共查询到20条相似文献，搜索用时 15 毫秒
1.
S. S. Hasan 《Journal of Astrophysics and Astronomy》2000,21(3-4):283-287
We model the dynamical interaction between magnetic flux tubes and granules in the solar photosphere which leads to the excitation
of transverse (kink) and longitudinal (sausage) tube waves. The investigation is motivated by the interpretation of network
oscillations in terms of flux tube waves. The calculations show that for magnetic field strengths typical of the network,
the energy flux in transverse waves is higher than in longitudinal waves by an order of magnitude. But for weaker fields,
such as those that might be found in internetwork regions, the energy fluxes in the two modes are comparable. Using observations
of footpoint motions, the energy flux in transverse waves is calculated and the implications for chromospheric heating are
pointed out. 相似文献
2.
Zongjun Ning 《Solar physics》2011,273(1):81-92
We explore the speed distributions of X-ray source motions after the start of chromospheric evaporation in two Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) flares. First, we make CLEAN images at 15 energy bands with a 12 second integration window; then, we outline a flaring
loop geometry to cover the looptop and footpoint sources as much as possible. Consistent with the previous steps, we find
converging motion of the double footpoint sources along the flaring loop in these two events. This motion is dependent on
the energy band and time and is typically seen at 3 – 25 keV, indicating a chromospheric evaporation origin. The speed distributions
at various energy bands are measured for the 10 September 2002 flare, which exhibits a separation-to-mergence motion pattern
well correlated with the rising-to-decay phases at 50 – 100 keV. 相似文献
3.
Periodic shaking or buffeting of magnetic flux tubes could generate magnetohydrodynamic waves which propagate along the flux tubes and dissipate energy in the chromosphere and/or corona. If we make an assumption that the G-band bright points represent flux tubes, then there should exist a relationship between the transverse motions and the brightening of these bright points. We tracked a total of 56 bright points, obtained their velocity and intensity power spectrum. We also estimated the r.m.s. velocity, average velocity, r.m.s. intensity and average intensity of these bright points. We do not see any clear evidence for a relationship between these estimated quantities. 相似文献
4.
In a sample of strong RHESSI M-class flares we have made a study of the relationship between the `hardness' of the HXR spectrum
and the intensity in the 30–50 keV energy range. In all events we find clear evidence for a `soft–hard–soft' pattern of correlation
between hardness and flux, on time scales as short as 10 s. We investigate whether or not this pattern is intrinsic to the
acceleration mechanism. The RHESSI images in this energy range are dominated by footpoint brightenings, and we have searched
for a correlation between footpoint separation velocity and spectral hardness, to be compared qualitatively with theoretical
flare models. We find quite systematic footpoint motions, and also note that episodes in which footpoint separation varies
rapidly often correspond with episodes of significant change in the flare spectral index, though not as the simplest flare
models would predict. We report also on one of our events, on 14 March 2002, which exhibits highly sheared HXR footpoint ribbons
extending over a scale of 100 arc sec. For this flare we find a correlation between footpoint motion and hard X-ray flux.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1022479610710 相似文献
5.
程久恒 《中国天文和天体物理学报》1994,(3)
从细磁通量管运动方程组导出了特征速度、特征线及其相容关系。这些结果是用特征线法研究细磁通量管运动的基础，也是正确提出定解问题的依据。表征细磁通量管横向波传播的特征速度与管内流动的ＡｌｆｖｅｎＭａｃｈ数有关。当管内流速超过ｋｅｌｖｉｎ－Ｈｅｌｍｈｏｌｔｚ不稳定性临界值时，不存在横向波模式。 相似文献
6.
In a highly dynamic environment with sources and sinks of energy, flux tubes do not in general obey local conservation laws,
nor do the ensembles of flux tubes that exhibit collective phenomena. We use the approach of energetically open dissipative
systems to study nonlinear waves in flux tubes and their role in the dynamics of the overlying atmosphere. We present results
of theoretical and observational studies of the properties of moving magnetic features (MMFs) around sunspots and the response
of the overlying atmosphere to various types of MMFs. We show that all types of MMFs, often having conflicting properties,
can be described on a unified basis by employing the model of shocks and solitons propagating along the penumbral filaments
co-aligned with Evershed flows. The model is also consistent with the response of the upper atmosphere to individual MMFs,
which depends on their type. For example, soliton-type bipolar MMFs mainly participate in the formation of a moat and do not
carry much energy into the upper atmosphere, whereas shock-like MMFs, with the appearance of single-polarity features, are
often associated with chromospheric jets and microflares. 相似文献
7.
