LASCO Field Of View Research Articles

Eruption of prominence initiated by loss of equilibrium: multipoint observations

ABSTRACT Using the SDO/AIA, SOHO/LASCO, STEREO/SECCHI, and ground-based H α, radio observations, we studied a prominence eruption (PE) from the western limb that occurred on 2013 December 4. PE is associated with a moderate coronal mass ejection (CME) and GOES class C4.7 flare. Before a couple of days, the prominence pre-existed as an inverse-S shaped filament lying above fragmented opposite polarities between two active regions. Initially, the prominence appears as kinked or writhed as observed from different vantage points. From a careful study of magnetic field observations, we infer that the flux emergence at one leg of the prominence causes the loss of equilibrium which then initiates the slow upward motion of the prominence followed by onset of the eruption at a projected height of 35 Mm. The fast rise motion is also in synchronization with the flare impulsive phase but the average acceleration is quite small (150 ms−2) compared to strong flare cases. In the LASCO field of view (FOV), the CME continues to accelerate at 3 ms−2 attaining a speed of 450 km s−1 at 16 R⊙. In the extended STEREO-A FOV upto 38 R⊙, the CME decelerates 0.82 m s−2. The PE launched type III bursts delayed by 14 min with respect to the flare peak time (04:58 UT). Since the prominence is lying in the fragmented polarities, it is likely that the sheared arcade has little contribution to the poloidal flux of the rising magnetic flux rope and subsequently weak flare is recorded. This study of PE emphasizes the influence of the magnetic reconnection on the CME speed, launch of type II, III burst, and the CME propagation distance farther away from the Sun.

Comparing the Features of Generation of CMEs Moving with Different Speed in the Field of View of the LASCO Coronagraphs

This study is aimed at finding an answer to the following question: are there any fundamental differences in the generation of coronal mass ejections (CMEs) with different speeds, especially low and high speeds, detected in the field of view of LASCO coronagraphs? Fast CMEs are conventionally understood as mass ejections with a linear projection velocity in LASCO field of view $${{V}_{{LIN}}}$$ > 1500 km/s; slow CMEs are those with $${{V}_{{LIN}}}$$ ≤ 600 km/s. CMEs with $${{V}_{{LIN}}}$$ between 600 and 1500 km/s are referred to as mass ejections with intermediate speed. The results of the analysis are presented by the example of three halo-type CME events (fast, slow, and intermediate) with sources in the sunspot groups removed from the center of the solar disk by no more than 45°. For analysis, we used data from SDO/AIA telescopes and the SDO/HMI instrument, as well as the LASCO C2 and C3 coronagraphs. The properties of active regions in which CMEs with different speeds have occurred are compared. The morphological features of the formation of the selected mass ejections based on the observations in the extreme ultraviolet lines are compared with features of their kinematics. Using the data of vector measurements of the photospheric magnetic field with the SDO/HMI instrument over the regions of CME formation, the altitude distributions of the magnetic field are calculated in the nonlinear force-free approximation. The analysis of these distributions showed that before the onset of a CME-related flare, the rate of altitude variation in the magnetic field above the CME generation site is noticeably different for all selected events.

Distinction in the Interplanetary Characteristics of Accelerated and Decelerated CMEs/Shocks

A set of 58 Coronal Mass Ejections (CMEs) with different kinematics near the sun in LASCO Field of view (FOV) is classified into two groups (i) CMEs which are accelerating (group-I) and (ii) CMEs which are decelerating (group-II). We analyze their interplanetary propagation characteristics to study the distinction between these two groups of events. Some of the following deviations are noted between the two groups as: (i) While group-II events have greater mean values of Standoff distance, Standoff time than the group-I events, the mean transit times of ICMEs and IP shocks are relatively lower for them. (ii) Group-II events are more (30%) radio-rich than the group-I (10%) and they are associated with type II solar radio burst in lower corona, (iii) The possibility of having excess magnetic energy that supports the propagation of CMEs to some extent is studied using estimated speed (VEST) and it is found that a slightly more number of events in group-I (48%) has VEST > VLASCO than group-II (33%). (iv) Net interplanetary acceleration is positive for 35% and 19% in group-I and group-II events respectively. (v) It is also found that ICME/IP shock characteristics of the two groups depend strongly on the CME acceleration.

