Type II bursts in Meter and Decameter – Hectometer Wavelength Ranges and Their Relation to Flares and CMEs

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.     

Type II Radio Bursts with High and Low Starting Frequencies

We report on the detailed analysis of i) differences between the properties of type IIs with various starting frequencies (high: ≥100 MHz; low: ≤50 MHz; mid: 50 MHz ≤f≤ 100 MHz) and ii) the properties of CMEs and flares associated with them. For this study, we considered a sample of type II radio bursts observed by Culgoora radio spectrograph from January 1998 to December 2000. The X-ray flares and CMEs associated with these events are identified using GOES and SOHO/LASCO data. The secondary aim is to study the frequency dependence on other properties of type IIs, flares, and CMEs. We found that the type IIs with high starting frequencies have larger drift rate, relative drift rate, and shock speed than the type IIs with low starting frequencies. The flares associated with high frequency type IIs are of impulsive in nature with shorter rise time, duration and delay between the flare start and type II start times than the low frequency type IIs. There is a distinct power – law relationship between the flare parameters and the starting frequencies of type II bursts, whereas the trend in the CME parameters shows low correlation. While the mean speed of CMEs is larger for the mid-frequency group, it is nearly the same for the high and low frequency groups. On the other hand, the percentage of CME association (90%) is larger for low frequency type IIs than for the high frequency type IIs (75%).     

Geoeffectiveness and flare properties of radio-loud CMEs

A detailed investigation on geoeffective CMEs associated with meter to Deca-Hectometer (herein after m- and DH-type-II) wavelengths range type-II radio bursts observed during the period 1997–2005 is presented. The study consists of three steps: i) the characteristics of m-and DH-type-II bursts associated with flares and geoeffective CMEs; ii) characteristics of geo and non-geoeffective radio-loud and quiet CMEs, iii) the relationships between the geoeffective CMEs and flares properties. Interestingly, we found that 92 % of DH-type-II bursts are extension of m-type-II burst which are associated with faster and wider geoeffective DH-CMEs and also associated with longer/stronger flares. The geoeffective CME-associated m-type-II bursts have higher starting frequency, lower ending frequency and larger bandwidth compared to the general population of m-type-II bursts. The geoeffective CME-associated DH-type-II bursts have longer duration (P?1 %), lower ending frequency (P=2 %) and lower drift rates (P=2 %) than that of DH-type-IIs associated with non-geoeffective CMEs. The differences in mean speed of geoeffective DH-CMEs and non-geoeffective DH-CMEs (1327 km?s^?1 and 1191 km?s^?1, respectively) is statistically insignificant (P=20 %).However, the mean difference in width (339^° and 251^°, respectively) is high statistical significant (P=0.8 %). The geo-effective general populations of LASCO CMEs speeds (545 km?s^?1 and 450 km?s^?1, respectively) and widths (252^° and 60^°, respectively) is higher than the non geo-effective general populations of LASCO CMEs (P=3 % and P=0.02 %, respectively). The geoeffective CMEs associated flares have longer duration, and strong flares than non-geoeffective DH-CMEs associated flares (P=0.8 % and P=1 %, respectively). We have found a good correlation between the geo-effective flare and DH-CMEs properties: i) CMEs speed—acceleration (R=?0.78, where R is a linear correlation coefficient), ii) acceleration—flare peak flux (R=?0.73) and, iii) acceleration—Dst index intensity (R=0.75). The radio-rich CMEs (DH-CMEs) produced more energetic storm than the radio-quiet CMEs (general populations of LASCO CMEs). The above results indicate that the DH-type-II bursts tend to be related with flares and geoeffective CMEs, although there is no physical explanation for the result. If the DH-type-II burst is a continuation of m-type-II burst, it could be a good indicator of geoeffective storms, which has important implications for space weather studies.     

