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We report multiwavelength study of a complex M-class solar eruptive flare that consists of three different sets of flare ribbons, viz. circular, parallel, and remote ribbons. Magnetic field modelling of source active region NOAA 12242 exhibits the presence of 3D null-point magnetic topology that encompasses an inner bipolar region. The event initiates with the faint signatures of the circular ribbon along with remote brightening right from the pre-flare phase that points toward the ongoing slow yet persistent null-point reconnection. We first detected flux cancellation and an associated brightening, which are likely signatures of tether-cutting reconnection that builds the flux rope near the polarity inversion line (PIL) of the inner bipolar region. In the next stage, with the onset of M8.7 flare, there is a substantial enhancement in the brightening of circular ribbon, which essentially suggests an increase in the rate of ongoing null-point reconnection. Finally, the eruption of underlying flux rope triggers ‘standard flare reconnection’ beneath it producing an abrupt rise in the intensity of the parallel ribbons as well as enhancing the rate of null-point reconnection by external forcing. We show that within the the fan dome, the region with magnetic decay index n > 1.5 borders the null-point QSL. Our analysis suggests that both the torus instability and the breakout model have played role toward the triggering mechanism for the eruptive flare. This event is a nice example of the dynamical evolution of a flux rope initially confined in a null-point topology that subsequently activates and erupts with the progression of the circular-cum-parallel ribbon flare.

We investigate the onsets of three consecutive coronal mass ejection (CME) eruptions in 12 hours from a large bipolar active region (AR) observed by SDO, STEREO, RHESSI, and GOES. Evidently, the AR initially had a triple-decker configuration: three flux ropes in a vertical stack above the polarity inversion line (PIL). Upon being bumped by a confined eruption of the middle flux rope, the top flux rope erupts to make the first CME and its accompanying AR-spanning flare arcade rooted in a far-apart pair of flare ribbons. The second CME is made by eruption of the previously-arrested middle flux rope, which blows open the flare arcade of the first CME and produces a flare arcade rooted in a pair of flare ribbons closer to the PIL than those of the first CME. The third CME is made by blowout eruption of the bottom flux rope, which blows open the second flare arcade and makes its own flare arcade and pair of flare ribbons. Flux cancellation observed at the PIL likely triggers the initial confined eruption of the middle flux rope. That confined eruption evidently triggers the first CME eruption. The lid-removal mechanism instigated by the first CME eruption plausibly triggers the second CME eruption. Further lid removal by the second CME eruption plausibly triggers the final CME eruption., Comment: 27 pages, 12 figures, Accepted for publication in ApJ Journal

We analyzed a small flux rope eruption converted into a helical blowout jet in a fan-spine configuration using multi-wavelength observations taken by SDO, which occurred near the limb on 2016 January 9. In our study, first, we estimated the fan-spine magnetic configuration with the potential field calculation and found a sinistral small filament inside it. The filament along with the flux rope erupted upward and interacted with the surrounding fan- spine magnetic configuration, where the flux rope breaks in the middle section. We observed compact brightening, flare ribbons and post-flare loops underneath the erupting filament. The northern section of the flux rope reconnected with the surrounding positive polarity, while the southern section straightened. Next, we observed the untwisting motion of the southern leg, which was transformed into a rotating helical blowout jet. The sign of the helicity of the mini-filament matches the one of the rotating jet. This is consistent with the jet models presented by Adams et al. (2014) and Sterling et al. (2015). We focused on the fine thread structure of the rotating jet and traced three blobs with the speed of 60-120 km/s, while the radial speed of the jet is approx 400 km/s. The untwisting motion of the jet accelerated plasma upward along the collimated outer spine field lines, and it finally evolved into a narrow coronal mass ejection at the height of approx 9 Rsun . On the basis of the detailed analysis, we discussed clear evidence of the scenario of the breaking of the flux rope and the formation of the helical blowout jet in the fan-spine magnetic configuration., Comment: 18 pages, 12 figures, Accepted for publication in MNRAS Jouranl

Correction to: Astrophys Space Sci (2017) 362:10 DOI There was an error in the sixth author’s name in the original publication. It is correctly shown here.

