Large Angle And Spectrometric Coronagraph Research Articles

Estimating Coronal Mass Ejection Mass and Kinetic Energy by Fusion of Multiple Deep-learning Models

Coronal mass ejections (CMEs) are massive solar eruptions, which have a significant impact on Earth. In this paper, we propose a new method, called DeepCME, to estimate two properties of CMEs, namely, CME mass and kinetic energy. Being able to estimate these properties helps better understand CME dynamics. Our study is based on the CME catalog maintained at the Coordinated Data Analysis Workshops Data Center, which contains all CMEs manually identified since 1996 using the Large Angle and Spectrometric Coronagraph (LASCO) on board the Solar and Heliospheric Observatory. We use LASCO C2 data in the period between 1996 January and 2020 December to train, validate, and test DeepCME through 10-fold cross validation. The DeepCME method is a fusion of three deep-learning models, namely ResNet, InceptionNet, and InceptionResNet. Our fusion model extracts features from LASCO C2 images, effectively combining the learning capabilities of the three component models to jointly estimate the mass and kinetic energy of CMEs. Experimental results show that the fusion model yields a mean relative error (MRE) of 0.013 (0.009, respectively) compared to the MRE of 0.019 (0.017, respectively) of the best component model InceptionResNet (InceptionNet, respectively) in estimating the CME mass (kinetic energy, respectively). To our knowledge, this is the first time that deep learning has been used for CME mass and kinetic energy estimations.

Numerical Simulation on the Leading Edge of Coronal Mass Ejection in the Near-Sun Region

The coronal mass ejections (CMEs) observed by white-light coronagraphs, such as the Large Angle and Spectrometric Coronagraph (LASCO) C2/C3, commonly exhibit the three-part structure, with the bright leading edge as the outermost part. In this work, we extend previous work on the leading edge by performing a large-scale 3D magnetohydrodynamic numerical simulation on the evolution of an eruptive magnetic flux rope (MFR) in a near-Sun region based on a radially stretched calculation grid in spherical coordination and the incorporation of solar wind. In the early stage, the new simulation almost repeats the previous results, i.e., the expanding eruptive MFR and associated CME bubble interact with the ambient magnetic field, which leads to the appearance of the helical current ribbon/boundary (HCB) wrapping around the MFR. The HCB can be interpreted as a possible mechanism of the CME leading edge. Later, the CME bubble propagates self-consistently to a larger region beyond a few solar radii from the solar center, similar to the early stage of evolution. The continuous growth and propagation of the CME bubbles leading to the HCB can be traced across the entire near-Sun region. Furthermore, we can observe the HCB in the white-light synthetic images as a bright front feature in the large field of view of LASCO C2 and C3.

Extracting the Heliographic Coordinates of Coronal Rays Using Images from WISPR/Parker Solar Probe

The Wide-field Imager for Solar Probe (WISPR) onboard Parker Solar Probe (PSP), observing in white light, has a fixed angular field of view, extending from 13.5 degree to 108 degree from the Sun and approximately 50 degree in the transverse direction. In January 2021, on its seventh orbit, PSP crossed the heliospheric current sheet (HCS) near perihelion at a distance of 20 solar radii. At this time, WISPR observed a broad band of highly variable solar wind and multiple coronal rays. For six days around perihelion, PSP was moving with an angular velocity exceeding that of the Sun. During this period, WISPR was able to image coronal rays as PSP approached and then passed under or over them. We have developed a technique for using the multiple viewpoints of the coronal rays to determine their location (longitude and latitude) in a heliocentric coordinate system and used the technique to determine the coordinates of three coronal rays. The technique was validated by comparing the results to observations of the coronal rays from Solar and Heliophysics Observatory (SOHO) / Large Angle and Spectrometric COronagraph (LASCO)/C3 and Solar Terrestrial Relations Observatory (STEREO)-A/COR2. Comparison of the rays' locations were also made with the HCS predicted by a 3D MHD model. In the future, results from this technique can be used to validate dynamic models of the corona.