The physical properties of the quiet solar chromosphere–corona transition region are studied. Here the structure of the solar atmosphere is governed by the interaction of magnetic fields above the photosphere. Magnetic fields are concentrated into thin tubes inside which the field strength is great. We have studied how the plasma temperature, density, and velocity distributions change along a magnetic tube with one end in the chromosphere and the other one in the corona, depend on the plasma velocity at the chromospheric boundary of the transition region. Two limiting cases are considered: horizontally and vertically oriented magnetic tubes. For various plasma densities we have determined the ranges of plasma velocities at the chromospheric boundary of the transition region for which no shock waves arise in the transition region. The downward plasma flows at the base of the transition region are shown to be most favorable for the excitation of shock waves in it. For all the considered variants of the transition region we show that the thermal energy transfer along magnetic tubes can be well described in the approximation of classical collisional electron heat conduction up to very high velocities at its base. The calculated extreme ultraviolet (EUV) emission agrees well with the present-day space observations of the Sun. 相似文献
8.
The goal of this paper is a detailed statistical analysis of the low-frequency Ca II line intensity oscillations containing information about the dynamics of the lower and middle chromosphere. A pixel-by-pixel analysis of the observed parameters has been performed. The following results have been obtained. (1) The low-frequency chromospheric oscillations (periods >400 s) are seen much more frequently in networks than in chromospheric network cells. (2) The relative fraction of the low-frequency chromospheric intensity oscillations increases with height. (3) The occurrence distribution of intensity oscillations as a function of the frequency is subdivided at least into two types. (4) In contrast to the low-frequency photospheric oscillations, the phase differences between the Ca II K and 849.8 nm line intensity oscillations do not give grounds to identify the low-frequency chromospheric oscillations with internal gravity waves. (5) The spectral composition of the oscillations in the network chromosphere resembles that expected in magnetic flux tubes in the nonlinear regime of conversion of transverse MHD waves at lower levels of the atmosphere into longitudinal MHD waves in its upper layer. 相似文献
9.
We analyzed chromospheric events and their connection to oscillation phenomena and photospheric dynamics. The observations were done with the New Solar Telescope of Big Bear Solar Observatory using a broad-band imager at the wavelength of a TiO band and FISS spectrograph scanning Ca?ii and Hα spectral lines. The event in Ca?ii showed strong plasma flows and propagating waves in the chromosphere. The movement of the footpoints of flux tubes in the photosphere indicated flux tube entanglement and magnetic reconnection as a possible cause of the observed brightening and waves propagating in the chromosphere. An upward propagating train of waves was observed at the site of the downflow event in Hα. There was no clear relationship between photospheric waves and the Ca?ii and Hα events. Our observations indicate that chromospheric waves that were previously thought to originate from the photosphere may be generated by some events in the chromosphere as well. 相似文献
10.
We study the response of the chromosphere and transition region to dynamic changes in the photospheric network magnetic fields. We present results from simultaneous measurements taken by TRACE in chromospheric and transition region (Civ) images, high-resolution magnetograms taken by MDI, and spectra of chromospheric (Cii) and transition region lines (Ovi) obtained with the SUMER instrument on SOHO. Enhanced emission in the Civ line is generally co-spatial with the magnetic pattern in the photosphere. We propose a mechanism of electro-mechanical coupling between the photosphere and upper layers of atmosphere based on hydrodynamic cumulation of energy produced by reconnecting flux tubes in the photosphere/chromosphere region (Tarbell et al., 1999). We believe that a basic process causing energetic events is the cascade of shock waves produced by colliding and reconnecting flux tubes. The continuous supply of flux tubes in the magnetic carpet ensures the ubiquitous nature of this process and its imprint on the upper atmosphere. The appearance of bright transients often, but not always, correlates with canceling mixed polarity magnetic elements in the photosphere. In other cases, transients occur in regions of unipolar flux tubes, suggesting reconnection of oblique components. Transients are also seen in regions with no fields detected with the MDI sensitivity; these may be reconnections of tiny features with diameters less than 100 km. Blinkers and other bright transients are often accompanied by two directional plasma jets. These may be generated by cylindrical self-focusing of shock fronts or by collision of shocks produced by neighboring reconnection processes. The observations suggest that stronger emissions correspond to lower velocity jets, and vice versa; this property is a natural consequence of the proposed mechanism. Plasma flows are always seen whenever the slit crosses strong magnetic flux tubes or vertices of converging flows in the supergranular network. The overall energy distribution between heating and plasma flows is an intrinsic feature of our mechanism. 相似文献
11.
