type-II Radio Bursts Research Articles

Properties of Type-II Radio Bursts in Relation to Magnetic Complexity of the Solar Active Regions

Properties of Type-II Radio Bursts in Relation to Magnetic Complexity of the Solar Active Regions

Relationship between solar energetic particle intensity and coronal mass ejections and its associated type II radio bursts

Based on the multiple-vantage observations of STEREO, SOHO, wind and other spacecraft, the fast and wide coronal mass ejections (CME) during the 24th solar cycle from January 2010 to September 2014 are selected in this paper. Using the outputs of Richardson’s (2014) empirical model of solar energetic particle (SEP) intensity under different conditions, the effects of its associations such as CME, pre-CME, and type II radio bursts, on SEP intensity are analyzed, and the relationship between SEP event and these characteristics is also discussed. The main conclusions are as follows. 1) The presence or absence of pre-CME within 13 h before fast CME significantly improves the model prediction effect and has a significant influence on whether fast CME produces SEP event. Compared with the events without pre-CMEs, the events with pre-CMEs have a low proportion of false alarms (FR: 47.7% <i>vs.</i> 70%). However, the number of pre-CMEs does not improve the model output. 2) CMEs with type-II radio bursts have significantly lower FR to generate SEP events than fast CMEs without type-II radio bursts (42% <i>vs.</i> 68%). And selecting type-II radio bursts as a constraint will filter out some small/weak SEP events, the relationship between model predictions and observations especially for large SEP events (e.g. <i>I</i><sub>p</sub> ≥ 0.01 pfu/MeV) will stand out. Moreover, if the type-II radio enhancement is taken into account, FR can be further reduced to 29.4%, and the proportion of hits can be further increased (HR: 48.5%), and the model prediction is significantly improved. 3) The larger the start frequency of type II radio bursts, the smaller the end frequency is, and FR decreases slightly, but at the same time, a large number of SEP events are excluded by this condition, and the results show that the constraints on the start/end frequency of type-II radio bursts do not improve the model predictions distinctly. 4) If the sub-classification of type-II radio bursts is considered as the model constraint, the CMEs associated with multi-band type-II radio bursts have better model predictions than those with single-band events. For example, m-DH-km type-II radio bursts have lower FR (35.4%) and higher HR (48%), and the accuracy of empirical model is higher. In summary, we find that in addition to the velocity and angular width of CME, the associations of pre-CME, type II radio bursts and their enhancement, and multi-band sub-classification are the favorable conditions for CME to generate SEP events. The SEP intensities obtained by the empirical model have better consistency with the observations, and better predictions can be obtained. This investigation indicates that SEP events are more likely generated by fast and wide CMEs accompanied by pre-CMEs, multi-band type II radio bursts and their enhancements, which seem to serve as discriminative signal for SEP-rich and SEP-poor CMEs.

Simulating Solar Radio Bursts Using Generative Adversarial Networks

Solar flares are one of the most extreme drivers of space weather in our solar system. The impulsive solar radio emission associated with a solar flare is known as a solar radio burst (SRB). They are generally studied in dynamic spectra and are classified into five major spectral classes, ranging from Type I to Type V, based on their form and frequency, and time duration. Due to their intricate characterisation, generating a training set for object-detection and classification models of such phenomena is a difficulty in machine learning. Current algorithms implement parametric modelling where the quantity, grouping, intensity, drift rate, heterogeneity, start–end frequency and start–end time of Type-III and Type-II radio bursts are all random. However, this model does not factor in the true shape or general features seen in real dynamic spectra observations of the Sun, which can be crucial when training classification or object-detection algorithms. In this research, we introduce a methodology named a Generative Adversarial Network (GAN) for generating realistic SRB simulations. By using real examples of Type-III and Type-II SRB data, we can train GANs to generate images almost comparable to real observed data. Furthermore, we evaluate the results of the generated model using human perception, then we compare and contrast the results using a metric known as the Fréchet Inception Distance.