Impacts of CMEs on Earth Based on Logistic Regression and Recommendation Algorithm

Coronal mass ejections (CMEs) are one of the major disturbance sources of space weather. Therefore, it is of great significance to determine whether CMEs will reach the earth. Utilizing the method of logistic regression, we first calculate and analyze the correlation coefficients of the characteristic parameters of CMEs. These parameters include central position angle, angular width, and linear velocity, which are derived from the Large Angle and Spectrometric Coronagraph (LASCO) images. We have developed a logistic regression model to predict whether a CME will reach the earth, and the model yields an F1 score of 30% and a recall of 53%. Besides, for each CME, we use the recommendation algorithm to single out the most similar historical event, which can be a reference to forecast CMEs geoeffectiveness forecasting and for comparative analysis.

Study of the Streamer Current Sheet with White-Light and UV Observations

Current sheets (CSs) are the main region where magnetic reconnections can convert magnetic energy into plasma thermal and kinetic energies. We have studied a CS in the streamer occurred on 3 January 2003 by combining the White-Light (WL) images observed by the Large Angle and Spectrometric Coronagraph (LASCO) and the EUV spectra detected by the Ultraviolet Coronagraph Spectrometer (UVCS). LASCO C2 WL data show that the speed of a blob in the CS increased from 60km·s−1 to 340km·s−1 with an acceleration of 60m·s−2 in its Field-of-View (FOV). By assuming the Light-of-Sight (LOS) depth of 0.3–1.5R⊙, the average electron number density of the CS is (1.52–7.60)×107cm−3 at the height of the UVCS slit. We investigate intensity distributions of the [Fexviii]974Å and Lyα lines along the UVCS slit. It is shown that the intensity of the [Fexviii] line at the CS is significantly higher than those of the surroundings, and the deduced electron temperature range of the CS is (2.94–4.04)×106K during the studied period. However, the intensity of the Lyα line at the CS does not change much when compared with those of the surroundings, and within the CS the intensity on both sides are slightly higher than that in the center. It is possible that the plasma move faster in the center resulting in stronger Doppler dimming effect. Using the observed intensity ratio of the Lyα and [Fexviii] lines provided by the UVCS and the calculated electron temperature as constraints, we find that the theoretically calculated emissivity ratio of the Lyα and [Fexviii] lines is close to their observed intensity ratio when the plasma speed range is 237–254km·s−1 at the position of the CS. The collisional component of the Lyα line is about 42%−57% of the radiative component in the CS within the speed range above. The streamer CS we studied has a higher plasma temperature and a faster blob speed than typical values in normal situations. The possible reason is that these two CMEs at the southern side enhanced the magnetic reconnection process in the CS, and more magnetic energy is released to heat and accelerate plasma. Our results on the CS can be regarded as pre-studies of the data analyses for the future mission of the Advanced Space-based Solar Observatory (ASO-S).

Multiwavelength Analysis of the Kinematics of a Long Duration Flare-CME Event on 27 January 2012

We present a detailed analysis of a long-duration flare associated with a coronal mass ejection (CME) event that occurred on 27 January 2012 in the active region (AR) 11402. We analyze the kinematics of the CME and the close relationship between the flare, radio burst, and CME. We used STEREO (Solar Terrestrial Relations Observatory)/EUVI A (Extreme Ultraviolet Imager) and white light data from STEREO (COR1 A and COR2 A) and LASCO (Large Angle and Spectrometric COronagraph) (C2/C3) coronagraphs, and X-ray data from the GOES (Geostationary Operational Environmental Satellite) spacecraft. The height of the CME is measured using the Graduated Cylindrical Shell (GCS) model. Our results show that: i) the speed of the CME (1460 km/s at $2.54~\mbox{R}_{\odot}$ ) is comparable to the speed of the type II radio burst (1581 km/s), ii) the height of the type II radio burst is lower than that of the CME leading edge, iii) the CME acceleration phase is found to be related to the rise time of the flare and its propagation phase is related to the decay phase of the flare, iv) the type II radio burst origin is likely to be near the CME region where a CME-streamer interaction takes place around $1.6~\mbox{R}_{\odot}$ , and v) the sequence of events and the CME kinematics show a close association between the CME and type II radio emissions.

