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1.
Instances of seismic transients emitted into the solar interior in the impulsive phases of some solar flares offer a promising diagnostic tool, both for understanding the physics of solar flares and for the general development of local helioseismology. Among the prospective contributors to flare acoustic emission that have been considered are: i) chromospheric shocks propelled by pressure transients caused by impulsive thick-target heating of the upper and middle chromosphere by high-energy particles, ii) heating of the photosphere by continuum radiation from the chromosphere or possibly by high-energy protons, and iii) magnetic-force transients caused by magnetic reconnection. Hydrodynamic modeling of chromospheric shocks suggests that radiative losses deplete all but a small fraction of the energy initially deposited into them before they penetrate the photosphere. Comparisons between the spatial distribution of acoustic sources, derived from seismic holography of the surface signatures of flare acoustic emission, and the spatial distributions of sudden changes both in visible-light emission and in magnetic signatures offer a possible means of discriminating between contributions to flare acoustic emission from photospheric heating and magnetic-force transients. In this study we develop and test a means for estimating the seismic intensity and spatial distribution of flare acoustic emission from photospheric heating associated with visible-light emission and compare this with the helioseismic signatures of seismic emission. Similar techniques are applicable to transient magnetic signatures. 相似文献
2.
A.-C. Donea D. Besliu-Ionescu P. S. Cally C. Lindsey V. V. Zharkova 《Solar physics》2006,239(1-2):113-135
Following the discovery of a few significant seismic sources at 6.0 mHz from the large solar flares of October 28 and 29,
2003, we have extended SOHO/MDI helioseismic observations to moderate M-class flares. We report the detection of seismic waves
emitted from the β γ δ active region NOAA 9608 on September 9, 2001. A quite impulsive solar flare of type M9.5 occurred from 20:40 to 20:48 UT.
We used helioseismic holography to image seismic emission from this flare into the solar interior and computed time series
of egression power maps in 2.0 mHz bands centered at 3.0 and 6.0 mHz. The 6.0 mHz images show an acoustic source associated
with the flare some 30 Mm across in the East – West direction and 15 Mm in the North – South direction nestled in the southern
penumbra of the main sunspot of AR 9608. This coincides closely with three white-light flare kernels that appear in the sunspot
penumbra. The close spatial correspondence between white-light and acoustic emission adds considerable weight to the hypothesis
that the acoustic emission is driven by heating of the lower photosphere. This is further supported by a rough hydromechanical
model of an acoustic transient driven by sudden heating of the low photosphere. Where direct heating of the low photosphere
by protons or high-energy electrons is unrealistic, the strong association between the acoustic source and co-spatial continuum
emission can be regarded as evidence supporting the back-warming hypothesis, in which the low photosphere is heated by radiation
from the overlying chromosphere. This is to say that a seismic source coincident with strong, sudden radiative emission in
the visible continuum spectrum indicates a photosphere sufficiently heated so as to contribute significantly to the continuum
emission observed. 相似文献
3.
A series of solar flares was observed near the same location in NOAA active region 8996 on 18–20 May 2000. A detailed analysis of one of these flares is presented where the emitting structures in soft and hard X-rays, EUV, H, and radio at centimeter wavelengths are compared. Hard X-rays and radio emission were observed at two separate loop footpoints, while soft X-rays and EUV emission were observed mainly above the nearby positive polarity region. The flare was confined although the observed type III bursts at the time of the flare maximum indicate that some field lines were open to the corona. No flux emergence was evident but moving magnetic features were observed around the sunspot region and within the positive polarity (plage) region. We suggest that the flaring was due to loop–loop interactions over the positive polarity region, where accelerated electrons gained access to the two separate loop systems. The repeated radio flaring at the footpoint of one loop was visible because of the strong magnetic fields near the large sunspot region while at the footpoint of the other loop the electrons could precipitate and emit in hard X-rays. The simultaneous emission and fluctuations in radio and X-rays – in two different loop ends – further support the idea of a single acceleration site at the loop intersection. 相似文献
4.