High-resolution observations with ARTEMIS/JLS and the NRH

Context.Narrowband bursts (spikes) are very small duration and bandwidth bursts which appear on dynamic spectra from microwave to decametric frequencies. They are believed to be manifestations of small-scale energy release through magnetic reconnection.Aims.We study the position of the spike-like structures relative to the front of type-II bursts and their role in the burst emission.Methods.We used high-sensitivity, low-noise dynamic spectra obtained with the acousto-optic analyzer (SAO) of the ARTEMIS-JLS solar radiospectrograph, in conjunction with high-time-resolution images from the Nançay Radioheliograph (NRH) in order to study spike-like bursts near the front of a type-II radio burst recorded at the west limb during the November 3, 2003 extreme solar event. The spike-like emission in the dynamic spectrum was enhanced by means of high-pass-time filtering.Results.We identified a number of spikes in the NRH images. Due to the lower temporal resolution of the NRH, multiple spikes detected in the dynamic spectrum appeared as single structures in the images. These spikes had an average size of ≈200″ and their observed brightness temperature was 1.4 to 5.6 × 109K, providing a significant contribution to the emission of the type-II burst front. At variance with a previous study on the type-IV associated spikes, we found no systematic displacement between the spike emission and the emission between spikes. At 327.0 MHz, the type II emission was located about 0.3R⊙above the pre-existing continuum emission, which, in turn, was located 0.1R⊙above the western limb.Conclusions.This study, combined with our previous results, indicates that the spike-like chains aligned along the type II burst MHD shock front are not a perturbation of the type II emission, as in the case of type IV spikes, but a manifestation of the type II emission itself. The preponderance of these chains, together with the lack of isolated structures or irregular clusters, points towards some form of small-scale magnetic reconnection, organized along the type-II propagating front.

Variations in the Solar Magnetic Fields and their Influence on Coronal Mass Ejections and Type-II Radio Bursts

Variations in the Solar Magnetic Fields and their Influence on Coronal Mass Ejections and Type-II Radio Bursts

Imaging and Spectral Observations of a Type-II Radio Burst Revealing the Section of the CME-Driven Shock That Accelerates Electrons

We report on a multi-wavelength analysis of the 26 January 2014 solar eruption involving a coronal mass ejection (CME) and a Type-II radio burst, performed by combining data from various space-and ground-based instruments. An increasing standoff distance with height shows the presence of a strong shock, which further manifests itself in the continuation of the metric Type-II burst into the decameter-hectometric (DH) domain. A plot of speed versus position angle (PA) shows different points on the CME leading edge travelled with different speeds. From the starting frequency of the Type-II burst and white-light data, we find that the shock signature producing the Type-II burst might be coming from the flanks of the CME. Measuring the speeds of the CME flanks, we find the southern flank to be at a higher speed than the northern flank; further the radio contours from Type-II imaging data showed that the burst source was coming from the southern flank of the CME. From the standoff distance at the CME nose, we find that the local Alfven speed is close to the white-light shock speed, thus causing the Mach number to be small there. Also, the presence of a streamer near the southern flank appears to have provided additional favorable conditions for the generation of shock-associated radio emission. These results provide conclusive evidence that the Type-II emission could originate from the flanks of the CME, which in our study is from the the southern flank of the CME.

Multi-wavelength analysis of CME-driven shock and Type II solar radio burst band-splitting

It is now well established that Coronal Mass Ejections (CMEs) may produce shocks in near Sun and interplanetary medium. A Type-II radio burst is characterized by shock and associated emission with very slow frequency drift rate (∼0.1 MHz/sec). A CME driven shock and their velocity, acceleration/deceleration signature can be observed by a Type-II solar radio burst which drifts with the shock speed and is split in bands of plasma radio emission. These emissions can be seen in radio spectrographs as split bands both in fundamental and harmonic frequencies close to a ratio of 1:2. In this paper, we present an analysis of a CME associated with a band splitting Type-II radio burst observed using multi-instruments in multi-wavelengths. We observed the CME event that occurred in 02 May 2013 (05:24 UT) and is associated with an M1.1 class solar flare from the active region NOAA 11731 located at N10W23 on the solar disk. We use the widely accepted Newkirk coronal density model to estimate the height in the solar atmosphere to compare our results. We conclude that the speed of CME is high enough to produce a Type-II solar radio burst. The analysis of this paper also involved an estimation of the coronal ambient magnetic field and its comparison with the empirical active region magnetic field model (Dulk and McLean in Sol. Phys. 57:279, 1978). This shows the good results. Observations provide sufficient evidence that the unusual patch signature in Type-II solar radio burst is due to the CME–CME interaction.

