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1.
Via the potential field extrapolation of the observed photospheric magnetic field, the structure of the photospheric magnetic fields above solar quiet regions is renewed. As revealed by the result, below 20 Mm the open magnetic lines exhibit many obvious small funnel structures. These funnels expand with height and at the height of about 20 Mm they combine into large funnel structures. By a systematic study of the tendency of change of the cross section areas of funnels, it is discovered that the cross section areas of funnels in solar quiet regions expand approximately linearly. The velocity of expansion of magnetic funnels at rather low altitudes (< 20 Mm) is larger than that at high altitudes (> 20 Mm). This phenomenon has important significance for the two-dimensional numerical simulations of the origin of solar wind and the mass flow in magnetic loops. At the same time it is found that the number of closed magnetic lines decreases in the form of exponential function. 相似文献
2.
We have measured the proper motion of magnetic elements on the quiet Sun by means of local correlation tracking. The existence of a pattern in the intranetwork (IN) flow is confirmed. This velocity field is consistent with the direct Doppler measurement of the horizontal component of the supergranular velocity field. The IN elements generally move toward the network boundaries. By tracking test points we confirm that the magnetic elements converge in areas corresponding to the magnetic network. But because the IN elements are of random polarity, they cannot contribute to the growth or maintenance of the magnetic network.By calculating the cross correlation between the magnetogram and Dopplergram, we confirm that the supergranule boundaries and the magnetic network are roughly correlated. 相似文献
4.
《New Astronomy》2007,12(6):479-482
We apply the method of MHD seismology to estimate the magnetic field in spicules using observed kink waves. We include the effects of gravitational stratification, the neglect of which leads to an error of around 30% in the estimation of the magnetic field. With stratification included, we find the magnetic field in spicules in the range of 8–16 G. We also estimate a density of 7.4 × 10−10 kg m−3 in spicules. The estimated values of magnetic field and density are in agreement with the available observations. Improved measurement of height, oscillation period, and plasma density in spicules will further enhance the precision of this method. 相似文献
5.
Coronal bright points, first identified as X-ray Bright Points (XBPs), are compact, short-lived and associated with small-scale, opposite polarity magnetic flux features. Previous studies have yielded contradictory results suggesting that XBPs are either primarily a signature of emerging flux in the quiet Sun, or of the disappearance of pre-existing flux. With the goal of improving our understanding of the evolution of the quiet Sun magnetic field, we present results of a study of more recent data on XBPs and small-scale evolving magnetic structures. The coordinated data set consists of X-ray images obtained during rocket flights on 15 August and 11 December, 1987, full-disk magnetograms obtained at the National Solar Observatory - Kitt Peak, and time-lapse magnetograms of multiple fields obtained at Big Bear Solar Observatory. We find that XBPs were more frequently associated with pre-existing magnetic features of opposite polarity which appeared to be cancelling than with emerging or new flux regions. Most young, emerging regions were not associated with XBPs. However, some XBPs were associated with older ephemeral regions, some of which were cancelling with existing network or intranetwork poles. Nearly all of the XBPs corresponded to opposite polarity magnetic features which wereconverging towards each other; some of these had not yet begun cancelling. We suggest that most XBPs form when converging flow brings oppositely directed field lines together, leading to reconnection and heating of the newly-formed loops in the low corona. 相似文献
6.
We present data and modelling for the quiet Sun that strongly suggest a ubiquitous small-scale atmospheric heating mechanism
that is driven solely by converging supergranular flows. A possible energy source for such events is the power transfer to
the plasma via the work done on the magnetic field by photospheric convective flows, which exert drag on the footpoints of
magnetic structures. We present evidence of small-scale energy release events driven directly by the hydrodynamic forces that
act on the magnetic elements in the photosphere, as a result of supergranular-scale flows. We show strong spatial and temporal
correlation between quiet-Sun soft X-ray emission (from Yohkoh SXT) and SOHO MDI-derived flux removal events driven by deduced photospheric flows. We also present a simple model of heating
generated by flux submergence, based on particle acceleration by converging magnetic mirrors. In the near future, high resolution
soft X-ray images from XRT on the Hinode satellite will allow definitive, quantitative verification of our results.
Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users. 相似文献
7.
《New Astronomy》2007,12(3):215-223
We compare the results of two calibration methods for deriving a photospheric vector magnetogram, as applied to the Fei 5324.19 Å line. The first method ignores the dependence of its calibration coefficients on the inclination angle. The second method is a multi-iteration, nonlinear calibration technique developed by [M.J. Hagyard, J.I. Kineke, Solar Phys. 158 (1995) 11], which allows the polarization signals to depend on both field strength and inclination angle. We compare the relationship between the derived solar magnetic field and the Stokes parameters under both methods. We find that the circular polarization signal of the Fei 5324.19 Å line is linearly proportional to the longitudinal strength, BL, when the field strength ranges from 0 to 1000 Gauss. For BL > 1000 G and inclination angles ranging from 30° to 90°, deviation from linearity is significant. For the transverse field, BT, the assumption of linearity only holds for 0 < BT < 300 G. In contrast to the former method of calibration, the improved calibration method accounts for the nonlinear relationship between polarization signals and the magnetic field strength. Using [A. Skumanich, in: J.H. Thomas and N.O. Weiss (Eds.), Sunspots: Theory and Observations. Kluwer, Dordrecht, 1992, p. 121] dipole field model, we show that the Fei 5324.19 Å line has more linear property than the Fei 6302.5 Å line. 相似文献
8.
《Planetary and Space Science》2007,55(9):1000-1009
We discuss different scenarios for the formation and dynamics of nanoparticles in the inner solar system. Particles up to a few tens of nanometer size, if formed at a distance larger than several 0.1 AU from the Sun, are picked up by the solar wind and therefore do not reach the regions closer to the sun. At distances ⩽0.1 AU particles of several tens of nanometer in size can stay in bound orbits and, aside from the Lorentz force, the plasma and the photon Poynting–Robertson effect determine their spatial distribution. Local sources of nanometer-sized particles in the inner solar system are collisional fragmentation and sublimation of dust and meteoroids. The most likely materials to survive in the very vicinity of the Sun are MgO particles from the sublimation of cometary and meteoritic silicates, nanodiamonds originating from meteoroid material, and possibly carbon structures formed by thermal alteration of organics. The nanoparticles may produce spectral features in a limited spectral interval, and this spectral interval varies with particle size, composition and temperature. Bearing in mind the wide size distribution of solar system dust and the preponderance of larger particles, it is unlikely that nanoparticles can be detected in thermal emission or scattered light brightness and we are unable to predict observable features for these nanoparticles. If the nanodust produced observable features, they are most likely to appear in the blue or near infrared. We suggest a more promising option is the in situ detection of the particles. 相似文献
9.
Y.-M. Wang 《Solar physics》2004,224(1-2):21-35
The Sun’s large-scale external field is formed through the emergence of magnetic flux in active regions and its subsequent
dispersal over the solar surface by differential rotation, supergranular convection, and meridional flow. The observed evolution
of the polar fields and open flux (or interplanetary field) during recent solar cycles can be reproduced by assuming a supergranular
diffusion rate of 500 – 600 km2 s−1 and a poleward flow speed of 10 –20 m s−1. The nonaxisymmetric component of the large-scale field decays on the flow timescale of ∼1 yr and must be continually regenerated
by new sunspot activity. Stochastic fluctuations in the longitudinal distribution of active regions can produce large peaks
in the Sun’s equatorial dipole moment and in the interplanetary field strength during the declining phase of the cycle; by
the same token, they can lead to sudden weakenings of the large-scale field near sunspot maximum (Gnevyshev gaps). Flux transport
simulations over many solar cycles suggest that the meridional flow speed is correlated with cycle amplitude, with the flow
being slower during less active cycles. 相似文献
10.