We analyze multi-wavelength and multi-viewpoint observations of a helically twisted plasma jet formed during a confined filament eruption on 10-11 April 2013. Given a rather large scale event with its high spatial and temporal resolution observations, it allows us to clearly understand some new physical details about the formation and triggering mechanism of twisting jet. We identify a pre-existing flux rope associated with a sinistral filament, which was observed several days before the event. The confined eruption of the filament within a null point topology, also known as an Eiffel tower (or inverted-Y) magnetic field configuration results in the formation of a twisted jet after the magnetic reconnection near a null point. The sign of helicity in the jet is found to be the same as that of the sign of helicity in the filament. Untwisting motion of the reconnected magnetic field lines gives rise to the accelerating plasma along the jet axis. The event clearly shows the twist injection from the pre-eruptive magnetic field to the jet.

Active region NOAA 11158 produced many flares during its disk passage. At least two of these flares can be considered as homologous: the C6.6 flare at 06:51 UT and C9.4 flare at 12:41 UT on February 14, 2011. Both flares occurred at the same location (eastern edge of the active region) and have a similar decay of the GOES soft X-ray light curve. The associated coronal mass ejections (CMEs) were slow (334 and 337 km/s) and of similar apparent widths (43deg and 44deg), but they had different radio signatures. The second event was associated with a metric type II burst while the first one was not. The COR1 coronagraphs on board the STEREO spacecraft clearly show that the second CME propagated into the preceding CME that occurred 50 min before. These observations suggest that CME-CME interaction might be a key process in exciting the type II radio emission by slow CMEs.

Utilizing multiwavelength observations and magnetic field data from SDO/AIA, SDO/HMI, GOES and RHESSI, we investigate a large-scale ejective solar eruption of 2014 December 18 from active region NOAA 12241. This event produced a distinctive three-ribbon flare, having two parallel ribbons corresponding to the ribbons of a standard two-ribbon flare, and a larger-scale third quasi-circular ribbon offset from the other two ribbons. There are two components to this eruptive event. First, a flux rope forms above a strong-field polarity-inversion line and erupts and grows as the parallel ribbons turn on, grow, and spread part from that polarity-inversion line; this evolution is consistent with the tether-cutting-reconnection mechanism for eruptions. Second, the eruption of the arcade that has the erupting flux rope in its core under goes magnetic reconnection at the null point of a fan dome that envelops the erupting arcade, resulting in formation of the quasi-circular ribbon; this is consistent with the breakout reconnection mechanism for eruptions. We find that the parallel ribbons begin well before (12 min) circular ribbon onset, indicating that tether-cutting reconnection (or a non-ideal MHD instability) initiated this event, rather than breakout reconnection. The overall setup for this large-scale (circular-ribbon diameter 100000 km) eruption is analogous to that of coronal jets (base size 10000 km), many of which, according to recent findings, result from eruptions of small-scale minifilaments. Thus these findings confirm that eruptions of sheared-core magnetic arcades seated in fan-spine null-point magnetic topology happen on a wide range of size scales on the Sun., 36 pages, 14 figures. Accepted for publication in ApJ

In this work, we present observations and interpretations of recurrent extreme ultraviolet (EUV) jets that occurred between 2012 July 1 21:00 UT and 2012 July 2 10:00 UT from the western edge of the NOAA active region 11513. Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA), SDO/Helioseismic and Magnetic Imager (SDO/HMI) and Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) observations have been used for the present study. Observations as well as potential-field source-surface (PFSS) extrapolation suggest an open field configuration in the vicinity of the jet activity area. 18 EUV jets were observed from the western edge of the active region along the open field channel. All the jet events appeared to be non-homologous and show different morphological properties and evolution. Some of the jets were small and narrow in size while the others were huge and wide. The average speed of these jets ranges from ${\sim}47\mbox{ to }{\sim}308~\mbox{km}\,\mbox{s}^{-1}$ . SDO/AIA 171 A intensity profiles at the base of these jets show bumps corresponding to each jet, which is an evidence of recurrent magnetic reconnections. The magnetic field observation at the foot points of the jets revealed a very complex and dynamic magnetic activity which includes flux emergence, flux cancellation, dynamic motions, merging, separation, etc. We suggest that the recurrent jets are the result of recurrent magnetic reconnections among the various emerging bipolar fields themselves as well as with the open fields.