Characteristics of DH type II bursts, CMEs and flares with respect to the acceleration of CMEs

A detailed investigation on DH-type-II radio bursts recorded in Deca-Hectometer (hereinafter DH-type-II) wavelength range and their associated CMEs observed during the year 1997–2008 is presented. The sample of 212 DH-type-II associated with CMEs are classified into three populations: (i) Group I (43 events): DH-type-II associated CMEs are accelerating in the LASCO field view (a>15 m s⁻²); (ii) Group II (99 events): approximately constant velocity CMEs (−15<a<15 m s⁻²) and (iii) Group III (70 events): represents decelerating CMEs (a<−15 m s⁻²). Our study consists of three steps: (i) statistical properties of DH-type-II bursts of Group I, II and III events; (ii) analysis of time lags between onsets of flares and CMEs associated with DH-type-II bursts and (iii) statistical properties of flares and CMEs of Group I, II and III events. We found statistically significant differences between the properties of DH-type-II bursts of Group I, II and III events. The significance (P _a ) is found using the one-way ANOVA-test to examine the differences between means of groups. For example, there is significant difference in the duration (P _a =5%), ending frequency (P _a =4%) and bandwidth (P _a =4%). The accelerating and decelerating CMEs have more kinetic energy than the constant speed CMEs. There is a significant difference between the nose height of CMEs at the end time of DH-type-IIs (P _a ≪1%). From the time delay analysis, we found: (i) there is no significant difference in the delay (flare start—DH-type-II start and flare peak—DH-type-II start); (ii) small differences in the time delay between the CME onset and DH-type-II start, delay between the flare start and CME onset times. However, there are high significant differences in: flare duration (P _a =1%), flare rise time (P _a =0.5%), flare decay time (P _a =5%) and CMEs speed (P _a ≪1%) of Group I, II and III events. The general LASCO CMEs have lower width and speeds when compared to the DH CMEs. It seems there is a strong relation between the kinetic energy of CMEs and DH-type-II properties.     

Distinctions between the characteristics of before and after DH CMEs associated flares

A detailed analysis of characteristics of coronal mass ejections and flares associated with deca-hectometer wavelength type-II radio bursts (DH-CMEs and DH-flares) observed in the period 1997–2008 is presented. A sample of 62 limb events is divided into two populations known as after-flare CMEs (AF-CMEs) and before-flare CMEs (BF-CMEs) based on the relative timing of the flare and CME onsets. On average, AF-CMEs (1589 km s⁻¹) have more speed than the BF-CMEs (1226 km s⁻¹) and the difference between mean values are highly significant (P∼2%). The average CME nose height at the time of type-II start is at larger distance for AF-CMEs than the BF-CMEs (4.89 and 3.84 R _o, respectively). We found a good anti-correlation for accelerating (R _a=−0.89) and decelerating (R _d=−0.78) AF-CMEs. In the case of decelerating BF-CMEs, the correlation seems to be similar to that for decelerating AF-CMEs (R _d=−0.83). The number of decelerating AF-CMEs is 51% only; where as, the number of decelerating BF-CMEs is 83%. The flares associated with BF-CMEs have shorter rise and decay times than flares related to AF-CMEs. We found statistically significant differences between the two sets of associated DH-type-II bursts characteristics: starting frequency (P∼4%), drift rate (P∼1%), and ending frequency (P∼6%). The delay time analysis of DH-type-II start and flare onset times shows that the time lags are longer in AF-CME events than in BF-CME events (P≪1%). From the above results, the AF-CMEs which are associated with DH-type-II bursts are found to be more energetic, associated with long duration flares and DH-type-IIs of lower ending frequencies.     