Planetary magnetic fields could impact the evolution of planetary atmospheres and have a role in the determination of the required conditions for the emergence and evolution of life (planetary habitability). We study here the role of rotation in the evolution of dynamo-generated magnetic fields in massive Earth-like planets, Super Earths (1–10 M⊕). Using the most recent thermal evolution models of Super Earths (Gaidos, E., Conrad, C.P., Manga, M., Hernlund, J. [2010]. Astrophys. J. 718, 596–609; Tachinami, C., Senshu, H., Ida, S. [2011]. Astrophys. J. 726, 70) and updated scaling laws for convection-driven dynamos, we predict the evolution of the local Rossby number. This quantity is one of the proxies for core magnetic field regime, i.e. non-reversing dipolar, reversing dipolar and multipolar. We study the dependence of the local Rossby number and hence the core magnetic field regime on planetary mass and rotation rate. Previous works have focused only on the evolution of core magnetic fields assuming rapidly rotating planets, i.e. planets in the dipolar regime. In this work we go further, including the effects of rotation in the evolution of planetary magnetic field regime and obtaining global constraints to the existence of intense protective magnetic fields in rapidly and slowly rotating Super Earths. We find that the emergence and continued existence of a protective planetary magnetic field is not only a function of planetary mass but also depend on rotation rate. Low-mass Super Earths (M ? 2 M⊕) develop intense surface magnetic fields but their lifetimes will be limited to 2–4 Gyrs for rotational periods larger than 1–4 days. On the other hand and also in the case of slowly rotating planets, more massive Super Earths (M ? 2 M⊕) have weak magnetic fields but their dipoles will last longer. Finally we analyze tidally locked Super Earths inside and outside the habitable zone of GKM stars. Using the results obtained here we develop a classification of Super Earths based on the rotation rate and according to the evolving properties of dynamo-generated planetary magnetic fields. 相似文献
11.
Helioseismic techniques such as ring-diagram analysis have often been used to determine the subsurface structural differences
between solar active and quiet regions. Results obtained by inverting the frequency differences between the regions are usually
interpreted as the sound-speed differences between them. These in turn are used as a measure of temperature and magnetic-field
strength differences between the two regions. In this paper we first show that the “sound-speed” difference obtained from
inversions is actually a combination of sound-speed difference and a magnetic component. Hence, the inversion result is not
directly related to the thermal structure. Next, using solar models that include magnetic fields, we develop a formulation
to use the inversion results to infer the differences in the magnetic and thermal structures between active and quiet regions.
We then apply our technique to existing structure inversion results for different pairs of active and quiet regions. We find
that the effect of magnetic fields is strongest in a shallow region above 0.985R
⊙ and that the strengths of magnetic-field effects at the surface and in the deeper (r<0.98R
⊙) layers are inversely related (i.e., the stronger the surface magnetic field the smaller the magnetic effects in the deeper layers, and vice versa). We also find that the magnetic effects in the deeper layers are the strongest in the quiet regions, consistent with the
fact that these are basically regions with weakest magnetic fields at the surface. Because the quiet regions were selected
to precede or follow their companion active regions, the results could have implications about the evolution of magnetic fields
under active regions. 相似文献
12.
《Planetary and Space Science》2007,55(6):770-791
Previous work by Scoffield, H.C., Yeoman, T.K., Wright, D.M., Milan, S.E., Wright, A.N., Strangeway, R.J. [2005. An investigation of the field aligned currents associated with a large scale ULF wave using data from CUTLASS and FAST. Ann. Geophys. 23, 487–498) investigated a large-scale ULF wave, occurring in the dusk sector (∼1900 MLT). The wave had a period of ∼800 s (corresponding to 1.2 mHz frequency), an azimuthal wave number of ∼7 and a full-width at half-maximum (FWHM) across the resonance of 350 km. IMAGE ground magnetometer and SuperDARN radar observations of the wave's spatial and temporal characteristics were used to parameterise a simple, two-dimensional field line resonance (FLR) model. The model-calculated field-aligned current (FAC) was compared with FACs derived from the FAST energetic particle spectra and magnetic field measurement. Here the authors use the same method to investigate the FAC structure of a second large-scale ULF wave, with a period of ∼450 s, occurring the dawn sector (∼0500 MLT) with an opposite sense background region 1–region 2 current system. This wave has a much larger longitudinal scale (m∼4.5) and a smaller latitude scale (FWHM=150 km). Unlike the dusk sector wave, which was dominated by upward FAC, FAST observations of the dawn sector wave show an interval of large-scale downward FAC of ∼1.5 μA m−2. Downgoing magnetospheric electrons with energies of a few keV were observed, which are associated with upward FACs of ∼1 μA m−2. For both wave studies, downward currents appear to be carried partially by upgoing electrons below the FAST energy detection threshold (5 eV), but also consist of a mixture of hotter downgoing magnetospheric electrons and upgoing ionospheric electrons of energies 30 eV–1 keV. Strong intervals of upward current show that small-scale structuring of scale ∼50 km has been imposed on the current carriers. In general, this study confirms the findings of Scoffield, H.C., Yeoman, T.K., Wright, D.M., Milan, S.E., Wright, A.N., Strangeway, R.J. [2005. An investigation of the FACs associated with a large-scale ULF wave using data from CUTLASS and FAST. Ann. Geophys. 23, 487–498). 相似文献
13.
