共查询到20条相似文献，搜索用时 31 毫秒
1.
Using proxy data for the occurrence of those mass ejections from the solar corona which are directed earthward, we investigate the association between the post-1970 interplanetary magnetic clouds of Klein and Burlaga (1982) and coronal mass ejections. The evidence linking magnetic clouds following shocks with coronal mass ejections is striking; six of nine clouds observed at Earth were preceded an appropriate time earlier by meter-wave type II radio bursts indicative of coronal shock waves and coronal mass ejections occurring near central meridian. During the selected control periods when no clouds were detected near Earth, the only type II bursts reported were associated with solar activity near the limbs. Where the proxy solar data to be sought are not so clearly suggested, that is, for clouds preceding interaction regions and clouds within cold magnetic enhancements, the evidence linking the clouds and coronal mass ejections is not as clear; proxy data usually suggest many candidate mass-ejection events for each cloud. Overall, the data are consistent with and support the hypothesis suggested by Klein and Burlaga that magnetic clouds observed with spacecraft at 1 AU are manifestations of solar coronal mass ejection transients. 相似文献
2.
We present observational imaging evidence for the existence of metric radio bursts closely associated with the front edge of coronal mass ejections (CMEs). These radio bursts drift in frequency similarly to type II bursts. They are weak and usually go undetected on spectrograph data. We find the same measured projected velocity for the displacement of, respectively, the radio source (when observed at two or more frequencies) and the CME leading edge. The position of the emitting source coincides with the CME leading edge. Among the events analyzed, the fastest of them, with a velocity over 1400 km s-1, was associated with interplanetary type II bursts. 相似文献
3.
S. Kahler N. R. Sheeley Jr. R. A. Howard M. J. Koomen D. J. Michels 《Solar physics》1984,93(1):133-141
We attempt to study the origin of coronal shocks by comparing several flare characteristics for two groups of flares: those with associated metric type II bursts and coronal mass ejections (CMEs) and those with associated metric type II bursts but no CMEs. CMEs accompany about 60% of all flares with type II bursts for solar longitudes greater than 30°, where CMEs are well observed with the NRL Solwind coronagraph. H flare areas, 1–8 Å X-ray fluxes, and impulsive 3 cm fluxes are all statistically smaller for events with no CMEs than for events with CMEs. It appears that both compact and large mass ejection flares are associated with type II bursts. The events with no CMEs imply that at least many type II shocks are not piston-driven, but the large number of events of both groups with small 3 cm bursts does not support the usual assumption that type II shocks are produced by large energy releases in flare impulsive phases. The poor correlation between 3 cm burst fluxes and the occurrence of type II bursts may be due to large variations in the coronal Alfvén velocity.Sachs/Freeman Associates, Inc., Bowie, MD 20715, U.S.A. 相似文献
4.
5.
We have analyzed a set of 147 metric Type II radio bursts observed by Culgoora radio spectrograph from November 1997 to December
2006. These events were divided into two sets: The first subset contains Type II events that started during the impulsive
phase of the associated solar flares and the second subset contains those starting during the decaying phase of flares. Our
main aim is to differentiate the metric Type IIs, flares and coronal mass ejections (CMEs) of these two subsets. It is found
that while Type II burst characteristics of both subsets are very similar, there are significant differences between flare
and CME properties for these two subsets. Considering all analyzed relationships between the characteristics of Type IIs,
flares and CMEs in these two Type II subsets, we conclude that most of the coronal shocks causing metric Type II bursts are
driven by CMEs, but that a fraction of events are probably ignited by solar flares. 相似文献
6.
Statistical analysis of the relationship between type II radio bursts appearing in the metric (m) and decameter-to-hectometer
(DH) wavelength ranges is presented. The associated X-ray flares and coronal mass ejections (CMEs) are also reported. The
sample is divided into two classes using the frequency-drift plots: Class I, representing those events where DH-type-II bursts
are not continuation of m-type-II bursts and Class II, where the DH-type-II bursts are extensions of m-type-II bursts. Our
study consists of three steps: i) comparison of characteristics of the Class I and II events; ii) correlation of m-type-II and DH-type-II burst characteristics with X-ray flare properties and iii) correlation of m-type-II and DH-type-II burst characteristics with CME properties. We have found no clear correlation between
properties of m-type-II bursts and DH-type-II bursts. For example, there is no correlation between drift rates of m-type-II
bursts and DH-type-II bursts. Similarly there is no correlation between their starting frequencies. In Class I events we found
correlations between X-ray flare characteristics and properties of m-type-II bursts and there is no correlation between flare
parameters and DH-type-II bursts. On the other hand, the correlation between CME parameters and m-type-II bursts is very weak,
but it is good for CME parameters and DH-type-II bursts. These results indicate that Class I m-type-II bursts are related
to the energy releases in flares, whereas DH-type-II bursts tend to be related to CMEs. On the contrary, for Class II events
in the case of m-type-II and DH-type-II bursts we have found no clear correlation between both flare and CMEs. 相似文献
7.
