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1.
We have studied the characteristics of coronal mass ejections (CMEs) associated with Deca-Hectometric (DH) type II radio bursts (1–14 MHz) in the interplanetary medium during the year 1997–2005. The DH CMEs are divided into two parts: (i) DH CMEs (All) and (ii) DH CMEs (Limb). We found that 65% (177/273) of all events have the speed >900 km?s?1 and the remaining 35% (96/273) events have the speed below 900 km?s?1. The average speed of all and limb DH CMEs are 1230 and 1288 km?s?1, respectively, which is nearly three times the average speed of general population of CMEs (473 km?s?1). The average widths of all and limb DH CMEs are 105° and 106°, respectively, which is twice the average width (52°) of the general population of CMEs. We found a better correlation between the speed and width of limb DH CMEs (R=?0.61) than all DH CMEs (R=?0.53). Only 28% (177/637) of fast >900 km?s?1 general population of CMEs are reported with DH type II bursts counterpart. The above results gives that the relation between the CME properties is better for limb events.  相似文献   

2.
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.  相似文献   

3.
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.  相似文献   

4.
We have investigated the characteristics of magnetic cloud (MC) and ejecta (EJ) associated coronal mass ejections (CMEs) based on the assumption that all CMEs have a flux rope structure. For this, we used 54 CMEs and their interplanetary counterparts (interplanetary CMEs: ICMEs) that constitute the list of events used by the NASA/LWS Coordinated Data Analysis Workshop (CDAW) on CME flux ropes. We considered the location, angular width, and speed as well as the direction parameter, D. The direction parameter quantifies the degree of asymmetry of the CME shape in coronagraph images, and shows how closely the CME propagation is directed to Earth. For the 54 CDAW events, we found the following properties of the CMEs: i) the average value of D for the 23 MCs (0.62) is larger than that for the 31 EJs (0.49), which indicates that the MC-associated CMEs propagate more directly toward the Earth than the EJ-associated CMEs; ii) comparison between the direction parameter and the source location shows that the majority of the MC-associated CMEs are ejected along the radial direction, while many of the EJ-associated CMEs are ejected non-radially; iii) the mean speed of MC-associated CMEs (946 km?s?1) is faster than that of EJ-associated CMEs (771 km?s?1). For seven very fast CMEs (≥?1500 km?s?1), all CMEs with large D (≥?0.4) are associated with MCs and the CMEs with small D are associated with EJs. From the statistical analysis of CME parameters, we found the superiority of the direction parameter. Based on these results, we suggest that the CME trajectory essentially determines the observed ICME structure.  相似文献   

5.
The subject of interaction between the Corona Mass Ejections (CMEs) is important in the concept of space-weather studies. In this paper, we analyzed a set of 15 interacting events taken from the list compiled by Manoharan et al. (in J. Geophys. Res. 109:A06109, 2004) and their associated DH type II radio bursts. The pre and primary CMEs, and their associated DH type II bursts are identified using the SOHO/LASCO catalog and Wind/WAVES catalog, respectively. All the primary CMEs are associated with shocks and interplanetary CMEs. These CMEs are found to be preceded by secondary slow CMEs. Most of primary CMEs are halo type CME and much faster (Mean speed = 1205 km?s?1) than the pre CME (Mean speed = 450 km?s?1). The average delay between the pre and primary CMEs, drift rate of DH type IIs and interaction height are found to be 211 min, 0.878 kHz/s and 17.87 Ro, respectively. The final observed distance (FOD) of all pre CMEs are found to be less than 15 Ro and it is seen that many of the pre CMEs got merged with the primary CMEs, and, they were not traced as separate CMEs in the LASCO field of view. Some radio signatures are identified for these events in the DH spectrum around the time of interaction. The interaction height obtained from the height-time plots of pre and primary CMEs is found to have correlations with (i) the time delay between the two CMEs and (ii) the central frequency of emission in the radio signatures in the DH spectrum around the time of interaction. The centre frequency of emission in the DH spectrum around the time of interaction seems to decrease when the interaction height increases. This result is compared with an interplanetary density model of Saito et al. (in Solar Phys. 55:121, 1977).  相似文献   