Atypical flares cannot be naturally explained with standard models. To predict such flares, we need to define their physical characteristics, in particular, their magnetic environment, and identify pairs of reconnected loops. Here, we present in detail a case-study of a confined flare preceded by flux cancellation that leads to the formation of a filament. The slow rise of the non-eruptive filament favours the growth and reconnection of overlying loops. The flare is only of C5.0 class but it is a long duration event. The reason is that it is comprised of three successive stages of reconnection. A non-linear force-free field extrapolation and a magnetic topology analysis allow us to identify the loops involved in the reconnection process and build a reliable scenario for this atypical confined flare. The main result is that a curved magnetic polarity inversion line in active regions is a key ingredient for producing such atypical flares. A comparison with previous extrapolations for typical and atypical confined flares leads us to propose a cartoon for generalizing the concept, Comment: 32 pages, 17 figures, Accepted for publication in ApJ Journal

We present a comparative study of the properties of coronal mass ejections (CMEs) and flares associated with the solar energetic particle (SEP) events in the rising phases of solar cycles (SC) 23 (1996–1998) (22 events) and 24 (2009–2011) (20 events), which are associated with type II radio bursts. Based on the SEP intensity, we divided the events into three categories, i.e. weak (intensity This result is consistent with the asymmetry found with sunspot area and intense flares.

Emergence of complex magnetic flux in the solar active regions lead to several observational effects such as a change in sunspot area and flux embalance in photospheric magnetograms. The flux emergence also results in twisted magnetic field lines that add to free energy content. The magnetic field configuration of these active regions relax to near potential-field configuration after energy release through solar flares and coronal mass ejections. In this paper, we study the relation of flare productivity of active regions with their evolution of magnetic flux emergence, flux imbalance and free energy content. We use the sunspot area and number for flux emergence study as they contain most of the concentrated magnetic flux in the active region. The magnetic flux imbalance and the free energy are estimated using the HMI/SDO magnetograms and Virial theorem method. We find that the active regions that undergo large changes in sunspot area are most flare productive. The active regions become flary when the free energy content exceeds 50% of the total energy. Although, the flary active regions show magnetic flux imbalance, it is hard to predict flare activity based on this parameter alone.

This paper presents a correlative study between the peak values of geomagnetic activity indices (Dst, Kp, ap and AE) and the peak values of various interplanetary field (Bt, Bz, E and σ B ) and plasma (T, D, V, P and β ) parameters along with their various products (BV, BzV and B 2 V) during intense geomagnetic storms (GMSs) for rising, maximum and decay phases as well as for complete solar cycle 23. The study leads to the conclusion that the peak values of different geomagnetic activity indices are in good correlation with Bt, Bz, σ B , V, E, BV, BzV and B 2 V, therefore these parameters are most useful for predicting GMSs and substorms. These parameters are also reliable indicators of the strength of GMSs. We have also presented the lag/lead time analysis between the maximum of Dst and peak values of geomagnetic activity indices, various interplanetary field/plasma parameters for all GMSs. We have found that the average of peak values of geomagnetic activity indices and various field/plasma parameters are larger in decay phase compare to rising and maximum phases of cycle 23. Our analyses show that average values of lag/lead time lie in the ≈−4.00 h interval for Kp, ap and AE indices as well as for Bt, Bz, σ B , E, D and P. For a more meaningful analysis we have also presented the above study for two different groups G1 (CME-driven GMSs) and G2 (CIR-driven GMSs) separately. Correlation coefficients between various interplanetary field/plasma parameters, their various products and geomagnetic activity indices for G1 and G2 groups show different nature. Three GMSs and associated solar sources observed during three different phases of this solar cycle have also been studied and it is found that GMSs are associated with large flares, halo CMEs and their active regions are close to the solar equator.

