Shocks driven by energetic coronal mass ejections and other interplanetary transients are mainly responsible for large disturbances in geomagnetic field of Earth and play a key role in producing a geomagnetic storm or substorm. A geomagnetic storm is a global disturbance in Earth's magnetic field usually occurred due to abnormal conditions in the IMF and solar wind plasma emissions caused by various solar phenomenon. Identifying intense geomagnetic storms with Dst decrease more than/or equal to 300 nT occurred during 1981-2001, a correlative study has been performed to analyze the associated solar and interplanetary causes of these 09 events using solar wind plasma, IMF and solar geophysical data. It is observed statistically that 55% storms have occurred during solar maximum and 45% occurred during minimum phase of solar cycles. Further, study reveals that 77% intense storms are associated with CMEs, which confirms earlier findings.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Solar energetic particle (SEP) fluxes measured by the ULYSSES (ULS)/HI-SCALE experiment during its second polar orbit as well as by the identical ACE/EPAM experiment at 1 AU are utilized as diagnostics of the large-scale structure and topology of the Interplanetary Magnetic Field (IMF) embedded within Interplanetary Coronal Mass Ejections (ICMEs). Survey results are also reported.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

By means of multiwavelength data, we study the eruptions of two filaments and the relationship between the first filament eruption and a subsequent CME. The main results are: (1) The disturbances of the two filaments showed different features, indicating that their eruptive mechanisms were possibly different. (2) A subsequent CME was well correlated with the first eruption in both time and space.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

Magnetic helicity, which is a measure of magnetic flux linking, is widely believed to play a crucial role for the solar coronal energetic processes, e.g. heating, flares and eruptions. In this paper, we introduce the several new findings of magnetic helicity physics in the solar corona both from the observational and theoretical points of view. The new observations based on the vector magnetograms successfully revealed that the solar coronal activity is indeed related not only to the intensity of magnetic helicity injection from the photosphere, but also to the complexity in the structure of magnetic shear. In particular, we recently found through the advanced analyses of vector magnetogram data that steep reversal of magnetic shear may efficiently activate the liberation of free energy stored in the coronal magnetic field. Motivated by the results, we developed the large scale three-dimensional simulation to investigate the causal relationship between the magnetic helicity injection and the energy liberation in the solar corona. The simulations clearly demonstrated that the reversal of the magnetic shear in a magnetic arcade can cause the sudden onset of plasmoid eruption. The mechanism is able to be explained as a self-exciting process of multiple magnetic reconnections. Finally, we propose a new scenario for the triggering mechanism of eruptive flares, which is called the reversed-shear flare model.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Using the observations of the EUV Imaging Telescope(EIT) and the Large Angle Spectrometric Coronagraph(LASCO) on the Solar and Heliospheric observatory(SOHO) and solar soft X-ray flux and radio bursts data, we study the low coronal signatures of a solar limb coronal mass ejection(CME) on November 4, 2003. The two prominent dimmings in EIT difference images were closely related to two large loops in this event. The onset time and height of the CME and the lower limit of the masses loss from dimming regions are estimated.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

By investigating ten typical magnetic clouds (MCs) associated with large geomagnetic storms (Dst $\leq-100$ nT) from 2000 to 2003, the geoeffectiveness of MCs with various orientations is addressed. It is found that the Dst peak values during the geomagnetic storms are well estimated by applying flux rope model to these magnetic clouds. A high correlation between estimated and observed Dst values is obtained. Moreover, the effect of orientations of MCs on intensities of geomagnetic storms is studied. It is found that the favorable orientations of MCs are approximately at $\theta\sim70^{\circ}$ and $\phi\sim40^{\circ}$ in GSE coordinates to cause large geomagnetic storms. Further, by analyzing solar observations of four associated erupted filaments, the question who determine the orientations of MCs is studied. The likelihood of predicting the intensities of a geomagnetic storms several tens hours before their occurrences is also discussed.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The paper describes our approach to simulations of real interplanetary events, consisting of four steps: (i) determination of background solar wind, (ii) parameterization of a model flux rope, (iii) launching it into the solar wind, and (iv) calculating its propagation and evolution.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

A brief review is given on the progress made in the study of the catastrophe of coronal magnetic flux ropes with implication in coronal mass ejections (CMEs). Relevant studies have been so far limited to 2.5-D cases, with a flux rope levitating in the corona, either parallel to the photosphere in Cartesian geometry or encircling the Sun like a torus in spherical geometry. The equilibrium properties of the system depend on the features of the flux rope and the surrounding background state. Under certain circumstances, the flux rope exhibits a catastrophic behavior, namely, the rope loses equilibrium and erupts upward upon an infinitesimal variation of any control parameter associated with the background state or the flux rope. The magnetic energy of the system right at the catastrophic point may exceed the corresponding open field energy so that after the background field is opened up by the erupting flux rope, a certain amount of magnetic free energy is left for the heating and acceleration of coronal plasma against gravity. The flux rope model has been used to reveal the common features of CMEs and to simulate typical CME events, proving to be a promising mechanism for the initiation of CMEs. Incidentally, the Aly conjecture on the maximum magnetic energy of force-free fields places a serious constraint on 2.5-D flux models. Nevertheless, current sheets must form during a catastrophe on the Alfvén timescale, and magnetic reconnection across the newly formed current sheets may contribute to circumventing such a constraint. In this sense, the catastrophe simply plays a role of driver for the fast magnetic reconnection, and a combination of them is thus responsible for the initiation of CMEs.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

