In a recent study Andrews found that approximately 40% of M-class flares between 1996 and 1999, classified according to GOES X-ray flux, are not associated with Coronal Mass Ejections (CMEs). Using 133 events from his dataset for which suitable photospheric magnetograms and coronal images were available, we studied the pre-flare coronal helicity of the active regions that produced big flares. The coronal magnetic field of 78 active regions was modeled under the “constant $\alpha$” linear force-free field assumption. We find that in a statistical sense the pre-flare value of $\alpha$ and coronal helicity of the active regions producing big flares that do not have associated CMEs is smaller than the coronal helicity of those producing CME-associated big flares. A further argument supporting this conclusion is that for the active regions whose coronal magnetic field deviates from the force-free model, the change of the coronal sign of $\alpha$ within an active region is twice more likely to occur when the active region is about to produce a confined flare than a CME-associated flare. Our study indicates that the amount of the stored pre-flare coronal helicity may determine whether a big flare will be eruptive or confined.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Using the observations of LASCO aboard SOHO in the interval from Mar. 1997 to Dec. 2003, 301 earth-directed halo CMEs are selected and the source regions are located in MDI synoptic charts. A statistical analysis has been made with the emphasis on the CMEs' large-scale source regions as well as the correlation between CMEs and solar surface activity. The statistics show that CMEs are intrinsically related to surface activity. Four groups of CMEs' large-scale source structures are identified on the photosphere. They are: I, Extended bipole regions (EBRs) with long magnetic neutral line; II, Closely packed active regions (ARs); III, Large-scale magnetic flux of the same polarity runs through the opposite hemisphere, along the boundary there appears transequatorial filaments; IV, Between two EBRs with long filament. The result shows that CME-associated source activity is closely related to the types of large-scale magnetic structures.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The methods of radioastronomy are in important observational tool to explore magnetic energy releases in the solar corona. When combined with the useful diagnostics provided by observations in other wavelengths, namely with data from space missions such as Yohkoh, SOHO, and more recently RHESSI, these datasets allow us to track the progression of solar eruptive events from the low corona into the interplanetary medium. One of the most dramatic forms of solar activity, coronal mass ejections (CMEs) encompass a large range of spatial scales in a question of a few minutes. These go from the very small like current sheets, to small like active regions, to the very big like trans-equatorial loops and the transient seen in white light images (with angular extents in excess of 100 degrees for some events). Hence, in order to understand the CME phenomenon, its origin, and early development, we need a set of observations able to image the whole Sun with time cadences of the order of the second. Radio observations can do that presently. Multifrequency radio observations of the solar corona in the metric domain provide diagnostics of a wide variety of phenomena that occur in association CMEs. Radio imaging instruments can follow the processes leading to CME initiation, follow the expansion of the CME in the low corona, both on disk, and above the solar limb, and as such make the link with coronagraphic data. The characteristic signatures of the many CME related phenomena go from thermal emission of the eruptive cavity in the low corona, to direct imaging of the CME loops from synchrotron emission, to radio continua and shock associated emissions, recent progress on the understanding of the early development of CMEs, and on the coronal restructuring in the aftermath of the mass ejection, based on solar radio imaging from the Nancay Radioheliograph, is reviewed here.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The internal magnetic field structure of CMEs and the field structure of the solar source regions were systematically investigated during different phases of the solar cycle in cycles 19-23 based on plasma and magnetic field measurements sampled by various satellites and through multi-wavelength remote sensing observations. It is found that: 1. To first order, the internal magnetic structure of CMEs varies systematically from one solar cycle to the next with respect to the prevailing hemispheric magnetic patterns of bipolar regions following the law of hemispheric helicity dependence. 2. To second order, the field structure in CMEs varies with respect to the complex spatial evolution of the magnetic flux in the photosphere in both hemispheres over the course of the cycle itself. The two effects can naturally explain the cyclic behavior of the SN, NS variations of the internal magnetic fields in CMEs in the solar wind as well as intermittent periods of mixed distributions.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