6.
We study the abundances of the elements He through Pb in Fe-rich impulsive solar energetic-particle (SEP) events with measurable abundances of ions with atomic number Z>2 observed on the Wind spacecraft, and their relationship with coronal mass ejections (CMEs) observed by the Large Angle and Spectrometric Coronagraph (LASCO) onboard the Solar and Heliospheric Observatory (SOHO). On an average the element abundances in these events are similar to coronal abundances at low Z but, for heavier elements, enhancements rise as a power law in the mass-to-charge ratio A/Q of the ions (at coronal temperatures of 2.5?–?3 MK) to a factor of 3 at Ne, 9 at Fe, and 900 for 76≤Z≤82. Energy dependences of abundances are minimal in the 2?–?15 MeV amu?1 range. The 111 of these Fe-rich impulsive SEP events we found, between November 1994 and August 2013 using the Wind spacecraft, have a 69 % association rate with CMEs. The CMEs are narrow with a median width of 75°, are characteristically from western longitudes on the Sun, and have a median speed of ≈?600 km?s?1. Nearly all SEP onsets occur within 1.5?–?5 h of the CME onset. The faster (>?700 km?s?1), wider CMEs in our sample are related to SEPs with coronal abundances indicating hot coronal plasma with fully ionized He, C, N and O and moderate enhancements of heavier elements, relative to He, but slower (<?700 km?s?1), narrower CMEs emerge from cooler plasma where higher SEP mass-to-charge ratios, A/Q, yield much greater abundance enhancements, even for C/He and O/He. Apparently, the open magnetic-reconnection region where the impulsive SEPs are accelerated also provides the energy to drive out CME plasma, accounting for a strong, probably universal, impulsive SEP-CME association.  相似文献   

7.
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.  相似文献   

8.
We statistically analyzed the kinematical evolution and wave pulse characteristics of 60 strong large-scale EUV wave events that occurred during January 2007 to February 2011 with the STEREO twin spacecraft. For the start velocity, the arithmetic mean is 312±115 km?s?1 (within a range of 100?–?630 km?s?1). For the mean (linear) velocity, the arithmetic mean is 254±76 km?s?1 (within a range of 130?–?470 km?s?1). 52 % of all waves under study show a distinct deceleration during their propagation (a≤?50 m?s?2), the other 48 % are consistent with a constant speed within the uncertainties (?50≤a≤50 m?s?2). The start velocity and the acceleration are strongly anticorrelated with c≈?0.8, i.e. initially faster events undergo stronger deceleration than slower events. The (smooth) transition between constant propagation for slow events and deceleration in faster events occurs at an EUV wave start-velocity of v≈230 km?s?1, which corresponds well to the fast-mode speed in the quiet corona. These findings provide strong evidence that the EUV waves under study are indeed large-amplitude fast-mode MHD waves. This interpretation is also supported by the correlations obtained between the peak velocity and the peak amplitude, impulsiveness, and build-up time of the disturbance. We obtained the following association rates of EUV wave events with other solar phenomena: 95 % are associated with a coronal mass ejection (CME), 74 % to a solar flare, 15 % to interplanetary type II bursts, and 22 % to coronal type II bursts. These findings are consistent with the interpretation that the associated CMEs are the driving agents of the EUV waves.  相似文献   

9.
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.  相似文献   

10.
We have estimated the speed and direction of propagation of a number of Coronal Mass Ejections (CMEs) using single-spacecraft data from the STEREO Heliospheric Imager (HI) wide-field cameras. In general, these values are in good agreement with those predicted by Thernisien, Vourlidas, and Howard in Solar Phys. 256, 111?–?130 (2009) using a forward modelling method to fit CMEs imaged by the STEREO COR2 coronagraphs. The directions of the CMEs predicted by both techniques are in good agreement despite the fact that many of the CMEs under study travel in directions that cause them to fade rapidly in the HI images. The velocities estimated from both techniques are in general agreement although there are some interesting differences that may provide evidence for the influence of the ambient solar wind on the speed of CMEs. The majority of CMEs with a velocity estimated to be below 400 km?s?1 in the COR2 field of view have higher estimated velocities in the HI field of view, while, conversely, those with COR2 velocities estimated to be above 400 km?s?1 have lower estimated HI velocities. We interpret this as evidence for the deceleration of fast CMEs and the acceleration of slower CMEs by interaction with the ambient solar wind beyond the COR2 field of view. We also show that the uncertainties in our derived parameters are influenced by the range of elongations over which each CME can be tracked. In order to reduce the uncertainty in the predicted arrival time of a CME at 1 Astronomical Unit (AU) to within six hours, the CME needs to be tracked out to at least 30 degrees elongation. This is in good agreement with predictions of the accuracy of our technique based on Monte Carlo simulations. Within the set of studied CMEs, there are two clear events that were predicted from the HI data to travel over another spacecraft; in-situ measurements at these other spacecraft confirm the accuracy of these predictions. The ability of the HI cameras to image Corotating Interaction Region (CIR)-entrained transients as well as CMEs can result in some ambiguity when trying to distinguishing individual signatures.  相似文献   