《New Astronomy》2007,12(2):146-160
We point out that although conventional stars are primarily fed by burning of nuclear fuel at their cores, in a strict sense, the process of release of stored gravitational energy, known as, Kelvin–Helmholtz (KH) process is either also operational albeit at an arbitrary slow rate, or lying in wait to take over at the disruption of the nuclear channel. In fact, the latter mode of energy release is the true feature of any self-gravity bound object including stars. We also highlight the almost forgotten fact that Eddington was the first physicist to introduce special relativity into the problem and correctly insist that, actually, total energy stored in a star is not the mere Newtonian energy but the total mass energy (E = Mc2). Accordingly, Eddington defined an “Einstein time scale” of Evolution where the maximum age of the Sun turned out to be tE ≈ 1.4 × 1013 yr. This concept has a fundamental importance though we know now that Sun in its present form cannot survive for more than 10 billion years. We extend this concept by introducing general relativity and show that the minimum value of depletion of total mass–energy is tE = ∞ not only for Sun but for and sufficiently massive or dense object. We propose that this time scale be known in the name of “Einstein–Eddington”. We also point out that, recently, it has been shown that as massive stars undergo continued collapse to become a Black Hole, first they become extremely relativistic radiation pressure supported stars. And the life time of such relativistic radiation pressure supported compact stars is indeed dictated by this Einstein–Eddington time scale whose concept is formally developed here. Since this observed time scale of this radiation pressure supported quasistatic state turns out to be infinite, such objects are called eternally collapsing objects (ECO). Further since ECOs are expected to have strong intrinsic magnetic field, they are also known as “Magnetospheric ECO” or MECO. 相似文献
14.
《New Astronomy》2015
We numerically integrate the Sun’s orbital movement around the barycenter of the solar system under the persistent perturbation of the planets from the epoch J2000.0, backward for about one millennium, and forward for another millennium to 3000 AD. Under the Sun–Planets Interaction (SPI) framework and interpretation of Wolff and Patrone (2010), we calculated the corresponding variations of the most important storage of the specific potential energy (PE) within the Sun that could be released by the exchanges between two rotating, fluid-mass elements that conserve its angular momentum. This energy comes about as a result of the roto-translational dynamics of the cell around the solar system barycenter. We find that the maximum variations of this PE storage correspond remarkably well with the occurrences of well-documented Grand Minima (GM) solar events throughout the available proxy solar magnetic activity records for the past 1000 yr. It is also clear that the maximum changes in PE precede the GM events in that we can identify precursor warnings to the imminent weakening of solar activity for an extended period. The dynamical explanation of these PE minima is connected to the minima of the Sun’s position relative to the barycenter as well as the significant amount of time the Sun’s inertial motion revolving near and close to the barycenter. We presented our calculation of PE forward by another 1000 yr until 3000 AD. If the assumption of the solar activity minima corresponding to PE minima is correct, then we can identify quite a few significant future solar activity GM events with a clustering of PE minima pulses starting at around 2150 AD, 2310 AD, 2500 AD, 2700 AD and 2850 AD. 相似文献
15.