A Statistical Study on CMEs Associated with DH-Type-II Radio Bursts Based on Their Source Location (Limb and Disk Events)

We have statistically studied the 344 Coronal Mass Ejections (CMEs) associated with flares and DH-type-II radio bursts (1??C?14 MHz) during 1997??C?2008. We found that only 3?% of the total CMEs (344) compared to the general population CMEs (13208) drives DH-type-II radio bursts (Gopalswamy in Solar Eruptions and Energetic Particles, AGU Geophys. Monogr. 165, 207, 2006). Out of 344 events we have selected 236 events for further analysis. We divided the events into two groups: i) disk events (within 45° from the disk center) and ii) limb events (beyond 45° but within 90° from the disk center). We find that the average CME speed of the limb events (1370?km?s^?1) is three times, while for the disk events (1055?km?s^?1) it is two times the average speed of the general population CMEs (433?km?s^?1). The average widths of the limb events (129°) and disk events (116°) are two times greater than the average width of the general population CMEs (58°). We found a better correlation between the CME speed and width (correlation coefficient R=0.56) for the limb events than that of the disk events (R=0.47). The shock speed of the CMEs associated with DH-type-II radio bursts is found by applying Leblanc, Dulk, and Bougeret??s (Solar Phys. 183, 165, 1998) electron density model; the disk events are found to have an average speed of 1190 km?s^?1 and that of the limb events is 1275 km?s^?1. From this study we compare the CME properties between limb and disk events. The properties like CME speed, width, shock speed, and correlation between CME speed and width are found to be higher for limb events than disk events. The results in disk events are subject to projection effects, and this study stresses the importance of these effects.     

Kinematics and Flare Properties of Radio-Loud CMEs

A detailed analysis of the characteristics of coronal mass ejections (CMEs) and flares associated with decameter-hectometer wavelength type-II radio bursts (hereafter DH-type-II radio bursts, DH-CMEs or radio-loud CMEs) observed in the period 1997??C?2008 is presented. A sample of 61 limb events is divided into two populations based on the residual acceleration: accelerating CMEs (a _r>0) and decelerating CMEs (a _r<0). We found that average speed (residual acceleration) of all limb DH-CMEs (called radio-loud CMEs) is nearly three (two) times greater than the average speed of the general population CMEs (radio-quiet CMEs). While the initial acceleration (a _i) of the accelerating DH-CMEs is smaller than that of decelerating DH-CMEs (0.79 and 1.62 km?s^?2, respectively), the average speed and magnitude of residual acceleration of the accelerating and decelerating DH-CMEs are similar (??V _CME??: 1254 km?s^?1 and 1303 km?s^?1; ??a _r??: 0.026 km?s^?2 and 0.028 km?s^?2, respectively). The accelerating DH-CMEs attain their peak speed at larger heights than decelerating DH-CMEs. A good positive and negative linear correlation for accelerating and decelerating DH-CMEs (R _a=0.74 and R _d=?0.77, respectively) is found. The flares associated with accelerating DH-CME events have longer rise times and decay times than flares of decelerating DH-CME. The accelerating and decelerating DH-CMEs events associated with DH-type-II bursts have similar ending frequencies. The analysis of time lags between DH-type-II start and the flare onset shows that the delays are longer in accelerating DH-CMEs than decelerating DH-CMEs (P??7 %). However, the time lags between the DH-type-II start and the CMEs onset are similar.     

Relationship of great soft X-ray flares with other solar activity phenomena

We present study of relationship of GSXR flares with Hα flares, hard X-ray (HXR) bursts, microwave (MW) bursts at 15.4 GHz, type II/IV radio bursts, coronal mass ejections (CMEs), protons flares (>10 MeV) and ground level enhancement (GLE) events we find that about 85.7%, 93%, 97%, 69%, 60%, 11.1%, 79%, 46%, and 23%% GSXR flares are related/associated with observed Hα flares, HXR bursts, MW bursts at 15.4 GHz, type II radio bursts, type IV radio bursts, GLE events, CMEs, halo CMEs, and proton flares (>10 MeV), respectively. In the paper we have studied the onset time delay of GSXR flares with Hα flares, HXR, and MW bursts which shows the during majority GSXR flares SXR emissions start before the Hα, HXR and MW emissions, respectively while during 15–20% of GSXR flares the SXR emissions start after the onset of Hα, HXT and MW emissions, respectively indicating two types of solar flares. The, onset time interval between SXR emissions and type II radio bursts, type IV radio bursts, GLE events CMEs, halo CMEs, and protons flares are 1–15 min, 1–20 min, 21–30 min, 21–40 min, 21–40 min, and 1–4 hrs, respectively. Following the majority results we are of the view that the present investigations support solar flares models which suggest flare triggering first in the corona and then move to chromospheres/ photosphere to starts emissions in other wavelengths. The result of the present work is largely consistent with “big flare syndrome” proposed by Kahler (1982).     