11.
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   

12.
The inner coronagraph (COR1) of the Solar Terrestrial Relations Observatory (STEREO) mission has made it possible to observe CMEs in the spatial domain overlapping with that of the metric type II radio bursts. The type II bursts were associated with generally weak flares (mostly B and C class soft X-ray flares), but the CMEs were quite energetic. Using CME data for a set of type II bursts during the declining phase of solar cycle 23, we determine the CME height when the type II bursts start, thus giving an estimate of the heliocentric distance at which CME-driven shocks form. This distance has been determined to be ～1.5R s (solar radii), which coincides with the distance at which the Alfvén speed profile has a minimum value. We also use type II radio observations from STEREO/WAVES and Wind/WAVES observations to show that CMEs with moderate speed drive either weak shocks or no shock at all when they attain a height where the Alfvén speed peaks (～3R s?–?4R s). Thus the shocks seem to be most efficient in accelerating electrons in the heliocentric distance range of 1.5R s to 4R s. By combining the radial variation of the CME speed in the inner corona (CME speed increase) and interplanetary medium (speed decrease) we were able to correctly account for the deviations from the universal drift-rate spectrum of type II bursts, thus confirming the close physical connection between type II bursts and CMEs. The average height (～1.5R s) of STEREO CMEs at the time of type II bursts is smaller than that (2.2R s) obtained for SOHO (Solar and Heliospheric Observatory) CMEs. We suggest that this may indicate, at least partly, the density reduction in the corona between the maximum and declining phases, so a given plasma level occurs closer to the Sun in the latter phase. In two cases, there was a diffuse shock-like feature ahead of the main body of the CME, indicating a standoff distance of 1R s?–?2R s by the time the CME left the LASCO field of view.  相似文献   

13.
The speed [v(R)] of coronal mass ejections (CMEs) at various distances from the Sun is modeled (as proposed by Vr?nak and Gopalswamy in J. Geophys. Res. 107, 2002, doi: 10.1029/2001/JA000120 ) by using the equation of motion a drag=γ(v?w) and its quadratic form a drag=γ(v?w)|v?w|, where v and w are the speeds of the CME and solar wind, respectively. We assume that the parameter γ can be expressed as γ=αR β , where R is the heliocentric distance, and α and β are constants. We extend the analysis of Vr?nak and Gopalswamy to obtain a more detailed insight into the dependence of the CME Sun–Earth transit time on the CME speed and the ambient solar-wind speed, for different combinations of α and β. In such a parameter-space analysis, the results obtained confirm that the CME transit time depends strongly on the state of the ambient solar wind. Specifically, we found that: i) for a particular set of values of α and β, a difference in the solar-wind speed causes larger transit-time differences at low CME speeds [v 0], than at high v 0; ii) the difference between transit times of slow and fast CMEs is larger at low solar-wind speed [w 0] than at high w 0; iii) transit times of fast CMEs are only slightly influenced by the solar-wind speed. The last item is especially important for space-weather forecasting, since it reduces the number of key parameters that determine the arrival time of fast CMEs, which tend to be more geo-effective than the slow ones. Finally, we compared the drag-based model results with the observational data for two CME samples, consisting of non-interacting and interacting CMEs (Manoharan et al. in J. Geophys. Res. 109, 2004). The comparison reveals that the model results are in better agreement with the observations for non-interacting events than for the interacting events. It was also found that for slow CMEs (v 0<500 km?s?1), there is a deviation between the observations and the model if slow-wind speeds (≈?300?–?400 km?s?1) are taken for the model input. On the other hand, the model values and the observed data agree for both the slow and the fast CMEs if higher solar-wind speeds are assumed. It is also found that the quadratic form of the drag equation reproduces the observed transit times of fast CMEs better than the linear drag model.  相似文献   

