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1.
Powerful flares are closely related to the evolution of the complex magnetic field configuration at the solar surface. The
strength of the magnetic field and speed of its evolution are two vital parameters in the study of the change of magnetic
field in the solar atmosphere. We propose a dynamic and quantitative depiction of the changes in complexity of the active
region: E=u×B, where u is the velocity of the footpoint motion of the magnetic field lines and B is the magnetic field. E represents the dynamic evolution of the velocity field and the magnetic field, shows the sweeping motions of magnetic footpoints,
exhibits the buildup process of current, and relates to the changes in nonpotentiality of the active region in the photosphere.
It is actually the induced electric field in the photosphere. It can be deduced observationally from velocities computed by
the local correlation tracking (LCT) technique and vector magnetic fields derived from vector magnetograms. The relationship
between E and ten X-class flares of four active regions (NOAA 10720, 10486, 9077, and 8100) has been studied. It is found that (1)
the initial brightenings of flare kernels are roughly located near the inversion lines where the intensities of E are very high, (2) the daily averages of the mean densities of E and its normal component (E
n) decrease after flares for most cases we studied, whereas those of the tangential component of E (E
t) show no obvious regularities before and after flares, and (3) the daily averages of the mean densities of E
t are always higher than those of E
n, which cannot be naturally deduced by the daily averages of the mean densities of B
n and B
t. 相似文献
2.
Solutions of the sine-Poisson equation are used to construct a class of isothermal magnetostatic atmospheres, with one ignorable coordinate corresponding to a uniform gravitational field in a plane geometry. The distributed current in the model j is directed along the x-axis, where x is the horizontal ignorable coordinate. The current j varies as the sine of the magnetostatic potential and falls off exponentially with distance vertical to the base with an e-folding distance equal to the gravitational scale height. We investigate in detail solutions for the magnetostatic potential A corresponding to the one-soliton, two soliton, and breather solutions of the sine-Gordon equation. Depending on the values of the free parameters in the soliton solutions, horizontally, periodic magnetostatic structures are obtained possessing either (a) a single X-type neutral point, (b) multiple neutral X-points, or (c) solutions without X-points. The solution cases (b) and (c) contain two families of intersecting current sheets, in which the line of intersection forms flux concentration points (or singularities) for the magnetic field. The solutions illustrate the contribution of the anisotropic J × B force (B, magnetic field induction), the gravitational force, and the gas pressure gradient to the force balance. 相似文献
3.
A possible correlation between the magnetic and velocity fields has been analyzed based on the SOHO/MDI magnetograms and Dopplergrams.
It is found that the observed large-scale weak magnetic field (weaker than 50 G (gauss)) is correlated with the velocity statistically.
The curves of u⋅b with latitude, where u and b are the velocity and magnetic fields in a rectangular region (±15○ in longitude, ±45○ in latitude) on the Sun, show the same patterns in the years 2000, 2004, and 2007. The patterns indicate that u and b are positively correlated near the equator but are anti-correlated at the middle latitudes. For a strong magnetic field between
50 G and 3000 G, the curves of u⋅b with latitude show the same tendencies at the middle latitudes. Near the equator, however, the slope of the curve is positive
in 2000 and is negative in 2004 and 2007. In addition, we give an estimation for the amplitude of the cross helicity h
χ
(hc=[`(u·b)]h_{\chi}=\overline{\mathbf{u}\cdot\mathbf{b}}) inferred from the MDI data, which is of the order of 103 G m s−1 near the center of the solar disk. 相似文献
4.
G. M. Webb 《Solar physics》1988,116(2):259-277
An investigation of a family of isothermal magneto-static atmospheres with one ignorable coordinate corresponding to a uniform gravitational field in a plane geometry is carried out. The distributed current in the model J is directed along the x-axis where x is the horizontal ignorable coordinate. The current J is taken proportional to the square of the magneto-static potential A and falls off exponentially with distance vertical to the base with an e-folding distance equal to the gravitational scale height. A range of solution examples are displayed depending on the four free parameters in the solutions. Three of these parameters determine the source currents for the potential field solution of the family, whereas the fourth parameter determines the magnitude of the distributed current. The solutions illustrate the contribution of the anisotropic J × B force (B, magnetic field induction), the gravitational force, and gas pressure gradient to the force balance. 相似文献
5.