This paper presents the study of normalized north–south asymmetry, cumulative normalized north–south asymmetry and cumulative difference indices of sunspot areas, solar active prominences (at total, low (⩽40°) and high (⩾50°) latitudes) and Hα solar flares from 1964 to 2008 spanning the solar cycles 20–23. Three different statistical methods are used to obtain the asymmetric behavior of different solar activity features. Hemispherical distribution of activity features shows the dominance of activities in northern hemisphere for solar cycle 20 and in southern hemisphere for solar cycles 21–23 excluding solar active prominences at high latitudes. Cumulative difference index of solar activity features in each solar cycle is observed at the maximum of the respective solar cycle suggesting a cyclic behavior of approximately one solar cycle length. Asymmetric behavior of all activity features except solar active prominences at high latitudes hints at the long term periodic trend of eight solar cycles. North–south asymmetries of SAP (H) express the specific behavior of solar activity at high solar latitudes and its behavior in long-time scale is distinctly opposite to those of other activity features. Our results show that in most cases the asymmetry is statistically highly significant meaning thereby that the asymmetries are real features in the N–S distribution of solar activity features.

A statistical study of different solar activity features (sunspot number, solar active prominences and Hα solar flares) with all India homogeneous rainfall (RF) is presented using 44 years (1963–2006) data. The correlation coefficient, significance of correlation coefficient and other statistical parameters are computed for the seasonal months of January–February (JF), March–April–May (MAM), June–July–August–September (JJAS), October–November–December (OND) and also annual. Correlation coefficient and its significance of two, four and six point moving average of RF with different solar activity features have also been calculated. A negative correlation is found between annual RF and solar activity features, and for sunspot number and solar flares with two, four and six point moving average of RF whereas moves from negative to positive for solar active prominences. Lag/lead analysis between RF and different solar activity features have also been analyzed and presented.

A study on North South (NS) asymmetry of different solar activity features (DSAF) such as solar proton events, solar active prominences, H alpha flare index, soft X ray flares, monthly mean sunspot area and monthly mean sunspot number were carried out from 1996 to 2008. It is found in our result that solar cycle 23 is magnetically weak compared to solar cycle 22. Study shows the Southern dominance of DSAF during the time period of study. During the rising phase of the cycle the numbers of DSAF approximately equal on the North and South Hemisphere. However, these activities tend to shift from Northern Hemisphere to Southern Hemisphere in between year 1998 to 1999. The statistical significance of the asymmetry time series using a chi square test of goodness of fit indicates that in most of the cases the asymmetry is highly significant, i.e., the asymmetry is a real feature in the NS distribution of DSAF., Comment: In this manuscript total 19 pages including 7 figures and 3 tables

We report and analyze the observational evidence of global kink oscillations in a solar filament as observed in H alpha by National Solar Observatory (NSO)/Global Oscillation Network Group (GONG) instrument. An M1.1-class flare in active region 11692 on 2013 March 15 induced a global kink mode in the filament lying in the south-west of AR11692.We find periods of about 61 - 67 minutes and damping times of 92 - 117 minutes at three vertical slice positions chosen in and around the filament apex. We find that the waves are damped. From the observed global kink mode period and damping time scale using the theory of resonant absorption we perform prominence seismology. We estimate a lower cut-off value for the inhomogeneity length-scale to be around 0.34 - 0.44 times the radius of the filament cross-section., 3 figures, Accepted for publication in RAA