A comparison of CME expansion speeds between solar cycles 23 and 24

We report on a comparison of the expansion speeds of limb coronal mass ejections (CMEs) between solar cycles 23 and 24. We selected a large number of limb CME events associated with soft X-ray flare size greater than or equal to M1.0 from both cycles. We used data and measurement tools available at the online CME catalog (https://cdaw.gsfc.nasa.gov) that consists of the properties of all CMEs detected by the Solar and Heliospheric Observatory’s (SOHO) Large Angle and Spectrometric Coronagraph (LASCO). We found that the expansion speeds in cycle 24 are higher than those in cycle 23. We also found that the relation between radial and expansion speeds has different slopes in cycles 23 and 24. The cycle 24 slope is 45% higher than that in cycle 23. The expansion speed is also higher for a given radial speed. The difference increases with speed. For a 2000 km/s radial speed, the expansion speed in cycle 24 is ∼48% higher. These results present additional evidence for the anomalous expansion of cycle 24-CMEs, which is due to the reduced total pressure in the heliosphere.

Kinematics of coronal mass ejections in the LASCO field of view

In this paper we present a statistical study of the kinematics of 28894 coronal mass ejections (CMEs) recorded by the Large Angle and Spectrometric Coronagraph (LASCO) on board the Solar and Heliospheric Observatory spacecraft from 1996 until mid-2017. The initial acceleration phase is characterized by a rapid increase in CME velocity just after eruption in the inner corona. This phase is followed by a non-significant residual acceleration (deceleration) characterized by an almost constant speed of CMEs. We demonstrate that the initial acceleration is in the range 0.24–2616 m s−2 with median (average) value of 57 m s−2 (34 m s−2) and it takes place up to a distance of about 28 RSUN with median (average) value of 7.8 RSUN (6 RSUN). Additionally, the initial acceleration is significant in the case of fast CMEs (V > 900 km s−1), where the median (average) values are about 295 m s−2 (251 m s−2), respectively, and much weaker in the case of slow CMEs (V < 250 km s−1), where the median (average) values are about 18 m s−2 (17 m s−2), respectively. We note that the significant driving force (Lorentz force) can operate up to a distance of 6 RSUN from the Sun during the first 2 hours of propagation. We found a significant anti-correlation between the initial acceleration magnitude and the acceleration duration, whereas the residual acceleration covers a range from −1224 to 0 m s−2 with a median (average) value of −34 m s−2 (−17 m s−2). One intriguing finding is that the residual acceleration is much smaller during the 24th cycle in comparison to the 23rd cycle of solar activity. Our study has also revealed that the considered parameters, initial acceleration (ACCINI), residual acceleration (ACCRES), maximum velocity (VMAX), and time at maximum velocity (TimeMAX) mostly follow solar cycles and the intensities of the individual cycle.

Relation between Coronal Mass Ejections and Sunspot Number during Solar Cycle 24

In this study, we report a statistical study for the relationship between coronal mass ejections (CMEs) and sunspot number (SSN) that were registered during the period 2008-2017 for the solar cycle 24. SSN was extracted from Sunspot Index and Long-term Solar Observations (SILSO), while CMEs number from observations made by the Large Angle and Spectrometric Coronagraph (LASCO) on board the Solar and Heliospheric Observatory mission (SOHO). The present period was adopted to conduct the investigation and obtain the mutual correlation between SSN and CMEs. The relationship between CME, the speed of halo CME, and partial halo CMEs for solar cycle 24 were studied. The analysis of results indicated that the average speed of halo CMEs is almost faster than the average speed of partial halo CMEs.Test results of the annual correlation between SSN and CMEs are simple and can be represented by a linear regression equation. Finally, Gaussian fit as a function of time was performed to compare behavior of numbers the CME and SSN with the years and the results show that the center of the peaks agrees with 2014.

