In recent times, there has been keen interest in understanding Sun-Earth connection events, such as solar flares, CMEs and concomitant magnetic storms. Magnetic storms are the most dramatic and perhaps important component of space weather effects on Earth. Super-intense magnetic storms (defined here as those with Dst $<$ −500 nT, where Dst stands for the disturbance storm time index that measures the strength of the magnetic storm) although relatively rare, have the largest societal and technological relevance. Such storms can cause life-threatening power outages, satellite damage, communication failures and navigational problems. However, the data for such magnetic storms is rather scarce. For example, only one super-intense magnetic storm has been recorded (Dst=−640 nT, March 13, 1989) during the space-age (since 1958), although such storms may have occurred many times in the last 160 years or so when the regular observatory network came into existence. Thus, research on historical geomagnetic storms can help to create a good data base for intense and super-intense magnetic storms. From the application of knowledge of interplanetary and solar causes of storms gained from the spaceage observations applied to the super-intense storm of September 1-2, 1859, it has been possible to deduce that an exceptionally fast (and intense) magnetic cloud was the interplanetary cause of this geomagnetic storm with a Dst −1760 nT, nearly 3 times as large as that of March 13, 1989 super-intense storm. The talk will focus on super-intense storms of September 1-2, 1859, and also discuss the results in the context of some recent intense storms.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The Solar and Heliospheric Observatory (SOHO), a space mission of international collaboration between ESA and NASA, has been operating almost continuosly since early 1996. The Sun and the heliosphere went through both: the minimum and maxumum of solar activity in 1996 and 2000, respectively. The perfectly working set of modern solar telescopes and insitu instrumentation has been producing an unprecedented set of most valuable observational data that are almost immediately available to the public via the Internet. A wealth of new results has been published in innumerable papers. For CME research in particular, SOHO has started a new era. CME evolution can now be studied from their initiation up to the arrival of the ejecta clouds at 1 AU. For the first time, helioseismological observations reveal flow vortices underneath sunspots, i.e., activity centers that are involved in subsequebt eruptions. Combined EUV disk observations and coronagraph images allow to differentiate between CMEs pointed towards to or away from the Earth. Thus, space weather predictions have achieved a new quality. The occurrence of “EIT waves” at CME onset was discovered, the internal structure of CMEs (including “disconnection”, magnetic topology and helicity, etc.) was made visible, statitics about CME properties and their change with solar activity were refined. Spectacular CME images and animations have been attracting the public to an unexpected extent, to the benefit of solar research in general.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

A multi-channel SPIRIT telescope/spectroheliograph aboard the CORONAS-F satellite operating in soft X-ray and EUV ranges ($T \sim $0.05–15 MK) is an effective instrument for complex studies of CME-associated phenomena such as eruptive filaments, dimmings, coronal waves, posteruptive arcades, etc. In particular, SRIRIT observations of high-temperature (T = 5–15 MK) plasma structures in the MgXII 8.42 Å line show specific pre-CME sigmoid magnetic field configurations. Eruptions of filaments (prominences) and dimmings in a CME process are seen with a high contrast in the coronal 175 Å band (FeIX–XI) and the transition-region 304 Å (HeII) images. Our results are illustrated by several powerful eruptive events of the current solar cycle. We compare SPIRIT data with observations at other spaceborne and ground-based instruments (SOHO/EIT, Yohkoh/SXT, and H$\alpha$ images, etc.)To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Why CMEs erupt is a major outstanding puzzle of solar physics. Signatures observable at the earliest stages of eruption onset may hold precious clues about the onset mechanism. We summarize and discuss observations from SOHO/EIT in EUV and from Yohkoh/SXT in soft X-rays of the pre-eruption and eruption phases of three CME expulsions, along with the eruptions' magnetic setting inferred from SOHO/MDI magnetograms. Our events involve clearly-observable filament eruptions and multiple neutral lines, and we use the magnetic settings and motions of the filaments to help infer the geometry and behavior of the associated erupting magnetic fields. Pre-eruption and early-eruption signatures include a relatively slow filament rise prior to eruption, and intensity dimmings and brightenings, both in the immediate neighborhood of the “core” (location of greatest magnetic shear) of the erupting fields and at locations remote from the core. These signatures and their relative timings place observational constraints on eruption mechanisms; our recent work has focused on implications for the so-called “tether cutting” and “breakout” models, but the same observational constraints are applicable to any model.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

