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1.
Structure of horizontal convective currents in the solar atmosphere has been investigated using profiles of the λ ≈ 532.42
nm neutral iron line which were observed at the solar limb with high spatial resolution. The asymmetry of the observed line
was shown to arise when approaching the solar limb. The spatial and time velocity variations were simulated using the λ-meter
technique. Acoustic waves were removed using the k-ω filters. The convection currents on various spatial scales were distinguished, namely, those connected with granulation,
mesogranulation, and supergranulation. The spatial and time distribution of the convection velocities in the photosphere and
in the low chromosphere has been analyzed. The horizontal currents were shown to exist on granulation, mesogranulation, and
supergranulation scales as low as h ≈ 250 km, and the granulation and mesogranulation horizontal velocities increase with height. In the photospheric layers,
the supergranulation vertical-velocity field appears almost invariable, while the supergranulation horizontal-velocity field
can vary with height. The horizontal velocity distribution within large convection currents is found to be asymmetric on granulation,
mesogranulation, and supergranulation scales. 相似文献
2.
Alfred Clark Jr. 《Solar physics》1968,4(4):386-400
Some theoretical models are given which illustrate the structure of chromospheric magnetic fields associated with supergranulation. It is found that the chromospheric fields depend critically on whether or not there are large-scale vertical motions at the level where the horizontal supergranule motions are observed. In the absence of such motions, the concentration of field produced in the photosphere does not persist more than a few scale heights into the chromosphere; however, the chromospheric mass density is increased above the supergranule boundaries in this case. Completely different results-such as a chromospheric potential field-may be obtained by the inclusion of vertical motions. It is concluded that a rather wide range of chromospheric-field structures is consistent with present observational knowledge of the supergranulation. 相似文献
3.
Jacques M. Beckers 《Solar physics》1968,5(3):309-322
The large scale (> 5000 km) intensity structure of the photosphere has been examined. The power per frequency unit indicates a continuous increase towards smaller spatial frequency. No excess power exists at wavelengths near the size of the supergranulation (30000 km) or at any other wavelength between 5000 and 100000 km. However, direct measurement of the intensity distribution in 1652 supergranulation cells shows a very small increase of the intensity towards the cell boundary. The amount of this increase is larger near the solar limb. It is probably due to a weak continuum emission associated with the chromospheric network. Any temperature difference arising from the supergranulation convection is obscured by this emission and is probably less than 1 K. 相似文献
4.
Berrilli F. Del Moro D. Consolini G. Pietropaolo E. Duvall T.L. Kosovichev A.G. 《Solar physics》2004,221(1):33-45
We investigate spatial dislocation ordering of the solar structures associated with supergranulation and granulation scales.
The supergranular and granular structures are automatically segmented from time-distance divergence maps and from broad-band
images, respectively. The spatial dislocation ordering analysis is accomplished by applying the statistical method of Pair
Correlation Function, g
2(r), to segmented features in the solar fields. We compare the computed g
2(r) functions obtained from both single and persistent, i.e., time-averaged, fields associated with supergranulation and granulation.
We conclude that supergranulation and granulation patterns present a different topological order both in single and persistent
fields. The analysis carried out on single fields suggests that the granulation behaves as an essentially random distribution
of soft plasma features with a very broad distribution in size, while supergranulation behaves as a random distribution of
close packed, coherent stiff features with a rather defined mean size. 相似文献
5.
Simple convection models estimate the depth of supergranulation at approximately 7500 km which suggests that supergranules would rotate at the rate of the plasma in the outer 1% of the solar radius. The supergranulation rotation obtained from MDI dopplergrams shows that supergranules rotate faster than the outer 5% of the convection zone and show zonal flows matching results from inversions of f-mode splittings. Additionally, the rotation rate depends on the size scale of the features. 相似文献
6.
Y. Nakagawa 《Solar physics》1973,33(1):87-101
Observations indicate modulations of the 5-min period of chromospheric oscillations in magnetically active regions of the Sun. Thee observations are examined on the basis of the diagnostic diagrams obtained previously in a theoretical study of trapped magnetoatmospheric waves, and it is shown that the observed results can be interpreted in terms of the modulations of characteristic period of the trapped magnetoatmospheric waves for various configurations and strengths of the magnetic field, such as the umbra and penumbra of a sunspot, plages, boundaries as well as inside of supergranulation cells. The physical significance of the results and the limitation of the present analysis are discussed together with the possible future direction of this type of study.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
7.
