Spectrometric Coronagraph Experiment Research Articles

Hemispheric Distribution of Halo Coronal Mass Ejection Source Locations

The hemispheric asymmetry of solar activity is one of the essential physical consequences of the interior dynamo process. However, the hemispheric distribution of halo coronal mass ejection (HCME) source locations has not been investigated in detail. Based on the HCME catalog identified from the Large Angle and Spectrometric Coronagraph Experiment on board the Solar and Heliospheric Observatory, we perform a hemispheric distribution analysis of the HCME source locations from 1996 April to 2022 June. The main results are as follows. (1) The HCME source locations are confined to the active region belt, and there is no “rush to the poles” phenomenon that is unique to large-scale magnetic activity. (2) The HCME source locations exhibit a general hemispheric asymmetry, and autoregressive moving-average model results show that the asymmetry of HCME source locations is significantly different from that of sunspot activity. (3) The hemispheric distribution of cycle 24 is different from that of cycle 23, potentially as a result of the heliospheric dynamic pressure having noticeably decreased after the polarity reversal of cycle 23. Our results contribute to a more comprehensive understanding of the hemispheric asymmetry of energetic magnetic structures and give a new perspective on understanding the geoeffectiveness of HCMEs.

A Machine Learning Approach to Predicting SEP Events Using Properties of Coronal Mass Ejections

AbstractSolar energetic particles (SEPs) can cause severe damage to astronauts and their equipment, and can disrupt communications on Earth. A lack of thorough understanding the eruption processes of solar activities and the subsequent acceleration and transport processes of energetic particles makes it difficult to forecast the occurrence of an SEP event and its intensity using conventional modeling with physics‐based parameters. Therefore, in order to provide an advance warning for astronauts to seek shelter in a timely manner, we apply neural networks to forecast the occurrence of SEP events. We use the properties of coronal mass ejections (CMEs) archived in the Coordinated Data Analysis Workshops catalog based on SOHO Large Angle and Spectrometric Coronagraph Experiment observations. We also derive some features based on these properties associated with the CME, and analyze the contribution of each feature to the overall prediction. Our algorithm achieves an average True Skill Statistic of 0.906, an average F1 score of 0.246, an average probability of detection of 0.920, and an average false alarm rate of 0.882. An analysis of the features shows that sunspot number and a feature based on Type II radio bursts contribute the most, but when grouped together, CME speed‐related features are the most important features.

From Pseudostreamer Jets to Coronal Mass Ejections: Observations of the Breakout Continuum

Abstract The magnetic breakout model, in which reconnection in the corona leads to destabilization of a filament channel, explains numerous features of eruptive solar events, from small-scale jets to global-scale coronal mass ejections (CMEs). The underlying multipolar topology, pre-eruption activities, and sequence of magnetic-reconnection onsets (first breakout, then flare) of many observed fast CMEs/eruptive flares are fully consistent with the model. Recently, we demonstrated that most observed coronal-hole jets in fan/spine topologies also are induced by breakout reconnection at the null point above a filament channel (with or without a filament). For these two types of eruptions occurring in similar topologies, the key question is, why do some events generate jets while others form CMEs? We focused on the initiation of eruptions in large bright points/small active regions that were located in coronal holes and clearly exhibited null-point (fan/spine) topologies: such configurations are referred to as pseudostreamers. We analyzed and compared Solar Dynamics Observatory/Atmospheric Imaging Assembly, Solar and Heliospheric Observatory/Large Angle and Spectrometric Coronagraph Experiment, and Reuven Ramaty High Energy Solar Spectroscopic Imager observations of three events. Our analysis of the events revealed two new observable signatures of breakout reconnection prior to the explosive jet/CME outflows and flare onset: coronal dimming and the opening up of field lines above the breakout current sheet. Most key properties were similar among the selected erupting structures, thereby eliminating region size, photospheric field strength, magnetic configuration, and pre-eruptive evolution as discriminating factors between jets and CMEs. We consider the factors that contribute to the different types of dynamic behavior, and conclude that the main determining factor is the ratio of the magnetic free energy associated with the filament channel compared to the energy associated with the overlying flux inside and outside the pseudostreamer dome.