M. A. Kazarian 《Astrophysics》1996,39(3):245-251
The results of a morphological classification of 580 galaxies with a UV excess, included in the lists in [M. A. Kazarian, Astrofizika,15, 5 (1979); ibid.,15, 193 (1979); M. A. Kazarian and É. S. Kazarian, ibid.,16, 17 (1980); ibid.,18, 512 (1982); ibid.,19, 213 (1983)], are presented. For this we have developed a set of symbols, using the types E, S, and Ir introduced by Hubble, as well as symbols introduced by other authors and us. This set enabled us to make the morphological classification. Direct photographs obtained on the 2.6-m and 6-m telescopes were used to classify 141 of the galaxies (over 24%), while Palomar Atlas charts were used for the remaining 439 galaxies. These galaxies were divided into two groups based on classification conditions, and data on each group are given in Tables 1 and 2, respectively. The results for each group, given in Table 3, show that with the transition from early types, such as C and E, to later types, such as S and Ir, the relative number of galaxies going into one group (Table 1), in which the classification was based on direct photographs, increases in comparison with the number going into the other group (Table 2).Translated from Astrofizika, Vol. 39, No. 3, pp. 431–439, July–September, 1996. 相似文献
6.
Anirudh Pradhan Hassan Amirhashchi Rekha Jaiswal 《Astrophysics and Space Science》2011,334(2):249-260
A new class of dark energy models in a Locally Rotationally Symmetric Bianchi type-II (LRS B-II) space-time with variable
equation of state (EoS) parameter and constant deceleration parameter have been investigated in the present paper. The Einstein’s
field equations have been solved by applying a variation law for generalized Hubble’s parameter given by Berman: Nuovo Cimento
74:182 (1983) which generates two types of solutions for the average scale factor, one is of power-law type and other is of the exponential-law
form. Using these two forms, Einstein’s field equations are solved separately that correspond to expanding singular and non-singular
models of the universe respectively. The dark energy EoS parameter ω is found to be time dependent and its existing range for both models is in good agreement with the three recent observations
of (i) SNe Ia data (Knop et al.: Astrophys. J. 598:102 (2003)), (ii) SNe Ia data collaborated with CMBR anisotropy and galaxy clustering statistics (Tegmark et al.: Astrophys. J. 606:702 (2004)) and latest (iii) a combination of cosmological datasets coming from CMB anisotropies, luminosity distances of high redshift
type Ia supernovae and galaxy clustering (Hinshaw et al.: Astrophys. J. Suppl. 180:225 (2009); Komatsu et al. Astrophys. J. Suppl. 180:330 (2009)). The cosmological constant Λ is found to be a positive decreasing function of time and it approaches a small positive value
at late time (i.e. the present epoch) which is corroborated by results from recent supernovae Ia observations. The physical
and geometric behaviour of the universe have also been discussed in detail. 相似文献
7.
It was discovered some years ago by Schiff that the equations divE = 4πQ and curlB - (1/c) ∂E/∂t = (4π/c)J for fields in vacuum do not carry over without change from an inertial frame to a frame with rotating axes of space coordinates,
even for a region with all velocities of orderv≪c. However, the belief that all four of the field equations are invariant under such conditions is still prevalent and causes
misconceptions in physical applications, including astrophysical and geophysical ones. The purpose of the present paper is
therefore to call attention to Schiff's discovery, discussing its basis and its extension to fields in material media, and
to interpret the additional terms that must be added to the equations in order to obtain valid transformations to rotating
axes of coordinates. 相似文献
8.
Axially symmetric cosmological models with cosmic string source are obtained in a scalar-tensor theory of gravitation proposed
by Saez and Ballester (Phys. Lett. A113, 467, 1985). The models obtained give us axially symmetric geometric (Nambu) string, p-string and Reddy string (Astrophys. Space Sci. 286, 2003b) in Saez-Ballester theory. Some physical properties of the models are also discussed. 相似文献
9.