A 2-dimensional Doppler coronagraph “NOGIS” (NOrikura Green-line Imaging System) at the Norikura Solar Observatory, NAOJ, is a unique imaging system that can provide both intensity and Doppler velocity of 2 MK plasma from the green coronal line emission $\lambda$5303 Å of Fe xiv. We present the first detection of a CME onset by NOGIS. The event was originally induced by a C9.1 confined flare that occurred on 2003 June 1 at an active region NOAA $\#$10365 near the limb. This flare triggered a filament eruption in AR 10365, which later evolved into a partial halo CME as well as an M6.5 flare at the same AR 10365 on 2003 June 2. The CME originated in a complex of two neighboring magnetic flux systems across the solar equator: AR 10365 and a bundle of face-on tall coronal loops. NOGIS observed i) a density enhancement in between the two flux systems in the early phase, ii) a blue-shifted bubble and jet that later appeared as (a part of) the CME, and iii) a red-shifted wave that triggered a periodic fluctuations in Doppler shifts in the face-on loops. These features are crucial to understand unsolved problems on a CME initiation (e.g., mass supply, magnetic configuration, and trigger mechanism) and on coronal loop oscillations (e.g., trigger and damping mechanisms). We stress a possibility that interaction between separatrices of the two flux systems played a key role on our event.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Recent studies show that the cone model with a circular cross section can be used to determine the geometrical and kinematical properties only for a class of halo CMEs with the semi-minor axis of the elliptic halo threading the solar disk center. This work shows how to use an improved cone model with an elliptic cross section to determine the geometrical and kinematical properties for another class of halo CMEs with the semi-major axis threading the solar disk center.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Based on the SOHO/LASCO dataset, a collection of “structured” coronal mass ejections (CMEs) has been compiled within the period 1996-2002, in order to analyze their three-dimensional configuration. These CME events exhibit white-light fine structures, likely indicative of their possible 3D topology. From a detailed investigation of the associated low coronal and photospheric source regions, a generic scheme has been deduced, which considers the white-light topology of a CME projected in the plane of the sky as being primarily dependent on the orientation and position of the source region's neutral line on the solar disk. The obtained results imply that structured CMEs are essentially organized along a symmetry axis, in a cylindrical manner. The measured dimensions of the cylinder's base and length yield a ratio of 1.6. These CMEs seem to be better approximated by elliptic cones, rather than by the classical ice cream cone, characterized by a circular cross section.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The discovery of “EIT waves” after the launch of SOHO spacecraft sparked wide interest among the coronal mass ejection (CME) community since they may be crucial to the understanding of CMEs. However, the nature of this phenomenon is still being hotly debated between fast-mode wave explanation and non-wave explanation. Accumulating observations have shown various features of the “EIT waves”. For example, they tend to be devoid of magnetic neutral lines and coronal holes; they may stop near the magnetic separatrix between the source region and a nearby active region; they may experience an acceleration from the vicinity of the source active region to the quiet region, and so on. This paper is aimed to review all these features, discuss how these observations may provide constraints for the theoretical models, and point out their implication to the understanding of CMEs.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present a statistical study on the acceleration of CMEs. This study is based on 23 CME events best observed by SOHO LASCO/C1 coronagraph, which observes the inner corona from 1.1 to 3.0 $R_S$. The kinematic evolution of a CME has a distinct acceleration phase that mainly takes place in the inner corona. We find that the acceleration duration distribution ranges from 10 to 1100 min with a median (average) value at 54 min (169 min). The acceleration magnitude distribution ranges from 6 m s$^{-2}$ to 947 m s$^{-2}$ with a median (average) value at 209 m s$^{-2}$ (280 m s$^{-2}$). We also find a good correlation between CME acceleration magnitude A (in unit of m s$^{-2}$) and acceleration duration T (in unit of min), which can be simply described as A=10000/T.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

A helical structure in the coronal mass ejection (CME) of 12 September 2000 was observed by the Ultraviolet Coronagraph Spectrometer (UVCS) aboard the Solar and Heliospheric Observatory (SOHO) at heliocentric distances of 3.5 and 6 R$_{\odot}$. A difference of 300 km sec$^{-1}$ in line-of-sight velocities for two segments of the helix obtained from Doppler measurements implies expansion and allows one to distinguish which segment was closest to the observer. The tilt of the segment then determines the handedness. Observed Ly$\alpha$ and C III line emissions indicate that the helix was threaded with filament plasma of varying density. While the helix constituted the bright core of filament plasma, the helix itself was most likely not the pre-existing filament structure.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Due to the optically thin nature of the white light emission, all measurements of the energetics and dynamics of a CME are based on sky-plane projected quantities. The extent and distribution of the CME material along the line of sight is unknown. Thus, CME measurements have an inherent degree of uncertainty. In this paper, I identify the various (possible) sources of errors associated with measurements of CME mass and energy (e.g., instrumental, random, projections effects, etc) and give an error budget for the final measurements. I apply these errors to the statistics of mass and energy for several thousand CMEs observed with LASCO in 1996-2003.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

