Study of large solar energetic particle events with halo coronal mass ejections and their associated solar flares

The purpose of the present study is to investigate the association of solar energetic particle (SEP) events with halo coronal mass ejections (CME) and with their associated solar flares during the period 1997–2014 (solar cycle 23 and 24). We have found that halo CMEs are more effective in producing SEP events. The occurrence probability and peak fluxes of SEPs strongly depend on the halo CMEs speed (V) as follows. The highest associations, 56% for occurrence probability and 90% for average peak fluxes, are found for the halo CMEs with V> 1400 km s⁻¹ but the lowest associations, 20% for occurrence probability and 5% for average peak fluxes, are found for halo CMEs with speed range 600 ≤ V ≤ 1000 km s⁻¹. We have also examined the relationship between SEP events and halo CME associated solar flares and found that 73% of events are associated with western solar flares while only 27% are with eastern solar flares. For longitudinal study, 0–20° belt is found to be more dominant for the SEP events. The association of SEP events with latitudinal solar flares is also examined in the study. 51% of events are associated with those halo CMEs associated solar flares which occur in the southern hemisphere of the Sun while 49% are with those solar flares that occur in the northern hemisphere of the Sun. Also, 10–20° latitudinal belt is found to be likely associated with the SEP events. Further, 45% of SEP events are associated with M-class solar flares while 44% and 11% are with X and C-class respectively. Maximum number of SEP events are found for the fast halo CME associated X- class solar flares (68%) than M and C- class solar flares.     

Propagation Characteristics of CMEs Associated with Magnetic Clouds and Ejecta

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.     

A Major Geoeffective CME from NOAA 12371: Initiation,CME–CME Interactions,and Interplanetary Consequences

In this article, we present a multi-wavelength and multi-instrument investigation of a halo coronal mass ejection (CME) from active region NOAA 12371 on 21 June 2015 that led to a major geomagnetic storm of minimum \(\mathrm{Dst} = -204\) nT. The observations from the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory in the hot EUV channel of 94 Å confirm the CME to be associated with a coronal sigmoid that displayed an intense emission (\(T \sim6\) MK) from its core before the onset of the eruption. Multi-wavelength observations of the source active region suggest tether-cutting reconnection to be the primary triggering mechanism of the flux rope eruption. Interestingly, the flux rope eruption exhibited a two-phase evolution during which the “standard” large-scale flare reconnection process originated two composite M-class flares. The eruption of the flux rope is followed by the coronagraphic observation of a fast, halo CME with linear projected speed of 1366 km?s^?1. The dynamic radio spectrum in the decameter-hectometer frequency range reveals multiple continuum-like enhancements in type II radio emission which imply the interaction of the CME with other preceding slow speed CMEs in the corona within \(\approx10\)?–?\(90~\mbox{R} _{\odot}\). The scenario of CME–CME interaction in the corona and interplanetary medium is further confirmed by the height–time plots of the CMEs occurring during 19?–?21 June. In situ measurements of solar wind magnetic field and plasma parameters at 1 AU exhibit two distinct magnetic clouds, separated by a magnetic hole. Synthesis of near-Sun observations, interplanetary radio emissions, and in situ measurements at 1 AU reveal complex processes of CME–CME interactions right from the source active region to the corona and interplanetary medium that have played a crucial role towards the large enhancement of the geoeffectiveness of the halo CME on 21 June 2015.     

On the statistical characteristics of radio-loud and radio-quiet halo coronal mass ejections and their associated flares during solar cycles 23 and 24