We studied the characteristics of the zebra-associated spike-like bursts that were recorded with high time resolution at 1420
MHz in four intervals (from 12:45 to 12:48 UT) during 5 August 2003. Our detailed analysis is based on the selection of more
than 500 such spike-like bursts and it is, at least to our knowledge, the first study devoted to such short-lived bursts.
Their characteristics are different from those pertinent to “normal” spike bursts, as presented in the paper by Güdel and
Benz (Astron. Astrophys.
231, 202, 1990); in particular, their duration (about 7.4 ms at half power) is shorter, so they should be members of the SSS (super short
structures) family (Magdalenić et al., Astrophys. J.
642, L77, 2006). The bursts were generally strongly R-polarized; however, during the decaying part of interval I a low R-polarized and L-polarized
bursts were also present. This change of polarization shows a trend that resembles the peculiar form of the zebra lines in
the spectral dominion (“V” like). A global statistical analysis on the bursts observed in the two polarimetric channels shows
that the highest cross-correlation coefficient (about 0.5) was pertinent to interval I. The zebras and the bursts can be interpreted
by the same double plasma resonance process as proposed by Bárta and Karlicky (Astron. Astrophys.
379, 1045, 2001) and Karlicky et al. (Astron. Astrophys.
375, 638, 2001); in particular, the spikes are generated by the interruption of this process by assumed turbulence (density or magnetic
field variations). This process should be present in the region close to the reconnection site (e.g., in the plasma reconnection outflows) where the density and the magnetic field vary strongly. 相似文献
10.
In the framework of ‘microscopic’ theory of black holes (J. Phys. Soc. Jpn. Suppl. B 70, 84, 2001; Astrophys. USSR 4, 659, 1996; 35, 335, 1991, 33, 143, 1990, 31, 345, 1989a; Astrophys. Space Sci. 1, 1992; Dokl. Akad. Nauk USSR 309, 97, 1989b), and references therein, we address the ‘pre-radiation time’ (PRT) of neutrinos from black holes, which implies the lapse
of time from black hole’s birth till radiation of an extremely high energy neutrinos. For post-PRT lifetime, the black hole
no longer holds as a region of spacetime that cannot communicate with the external universe. We study main features of spherical
accretion onto central BH and infer a mass accretion rate onto it, and, further, calculate the resulting PRT versus bolometric
luminosity due to accretion onto black hole. We estimate the PRTs of AGN black holes, with the well-determined masses and
bolometric luminosities, collected from the literature by Woo Jong-Hak and Urry (Astrophys. J. 579, 530, 2002) on which this paper is partially based. The simulations for the black holes of masses M
BH
≃(1.1⋅106
÷4.2⋅109) M
⊙ give the values of PRTs varying in the range of about T
BH
≃(4.3⋅105
÷5.6⋅1011) yr. The derived PRTs for the 60 AGN black holes are longer than the age of the universe (∼13.7 Gyr) favored today. At present,
some of remaining 174 BHs may radiate neutrinos. However, these results would be underestimated if the reservoir of gas for
accretion in the galaxy center is quite modest, and no obvious way to feed the BHs with substantial accretion. 相似文献
11.
Triple F—a comet nucleus sample return mission 总被引：1，自引：0，他引：1
《Experimental Astronomy》2009,23(3):809-847
The Triple F (Fresh From the Fridge) mission, a Comet Nucleus Sample Return, has been proposed to ESA’s Cosmic Vision program. A sample return from a comet
enables us to reach the ultimate goal of cometary research. Since comets are the least processed bodies in the solar system,
the proposal goes far beyond cometary science topics (like the explanation of cometary activity) and delivers invaluable information
about the formation of the solar system and the interstellar molecular cloud from which it formed. The proposed mission would
extract three sample cores of the upper 50 cm from three locations on a cometary nucleus and return them cooled to Earth for
analysis in the laboratory. The simple mission concept with a touch-and-go sampling by a single spacecraft was proposed as
an M-class mission in collaboration with the Russian space agency ROSCOSMOS. 相似文献
12.