14.
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.  相似文献   

15.
We study the solar sources of an intense geomagnetic storm of solar cycle 23 that occurred on 20 November 2003, based on ground- and space-based multiwavelength observations. The coronal mass ejections (CMEs) responsible for the above geomagnetic storm originated from the super-active region NOAA 10501. We investigate the H?? observations of the flare events made with a 15 cm solar tower telescope at ARIES, Nainital, India. The propagation characteristics of the CMEs have been derived from the three-dimensional images of the solar wind (i.e., density and speed) obtained from the interplanetary scintillation data, supplemented with other ground- and space-based measurements. The TRACE, SXI and H?? observations revealed two successive ejections (of speeds ???350 and ???100 km?s?1), originating from the same filament channel, which were associated with two high speed CMEs (???1223 and ???1660 km?s?1, respectively). These two ejections generated propagating fast shock waves (i.e., fast-drifting type II radio bursts) in the corona. The interaction of these CMEs along the Sun?CEarth line has led to the severity of the storm. According to our investigation, the interplanetary medium consisted of two merging magnetic clouds (MCs) that preserved their identity during their propagation. These magnetic clouds made the interplanetary magnetic field (IMF) southward for a long time, which reconnected with the geomagnetic field, resulting the super-storm (Dst peak=?472 nT) on the Earth.  相似文献   

16.
We report on the coronal hole (CH) influence on the 54 magnetic cloud (MC) and non-MC associated coronal mass ejections (CMEs) selected for studies during the Coordinated Data Analysis Workshops (CDAWs) focusing on the question if all CMEs are flux ropes. All selected CMEs originated from source regions located between longitudes 15E?–?15W. Xie, Gopalswamy, and St. Cyr (2013, Solar Phys., doi: 10.1007/s11207-012-0209-0 ) found that these MC and non-MC associated CMEs are on average deflected towards and away from the Sun–Earth line, respectively. We used a CH influence parameter (CHIP) that depends on the CH area, average magnetic field strength, and distance from the CME source region to describe the influence of all on-disk CHs on the erupting CME. We found that for CHIP values larger than 2.6 G the MC and non-MC events separate into two distinct groups where MCs (non-MCs) are deflected towards (away) from the disk center. Division into two groups was also observed when the distance to the nearest CH was less than 3.2×105 km. At CHIP values less than 2.6 G or at distances of the nearest CH larger than 3.2×105 km the deflection distributions of the MC and non-MCs started to overlap, indicating diminishing CH influence. These results give support to the idea that all CMEs are flux ropes, but those observed to be non-MCs at 1 AU could be deflected away from the Sun–Earth line by nearby CHs, making their flux rope structure unobservable at 1 AU.  相似文献   

17.
In this study, we investigate the interplanetary consequences and travel time details of 58 coronal mass ejections (CMEs) in the Sun–Earth distance. The CMEs considered are halo and partial halo events of width \({>}\,120\)°. These CMEs occurred during 2009?–?2013, in the ascending phase of the Solar Cycle 24. Moreover, they are Earth-directed events that originated close to the centre of the solar disk (within about \(\pm30\)° from the Sun’s centre) and propagated approximately along the Sun–Earth line. For each CME, the onset time and the initial speed have been estimated from the white-light images observed by the LASCO coronagraphs onboard the SOHO space mission. These CMEs cover an initial speed range of \({\sim}\,260\,\mbox{--}\,2700~\mbox{km}\,\mbox{s}^{-1}\). For these CMEs, the associated interplanetary shocks (IP shocks) and interplanetary CMEs (ICMEs) at the near-Earth environment have been identified from in-situ solar wind measurements available at the OMNI data base. Most of these events have been associated with moderate to intense IP shocks. However, these events have caused only weak to moderate geomagnetic storms in the Earth’s magnetosphere. The relationship of the travel time with the initial speed of the CME has been compared with the observations made in the previous Cycle 23, during 1996?–?2004. In the present study, for a given initial speed of the CME, the travel time and the speed at 1 AU suggest that the CME was most likely not much affected by the drag caused by the slow-speed dominated heliosphere. Additionally, the weak geomagnetic storms and moderate IP shocks associated with the current set of Earth-directed CMEs indicate magnetically weak CME events of Cycle 24. The magnetic energy that is available to propagate CME and cause geomagnetic storm could be significantly low.  相似文献   