Statistical analysis of the relationship between type II radio enhancement and solar energetic particle event

In this paper, we investigated 82 type-II radio burst events detected by some ground stations Learmonth, YNAO, and BIRS and spacecraft Wind/WAVES, STEREO/WAVES from January 2007 to December 2015. And we identified 39 events associated with radio enhancement and 43 events without enhancement. We found that: 1) The CME velocity, mass, kinetic energy and flare class with respect to type II radio enhancement events were generally higher than that of no enhancement events, and these properties in the solar energetic particle (SEP) events were significantly higher than that no SEP event, regardless of whether radio enhancement or not. 2) As shown in the characteristic time analysis, the initial release time of SEPs is generally earlier than the start time of radio enhancement, so we can the radio enhancement is only as a signature of the shock enhancement rather than the direct generator of SEP events. 3) Whether radio enhancement or not, the onset height of type IIs associated with SEP event is slightly lower than that of event without SEP. For the absence height, the SEP events are significantly higher than the no-SEP events, and that the absence height of enhancement events are also distinctly higher than that non-enhancement events, which reveals that the enhanced CME shock characterized by enhanced radio burst can keep propagating to more higher or further space. 4) When one fast and wide CME fully sweeps over another slow and narrow preceding CME, CME interaction can more easily generate radio enhancement, but no distinctive difference between SEP events and non-SEP events. So the results of this paper reveal that radio enhancement can be regarded as a manifestation of CME shock becoming strong during interacting with other CME, and the enhanced shock can accelerate the particle to generate large SEP events more easily. However, the type II radio enhancement is not the direct producer or causer that generate large SEP event.

Evolution of Coronal and Interplanetary Shock Waves Inferred from a Radio Burst

Studying the evolution of the source of a radio burst, which is recognized as a shock wave, is important for understanding its generation mechanism and predicting its hazards. Estimating the kinematics of radio-burst sources using electron-density models is not easy. In this article, the kinematics of the Type-II radio-burst source is estimated without using electron-density models by studying the density variation along the leading surface of the coronal mass ejections (CMEs) (hereafter ejecta) during Type-II radio-burst emission. This technique is valid for analyzing the Type-II radio-burst spectrum in metric and DH ranges, from which we can infer ejecta propagation from the corona into interplanetary space. It is found that the Type-II radio burst can be described by the Sedov–Taylor blast-wave equation by matching the calculated theoretical frequencies with that observed by the RAD1 and RAD2 receivers. The theoretical model showed a good fit with the observed spectra of Type-II radio bursts of different Type-II events. The analysis was consistent with the previous work regarding the conditions of the Sedov–Taylor equation and statistical studies of the density variation on the surface area of an interplanetary CME. The kinematics of a Type-II radio-burst source and the temporal variation of its energy are estimated during the Type-II radio-burst emission. The results of the two cases studied show that the energy of ejecta degraded by $\approx 14\% $ of its initial energy at the beginning of metric Type-II radio emission on 16 March 2016, while the energy of ejecta degraded by $\approx 86\%$ and $\approx 20 \% $ for DH Type-II radio burst as recorded by RAD1 and RAD2 on 7 November 2004, respectively. The analysis shows that the radial speed of the blast wave is lower than its transversal speed along the surface of ejecta and extends to a small fraction of R⊙ from its source point on the ejecta. The magnetic-field strength of the ejecta and the ambient medium are estimated during the Type-II radio-burst emission. This study emphasizes that the emission of a blast wave from the reconnection sites within the ejecta is one of the processes that degrades the energy of ejecta during their propagation.

