共查询到20条相似文献，搜索用时 562 毫秒
1.
This contribution deals with the properties of small-scale magnetic elements at the polar caps of the Sun. Spectro-polarimetric observations, obtained with high spatial resolution with the Gregory Coudé Telescope at the Observatorio del Teide on Tenerife, were analysed. We find, though with limited data sets, that polar faculae differ in two aspects from faculae of the network in non-active regions near the equator (equatorial faculae): (1) Polar faculae appear to have the same magnetic polarity as the general polar magnetic field. Presumably, the latter is rooted in the small-scale faculae. The equatorial faculae show both magnetic polarities. (2) Polar faculae, with a size of 3.5 ± 1.3, are larger than equatorial faculae with 2.1 ± 0.4. Yet as for equatorial faculae, polar faculae possess kilogauss magnetic fields. 相似文献
2.
We analyze a time series of high resolution observations near the solar limb, obtained in H and the Mg b1 line. We identified arch-shaped dark mottles, which are thin, faint H structures observable under very good seeing conditions, best seen in H +0.75 Å. Their mean length is about 15, their mean height about 6 and indicative lifetimes is of the order of 5 min. They show negative (away from the observer) line-of-sight velocities. A possible interpretation is that material flows from the apex towards the feet of the arches. 相似文献
3.
To examine the stray-light effect in magnetograph observations, we have determined the point spread functions of the vector magnetograph mounted on the Japanese Solar Flare Telescope based on two indirect methods, one analyzing the solar limb intensity profile, and the other using the Fourier power spectra of photospheric intensity distributions. Point spread functions consist of two parts: a blurring part which describes seeing and small-spread-angle stray light, and a scattering part which describes large-spread-angle stray light. The FWHM spatial resolution is typically 3.0, and the amount of scattered light is about 15% on clear days. We find that the blurring part is well described by a Moffat function whose Fourier transform is given by an exponential function. Our results indicate that polarization measurements of low-intensity magnetic elements like sunspots may be significantly underestimated due to the large-spread-angle stray light, and polarization measurements of magnetic elements which are smaller than 5–7 appear to be disturbed by small-spread-angle stray light. 相似文献
4.
The CCD spectroheliograph-magnetograph is a focal-plane ancillary instrument for the Pulkovo horizontal solar telescope ACU-5. The instrument is placed at an exit port of an isothermal high-resolution diffraction-grating spectrograph. A modified Leighton optical scheme for registration of sunspot magnetic fields is used. The instrument provides FITS-format digital video maps of radial velocities, magnetic fields, and spectroheliograms in any line of the spectral region 3900–11000 Å. The time to obtain one video map of size 91×154 is equal to 10.24 s. The angular resolution of the instrument is 0.8; spectral resolution is 0.01–0.03 Å. Since 1996 the Pulkovo CCD spectroheliograph-magnetograph has been used to obtain high spatial and temporal resolution observations of oscillations of radial velocities and magnetic fields in the photospheric layers of sunspots. 相似文献
5.
Two dimensional source brightness distributions at 26.4 MHz for solar bursts of spectral type II, III, IV, and V are derived from observations with a multiple-baseline, time-sharing interferometer system. It was designed explicitly to study the large angle (40 halo) component of low frequency solar bursts first reported by Weiss and Sheridan (1962). Thirty-two bursts occurring in the interval of June–August, 1975, were fit with a circular gaussian core and an elliptical gaussian halo component. Half-power halo diameters (E-W×N-S) averaged 30×28 for type III bursts and 42×27, 28×37, 30×25 for type V, II and IV bursts respectively. Typical core sizes fell in the range of 10±4 giving 31 halo to core size ratio. All burst types were found to have some large angle structure: the specific intensity was 10% compared to the core but the total power in each component was comparable. Two processes for producing the core-halo structure of type III bursts are compared: scattering and refraction of a point source and refraction from many sources over an extended region. It is concluded that the core can be explained by either model but the halo is more consistent with emission from an extended source region of 40° in longitude. 相似文献
6.
