Ooty Interplanetary Scintillation – Remote-Sensing Observations and Analysis of Coronal Mass Ejections in the Heliosphere

In this paper, I investigate the three-dimensional evolution of solar wind density and speed distributions associated with coronal mass ejections (CMEs). The primary solar wind data used in this study has been obtained from the interplanetary scintillation (IPS) measurements made at the Ooty Radio Telescope, which is capable of measuring scintillation of a large number of radio sources per day and solar wind estimates along different cuts of the heliosphere that allow the reconstruction of three-dimensional structures of propagating transients in the inner heliosphere. The results of this study are: i) three-dimensional IPS images possibly show evidence for the flux-rope structure associated with the CME and its radial size evolution; the overall size and features within the CME are largely determined by the magnetic energy carried by the CME. Such a magnetically energetic CME can cause an intense geomagnetic storm, even if the trailing part of the CME passes through the Earth; ii) IPS measurements along the radial direction of a CME at ～?120 R_⊙ show density turbulence enhancements linked to the shock ahead of the CME and the core of the CME. The density of the core decreases with distance, suggesting the expansion of the CME. However, the density associated with the shock increases with distance from the Sun, indicating the development of a strong compression at the leading edge of the CME. The increase of stand-off distance between ～?120 R_⊙ and 1 AU is consistent with the deceleration of the CME and the continued outward expansion of the shock. The key point in this study is that the magnetic energy possessed by the transient determines its radial evolution.     

Waiting Time Distribution of Coronal Mass Ejections

Inspired by the finding that the large waiting time of solar flares presents a power-law distribution, we investigate the waiting time distribution (WTD) of coronal mass ejections (CMEs). SOHO/LASCO CME observations from 1996 to 2003 are used in this study. It is shown that the observed CMEs have a similar power-law behavior to the flares, with an almost identical power-law index. This strongly supports the viewpoint that solar flares and CMEs are different manifestations of the same physical process. We have also investigated separately the WTDs of fast-type and slow-type CMEs and found that their indices are identical, which imply that both types of CME may originate from the same physical mechanism.     

Three-Dimensional Kinematics of Coronal Mass Ejections from STEREO/SECCHI-COR2 Observations in 2007 – 2008

We present a new method to perform the three dimensional characterization of coronal mass ejections (CMEs) using stereoscopic images obtained with the STEREO/SECCHI-COR2 coronagraphs. Two approaches are proposed, and each associated algorithm gives the trajectory of the CME and its kinematical properties (velocity and acceleration profiles) intended for space weather forecast. The first approach is based on forward modeling appropriate to the reconstruction of surfaces in an optically thin medium, and performs a local approximation of the observed CME by a hemispherical shell, thus tracking the leading edge of the event. The second approach is based on tracking the center of gravity of the radiance of the CME in the images. More than 16?000 blind tests have been performed to assess the performance of each algorithm. For that purpose, we used three distinct libraries of simulated images of CMEs that correspond to three CME models: hemispherical shell, flux rope, and cloud-like. The two methods are applied to a set of CMEs observed in 2007 and 2008 by the SECCHI-COR2 coronagraphs, and when possible, our results are compared to those already published. The determinations of the direction of propagation and of the velocity are generally found in good agreement.     

Sequential Coronal Mass Ejections from AR8038 in May 1997

Three homologous coronal mass ejections (CMEs) occurred on 5, 12 and 16 May 1997 from the single magnetic polarity inversion line (PIL) of AR8038. The three events together provide STEREO-like quadrature views of the 12 May 1997 CME and EIT double dimming. The recurrent CMEs with the nearly identical post-CME potential state and the ‘sigmoid to arcade to sigmoid’ transformations indicate a repeatable store?–?release?–?restore process of the free energy. How was the free magnetic energy re-introduced to the potential state corona after each release in this decaying active region? Making use of the known time interval bounded by the adjacent homologous CMEs, we made the following measures. The unsigned magnetic flux of AR8038, Φ_AR, decreased by approximately 18% during 66 h, while the unsigned flux, Φ_PIL, in a Gaussian-weighted PIL-region containing the flare site increased by about 50% during 36 hrs prior to the C1.3 flare on 12 May 1997. The significant increase of Φ_PIL demonstrates the magnetic gradient increase and the build-up of free energy in the PIL-region during the time leading to the eruption. Fourier local correlation tracking (FLCT) flow speed in AR8038 ranges from 0 to 292.8 m?s^?1 with a mean value of 63.2 m?s^?1. The flow field contains a persistent converging flow towards the flaring PIL and an effective shear flow distributed in the AR. Minor angular motions were found. An integrated proxy Poynting flux S _h estimates the energy input to the corona to be on the order of 1.15×10³² erg during the 66 hrs before the C1.3 flare. It suggests that sufficient energy for a flare/CME can be introduced to the corona on the order of several days by the flows deduced from photospheric magnetic field motions in this small decaying active region.     