Predicting the arrival time of CME associated with type-II radio burst using neural networks technique

Type-II radio bursts have been extensively studied as it is considered as a means of inspecting the coronal shock speeds effectively. In this paper, we study the type-II radio burst that occurred on 2 May 2013 through combined observations from the Solar and Heliospheric Observatory (SOHO) and the Solar Terrestrial Relations Observatory (STEREO), in parallel with the ground-based observation from the DARO-CALLISTO station in Germany. We calculate the shock parameters by employing the clear band-splitting of the type-II burst. By using the Newkirk electron density model, we trace the height at which the emission has been produced. Then we trace the shock speed, the Alfven speed, and the coronal magnetic field strength at heights ranging from 1.96–1.99 Rs. We trace the evolution of the accompanied partial-halo Coronal Mass Ejection (CME) event in the inner corona through combined observations from STEREO-A and SOHO. Finally, we establish a prediction model based on artificial Neural Networks (NN) to estimate the arrival time of the CME (May 4th, 20:18), which is close to the actual arrival time (May 5th, ∼ 08:00).

Statistical analysis of shock properties driven by coronal mass ejections based on observations of type II radio bursts

In this paper, we investigate 77 type-II radio burst events' data observed by Wind/WAVES and STEREO/SWAVES from January 2007 to December 2015. By fitting the frequency-time profile to obtain the corresponding shock velocity, we study the relationship between the parameters of shock and those of coronal mass ejection (CME), solar flare and the associated SEP events, and explore the influences of type II radio enhancement on these relationships. Our findings are as follows. 1) In general, at the onset time of type II radio bursts within deca-hectometric (DH) waveband, the shock front is about 0.4Rs ahead of the leading edge of CME (shock standoff distance), and this distance increases as the CME propagates outward. In the low and high corona, the relationship between shock standoff distance and CME speed indicates a significant difference; the shock standoff distance is correlated with the CME speed positively at the low altitude, but negatively at high altitude. 2) The CME speed of the events with radio enhancement is significantly larger than that with no radio enhancement; and comparing with the events with no radio enhancement, the correlation coefficient between the shock speed and the mass and kinetic energy of the associated CME is significantly high for the events with radio enhancement. 3) There is no correlation between the duration of type II radio burst in DH waveband with enhancement and the speed, mass and kinetic energy of CME. However, it presents a positive correlation for the events with no radio enhancement. 4) Usually the speed of shock that can produce SEP event is obviously higher than that with producing no SEP event. The probability of the SEP generated by the events associated with radio enhancement is slightly higher than with no radio enhancement (73.5% > 67.4%), but for the large SEP events, the generation probability (67.6%) associated with radio enhancement is about one-order of magnitude higher than that with no radio enhancement (37.2%). This conclusion indicates that the type II radio enhancement can be used as one of the signatures of the shock or the radio source that more probably produces a large SEP event.

Investigating the Coronal Mass Ejections associated with DH type-II radio bursts and solar flares during the ascending phase of the solar cycle 24

We studied a set of 74 CMEs, with shedding the light on the halo-CMEs (HCMEs), that are associated with decametric – hectometric (DH) type-II radio bursts (1–16 MHz) and solar flares during the period 2008–2014. The events were classified into 3 groups (disk, intermediate, and limb events) based on their longitudinal distribution.We found that the events are mostly distributed around 15.32° and 15.97° at the northern and southern solar hemispheres, respectively. We found that there is a clear dependence between the longitude and the CME’s width, speed, acceleration, mass, and kinetic energy. For the CMEs’ widths, most of the events were HCMEs (∼62%), while the partial HCMEs comprised ∼35% and the rest of events were CMEs with widths less than 120°. For the CMEs’ speeds, masses, and kinetic energies, the mean values showed a direct proportionality with the longitude, in which the limb events had the highest speeds, the largest masses, and the highest kinetic energies. The mean peak flux of the solar flares for different longitudes was comparable, but the disk flares were more energetic. The intermediate flares were considered as gradual flares since they tended to last longer, while the limb flares were considered as impulsive flares since they tended to last shorter.A weak correlation (R = 0.32) between the kinetic energy of the CMEs and the duration of the associated flares has been noticed, while there was a good correlation (R = 0.76) between the kinetic energy of the CMEs and the peak flux of the associated flares. We found a fair correlation (R = 0.58) between the kinetic energy of the CMEs and the duration of the associated DH type-II radio bursts.