An analysis of the two-dimensional flow of water at 4°C past an infinite porous plate is presented, when the plate is subjected to a normal suction velocity and the heat flux at the plate is constant. Approximate solutions are derived for the velocity and temperature fields and the skin-friction. The effects ofG (Grashof number) andE (Eckert number) on the velocity and temperature fields are discussed.Nomenclature
u, v
velocity components of the fluid inx, y direction
-
g
acceleration due to gravity
-
coefficient of thermal expansion of water at 4°C
-
v
kinematic viscosity
-
density
-
T
temperature inside thermal boundary layer
-
T
free-stream temperature
-
k
thermal conductivity
-
C
p
specific heat at constant pressure 相似文献
7.
An analysis of the effects of Hall current on hydromagnetic free-convective flow through a porous medium bounded by a vertical plate is theoretically investigated when a strong magnetic field is imposed in a direction which is perpendicular to the free stream and makes an angle to the vertical direction. The influence of Hall currents on the flow is studied for various values of .Nomenclature
c
p
specific heat at constant pressure
-
e
electrical charge
-
E
Eckert number
-
E
electrical field intensity
-
g
acceleration due to gravity
-
G
Grashof number
-
H
0
applied magnetic field
-
H
magnetic field intensity
- (j
x
, j
y
, j
z
)
components of current densityJ
-
J
current density
-
K
permeability of porous medium
-
M
magnetic parameter
-
m
Hall parameter
-
n
e
electron number density
-
P
Prandtl number
-
q
velocity vector
- (T, T
w
, T
)
temperature
-
t
time
- (u, v, w)
components of the velocity vectorq
-
U
0
uniform velocity
-
v
0
suction velocity
- (x, y, z)
Cartesian coordinates
Greek Symbols
angle
-
coefficient of volume expansion
- e
cyclotron frequency
-
frequency
-
dimensionless temperature
-
thermal conductivity
-
coefficient of viscosity
-
magnetic permeability
-
kinematic viscosity
-
mass density of fluid
- e
charge density
-
electrical conductivity
- e
electron collision time 相似文献
8.
We report here on high angular resolution observations of solar noise storm sources at a frequency of 75 MHz. The data for the study were obtained at the Gauribidanur Radio Observatory (long.: 77°2612 E, lat.: 13°3612 N) about 100 km north of Bangalore, India, during the solar eclipse of 24 October 1995. Our main conclusion is that there are structures of angular size 2.5 arc min in the outer solar corona. 相似文献
9.
T. P. Singh A. K. Agrawal H. L. Agrawal A. Raptis 《Astrophysics and Space Science》1991,181(2):171-181
The Hall effect on the unsteady hydromagnetic free-convection resulting from the combined effects of thermal and mass diffusion of an electrical-conducting liquid through a porous medium past an infinite vertical porous plate in a rotating system have been analysed. The expressions for the mean velocity, mean skin friction, and mean rate of heat transfer on the plate are derived. The effects of magnetic parameterM, Hall parameterm, Ekman numberE, and permeability parameterK
* on the flow field are discussed with the help of graphs and tables.Nomenclature
C
p
specific heat at constant pressure
-
C
the species concentration inside the boundary layer
-
C
w
the species concentration at porous plate
-
C
the species concentration of the fluid at infinite
-
C
dimensionless species concentration
-
D
chemical molecular diffusivity
-
E
Ekman number
- Ec
Eckert number
-
g
acceleration due to gravity
- Gr
Grashof number
- Gm
modified Grashof number
-
H
0
applied magnetic field
- (J
x, Jy, Jz)
components of current density
-
M
magnetic parameter
-
m
Hall parameter
-
P
Prandtl number
-
q
m
mean rate of heat transfer
- Sc
Schmidt number
-
t
time
-
t
dimensionless time
-
T
temperature of fluid
-
T
w
temperature of the plate
-
T
temperature of fluid at infinite
-
T
dimensionless temperature
- (u, v, w)
components of the velocityq
-
w
0
suction velocity
- (x, y, z)
Cartesian coordinates
-
z
dimensionless coordinate normal to the plate
Greek symbols
coefficient of volume expansion
- *
coefficient of thermal expansion with concentration
-
frequency
-
dimensionless frequency
-
k
thermal conductivity
-
K
*
permeability parameter
-
dinematic viscosity
-
density of the fluid in the boundary layer
-
coefficient of viscosity
- e
magnetic permeability
-
angular velocity
-
electrical conductivity of the fluid
- m
mean skin friction
- mn
mean skin friction in the direction ofx
- mv
mean skin friction in the direction ofy 相似文献
10.