Some theoretical models illustrating the growth of magnetic fields around the boundaries of supergranulation cells are given. The evolution of a magnetic field in a prescribed velocity field is calculated for the idealized case of hexagonal cells. The calculations are carried out both for a perfect conductor and a fluid of finite conductivity. The theory is developed in such a way as to be virtually free of specific assumptions about the depth dependence of the supergranulation flow. The results demonstrate the tendency of the field to accumulate at those boundary points where the flow is most strongly converging. 相似文献
8.
We employ fractal analysis to study the complexity of supergranulation structure using the Solar and Heliospheric Observatory
(SOHO) dopplergrams. Our data consists of 200 visually selected supergranular cells, for which we find a broad, slightly asymmetric
dispersion in the size distribution, with the most probable size around 31.9 Mm. From the area–perimeter relation, we deduce
a fractal dimension D of about 1.25. This is consistent with that for isobars, and suggests a possible turbulent origin of supergranulation. By
relating this to the variances of kinetic energy, temperature and pressure, it is concluded that the supergranular network
is close to being isobaric and that it has a possible turbulent origin. 相似文献
9.
10.
Three independent observations by rocket, Skylab, and OSO-8 have all indicated the presence of steady downflows of the order of a few kilometers per second in the solar transition region overlying the chromospheric network. Using density estimates at these heights from traditional transition region models, we find that the downward mass fluxes associated with these velocities are comparable with the estimated upward mass flux in spicules, originating in the same regions. Since both observations and theoretical calculations show that the solar wind can accept only a small fraction of the upward spicule flux, we suggest that the downflow represents spicular material returning to the chromosphere after being heated to coronal temperatures. In this context, the differential velocity measurement of Cushman and Rense is interpreted as indicating a difference in downflow speeds rather than a difference in expansion speeds.Moreover, the enthalpy flux associated with the downflow of coronal material into these regions is shown by various estimates to exceed the inward heat flow expected by thermal conduction and it may constitute the dominant energy source for the transition region. Simplified analytical models are used to explore the nature of the transition region overlying the supergranulation boundaries, under the assumption that the thermal structure results from a balance of the downward convection of enthalpy and radiative losses. Models based upon these considerations are shown to be consistent with the observed emission measures.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
11.
The concepts of magnetic reconnection that have been developed in two dimensions need to be generalised to three-dimensional configurations. Reconnection may be defined to occur when there is an electric field (E) parallel to field lines (known as potential singular lines) which are potential reconnection locations and near which the field has an X-type topology in a plane normal to that field line. In general there is a continuum of neighbouring potential singular lines, and which one supports reconnection depends on the imposed flow or electric field. For steady reconnection the nearby flow and electric field are severely constrained in the ideal region by the condition that E = 0 there. Potential singular lines may occur in twisted prominence fields or in the complex magnetic configuration above sources of mixed polarity of an active region or a supergranulation cell. When reconnection occurs there is dynamic MHD behaviour with current concentration and strong plasma jetting along the singular line and the singular surfaces which map onto them. 相似文献
12.
V. V. Zaitsev 《Astronomy Letters》2005,31(9):620-626
We analyze the electric fields that arise at the footpoints of a coronal magnetic loop from the interaction between a convective flow of partially ionized plasma and the magnetic field of the loop. Such a situation can take place when the loop footpoints are at the nodes of several supergranulation cells. In this case, the neutral component of the converging convective flows entrain electrons and ions in different ways, because these are magnetized differently. As a result, a charge-separating electric field emerges at the loop footpoints, which can efficiently accelerate particles inside the magnetic loop under appropriate conditions. We consider two acceleration regimes: impulsive (as applied to simple loop flares) and pulsating (as applied to solar and stellar radio pulsations). We have calculated the fluxes of accelerated electrons and their characteristic energies. We discuss the role of the return current when dense beams of accelerated particles are injected into the corona. The results obtained are considered in light of the currently available data on the corpuscular radiation from solar flares. 相似文献
13.
In the standard model of the solar convective zone, turbulent eddies transport entropy rather than temperature. We consider the turbulent mean field equations for the convective zone, including entropy transport, and show that the zone can be unstable to larger scale motion which we identify with the supergranulation and giant cells. 相似文献
14.
The characteristics of the most unstable fundamental mode and the first harmonic excited in the convection zone of a variety
of solar envelope models are shown to be in reasonable agreement with the observed features of granulation and supergranulation.
On leave of absence from Government Digvijai College, Rajnandgaon 491441 相似文献
15.