Study of the early phase of a Coronal Mass Ejection driven shock in EUV images

The November 1st, 2014 prominence eruption (associated with a C2.7 class flare) resulted in a fast, partial-halo Coronal Mass Ejection (CME). During its early propagation, the CME produced a type II radio burst (seen by the Bruny Island Radio Spectrometer) starting around 04:57 UT when the front entered into the LASCO/C2 field of view (FOV) and the top of the CME front was at the heliocentric distance of about 2.5 $R_{\odot}$ . In order to identify the source of the type II radio burst, we studied the kinematic of the eruption with EUV images acquired by SDO/AIA. Profiles of the observed EUV front speed have been compared with the Alfven speed profiles derived by combining the plasma electron densities obtained from Emission Measure analysis and model magnetic fields extrapolated on the plane of the sky. Our results show that the northern half of the front became super-Alfvenic at approximately the same time when the type-II radio burst started. A comparison between the starting frequency of the type II emission and the frequencies corresponding to the coronal densities of the locations where the EUV front became super-Alfvenic suggests that the radio sources should be located in the northern flank of the front.

Heights of Coronal Mass Ejections and Shocks Inferred from Metric and DH Type II Radio Bursts

A set of 27 continuous events that showed extension of metric Type-II radio bursts (m-Type IIs) into the deca–hectometric (DH) domain is considered. The coronal mass ejections (CMEs) associated with this type of continuous event supply more energy to produce space-weather effects than the CMEs that produce Type-II bursts in any one region. Since the heights of shock formation at the start of m-Type IIs were not available from observations, they were estimated using kinematic modeling in previous studies. In the present study, the heights of shock formation during metric and DH Type-II bursts are determined using two methods: i) the CME leading-edge method and ii) a method employing known electron-density models and start/end frequencies. In the first method, assuming that the shocks are generated by the associated CMEs at the leading edge, the height of the CME leading edge (LE) is calculated at the onset and end of m-Type IIs using the kinematic equation with constant acceleration or constant speed. The LE heights of CMEs that are assumed to be the heights of shock formation/end of nearly 79% of m-Type IIs are found to be within the acceptable range of \(1\,\mbox{--}\,3~\mbox{R}_{\odot}\). For other events, the heights are beyond this range, for which the shocks might either have been generated at the CME flanks/flare-blast waves, or the initial CME height might have been different. The CME/shock height at the onset and end of 17 DH Type IIs are found to be in the range of \(2\,\mbox{--}\,6~\mbox{R}_{\odot}\) and within \(30~\mbox{R}_{\odot}\), respectively. In addition, the CME LE heights from observations at the onset and end of metric/DH Type IIs are compared with the heights corresponding to the observed frequency that is determined using the known electron-density models, and they are in agreement with the model results. The heights are also estimated using the space speed available for 15 halo CMEs, and it is found that the difference is smaller at the m-Type II start/end (0.02 to \(0.66~\mbox{R}_{\odot}\)) and slightly greater at the DH Type II end (0.19 to \(1.94~\mbox{R}_{\odot}\)). Finally, the possibility of CME–streamer interactions at the start of DH Type IIs is checked, and it is found that many of the events with streamers have lower start frequencies. In addition, these results are discussed in comparison with the values reported in the literature. This study will be useful to find the source region of metric and DH Type IIs and to understand the CME-shock propagation.