The question about the interpretation of numerical experiments on magnetic reconnection in solar flares is considered. A correspondence
between the standard classification of magnetohydrodynamic discontinuities and the parameters characterizing the mass flux
through a discontinuity and the magnetic field configuration has been established within a classical formulation of the problem
on discontinuous magnetohydrodynamic flows. A pictorial graphical representation of the relationship between the angles of
the magnetic field vector relative to the normal to the discontinuity plane on both its sides has also been found. The relations
between the parameters of a two-dimensional discontinuous flow have the simplest form in a frame of reference where the magnetic
field lines (B) are parallel to the matter velocity (u)—the deHoffmann-Teller frame. The question about the transformation of the magnetic field configuration when passing to a
“laboratory” frame of reference where (v · B) ≠ 0, i.e., an electric field is present, is considered in this connection. The result is applied to the analytical solution
of the problem on the magnetic field structure in the vicinity of a reconnecting current sheet obtained previously by Bezrodnykh
et al. The regions of nonevolutionary shocks are shown to appear near the endpoints of a current sheet with reverse currents. 相似文献
13.
Carolus J. Schrijver Marc L. Derosa Thomas R. Metcalf Yang Liu Jim Mctiernan Stéphane Régnier Gherardo Valori Michael S. Wheatland Thomas Wiegelmann 《Solar physics》2006,235(1-2):161-190
We compare six algorithms for the computation of nonlinear force-free (NLFF) magnetic fields (including optimization, magnetofrictional,
Grad–Rubin based, and Green's function-based methods) by evaluating their performance in blind tests on analytical force-free-field
models for which boundary conditions are specified either for the entire surface area of a cubic volume or for an extended
lower boundary only. Figures of merit are used to compare the input vector field to the resulting model fields. Based on these
merit functions, we argue that all algorithms yield NLFF fields that agree best with the input field in the lower central
region of the volume, where the field and electrical currents are strongest and the effects of boundary conditions weakest.
The NLFF vector fields in the outer domains of the volume depend sensitively on the details of the specified boundary conditions;
best agreement is found if the field outside of the model volume is incorporated as part of the model boundary, either as
potential field boundaries on the side and top surfaces, or as a potential field in a skirt around the main volume of interest.
For input field (B) and modeled field (b), the best method included in our study yields an average relative vector error En = 〈 |B−b|〉/〈 |B|〉 of only 0.02 when all sides are specified and 0.14 for the case where only the lower boundary is specified, while the total
energy in the magnetic field is approximated to within 2%. The models converge towards the central, strong input field at
speeds that differ by a factor of one million per iteration step. The fastest-converging, best-performing model for these
analytical test cases is the Wheatland, Sturrock, and Roumeliotis (2000) optimization algorithm as implemented by Wiegelmann
(2004). 相似文献
14.
We develop a diagnostic tool for determination of the electron densities in solar prominences using eclipse data. The method
is based on analysis of the hydrogen Balmer-line intensities (namely Hα and Hβ) and the white-light emission due to Thomson
scattering on the prominence electrons. Our approach represents a generalization of the ratio method already used by Koutchmy,
Lebecq, and Stellmacher (Astron. Astrophys.
119, 261, 1983). In this paper we use an extended grid of non-LTE prominence models of Gouttebroze, Heinzel, and Vial (Astron. Astrophys. Suppl. Ser.
99, 513, 1993) and derive various useful relations between prominence radiation properties and electron densities. Simultaneously, an effective
geometrical thickness of the prominence can also be obtained. As an example we apply our general technique to original eclipse
data of Koutchmy, Lebecq, and Stellmacher (Astron. Astrophys.
119, 261, 1983). Finally, we use our results to determine the color of prominences as it should be seen during total eclipses. 相似文献
15.
Three dimensional vector magnetic field structure throughout the chromosphere above an active region is deduced by combining high resolution H filtergrams with a simultaneous digital magnetogram. An analog model of the field is made with 400 metal wires representing fieldlines which are assumed to outline the H structure. The height extent of the field is determined from vertical field gradient observations around sunspots, from observed fibril heights and from an assumption that the sources of the field should be largely local. After digitization the magnetic field H matrix is retrieved. Electric current densities j are computed from j=curl H. The currents (typically 10 mA m–2) flow in patterns not similar to observed features and not parallel to magnetic fields. Lorentz forces are computed from {ie0323-01}. The force structures correspond to observed solar features and a series of observed dynamics may be expected: downward motion in bipolar areas in lower chromosphere, an outflow of the outer chromosphere into the corona with radially outward flow above bipolar plage regions (where coronal streamers are observed) and motions of arch filament systems. Observed current structure and magnitude agree well with previous vector magnetograph observations but disagree with theoretical current-free or force-free concepts. A dynamic chromosphere with electromagnetic forces in action is thus inferred from observations. 相似文献
16.