Automatic Coronagraph Image Classification with Machine Learning Methods

The detection of Coronal Mass Ejections (CMEs) is an important prerequisite for establishing a CME event database and realizing the prediction of CME interplanetary propagation. The Lyman-alpha Solar Telescope (LST) aboard the ASO-S (Advanced Space-based Solar Observatory) satellite will be equipped with a white-light coronagraph. The images with CME detected will be contributed to various space weather prediction centers in China for CME early warning. The Visual Geometry Group (VGG) 16 convolutional neural network method is applied by us to automatically and effectively classify coronagraph images. Firstly, based on the image of the white light coronagraph of Large Angle and Spectrometric Coronagraph Experiment (LASCO) C2, we labeled the images according to whether a CME is observed. Then, the data set was used for training the VGG model. We find that the accuracy of the model in the test set classification reaches 92.5%. Next, according to the obtained classification results and combined with the space-time continuity rules, we corrected the mislabeling of images, and derived our final CME image sequences. Compared with the manual CME catalog of Coordinated Data Analysis Workshops (CDAW), the classified CME image sequences can include CME data more completely, and have higher detection sensitivity for weak CME structures.

A Solar‐Centric Approach to Improving Estimates of Exposure Processes for Coronal Mass Ejections

We present a solar-centric approach to estimating the probability of extreme coronal mass ejections (CME) using the Solar and Heliospheric Observatory (SOHO)/Large Angle and Spectrometric Coronagraph Experiment (LASCO) CME Catalog observations updated through May 2018 and an updated list of near-Earth interplanetary coronal mass ejections (ICME). We examine robust statistical approaches to the estimation of extreme events. We then assume a variety of time-independent distributions fitting, and then comparing, the different probability distributions to the relevant regions of the cumulative distributions of the observed CME speeds. Using these results, we then obtain the probability that the velocity of a CME exceeds a particular threshold by extrapolation. We conclude that about 1.72% of the CMEs recorded with SOHO LASCO arrive at the Earth over the time both data sets overlap (November 1996 to September 2017). Then, assuming that 1.72% of all CMEs pass the Earth, we can obtain a first-order estimate of the probability of an extreme space weather event on Earth. To estimate the probability over the next decade of a CME, we fit a Poisson distribution to the complementary cumulative distribution function. We inferred a decadal probability of between 0.01 and 0.09 for an event of at least the size of the large 2012 event, and a probability between 0.0002 and 0.016 for the size of the 1859 Carrington event.

Three-dimensional Density Structure of a Solar Coronal Streamer Observed by SOHO/LASCO and STEREO/COR2 in Quadrature

Abstract Helmet streamers are a prominent manifestation of magnetic structures with current sheets in the solar corona. These large-scale structures are regions with high plasma density, overlying active regions and filament channels. We investigate the three-dimensional (3D) structure of a coronal streamer, observed simultaneously by white-light coronagraphs from two vantage points near quadrature (the Solar and Heliospheric Observatory (SOHO)/Large Angle and Spectrometric Coronagraph Experiment (LASCO) and the Solar Terrestrial Relations Observatory (STEREO)/Coronagraph 2 (COR2)). We design a forward model based on plausible assumptions about the 3D streamer structure taken from physical models (a plasma slab centered around a current sheet). The streamer stalk is approximated by a plasma slab, with an electron density that is characterized by three separate functions describing the radial, transverse, and face-on profiles, respectively. For the first time, we simultaneously fit the observational data from SOHO and STEREO using a multivariate minimization algorithm. The streamer plasma sheet contains a number of brighter and darker ray-like structures with the density contrast up to about a factor of 3 between them. The densities derived using polarized and unpolarized data are similar. We demonstrate that our model corresponds well to the observations.