Observations of a Flare-Generated Blast Wave in a Pseudo Coronal Mass Ejection Event

We present an analysis of the event near the east limb, SOL2014-03-06T09:23, in which a pseudo coronal mass ejection (CME) was detected by the Large Angle and Spectrometric Coronagraph (LASCO) C2 instrument and indicated as “Poor Event; Only C2” in the Solar and Heliospheric Observatory (SOHO) LASCO CME Catalog. The analysis was performed based on two main methods: 1) investigation of the difference brightness profiles along specific directions in the solar corona using the EUV observations by the Atmospheric Imaging Assembly (AIA) instrument onboard the Solar Dynamics Observatory (SDO); 2) investigation of the spatially-resolved observations of the type II radio bursts made with the Nancay Radioheliograph. Based on the analysis performed we argue that the observed pseudo-CME could be a blast wave caused by impulsive flare energy release in the low corona. We also argue that, in the limited height range of ${\approx}\,0.2 \mathrm{R_{\odot }}\,\mbox{--}\,0.5 \mathrm{R}_{\odot}$, the front of this blast wave could steepen into a shock front.

Shock location and CME 3D reconstruction of a solar type II radio burst with LOFAR

Context. Type II radio bursts are evidence of shocks in the solar atmosphere and inner heliosphere that emit radio waves ranging from sub-meter to kilometer lengths. These shocks may be associated with coronal mass ejections (CMEs) and reach speeds higher than the local magnetosonic speed. Radio imaging of decameter wavelengths (20–90 MHz) is now possible with the Low Frequency Array (LOFAR), opening a new radio window in which to study coronal shocks that leave the inner solar corona and enter the interplanetary medium and to understand their association with CMEs. Aims. To this end, we study a coronal shock associated with a CME and type II radio burst to determine the locations at which the radio emission is generated, and we investigate the origin of the band-splitting phenomenon. Methods. Thetype II shock source-positions and spectra were obtained using 91 simultaneous tied-array beams of LOFAR, and the CME was observed by the Large Angle and Spectrometric Coronagraph (LASCO) on board the Solar and Heliospheric Observatory (SOHO) and by the COR2A coronagraph of the SECCHI instruments on board the Solar Terrestrial Relation Observatory(STEREO). The 3D structure was inferred using triangulation of the coronographic observations. Coronal magnetic fields were obtained from a 3D magnetohydrodynamics (MHD) polytropic model using the photospheric fields measured by the Heliospheric Imager (HMI) on board the Solar Dynamic Observatory (SDO) as lower boundary. Results. The type II radio source of the coronal shock observed between 50 and 70 MHz was found to be located at the expanding flank of the CME, where the shock geometry is quasi-perpendicular with θBn ~ 70°. The type II radio burst showed first and second harmonic emission; the second harmonic source was cospatial with the first harmonic source to within the observational uncertainty. This suggests that radio wave propagation does not alter the apparent location of the harmonic source. The sources of the two split bands were also found to be cospatial within the observational uncertainty, in agreement with the interpretation that split bands are simultaneous radio emission from upstream and downstream of the shock front. The fast magnetosonic Mach number derived from this interpretation was found to lie in the range 1.3–1.5. The fast magnetosonic Mach numbers derived from modelling the CME and the coronal magnetic field around the type II source were found to lie in the range 1.4–1.6.