18.
It is well known that there is a temporal relationship between coronal mass ejections (CMEs) and associated flares. The duration of the acceleration phase is related to the duration of the rise phase of a flare. We investigate CMEs associated with slow long duration events (LDEs), i.e. flares with the long rising phase. We determined the relationships between flares and CMEs and analyzed the CME kinematics in detail. The parameters of the flares (GOES flux, duration of the rising phase) show strong correlations with the CME parameters (velocity, acceleration during main acceleration phase, and duration of the CME acceleration phase). These correlations confirm the strong relation between slow LDEs and CMEs. We also analyzed the relation between the parameters of the CMEs, i.e. a velocity, an acceleration during the main acceleration phase, a duration of the acceleration phase, and a height of a CME at the end of the acceleration phase. The CMEs associated with the slow LDEs are characterized by high velocity during the propagation phase, with the median equal to 1423 km?s?1. In half of the analyzed cases, the main acceleration was low (a<300 m?s?2), which suggests that the high velocity is caused by the prolonged acceleration phase (the median for the duration of the acceleration phase is equal 90 minutes). The CMEs were accelerated up to several solar radii (with the median ≈?7 R ⊙), which is much higher than in typical impulsive CMEs. Therefore, slow LDEs may potentially precede extremely strong geomagnetic storms. The analysis of slow LDEs and associated CMEs may give important information for developing more accurate space-weather forecasts, especially for extreme events.  相似文献   

19.
We identify 565 coronal mass ejections (CMEs) between January 2007 and December 2010 in observations from the twin STEREO/SECCHI/COR2 coronagraphs aboard the STEREO mission. Our list is in full agreement with the corresponding SOHO/LASCO CME Catalog ( http://cdaw.gsfc.nasa.gov/CME_list/ ) for events with angular widths of 45° and up. The monthly event rates behave similarly to sunspot rates showing a three- to fourfold rise between September 2009 and March 2010. We select 51 events with well-defined white-light structure and model them as three-dimensional (3D) flux ropes using a forward-modeling technique developed by Thernisien, Howard and Vourlidas (Astrophys. J. 652, 763??C?773, 2006). We derive their 3D properties and identify their source regions. We find that the majority of the CME flux ropes (82?%) lie within 30° of the solar equator. Also, 82?% of the events are displaced from their source region, to a lower latitude, by 25° or less. These findings provide strong support for the deflection of CMEs towards the solar equator reported in earlier observations, e.g. by Cremades and Bothmer (Astron. Astrophys. 422, 307??C?322, 2004).  相似文献   

20.
We have conducted a statistical study 27 coronal mass ejections (CMEs) from January 2007 – June 2008, using the stereoscopic views of STEREO SECCHI A and B combined with SOHO LASCO observations. A flux-rope model, in conjunction with 3D triangulations, has been used to reconstruct the 3D structures and determine the actual speeds of CMEs. The origin and the dynamic evolution of the CMEs are investigated using COR1, COR2 and EUVI images. We have identified four types of solar surface activities associated with CMEs: i) total eruptive prominence (totEP), ii) partially eruptive prominence (PEP), iii) X-ray flare, and iv) X-type magnetic structure (X-line). Among the 27 CMEs, 18.5% (5 of 27) are associated with totEPs, 29.6% (8 of 27) are associated with PEPs, 26% (7 of 27) are flare related, and 26% (7 of 27) are associated with X-line structures, and 43% (3 of 7) are associated with both X-line structures and PEPs. Three (11%) could not be associated with any detectable activity. The mean actual speeds for totEP-CMEs, PEP-CMEs, flare-CMEs, and X-line-CMEs are 404 km?s?1,247 km?s?1,909 km?s?1, and 276 km?s?1, respectively; the average mean values of edge-on and broadside widths for the 27 CMEs are 52 and 85 degrees, respectively. We found that slow CMEs (V≤400 km?s?1) tend to deflect towards and propagate along the streamer belts due to the deflections by the strong polar magnetic fields of corona holes, while some faster CMEs show opposite deflections away from the streamer belts.  相似文献   

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