Observational Study of an Earth-affecting Problematic ICME from STEREO

Abstract We present a study of the origin of one interplanetary coronal mass ejection (ICME) that lacked an easily identifiable signature of an associated progenitor coronal mass ejection (CME) near the Sun in the observations of SOHO/LASCO at the L1 point. We consider these kinds of ICMEs as problematic, as they pose the difficulty of understanding the Sun–Earth connection and providing space weather warnings; understanding the causes of problematic ICMEs is important for space weather forecasting. This study presents the first detailed analysis of a geoeffective problematic ICME that occurred on 2011 May 28, whose progenitor CMEs are difficult to identify in LASCO images, but fortunately they were captured by SECCHI on board the STEREO spacecraft in the quadrature configuration. There are two progenitor CMEs launching from the Sun in succession of 8 hours. We apply the graduated cylindrical shell model to reconstruct the 3D geometry, propagating direction, velocity, and brightness of the two CMEs. The main cause of the first CME (CME-1) invisible in SOHO/LASCO is due to its low mass; that is, when the CME emerges above the occulter, its brightness is as faint as the noise. The second CME (CME-2) is small, including a narrow angular width and a small cross-section of the magnetic flux rope. Even though propagating toward the Earth, CME-2 appeared as a narrow CME instead of as a halo or partial halo CME in the LASCO field of view. We also show that CME-2 propagates faster than CME-1, and that they might have interacted in the interplanetary space.

Characteristics of events with metric-to-decahectometric type II radio bursts associated with CMEs and flares in relation to SEP events

A gradual solar energetic particle (SEP) event is thought to happen when particles are accelerated at a shock due to a fast coronal mass ejection (CME). To quantify what kind of solar eruptions can result in such SEP events, we have conducted detailed investigations on the characteristics of CMEs, solar flares and m-to-DH wavelength type II radio bursts (herein after m-to-DH type II bursts) for SEP-associated and non-SEP-associated events, observed during the period of 1997-2012. Interestingly, 65% of m-to-DH type II bursts associated with CMEs and flares produced SEP events. The SEP-associated CMEs have higher sky-plane mean speed, projection corrected speed, and sky-plane peak speed than those of non-SEP-associated CMEs respectively by 30%, 39%, and 25%, even though the two sets of CMEs achieved their sky-plane peak speeds at nearly similar heights within LASCO field of view. We found Pearson's correlation coefficients between the speeds of CMEs speeds and logarithmic peak intensity of SEP events are cc = 0.62 and cc = 0.58, respectively. We also found that the SEP-associated CMEs are on average of three times more decelerated (-21.52 m/s2) than the non-SEP-associated CMEs (-5.63 m/s2). The SEP-associated m type II bursts have higher frequency drift rate and associated shock speed than those of the non-SEP-associated events by 70% and 25% respectively. The average formation heights of m and DH type II radio bursts for SEP-associated events are lower than for non-SEP-associated events. 93% of SEP-associated events originate from the western hemisphere and 65% of SEP-associated events are associated with interacting CMEs. The obtained results indicate that, at least for the set of CMEs associated with m-to-DH type II bursts, SEP-associated CMEs are more energetic than those not associated with SEPs, thus suggesting that they are effective particle accelerators.