We study the temporal, spatial and spectral evolution of the M1.8 flare, which occurred in NOAA AR 11195 (S17E31) on 22 April 2011, and explore the underlying physical processes during the precursors and their relation to the main phase. The study of the source morphology using the composite images in 131 {\deg}A wavelength observed by the SDO/AIA and 6-14 keV revealed a multiloop system that destabilized systematically during the precursor and main phases. In contrast, HXR emission (20-50 keV) was absent during the precursor phase, appearing only from the onset of the impulsive phase in the form of foot-points of emitting loop/s. This study has also revealed the heated loop-top prior to the loop emission, although no accompanying foot-point sources were observed during the precursor phase. We estimate the flare plasma parameters viz. T, EM, power-law index, and photon turn-over energy by forward fitting RHESSI spectral observations. The energy released in the precursor phase was thermal and constituted ~1 per cent of the total energy released during the flare. The study of morphological evolution of the filament in conjunction with synthesized T and EM maps has been carried out which reveals (a) Partial filament eruption prior to the onset of the precursor emission, (b) Heated dense plasma over the polarity inversion line and in the vicinity of the slowly rising filament during the precursor phase. Based on the implications from multi-wavelength observations, we propose a scheme to unify the energy release during the precursor and main phase emissions in which, the precursor phase emission has been originated via conduction front formed due to the partial filament eruption. Next, the heated leftover S-shaped filament has undergone slow rise and heating due to magnetic reconnection and finally erupted to produce emission during the impulsive and gradual phases., Comment: 16 Pages, 11 Figures, Accepted for Publication in MNRAS Main Journal

We report an observation of a partially erupting prominence and associated dynamical plasma processes based on observations recorded by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). The prominence first goes through a slow rise (SR) phase followed by a fast rise (FR). The slow rise phase started after a couple of small brightenings seen toward the footpoints. At the turning point from SR to FR, the prominence had already become kinked. The prominence shows strong brightening at the central kink location during the start of FR. We interpret this as internal magnetic reconnection occurring at a vertical current sheet forming between the two legs of the erupting prominence (flux-rope). The brightening at the central kink location is seen in all the EUV channels of AIA. The contributions of differential emission at higher temperatures are larger compared to that for typical coronal temperatures supporting a reconnection scenario at the central kink location. The plasma above the brightening location gets ejected as a hot plasmoid-like structure embedded in a CME, and those below drain down in the form of blobs moving towards the Sun's surface. The unique time resolution of the AIA has allowed all of these eruptive aspects, including SR-to-FR, kinking, central current sheet formation, plasmoid-like eruption, and filament "splitting", to be observed in a single event, providing strong and comprehensive evidence in favour of the model of partially erupting flux ropes., 16 pages, 5 figures, Accepted for Publication in ApJ

We use multiwavelength data from space and ground based instruments to study the solar flares and coronal mass ejections (CMEs) on January 23, 2012 that were responsible for one of the largest solar energetic particle (SEP) events of solar cycle 24. The eruptions consisting of two fast CMEs (1400 km/s and 2000 km/s) and M-class flares that occurred in active region 11402 located at N28 W36. The two CMEs occurred in quick successions, so they interacted very close to the Sun. The second CME caught up with the first one at a distance of 11-12 Rsun. The CME interaction may be responsible for the elevated SEP flux and significant changes in the intensity profile of the SEP event. The compound CME resulted in a double-dip moderate geomagnetic storm (Dst = -73 nT). The two dips are due to the southward component of the interplanetary magnetic field in the shock sheath and the ICME intervals. One possible reason for the lack of a stronger geomagnetic storm may be that the ICME delivered a glancing blow to Earth., 29 pages, 11 figures, Accepted for publication in ADSPR

