共查询到20条相似文献，搜索用时 46 毫秒
1.
We investigate the structure of convective flows in the solar photosphere on subgranulation scales. The solar granulation pattern is reproduced by solving the inverse problem of nonequilibrium radiation transfer on the basis of the profiles of the neutral iron line λ 523.42 nm. The wave motions are excluded by the k-ω filtration. The line-of-sight velocity has an asymmetric distribution inside the convective flows in large granules (1.5″ and larger) in the lower photosphere and at the bottom of the middle photosphere. This asymmetry is weaker in the upper photosphere. For smaller flows the distribution is more symmetric at all heights. The asymmetry of the temperature distribution is less pronounced. Large convective flows were found to have a fine structure: they are fragmentized into several smaller flows. The fine structure of large flows and spatial smearing are responsible for the observed asymmetry of the convection velocity distribution inside flows. 相似文献
2.
We study the temporal variation of subsurface flows of 788 active regions and 978 quiet regions. The vertical-velocity component
used in this study is derived from the divergence of the measured horizontal flows using mass conservation. The horizontal
flows cover a range of depths from the surface to about 16 Mm and are determined by analyzing about five years of GONG high-resolution
Doppler data with ring-diagram analysis. We determine the change in unsigned magnetic flux during the disk passage of each
active region using MDI magnetograms binned to the ring-diagram grid. We then sort the data by their flux change from decaying
to emerging flux and divide the data into five subsets of equal size. The average vertical flows of the emerging-flux subset
are systematically shifted toward upflows compared to the grand average values of the complete data set, whereas the average
flows of the decaying-flux subset show comparably more pronounced downflows especially near 8 Mm. For flux emergence, upflows
become stronger with time with increasing flux at depths greater than about 10 Mm. At layers shallower than about 4 Mm, the
flows might start to change from downflows to upflows, when flux emerges, and then back to downflows after the active regions
are established. The flows in the layers between these two depth ranges show no response to the emerging flux. In the case
of decaying flux, the flows change from strong upflows to downflows at depths greater than about 10 Mm, whereas the flows
do not change systematically at other depths. A cross-correlation analysis shows that the flows in the near-surface and the
deeper layers might change about one day before flux emerges. The flows associated with the quiet regions fluctuate with time
but do not show any systematic variation. 相似文献
3.
We compare horizontal flow fields in the photosphere and in the subphotosphere (a layer 0.5 Mm below the photosphere) in two solar active regions: AR?11084 and AR?11158. AR?11084 is a mature, simple active region without significant flaring activity, and AR?11158 is a multipolar, complex active region with magnetic flux emerging during the period studied. Flows in the photosphere are derived by applying the Differential Affine Velocity Estimator for Vector Magnetograms (DAVE4VM) on HMI-observed vector magnetic fields, and the subphotospheric flows are inferred by time–distance helioseismology using HMI-observed Dopplergrams. Similar flow patterns are found for both layers for AR?11084: inward flows in the sunspot umbra and outward flows surrounding the sunspot. The boundary between the inward and outward flows, which is slightly different in the photosphere and the subphotosphere, is within the sunspot penumbra. The area having inward flows in the subphotosphere is larger than that in the photosphere. For AR?11158, flows in these two layers show great similarities in some areas and significant differences in other areas. Both layers exhibit consistent outward flows in the areas surrounding sunspots. On the other hand, most well-documented flux-emergence-related flow features seen in the photosphere do not have counterparts in the subphotosphere. This implies that the horizontal flows caused by flux emergence do not extend deeply into the subsurface. 相似文献
4.
Laurent Gizon 《Solar physics》2004,224(1-2):217-228
Flows in the upper convection zone are measured by helioseismology on a wide variety of scales. These include differential
rotation and meridional circulation, local flows around complexes of magnetic activity and sunspots, and convective flows.
The temporal evolution of flows through cycle 23 reveals connections between mass motions in the solar interior and the large-scale
characteristics of the magnetic cycle. Here I summarize the latest observations and their implications. Observations from
local helioseismology suggest that subsurface flows around active regions introduce a solar-cycle variation in the meridional
circulation. 相似文献
5.