We have studied the characteristics of radio-loud (RL) and radio-quiet (RQ) front side halo coronal mass ejections (HCMEs) (angular width 360^°) observed between the time period years 1996–2014. RL-HCMEs are associated with type II radio bursts, while RQ-HCMEs are not associated with type II radio bursts. CMEs near the Sun in the interplanetary medium associated with radio bursts also affect the magnetosphere. The type II radio burst data was observed by WIND/WAVES instrument and HCMEs were observed by LASCO/ SOHO instruments. In our study, we have examined the properties of RL-HCMEs and RQ-HCMEs and found that RL-HCMEs follow the solar cycle variation. Our study also shows that the 26% of slow speed HCMEs and 82% of fast speed HCMEs are RL. The average speed of RL-HCMEs and RQ-HCMEs are 1370 km/s and 727 km/s, respectively. Most of the RQ-HCMEs occur around the solar disc center while most of RL-HCMEs are uniformly distributed across the solar disc. The mean value of acceleration of RL-HCMEs is more than twice that of RQ-HCMEs and mean value of deceleration of RL- HCMEs is very small compare to RQ-HCMEs events. It is also found that RQ-HCMEs events are associated with C- and M-class of SXR flares, while RL-HCMEs events are associated with M and X-class of SXR flares, which indicates that the RQ-HCMEs are less energetic than the RL-HCMEs. We have also discussed the various results obtained in present investigation in view of recent scenario of solar physics.     

The Gas to Dust Ratio in Three Star Forming Regionstwo

Gas to Dust Ratio (GDR) indicates the mass ratio of interstellar gas to dust. It is widely adopted that the GDR in our Galaxy is 100～150. We choose three typical star forming regions to study the GDR: the Orion molecular cloud — a massive star forming region, the Taurus molecular cloud — a low-mass star forming region, and the Polaris molecular cloud — a region with no or very few star formation activities. The mass of gas only takes account of the neutral gas, i.e. only the atomic and molecular hydrogen, because the amount of ionized gas is very small in a molecular cloud. The column density of atomic hydrogen is taken from the high-resolution and high-sensitivity all-sky survey EBHIS (Effelsberg-Bonn HI Survey). The CO J = 1 →0 line is used to trace the molecular hydrogen, since the spectral lines of molecular hydrogen which can be detected are rare. The intensity of CO J = 1 →0 line is taken from the Planck all-sky survey. The mass of dust is traced by the interstellar extinction based on the 2MASS (Two Micron All Sky Survey) photometric database in the direction of anti-Galactic center. Adopting a constant conversion coefficient from the integrated intensity of the CO line to the column density of molecular hydrogen, X_CO = 2.0 × 10²⁰ cm^?2 · (K · km/s)^?1, the gas to dust ratio N(H)/A_V is calculated, which is 25, 38, and 55 (in units of 10²⁰ cm^?2 · mag^?1) for the Orion, Taurus, and Polaris molecular clouds, respectively. These values are significantly higher than the previously obtained average value of the Galaxy. Adopting the WD01 interstellar dust model (when the V-band selective extinction ratio is R_V = 3.1), the derived GDRs are 160, 243, and 354 for the Orion, Taurus, and Polaris molecular clouds, respectively, which are apparently higher than 100～150, the commonly accepted GDR of the diffuse interstellar medium. The high N(H)/A_V values in the star forming regions may be explained by the growth of dust in the molecular clouds because of either the particle collision or accretion, which can lead to the reduction of extinction efficiency per unit mass in the V band, rather than the increase of the GDR itself.     

A Study of Surges: II. On the Relationship between Chromospheric Surges and Coronal Mass Ejections

Liu et al. (Astrophys. J. 628, 1056, 2005a) described one surge – coronal mass ejection (CME) event showing a close relationship between solar chromospheric surge ejection and CME that had not been noted before. In this work, large Hα surges (>72 Mm, or 100 arcsec) are studied. Eight of these were associated with CMEs. According to their distinct morphological features, Hα surges can be classified into three types: jetlike, diffuse, and closed loop. It was found that all of the jetlike surges were associated with jetlike CMEs (with angular widths ≤30 degrees); the diffuse surges were all associated with wide-angle CMEs (e.g., halo); the closed-loop surges were not associated with CMEs. The exclusive relation between Hα surges and CMEs indicates difference in magnetic field configurations. The jetlike surges and related narrow CMEs propagate along coronal fields that are originally open. The unusual transverse mass motions in the diffuse surges are suggested to be due to magnetic reconnections in the corona that produce wide-angle CMEs. For the closed-loop surges, their paths are just outlining stable closed loops close to the solar surface. Thus no CMEs are associated with them.     