Multiple Type II Solar Radio Bursts

We report on the detailed analysis of a set of 38 multiple type II radio bursts observed by Culgoora radio spectrograph from January 1997 to July 2003. These events were selected on the basis of the following criteria: (i) more than one type II were reported within 30 min interval, (ii) both fundamental and harmonic were identified for each of them. The X-ray flares and CMEs associated with these events are identified using GOES, Yohkoh SXT, SOHO/EIT, and SOHO/LASCO data. From the analysis of these events, the following physical characteristics are obtained: (i) In many cases, two type IIs with fundamental and harmonic were reported, and the time interval between the two type IIs is within 15 min; (ii) The mean values of starting frequency, drift rate, and shock speed of the first type II are significantly higher than those of the second type II; (iii) More than 90% of the events are associated with both X-ray flares and CMEs; (iv) Nearly 75% of the flares are stronger than M1 X-ray class and 50% of CMEs have their widths larger than 200^∘ or they are halo CMEs; (v) While most of the first type IIs started within the flare impulsive phase, 22 out of 38 second type IIs started after the flare impulsive phase. Weak correlations are found between the starting and ending frequencies of these type II events. On the other hand, there was no correlation between two shock speeds between the first and the second type II. Since most of the events are associated with both the flares and CMEs, and there are no events which are only associated with multiple impulsive flares or multiple mass ejections, we suggest that the flares and CMEs (front or flank) both be sources of multiple type IIs. Other possibilities on the origin of multiple type IIs are also discussed.     

Statistical Characteristics on SEPs,Radio-Loud CMEs,Low Frequency Type II and Type III Radio Bursts Associated with Impulsive and Gradual Flares

We have statistically analyzed a set of 115 low frequency (Deca-Hectometer wavelengths range) type II and type III bursts associated with major Solar Energetic Particle (SEP: E_p?>?10 MeV) events and their solar causes such as solar flares and coronal mass ejections (CMEs) observed from 1997 to 2014. We classified them into two sets of events based on the duration of the associated solar flares:75 impulsive flares (duration <?60 min) and 40 gradual flares (duration >?60 min).On an average, the peak flux (integrated flux) of impulsive flares?×?2.9 (0.32 J m^?2) is stronger than that of gradual flares M6.8 (0.24 J m^?2). We found that impulsive flare-associated CMEs are highly decelerated with larger initial acceleration and they achieved their peak speed at lower heights (??27.66 m s^?2 and 14.23 R_o) than the gradual flare-associated CMEs (6.26 m s^?2 and 15.30 R_o), even though both sets of events have similar sky-plane speed (space speed) within LASCO field of view. The impulsive flare-associated SEP events (R_t?=?989.23 min: 2.86 days) are short lived and they quickly reach their peak intensity (shorter rise time) when compared with gradual flares associated events (R_t?=?1275.45 min: 3.34 days). We found a good correlation between the logarithmic peak intensity of all SEPs and properties of CMEs (space speed: cc?=?0.52, SE_cc?=?0.083), and solar flares (log integrated flux: cc?=?0.44, SE_cc?=?0.083). This particular result gives no clear cut distinction between flare-related and CME-related SEP events for this set of major SEP events. We derived the peak intensity, integrated intensity, duration and slope of these bursts from the radio dynamic spectra observed by Wind/WAVES. Most of the properties (peak intensity, integrated intensity and starting frequency) of DH type II bursts associated with impulsive and gradual flare events are found to be similar in magnitudes. Interestingly, we found that impulsive flare-associated DH type III bursts are longer, stronger and faster (31.30 min, 6.43 sfu and 22.49 MHz h^?1) than the gradual flare- associated DH type III bursts (25.08 min, 5.85 sfu and 17.84 MHz h^?1). In addition, we also found a significant correlation between the properties of SEPs and key parameters of DH type III bursts. This result shows a closer association of peak intensity of the SEPs with the properties of DH type III radio bursts than with the properties DH type II radio bursts, atleast for this set of 115 major SEP events.