Low Frequency Radio Experiment (LORE)

In this paper, we present a case study of Low Frequency Radio Experiment (LORE) payload to probe the corona and the solar disturbances at solar offsets greater than 2 solar radii, i.e., at frequencies below 30 MHz. The LORE can be complimentary to the planned Indian solar mission, “Aditya-L1” and its other payloads as well as synergistic to ground-based interplanetary scintillation (IPS) observations, which are routinely carried out by the Ooty Radio Telescope. We discuss the baseline design and technical details of the proposed LORE and its particular suitability for providing measurements on the detailed time and frequency structure of fast drifting type-III and slow drifting type-II radio bursts with unprecedented time and frequency resolutions. We also brief the gonio-polarimetry, which is possible with better-designed antennas and state-of-the-art electronics, employing FPGAs and an intelligent data management system. These would enable us to make a wide range of studies, such as nonlinear plasma processes in the Sun-Earth distance, in-situ radio emission from coronal mass ejections (CMEs), interplanetary CME driven shocks, nature of ICMEs driving decelerating IP shocks and space weather effects of solar wind interaction regions.

PLASMA EMISSION BY COUNTER-STREAMING ELECTRON BEAMS

ABSTRACT The radiation emission mechanism responsible for both type-II and type-III solar radio bursts is commonly accepted as plasma emission. Recently Ganse et al. suggested that type-II radio bursts may be enhanced when the electron foreshock geometry of a coronal mass ejection contains a double hump structure. They reasoned that the counter-streaming electron beams that exist between the double shocks may enhance the nonlinear coalescence interaction, thereby giving rise to more efficient generation of radiation. Ganse et al. employed a particle-in-cell simulation to study such a scenario. The present paper revisits the same problem with EM weak turbulence theory, and show that the fundamental (F) emission is not greatly affected by the presence of counter-streaming beams, but the harmonic (H) emission becomes somewhat more effective when the two beams are present. The present finding is thus complementary to the work by Ganse et al.

PHYSICAL CONDITIONS OF CORONAL PLASMA AT THE TRANSIT OF A SHOCK DRIVEN BY A CORONAL MASS EJECTION

We report here on the determination of plasma physical parameters across a shock driven by a Coronal Mass Ejection using White Light (WL) coronagraphic images and Radio Dynamic Spectra (RDS). The event analyzed here is the spectacular eruption that occurred on June 7th 2011, a fast CME followed by the ejection of columns of chromospheric plasma, part of them falling back to the solar surface, associated with a M2.5 flare and a type-II radio burst. Images acquired by the SOHO/LASCO coronagraphs (C2 and C3) were employed to track the CME-driven shock in the corona between 2-12 R$_\odot$ in an angular interval of about 110$^\circ$. In these intervals we derived 2-Dimensional (2D) maps of electron density, shock velocity and shock compression ratio, and we measured the shock inclination angle with respect to the radial direction. Under plausible assumptions, these quantities were used to infer 2D maps of shock Mach number $M_\text{A}$ and strength of coronal magnetic fields at the shock's heights. We found that in the early phases (2-4 R$_\odot$) the whole shock surface is super-Alfv\'enic, while later on (i.e. higher up) it becomes super-Alfvenic only at the nose. This is in agreement with the location for the source of the observed type-II burst, as inferred from RDS combined with the shock kinematic and coronal densities derived from WL. For the first time, a coronal shock is used to derive a 2D map of the coronal magnetic field strength over a 10 R$_\odot$ altitude and $\sim 110^\circ$ latitude intervals.