An exact analysis of the effects of mass transfer on the flow of a viscous incompressible fluid past an uniformly accelerated vertical porous and non-porous plate has been presented on taking into account the free convection currents. The results are discussed with the effects of the Grashof number Gr, the modified Grashof number Sc, the Schmidt number Sc, and the suction parametera for Pr (the Prandtl number)=0.71 representating air at 20°C.Nomenclature
a
suction parameter
-
C
species concentration
-
C
species concentration at the free stream
-
g
acceleration due gravity
- Gc
modified Grashof number (vg*(C
–C
)/U
0
3
)
- Pr
Prandtl number (C
p/K)
-
T
temperature of the fluid near the plate
-
T
dimensionless temperature near the plate ((T-T
)/(T
-T
))
-
U(t)
dimensionless velocity of the plate (U/U
0)
-
v
normal velocity component
-
v
0
suction/injection velocity
-
x, y
coordinate along and normal to the plate
-
v
kinematic viscosity (/gr)
-
C
p
specific heat at constant pressure
-
C
w
species concentration at the plate
-
C
non-dimensional species concentration ((C-C
)/(C
w
-C
))
- Gr
Grashof number (g(T
w
-T
)/U
0
3
)
-
D
chemical molecular diffusivity
- K
thermal conductivity
- Sc
Schmidt number (/D)
-
T
w
temperature of the plate
-
T
free stream temperature
-
t
time variable
-
t
dimensionless time (tU
0
2
/)
-
U
0
reference velocity
-
u
velocity of the fluid near the plate
-
u
non-dimensional velocity (u/U
0)
-
v
dimensionless velocity (v/U
0)
-
v
0
non-dimensionalv
0
(v
0
/U0)=–at–1/2
-
y
dimensionless ordinate (yU
0/)
-
density of the fluid
-
coefficient of viscosity 相似文献
11.
We have investigated the role of the 200yr period discovered by Vienne and Duriez (1992) on the tidal evolution of the Mimas–Tethys system through the 2:4 ii present resonance. Three terms are found to generate this period. We present a perturbedpendulum model in which these terms bring about a perturbation to the ideal ii resonance pendulum, which is in a direct ratio to the eccentricity e of Tethys. Although e is now very small, it is shown that this quantity could have been much greater in the past. We also show, thanks to this model, that these terms may have brought about a stochastic layer of noticeable width at the time of capture in the ii resonance, with the consequence that the possible values of the inclination i of Mimas before capture range from 0.4° to 0.6° (these uncertainties arise from the present uncertainties on e). The role of each one of the three terms is examined in the appearance of chaos. A capture into the 1/1 secondary resonance (between the libration period of the primary ii resonance and the period of about 200yr) is found possible. It means that the system could have experienced several captures in the primary resonance, instead of a single one, and that i could have been, with this assumption, much lower than 0.4°. A probability of capture into this secondary resonance as a function of the eccentricity of Tethys on encounter is derived, using Malhotra's method (Malhotra, 1990). Allan's values of i = 0.42° and e 0 (Allan, 1969) are therefore called into question, and taking e 0 is shown to be absolutely necessary if we want to understand the phenomena at work in the Mimas–Tethys system. 相似文献
12.