L. K. Harra V. Archontis E. Pedram A. W. Hood D. L. Shelton L. van Driel-Gesztelyi 《Solar physics》2012,278(1):47-71
In this paper we analyse the flux emergence that occurred in the following polarity area of an active region on 1 – 2 December
2006. Observations have revealed the existence of fast outflows at the edge of the emerging flux region. We have performed
3-D numerical simulations to study the mechanisms responsible for these flows. The results indicate that these outflows are
reconnection jets or pressure-driven outflows, depending on the relative orientation of the magnetic fields in contact (i.e. the emerging flux and the active region’s field which is favourable for reconnection on the west side and nearly parallel
with the pre-existing field on the east side of the emerging flux). In the observations, the flows are larger on the west
side until late in the flux emergence, when the reverse is true. The simulations show that the flows are faster on the west
side, but do not show the east flows increasing with time. There is an asymmetry in the expansion of the emerging flux region,
which is also seen in the observations. The west side of the emerging flux region expands faster into the corona than the
other side. In the simulations, efficient magnetic reconnection occurs on the west side, with new loops being created containing
strong downflows that are clearly seen in the observations. On the other side, the simulations show strong compression as
the dominant mechanism for the generation of flows. There is evidence of these flows in the observations, but the flows are
stronger than the simulations predict at the later stages. There could be additional small-angle reconnection that adds to
the flows from the compression, as well as reconnection occurring in larger loops that lie across the whole active region. 相似文献
6.
L.J. Lanzerotti C.G. Maclennan R.P. Lepping S.M. Krimigis 《Planetary and Space Science》1980,28(12):1163-1169
Voyager 1, exiting the earth's magnetosphere along the dawn meridian at a velocity of ~11 km/sec, measured strong tailward flows of ions (E30keV) immediately outside the magnetopause. These flows are found to originate sunward of the dawn meridian and to exhibit significant variabilities on the time scale of 400 msec. The variations are not related to changes in the magnetosheath magnetic fields and are likely produced up-stream by the leakage of magnetosphere protons or by a magnetopause particle energization process. The intensities of the dawn meridian ion flows are greater in the magnetosheath than in the magnetosphere. The flows appear to penetrate inside the dawn magnetosphere to a depth 0.1 R>E, less than an ion gyroradius. 相似文献
7.
We study the ionization, thermal structure and dynamics of active galactic nuclei (AGN) flows that are partially shielded from the central continuum. We utilize a detailed non-local thermodynamic equilibrium photoionization and radiative transfer code using exact (non-Sobolev) calculations. We find that shielding has a pronounced effect on the ionization, thermal structure and the dynamics of such flows. Moderate shielding is especially efficient in accelerating flows to high velocities because it suppresses the ionization level of the gas. The ionization structure of shielded gas tends to be distributed uniformly over a wide range of ionization levels. In such gas, radiation pressure due to trapped line photons can dominate over the thermal gas pressure and have a significant effect on the thermal stability of the flow. Heavily shielded flows are driven mainly by line radiation pressure, and so line locking has a large effect on the flow dynamics. We show that the observed 'Lα ghost' is a natural outcome in highly ionized flows that are shielded beyond the Lyman limit. We suggest that high-velocity AGN flows occupy only a small fraction of the volume and that their density depends only weakly on the velocity field. 相似文献
8.
《天文和天体物理学研究(英文版)》2015,(10)
Study of the small-scale structures and material flows associated with solar quiescent filaments is very important for understanding the formation and equilibrium of solar filaments.Using high resolution Ha data observed by the New Vacuum Solar Telescope,we present the structures of barbs and material flows along the threads across the spine in two quiescent filaments on 2013 September 29 and on 2012 November 2,respectively.During the evolution of the filament barb,several parallel tube-shaped structures formed and the width of the structures ranged from about2.3 Mm to 3.3 Mm.The parallel tube-shaped structures merged together accompanied by material flows from the spine to the barb.Moreover,the boundary between the barb and surrounding atmosphere was very neat.The counter-streaming flows were not found to appear alternately in the adjacent threads of the filament.However,the large-scale patchy counter-streaming flows were detected in the filament.The flows in one patch of the filament have the same direction but flows in the adjacent patch have opposite direction.The patches of two opposite flows with a size of about 10" were alternately exhibited along the spine of the filament.The velocity of these material flows ranged from 5.6 km s~(-1) to 15.0 km s~(-1).The material flows along the threads of the filament did not change their direction for about two hours and fourteen minutes during the evolution of the filament.Our results confirm that the large-scale counterstreaming flows with a certain width along the threads of solar filaments exist and are coaligned well with the threads. 相似文献
9.
