbations to a fully symmetric potential field model, we show that isolated magnetic nulls generally exist above the photosphere. These nulls are physically important because they determine the magnetic topology above the photosphere. In some special cases, there may be a single null above the photosphere with quasi two-dimensional properties. For such a model, aquasi null line connects the null to the photosphere. In the limit of small non-ideal effects, boundary layers and current sheetsmay develop along the quasi null line and the associated separatrix surfaces. Field lines can then reconect across the quasi null line, as in two-dimensional reconnection. In a more general force-free case, the field contains a pair of nulls above the photosphere, with a field line (theseparator) connecting the two nulls. In the limit of small non-ideal effects, boundary layers and current sheets develop along the separator and the associated separatrix surfaces. The system exhibits three-dimensional reconnection across the separator, over which field lines exchange identity. The separatrices are related to preferable sites of energy release during solar flares. 相似文献
7.
V. E. Abramov-Maksimov G. F. Vyalshin G. B. Gelfreikh V. I. Shatilov 《Solar physics》1996,164(1-2):333-343
In the present paper we present the results of measurement of magnetic fields in some sunspots at different heights in the solar atmosphere, based on simultaneous optical and radio measurements. The optical measurements were made by traditional photographic spectral observations of Zeeman splitting in a number of spectral lines originating at different heights in the solar photosphere and chromosphere. Radio observations of the spectra and polarization of the sunspot - associated sources were made in the wavelength range of 2–4 cm using large reflector-type radio telescope RATAN-600. The magnetic field penetrating the hot regions of the solar atmosphere were found from the shortest wavelength of generation of thermal cyclotron emission (presumably in the third harmonic of electron gyrofrequency). For all the eight cases under consideration we have found that magnetic field first drops with height, increases from the photosphere to lower chromosphere, and then decreases again as we proceed to higher chromosphere and chromosphere-corona transition region. Radio measurements were found to be well correlated with optical measurements of magnetic fields for the same sunspot. An alternative interpretation implies that different lines used for magnetic field measurements refer to different locations on the solar surface. If this is the case, then the inversion in vertical gradients of magnetic fields may not exist above the sunspots. Possible sources of systematic and random errors are also discussed. 相似文献
8.
E. S. Andriets N. N. Kondrashova E. V. Kurochka V. G. Lozitsky 《Bulletin of the Crimean Astrophysical Observatory》2012,108(1):1-3
We investigate the photosphere parameters of a 2N/M2 solar flare that occurred in the NOAA 9077 active area on 18 July, 2000 before its maximum. We use Echelle Zeeman spectrograms obtained in orthogonal circular polarizations by means of a solar spectrograph of the astronomical observatory of Kiev National University, Ukraine (Kurochka, E.V., et. al, 1980). The photosphere is simulated by SIR software (Ruiz Cobo, B. and del Toro Inesta, J.C., 1992). The model of the flare??s photosphere is characterized by a two-component structure, including a magnetic flux tube and its nonmagnetic environment. For both components, we obtain the height distribution of the following parameters: temperature, magnetic field density and line-of-sight velocity. The temperature in the magnetic flux tube increases to approximately 5100 K in the upper photosphere layer of 250?C400 km. The magnetic field intensity decreases sharply from 2600 G (lower photosphere) to 100 G (middle photosphere) with a gradient of about 12 G/km. The model of the nonmagnetic environment differs slightly from the model of undisturbed photosphere. 相似文献
9.
The Sun's magnetic field extends far from the photosphere, into the corona, defining a magnetically dominated region before being drawn out radially by the solar wind flow. This region, where the internal sources of the solar field dominate the plasma structures and the energetic particle movement, can be properly considered the solar magnetosphere. The magnetic field in this region can be approximately described by models that extrapolate photospheric magnetic field observations under some simplifying assumptions. In this paper we use a potential field model which describes the solar field up to a source surface at 3.25 Rs, where the field is constrained to become radial. We present the variation of the magnitude and inclination of the various multipolar components throughout the solar magnetic cycle that characterise the changes in the structure of the solar magnetosphere over a period of 22 years. We also present some 3-D images of the coronal magnetic structure to show the global evolution of the solar magnetosphere throughout the solar cycle and discuss the importance of taking this structure into account in order to relate interplanetary and solar features. 相似文献
10.
Many authors use magnetic-field models to extrapolate the field in the solar corona from magnetic data in the photosphere. The accuracy of such extrapolations is usually judged qualitatively by eye, where a less judgemental quantitative approach would be more desirable. In this paper, a robust method for obtaining the best fit between a theoretical magnetic field and intensity observations of coronal loops on the solar disk will be presented. The method will be applied to Yohkoh data using a linear force-free field as an illustration. Any other theoretical model for the magnetic field can be used, provided there is enough freedom in the model to optimize the fit. 相似文献
11.
Randolph H. Levine 《Solar physics》1979,62(2):277-303
The spatial organization of the observed photospheric magnetic field, as well as its relation to the polarity of the interplanetary field, have been studied using high resolution magnetograms from Kitt Peak National Observatory. Systematic patterns in the large scale field have been found to be due to contributions from both concentrated flux and more diffuse flux. It is not necessary to assume, as has often been done in previous studies, that there is a weak background solar magnetic field causing the large-scale patterns in the photosphere, although the existence of such a field cannot be excluded. The largest scale structures in the photosphere correspond to the expected pattern at the base of a warped heliomagnetic equator.The polarity of the photospheric field, determined on various spatial scales, correlates with the polarity of the interplanetary field, with the most significant correlation due to mid-latitude fields. However, because the interplanetary field is likely to be rooted in concentrated photospheric regions, rather than across an entire polarity region, both the strength and polarity of the field are important in determining the interplanetary field. Thus studies of the interplanetary field which are based on either instrumental or numerical averaging of fields in the solar photosphere are subject to serious inherent limitations.Analyses based on several spatial scales in the photosphere suggest that new flux in the interplanetary medium is often due to relatively small photospheric features which appear in the photosphere up to one month before they are manifest at the Earth. The evolution of the over-all photospheric pattern may be due to individual sub-patterns which have slightly different rotation properties and which alternate in their relative dominance of the interplanetary medium. 相似文献
12.