In the present paper, the effects of free convection currents and the viscous dissipation on the unsteady flow of an electrically conducting and viscous incompressible fluid around an uniformly accelerated vertical porous plate subjected to a suction or injection velocity inversely proportional to the square root of time, in presence of a transverse magnetic field, have been investigated. Analytical solutions for the velocity and the temperature distributions, the skin-friction and the rate of heat transfer are obtained for small magnetic parameterM. During the course of discussion the effects of the Grashof number Gr, the Eckert number Ec, the suction/injection parametera have been considered for unit value of the Prandtl number Pr.Nomenclature
a
suction/injection parameter
-
C
p
specific heat at constant pressure
-
B
0
magnetic induction
-
g
acceleration due to gravity
- Gr
Grashof number (g(T
w
–T
)/U
0
3
)
-
K
thermal conductivity
-
M
magnetic field parameter (B
0
2
/U
0
2
)
- Pr
Prandtl number (C
p/K)
-
T
temperature of the fluid near the plate
-
T
w
temperature of the plate
-
T
temperature of the fluid at infinity
-
t
time
-
t
dimensionless time (tU
0
2
/)
-
u
velocity of the fluid
-
u
non-dimensional velocity (u/U
0)
-
U
velocity of the plate
-
U
dimensionless velocity of the plate (U/U
0)
-
U
0
reference velocity
-
v
0
suction velocity
-
v
0
non-dimensional suction velocity (v
0/U
0)=at
–1/2
- Ec
Eckert number ((U
0)2/3/C
p(T
w
–T
))
-
T
dimensionless temperature of the fluid near the plate ((T–T
)/(T
w
–T
))
-
x, y
coordinates along and normal to the plate
-
x, y
dimensionless coordinates (y=yU
0/)
-
kinematic viscosity
-
coefficient of volume expansion
-
electric conductivity of the fluid
-
y/2t
1/2
-
density of the fluid
-
skin-friction
-
dimensionless skin-friction
-
q
rate of heat transfer
-
q
non-dimensional rate of heat transfer
-
coefficient of viscosity
- e
magnetic permeability
On leave of absence from Department of Mathematics, University of Dhaka, Bangladesh 相似文献
13.
The effect of small perturbations and in the coriolis and the centrifugal forces respectively on the stability of the triangular points in the restricted problem of three bodies with variable mass has been studied. It is found that the range of stability of triangular points increases or decreases depending upon whether the perturbation point (, ) lies in one or the other of the two parts in which the (, ) plane is divided by the line J8–J9=0 where J8 and J9 depend upon , the constant due to the variation in mass governed by Jeans' law. 相似文献
14.
The microwave circular polarization of the active region (AR) NOAA 7260 on 21–23 August 1992 is analyzed. Two-dimensional images at 1.76 cm with spatial resolution of =10 from the Nobeyama radioheliograph and one-dimensional scans at 9 wavelengths in the range of 1.81–3.43 cm and =16.3–31.1 from the radio telescope RATAN-600 were used. An inversion of the sense of circular polarization through the wavelength range was recorded on 22 August. It is shown that both the wavelength and the time dependence of the inversion are consistent with quasi-transverse (QT) propagation of the radiation in the solar corona. From this, the strength of the coronal magnetic field in the active region was found to be H=20–65 G at a height of h= (5.7–8.7)×109 cm above the photosphere on 22 and 30 August and 125 G at the lower height of (3.7–6.4)×109 cm on 23 August. We present a new technique, based on the radio mapping (in both Stokes I and V) of an AR undergoing circular polarization inversion; applying this method to the Nobeyama data we obtained, for the first time, a magnetogram of the coronal magnetic field. For AR 7260 we found values in the range of 70–100 G at heights of (4–6)×109 cm on 23 August, adopting a constant value of NL (where N is the electron density and L is the scale of the coronal field divergence) of 2.5×1018 cm–2. We compare our results with force-free extrapolations of the photospheric magnetic field from a MSFC magnetogram obtained on 20 August. 相似文献
15.
Spectra around the 6374 Å [Fex] and 7892 Å [Fexi] emission lines were obtained simultaneously with the 25-cm coronagraph at Norikura Observatory covering an area of 200 ×500 of the solar corona. The line width, peak intensity and line-of-sight velocity for both the lines were computed using Gaussian fits to the observed line profiles at each location (4 ×4 ) of the observed coronal region. The line-width measurements show that in steady coronal structures the FWHM of the 6374 Å emission line increases with height above the limb with an average value of 1.02 mÅ arc sec–1. The FWHM of the 7892 Å line also increases with height but at a smaller average value of 0.55 mÅ arc sec–1. These observations agree well with our earlier results obtained from observations of the red, green, and infrared emission lines that variation of the FWHM of the coronal emission lines with height in steady coronal structures depends on plasma temperatures they represent. The FWHM gradient is negative for high-temperature emission lines, positive for relatively low-temperature lines and smaller for emission lines in the intermediate temperature range. Such a behaviour in the variation of the FWHM of coronal emission lines with height above the limb suggests that it may not always be possible to interpret an increase in the FWHM of emission line with height as an increase in the nonthermal velocity, and hence rules out the existence of waves in steady coronal structures. 相似文献
16.