Halo Coronal Mass Ejections and Their Relation to DH Type-II Radio Bursts

A set of 88 halo CMEs observed by the Solar and Heliospheric Observatory/Large Angle Solar Coronagraph (SOHO/LASCO) during the period 2005 to 2010 is considered to study the relationship of these halo CMEs with Type-II radio bursts in the deca–hectametric (DH) wavelength range observed by Wind/(Plasma and Radio Waves: WAVES). Among the 88 events, 39 halo CMEs are found to be associated with DH Type-II radio bursts and their characteristics are analyzed with the following results: i) The heights of the CME leading edge at the time of the starting frequencies of many of the selected DH Type-II events (74 %) are in the range ( $2\,\mbox{--}\,10~\mathrm{R}_{\odot}$ ) where the shocks are formed. ii) The mean speed of DH-associated halo CMEs (1610 km s−1) is nearly twice the mean speed (853 km s−1) of halo CMEs without DH Type-II radio bursts, implying that the peak of the Alfven speed profile in the outer corona where DH Type-II radio bursts start might be around 800 km s−1. iii) The shock speed of DH Type-II radio bursts calculated using the heights of shock signatures of the corresponding CME events is found to be slightly higher than the CME speed. iv) The CME speed plays a major role in the determination of the ending frequency of DH Type-II radio bursts but not the starting frequency. v) The relationship between the characteristics of DH Type-II radio bursts and CMEs is explained in the context of the universal drift-rate spectrum.

Excitation of kink oscillations of coronal loops: statistical study

Context. Solar flares are often accompanied by kink (transverse) oscillations of coronal loops. Despite intensive study of these oscillations in recent years, the mechanisms that excite them are still not known. Aims. We aim to clarify the excitation mechanisms for these kink oscillations of coronal loops. Methods. Weanalysed 58 kink-oscillation events observed by the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) during its first four years (2010‐2014) with the use of the JHelioviewer. Association of these oscillation events with flares, lower coronal (r 1.4R� ) eruptions and plasma ejections, coronal mass ejections (CMEs), and coronal Type-II radio bursts is studied. Results. We find that 44 of these 58 oscillation events (76%) were associated with CMEs observed in the white light emission. Moreover, 57 events (98%) were accompanied by lower coronal eruptions/ejections (LCEs) observed in the extreme-ultraviolet band in the parental active regions. In the remaining event an LCE was not clearly seen, but it was definitely associated with a CME too. The main observational finding is that the kink oscillations were excited by the deviation of loops from their equilibria by a nearby LCE in 55 events (95%). In three remaining events, it was difficult to reliably determine the cause of the oscillations because of limitations in the observational data. We also found that 53 events (91%) were associated with flares. In five remaining events, the parental active regions were behind the limb and we could not directly see flare sites. It indicates that there is a close relationship between these two kinds of solar activity. However, the estimated speeds of a hypothetical driver of kink oscillations by flares were found to be lower than 500 kms −1 in 80% of the cases. Such low speeds do not favour the association of the oscillation excitation with a shock wave, as usually assumed. That only 23 (40%) of the oscillation events were found to be associated with coronal Type-II radio bursts also goes against the shock wave mechanism for the excitation of kink oscillations. Conclusions. The statistical analysis shows that the most probable mechanism for exciting the kink oscillations of coronal loops is the deviation of loops from their equilibrium by nearby eruptions or plasma ejections rather than a blast shock wave ignited by a flare.

PROMINENCE ACTIVATION BY CORONAL FAST MODE SHOCK

An X5.4 class flare occurred in active region (AR) NOAA11429 on 2012 March 7. The flare was associated with very fast coronal mass ejection (CME) with its velocity of over 2500 km/s. In the images taken with STEREO-B/COR1, a dome-like disturbance was seen to detach from expanding CME bubble and propagated further. A Type-II radio burst was also observed at the same time. On the other hand, in EUV images obtained by SDO/AIA, expanding dome-like structure and its foot print propagating to the north were observed. The foot print propagated with its average speed of about 670 km/s and hit a prominence located at the north pole and activated it. While the activation, the prominence was strongly brightened. On the basis of some observational evidence, we concluded that the foot print in AIA images and the ones in COR1 images are the same, that is MHD fast mode shock front. With the help of a linear theory, the fast mode mach number of the coronal shock is estimated to be between 1.11 and 1.29 using the initial velocity of the activated prominence. Also, the plasma compression ratio of the shock is enhanced to be between 1.18 and 2.11 in the prominence material, which we consider to be the reason of the strong brightening of the activated prominence. The applicability of linear theory to the shock problem is tested with nonlinear MHD simulation.