The relationship between metric type II radio bursts and solar flares is studied. Well-defined correlations between the properties of type II bursts and the characteristics of associated microwave and soft X-ray bursts are established in two entirely independent data sets. It is shown that the correlations are strongly affected by the wide range of coronal Alfvén velocities involved, comprising values from only 150 up to 800 km s–1, with a typical value of 400 km s–1. After careful data analysis it was inferred that type II bursts are more closely related to the soft X-ray bursts than they are to microwave bursts. The correlations indicate that type II burst shocks are preferably generated by flares with a relatively strong thermal component, and that the shocks are probably ignited by the plasma expansion associated with the 'evaporation' process in the transition region. Although the results imply that the majority of metric type II bursts are caused by flares, a simple geometrical consideration shows that a fraction of non-flare type II bursts cannot be explained by behind-limb events and that roughly 10% of metric type II bursts should be attributed to non-flare coronal mass ejections. 相似文献
8.
Large-scale, wave-like disturbances in extreme-ultraviolet (EUV) and type II radio bursts are often associated with coronal mass ejections (CMEs). Both phenomena may signify shock waves driven by CMEs. Taking EUV full-disk images at an unprecedented cadence, the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory has observed the so-called EIT waves or large-scale coronal propagating fronts (LCPFs) from their early evolution, which coincides with the period when most metric type II bursts occur. This article discusses the relation of LCPFs as captured by AIA with metric type II bursts. We show examples of type II bursts without a clear LCPF and fast LCPFs without a type II burst. Part of the disconnect between the two phenomena may be due to the difficulty in identifying them objectively. Furthermore, it is possible that the individual LCPFs and type II bursts may reflect different physical processes and external factors. In particular, the type II bursts that start at low frequencies and high altitudes tend to accompany an extended arc-shaped feature, which probably represents the 3D structure of the CME and the shock wave around it, and not just its near-surface track, which has usually been identified with EIT waves. This feature expands and propagates toward and beyond the limb. These events may be characterized by stretching of field lines in the radial direction and may be distinct from other LCPFs, which may be explained in terms of sudden lateral expansion of the coronal volume. Neither LCPFs nor type II bursts by themselves serve as necessary conditions for coronal shock waves, but these phenomena may provide useful information on the early evolution of the shock waves in 3D when both are clearly identified in eruptive events. 相似文献
9.
D–H type II radio bursts are widely thought to be caused by coronal mass ejections (CMEs). However, it is still unclear where the exact source of the type IIs on the shock surface is. We identify the source regions of the decameter–hectometric (D–H) type IIs based on imaging observations from SOHO/LASCO and the radio dynamic spectrum from Wind/Waves. The analysis of two well-observed events suggests that the sources of these two events are located in the interaction regions between shocks and streamers, and that the shocks are enhanced significantly in these regions. 相似文献
10.
We investigate the correlation of the occurrence of the herringbone phenomenon in type II solar radio bursts with various flare properties. We show that herringbone is strongly correlated with the intensity of the type II burst: whereas about 21% of all type II bursts show herringbone, about 60% of the most intense bursts contain herringbone. This fact can explain most of the correlations between herringbone and other properties such as intense type III bursts, type IV emission, and high type II starting frequencies. We also show that when this is taken into account, there is no need to postulate two classes of type II burst in order to explain why there appears to be a difference in herringbone occurrence between the set of type II bursts associated with the leading edges of coronal mass ejections, and those not so associated. We argue that the data are consistent with the idea that all coronal type II bursts are due to blast waves from flares. 相似文献
11.
A new solar radio spectrograph to observe solar radio bursts has been installed at the Ichon branch of the Radio Research
Laboratory, Ministry of Information and Communication, Korea. The spectrograph consists of three different antennas to sweep
a wide band of frequencies in the range of 30 MHz ∼ 2500 MHz. Its daily operation is fully automated and typical examples
of solar radio bursts have been successfully observed. In this paper we describe briefly its hardware and data processing
methods. Then we present coronal shock speeds estimated for 34 type II bursts from May 1998 to November 2000 and compare them
with those from other observatories. We also present the close relationship between onset time of type II bursts and X-ray
flares as well as their associations with coronal mass ejections. 相似文献
12.