Erratum to: Dynamics of CMEs in the LASCO Field of View

Erratum to: Dynamics of CMEs in the LASCO Field of View

Erratum to: Dynamics of CMEs in the LASCO Field of View – Statistical Analysis

Erratum to: Dynamics of CMEs in the LASCO Field of View – Statistical Analysis

Dynamics of CMEs in the LASCO Field of View

A large set (16 000) of coronal mass ejections (CMEs) observed during 1996 – 2011 was selected to study their dynamics in the LASCO field of view (LFOV). These events were selected based on the criterion that at least three height–time measurements were available for each CME. The height–time measurements included in the SOHO/LASCO catalog were used to determine velocities and accelerations of the respective CMEs at successive distances from the Sun. Next, these parameters were sorted into 30 subsamples depending on the distance from the Sun at which they were determined. The mean velocities and accelerations calculated for the successive distance-dependent subsamples of CMEs were used to study their dynamics. We demonstrate that CMEs in the LFOV manifest three distinct phases of propagation: (i) The propelling Lorentz force dominates the dynamics of CMEs in the inner (C2 LASCO) FOV, (ii) a stable propagation occurs as a result of the balance between the propelling and drag forces, (iii) the drag force dominates at the outer edge of the LFOV. When we considered different categories of CME separately, we found different acceleration–distance profiles for different categories.

Transit time of CME/shock associated with four major geo-effective CMEs in solar cycle 24

The kinematics of coronal mass ejection (CME) in the interplanetary medium is very important in the concept of space-weather. Main aim of this paper is to study the propagation of four major geo-effective CMEs and their associated shocks observed in solar cycle 24. The arrival of interplanetary shocks and CMEs of these events near the Earth is seen from the ACE/wind in situ data available in OMNI data base. The CMEs considered in this study have a wide range of initial speeds 500–1900km/s in the LASCO field of view, comprising of two slow CMEs (V∼500km/s), one fast CME (V∼1800km/s) and one moderate speed CME (V∼800km/s). The observed transit time of these events are compared with transit time estimated using the empirical shock arrival model (ESA). Especially, we utilize (i) different acceleration – speed equations reported in the literature from the observations made in the last few decades and (ii) various acceleration cessation distances (Acd) In addition, we compared the estimated and observed transit time with that from the Drag Based Model (DBM). From the result of this analysis, we demonstrated that each CME behaves in its own way in the interplanetary medium and their propagation is governed by the CME initial speed, interplanetary acceleration and acceleration cessation distances. In the present paper, we found (i) which acceleration equation is better for the transit time calculations (ii) importance of the CME acceleration cessation distances (iii) reducing the transit time error in CME forecasting. Based on these results and on Zhao and Dryer (2014) review (that included physics-based models), the realistic statistics should be based on real-time studies, not on post-mortem case studies.

Testing the asymmetric cone model for halo CMEs using STEREO/SECCHI coronagraphic observations

Space weather is significantly controlled by halo coronal mass ejections (HCMEs) originating close to the central meridian and directing toward the Earth. Unfortunately, coronagraphic observations (especially for HCMEs) are subject to a projection effect which makes it impossible to determine the true radial velocity and width of CMEs. However, these parameters can be estimated by correcting for the projection effect using the asymmetric cone model (Michalek, 2006). A set of 20 CMEs, observed as halo events in the LASCO field of view and simultaneously as limb events in the STEREO/SECCHI field of view, are used to check the accuracy of the asymmetric cone model. For this purpose, characteristics of the considered CMEs (angular widths and radial speeds) measured in STEREO/SECCHI images are compared with those obtained by the asymmetric cone model. We demonstrate that the widths and speeds determined by both methods are very similar. Correlation coefficients for speeds and angular widths are 0.99 and 0.96, respectively. We have also shown that the projection effect is unpredictable and could sometimes be very significant (up to 100% of the velocity measured in the LASCO field of view). On average, the SOHO/LASCO projected speeds for the HCMEs are 23% smaller than the radial velocities obtained from the STEREO/SECCHI images.