Gradual Streamer Expansions and the Relationship between Blobs and Inflows

Abstract Coronal helmet streamers show a continual tendency to expand outward and pinch off, giving rise to flux ropes that are observed in white light as “blobs” propagating outward along the heliospheric current/plasma sheet. The blobs form within the r ∼ 2–6 R ⊙ heliocentric range of the Large Angle and Spectrometric Coronagraph (LASCO) C2 instrument, but the expected inward-moving counterparts are often not detected. Here we show that the height of blob formation varies as a function of the underlying photospheric field, with the helmet streamer loops expanding to greater heights when active regions (ARs) emerge underneath them. When the pinch-offs occur at r ∼ 3–4 R ⊙, diverging inward/outward tracks sometimes appear in height–time maps constructed from LASCO C2 running-difference images. When the underlying photospheric field is weak, the blobs form closer to the inner edge of the C2 field of view and only the outward tracks are clearly visible. Conversely, when the emergence of large ARs leads to a strengthening of the outer coronal field and an increase in the total white-light radiance (as during late 2014), the expanding helmet-streamer loops pinch off beyond r ∼ 4 R ⊙, triggering strong inflow streams whose outgoing counterparts are usually very faint. We deduce that the visibility of the blobs and inflows depends on the amount of material that the diverging components sweep up within the 2–6 R ⊙ field of view. We also note that the rate of blob production tends to increase when a helmet streamer is “activated” by underlying flux emergence.

Determination of projection effects of CMEs using quadrature observations with the two STEREO spacecraft

Since 1995 coronal mass ejections (CMEs) have been routinely observed thanks to the sensitive Large Angle and Spectrometric Coronagraphs (LASCO) on board the Solar and Heliospheric Observatory (SOHO) mission. Their observed characteristics are stored, among other, in the SOHO/LASCO catalog. These parameters are commonly used in scientific studies. Unfortunately, coronagraphic observations of CMEs are subject to projection effects. This makes it practically impossible to determine the true properties of CMEs and therefore makes it more difficult to forecast their geoeffectiveness. In this study, using quadrature observations with the two Solar Terrestrial Relations Observatory (STEREO) spacecrafts, we estimate the projection effect affecting velocity of CMEs included in the SOHO/LASCO catalog. It was demonstrated that this effect depends significantly on width and source location of CMEs. It can be very significant for narrow events and originating from the disk center. The effect diminishes with increasing width and absolute longitude of source location of CMEs. For very wide (width ⩾ 250°) or limb events (|longitude ⩾ 70°) projection effects completely disappears.

Auto-detection of Halo CME Parameters as the Initial Condition of Solar Wind Propagation

Halo coronal mass ejections (CMEs) originating from solar activities give rise to geomagnetic storms when they reach the Earth. Variations in the geomagnetic field during a geomagnetic storm can damage satellites, communication systems, electrical power grids, and power systems, and induce currents. Therefore, automated techniques for detecting and analyzing halo CMEs have been eliciting increasing attention for the monitoring and prediction of the space weather environment. In this study, we developed an algorithm to sense and detect halo CMEs using large angle and spectrometric coronagraph (LASCO) C3 coronagraph images from the solar and heliospheric observatory (SOHO) satellite. In addition, we developed an image processing technique to derive the morphological and dynamical characteristics of halo CMEs, namely, the source location, width, actual CME speed, and arrival time at a 21.5 solar radius. The proposed halo CME automatic analysis model was validated using a model of the past three halo CME events. As a result, a solar event that occurred at 03:38 UT on Mar. 23, 2014 was predicted to arrive at Earth at 23:00 UT on Mar. 25, whereas the actual arrival time was at 04:30 UT on Mar. 26, which is a difference of 5 hr and 30 min. In addition, a solar event that occurred at 12:55 UT on Apr. 18, 2014 was estimated to arrive at Earth at 16:00 UT on Apr. 20, which is 4 hr ahead of the actual arrival time of 20:00 UT on the same day. However, the estimation error was reduced significantly compared to the ENLIL model. As a further study, the model will be applied to many more events for validation and testing, and after such tests are completed, on-line service will be provided at the Korean Space Weather Center to detect halo CMEs and derive the model parameters.