     

Characteristics of CMEs associated with solar flares and DH type II radio bursts based on source position

We studied the characteristics of Coronal Mass Ejections (CMEs) associated with solar flares and Deca-Hectometric (DH) type II radio bursts, based on source position during 23rd solar cycle (1997–2007). We classified these CME events into three groups using solar flare locations as, (i) disk events (0–30^∘); (ii) intermediate events (31–60^∘) and (iii) limb events (61–90^∘). Main results from this studies are, (i) the number of CMEs associated with solar flares and DH-type IIs decreases as the source position approaches from disk to limb, (ii) most of the DH CMEs are halo (72%) in disk events and the number of occurrence of halo CMEs decreases from disk to limb, (iii) the average width and speed of limb events (164^∘ and 1447 km s⁻¹) are higher than those of disk events (134^∘ and 1035 km s⁻¹) and intermediate events (146^∘ and 1170 km s⁻¹) and (iv) the average accelerations for disk, intermediate and limb events are −8.2 m s⁻², −10.3 m s⁻² and −4.5 m s⁻² respectively. These analysis of CMEs properties show more dependency on longitude and it gives strong evidence for projection effect.     

Solar Type II Radio Bursts Recorded by the Compound Astronomical Low-Frequency Low-Cost Instrument for Spectroscopy in Transportable Observatories in Brazil

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.     

Are There Radio-quiet Solar Flares?

Some 15% of solar flares having a soft X-ray flux above GOES class C5 are reported to lack coherent radio emission in the 100 – 4000 MHz range (type I – V and decimetric emissions). A detailed study of 29 such events reveals that 22 (76%) of them occurred at a radial distance of more than 800″ from the disk center, indicating that radio waves from the limb may be completely absorbed in some flares. The remaining seven events have statistically significant trends to be weak in GOES class and to have a softer non-thermal X-ray spectrum. All of the non-limb flares that were radio-quiet above 100 MHz were accompanied by metric type III emission below 100 MHz. Out of 201 hard X-ray flares, there was no flare except near the limb (R>800″) without coherent radio emission in the entire meter and decimeter range. We suggest that flares above GOES class C5 generally emit coherent radio waves when observed radially above the source.     

Coronal Shocks Associated with Impulsive and Decaying Phases of Solar Flares

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.     

Observations of Powerful Type III Bursts in the Frequency Range 10 – 30 MHz

The properties of powerful (flux >10⁻¹⁹ W m⁻² Hz⁻¹) type III bursts observed in July – August 2002 by the radio telescope UTR-2 at frequencies 10 – 30 MHz are analyzed. Most bursts have been registered when the active regions associated to these bursts were located near the central meridian or at 40° – 60° to the East or West from it. All powerful type III bursts drift from high to low frequencies with frequency drift rates 1 – 2.5 MHz s⁻¹. It is important to emphasize that according to our observations the drift rate is linearly increasing with frequency. The duration of the bursts changes mainly from 6 s at frequency 30 MHz up to 12 s at 10 MHz. The instantaneous frequency bandwidth does not depend on the day of observations, i.e. on the disk location of the source active region, and is increasing with frequency.     