Study of interacting CMEs and DH type II radio bursts

The subject of interaction between the Corona Mass Ejections (CMEs) is important in the concept of space-weather studies. In this paper, we analyzed a set of 15 interacting events taken from the list compiled by Manoharan et al. (in J. Geophys. Res. 109:A06109, 2004) and their associated DH type II radio bursts. The pre and primary CMEs, and their associated DH type II bursts are identified using the SOHO/LASCO catalog and Wind/WAVES catalog, respectively. All the primary CMEs are associated with shocks and interplanetary CMEs. These CMEs are found to be preceded by secondary slow CMEs. Most of primary CMEs are halo type CME and much faster (Mean speed = 1205 km s−1) than the pre CME (Mean speed = 450 km s−1). The average delay between the pre and primary CMEs, drift rate of DH type IIs and interaction height are found to be 211 min, 0.878 kHz/s and 17.87 Ro, respectively. The final observed distance (FOD) of all pre CMEs are found to be less than 15 Ro and it is seen that many of the pre CMEs got merged with the primary CMEs, and, they were not traced as separate CMEs in the LASCO field of view. Some radio signatures are identified for these events in the DH spectrum around the time of interaction. The interaction height obtained from the height-time plots of pre and primary CMEs is found to have correlations with (i) the time delay between the two CMEs and (ii) the central frequency of emission in the radio signatures in the DH spectrum around the time of interaction. The centre frequency of emission in the DH spectrum around the time of interaction seems to decrease when the interaction height increases. This result is compared with an interplanetary density model of Saito et al. (in Solar Phys. 55:121, 1977).

Dynamics of CMEs in the LASCO Field of View – Statistical Analysis

A large set of CMEs (2207) has been selected to study their dynamics in the SOHO/LASCO field of view (LFOV). These selected events have at least seven height–time measurements and their acceleration can be determined separately in the C2 and C3 LFOVs. It was demonstrated that the balance between the aerodynamic drag and driving Lorentz forces may change during CME propagation in the LFOV. The drag force dominates the CME propagation close to the Sun (in the C2 LFOV), but farther from the Sun (in the C3 LFOV) the Lorentz force takes over the drag force. We also demonstrated that the acceleration of CMEs depends not only on their velocities but also on their masses and widths. Less massive CMEs (mass 3×1014 kg) are accelerated in the LFOV. Based on the acceleration behavior we are able to classify the observed events into four different types.

Coronal mass ejections—Propagation time and associated internal energy

In this paper, we analyze 91 coronal mass ejection (CME) events studied by Manoharan et al. (2004) and Gopalswamy and Xie (2008). These earth-directed CMEs are large (width > 160 ∘ ) and cover a wide range of speeds ( ∼ 120 – 2400 km s − 1 ) in the LASCO field of view. This set of events also includes interacting CMEs and some of them take longer time to reach 1 AU than the travel time inferred from their speeds at 1 AU. We study the link between the travel time of the CME to 1 AU (combined with its final speed at the Earth) and the effective acceleration in the Sun–Earth distance. Results indicate that (1) for almost all the events (85 out of 91 events), the speed of the CME at 1 AU is always less than or equal to its initial speed measured at the near-Sun region, (2) the distributions of initial speeds, CME-driven shock and CME speeds at 1 AU clearly show the effects of aero-dynamical drag between the CME and the solar wind and in consequence, the speed of the CME tends to equalize to that of the background solar wind, (3) for a large fraction of CMEs (for ∼ 50 % of the events), the inferred effective acceleration along the Sun–Earth line dominates the above drag force. The net acceleration suggests an average dissipation of energy ∼ 10 31 – 32 ergs, which is likely provided by the Lorentz force associated with the internal magnetic energy carried by the CME.