An Atlas of Coronal Electron Density at 5R⊙. II. A Spherical Harmonic Method for Density Reconstruction

Abstract This is the second of a series of three papers that present a methodology with the aim of creating a set of maps of the coronal density over a period of many years. This paper describes a method for reconstructing the coronal electron density based on spherical harmonics. By assuming a radial structure to the corona at the height of interest, line-of-sight integrations can be made individually on each harmonic basis prior to determining coefficients, i.e., the computationally expensive integrations are calculated only once during initialization. This approach reduces the problem to finding the set of coefficients that best match the observed brightness using a regularized least-squares approach and is very efficient. The method is demonstrated on synthetic data created from both a simple and an intricate coronal density model. The quality of reconstruction is found to be reasonable in the presence of noise and large gaps in the data. The method is applied to both Large Angle and Spectrometric Coronagraph Experiment C2 and Solar Terrestrial Relations Observatory Cor2 coronagraph observations from 2009 March 20, and the results from both spacecraft compared. Future work will apply the method to large data sets.

Evolution of the Coronal Cavity From the Quiescent to Eruptive Phase Associated with Coronal Mass Ejection

Abstract We present the evolution of a coronal cavity encompassing its quiescent and eruptive phases in the lower corona. Using multiple vantage-point observations from the SDO/AIA, STEREO SECCHI/EUVI, and PROBA2/Sun Watcher with the APS and Image Processing (SWAP) extreme ultraviolet (EUV) imagers, we capture a sequence of quasi-static equilibria of the quiescent cavity, which exhibited a slow rise and an expansion phase during its passage on the solar disk from 2010 May 30 to June 13. By comparing the decay-index profiles of the cavity system during the different stages of its quiescent and pre-eruptive phases, we find that the decay-index value at the cavity centroid height can be used as a good indicator to predict the cavity eruption in the context of torus instability. Combining the observations of SWAP and the Large Angle and Spectrometric Coronagraph Experiment C2/C3, we show the evolution of the EUV cavity into the white-light cavity as a three-part structure of the associated coronal mass ejection that was observed to erupt on 2010 June 13. By applying successive geometrical fits to the cavity morphology, we find that the cavity exhibited non-self-similar expansion in the lower corona, below 2.2 ± 0.2 R S, which points to the spatial scale for the radius of the source surface where the coronal magnetic field lines are believed to become radial. Furthermore, the kinematic study of the erupting cavity captures both the “impulsive” and “residual” phases of acceleration along with a strong deflection of the cavity at 1.3 R S. We also discuss the role of driving forces behind the dynamics of the morphological and kinematic evolution of the cavity.

Three case studies of height-time profiles of prominence eruptions observed by AIA and LASCO

The motions of three solar eruptive prominences are studied. The behaviour of the rising prominence body during the eruption is tracked. Height-time profiles of the eruption up to 6 R⊙ (based on observations by Solar Dynamics Observatory/Atmospheric Imaging Assembly (HeII 304 Å) and Large Angle and Spectrometric Coronagraph Experiment (LASCO) C2/Solar and Heliospheric Observatory (SOHO)) and possible changes of the velocity of the prominence material are presented. The mechanisms that generate the variations in the material movement are discussed.

Is There a CME Rate Floor? CME and Magnetic Flux Values for the Last Four Solar Cycle Minima

Abstract The recent prolonged activity minimum has led to the question of whether there is a base level of the solar magnetic field evolution that yields a “floor” in activity levels and also in the solar wind magnetic field strength. Recently, a flux transport model coupled with magneto-frictional simulations has been used to simulate the continuous magnetic field evolution in the global solar corona for over 15 years, from 1996 to 2012. Flux rope eruptions in the simulations are estimated (Yeates), and the results are in remarkable agreement with the shape of the SOlar Heliospheric Observatory/Large Angle and Spectrometric Coronagraph Experiment coronal mass ejection (CME) rate distribution. The eruption rates at the two recent minima approximate the observed-corrected CME rates, supporting the idea of a base level of solar magnetic activity. In this paper, we address this issue by comparing annual averages of the CME occurrence rates during the last four solar cycle minima with several tracers of the global solar magnetic field. We conclude that CME activity never ceases during a cycle, but maintains a base level of 1 CME every 1.5 to ∼3 days during minima. We discuss the sources of these CMEs.