Downflow-induced brightening following a filament eruption

The plasma from solar filament eruptions sometimes falls down to the lower solar atmosphere. These interesting events can help us to understand the properties of downflows, such as the temperature and the conversion between kinetic energy and thermal energy. We analyze the case of a filament eruption in active region NOAA 11283 and brightening caused by the return of filament material on September 7 and 8, 2011, observed by the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager (HMI) aboard the Solar Dynamics Observatory (SDO). Magnetic flux cancellation was observed as a result of the eruption after the eruptive filament started to ascend. Another filament near the eruptive filament was disturbed by an extreme ultraviolet (EUV) wave that was triggered by the eruptive filament, causing it to oscillate. Based on coronal seismology, the mean magnetic field strength in the oscillatory filament was estimated to be approximately 18 ± 2 G. Some plasma separated from the filament and fell down to the solar northwest surface after the filament eruption. The velocities of the downflows increased at accelerations lower than the gravitational acceleration. The main characteristic temperature of the downflows was about 5 × 10⁴ K. When the plasma blobs fell down to lower atmospheric heights, the high-speed downward-travelling plasma collided with plasma at lower atmospheric heights, causing the plasma to brighten. The brightening was observed in all 8 AIA channels, demonstrating that the temperature of the plasma in the brightening covered a wide range of values, from 10⁵ K to 10⁷ K. This brightening indicates the conversion between kinetic energy and thermal energy.     

伴随CME的微波爆发的特征

分析了与日冕物质抛射(CME)有关的太阳微波爆发(SMB)的特征,包括持 续时间、峰值流量、爆发类型、谱指数等．选取了从1999年11月至2003年9月的136 个事件,包括60个部分晕状CME(120°<宽度<360°)／晕状CME(宽度=360°)和 76个正常CME(20°<宽度<120°)／窄CME(0°<宽度<20°)． 研究发现: (1)与正常CME／窄CME有关的微波爆发持续时间较短,与部分晕状 ／晕状CME有关的微波爆发持续时间有长有短; (2)与慢CME有关的微波爆发持续时 间较短,与快CME有关的微波爆发持续时间可长可短;(3)与正常／窄CME有关的微 波爆发峰值辐射流量比较小,与部分晕状／晕状CME有关的微波爆发峰值辐射流量有大 有小;(4)与慢CME有关的微波爆发峰值辐射流量较小,与快CME有关的微波爆发峰 值辐射流量可长可短; (5)与正常／窄CME有关的微波爆发绝大多数为简单(simple) 型,与晕状CME有关的微波爆发绝大多数为复杂(C)／大爆发(GB)型; (6)与CME 有关的事件在频率,f相似文献   

Propagation of Coronal Mass Ejections Observed During the Rising Phase of Solar Cycle 24

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.     

投影改正后CME的速度分布

目前观测的CME(日冕物质抛射)是其在天空平面的投影,这就导致CME的观测参量与真实参量之间存在一定的差异,比如说观测到的CME速度一般要比CME的真实速度小.运用基于锥状模型对CME的速度进行投影改正的方法,分析1996年9月到2007年9月(将近1个活动周)SOHO/LASCO日冕仪观测到的1 691个仅与耀斑相关的CME(简称FL类CME)和610个仅与暗条爆发相关的CME(简称FE类CME)投影改正前后的速度分布,得到如下结果:(1)投影改正前后,FL类CME和FE类CME的速度分布非常相似.且投影改正前后,两类CME的平均速度几乎相同; (2)投影改正前后,FL类CME和FE类CME速度的自然对数分布也非常相似.     