Employing coronagraphic and EUV observations close to the solar surface made by the Solar Terrestrial Relations Observatory (STEREO) mission, we determined the heliocentric distance of coronal mass ejections (CMEs) at the starting time of associated metric type II bursts. We used the wave diameter and leading edge methods and measured the CME heights for a set of 32 metric type II bursts from solar cycle 24. We minimized the projection effects by making the measurements from a view that is roughly orthogonal to the direction of the ejection. We also chose image frames close to the onset times of the type II bursts, so no extrapolation was necessary. We found that the CMEs were located in the heliocentric distance range from 1.20 to 1.93 solar radii (Rs), with mean and median values of 1.43 and 1.38 Rs, respectively. We conclusively find that the shock formation can occur at heights substantially below 1.5 Rs. In a few cases, the CME height at type II onset was close to 2 Rs. In these cases, the starting frequency of the type II bursts was very low, in the range 25 to 40 MHz, which confirms that the shock can also form at larger heights. The starting frequencies of metric type II bursts have a weak correlation with the measured CME/shock heights and are consistent with the rapid decline of density with height in the inner corona., 14 pages, 4 figures, 2 tables, COSPAR 2012

We present the first observational evidence of the evolution of sausage-pinch instability in Active Region 11295 during a prominence eruption using data recorded on 12 September 2011 by the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO). We have identified a magnetic flux tube visible in AIA 304 \AA\ that shows curvatures on its surface with variable cross-sections as well as enhanced brightness. These curvatures evolved and thereafter smoothed out within a time-scale of a minute. The curved locations on the flux tube exhibit a radial outward enhancement of the surface of about 1-2 Mm (factor of 2 larger than the original thickness of the flux tube) from the equilibrium position. AIA 193 \AA\ snapshots also show the formation of bright knots and narrow regions inbetween at the four locations as that of 304 \AA\ along the flux tube where plasma emission is larger compared to the background. The formation of bright knots over an entire flux tube as well as the narrow regions in < 60 s may be the morphological signature of the sausage instability. We also find the flows of the confined plasma in these bright knots along the field lines, which indicates the dynamicity of the flux tube that probably causes the dominance of the longitudinal field component over short temporal scales. The observed longitudinal motion of the plasma frozen in the magnetic field lines further vanishes the formed curvatures and plasma confinements as well as growth of instability to stablize the flux tube., Comment: 12 pages, 5 figures

We present observations of interactions between the two filament channels of different chiralities and associated dynamics that occurred during 2014 April 18 -- 20. While two flux ropes of different helicity with parallel axial magnetic fields can only undergo a bounce interaction when they are brought together, the observations at the first glance show that the heated plasma is moving from one filament channel to the other. The SDO/AIA 171 A observations and the PFSS magnetic field extrapolation reveal the presence of fan-spine magnetic configuration over the filament channels with a null point located above them. Three different events of filament activations, partial eruptions, and associated filament channel interactions have been observed. The activation initiated in one filament channel seems to propagate along the neighbour filament channel. We believe that the activation and partial eruption of the filaments bring the field lines of flux ropes containing them closer to the null point and trigger the magnetic reconnection between them and the fan-spine magnetic configuration. As a result, the hot plasma moves along the outer spine line toward the remote point. Utilizing the present observations, for the first time we have discussed how two different-chirality filament channels can interact and show interrelation., Comment: 30 pages, 13 figures, Accepted for Publication in ApJ

The nature of various plausible causal links between sympathetic events is still a controversial issue. In this work, we present multi-wavelength observations of sympathetic eruptions, associated flares and coronal mass ejections (CMEs) occurring on 2013 November 17 in two close-by active regions. Two filaments i.e., F1 and F2 are observed in between the active regions. Successive magnetic reconnections, caused by different reasons (flux cancellation, shear and expansion) have been identified during the whole event. The first reconnection occurred during the first eruption via flux cancellation between the sheared arcades overlying filament F2, creating a flux rope and leading to the first double ribbon solar flare. During this phase we observed the eruption of overlaying arcades and coronal loops, which leads to the first CME. The second reconnection is believed to occur between the expanding flux rope of F2 and the overlying arcades of the filament F1. We suggest that this reconnection destabilized the equilibrium of filament F1, which further facilitated its eruption. The third stage of reconnection occurred in the wake of the erupting filament F1 between the legs of overlying arcades. This may create a flux rope and the second double ribbon flare and a second CME. The fourth reconnection was between the expanding arcades of the erupting filament F1 and the nearby ambient field, which produced the bi-directional plasma flows towards both upward and downward. Observations and a nonlinear force-free field extrapolation confirm the possibility of reconnection and the causal link between the magnetic systems., 37 pages, 17 figures, Accepted for publication in ApJ