Coronal mass ejections (CME) from the solar corona are the most spectacular phenomena of solar activity. Solar physicists are tried to relate CME with other forms of solar activities. CMEs are the result of a large scale rearrangement of solar magnetic field and they are often observed as an eruption of twisted magnetic fields from the solar atmosphere. SOHO/LASCO detected (http://cdaw.gsfc.nasa.gov/CME_list) more than 7500 CMEs during 1996-2003 June. The catalog contains all the CMEs with primary characteristics e.g. linear speed, central position angle, and the angular width. We will use these characteristics to study the variations of CME within these periods. The period starts from the sunspot minimum to entire sunspot maximum range where the solar activity is high. Solar proton events ($E>10MeV$) were collected from NOAA website (http:/www.lep.gsfc.nasa.gov/waves) of the associated CMEs with halo CMEs. We find from CMEs data that the occurrence of average CME rate is 121.51 per month during June 1999 to June 2003 (sunspot maximum range) whereas the occurrence of average CME rate is 41.24 per month during January 1996 to May 1999 (sunspot minimum range), although during the year 1996 (when the average sunspot number is 8.6 per month) occurrence of average CME rate is 18.16 per month. The CME occurrence rate is also correlated with the sunspot numbers with high statistically significant level. The CME number is highest in 2002 but CME is higher in 2000 than in 2001. There is an overall similarity between sunspot number and CME rates but there are differences particularly from June 1999 which is the beginning of the sunspot maximum range. The CME rate peaks in September 2001 to October 2002, which is about 1.25 year after the sunspot maximum. Similarly the average speed of CME at the time of sunspot maximum range and sunspot minimum range are 575 km/sec. and 266 km/sec. respectively. This means that the average speed of CME increases from 1996 to June 2003. The CME speed is also correlated with the sunspot numbers with less significant level than the average rate of CME occurrence. The maximum monthly average speed is about 677.3 km/sec. at the time of April 2001, which is about 5 months earlier than the second sunspot maximum. From the preliminary list of halo CME events from SOHO/LASCO during January 1996 to June 2003 we find that the occurrence rate of average halo CME events during January 1996 to May 1999 is about 1.10 per month whereas during June 1999 to June 2003 is about 4.00 per month, during the year 1996 only two halo CMEs is occurred. We also find that the average speed of halo CME events during sunspot minimum range is 838 km/sec, whereas average speed of the halo CME events during sunspot maximum range is 1000 km/sec. Although during the year 1996 the average speed of halo CME events is 451 km/sec. From the characteristics of halo CMEs in years we find that the number of halo CME increases from 1996 to 2001 and the number of halo CME is maximum in the year 2001, after that number of halo CME decreases. In the 23rd solar cycle maximum solar activity occurred during June to September 2001 we call the time as 2nd sunspot maximum time. We also find that number of high speed ($>1000\,km/sec.$) halo CME is highest during 2nd sunspot maximum range (i.e., during 2001-2002). We find from the halo CME data that average halo CME speed increases from 1996 to 1998 and then decreases from 1998 to 2000 and again increases from 2000 to 2003 and we expect that the average speed of halo CME will decrease after 2003. We find 78 solar proton events ($E >10MeV$) from CME and about 43 of them are from halo CME during 1996 to 2003. We noticed that the maximum solar proton events occurred at the second sunspot maximum, which is occurred after $1\frac12$ sunspot maximum in the 23rd solar cycle. We find there exist 5 phases of solar proton events ($E >10MeV$) data in the 23rd solar cycle. The first phase is at the sunspot minimum, 2nd phase is after two years from the sunspot minimum, 3rd phase is at the time of sunspot maximum and 4th phase occurs just one and half year (usually it is about 2/3 years) after the sunspot maximum and 5th phase occurs 2/3 years before the sunspot minimum. We find six solar proton events ($E >10MeV$) data within 1999 to 2003 with 12900 to 31700 pfu which produced strong geomagnetic storms and all of them are very high-speed halo CME. It is known that very fast CMEs $(V_{p}> 1000$km/sec.) are capable of causing extremely intensive geomagnetic storm when $D_{st} $ index ${<}\,{ -}300nT$. We find that there is a significant correlation between the speed of the CME and solar proton events ($E>10MeV$) data. Solar radius measurement at Rio de Janeiro from 1997-2000 shows that the solar radius varies in phase with the solar cycle. Astrolabes of Antalya, Rio de Janeiro and Santiago suggest that the solar radius varies in phase with the solar cycle. From the detection of solar radius variations with MDI on board SOHO it is found that the solar radius increases with the number of sunspots[l]. It appears that solar radius variation and solar neutrino flux variation with the solar cycle is due to the variation of solar core pulsations and is mainly responsible for the variation of CME and its speed that is in phase with the solar cycle. We suggest that the above-mentioned characteristics are interrelated and that a pulsating solar core may be their common origin [2].To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Using the list of CMEs observed by SOHO/LASCO, we compile a daily CME counts from January 1996 to December 2003. Cross-correlations between the CME counts and other three solar activity indices, i.e., flare index, sunspot number, and photospheric magnetic flux, are examined in both real and Fourier spaces. We find that correlations are all significant in real space, but only photospheric magnetic flux has good correlation with CME counts in Fourier space. Typical periods of CME occurrence are presented and discussed.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

A class of large-scale magnetic compositions have been identified to be CME-prolific, which is characterized by a huge unipolar sunspot appearing in a large-scale extended bipolar region in synoptic magnetic charts. To understand the CMEs' origin and the nature of flux appearance, we scrutinize the long time-sequence of MDI magnetograms of high-resolution mode for super active region AR9236. Two types of magnetic features are clearly identified. They are moving magnetic features (MMFs) emanated radially from the penumbral boundary and emerging flux regions (EFRs) whose growing opposite polarities rotate out from the inner boundary of sunspot moat along helical paths in opposite directions. The interaction between the MMFs and EFRs often creates multi-fold magnetic neutral lines where the flare/CMEs initiated.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Observations suggest that solar coronal mass ejections (CMEs) are closely associated with reconnection-favored flux emergence, which was explained as the emerging flux trigger mechanism for CMEs by Chen and Shibata (2000) based on numerical simulations. This paper presents a parametric survey of the CME-triggering environment. Our numerical results show that whether the CMEs can be triggered depends on both the amount and the location of the emerging flux. The results are useful for space weather forecast.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