We study how active-region-scale flux tubes rise buoyantly from the base of the convection zone to near the solar surface by embedding a thin flux tube model in a rotating spherical shell of solar-like turbulent convection. These toroidal flux tubes that we simulate range in magnetic field strength from 15 kG to 100 kG at initial latitudes of 1° to 40° in both hemispheres. This article expands upon Weber, Fan, and Miesch (Astrophys. J. 741, 11, 2011) (Article 1) with the inclusion of tubes with magnetic flux of 1020 Mx and 1021 Mx, and more simulations of the previously investigated case of 1022 Mx, sampling more convective flows than the previous article, greatly improving statistics. Observed properties of active regions are compared to properties of the simulated emerging flux tubes, including: the tilt of active regions in accordance with Joy’s Law as in Article 1, and in addition the scatter of tilt angles about the Joy’s Law trend, the most commonly occurring tilt angle, the rotation rate of the emerging loops with respect to the surrounding plasma, and the nature of the magnetic field at the flux tube apex. We discuss how these diagnostic properties constrain the initial field strength of the active-region flux tubes at the bottom of the solar convection zone, and suggest that flux tubes of initial magnetic field strengths of ≥?40 kG are good candidates for the progenitors of large (1021 Mx to 1022 Mx) solar active regions, which agrees with the results from Article 1 for flux tubes of 1022 Mx. With the addition of more magnetic flux values and more simulations, we find that for all magnetic field strengths, the emerging tubes show a positive Joy’s Law trend, and that this trend does not show a statistically significant dependence on the magnetic flux. 相似文献
12.
Some recent observations at Pic-du-Midi (Mulleret al., 1992a) suggest that the photospheric footpoints of coronal magnetic field lines occasionally move rapidly with typical velocities of the order 3 km s–1 for about 3 or 4 min. We argue that such occasional rapid footpoint motions could have a profound impact on the heating of the quiet corona. Qualitative estimates indicate that these occasional rapid motions can account for the entire energy flux needed to heat the quiet corona. We therefore carry out a mathematical analysis to study in detail the response of a vertical thin flux tube to photospheric footpoint motions in terms of a superposition of linear kink modes for an isothermal atmosphere. We find the resulting total energy that is asymptotically injected into an isothermal atmosphere (i.e., an atmosphere without any back reflection). By using typical parameter values for fast and slow footpoint motions, we show that, even if the footpoints spend only 2.5% of the time undergoing rapid motions, still these rapid motions could be more efficient in transporting energy to the corona than the slow motions that take place most of the time. 相似文献
13.
Torsional waves supported by magnetic flux tubes have long been thought to bear a high potential for supplying energy and momentum to the upper solar atmosphere, thereby contributing to its heating and to the driving of dynamic events like spicules. This hope rested on the belief that their propagation is not impeded by cutoff restrictions, unlike longitudinal and kink waves. We point out that this applies only to thin, isothermal tubes. When they widen in the chromosphere, and as a result of temperature gradients, cutoff restrictions arise. We compare them to recent observational reports of such waves and of vortex motions and find that their long period components are already affected by cutoff restrictions. An observational strategy is proposed that should permit the derivation of better information on vortex flows from off‐center observations with next generation telescopes (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
14.
The emergence of magnetic flux 总被引：1，自引：0，他引：1
Cornelis Zwaan 《Solar physics》1985,100(1-2):397-414
This paper first summarizes the morphology and dynamics of emerging flux regions and arch filament systems and then discusses detailed observations of a particular active region with emerging magnetic flux.The central part of the growing active region shows abnormal granulation and a weak magnetic field that, locally, is transverse. In the border zone, strong downward flows occur in the chromopshere and photosphere (small features with strong magnetic fields (faculae, pores) are formed here.) Near the leading and following edge, sunspots are formed by the coalescence of such small magnetic elements.The observational data are interpreted by means of a heuristic model of an emergent magnetic loop-shaped bundle consisting of many flux tubes. In this model we incorporate the theory of convective collapse and the buoyancy of flux tubes. The observed complexity in the structure and dynamics, including strong transverse fields and velocity shear, is attributed to the emergence of several flux regions within the active region at different orientations. 相似文献
15.