J. C. Martínez-Oliveros H. Moradi D. Besliu-Ionescu A.-C. Donea P. S. Cally C. Lindsey 《Solar physics》2007,245(1):121-139
We carried out an electromagnetic acoustic analysis of the solar flare of 14 August 2004 in active region AR10656 from the
radio to the hard X-ray spectrum. The flare was a GOES soft X-ray class M7.4 and produced a detectable sun quake, confirming
earlier inferences that relatively low energy flares may be able to generate sun quakes. We introduce the hypothesis that
the seismicity of the active region is closely related to the heights of coronal magnetic loops that conduct high-energy particles
from the flare. In the case of relatively short magnetic loops, chromospheric evaporation populates the loop interior with
ionised gas relatively rapidly, expediting the scattering of remaining trapped high-energy electrons into the magnetic loss
cone and their rapid precipitation into the chromosphere. This increases both the intensity and suddenness of the chromospheric
heating, satisfying the basic conditions for an acoustic emission that penetrates into the solar interior. 相似文献
5.
Broadband soft solar X-rays monitored by the GOES satellites have been used to detect high-temperature flares (> 25 MK). The data suggest that there are two general categories of high-temperature flares: those that are intrinsically hot and recur repeatedly in particular active regions and those that show enhanced temperatures because of their proximity to the solar limb. Intrinsically hot flares associate with gamma-ray flares and impulsive hard X-ray flares. Hot flares show a small incidence with gradual hard X-ray flares, but those cases are either extremely intense flares or limb flares. The apparently hot flares occur near the visible limb, which suggests the strong thermal stratification of flare plasmas as demonstrated by over-the-limb events; even on the visible disk near the limb, the lower, cooler plasmas are somehow partially occulted. 相似文献
6.
A. O. Benz T. Kosugi M. J. Aschwanden S. G. Benka E. L. Chupp S. Enome H. Garcia G. D. Holman V. G. Kurt T. Sakao A. V. Stepanov M. Volwerk 《Solar physics》1994,153(1-2):33-53
Particle acceleration is intrinsic to the primary energy release in the impulsive phase of solar flares, and we cannot understand flares without understanding acceleration. New observations in soft and hard X-rays, -rays and coherent radio emissions are presented, suggesting flare fragmentation in time and space. X-ray and radio measurements exhibit at least five different time scales in flares. In addition, some new observations of delayed acceleration signatures are also presented. The theory of acceleration by parallel electric fields is used to model the spectral shape and evolution of hard X-rays. The possibility of the appearance of double layers is further investigated.Report of Team 3, Flares 22 Workshop, Ottawa, May 25–28, 1993. 相似文献
7.
We investigate temporal and spatial correlations in solar flares of hard X-rays (HXR) and decimetric continuum emissions,
ejecta, and CMEs. The focus is on three M-class flares, supported by observations from other flares. The main conclusions
of our observations are that (1) major hard X-ray flares are often associated with ejecta seen in soft X-rays or EUV. (2)
Those ejecta seem to start before HXR or related decimetric radio continua (DCIM emission). (3) DCIM occurring nearly simultaneously
with the first HXR peak are located very close to the HXR source. Later in the flare, DCIM generally becomes stronger, drifts
to lower frequency and occurs far from the HXR source. Thus the positions at high frequency are generally closer to the HXR
source. DCIM emission consists of pulses that drift in frequency. The very high and sometimes positive drift rate suggests
spatially extended sources or type III like beams in an inhomogeneous source. Movies of selected flares used in this study
can be found on the CD-ROM accompanying this volume.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1026194227110 相似文献
8.
K. Ohki 《Solar physics》1975,45(2):435-452
Interferometric radio observations together with soft X-ray observations are presented here to show that during the growth phase of soft X-ray flares, a large mass increase occurs simultaneously with the creation of an X-ray hot region in the corona. The lack of an increase of radio flux from pre-flare active regions absolutely excludes the possibility of the coronal accumulation of low-temperature matter just prior to flare onset. Therefore we suggest a hypothesis that a large amount of hot matter, which contains almost the entire energy in the flare, is supplied from the chromosphere into the corona during each flare. Since even small flares produce coronal hot regions radiating thermal soft X-rays and microwaves, the formation of the hot region may be a basic process in most flares. Energy, created by some instability in the corona, travels by thermal conduction to the chromosphere where the dense matter is heated and subsequently expands into the corona, producing the observed hot region. Impulsive heating of the chromosphere by nonthermal electrons which simultaneously emit hard X-rays is not sufficient to be the energy source in our model. Slower heating, which supplies the flare more energy than that supplied in the impulsive phase, is required. If the temperature of the energy source in the corona exceeds 2 × 107 K, the conductive energy flux becomes sufficient to exceed the radiation loss from the chromosphere-corona transition region. This excess energy may cause the chromospheric gas expansion. 相似文献
9.