G. M. Webb 《Solar physics》1986,106(2):287-313
The equations of magnetohydrostatic equilibria for a plasma in a gravitational field are investigated analytically. For equilibria with one ignorable spatial coordinate, the equations reduce to a single nonlinear elliptic equation for the magnetic potential A. Similarity solutions of the elliptic equation are obtained for the case of an isothermal atmosphere in a uniform gravitational field. The solutions are obtained from a consideration of the invariance group of the elliptic equation. The importance of symmetries of the elliptic equation also appears in the determination of conservation laws. It turns out that the elliptic equation can be written as a variational principle, and the symmetries of the variational functional lead (via Noether's theorem) to conservation laws for the equation. As an example of the application of the similarity solutions, we construct a model magnetostatic atmosphere in which the current density J is proportional to the cube of the magnetic potential, and falls off exponentially with distance vertical to the base, with an e-folding distance equal to the gravitational scale height. The solutions show the interplay between the gravitational force, the J × B force (B, magnetic field induction) and the gas pressure gradient. 相似文献
17.
H. Kiliç 《Solar physics》2009,255(1):155-162
The short-term periodicities in sunspot numbers, sunspot areas, and flare index data are investigated in detail using the
Date Compensated Discrete Fourier Transform (DCDFT) for the full disk of the Sun separately over the rising, the maximum,
and the declining portions of solar cycle 23 (1996 – 2006). While sunspot numbers and areas show several significant periodicities
in a wide range between 23.1 and 36.4 days, the flare index data do not exhibit any significant periodicity. The earlier conclusion
of Pap, Tobiska, and Bouwer (1990, Solar Phys.
129, 165) and Kane (2003, J. Atmos. Solar-Terr. Phys.
65, 1169), that the 27-day periodicity is more pronounced in the declining portion of a solar cycle than in the rising and maximum
ones, seems to be true for sunspot numbers and sunspot area data analyzed here during solar cycle 23. 相似文献
18.
An elementary analysis based on Ampére's Law is given to separate the general magnetic field above the photosphere into two parts B=B
1+B
*. The field B
1 is a potential field due to electric currents below the photosphere. The field B
* is produced by electric currents above the photosphere combined with the induced mirror currents. By symmetry, B
* has a set of field lines lying entirely in the plane z = 0 taken to be the photosphere. This set of field lines can be constructed from given vector magnetograph measurements and represents all the information on the electric currents above the photosphere that a magnetograph can provide. Theoretical illustrations are given and the implications for data analysis are discussed. 相似文献
19.
J. Roosen 《Solar physics》1969,8(2):450-463
The distinction between faint and bright sources of the slowly varying component of the solar microwave emission (Paper II) is applied to statistics of the geomagnetic activity. Superposed epoch diagrams (recurrent disturbances excluded) show that the increased number of disturbed days after the CMP of sunspot groups can almost exclusively be ascribed to the spot groups associated with faint sources. The variation of the disturbance amplitude with the heliographic latitude of the spot groups is discussed. A tentative model for the solar-wind enhancement associated with a faint source is presented.For Paper I see Solar Phys.
7, 448; for Paper II see Solar Phys.
8, 204. 相似文献
20.
Five-dimensional spherically symmetric space-time is considered in bimetric theory of gravitation formulated by Rosen (Gen.
Rel. Grav. 4, 435, 1973) in the presence of cosmic string dust cloud. Exact cosmological models which represent geometric (Nambu) string, p-string
(Takabayasi string) and Reddy string (Astrophys. Space Sci. 301, 2006) are obtained in the static and non-static cases. Some physical properties of the models are also discussed. 相似文献