Comparison of CME and ICME Structures Derived from Remote-Sensing and In Situ Observations

We present results from the comparison of the near-Sun and in situ analysis of two Earth-directed coronal mass ejections (CMEs) with different 3D orientations and solar source region characteristics. The CME on 14 July 2000, the so-called Bastille Day storm, a well-studied event, was observed from a single-point perspective by the Large Angle and Spectrometric Coronagraph (LASCO) onboard the Solar and Heliospheric Observatory (SOHO). It caused a major geomagnetic storm with a peak Kp of 9. The CME originated from a magnetic bipolar photospheric source region with the polarity inversion line being oriented rather parallel to the heliographic equator. In contrast, the CME on 29 September 2013, which caused a geomagnetic storm with a peak Kp intensity of 8-, originated from a magnetic quadrupolar photospheric source region with the polarity inversion line between the two bipoles almost vertically oriented with respect to the heliographic equator. The results of a graduated cylindrical shell (GCS) analysis of the CMEs near the Sun are compared with the minimum variance analysis (MVA) of the magnetic field structure of the interplanetary CME (ICME) measured in situ near Earth’s orbit. The results are in good agreement for the September 2013 CME and ICME, whereas the July 2000 ICME appears substantially inclined near Earth’s orbit. The discrepancy can likely be explained taking into account kinks in the CME’s near-Sun structure of the CME that expands into the interplanetary medium.

Multi-label Learning for Detection of CME-Associated Phenomena

Coronal mass ejections (CMEs) are considered as one of the driving sources of space weather. They are usually associated with many physical phenomena, e.g. flares, coronal dimmings, and sigmoids. To detect these phenomena, traditional supervised-learning methods assumed that at most one event occurred in a CME; therefore each CME instance is associated with a single label and the phenomenon is processed in isolation. This simplifying assumption does not fit well, as CMEs might have multiple events simultaneously. We propose to detect multiple CME-associated events by multi-label learning methods. With the data available from the Atmospheric Imaging Assembly (AIA) and the Large Angle and Spectrometric Coronagraph (LASCO), texture features representing the events are extracted from all of the associated and not-associated CMEs and converted into feature vectors for multi-label learning use. Then a function is learned to predict the proper label sets for CMEs, such that eight events, i.e. coronal dimming, coronal hole, coronal jet, coronal wave, filament, filament eruption, flare, and sigmoid, are detected explicitly. To test the proposed detection algorithm, we adopt the four-fold cross-validation strategy on a set of 551 labeled CMEs from AIA. Experimental results demonstrate the good performance of the multi-label classification methods in terms of test error.

CME Velocity and Acceleration Error Estimates Using the Bootstrap Method

The bootstrap method is used to determine errors of basic attributes of coronal mass ejections (CMEs) visually identified in images obtained by the Solar and Heliospheric Observatory (SOHO) mission’s Large Angle and Spectrometric Coronagraph (LASCO) instruments. The basic parameters of CMEs are stored, among others, in a database known as the SOHO/LASCO CME catalog and are widely employed for many research studies. The basic attributes of CMEs (e.g. velocity and acceleration) are obtained from manually generated height-time plots. The subjective nature of manual measurements introduces random errors that are difficult to quantify. In many studies the impact of such measurement errors is overlooked. In this study we present a new possibility to estimate measurements errors in the basic attributes of CMEs. This approach is a computer-intensive method because it requires repeating the original data analysis procedure several times using replicate datasets. This is also commonly called the bootstrap method in the literature. We show that the bootstrap approach can be used to estimate the errors of the basic attributes of CMEs having moderately large numbers of height-time measurements. The velocity errors are in the vast majority small and depend mostly on the number of height-time points measured for a particular event. In the case of acceleration, the errors are significant, and for more than half of all CMEs, they are larger than the acceleration itself.