M. R. Kundu S. M. White V. I. Garaimov P. Subramanian S. Ananthakrishnan P. Janardhan 《Solar physics》2006,236(2):369-387
Observations of a solar flare at 617 MHz with the Giant Meter-wave Radio Telescope (GMRT) are used to study the morphology
of flare radio emission at decimetric wavelengths. There has been very little imaging in the 500 – 1000 MHz frequency range,
but it is of great interest, since it corresponds to densities at which energy is believed to be released in solar flares.
This event has a very distinctive morphology at 617 MHz: the radio emission is clearly resolved by the 30″ beam into arc-shaped
sources seeming to lie at the tops of long loops, anchored at one end in the active region in which the flare occurs, with
the other end lying some 200 000 km away in a region of quiet solar atmosphere. Microwave images show fairly conventional
behaviour for the flare in the active region: it consists of two compact sources overlying regions of opposite magnetic polarity
in the photosphere. The decimetric emission is confined to the period leading up to the impulsive phase of the flare, and
does not extend over a wide frequency range. This fact suggests a flare mechanism in which the magnetic field at considerable
height in the corona is destabilized a few minutes prior to the main energy release lower in the corona. The radio morphology
also suggests that the radiating electrons are trapped near the tops of magnetic loops, and therefore may have pitch angles
near 90˚. 相似文献
10.
We analyze hard and soft X-ray, microwave and meter wave radio, interplanetary particle, and optical data for the complex energetic solar event of 22 July 1972. The flare responsible for the observed phenomena most likely occurred 20° beyond the NW limb of the Sun, corresponding to an occultation height of 45 000 km. A group of type III radio bursts at meter wavelengths appeared to mark the impulsive phase of the flare, but no impulsive hard X-ray or microwave burst was observed. These impulsive-phase phenomena were apparently occulted by the solar disk as was the soft X-ray source that invariably accompanies an H flare. Nevertheless essentially all of the characteristic phenomena associated with second-stage acceleration in flares - type II radio burst, gradual second stage hard X-ray burst, meter wave flare continuum (FC II), extended microwave continuum, energetic electrons and ions in the interplanetary medium - were observed. The spectrum of the escaping electrons observed near Earth was approximately the same as that of the solar population and extended to well above 1 MeV.Our analysis of the data leads to the following results: (1) All characteristics are consistent with a hard X-ray source density n
i
108 cm–3 and magnetic field strength 10 G. (2) The second-stage acceleration was a physically distinct phenomenon which occurred for tens of minutes following the impulsive phase. (3) The acceleration occurred continuously throughout the event and was spatially widespread. (4) The accelerating agent was very likely the shock wave associated with the type II burst. (5) The emission mechanism for the meter-wave flare continuum source may have been plasma-wave conversion, rather than gyrosynchrotron emission. 相似文献
11.
12.
Very-Large-Array (VLA) observations of the Sun at 20, 91 and 400 cm have been combined with data from the SOHO, TRACE and Wind solar missions to study the properties of long-lasting Type I noise storms and impulsive metric and decimetric bursts during solar flares and associated coronal mass ejections. These radio observations provide information about the acceleration and propagation of energetic electrons in the low and middle corona as well as their interactions with large-scale magnetic structures where energy release and transport takes place. For one flare and its associated CME, the VLA detected impulsive 20 and 91 cm bursts that were followed about ten minutes later by 400 cm burst emission that appeared to move outward into the corona. This event was also detected by the Waves experiment on Wind which showed intense, fast-drifting interplanetary Type III bursts following the metric and decimetric bursts detected by the VLA. For another event, impulsive 91 cm emission was detected about a few minutes prior to impulsive bursts at 20.7 cm, suggesting an inwardly propagating beam of electrons that excited burst emission at lower levels and shorter wavelengths. We also find evidence for significant changes in the intensity of Type I noise storms in the same or nearby active region during impulsive decimetric bursts and CMEs. These changes might be attributed to flare-initiated heating of the Type I radio source plasma by outwardly-propagating flare ejecta or to the disruption of ambient magnetic fields by the passage of a CME. 相似文献
13.