Condition monitoring and fault diagnosis of equipment and processes are of great concern in industries. Early fault detection in machineries can save money in emergency maintenance cost. Therefore, it is necessary to fault detection of various parts of the machine. In this paper we present the detection of running speed frequency and bearing defect frequencies of an induction motor using vibration data through the wavelet transform and the Hilbert transform. Bearing defect frequencies are frequencies at which roller elements pass over a defect point. The analysis result shows that the proposed method can diagnose faulty bearing.

This paper presents a statistical analysis of Soft X-ray (SXR) flares during the period January 1976 to December 2007 covering solar cycles (SCs) 21, 22, and 23. We have analysed north-south (N-S) and east-west (E-W) asymmetry of SXR at low (less than equal to 40 degree), high (greater than equal to 50 degree) and total latitudes and center meridian distances (CMDs) respectively. We have also presented the N-S and E-W asymmetry of different intensity classes (B, C, M, and X) during the period of investigation. A slight southern and eastern excess is found after analysis during SC 21, 22, and 23. We found that the annual N-S and E-W hemispheric asymmetry at low latitudes and CMDs is the same as total latitudes and CMDs respectively. E-W asymmetry is different at low and high CMDs. Our statistical result shows that N-S asymmetry is statistically more significant than E-W asymmetry. Total SXR flare activity during SC 23 is high compared to SC 21 and 22. The B class flare activity is higher for SC 23 where as C, M and X class activities are higher for SC 21. We have also analysied the flare evolution parameters, i.e. duration, rise time, decay time and event asymmetry for total SXR as well as for different classes for last three SCs. The duration, rise time and decay time increase with increasing intensity class. On analysing event asymmetry indices, we found more positive values during SC 21 (64.86 per cent) and SC 22 (54.31 per cent), but for SC 23 we have more negative values (48.08 per cent). Our study shows that during SC 23 we have more SXR flare events having shorter decay time as compared to SC 21 and SC 22., 22 Pages, 14 figures, submitted to New Astronmy Journal

In this paper we present the results of a study of the spatial distribution and asymmetry of solar active prominences (SAP) for the period 1996-2007 (solar cycle 23). For more meaningful statistical analysis we have analysed the distribution and asymmetry of SAP in two subdivisions viz. Group1 (ADF, APR, DSF, CRN, CAP) and Group2 (AFS, ASR, BSD, BSL, DSD, SPY, LPS). The north-south (N-S) latitudinal distribution shows that the SAP events are most prolific in the 21-30degree slice in the northern and southern hemispheres and east-west (E-W) longitudinal distribution study shows that the SAP events are most prolific (best visible) in the 81-90degree slice in the eastern and western hemispheres. It has been found that the SAP activity during this cycle is low compared to previous solar cycles. The present study indicates that during the rising phase of the cycle the number of SAP events were roughly equal on the north and south hemispheres. However, activity on the southern hemisphere has been dominant since 1999. Our statistical study shows that the N-S asymmetry is more significant then the E-W asymmetry., 21 pages 5 figures; Published online; 02 October, 2009; Solar Physics Journal