P. J. Bushby S. M. Houghton M. R. E. Proctor N. O. Weiss 《Monthly notices of the Royal Astronomical Society》2008,387(2):698-706
Kilogauss-strength magnetic fields are often observed in intergranular lanes at the photosphere in the quiet Sun. Such fields are stronger than the equipartition field B e , corresponding to a magnetic energy density that matches the kinetic energy density of photospheric convection, and comparable with the field B p that exerts a magnetic pressure equal to the ambient gas pressure. We present an idealized numerical model of three-dimensional compressible magnetoconvection at the photosphere, for a range of values of the magnetic Reynolds number. In the absence of a magnetic field, the convection is highly supercritical and characterized by a pattern of vigorous, time-dependent, 'granular' motions. When a weak magnetic field is imposed upon the convection, magnetic flux is swept into the convective downflows where it forms localized concentrations. Unless this process is significantly inhibited by magnetic diffusion, the resulting fields are often much greater than B e and the high magnetic pressure in these flux elements leads to their being partially evacuated. Some of these flux elements contains ultraintense magnetic fields that are significantly greater than B p . Such fields are contained by a combination of the thermal pressure of the gas and the dynamic pressure of the convective motion, and they are constantly evolving. These ultraintense fields develop owing to non-linear interactions between magnetic fields and convection; they cannot be explained in terms of 'convective collapse' within a thin flux tube that remains in overall pressure equilibrium with its surroundings. 相似文献
16.
We report an instance of localized chromospheric polarity reversal in a rapidly-formed sunspot which appears to be part of new emerging flux. The chromospheric polarity reversal is preceded by extraordinarily fast growth of the transverse magnetic field and an increase in the line-of-sight magnetic flux of the newly formed sunspot in the photosphere. The strength of this reversal is more than 350 G at maximum, in contrast to approximately - 1300 G for the line-of-sight field and 400 G for the transverse field in the photosphere. Continued flare activity takes place around the site of the reversal with progressively increasing flare size and extent. It is suggested that a kinked or knotted flux loop, or a self-closed flux system developed above the fast-forming sunspot. So far, this phenomenon has been revealed in several active regions. 相似文献
17.
B. V. Somov 《Astronomy Letters》2010,36(7):514-519
In connection with the RHESSI satellite observations of solar flares, which have revealed new properties of hard X-ray sources
during flares, we offer an interpretation of these properties. The observed motions of coronal and chromospheric sources are
shown to be the consequences of three-dimensional magnetic reconnection at the separator in the corona. During the first (initial)
flare phase, the reconnection process releases an excess of magnetic energy related predominantly to themagnetic tensions
produced before the flare by shear plasma flows in the photosphere. The relaxation of a magnetic shear in the corona also
explains the downward motion of the coronal source and the decrease in the separation between chromospheric sources. During
the second (main) flare phase, ordinary reconnection dominates; it describes the energy release in the terms of the “standard
model” of large eruptive flares accompanied by the rise of the coronal source and an increase in the separation between chromospheric
sources. 相似文献
18.
G. M. Simnett 《Solar physics》1983,86(1-2):289-299
High resolution X-ray images are used to study the temperature structure and evolution of two spatially resolved, but compact, solar flares. Both flares developed within a magnetic loop whose footpoints were separated by typically 15000 km, and involved primary energy release at one footpoint. This was followed by transfer of chromospheric material into and around the loop. The flares involved total energies differing by over an order of magnitude, and they follow different evolutionary paths because of this. 相似文献
19.
An active region loop system was observed in a decaying active region for three hours by TRACE and BBSO in a joint campaign on September 27, 1998. Continuous mass motion was seen in Hα offband filtergrams throughout the three hours, and some UV loops were exhibited transient brightenings. We find that: (1) cool material was flowing along the loops at a speed of at least 20 km s?1. Further, in Hα red and blue wings, we see mass motion along different loops in opposite directions. This is the first report of a counter-streaming pattern of mass motion in an Hα loop system. (2) Transient brightenings of different UV loops at different times were observed at C?iv 1550 Å. These brightened UV loops were located in the same region and at the same altitudes as the Hα loops. The observations show a clear correlation between the transient brightenings of UV loops and mass motion in Hα loops. (3) Both footpoints of the loop system were located in regions of mixed magnetic polarities. Frequent micro-flares at one footpoint of the loops with small-scale brightenings spreading along the loop leg were observed before the brightening and rising of one C?iv loop. Similar to the case of a filament, the continuous mass motion along the loops seems important for maintaining the cool Hα loop system at coronal height. There may be an indication that the mass motion in cool Hα loops and the correlated transient brightening of the active region loops were due to the small-scale chromospheric magnetic reconnection at the footpoint regions of the loop system.
相似文献20.
We present a combined model for magnetic field generation and transport in cool stars with outer convection zones. The mean toroidal magnetic field, which is generated by a cyclic thin-layer α Ω dynamo at the bottom of the convection zone is taken to determine the emergence probability of magnetic flux tubes in the photosphere. Following the nonlinear rise of the unstable thin flux tubes, emergence latitudes and tilt angles of bipolar magnetic regions are determined. These quantities are put into a surface flux transport model, which simulates the surface evolution of magnetic flux under the effects of large-scale flows and turbulent diffusion. First results are discussed for the case of the Sun and for more rapidly rotating solar-type stars. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献