P. Kaufmann 《Solar physics》1996,169(2):377-388
The time profiles of electromagnetic fluxes at hard X-rays and short microwaves are signatures of the energy conversion mechanisms at the origin of solar flares. The distinction between continuum and discrete energy production brings drastic conceptual consequences for the interpretation of the energy conversion processes. As more sensitive detectors were used on measurements with higher time resolution, the notion of continuum energy release in the impulsive phase is being replaced by the concept of repetitive energy production or Elementary Flare Bursts manifested at hard X-rays and by rapid time structures in microwave emissions. These discrete time structures are now known to be as short as tens of milliseconds, and part of their emissions are possibly produced by the same populations of accelerated electrons. Fast spikes, with mm-wave emission fluxes increasing for shorter wavelengths, simultaneous with hard X-rays, bring severe constraints for interpretation. This problem is reviewed, with the suggestion of a possible significant burst emission component in the sub-mm-IR range, due to primeval short-lived explosive compact sources, for which there are still no diagnostics.Dedicated to Cornelis de Jager 相似文献
14.
Bhuwan Joshi P. K. Manoharan Astrid M. Veronig P. Pant Kavita Pandey 《Solar physics》2007,242(1-2):143-158
The evolution of an X2.7 solar flare, that occurred in a complex β γ δ magnetic configuration region on 3 November 2003 is discussed by utilizing a multi-wavelength data set. The very first signature of pre-flare coronal activity is observed in radio wavelengths as a type III burst that occurred several minutes prior to the flare signature in Hα. This type III burst is followed by the appearance of a loop-top source in hard X-ray (HXR) images obtained from RHESSI. During the main phase of the event, Hα images observed from ARIES solar tower telescope, Nainital, reveal well-defined footpoint (FP) and loop-top (LT) sources. As the flare evolves, the LT source moves upward and the separation between the two FP sources increases. The co-alignment of Hα with HXR images shows spatial correlation between Hα and HXR footpoints, whereas the rising LT source in HXR is always located above the LT source seen in Hα. The evolution of LT and FP sources is consistent with the reconnection models of solar flares. The EUV images at 195 Å taken by SOHO/EIT reveal intense emission on the disk at the flaring region during the impulsive phase. Further, slow-drifting type IV bursts, observed at low coronal heights at two time intervals along the flare period, indicate rising plasmoids or loop systems. The intense type II radio burst at a time in between these type IV bursts, but at a relatively greater height, indicates the onset of CME and its associated coronal shock wave. The study supports the standard CSHKP model of flares, which is consistent with nearly all eruptive flare models. More importantly, the results also contain evidence for breakout reconnection before the flare phase. 相似文献
15.
A method to determine the emission measure and hence the effective extension of solar flares is described. The conditions for the Balmer continuum to be visible in disk flares is also considered. The concept of the effective mass is introduced and it is shown that this mass is a little less than that of a plasma filling the whole spectroscopic volume and including thin and dense filaments and the intervals between them as well. In this connection it is necessary to have high energy electron fluxes. It is assumed that these electrons maintian a high temperature in the interval volume; being a source of powerful X-rays, such hot intervals can heat cool filaments and they in their turn reradiate in the visible and ultraviolet regions of the flare spectrum. Taking one flare as an example, we give curves of the emission measure, effective mass and numbers of hydrogen atoms in the second quantum state versus time. These curves agree qualitatively with the light curve characteristics for most of the flares. 相似文献
16.
Radio-silent -ray flares are solar flares that lack any significant emission in the (non-thermal) radio wave band during their impulsive hard X-ray and -ray emission phases. Flares with extremely suppressed long-wavelength spectra have previously been reported by White et al. (1992) and have been discussed in different context by Hudson and Ryan (1995). A striking example of a radio-silent flare was observed by SMM during the onset of the 6 March 1989 energetic -ray flare. We argue that the absence of radio emission at wavelengths longer than microwave wavelengths is an indication of the compactness of the flare rather than that the flare did not exhibit non-thermal properties. Probably the flare site was restricted to altitudes above the photosphere in a newly emerging loop configuration lower than the equivalent altitude corresponding to an emission frequency of 1.4 GHz. This implies the presence of a dense and highly magnetized closed field configuration confining the electron component which causes the impulsive -ray continuum. Reconnection in such a configuration did not lead to open magnetic fields and streamer formation. Acceleration of particles in the and hard X-ray bursts was restricted to closed field lines. Thermal expansion of the loop system may subsequently lead to the generation of radially propagating blast waves in the solar corona which are accompanied by type II solar radio bursts and decimetre emissions. The emission during the onset of the flare was dominated by a continuum originating from electron bremsstrahlung at X-ray and -ray energies with only little evidence for the presence of energetic ions. It is, therefore, concluded that energetic electrons have been primary and not secondary products of the particle acceleration process. 相似文献
17.