The radial width of a Coronal Mass Ejection between 0.1 and 0.4 AU estimated from the Heliospheric Imager on STEREO

Abstract. On 15–17 February 2008, a CME with an approximately circular cross section was tracked through successive images obtained by the Heliospheric Imager (HI) instrument onboard the STEREO-A spacecraft. Reasoning that an idealised flux rope is cylindrical in shape with a circular cross-section, best fit circles are used to determine the radial width of the CME. As part of the process the radial velocity and longitude of propagation are determined by fits to elongation-time maps as 252±5 km/s and 70±5° respectively. With the longitude known, the radial size is calculated from the images, taking projection effects into account. The radial width of the CME, S (AU), obeys a power law with heliocentric distance, R, as the CME travels between 0.1 and 0.4 AU, such that S=0.26 R0.6±0.1. The exponent value obtained is compared to published studies based on statistical surveys of in situ spacecraft observations of ICMEs between 0.3 and 1.0 AU, and general agreement is found. This paper demonstrates the new opportunities provided by HI to track the radial width of CMEs through the previously unobservable zone between the LASCO field of view and Helios in situ measurements.

DRIVING CURRENTS FOR FLUX ROPE CORONAL MASS EJECTIONS

We present a method for measuring electrical currents enclosed by flux rope structures that are ejected within solar coronal mass ejections (CMEs). Such currents are responsible for providing the Lorentz self-force that propels CMEs. Our estimates for the driving current are based on measurements of the propelling force obtained using data from the LASCO coronagraphs aboard the SOHO satellite. We find that upper limits on the currents enclosed by CMEs are typically around $10^{10}$ Amperes. We estimate that the magnetic flux enclosed by the CMEs in the LASCO field of view is a few $\times 10^{21}$ Mx.

The expansion of a coronal mass ejection within LASCO field of view: some regularities

AbstractForty five limb CMEs related with eruptive prominences and/or near-to-limb post-eruptive arcades have been tested. It is shown that CMEs can be divided into two groups. The first group includes coronal mass ejections whose “2α” latitude angular sizes apparent in the plane of the sky remain unchanged within measurement accuracy of several degrees. The second one is formed by CMEs that expand “non-radially”, namely, their angular sizes increase by the relative value (10-30)% up to the position of the ejection front RF = Rαm and run to the maximal value 2αm at this distance. It has been found that CMEs of the second type are, on the average, wider, faster and have an outer shell brighter and with higher plasma density for long distances. It is shown that on average Rαm increases as 2αm rises.

Investigation of CME dynamics in the LASCO field of view

Context. The speed-distance profile of CMEs is important for understanding the propagation of CMEs. Aims. Our main aim is to study the initial speed of CMEs in the LASCO field of view and its role in subsequent CME propagation using the acceleration-speed profile. The secondary aim is to obtain the speed growth rate. Methods. We considered the height-time data of 307 CMEs observed by SOHO/LASCO during January−March 2005. To study the CME speed profile, we used only 116 events for which there were at least 10 height-time measurements in the LASCO field of view. Using this data, we obtained their initial speed, extrapolated initial speed, and growth rate. Results. The following results were found from this analysis. (i) The initial speed obtained from the first two data points is in the range 24−1208 km s −1 , which is nearly similar to the range of linear speed (67−920 km s −1 ) obtained from a least squares fit through the entire h-t data set for each CME. (ii) However, the initial speed or extrapolated initial speed is much better correlated with acceleration and growth rate than the linear speed. (iii) Nearly two thirds of the events (74/116) are found to be accelerating. (iv) The speed growth rate is within the range −0.058 to 0.061 × 10 −3 s −1 , and it decreases with the distance. (v) The final observed distance in the LASCO field of view depends very weakly upon the initial speed, or extrapolated initial speed whereas it depends strongly on the linear speed. The above results demonstrate the role played by the initial speed of the CMEs.