Global Energetics of Solar Flares. VI. Refined Energetics of Coronal Mass Ejections

Abstract In this study, we refine the coronal mass ejection (CME) model that was presented in an earlier study of the global energetics of solar flares and associated CMEs and apply it to all (860) GOES M- and X-class flare events observed during the first seven years (2010–2016) of the Solar Dynamics Observatory (SDO) mission. The model refinements include (1) the CME geometry in terms of a 3D volume undergoing self-similar adiabatic expansion, (2) the solar gravitational deceleration during the propagation of the CME, which discriminates between eruptive and confined CMEs, (3) a self-consistent relationship between the CME center-of-mass motion detected during EUV dimming and the leading-edge motion observed in white-light coronagraphs, (4) the equipartition of the CME’s kinetic and thermal energies, and (5) the Rosner–Tucker–Vaiana scaling law. The refined CME model is entirely based on EUV-dimming observations (using Atmospheric Imager Assembly (AIA)/SDO data) and complements the traditional white-light scattering model (using Large-Angle and Spectrometric Coronagraph Experiment (LASCO)/Solar and Heliospheric Observatory data), and both models are independently capable of determining fundamental CME parameters. Comparing the two methods, we find that (1) LASCO is less sensitive than AIA in detecting CMEs (in 24% of the cases), (2) CME masses below g are underestimated by LASCO, (3) AIA and LASCO masses, speeds, and energies agree closely in the statistical mean after the elimination of outliers, and (4) the CME parameters speed v, emission measure-weighted flare peak temperature T e , and length scale L are consistent with the following scaling laws: , , and .

Photometric and Statistical Analysis of Solar Energetic Particle (SEP) for the Peak of Solar Cycle 24

The major solar energetic particle events for the peak of solar cycle (24) for years (2012-2015) are analyzed by using the Energetic and Relativistic Nucleus and Electrons (ERNE) detectors and Large Angle and Spectrometric Coronagraph Experiment (LASCO) on board SOHO. It is found that the number of events which satisfies the required condition was 82 events. LASCO give information about Central Position Angle (CPA), Angular Width (AW), the speed of associated Coronal Mass Ejections (CMEs) and their basic features which cataloged in a data base SOHO/LASCO. The logarithmic intensity-time profile of SEP for the peak of solar cycle (24) was provided by ERNE, and from this profile the injection time, width, speed and onset time were estimated. All results that arise from these photometric analysis were statistically analyzed by using the statistical program SPSS (version 19). It have been concluded that 90% of these events were halo (360°) CPA, 1% of North West, 4% South West and 2% North East and South East, as well as it was found that 39% gradual events and 29% impulsive events while 32% were not clear events, and also the acceleration of the energetic particle is not only in the interplanetary but also in the location of the event. We found from the statistical analysis for these events that the acceleration is inversely proportional to speed and the relationship between them is not relevant and also the speed increase in two regions, from year 2012 and 2014. This confirms that the peak of solar cycle (24) really is double peak. All these investigations were employed as data base for the space agencies to protect the solar wind.

Characteristics of the motion of coronal mass ejections and related shocks depending on the heliocentric distance

The 3D characteristics of the coronal mass ejection (CME) body and shock at different distances (R) from the Sun’s center have been determined for several fast halo CMEs based on data from the Large Angle and Spectrometric Coronagraph Experiment (LASCO): the positions of the CME body boundary and the related shock on their axes, the directions and velocities of these points, the distance between a shock and the CME body boundary ΔR(R), and the difference between the velocities of these structures ΔV(R) and their angular dimensions. It was shown that the character of variations in the positions and velocities of the CME body boundary and a shock differs at different distances. The dependences of parameter [ΔR/Rcme](R), where Rcme is the curvature radius of the CME body boundary on the CME axis, were constructed. The obtained dependence was compared with the ΔR/Rcme (MA(R)) dependence. Here MA is the Alfven Mach number. The relation of ΔR/Rcme to MA was obtained by Russell and Mulligan (2002) for shocks in the Earth’s orbit. A comparison of [ΔR/Rcme](R) performed in two ways makes it possible to conclude that shocks related to a CME body are piston-like, with the CME body as a piston, at least at a distance of R > 10R0 (R0 is the solar radius).