V. K. Verma 《Solar physics》1988,114(1):185-188
The present paper investigates the north-south asymmetry for major flares (solar cycles 19 and 20), type II radio bursts (solar cycles 19,20 and 21), white light flares (solar cycle 19,20 and 21), and gamma ray bursts, hard X-ray bursts and coronal mass ejections (solar cycle 21). The results are compared with the found asymmetry in favour of the northern hemisphere during solar cycles 19 and 20 in favour of the southern hemisphere during solar cycle 21. 相似文献
13.
The vast majority of solar flares are not associated with metric Type II radio bursts. For example, for the period February 1980–July 1982, corresponding to the first two and one-half years of the Solar Maximum Mission, 95% of the 2500 flares with peak >25 keV count rates >100 c s–1lacked associated Type II emission. Even the 360 largest flares, i.e., those having >25 keV peak count rates >1000 c s–1, had a Type II association rate of only 24%. The lack of a close correlation between flare size and Type II occurrence implies the need for a 'special condition' that distinguishes flares that are accompanied by metric Type II radio bursts from those of comparable size that are not. The leading candidates for this special condition are: (1) an unusually low Alfvén speed in the flaring region; and (2) fast material motion. We present evidence based on SMM and GOES X-ray data and Solwind coronagraph data that argues against the first of these hypotheses and supports the second. Type II bursts linked to flares within 30° of the solar limb are well associated (64%; 49/76) with fast (>400 km s–1) coronal mass ejections (CMEs); for Type II flares within 15° of the limb, the association rate is 79% (30/38). An examination of the characteristics of 'non-CME' flares associated with Type IIs does not support the flare-initiated blast wave picture that has been proposed for these events and suggests instead that CMEs may have escaped detection. While the degree of Type II–CME association increases with flare size, there are notable cases of small Type II flares whose outstanding attribute is a fast CME. Thus we argue that metric Type II bursts (as well as the Moreton waves and kilometric Type II bursts that may accompany them) have their root cause in fast coronal mass ejections. 相似文献
14.
We study interplanetary (IP) solar radio type II bursts from 2011?–?2014 in order to determine the cause of the intense enhancements in their radio emission. Type II bursts are known to be due to propagating shocks that are often associated with fast halo-type coronal mass ejections (CMEs). We analysed the radio spectral data and the white-light coronagraph data from 16 selected events to obtain directions and heights for the propagating CMEs and the type II bursts. CMEs preceding the selected events were included in the analysis to verify whether CME interaction was possible. As a result, we were able to classify the events into five different groups. 1) Events where the heights of the CMEs and type II bursts are consistent, indicating that the shock is located at the leading front of the CME. The radio enhancements are superposed on the type II lanes, and they are probably formed when the shock meets remnant material from earlier CMEs, but the shock continues to propagate at the same speed. 2) Events where the type II heights agree with the CME leading front and an earlier CME is located at a height that suggests interaction. The radio enhancements and frequency jumps could be due to the merging process of the CMEs. 3) Events where the type II heights are significantly lower than the CME heights almost from the start. Interaction with close-by streamers is probably the cause for the enhanced radio emission, which is located at the CME flank region. 4) Events where the radio enhancements are located within wide-band type II bursts and the causes for the radio enhancements are not clear. 5) Events where the radio enhancements are associated with later-accelerated particles (electron beams, observed as type III bursts) that stop at the type II burst emission lane, and no other obvious reason for the enhancement can be identified.Most of the events (38%) were due to shock–streamer interaction, while one quarter of the events was due to possible CME–CME interaction. The drift rates, bandwidth characteristics, or cross-correlations of various characteristics did not reveal any clear association with particular category types. The chosen atmospheric density model causes the largest uncertainties in the derived radio heights, although in some cases, the emission bandwidths also lead to relatively large error margins.Our conclusion is that the enhanced radio emission associated with CMEs and propagating shocks can have different origins, depending on their overall configuration and the associated processes. 相似文献
15.
Coronal mass ejections (CMEs) are large-scale eruptive events in the solar corona. Once they are expelled into the interplanetary (IP) medium, they propagate outwards and “evolve” interacting with the solar wind. Fast CMEs associated with IP shocks are a critical subject for space weather investigations. We present an analytic model to study the heliocentric evolution of fast CME/shock events and their association with type II radio-burst emissions. The propagation model assumes an early stage where the CME acts as a piston driving a shock wave; beyond this point the CME decelerates, tending to match the ambient solar wind speed and its shock decays. We use the shock speed evolution to reproduce type II radio-burst emissions. We analyse four fast CME halo events that were associated with kilometric type II radio bursts, and in-situ measurements of IP shock and CME signatures. The results show good agreement with the dynamic spectra of the type II frequency drifts and the in-situ measurements. This suggests that, in general, IP shocks associated with fast CMEs evolve as blast waves approaching 1 AU, implying that the CMEs do not drive their shocks any further at this heliocentric range. 相似文献
16.