On the Evolution of Coronal Mass Ejections in the Interplanetary Medium

Two coronal mass ejections (CMEs) are presented which were tracked through the LASCO field of view (FOV) within 30 R? and later as interplanetary CMEs (ICMEs) through the SMEI FOV from 80 to 150 R?. They were also associated with erupting filaments observed by EIT, providing information on trajectory of propagation. This allowed three-dimensional reconstructions of CME/ICME geometry, along with corrected (not sky plane projected) measurements of distance-time (DT) plots for each event to ~0.5 AU. An investigation of morphology was conducted. The results suggest that fine structures of the CMEs are eroded by the solar wind, and curvature becomes more sharply convex outward, suggesting that ICME footpoints remain fixed to the Sun even at 0.5 AU. We also present two models describing the evolution of CMEs/ICMEs at large distances from the Sun (far from the launch mechanism and effects of gravity and solar pressure) and consider two drag models: aerodynamic drag and snowplow. There was little difference between these, and their DT profiles matched well with the SMEI data for event 1. Event 2 showed a net acceleration between the LASCO and SMEI FOVs and we could match the data for this event well by introducing a driving Lorentz force. ICME mass almost doubled as a result of swept-up solar wind material from the snowplow model. Finally, we compared the geometry and kinematics of the ICME with that produced by the HAFv2 model and found that the model reasonably matched the geometry, but overestimated the ICME speed.

Are halo coronal mass ejections special events?

We revisited the properties of wide coronal mass ejections (CMEs) called halo CMEs. Using the large LASCO/SOHO CMEs data set, from 1996 to 2004, we examined the statistical properties of (partial and full) halo CMEs and compare with the same properties of “normal” width (lower than 120°) CMEs. We found that halo CMEs have different properties than “normal” CMEs, which cannot be explained merely by the current geometric interpretation that they are seen as halos because they are traveling in the Sun Earth direction. We found that the CME width distribution is formed by, at least, three different populations: Two gaussians: a narrow and a medium distribution centered at ∼17° and ∼38°, respectively; the narrow population most likely corresponds to the “true” observed widths, whereas the medium width population is the product of projection effects. The third distribution corresponds to wider CMEs (80° < W < 210°) which behaves as a power law. Partial and full halo CMEs wider than these do not follow any particular distribution. This lack of regularity may be due to the small number of such events. In particular, we found (and test by a statistical approach) that the number of observed full halo CMEs is lower than expected. The CME speed follows a log‐normal distribution, except for the very low speed CME population, which follows a gaussian distribution centered at ∼100 km/s and is probably due to projection effects. When the CMEs are divided by width into nonhalo, partial halo, and full halo, we found that the peaks of the distributions are shifted toward higher speeds, ∼300, ∼400 and ∼600 km/s for nonhalo, partial halo, and full halo CMEs, respectively. This confirms that halo CMEs tend to be high speed CMEs. The acceleration of full halo CMEs tends to be more negative compared with nonhalo and partial halo CMEs. We introduce a new observational CME parameter: The final observed distance (FOD), i.e., the highest point within the coronograph field of view where a CME can be distinguished from the background. In other words, the highest CME altitude measured. The FOD for nonhalo CMEs decreases exponentially from ∼5 to ∼30 R⊙ in the LASCO field of view. On the other hand, the FOD of halo CMEs increase with distance. This means that it is more likely to see halo CMEs at large distances (from the Sun) than nonhalo CMEs. These halo CME properties may be explained if the white light wide enhancements (or halo) seen by coronographs correspond to a combination of an expanding (shock) wave which disturbs and/or compresses the ambient material and the CME material itself.

Energetics of Coronal Mass Ejections

We examine the energetics of the best examples of flux-rope CMEs observed by LASCO in 1996-2001. We find that 69% of the CMEs in our sample experience a driving power in the LASCO field of view. For these CMEs which are driven, we examine if they might be deriving most of their driving energy by coupling to the solar wind. We do not find conclusive evidence to support this hypothesis. We adopt two different methods to estimate the energy that can possibly be released by the internal magnetic fields of the CMEs. We find that the internal magnetic fields are a viable source of driving power for these CMEs.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html