We present numerical simulations of the axisymmetric accretion of a massive magnetized plasma torus on a rotating black hole. We use a realistic equation of state, which takes into account neutrino cooling and energy loss due to nucleus dissociations. The calculation are performed in the ideal relativistic MHD approximation using an upwind conservative scheme that is based on a linear Riemann solver and the constrained transport method to evolve the magnetic field. The gravitational attraction of the black hole is introduced via the Kerr metric in the Kerr–Schild coordinates. We simulate various magnetic field configurations and torus models, both optically thick and thin for neutrinos.We have found an effect of alternation of the magnetic field orientation in the ultrarelativistic jet formed as a result of the collapse. The calculations show evidence for heating of the wind surrounding the collapsar by the shock waves generated at the jet–wind border. It is shown that the neutrino cooling does not significantly change either the structure of the accretion flow or the total energy release of the system. The angular momentum of the accreting matter defines the time scale of the accretion. Due to the absence of the magnetic dynamo in our calculations, the initial strength and topology of the magnetic field determines the magnetization of the black hole, jet formation properties and the total energy yield. We estimate the total energy of accretion which transformed to jets as 1.3 × 1052 ergs which was sufficient to explain hypernova explosions like GRB 980425 or GRB 030329. 相似文献
16.
《Astroparticle Physics》2009,30(6):366-372
We present results of a search for relativistic magnetic monopoles with the Baikal neutrino telescope NT200, using data taken between April 1998 and February 2003. No monopole candidates have been found. We set an upper limit 4.6 × 10−17 cm−2 s−1 sr−1 for the flux of monopoles with βm = 1. This is a factor of 20 below the Chudakov–Parker bound which is inferred from the very existence of large-scale galactic magnetic fields. 相似文献
17.
Using velocity and magnetogram data extracted from the full-disk field of view of MDI during the 1999 Dynamics Program, we have studied the dynamics of small-scale magnetic elements (3–7 Mm in size) over time periods as long as six days while they are readily visible on the solar disk. By exploiting concurrent time series of magnetograms and Doppler images, we have compared the motion of magnetic flux elements with the supergranular velocity field inferred from the correlation tracking of mesogranular motions. Using this new method (which combines the results from correlation tracking of mesogranules with detailed analysis of simultaneous magnetograms), it is now possible to correlate the motions of the velocity field and magnetic flux for long periods of time and at high temporal resolution. This technique can be utilized to examine the long-term evolution of supergranulation and associated magnetic fields, for it can be applied to data that span far longer time durations than has been possible previously. As tests of its efficacy, we are able to use this method to verify many results of earlier investigations. We confirm that magnetic elements travel at approximately 350 m s –1 throughout the duration of their lifetime as they are transported by supergranular outflows. We also find that the positions of the magnetic flux elements coincide with the supergranular network boundaries and adjust as the supergranular network itself evolves over the six days of this data set. Thus we conclude that this new method permits us to study the extended evolution of the supergranular flow field and its advection of magnetic elements. Since small-scale magnetic elements are strongly advected by turbulent convection, their dynamics can give important insight into the properties of the subsurface convection. 相似文献
18.
A. Boesswetter H. Lammer Y. Kulikov U. Motschmann S. Simon 《Planetary and Space Science》2010,58(14-15):2031-2043
In this study we analyze the non-thermal loss rates of O+, O2+ and CO2+ ions over the last 4.5 billion years (Gyr) in the Martian history by using a 3D hybrid model. For this reason we derived the past solar wind conditions in detail. We take into account the intensified particle flux of the early Sun as well as an Martian atmosphere, which was exposed to a sun's extreme ultraviolet (EUV) radiation flux 4.5 Gyr ago that was 100 times stronger than today. Furthermore, we model the evolution of the interplanetary magnetic field by a Weber & Davis solar wind model. The ‘external’ influences of the Sun's radiation flux and solar wind flux lead to the formation of an ionospheric obstacle by photoionization, charge exchange and electron impact. For the early Martian conditions we could show that charge exchange was the dominant ionization mechanism. Several hybrid simulations for different stages in the evolution of the Martian atmosphere, at 1, 2, 5, 10, 30 and 100 EUV, were performed to analyze the non-thermal escape processes by ion pick-up, momentum transfer from the solar wind to the ionosphere and detached ionospheric plasma clouds. Our results show a non-linear evolution of the loss rates. Using mean solar wind parameters the simulations result in an oxygen loss equivalent to the depth of a global Martian ocean of about 2.6 m over the last 4.5 Gyr. The induced magnetic field strength could be increased up to about 2000 nT. A simulation run with high solar wind density results in an oxygen loss of a Martian ocean up to 205 m depth during 150 million years after the sun reached the zero age mean sequence (ZAMS). 相似文献
19.