To examine the stray light in magnetograph observations, we determined the point spread function of the Video Vector Magnetograph mounted on the Solar Magnetic Field Telescope (SMFT) installed at the Huairou Solar Observing Station (HSOS). Then we obtained the curve on large-spread-angle (LSA) stray light intensity as a function of distance from disk center. A new way to correct LSA stray light is proposed.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Four coronal mass ejections (CMEs) occurs successively from the solar disk near the west limb on October 26, 2003. They, together with the associated activities of the solar surface, were observed by various instruments both in space and on ground, such as the Large Angle and Spectrometric Coronagraph Experiment (LASCO), the Extreme Ultraviolet Imaging Telescope, and the Michelson Doppler Imager on board the Solar and Heliospheric Observatory, as well as the Huairou Solar Observing Station and the Big Bear Solar Observatory. These four events start with a filament eruption that manifests a two-ribbon flare in a spotless region, destroyed a helmet streamer, and give rise to an X1.2 flare in the active region AR0484. We notice that these eruptions occur either in active region, or in quiescent region, or in the region without any precursors. The time profiles of the CME (filament) heights show that the main acceleration takes place within one solar radius $(R_\odot)$ from the solar surface, and that all the CMEs almost propagate at constant speeds as they appear in the field of view of LASCO C2. We conclude that the most dynamical process of each of these CMEs happens at the altitudes lower than one $R_\odot$ from the surface. Among the four activities, the fourth one comes from AR10484 and shows the largest speed projected on the sky plane, which is about 1500 km s$^{-1}$; and the first filament shows the largest acceleration, $\sim 50$m s$^{-2}$.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We investigated the complex subsurface magnetic rope structure of a super-active region NOAA 10488. With the set of twisted magnetic loop, knot and bifurcate configuration ,we could explain the complicated flux emerging, developing and disappearing by following Tanaka model (Tanaka, 1991). Based on Huairou photospheric vector magnetograms, we calculated the current helicity and found the dominant helicity sign is positive. We deduced that the whole active region might be one twisted magnetic rope.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We have studied the magnetic helicity transport rate and the current helicity for solar active region (AR) NOAA 10488 and find a complex relationship between them. We further extend this study to a statistical one, and find that 33 among the selected 57 ARs show opposite sign for the two parameter.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

On 28 Oct 2003, one of the biggest flares (4B/X17.2) seen in recent years occurred in Active Region (AR) NOAA 10486 associated with a violent halo coronal mass ejection. It was a complex $\beta\gamma\delta$ region. After studying the evolution of the AR and the phenomena of this powerful flare, we obtained the following result. (1) Highly sheared transverse field was formed gradually on both sides of the neutral line by squeeze during the AR development; (2) Rotations of penumbra of main polarities were discerned, and the average horizontal velocities was as large as 0.55 km/s; (3) The spiral transverse field of main positive polarity was diffused after the large flare; (4) Some magnetic features submerged or emerged in the vicinity of the flare onset point. The emergence of this rotational and complex magnetic topology implies a transport of magnetic energy and complexity from the low atmosphere to the corona. Moreover, the rapidly submergence (emergence) and movements of the small magnetic features which represent the enhancement (cancellation) and squeeze of the magnetic field play a key role in the onset of the flare.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The sporadic solar radio emission of patrol solar radio observations within the periods 1980, 1984–1989 and of observations with high temporal and spectral resolution in 1989 are used to find the manifestation of pre CMEs activity.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The results of solar microwave observations in the Radio Astronomical Observatory NIRFI “Zimenki” are examined. Data analysis shows the presence of periodic component, that arose prior to burst connected to CMEs onset, and its absence after burst. Obtained data are compared with the dynamics of the development of activity on the solar disk. Results can be considered as the illustration of the dynamics of wave motions in the periods of flare activity.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

We include gravity in a loss of equilibrium model for the initiation of coronal mass ejections (CMEs). We examine equilibria for both normal and inverse polarity and neglect the effects of current sheets. Although equilibria exist for normal polarities, in the absence of current sheets, the equilibria are unstable to horizontal perturbations. For the inverse polarity configuration, we find that gravity generally has a negligible effect if the magnetic field is strong ($>$50 G) but that it can have a significant effect if the magnetic field is weak. Specifically, if the characteristic magnetic field is less than about 6 G, no eruption occurs if the CME mass is on the order of 2 $\times 10^{16}$ gm.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