B. V. Somov 《Astronomy Letters》2012,38(2):128-138
The role of the electric currents distributed over the volume of an active region on the Sun is considered from the standpoint
of solar flare physics. We suggest including the electric currents in a topological model of the magnetic field in an active
region. Typical values of the mutual inductance and the interaction energy of the coronal electric currents flowing along
magnetic loops have been estimated for the M7/1N flare on April 27, 2006. We show that if these currents actually make a significant
contribution to the flare energetics, then they must manifest themselves in the photosphericmagnetic fields. Depending on
their orientation, the distributed currents can both help and hinder reconnection in the current layer at the separator during
the flare. Asymmetric reconnection of the currents is accompanied by their interruption and an inductive change in energy.
The reconnection of currents in flares differs significantly from the ordinary coalescence instability of magnetic islands
in current layers. Highly accurate measurements of the magnetic fields in active regions are needed for a quantitative analysis
of the role of distributed currents in solar flares. 相似文献
16.
The evolution of the velocity and magnetic fields associated with supergranulation has been investigated using the Sacramento Peak Observatory Diode Array Magnetograph. The observations consist of time sequences of simultaneous velocity, magnetic field, and chromospheric network measurements. From these data it appears that the supergranular velocity cells may have lifetimes in excess of the accepted value of 24 hours. Magnetic field motions associated with supergranulation were infrequent and seem to be accompanied by changes in the velocity field. More prevalent were the slow dissipation and diffusion of stationary flux points. Vertical velocity fields of 200 m s–1 appear to be confined to downflows in magnetic field regions at supergranular boundaries. These downflows are only observed using certain absorption lines. Corresponding upflows in the center of supergranules of less than 50 m s–1 may be present but cannot be confirmed. 相似文献
17.
O.A. Troshichev V.A. Gizler I.A. Ivanova A.Yu. Merkuryeva 《Planetary and Space Science》1979,27(12):1451-1459
The distant effects of the field-aligned currents (FAC) observed by TRIAD are computed for conditions of low and moderate activity. The systems of total ionospheric currents (both Hall and Pedersen) generated by corresponding FAC are also examined and the contribution of the distant effects and the ionospheric currents into the total equivalent current system is estimated. The conclusions are as follows. In cases of low magnetic activity the magnetic effects produced by Pedersen currents are mainly cancelled by the FAC distant effect in accord with Fukushima's theorem. In cases of moderate activity when the zone of high ionospheric conductivity and the two-sheet FAC structure are present the FAC distant effect is too small to cancel the effect of Pedersen currents. For these conditions the system of total ionospheric currents shows the best correspondence with the experimental equivalent current system. Effects produced by the IMF azimuthal component are also analysed. 相似文献
18.
Diaa E. Fawzy 《New Astronomy》2010,15(8):717-725
The formation of shocks and shock heating by radiatively damped longitudinal waves in solar magnetic flux tubes of different filling factors is studied. We consider three flux tubes of filling factors: 1%, 20%, and exponentially spreading which represent normal, enhanced network regions and the interior of supergranulation cells respectively. Monochromatic waves with periods 60 s and energy fluxes of 4.0 · 108 erg cm?2 s?1 are assumed to propagate in the tubes. We find that the H?-continuum losses and the Mg II line emission are much reduced in the tube of small filling factor while the mean temperatures are roughly similar in both tubes. The exponential flux tube shows little or no shock heating and no radiation damping. Shocks form earlier in the tube of high filling factor, and have larger strength. 相似文献
19.
Tyan Yeh 《Solar physics》1978,56(2):439-447
The topological structure of the coronal-interplanetary magnetic field is determined by the arrangement of the neutral lines at the coronal base. It is characterized by nested separatrices, which are interfaces between closed and open field lines or between oppositely directed open field lines, in the coronal-interplanetary space. In the neighborhoods of these separatrices there are important electric currents. These currents form the basis for the sheet-current model.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
20.
The interaction between small-scale magnetic fields and horizontal photospheric flows has been studied from observations of high angular resolution
obtained with the Lockheed narrowband filter in the Swedish Vacuum Solar Telescope at La Palma. The measured magnetic flux density (B
) is in the range from a detection limit of 10 G to about 500 G, showing a good correspondence with the filigree. The magnetic flux elements take part in the local flows towards downdrafts at the supergranulation cell boundaries. The measured flux density, as well as the associated filigree intensity, decrease as the structures approach the downdrafts, presumably as a result of increased tilting and possibly submergence of flux into the downdrafts. 相似文献