Propagation of Fast Coronal Mass Ejections and Shock Waves Associated with Type II Radio-Burst Emission: An Analytic Study

Coronal mass ejections (CMEs) are large-scale eruptive events in the solar corona. Once they are expelled into the interplanetary (IP) medium, they propagate outwards and “evolve” interacting with the solar wind. Fast CMEs associated with IP shocks are a critical subject for space weather investigations. We present an analytic model to study the heliocentric evolution of fast CME/shock events and their association with type II radio-burst emissions. The propagation model assumes an early stage where the CME acts as a piston driving a shock wave; beyond this point the CME decelerates, tending to match the ambient solar wind speed and its shock decays. We use the shock speed evolution to reproduce type II radio-burst emissions. We analyse four fast CME halo events that were associated with kilometric type II radio bursts, and in-situ measurements of IP shock and CME signatures. The results show good agreement with the dynamic spectra of the type II frequency drifts and the in-situ measurements. This suggests that, in general, IP shocks associated with fast CMEs evolve as blast waves approaching 1 AU, implying that the CMEs do not drive their shocks any further at this heliocentric range.     

High abnormal rotation rates of sunspots and flare productivity

Solar activity, such as flares and CMEs, affect the interplanetary medium, and Earth’s atmosphere. Therefore, to understand the Space Weather, we need to understand the mechanisms of solar activity. Towards this end, we use 1135 events of solar H_α flares and the positional data of sunspots from the archive of Solar Geophysical Data (SGD) for the period January–April, 2000 and compute the abnormal rotation rates that lead to high flare productivity. We report that the occurrence of 5 or more flares in a day in association with a given sunspot group can be defined as high flare productivity and the sunspots that have an abnormal rotation rates of ～4–10 deg day^?1 trigger high flare productivity. Further, in order to compare the flare productivity expressed as the strength of the flux emitted, especially the soft X-ray (SXR) flares in the frequency range of 1–8 Å, we compute the flare index of SXR flares and find that 8 out of 28 active regions used in this study satisfy the requirement for being flare productive. This enables us to conclude that the high rotation rates of sunspots are an important mechanism to understand the flare productivity, especially numerical flare productivity that includes flares of all class.     

Numerical simulations of fast and slow coronal mass ejections

Solar coronal mass ejections (CMEs) show a large variety in their kinematic properties. CMEs originating in active regions and accompanied by strong flares are usually faster and accelerated more impulsively than CMEs associated with filament eruptions outside active regions and weak flares. It has been proposed more than two decades ago that there are two separate types of CMEs, fast (impulsive) CMEs and slow (gradual) CMEs. However, this concept may not be valid, since the large data sets acquired in recent years do not show two distinct peaks in the CME velocity distribution and reveal that both fast and slow CMEs can be accompanied by both weak and strong flares. We present numerical simulations which confirm our earlier analytical result that a flux‐rope CME model permits describing fast and slow CMEs in a unified manner. We consider a force‐free coronal magnetic flux rope embedded in the potential field of model bipolar and quadrupolar active regions. The eruption is driven by the torus instability which occurs if the field overlying the flux rope decreases sufficiently rapidly with height. The acceleration profile depends on the steepness of this field decrease, corresponding to fast CMEs for rapid decrease, as is typical of active regions, and to slow CMEs for gentle decrease, as is typical of the quiet Sun. Complex (quadrupolar) active regions lead to the fastest CMEs. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Deflection of coronal mass ejection in the interplanetary medium

A solar coronal mass ejection (CME) is a large-scale eruption of plasma and magnetic fields from the Sun. It is believed to be the main source of strong interplanetary disturbances that may cause intense geomagnetic storms. However, not all front-side halo CMEs can encounter the Earth and produce geomagnetic storms. The longitude distribution of the Earth-encountered front-side halo CMEs (EFHCMEs) has not only an east–west (E–W) asymmetry  (Wang et al., 2002), but also depends on the EFHCMEs' transit speeds from the Sun to 1 AU. The faster the EFHCMEs are, the more westward does their distribution shift, and as a whole, the distribution shifts to the west. Combining the observational results and a simple kinetic analysis, we believe that such E–W asymmetry appearing in the source longitude distribution is due to the deflection of CMEs' propagation in the interplanetary medium. Under the effect of the Parker spiral magnetic field, a fast CME will be blocked by the background solar wind ahead and deflected to the east, whereas a slow CME will be pushed by the following background solar wind and deflected to the west. The deflection angle may be estimated according to the CMEs' transit speed by using a kinetic model. It is shown that slow CMEs can be deflected more easily than fast ones. This is consistent with the observational results obtained by Zhang et al. (2003), that all four Earth-encountered limb CMEs originated from the east. On the other hand, since the most of the EFHCMEs are fast events, the range of the longitude distribution given by the theoretical model is E40°,W70°, which is well consistent with the observational results (E40°,W75°).     