We present the observations of compound flux rope formation via merging of two nearby filament channels, associated dynamics and its stability that occurred on 2014 January 1 using multiwavelength data. We have also discussed the dynamics of cool and hot plasma moving along the newly formed compound flux rope. The merging started after the interaction between the southern leg of northward filament and the northern leg of the southward filament at around 01:21 UT and continue until a compound flux rope formed at around 01:33 UT. During the merging the cool filaments plasma heated up and started to move along the both side of the compound flux rope i.e., toward north (approx 265 km/s) and south (approx 118 km/s) from the point of merging. After travelling a distance of approx 150 Mm towards north the plasma become cool and started to returns back towards south ( approx 14 km/s) after 02:00 UT. The observations provide an clear example of compound flux rope formation via merging of two different flux ropes and occurrence of flare through tether cutting reconnection. However, the compound flux rope remained stable in the corona and made an confined eruption. The coronal magnetic field decay index measurements revealed that both the filaments and the compound flux rope axis lies within the stability domain (decay index less than 1.5), which may be the possible cause for their stability. The present study also deals with the relationship between the filaments chirality (sinistral) and the helicity (positive) of the surrounding flux rope., Comment: 36 pages, 15 figures, accepted for publication in ApJ

We present observations of a confined partial eruption of a filament on 2012 August 4, which restores its initial shape within 2 hr after eruption. From the Global Oscillation Network Group Hα observations, we find that the filament plasma turns into dynamic motion at around 11:20 UT from the middle part of the filament toward the northwest direction with an average speed of 105 km s–1. A little brightening underneath the filament possibly shows the signature of low-altitude reconnection below the filament eruptive part. In Solar Dynamics Observatory/Atmospheric Imaging Assembly 171 A images, we observe an activation of right-handed helically twisted magnetic flux rope that contains the filament material and confines it during its dynamical motion. The motion of cool filament plasma stops after traveling a distance of 215 Mm toward the northwest from the point of eruption. The plasma moves partly toward the right foot point of the flux rope, while most of the plasma returns after 12:20 UT toward the left foot point with an average speed of 60 km s–1 to reform the filament within the same stable magnetic structure. On the basis of the filament internal fine structure and its position relative to the photospheric magnetic fields, we find filament chirality to be sinistral, while the activated enveloping flux rope shows a clear right-handed twist. Thus, this dynamic event is an apparent example of one-to-one correspondence between the filament chirality (sinistral) and the enveloping flux rope helicity (positive). From the coronal magnetic field decay index, n, calculation near the flux rope axis, it is evident that the whole filament axis lies within the domain of stability (i.e., n < 1), which provides the filament stability despite strong disturbances at its eastern foot point.

We present multi-wavelength observations of an asymmetric filament eruption and associated coronal mass ejection (CME) and coronal downflows on 2012 June 17 and 18 from 20:00-05:00?UT. We use SDO/AIA and STEREO-B/SECCHI observations to understand the filament eruption scenario and its kinematics, while LASCO C2 observations are analyzed to study the kinematics of the CME and associated downflows. SDO/AIA limb observations show that the filament exhibits a whipping-like asymmetric eruption. STEREO/EUVI disk observations reveal a two-ribbon flare underneath the southeastern part of the filament that most probably occurred due to reconnection processes in the coronal magnetic field in the wake of the filament eruption. The whipping-like filament eruption later produces a slow CME in which the leading edge and the core propagate, with an average speed of 540?km?s?1 and 126?km?s?1, respectively, as observed by the LASCO C2 coronagraph. The CME core formed by the eruptive flux rope shows outer coronal downflows with an average speed of 56?km?s?1 after reaching 4.33?R ?. Initially, the core decelerates at 48?m?s?2. The plasma first decelerates gradually up to a height of 4.33 R ? and then starts accelerating downward. We suggest a self-consistent model of a magnetic flux rope representing the magnetic structure of the CME core formed by an eruptive filament. This rope loses its previous stable equilibrium when it reaches a critical height. With some reasonable parameters, and inherent physical conditions, the model describes the non-radial ascending motion of the flux rope in the corona, its stopping at some height, and thereafter its downward motion. These results are in good agreement with observations.

A kind of misconceived debate has been going on in developing countries of the world as to whether economic growth can be achieved through capital-intensive or labour-intensive techniques of production or with an appropriate mixture of both. It is, however, not fully appreciated that more than making a choice for technology, there are certain bitter pills that have to be swallowed first.