Speeds of vertical flows in quiescent solar filaments are typically much less than the local Alfvén speed. This is why the flows in filament barbs can be modeled by perturbing a magnetostatic solution describing a balance between the Lorentz force, gravity, and gas pressure in a barb. This approach explains why some of the flows are neither aligned with the magnetic field nor controlled by gravity. Both the observed upflows and the magnetic field dips in barbs are likely to be caused by photospheric magnetic reconnection. 相似文献
10.
A study is made of axisymmetric, low sonic-Mach-number flows of a viscous fluid with angular momentum outside of a black-hole. The viscosity is an eddy viscosity due to turbulence in the sheared flows. Self-similar solutions arise naturally, reducing the Navier-Stokes equations to a set of nonlinear ordinary differential equations. These equations are solved analytically for flows of constant specific angular momentum and numerically for more general flows. For flows with non-constant specific angular momentum, the momentum flux density includes a planar discontinuity which is interpreted as an accretion disc. In general, two flow regions appear on each side of the disk, corresponding to accretion onto the disk and jet-like outflows along the ±z-axes. Physical interpretations of the solutions show that these flows arise in response to point sources of axial momentum at the origin directed in the ±z-directions. The power needed to maintain this momentum input is assumed to come from the mass accretion onto the black hole.The hydrodynamic flows are generalized to include a magnetic field. In the limit of infinite electrical conductivity, the possible types of flow patterns are the same as in hydrodynamic case. The magnetic field alters the relative amounts of reversible and irreversible momentum and angular momentum transport by the flow. For a flow with turbulent viscosity, the magnetic field acts to reduce the level of the turbulence and the effective value of the eddy viscosity. 相似文献
11.
Self-similar flows of a gas, moving under the gravitational force of attraction behind a spherical shock wave, which are driven out by a propelling contact surface and propagating into a uniform atmosphere at rest are investigated. The energy of the expanding wave has been assumed to be time-dependent, obeying a power law. In the last section the self-similar homothermal flows of self-gravitating gas has been also discussed. A comparative study has been made between the nature of flow variables for adiabatic and homothermal flows. 相似文献
12.
It is shown that endogenic lava flow processes can be identified by their characteristic effects on lunar crater size distributions without necessarily being able to recognise individual flows on the photographs studied. The thickness of lava flows or a series of flows can be estimated from these crater size distribution characteristics. The lava flow histories of the Apollo landing sites 11, 12 and 15 are discussed in detail. The thicknesses of the most recent (3–3.4 × 109 years ago) flows there and of the youngest flows in an area in south-west Mare Imbrium (3 × 109 years) are found to range between 30 and 60 m. The subsequent flow episodes at the landing sites showing up in the crater size distributions can be related to differences in the radiometric ages of the respective lunar rocks. 相似文献
13.
Toshiki Aikawa 《Astrophysics and Space Science》1979,66(2):277-285
The stability of spherically symmetric accretion flows is reconsidered. An analytical proof on stability for isothermal critical flow is given and numerical stability analyses are carried out for critical accretion flows in the range of 1<<5/3. Moreover, numerical results for subsonic flows are given. 相似文献
14.
15.
S. W. Allen A. C. Fabian R. M. Johnstone K. A. Arnaud P. E. J. Nulsen 《Monthly notices of the Royal Astronomical Society》2001,322(3):589-613
We present a detailed analysis of the X-ray properties of the cooling flows in a sample of nearby, X-ray-bright clusters of galaxies using high-quality ASCA spectra and ROSAT X-ray images. We demonstrate the need for multiphase models to consistently explain the spectral and imaging X-ray data for the clusters. The mass deposition rates of the cooling flows, independently determined from the ASCA spectra and ROSAT images, exhibit reasonable agreement. We confirm the presence of intrinsic X-ray absorption in the clusters using a variety of spectral models. We also report detections of 100-μm infrared emission, spatially coincident with the cooling flows, in several of the systems studied. The observed infrared fluxes and flux limits are in good agreement with the predicted values owing to reprocessed X-ray emission from the cooling flows. We present precise measurements of the abundances of iron, magnesium, silicon and sulphur in the central regions of the Virgo and Centaurus clusters. Our results firmly favour models in which a high mass fraction (70–80 per cent) of the iron in the X-ray gas in these regions originates from Type Ia supernovae. Finally, we present a series of methods which may be used to estimate the ages of cooling flows from X-ray data. The results for the present sample of clusters indicate ages of between 2.5 and 7 Gyr. If the ages of cooling flows are primarily set by subcluster merger events, then our results suggest that in the largest clusters, mergers with subclusters with masses of ∼30 per cent of the final cluster mass are likely to disrupt cooling flows. 相似文献
16.
