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2.
David Alexander 《Astrophysics and Space Science》2007,307(1-3):197-202
The solar atmosphere displays a wide variety of dynamic phenomena driven by the interaction of magnetic fields and plasma.
In particular, plasma jets in the solar chromosphere and corona, coronal heating, solar flares and coronal mass ejections
all point to the presence of magnetic phenomena such as reconnection, flux cancellation, the formation of magnetic islands,
and plasmoids. While we can observe the signatures and gross features of such phenomena we cannot probe the essential physics
driving them, given the spatial resolution of current instrumentation. Flexible and well-controlled laboratory experiments,
scaled to solar parameters, open unique opportunities to reproduce the relevant unsteady phenomena under various simulated
solar conditions. The ability to carefully control these parameters in the laboratory allows one to diagnose the dynamical
processes which occur and to apply the knowledge gained to the understanding of similar processes on the Sun, in addition
directing future solar observations and models. This talk introduces the solar phenomena and reviews the contributions made
by laboratory experimentation. 相似文献
3.
Coronal density, temperature, and heat-flux distributions for the equatorial and polar corona have been deduced from Saito’s model of averaged coronal white-light (WL) brightness and polarization observations. These distributions are compared with those determined from a kinetic collisionless/exospheric model of the solar corona. This comparison indicates similar distributions at large radial distances (>?7 R⊙) in the collisionless region. However, rather important differences are found close to the Sun in the acceleration region of the solar wind. The exospheric heat flux is directed away from the Sun, while that inferred from all WL coronal observations is in the opposite direction, i.e. conducting heat from the inner corona toward the chromosphere. This could indicate that the source of coronal heating extends up into the inner corona, where it maximizes at r>1.5 R⊙, well above the transition region. 相似文献
4.
Particle Acceleration and Propagation in Strong Flares without Major Solar Energetic Particle Events
Solar energetic particles (SEPs) detected in space are statistically associated with flares and coronal mass ejections (CMEs).
But it is not clear how these processes actually contribute to the acceleration and transport of the particles. The present
work addresses the question why flares accompanied by intense soft X-ray bursts may not produce SEPs detected by observations
with the GOES spacecraft. We consider all X-class X-ray bursts between 1996 and 2006 from the western solar hemisphere. 21
out of 69 have no signature in GOES proton intensities above 10 MeV, despite being significant accelerators of electrons,
as shown by their radio emission at cm wavelengths. The majority (11/20) has no type III radio bursts from electron beams
escaping towards interplanetary space during the impulsive flare phase. Together with other radio properties, this indicates
that the electrons accelerated during the impulsive flare phase remain confined in the low corona. This occurs in flares with
and without a CME. Although GOES saw no protons above 10 MeV at geosynchronous orbit, energetic particles were detected in
some (4/11) confined events at Lagrangian point L1 aboard ACE or SoHO. These events have, besides the confined microwave emission,
dm-m wave type II and type IV bursts indicating an independent accelerator in the corona. Three of them are accompanied by
CMEs. We conclude that the principal reason why major solar flares in the western hemisphere are not associated with SEPs
is the confinement of particles accelerated in the impulsive phase. A coronal shock wave or the restructuring of the magnetically
stressed corona, indicated by the type II and IV bursts, can explain the detection of SEPs when flare-accelerated particles
do not reach open magnetic field lines. But the mere presence of these radio signatures, especially of a metric type II burst,
is not a sufficient condition for a major SEP event. 相似文献
5.
We calculate charge state distributions of Kr and Xe in a model for two different types of solar wind using the effective ionization and recombination rates provided from the OPEN_ADAS data base. The charge states of heavy elements in the solar wind are essential for estimating the efficiency of Coulomb drag in the inner corona. We find that xenon ions experience particularly low Coulomb drag from protons in the inner corona, comparable to the notoriously weak drag of protons on helium ions. It has been found long ago that helium in the solar wind can be strongly depleted near interplanetary current sheets, whereas coronal mass ejecta are sometimes strongly enriched in helium. We argue that if the extraordinary variability of the helium abundance in the solar wind is due to inefficient Coulomb drag, the xenon abundance must vary strongly. In fact, a secular decrease of the solar wind xenon abundance relative to the other heavier noble gases (Ne, Ar, Kr) has been postulated based on a comparison of noble gases in recently irradiated and ancient samples of ilmenite in the lunar regolith. We conclude that decreasing solar activity and decreasing frequency of coronal mass ejections over the solar lifetime might be responsible for a secularly decreasing abundance of xenon in the solar wind. 相似文献
6.