Two-Step Filament Eruption During 14 – 15 March 2015

We present here an interesting two-step filament eruption during 14-15 March 2015. The filament was located in NOAA AR 12297 and associated with a halo Coronal Mass Ejection (CME). We use observations from the Atmospheric Imaging Assembly (AIA) and Heliospheric Magnetic Imager (HMI) instruments onboard the Solar Dynamics Observatory (SDO), and from the Solar and Heliospheric Observatory (SOHO) Large Angle and Spectrometric Coronagraph (LASCO). We also use H-alpha data from the Global Oscillation Network Group (GONG) telescope and the Kanzelhoehe Solar Observatory. The filament shows a first step eruption on 14 March 2015 and it stops its rise at a projected altitude ~ 125 Mm on the solar disk. It remains at this height for ~ 12 hrs. Finally it eruptes on 15 March 2015 and produced a halo CME. We also find jet activity in the active region during both days, which could help the filament de-stabilization and eruption. The decay index is calculated to understand this two-step eruption. The eruption could be due to the presence of successive instability-stability-instability zones as the filament is rising.

Development of a Full Ice-cream Cone Model for Halo Coronal Mass Ejections

Abstract It is essential to determine three-dimensional parameters (e.g., radial speed, angular width, and source location) of coronal mass ejections (CMEs) for the space weather forecast. In this study, we investigate which cone type represents a halo CME morphology using 29 CMEs (12 Solar and Heliospheric Observatory (SOHO)/Large Angle and Spectrometric Coronagraph (LASCO) halo CMEs and 17 Solar Terrestrial Relations Observatory (STEREO)/Sun–Earth Connection Coronal and Heliospheric Investigation COR2 halo CMEs) from 2010 December to 2011 June. These CMEs are identified as halo CMEs by one spacecraft (SOHO or one of STEREO A and B) and limb ones by the other spacecraft (One of STEREO A and B or SOHO). From cone shape parameters of these CMEs, such as their front curvature, we find that the CME observational structures are much closer to a full ice-cream cone type than a shallow ice-cream cone type. Thus, we develop a full ice-cream cone model based on a new methodology that the full ice-cream cone consists of many flat cones with different heights and angular widths to estimate the three-dimensional parameters of the halo CMEs. This model is constructed by carrying out the following steps: (1) construct a cone for a given height and angular width, (2) project the cone onto the sky plane, (3) select points comprising the outer boundary, and (4) minimize the difference between the estimated projection speeds with the observed ones. By applying this model to 12 SOHO/LASCO halo CMEs, we find that 3D parameters from our method are similar to those from other stereoscopic methods (i.e., a triangulation method and a Graduated Cylindrical Shell model).

THE BLOB CONNECTION: SEARCHING FOR LOW CORONAL SIGNATURES OF SOLAR POST-CME BLOBS

ABSTRACT Bright linear structures, thought to be indicators of a current sheet (CS), are often seen in Large Angle and Spectrometric Coronagraph (LASCO) on the Solar and Heliospheric Observatory (SOHO) white-light data in the wake of coronal mass ejections (CMEs). In a subset of these post-CME structures, relatively bright blobs are seen moving outward along the rays. These blobs have been interpreted as consequences of the plasmoid instability in the CS, and can help us to understand the dynamics of the reconnection. We examine several instances, taken largely from the SOHO/LASCO CME-rays Catalog, where these blobs are clearly visible in white-light data. Using radially filtered, difference, wavelet enhanced, and multiscale Gaussian normalized images to visually inspect Solar Dynamics Observatory/Atmospheric Imaging Assembly (AIA) data in multiple wavelengths, we look for signatures of material that correspond both temporally and spatially to the later appearance of the blobs in LASCO/C2. Constraints from measurements of the blobs allow us to predict the expected count rates in DN pixel−1 s−1 for each AIA channel. The resulting values would make the blobs bright enough to be detectable at 1.2 R ⊙. However, we do not see conclusive evidence for corresponding blobs in the AIA data in any of the events. We do the same calculation for the “cartwheel CME,” an event in which blobs were seen in X-rays, and find that our estimated count rates are close to those observed. We suggest several possibilities for the absence of the EUV blobs including the formation of the blob higher than the AIA field of view, blob coalescence, and overestimation of blob densities.