ON THE ENHANCED CORONAL MASS EJECTION DETECTION RATE SINCE THE SOLAR CYCLE 23 POLAR FIELD REVERSAL

Coronal mass ejections (CMEs) with angular width $> 30^{\circ}$ have been observed to occur at a higher rate during solar cycle 24 compared to cycle 23, per sunspot number. This result is supported by data from three independent databases constructed using Large Angle and Spectrometric Coronagraph Experiment (LASCO) coronagraph images, two employing automated detection techniques and one compiled manually by human observers. According to the two databases that cover a larger field of view, the enhanced CME rate actually began shortly after the cycle 23 polar field reversal, in 2004, when the polar fields returned with a 40\% reduction in strength and interplanetary radial magnetic field became $\approx 30\%$ weaker. This result is consistent with the link between anomalous CME expansion and heliospheric total pressure decrease recently reported by Gopalswamy et al.

Photometric Analysis of CME in the rising phase of solar cycle 24

As world become more technologically advanced it become more important to study and forecast solar events which materialize by solar activity, the Sun goes through solar activity cycle, where every 11 year. In this investigation the highest position in the rising phase of solar cycle 24 had been studied by analyzing the photometric observations of coronal mass ejection (CME) for the year 2013 for the months 2,3,4,5that were derived from Large Angle and Spectrometric Coronagraph Experiment (LASCO), which is one of the scientific systems in the spacecraft Solar and Heliospheric Observatory (SOHO), that was located close Lagrangian point L1. From all previous observations and from the intensity time profile of it, the onset time had been calculated and from it the injection time of CMEhad been measured in order to find the lift of time and the associated flares. And also from the intensity-time profile any clear raising from background give indication for solar event, thus, the roots of the eruption in the sun will be determined.It had been concluded that The important event for this year in March and May also the acceleration of the energetic particle not only in the interplanetary, but also in the location of the event in the corona of the Sun, and it had been found that the event increased gradually with adopted months (2,3, 4, 5). Also it has been noticed that most of solar events have multi eruption phenomena.

EVOLUTION OF THE MAGNETIC HELICITY FLUX DURING THE FORMATION AND ERUPTION OF FLUX ROPES

We describe the evolution and the magnetic helicity flux for two active regions (ARs) since their appearance on the solar disk: NOAA 11318 and NOAA 11675. Both ARs hosted the formation and destabilization of magnetic flux ropes. In the former AR, the formation of the flux rope culminated in a flare of C2.3 GOES class and a coronal mass ejection (CME) observed by Large Angle and Spectrometric Coronagraph Experiment. In the latter AR, the region hosting the flux rope was involved in several flares, but only a partial eruption with signatures of a minor plasma outflow was observed. We found a different behavior in the accumulation of the magnetic helicity flux in the corona, depending on the magnetic configuration and on the location of the flux ropes in the ARs. Our results suggest that the complexity and strength of the photospheric magnetic field is only a partial indicator of the real likelihood of an AR producing the eruption of a flux rope and a subsequent CME.

KELVIN-HELMHOLTZ INSTABILITY OF A CORONAL STREAMER

The shear-flow-driven instability can play an important role in energy transfer processes in coronal plasma. We present for the first time the observation of a kink-like oscillation of a streamer probably caused by the streaming kinkmode Kelvin-Helmholtz instability. The wave-like behavior of the streamer was observed by Large Angle and Spectrometric Coronagraph Experiment (LASCO) C2 and C3 aboard SOlar and Heliospheric Observatory (SOHO). The observed wave had a period of about 70 to 80 minutes, and its wavelength increased from 2 Rsun to 3 Rsun in about 1.5 hours. The phase speeds of its crests and troughs decreased from 406 \pm 20 to 356 \pm 31kms^{-1} during the event. Within the same heliocentric range, the wave amplitude also appeared to increase with time. We attribute the phenomena to the MHD Kelvin-Helmholtz instability which occur at a neutral sheet in a fluid wake. The free energy driving the instability is supplied by the sheared flow and sheared magnetic field across the streamer plane. The plasma properties of the local environment of the streamer were estimated from the phase speed and instability threshold criteria.