Guan-Nan Gao ;Min Wang ;Jun Lin ;Ning Wu ;Cheng-Ming Tan ;Berhard Kliem ;Yang Su 《中国天文和天体物理学报》2014,(7):843-854
A solar radio burst was observed in a coronal mass ejection/flare event by the Solar Broadband Radio Spectrometer at the Huairou Solar Observing Station on2004 December 1. The data exhibited various patterns of plasma motions, suggestive of the interaction between sunward moving plasmoids and the flare loop system during the impulsive phase of the event. In addition to the radio data, the associated whitelight, Hα, extreme ultraviolet light, and soft and hard X-rays were also studied. 相似文献
17.
G.S. Suryanarayana 《New Astronomy》2012,17(2):117-129
We study solar radio type II bursts combining with Wind/WAVES type II bursts and coronal mass ejections (CMEs). The aim of the present work is to investigate the effectiveness of shocks to cause type II bursts in the solar corona and the interplanetary space. We consider the following findings. The distribution of the cessation heights of type II emission is confined to a rather narrow range of height than the distribution of the heights of start frequencies. This is suggestive of the presence of a gradient for the Alfvén speed from the heliocentric height of ∼1.4 solar radii. The range of the kinetic energy of CMEs associated with coronal type II emission taken together with the suggested computation method and the Alfvén speed gradient, indicates the limit to the height up to which type II emission could be expected. This height is ∼2 solar radii from the center of the Sun. Further, the large time gap between the cessation time and heights of coronal type II emission and the commencement time and heights of most of the IP type II bursts do not account for the difference between the two heights and the average shock speed. Also, there is clear difference in the magnitude of the kinetic energies and the distinct characteristics of the CMEs associated with coronal and IP type II bursts. Hence, we suggest that in most instances the coronal type II bursts and IP type II bursts occur due to distinct shocks. We also address the question of the origin of type II bursts and discuss the possible explanation of observed results. 相似文献
18.
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
19.
G. M. Simnett 《Solar physics》1986,104(1):67-91
The relationship between solar radio emissions and transient interplanetary phenomena is reviewed. It is believed that the most significant advance in recent years has come from coordinated studies of coronal mass ejections and moving type IV bursts, where the evidence appears to favour the Langmuir wave hypothesis as the emission mechanism. Type II bursts are not generally a signature of the main energetic particle acceleration in flares. They do, however, occasionally propagate to 1 AU, and beyond, where they are normally accompanied by protons in the 20 MeV region. Apart from the impulsive microwave burst, there is no reliable radio signature associated with energetic particle acceleration in flares, although many phenomena have high correlations with radio emissions. The exceptions suggest that such correlations may be incidental. Therefore, it is concluded that attention should also be given to events with a positive absence of radio emission in order to make progress in understanding solar processes.Proceedings of the Workshop on Radio Continua during Solar Flares, held at Duino (Trieste), Italy, 27–31 May, 1985. 相似文献
20.
We have analyzed radio type IV bursts in the interplanetary (IP) space at decameter–hectometer (DH) wavelengths to determine their source origin and a reason for the observed directivity. We used radio dynamic spectra from the instruments on three different spacecraft, STEREO-A, Wind, and STEREO-B, which were located approximately 90 degrees apart from each other in 2011?–?2012, and thus gave a 360 degree view of the Sun. The radio data were compared to white-light and extreme ultraviolet (EUV) observations of flares, EUV waves, and coronal mass ejections (CMEs) in five solar events. We find that the reason that compact and intense DH type IV burst emission is observed from only one spacecraft at a time is the absorption of emission in one direction and that the emission is blocked by the solar disk and dense corona in the other direction. The geometry also makes it possible to observe metric type IV bursts in the low corona from a direction where the higher-located DH type IV emission is not detectable. In the absorbed direction we found streamers, and they were estimated to be the locations of type II bursts, caused by shocks at the CME flanks. The high-density plasma was therefore most probably formed by shock–streamer interaction. In some cases, the type II-emitting region was also capable of stopping later-accelerated electron beams, which were visible as type III bursts that ended near the type II burst lanes. 相似文献