Variations of solar emission in the spectral ranges corresponding to the transition region (304 Å) and corona (175 Å) and their relation to solar wind parameters are investigated for the maximum and declining phase of solar cycle 23 (2001–2004) based on the CORONAS-F/SPIRIT data. It is shown that the variations of solar flux in both ranges are similar and demonstrate a high correlation for long data series. Meanwhile, some time intervals were registered when the intensity variations at 304 Å are delayed with respect to those in 175 Å by, on average, two days. For long periods, the spectra of the full-disk flux at 175 Å and of the solar wind density are close to each other; the same is true for the solar flux spectrum in the 304-Å range and the spectrum of the solar wind velocity. The assumption is made that active processes in the lower corona mainly affect long-period density variations, while the velocity characterizes the kinetics of the total stream of the outflowing matter and its long-term variations are considerably related to the physics of processes occurring deeper in the Sun. 相似文献
7.
We summarize ERNE/SOHO observations of solar energetic particle events associated with impulsive soft X-ray flares and LASCO coronal mass ejections (CMEs). The new observational data support an idea that the >10 MeV proton acceleration may be initiated at different coronal sources, operating in the flaring active region and on the global coronal scale, in concert with CME development. However, the particle acceleration continues beyond the coronal scales and may culminate at the interplanetary CME well after the flare. We emphasize the importance of CME liftoff/aftermath processes in the solar corona and the possible role of seed particle re-acceleration, which may explain the existence of hybrid solar energetic particle events. 相似文献
8.
Milan Maksimovic Viviane Pierrard Joseph Lemaire 《Astrophysics and Space Science》2001,277(1-2):181-187
We present the basics of the exospheric models of the solar wind acceleration. In these models the plasma is assumed fully
collisionless above a typical altitude in the corona. The solar wind is accelerated by the interplanetary electrostatic potential
which is needed to warrant the equality of the proton and electron fluxes. These models suggest that the fast wind emanating
from the polar regions could be due to the presence of non-thermal electron distributions in the corona.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
9.
It is well established that solar Type-II radio bursts are signatures of magnetohydrodynamical (MHD) shock waves propagating outward through the solar corona. Nevertheless, there are long-standing controversies about how these shocks are formed; solar flares and the coronal mass ejections (CMEs) are considered to be the most likely drivers. We present the results of the analysis of four solar Type-II bursts recorded between 20 January 2010 and 17 November 2011 by the Compound Astronomical Low-frequency Low-cost Instrument for Spectroscopy in Transportable Observatories (CALLISTO-BR) (in Brazil), which operates in the frequency range of 45?–?870 MHz. For all four solar Type-II radio bursts, which consisted of one event without band splitting and three split-band variants, the outcomes are consistent with those reported in the literature. All four Type-II radio bursts were accompanied by both solar flares and CMEs, which are associated with the impulsive phase of the flares and, very likely, with the acceleration phase of the CMEs. 相似文献
10.
Paul A. Crowther Peter S. Conti 《Monthly notices of the Royal Astronomical Society》2003,343(1):143-163
In solar extreme ultraviolet spectra the He i and He ii resonance lines show unusual behaviour and have anomalously high intensities compared with other transition region lines. The formation of the helium resonance lines is investigated through extensive non-local thermal equilibrium radiative transfer calculations. The model atmospheres of Vernazza, Avrett & Loeser are found to provide reasonable matches to the helium resonance line intensities but significantly overestimate the intensities of other transition region lines. New model atmospheres have been developed from emission measure distributions derived by Macpherson & Jordan, which are consistent with SOHO observations of transition region lines other than those of helium. These models fail to reproduce the observed helium resonance line intensities by significant factors. The possibility that non-Maxwellian electron distributions in the transition region might lead to increased collisional excitation rates in the helium lines is studied. Collisional excitation and ionization rates are recomputed for distribution functions with power-law suprathermal tails that may form by the transport of fast electrons from high-temperature regions. Enhancements of the helium resonance line intensities are found, but many of the predictions of the models regarding line ratios are inconsistent with observations. These results suggest that any such departures from Maxwellian electron distributions are not responsible for the helium resonance line intensities. 相似文献
11.