Broadband sensors aboard the Naval Research Laboratory's SOLRAD 11 satellites measured solar emission in the 0.5 to 3 Å, 1 to 8 Å, 8 to 20 Å, 100 to 500 Å, 500 to 800 Å, and 700 to 1030 Å bands. Data from sixteen large flares show that the EUV emission is dominated by gradual emission which parallels the soft X-ray emission in duration and magnitude. The data are consistent with the separation of EUV and X-ray flare emission into two distinct components. A persistent component is made up of gradual EUV and gradual soft X-ray emissions. A brief component consists of hard X-rays, impulsive soft X-rays, and impulsive EUV emission. 相似文献
18.
Observations of gamma-ray lines from solar flares by SMM demonstrated that energetic protons and heavy ions are accelerated during the impulsive phase. In order to understand the acceleration mechanism for gamma-ray producing protons and heavy ions, we have studied the characteristics of the flares from which gamma-ray lines were observed by SMM In order to identify the characteristics unique to the gamma-ray line flares, we have also studied intense hard X-ray flares with no gamma-ray line emissions. We have found the following characteristics: 1) Most of the gamma-ray line flares produced intense radio bursts of types II and IV. 2) For most of the gamma-ray line flares, the time profiles of high-energy (? 300 keV) hard X-rays are delayed by order of several seconds with respect to those of low-energy hard X-rays. The delay times seem to be correlated with the spatial sizes of the flares. 3) In Hα importance, the gamma-ray line flares range from sub-flares to importance-3 flares. 4) The hard X-ray spectra of the gamma-ray line flares are generally flatter (harder) than those of flares with no gamma-ray line emission. From these characteristics, we conclude that the first-order Fermi acceleration operating in a flare loop is likely to be the acceleration mechanism for energetic protons and heavy ions as well as relativistic electrons. 相似文献
19.
We present a multi-wavelength study of a solar eruption event on 20 July 2004, comprising observations in H??, EUV, soft X-rays, and in radio waves with a wide frequency range. The analyzed data show both oscillatory patterns and shock wave signatures during the impulsive phase of the flare. At the same time, large-scale EUV loops located above the active region were observed to contract. Quasi-periodic pulsations with ???10 and ???15 s oscillation periods were detected both in microwave??C?millimeter waves and in decimeter??C?meter waves. Our calculations show that MHD oscillations in the large EUV loops ?C but not likely in the largest contracting loops ?C could have produced the observed periodicity in radio emission, by triggering periodic magnetic reconnection and accelerating particles. As the plasma emission in decimeter??C?meter waves traces the accelerated particle beams and the microwave emission shows a typical gyrosynchrotron flux spectrum (emission created by trapped electrons within the flare loop), we find that the particles responsible for the two different types of emission could have been accelerated in the same process. Radio imaging of the pulsed decimetric??C?metric emission and the shock-generated radio type II burst in the same wavelength range suggest a rather complex scenario for the emission processes and locations. The observed locations cannot be explained by the standard model of flare loops with an erupting plasmoid located above them, driving a shock wave at the CME front. 相似文献
20.
Various mechanisms have been proposed to explain how seismic waves can be generated during a solar flare, several of which
include a major role for accelerated electrons. To address this question further, we have selected two samples of white-light
flares (WLFs): one that has associated sunquakes, and one that does not. We focus particularly on the spatial characteristics
of the hard X-ray (HXR) and WL emission, and the HXR spectral characteristics associated with the flares in both samples,
including spectral hardness, HXR source size, and total injected electron power. Coupling the determined rate of energy deposition
with the area over which the energy is being deposited suggests that in general the acoustically active flares are associated
with a larger and more impulsive deposition of electron energy. However, this does not always correspond to a higher WL contrast. 相似文献