R. Muller 《Solar physics》1983,85(1):113-121
A high resolution time series of pictures, obtained at Pic du Midi Observatory, is used to analyze the dynamical behavior of facular points in the quiet Sun. The following characteristics of the behavior are revealed: (a) relative to the supergranular pattern, facular points appear at the supergranular boundaries, rarely inside the cells; (b) relative to the pattern of the granulation, they appear in spaces at the junction of several granules, never inside a granule nor in a space between two granules only; (c) their mean lifetime is 18 min; (d) they remain in intergranular lanes during their whole life; (e) their observed size never significantly exceeds 0″. 5; (f) they have a strong tendency to appear very close to an already existing facular point; (g) about 15% of them seem to split in two facular points; (h) they disappear simply by fading away in an intergranular space; (i) they never merge with another facular point or with a granule. The formation of facular points in the quiet photosphere is very closely connected to both granular and supergranular patterns. Some possible consequences on the behavior of the associated magnetic flux tubes are discussed. 相似文献
20.
We present results of our study of the rheologies and ages of lava flows in the Elysium Mons region of Mars. Previous studies have shown that the geometric dimensions of lava flows reflect rheological properties such as yield strength, effusion rate and viscosity. In this study the rheological properties of lava flows in the Elysium Mons region were determined and compared to the rheologies of the Ascraeus Mons lava flows. We also derived new crater size-frequency distribution measurements (CSFDs) for the Elysium lava flows to identify possible changes in the rheological properties with time. In addition, possible changes in the rheological properties with the distance from the caldera of Elysium Mons were analyzed.In total, 35 lava flows on and around Elysium Mons were mapped, and divided into three groups, lava flows on the flanks of Elysium Mons, in the plains between the three volcanoes Elysium Mons, Hecates and Albor Tholus and lava flows south of Albor Tholus. The rheological properties of 32 of these flows could be determined. Based on our morphometric measurements of each individual lava flow, estimates for the yield strengths, effusion rates, viscosities, and eruption duration of the studied lava flows were made. The yield strengths of the investigated lava flows range from ～3.8 × 102 Pa to ～1.5 × 104 Pa, with an average of ～3.0 × 103 Pa. These yield strengths are in good agreement with estimates for terrestrial basaltic lava flows. The effusion rates are on average ～747 m3 s?1, ranging from ～99 to 4450 m3 s?1. The viscosities are on average ～4.1 × 106 Pa s, with a range of 1.2 × 105 Pa s to 3.1 × 107 Pa s. The eruption durations of the flows were calculated to be between 6 and 183 days, with an average of ～51 days. The determined rheological properties are generally very similar to those of other volcanic regions on Mars, such as on Ascraeus Mons in the Tharsis region. Calculated yield strengths and viscosities point to a basaltic/andesitic composition of the lava flows, similar to basaltic or andesitic a’a lava flows on Earth.Absolute model ages of all 35 lava flows on Elysium Mons were derived from crater size-frequency distribution measurements (CSFD). The derived model ages show a wide variation from about 632 Ma to 3460 Ma. Crater size-frequency distribution measurements of the Elysium Mons caldera show an age of ～1640 Ma, which is consistent with the resurfacing age of Werner (2009). Significant changes of the rheologies with time could not be observed. Similarly, we did not observe systematic changes in ages with increasing distances of lava flows from the Elysium Mons caldera. 相似文献