Radio Observations of the 20 January 2005 X-class Flare

We present a multi-frequency and multi-instrument study of the 20 January 2005 event. We focus mainly on the complex radio signatures and their association with the active phenomena taking place: flares, CMEs, particle acceleration, and magnetic restructuring. As a variety of energetic-particle accelerators and sources of radio bursts are present, in the flare – ejecta combination, we investigate their relative importance in the progress of this event. The dynamic spectra of ARTEMIS-IV – Wind/Waves – HiRAS, with 2000 MHz – 20 kHz frequency coverage, were used to track the evolution of the event from the low corona to the interplanetary space; these were supplemented with SXR, HXR, and γ-ray recordings. The observations were compared with the expected radio signatures and energetic-particle populations envisaged by the Standard Flare – CME model and the reconnection outflow termination shock model. A proper combination of these mechanisms seems to provide an adequate model for the interpretation of the observational data.     

An Investigation of Solar Maximum Metric Type ii Radio Bursts: do two Kinds of Coronal Shock Sources Exist?

A detailed statistical investigation of solar Type II radio bursts during the last solar maximum period 1999–2001 has been made to address the question if there exist two kinds of coronal shock sources. For this, the Type II bursts were classified into two classes: (i) those associated with flares only (Class I); and (ii) those associated with flares and CMEs (Class II) according to their temporal association. While the properties of all the type IIs agree in general with the common range of values, the properties of the shocks of the two classes differ slightly. For example, while the duration and shock speed for Class II are higher than those of Class I, the ending frequency for Class II is significantly lower. We have also examined in detail the physical association with other solar and interplanetary activities (Type IV bursts, Long Duration Events, Wind/WAVES deca-hectometric Type IIs, and interplanetary shocks) using the data in 2000. As a result, we have found noticeable differences between these two classes in terms of the following physical characteristics: First, the associations of these activities for Class II are much higher than those of Class I. Second, the correlation values between the flare parameters and the Type II properties for Class II are significantly smaller. Third, observed double Type IIs exist in only Class II events. The above results suggest that there are two kinds of coronal shocks or, rather, two general classes of coronal shock sources.     

Interplanetary type II radio bursts and their association with CMEs and flares

We study the characteristics of the CMEs and their association with the end-frequency of interplanetary (IP)-type-II bursts by analyzing a set of 138 events (IP-type-II bursts–flares–CMEs) observed during the period 1997–2012. The present analysis consider only the type II bursts having starting frequency \(< 14~\mbox{MHz}\) to avoid the extension of coronal type IIs. The selected events are classified into three groups depending on the end-frequency of type IIs as follows, (A) Higher, (B) Intermediate and (C) Lower end-frequency. We compare characteristics of CMEs, flares and type II burst for the three selected groups of events and report some of the important differences. The observed height of CMEs is compared with the height of IP type IIs estimated using the electron density models. By applying a density multiplier (\(m\)) to this model, the density has been constrained both in the upper corona and in the interplanetary medium, respectively as \(m= 1 \mbox{ to } 10\) and \(m = 1 \mbox{ to } 3\). This study indicates that there is a correlation between the observed CME height and estimated type II height for groups B and C events whereas this correlation is absent in group A. In all the groups (A, B & C), the different heights of CMEs and type II reveal that the type IIs are not only observed at the nose but also at the flank of the CMEs.     

Characteristics of flares producing metric type II bursts and coronal mass ejections

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.     

Statistical Analysis of Decimetric Radio Bursts,Flares, and Coronal Mass Ejections

A statistical analysis of decimetric radio bursts (RBs), X-ray flares and coronal mass ejections (CMEs) is carried out. We consider all radio bursts recorded by the Cracow Solar Radio Telescope from the beginning of 1996 until the end of 2004. It is found that the decimetric radio bursts are associated and strongly correlated with X-ray flares. Correlation coefficients between RBs durations and the maximal fluxes of the radio bursts and flares are found to be 0.60 and 0.87, respectively. We also demonstrated that a significant population of the decimetric radio bursts are associated with CMEs. The correlation coefficient between the maximal radio flux density multiplied by the duration of the RBs versus velocity multiplied by width of CMEs is found to be 0.55.