THE EXPANSION OF ACTIVE REGIONS INTO THE EXTENDED SOLAR CORONA

Advanced image processing of Large Angle and Spectrometric Coronagraph Experiment (LASCO) C2 observations reveals the expansion of the active region closed field into the extended corona. The nested closed-loop systems are large, with an apparent latitudinal extent of 50 Degree-Sign , and expanding to heights of at least 12 R{sub Sun }. The expansion speeds are {approx}10 km s{sup -1} in the AIA/SDO field of view, below {approx}20 km s{sup -1} at 2.3 R{sub Sun }, and accelerate linearly to {approx}60 km s{sup -1} at 5 R{sub Sun }. They appear with a frequency of one every {approx}3 hr over a time period of around three days. They are not coronal mass ejections (CMEs) since their gradual expansion is continuous and steady. They are also faint, with an upper limit of 3% of the brightness of background streamers. Extreme ultraviolet images reveal continuous birth and expansion of hot, bright loops from a new active region at the base of the system. The LASCO images show that the loops span a radial fan-like system of streamers, suggesting that they are not propagating within the main coronal streamer structure. The expanding loops brighten at low heights a few hours prior to amore » CME eruption, and the expansion process is temporarily halted as the closed field system is swept away. Closed magnetic structures from some active regions are not isolated from the extended corona and solar wind, but can expand to large heights in the form of quiescent expanding loops.« less

Periodicity in the most violent solar eruptions: recent observations of coronal mass ejections and flares revisited

Using the Hilbert-Huang Transform method, we investigate the periodicity in the monthly occurrence numbers and monthly mean energy of coronal mass ejections (CMEs) observed by the Large Angle and Spectrometric Coronagraph Experiment on board the Solar and Heliographic Observatory from 1999 March to 2009 December. We also investigate the periodicity in the monthly occurrence numbers of Hα flares and monthly mean flare indices from 1996 January to 2008 December. The results show the following. (1) The period of 5.66 yr is found to be statistically significant in the monthly occurrence numbers of CMEs; the period of 10.5 yr is found to be statistically significant in the monthly mean energy of CMEs. (2) The periods of 3.05 and 8.70yr are found to be statistically significant in the monthly occurrence numbers of Hα flares; the period of 9.14yr is found to be statistically significant in the monthly mean flare indices.

CMEs FROM AR 10365: MORPHOLOGY AND PHYSICAL PARAMETERS OF THE EJECTIONS AND OF THE ASSOCIATED CURRENT SHEET

We study the evolution and physical parameters of three consecutive coronal mass ejections (CMEs) that occurred at the west limb of the Sun on 2003 June 2 at 00:30, 08:54, 16:08 UT, respectively. The Large Angle and Spectrometric Coronagraph Experiment (LASCO) CME catalog shows that the CMEs entered the C2 field of view with position angles within a 5° interval. This suggests a common origin for the ejections, to be identified with the magnetic system associated with the active region that lies below the CMEs. The close proximity in time and source location of the events prompted us to analyze LASCO white light data and Ultraviolet Coronagraph Spectrometer (UVCS) spectra with the aim of identifying similarities and differences among the three CMEs. It turns out that two of them display the typical three-part structure, while no conclusion can be drawn about the morphology of the third ejection. The CMEs plasma is cool, i.e., electron temperatures in the CMEs front are of the order of 2 × 105 K, with no significant variation between different events. However, ejection speeds vary by a factor of ~1.5 between consecutive events and electron densities (more precisely emission measures) by a factor of ~6 between the first CME and the second and third CMEs. In the aftermath of all events, we found evidence of current sheets (CSs) both in LASCO and UVCS. We give here the CS physical parameters (electron temperature, density, and kinetic temperature) and follow, in one of the events, their temporal evolution over a 6 hr time interval. A discussion of our results, in the framework of previous findings, concludes the paper.