Walter Petry 《Astrophysics and Space Science》1986,124(1):63-82
We start from a reference frame for which the pseudo-Euclidean geometry holds, i.e., all laws in have the form of special relativity. The geometry of a reference frame , moving with constant velocity with regard to , is received by using the well-known Galilei-transformation for the covariant space-time vector. In the geometry is different from the pseudo-Euclidean one, i.e., the principle of special relativity does not hold. The velocity of light in is direction dependent but the null result of the Michelson-Morley experiment is received. Several useful transformation formulae are given. In particular, we obtain the Marinov-transformation as transformation from the frame to , and conversely. Maxwell's equations and the equations of motion in the reference frame are given. The theory is applied to some examples, e.g., the Doppler effect, the Fizeau experiment, the field of a charged particle, etc. The method can be generalized to an accelerated reference frame . 相似文献
17.
The energy levels and wave functions of hydrogen and helium atoms in the presence of large (107G) magnetic fields are found by assuming that the eigenvalues and eigenvectors may be approximated by those of a truncated Hamiltonian matrix. In these atoms, fields of this size produce, in addition to the usual Paschen-Back effect, a quadratic Zeeman effect. This contributes an upward shift to the energy of all levels, which at sufficiently high fields dominates the Paschen-Back splitting.The behavior of a number of eigenvalues and wave functions as a function of magnetic field is presented. The effects of the field on the wavelengths and strengths of the components of H and the helium lines 4471, 4026 and 4120 as well as the forbidden 4025 are examined. In hydrogen the lines are split into components attributed to the now nondegenerate transitionsnlm
lnlml. In helium forbidden lines are excited, which may develop strengths larger than those of the allowed lines. 相似文献
18.
Light refraction by the Sun's atmosphere is calculated.As detected from the Earth, the refraction can deflect a light ray emitted from the Sun's limb by 13 or a starlight ray grazing the solar limb by 26, an effect 15 times larger than the gravitational deflection. 相似文献
19.
Kenneth R. Lang 《Solar physics》1978,58(2):337-342
Unique long-term visibility variations are detected when the quiet Sun is observed with interferometers operating at 8 mm and 11 cm wavelength with angular resolutions of 0.5. Quasiperiodic fluctuations in fringe amplitude are observed with periods between 20 and 30 min, and with amplitude nulls which are correlated with 180° phase changes. These variations are interpreted in terms of a changing projected baseline while viewing a few sources with angular sizes of 0.5 which are distributed within the main interferometer beam with typical angular separations of 7. The observed variations cannot be due to expanding or contracting sources of the type envisaged by Bocchia and Poumeyrol (1976) when explaining similar variations observed at 8 mm wavelength. A comparison of the flux observed at 8 mm and 11 cm indicates that the individual sources are optically thick thermal radiators with a flux which decreases with increasing wavelength, but with a temperature which increases with increasing wavelength where higher, hotter levels of the chromosphere are observed. For a source whose angular size is 0.5, the observed flux values correspond to respective temperatures of 5000 K and 19 000 K at 8 mm and 11cm - suggesting that elements of the chromospheric network are being observed. A thermal origin for the individual sources is consistent with the lack of any detectable circular or linear polarization (< 10%) in the interferometer signal. 相似文献
20.
In a statistical analysis of Debrecen Photoheliographic Results sunspot area data we find that the logarithmic deviation (logD) of the area decay rate D from the parabolic mean decay law (derived in the first paper in this series) follows a Gaussian probability distribution. As a consequence, the actual decay rate D and the time-averaged decay rate
are also characterized by approximately lognormal distributions, as found in an earlier work. The correlation time of (logD) is about 3 days. We find a significant physical anticorrelation between (logD) and the amount of plage magnetic flux of the same polarity in an annulus around the spot on Kitt Peak magnetograms. The anticorrelation is interpreted in terms of a generalization of the turbulent erosion model of sunspot decay to the case when the flux tube is embedded in a preexisting homogeneous plage field. The decay rate is found to depend inversely on the value of this plage field, the relation being very close to logarithmic, i.e., the plage field acts as multiplicative noise in the decay process. A Gaussian probability distribution of the field strength in the surrounding plage will then naturally lead to a lognormal distribution of the decay rates, as observed. It is thus suggested that, beside other multiplicative noise sources, the environmental effect of surrounding plage fields is a major factor in the origin of lognormally distributed large random deviations from the mean law in the sunspot decay rates. 相似文献