S. -I. Akasofu 《Astrophysics and Space Science》1988,144(1-2):303-309
The presently prevailing theories of 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 to solar flare energy. In this paper, we discuss solar flares from an entirely different point of view, namely in terms of power supply by a dynamo process in the photosphere. By this process, electric currents flowing along the magnetic field lines are generated and the familiar ‘force-free’ fields or the ‘sheared’ magnetic fields are produced. Upward field-aligned currents thus generated are carried by downward streaming electrons; these electrons can excite hydrogen atoms in the chromosphere, causing the optical Hα flares or ‘low temperature flares’. It is thus argued that as the ‘force-free’ fields are being built up for the magnetic energy storage, a flare must already be in progress. 相似文献
13.
High-quality stratospheric photographs in the continuum were used to investigate spatial scales of the solar granulation field. Two-dimensional intensity power spectra are shown to contain most frequently the modes corresponding to the sizes of granules, protogranules, mesogranules, and supergranules. The place of these four, the most steady formations of the quiet Sun in the global structure of the solar photosphere, is discussed as well as their interconnection and their relation to weak and strong magnetic fields. The protogranulation scale is argued to play an important role in organization of the fine structure of the photosphere and magnetic fields in the quiet and active regions of the Sun. 相似文献
14.
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
15.
Ronald L. Rosenberg 《Solar physics》1970,15(1):72-78
A simple model is used to present a unified picture of the polarity pattern of the interplanetary magnetic field observed during the solar cycle. Emphasis in this paper is on the field near solar maximum. The heliographic latitude dependence of the dominant polarity of the interplanetary magnetic field is explained in terms of weak poloidal (dipolar) field sources in the sun's photosphere. Unlike the Babcock theory, the author hypothesizes that the dipolar field exists at equatorial latitudes (0–20°), too, (as well as in polar regions) and that the major source of the interplanetary magnetic field observed near the ecliptic plane is the dipolar field from equatorial latitudes. The polarity of the interplanetary field data taken in 1968 and in the first half of 1969 near solar maximum may possibly be explained in terms of a depression of the dipolar field boundary in space. The effect on the solar wind of the greater activity in the northern hemisphere of the sun that existed in 1968 and in the first half of 1969 is believed responsible for this hypothesized depression, especially near solar maximum, of the plane separating the + and - dipolar polarity below the solar equatorial plane in space. Predictions are made concerning the interplanetary field to be observed near the ecliptic plane in each portion of the next solar cycle. 相似文献
16.
By analyzing a canopy tube described by Athay, we point out the possibility that the different canopy heights given by different authors are caused by different definitions of canopy heights. For the same canopy tube, those heights where the magnetic field has horizontal components, where neighboring magnetic tubes meet each other and where the magnetic field becomes uniform or vertical range from near the solar photosphere to the solar corona. 相似文献
17.
Xing-Ming Bao Hong-Qi ZhangNational Astronomical Observatories Chinese Academy of Sciences Beijing baoxm@sunlO.bao.ac.cn 《中国天文和天体物理学报》2003,3(1):87-97
We observed the line-of-sight magnetic field in the chromosphereand photosphere of a large quiescent filament on the solar disk on September 6, 2001 using the Solar Magnetic Field Telescope in Huairou Solar Observing Station. The chromospheric and photospheric magnetograms together with Hβ filtergrams of the filament were examined. The filament was located on the neutral line of the large scale longitudinal magnetic field in the photosphere and the chromosphere. The lateral feet of the filament were found to be related to magnetic structures with opposite polarities. Two small lateral feet are linked to weak parasitic polarity. There is a negative magnetic structure in the photosphere under a break of the filament. At the location corresponding to the filament in the chromospheric magnetograms, the magnetic strength is found to be about 40-70 Gauss (measuring error about 39 Gauss). The magnetic signal indicates the amplitude and orientation of the internal magnetic field in the filament. We discuss several possible causes which may produce such a measured signal. A twisted magnetic configuration inside the filament is suggested . 相似文献
18.
19.
H. Frisch 《Solar physics》1996,164(1-2):49-66
Resonance polarization, which is created by the scattering of an anisotropic radiation field in regions of zero or weak magnetic fields, is strongly dependent on the frequency redistribution taking place during the scatterings. Here we discuss the frequency redistribution matrix relevant to resonance lines, concentrating on linear polarization. First we analyze in detail the redistribution matrix in a zero magnetic field given by the theory of Omont, Smith and Cooper (1972), revisited by Domke and Hubeny (1988). We explain that the linear polarization maxima which may appear in the wings of the Stokes Q profiles of strong resonances lines such as the Ca I 4227 Å line are coherent frequency redistribution effects. Various approximate forms of the frequency redistribution matrix are also examined. For resonance polarization in a weak magnetic field, we suggest a new expression for the redistribution matrix which can be used at all line frequencies, and is consistent with the condition that the Hanle effect acts only in the line core. 相似文献
20.
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