I. S. Veselovsky A. V. Dmitriev A. V. Suvorova M. V. Tarsina 《Journal of Astrophysics and Astronomy》2000,21(3-4):423-429
The cyclic evolution of the heliospheric plasma parameters is related to the time-dependent boundary conditions in the solar
corona. “Minimal” coronal configurations correspond to the regular appearance of the tenuous, but hot
and fast plasma streams from the large polar coronal holes. The denser, but cooler and slower solar wind is adjacent to coronal
streamers. Irregular dynamic manifestations are present in the corona and the solar wind everywhere and always. They follow
the solar activity cycle rather well. Because of this, the direct and indirect solar wind measurements demonstrate clear variations
in space and time according to the minimal, intermediate and maximal conditions of the cycles. The average solar wind density,
velocity and temperature measured at the Earth’s orbit show specific decadal variations and trends, which are of
the order of the first tens per cent during the last three solar cycles. Statistical, spectral and correlation characteristics
of the solar wind are reviewed with the emphasis on the cycles. 相似文献
12.
S. Rifai Habbal H. Morgan M. Druckmüller A. Ding J. F. Cooper A. Daw E. C. Sittler Jr. 《Solar physics》2013,285(1-2):9-24
Imaging and spectroscopy of the solar corona, coupled with polarimetry, are the only tools available at present to capture signatures of physical processes responsible for coronal heating and solar wind acceleration within the first few solar radii above the solar limb. With the recent advent of improved detector technology and image processing techniques, broad-band white light and narrow-band multi-wavelength observations of coronal forbidden lines, made during total solar eclipses, have started to yield new views about the thermodynamic and magnetic properties of coronal structures. This paper outlines these unique capabilities, which until present, have been feasible primarily with observations during natural total solar eclipses. This work also draws attention to the exciting possibility of greatly increasing the frequency and duration of solar eclipse observations with Moon orbiting observatories utilizing lunar limb occultation of the solar disk for coronal measurements. 相似文献
13.
K. Wilhelm W. Curdt E. Marsch U. Schühle P. Lemaire A. Gabriel J. -C. Vial M. Grewing M. C. E. Huber S. D. Jordan A. I. Poland R. J. Thomas M. Kühne J. G. Timothy D. M. Hassler O. H. W. Siegmund 《Solar physics》1995,162(1-2):189-231
The instrument SUMER - Solar Ultraviolet Measurements of Emitted Radiation is designed to investigate structures and associated dynamical processes occurring in the solar atmosphere, from the chromosphere through the transition region to the inner corona, over a temperature range from 104 to 2 × 106
K and above. These observations will permit detailed spectroscopic diagnostics of plasma densities and temperatures in many solar features, and will support penetrating studies of underlying physical processes, including plasma flows, turbulence and wave motions, diffusion transport processes, events associated with solar magnetic activity, atmospheric heating, and solar wind acceleration in the inner corona. Specifically, SUMER will measure profiles and intensities of EUV lines; determine Doppler shifts and line broadenings with high accuracy; provide stigmatic images of the Sun in the EUV with high spatial, spectral, and temporal resolution; and obtain monochromatic maps of the full Sun and the inner corona or selected areas thereof. SUMER will be flown on the Solar and Heliospheric Observatory (SOHO), scheduled for launch in November, 1995. This paper has been written to familiarize solar physicists with SUMER and to demonstrate some command procedures for achieving certain scientific observations. 相似文献
14.
In coronal holes the electron (proton) density is low, and heating of the proton gas produces a rapidly increasing proton temperature in the inner corona. In models with a reasonable electron density in the upper transition region the proton gas becomes collisionless some 0.2 to 0.3 solar radii into the corona. In the collisionless region the proton heat flux is outwards, along the temperature gradient. The thermal coupling to electrons is weak in coronal holes, so the heat flux into the transition region is too small to supply the energy needed to heat the solar wind plasma to coronal temperatures. Our model studies indicate that in models with proton heating the inward heat conduction may be so inefficient that some of the energy flux must be deposited in the transition region to produce the proton fluxes that are observed in the solar wind. If we allow for coronal electron heating, the energy that is needed in the transition region to heat the solar wind to coronal temperatures, may be supplied by heat conduction from the corona. 相似文献
15.
New results of the numerical modeling of the response of the outer atmosphere of the Sun to an impulsive heating are presented.