We selected 133 solar microwave bursts (SMBs) recorded by SGD and 133 CMEs observed by SOHO/LASCO from November 1999 through September 2003. These SMBs are associated with CMEs and flares. We analyzed the characteristics of the SMBs, including duration, flux peak, burst type, and spectral index. Correlated events were distinguished by time and the location of flare associated with the SMB. We find that (1)The duration of SMBs associated with narrow(0°<width<20°)/normal CMEs(20°<width<120°) or slow CMEs is below 40 minutes. (2)The duration of SMBs associated with Halo-like CMEs(120°<width<360°) or fast CMEs is from several minutes to 200 minutes. (3)The flux peak of SMBs associated with narrow CMEs/normal CMEs or slow CMEs is below 400sfu. (4)The flux peak of SMBs associated with Halo-like CMEs or fast CMEs is from several sfu to several thousands sfu. (5)the majority of SMBs,which are associated with Full Halo CMEs, are Complex/GB bursts. The majority of SMBs, which are associated with narrow CMEs/normal CMEs, are simple bursts. (6)U-shape spectra are observed. The spectra of SMB associated with CME is very flat when f>fmax. A statistical result suggest that CME/flares and SMBs is probably a different manifestation of the same physical process. CME/flare and SMB have intrinsically a physical relationship.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

As young stars evolve from the time of their formation onto the main sequence, they lose mass in a variety of ways. At the very earliest stages, mass loss may be in the form of jets associated with accretion from a surrounding disk. These cool jets carve out the surrounding gas and their changes over time may indicate changes in the star-formation process. At later stages, mass loss is predominantly in the form of a hot, magnetically channelled wind that carries mass, but more importantly angular momentum, away from the star. This wind determines the rotational evolution of cool stars and is intimately connected to the process of field generation deep inside the star. Mass loss also occurs in a sporadic way in the form of the ejection of cool clouds of coronal gas. The coronal distribution and evolution of these clouds (or prominences) gives us vital clues about the structure and short-timescale evolution of stellar coronae. In this review I will discuss recent advances in our understanding of the coronae, winds and accretion processes in cool stars and show how these processes may be related at different stages of evolution.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

The Ulysses spacecraft has now completed its second orbit over the poles of the Sun. Energetic particles associated with CMEs were observed at the highest latitudes over both poles, quite unlike the first polar pass when virtually no CME or CIR accelerated particles were observed at the very highest latitudes. We present observations of solar energetic particle events observed in the energy range $\sim$1 MeV to $\sim$100 MeV made by the COSPIN instrument, when the spacecraft was at high heliographic latitude over the northern pole, above the current sheet, and immersed in high-speed solar-wind flow coming from the northern polar coronal hole. We discuss the rise to maximum, the onset time and the anisotropy of the energetic particles. We find that, unlike the events observed at mid and low latitudes, the particle angular distributions were almost isotropic, but with a net outward flow along the magnetic field lines. We compare these events with other events observed at lower latitudes.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Based on the solar energetic particle (SEP) data from ACE and GOES satellites, the acceleration of SEP by CME-driven shock in interplanetary space was investigated. The results showed that the acceleration process of SEP by the Bastille CME-driven shock ran through the whole space from the sun to the magnetosphere. The highest energy of SEP accelerated by the shock was greater than 100MeV. A magnetic bottle associated with the CME captured a lot of high energy particles with some of them having energy greater than 100MeV. Based on magnetic field data of solar wind observed by ACE data, we found that the the magnetic bottle associated with the Bastille CME was the sheath caused by the CME in fact.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Recent progress of theories of eruptive flares (and CMEs) is reviewed within a framework of reconnection model with emphasis on development of basic idea and concept.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

A coronal current-free field model, which applies the asymptotic condition of no field at infinity and the boundary condition on the solar surface specified, is presented. Some Applications of the method to practical solar events indicate that the extrapolated global magnetic field structures effectively demonstrate the case for the disk signature of the radio CME and the evolution of the radio sources during the CME/flare processes.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

A fast halo CME and correspondingly strong solar burst that occurred in NOAA9684 led to intense geo-effectiveness. The analysis and study in this paper were focused on the evolution of this active region.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