In this work we focus on UVCS data acquired during the November 2002 SOHO–Ulysses quadrature, at an altitude of 1.7 R$_{\odot}$ over a range of latitudes centered around 27$^{\circ}$N in the western quadrant. A couple of hours before our observations started, a CME event (November 26, 15:30 UT) originating at about 27$^\circ$N, disrupted the coronal configuration of the region. In the $\sim$ 2.3 days following the event UVCS detected emission in the neutral H $Ly \beta$ and $Ly \gamma$ lines as well as in lines from both high and low ionization ions such as C iii, O vi, Si viii, ix and xii, Fe x and xviii. Enhanced emission from the hot Fe xviii ion ($\log T_{max} = 6.7$), lasting nearly to the end of our observations and originating in a region between 10$^\circ$N and 30$^\circ$N, has been identified with a post–CME current sheet. Our interpretation is supported by EIT Fe xii images which show a system of loops at increasingly higher altitudes after the event. Northward of the CME, UVCS observed repeated, sudden and short lived emission peaks in the “cool” $Ly \beta$, $Ly \gamma$, C iii and O vi lines. These events seem to be the extension at higher altitudes of the chromospheric plasma jets observed in the EIT He ii images. Electron temperatures of both the hot and cool region will be presented here and their time evolution will also be illustrated.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Ground based radio imaging observations play an useful role in the study of mass ejections from the solar corona since they do not have the limitation of an occulter and both the disk/limb events can be detected early in their development, particularly via the thermal bremmstrahlung emission from the frontal loop of the CME. I present here some of the recent results on the above topic using data obtained with the Gauribidanur radioheliograph, near Bangalore in India.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The time and location of magnetic reconnection are indicated by radio (Nobeyama Radio Heliograph and Polarimeters, Hiraiso and Chinese radio spectrographs) and multi-wavelength (SOHO and TRACE satellites) data in a selected flare-CME event on April 21, 2002. Two hour radio burst started at high frequencies (maximum around 10 GHz). After that, a radio ejection at 17 GHz from one foot point was coincident with the expanded flare and post-flare loops. The reversal of polarization sense at the radio loop-top is associated with the strong coherent emissions around 2 GHz, which should be located above the loop-top at 17/34 GHz. The radio ejection and coherent emissions are also associated with a pair of moving type $I\!V$ bursts at 0.2-2 GHz from high to low frequencies and 2.6-3.8 GHz from low to high frequencies, respectively. High time resolution (8 ms) data show three components of the frequency drifts at 2.6-3.8 GHz: very slow (5 MHz/s) of moving type $I\!V$, slow (50 MHz/s) of zebra strips, and fast (several GHz/s) of type $I\!I\!I$, which may represent respectively the speeds of flare loop or current sheet, outflows, and energetic electrons from the reconnection site.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The solar radio bursts and accompanying fine structures recorded by spectrometers at Huairou, Beijing during 1999-2003 are presented. The spectrometers are with high temporal (5-10 ms) and spectral (4-20 MHz) resolutions. We found 91 radio burst events that occurred within half hour of the onset of the CME events which cause solar energetic particle events. The associations of radio fine structures with CME events are discussed.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Using multi-spectral data, we estimate plasma parameters in the post-eruptive arcade observed on October 22, 2001 at 100 Mm above the limb: the temperature is 6 MK and the plasma density is $(5-9) \cdot 10^9$ cm$^{-3}$. We state a problem of the long-term equilibrium of the hot top of the arcade high in the corona: either the magnetic field surrounding the arcade well exceeds that one extrapolated in the potential approximation, or $\beta > 1$ both inside and outside the arcade. A downflow observed in soft X-rays can contribute to the equilibrium.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Conventionally coronal mass ejections (CMEs) are categorized into flare-associated and filament-associated types. Since there are also many CMEs of the overlapping type, we classify CMEs into three types in order to compare their characteristics. It is found that the three types of CMEs have quite similar distributions of apparent speeds, with small difference in the average speeds.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

In order to explain the different average speeds between halo and limb CMEs, we investigate the relationship between the brightness and speed for 17 halo CMEs. It is found that faster CMEs tend to be brighter, which implies that many halo CMEs with slow speeds are missed in observation owing to the limited sensitivity of LASCO detectors or identifications. As a result, the statistical average speed of halo CMEs turns to be much larger than that of limb CMEs.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The degree of polarization of Compton-scattered photospheric light observed in a coronagraph is dependent on the distance of the scattering electrons from the plane of the sky. Measurements of the polarization of light scattered by CME structures have been observed by LASCO C2. We have reduced and analyzed a month long sequence of such measurements which were taken at a cadence of 1 hour. The CME brightness has been distributed throughout a 3 dimensional cube and visualized at a variety of angles. Several CMEs are found to have considerable fine-structure consistent with expanding loop arcades. The analysis is subject to a variety of assumptions such as a lack of knowledge of whether a source is before or behind the plane of the sky. Nevertheless, the results obtained to date are intriguing.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We report the eruption of a small $H_{\alpha}$ filament and associated partial halo coronal mass ejection (CME) occurring in NOAA AR 9616. Accompanied by a M1.5 flare, the filament quickly erupted, a remote coronal dimming region far away from the eruption site was formed above quiet-sun area, and then a long $H_{\alpha}$ surge developed from the flare site. During the eruption, remote $H_{\alpha}$ and EUV brightenings appeared near the dimming, along the dimming boundary in EUV and in its interior in $H_{\alpha}$, leaving behind EUV loops connecting the eruption source region and the remote EUV brightenings. Finnally, as a definite indication of the CME, a huge dark loop appeared to span the eruption region. These observations indicate that a much larger-scale rearrangement of the corona magnetic fields, eventually represented by the CME, was involved in the eruption of the small filament.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html