Features of the general process are considered both for powerful and weak solar flares. For the most powerful flares it is
necessary to take into account the effect of a saturation of the heat flow. Though for the most powerful solar flares the
saturation of a thermal flow is not such large, the influence of this effect is important for cases of powerful flares on
red dwarf stars, strongly limiting the input of the thermal energy downwards. The response of the atmosphere, which consists
of the chromosphere, the transition region and the corona, to weak heating is characterized by creation no one as usually
but two ascending coronal flows. The occurrence of the additional flow at coronal heights is caused by the inhomogeneous initial
heating of the outer atmosphere. Some types of soft X-ray and UV-jets can be associated with such additional flow.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
16.
Solar eruptions are the most spectacular events in our solar system and are associated with many different signatures of energy release including solar flares, coronal mass ejections, global waves, radio emission and accelerated particles. Here, we apply the Coronal Pulse Identification and Tracking Algorithm (CorPITA) to the high-cadence synoptic data provided by the Solar Dynamics Observatory (SDO) to identify and track global waves observed by SDO. 164 of the 362 solar flare events studied (45%) were found to have associated global waves with no waves found for the remaining 198 (55%). A clear linear relationship was found between the median initial velocity and the acceleration of the waves, with faster waves exhibiting a stronger deceleration (consistent with previous results). No clear relationship was found between global waves and type II radio bursts, electrons or protons detected in situ near Earth. While no relationship was found between the wave properties and the associated flare size (with waves produced by flares from B to X-class), more than a quarter of the active regions studied were found to produce more than one wave event. These results suggest that the presence of a global wave in a solar eruption is most likely determined by the structure and connectivity of the erupting active region and the surrounding quiet solar corona rather than by the amount of free energy available within the active region. 相似文献
17.
On 10 March 2001 the active region NOAA 9368 produced an unusually impulsive solar flare in close proximity to the solar limb. This flare has previously been studied in great detail, with observations classifying it as a type 1 white-light flare with a very hard spectrum in hard X-rays. The flare was also associated with a type II radio burst and coronal mass ejection. The flare emission characteristics appeared to closely correspond to previous instances of seismic emission from acoustically active flares. Using standard local helioseismic methods, we identified the seismic signatures produced by the flare that, to date, is the least energetic (in soft X-rays) of the flares known to have generated a detectable acoustic transient. Holographic analysis of the flare shows a compact acoustic source strongly correlated with the impulsive hard X-rays, visible continuum, and radio emission. Time?–?distance diagrams of the seismic waves emanating from the flare region also show faint signatures, mainly in the eastern sector of the active region. The strong spatial coincidence between the seismic source and the impulsive visible continuum emission reinforces the theory that a substantial component of the seismic emission seen is a result of sudden heating of the low photosphere associated with the observed visible continuum emission. Furthermore, the low-altitude magnetic loop structure inferred from potential-field extrapolations in the flaring region suggests that there is a significant anti-correlation between the seismicity of a flare and the height of the magnetic loops that conduct the particle beams from the corona. 相似文献
18.
主要论述宁静日冕洞，以及日冕加热问题的研究现状。讨论了宁静日冕的理论模型、观测模型和混合模型，以及冕洞区大气模型和太阳风加热问题。最后对计划中的日冕空间探测作了简要介绍。 相似文献
19.
Solar p modes are one of the dominant types of coherent signals in Doppler velocity in the solar photosphere, with periods showing
a power peak at five minutes. The propagation (or leakage) of these p-mode signals into the higher solar atmosphere is one of the key drivers of oscillatory motions in the higher solar chromosphere
and corona. This paper examines numerically the direct propagation of acoustic waves driven harmonically at the photosphere,
into the nonmagnetic solar atmosphere. Erdélyi et al. (Astron. Astrophys.
467, 1299, 2007) investigated the acoustic response to a single point-source driver. In the follow-up work here we generalise this previous
study to more structured, coherent, photospheric drivers mimicking solar global oscillations. When our atmosphere is driven
with a pair of point drivers separated in space, reflection at the transition region causes cavity oscillations in the lower
chromosphere, and amplification and cavity resonance of waves at the transition region generate strong surface oscillations.
When driven with a widely horizontally coherent velocity signal, cavity modes are caused in the chromosphere, surface waves
occur at the transition region, and fine structures are generated extending from a dynamic transition region into the lower
corona, even in the absence of a magnetic field. 相似文献