On properties of narrow CMEs observed with SOHO/LASCO

We have investigated properties such as speed, angular width, location, acceleration and occurrence rate of narrow CMEs (defined as having angular width ≤20°) observed during 1996–2007 by SOHO/LASCO. The results obtained are compared with those of normal CMEs (angular width >20°) from the same time interval to find whether there are any real differences between the two populations. Our study of 3464 narrow CMEs from the online SOHO/LASCO, CME catalogue leads us to conclude that (1) the fraction of narrow CMEs during solar minimum is 38% and during solar maximum 19%, (2) during solar maximum narrow CMEs are generally faster than normal CMEs, (3) the maximum speed of narrow CMEs is much smaller than that of the normal CMEs, (4) during solar maximum narrow CMEs appear at all latitudes similar to normal CMEs, (5) narrow and normal CMEs have unequal deceleration and (6) the occurrence rate of narrow CMEs remain constant after 1998 until the beginning of 2006 while the normal CMEs occurrence rate seems to follow solar cycle variation until 2004. Thus narrow CMEs and normal CMEs have some differences, in disagreement with previous studies.     

Characteristics of coronal mass ejection associated with DH type II radio bursts (All and Limb events)

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.     

The challenge of predicting the occurrence of intense storms

Geomagnetic super-storms of October and November 2003 are compared in order to identify solar and interplanetary variables that influence the magnitude of geomagnetic storms. Although these superstorms (D_ST < -300 nT) are associated with high speed CMEs, their DST indices show large variation. The most intense storm of November 20, 2003 (D_St∼ - 472 nT) had its source in a comparatively small active region and was associated with a relatively weaker, M-class flare, while the others had their origins in large active regions and were associated with strong X-class flares. An attempt has been made to implement a logistic regression model for the prediction of the occurrence of intense/superintense geomagnetic storms. The model parameters (regression coefficients) were estimated from a training data-set extracted from a data-set of 64 geo-effective CMEs observed during 1996–2002. The results indicate that logistic regression models can be effectively used for predicting the occurrence of major geomagnetic storms from a set of solar and interplanetary factors. The model validation shows that 100% of the intense storms (-200 nT < D_St < -100 nT) and only 50% of the super-intense (DST < -200 nT) storms could be correctly predicted.     

Study of interacting CMEs and DH type II radio bursts

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).     

Multiwavelength Study on Solar and Interplanetary Origins of the Strongest Geomagnetic Storm of Solar Cycle 23

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.     

Lasco and eit Observations of the Bastille day 2000 Solar Storm

The period of 10–14 July 2000 saw a large number of energetic solar events ending with a very energetic flare that was associated with a large solar energetic particle event and a fast halo coronal mass ejection (CME) that produced the largest geomagnetic disturbance since 1989. This paper tries to summarize the complex coronal activity observed during this period, in order to establish a background for a number of papers in this topical issue. The GOES X-ray data are presented. Data animations of observations from EIT and LASCO C2 and C3 are presented on the accompanying CD-ROM. The observations around the time of the three X-class flares are considered. EIT observations of the Bastille Day flare show coronal brightening followed by dimming. LASCO had good data coverage for all three events. For one of the flares, no coronal response was seen. The other two flares are associated with halo CMEs. The timing suggests that the start of the flares and CMEs are simultaneous to approximately 30 min. Analysis of the LASCO and EIT images following the Bastille Day flare show the arrival of energetic particles at SOHO at approximately 10:41 UT on 14 July. Individual features of these CMEs have been tracked and the height–time plots used to estimate the dynamics of the CMEs. The initial speed and deceleration of the halo CMEs estimated from the fitting of height–time plots are compared with the in-situ observations at L1. The three flares are identified as the solar sources of three shocks observed at 1 AU. Finally, it is stressed that global heliospheric effects during periods of exceptional activity should consider a cumulative scenario rather than events in isolation.