The HRSC (image 0037) and MOC imagery and MOLA altimetry were used to determine the following parameters of the lava flows typical of the southern slope of the Martian volcano Olympus: the length (13–35 km), the width (0.2–4.8 km), and the angles of ground slopes along which these flows advanced (3.4°–6.9°). To measure the thickness of the flows, we applied a method which had never been used before for Mars. In this method, the apparent thickness obtained from the MOC images and the slope steepness obtained from the MOLA data are used to determine the true thickness. The average estimates of the thickness of lava flows vary from 4 to 11 m and from 4 to 26 m for the volcano flanks and caldera scarps, respectively. These values are close to those of terrestrial basalt flows and to the lower limit found for the Martian flows by other researchers. Based on the performed measurements, we estimated the lava yield strength (0.9 × 103?3.6 × 104 Pa), the supply rate (24–137 m3/s), and the viscosity (1.4 × 103?2.8 × 107 kg/m s). These values are close to the estimates found for the Martian lavas by other researchers and to the characteristic values of these parameters for terrestrial lava flows with basalt and basalt-andesite composition. 相似文献
17.
Durga Dutt Tripathi 《Astrophysics and Space Science》1990,174(2):229-234
The flow equations of non-Newtonian EMFD flows are formulated in terms of stream function and magnetic flux function as a independent variable. The exact analytical solution of physical importance is obtained for orthogonal and radial flows. 相似文献
18.
In recent high-resolution observations of complex active regions, long-lasting and well-defined regions of strong flows were
identified in major flares and associated with bright kernels of visible, near-infrared, and X-ray radiation. These flows,
which occurred in the proximity of the magnetic neutral line, significantly contributed to the generation of magnetic shear.
Signatures of these shear flows are strongly curved penumbral filaments, which are almost tangential to sunspot umbrae rather
than exhibiting the typical radial filamentary structure. Solar active region NOAA 10756 was a moderately complex β
δ sunspot group, which provided an opportunity to extend previous studies of such shear flows to quieter settings. We conclude
that shear flows are a common phenomenon in complex active regions and δ spots. However, they are not necessarily a prerequisite condition for flaring. Indeed, in the present observations, the photospheric
shear flows along the magnetic neutral line are not related to any change of the local magnetic shear. We present high-resolution
observations of NOAA 10756 obtained with the 65-cm vacuum reflector at Big Bear Solar Observatory (BBSO). Time series of speckle-reconstructed
white-light images and two-dimensional spectroscopic data were combined to study the temporal evolution of the three-dimensional
vector flow field in the β
δ sunspot group. An hour-long data set of consistent high quality was obtained, which had a cadence of better than 30 seconds
and subarcsecond spatial resolution. 相似文献
19.
M. S. Ruderman 《Solar physics》2010,267(2):377-391
In this paper we study kink oscillations of coronal loops in the presence of flows. Using the thin-tube approximation we derive
the general governing equation for kink oscillations of a loop with the density varying along the loop in the presence of
flows. This equation remains valid even when the density and flow are time dependent. The derived equation is then used to
study the effect of flows on eigenfrequencies of kink oscillations of coronal loops. The implication of the obtained results
on coronal seismology is discussed. 相似文献
20.
We investigate the distinctive distribution and pattern of subkilometer-sized cones in Isidis Planitia, and their relationship to the material that fills the basin. We observe that: (1) the cones show uniform size, spacing, and morphology across the entire basin; (2) they have large central depressions (relative to cone basal diameters) that are generally filled in and commonly show layering; (3) cone chains form highly organized spatial patterns; cones are also found in isolation and in dense fields; (4) many adjacent chains are parallel, and evenly spaced, creating a pattern that mimics lava flows that have experienced compressional folding; (5) no flows are associated with the cones, even where summit crater rims are breached; (6) the cones are at least temporally related to basin fill; (7) the basin fill material is largely fine-grained, but with locally indurated layers at shallow depth; blocks ejected by small craters from these locally indurated layers are commonly dark in color; and (8) relationships between cones along a chain show no systematic temporal formation sequence along the chain. We conclude that the basin was likely inundated by one or more hot, partially welded pyroclastic flows; devolatilization of these flows remobilized volcaniclastic material to form the cones without associated lava flows. The volume of gas required to account for the observed number of cones is low and does not require the presence of ground water or ice. 相似文献