Effect of Electron Pressure on the Grad–Shafranov Reconstruction of Interplanetary Coronal Mass Ejections

We investigate the effect of electron pressure on the Grad–Shafranov (GS) reconstruction of Interplanetary Coronal Mass Ejection (ICME) structures. The GS method uses in situ magnetic field and plasma measurements to solve for a magnetohydrostatic quasi-equilibrium state of space plasmas. For some events, a magnetic flux-rope structure embedded within the ICME can be reconstructed. The electron temperature contributes directly to the calculation of the total plasma pressure, and in ICMEs its contribution often substantially exceeds that of proton temperature. We selected ICME events observed with the Wind spacecraft at 1 AU and applied the GS reconstruction method to each event for cases with and without electron temperature measurements. We sorted them according to the proton plasma β (the ratio of proton plasma pressure to magnetic pressure) and the electron-to-proton temperature ratio. We present case studies of three representative events, show the cross sections of GS reconstructed flux-rope structure, and discuss the electron pressure contribution to key quantities in the numerical reconstruction procedure. We summarize and compare the geometrical and physical parameters derived from the GS reconstruction results for cases with and without electron temperature contribution. We conclude that overall the electron pressure effect on the GS reconstruction results contributes to a 10?–?20 % discrepancy in some key physical quantities, such as the magnetic flux content of the ICME flux rope observed at 1 AU.     

Energetics and Propagation of Coronal Mass Ejections in Different Plasma Environments

Based on previous work, we investigate the propagation of CMEs in a more realistic plasma environment than the isothermal atmosphere, and find that it is a slightly faster reconnection for flux ropes to break free. The average Alfven Mach number MA for the inflow into the reconnection site has to be at least 0.013 in order to give a plausible eruption (compared to MA = 0.005 for the isothermal atmosphere). Taking MA = 0.1, we find that the energy output and the electric field induced inside the current sheet match the temporal behavior inferred from the energetic, long duration, CME-associated X-ray events. The results indicate that catastrophic loss of equilibrium in the coronal magnetic field provides the most promising mechanism for major solar eruptions, and that the more energetic the eruption is, the earlier the associated flare peaks. The variation of the output power with the background field strength revealed by our calculations implies the poor correlation between slow CMEs and solar flares. Th     

Relative Kinematics of the Leading Edge and the Prominence in Coronal Mass Ejections

We present a statistical analysis of the relationship between the kinematics of the leading edge and the eruptive prominence in coronal mass ejections (CMEs). We study the acceleration phase of 18 CMEs in which kinematics was measured from the pre-eruption stage up to the post-acceleration phase. In all CMEs, the three part structure (the leading edge, the cavity, and the prominence) was clearly recognizable from early stages of the eruption. The data show a distinct correlation between the duration of the leading edge (LE) acceleration and eruptive prominence (EP) acceleration. In the majority of events (78%) the acceleration phase onset of the LE is very closely synchronized (within ± 20 min) with the acceleration of EP. However, in two events the LE acceleration started significantly earlier than the EP acceleration (> 50 min), and in two events the EP acceleration started earlier than the LE acceleration (> 40 min). The average peak acceleration of LEs (281 m s⁻²) is about two times larger than the average peak acceleration of EPs (136 m s⁻²). For the first time, our results quantitatively demonstrate the level of synchronization of the acceleration phase of LE and EP in a rather large sample of events, i.e., we quantify how often the eruption develops in a “self-similar” manner.     

Detection of Coronal Mass Ejections Using Multiple Features and Space–Time Continuity

Coronal Mass Ejections (CMEs) release tremendous amounts of energy in the solar system, which has an impact on satellites, power facilities and wireless transmission. To effectively detect a CME in Large Angle Spectrometric Coronagraph (LASCO) C2 images, we propose a novel algorithm to locate the suspected CME regions, using the Extreme Learning Machine (ELM) method and taking into account the features of the grayscale and the texture. Furthermore, space–time continuity is used in the detection algorithm to exclude the false CME regions. The algorithm includes three steps: i) define the feature vector which contains textural and grayscale features of a running difference image; ii) design the detection algorithm based on the ELM method according to the feature vector; iii) improve the detection accuracy rate by using the decision rule of the space–time continuum. Experimental results show the efficiency and the superiority of the proposed algorithm in the detection of CMEs compared with other traditional methods. In addition, our algorithm is insensitive to most noise.     

Different Periodicities in the Sunspot Area and the Occurrence of Solar Flares and Coronal Mass Ejections in Solar Cycle 23 – 24

In order to investigate the relationship between magnetic-flux emergence, solar flares, and coronal mass ejections (CMEs), we study the periodicity in the time series of these quantities. It has been known that solar flares, sunspot area, and photospheric magnetic flux have a dominant periodicity of about 155 days, which is confined to a part of the phase of the solar cycle. These periodicities occur at different phases of the solar cycle during successive phases. We present a time-series analysis of sunspot area, flare and CME occurrence during Cycle 23 and the rising phase of Cycle 24 from 1996 to 2011. We find that the flux emergence, represented by sunspot area, has multiple periodicities. Flares and CMEs, however, do not occur with the same period as the flux emergence. Using the results of this study, we discuss the possible activity sources producing emerging flux.     

Expected in Situ Velocities from a Hierarchical Model for Expanding Interplanetary Coronal Mass Ejections

In situ data provide only a one-dimensional sample of the plasma velocity along the spacecraft trajectory crossing an interplanetary coronal mass ejection (ICME). Then, to understand the dynamics of ICMEs it is necessary to consider some models to describe it. We derive a series of equations in a hierarchical order, from more general to more specific cases, to provide a general theoretical basis for the interpretation of in situ observations, extending and generalizing previous studies. The main hypothesis is a self-similar expansion, but with the freedom of possible different expansion rates in three orthogonal directions. The most detailed application of the equations is though for a subset of ICMEs, magnetic clouds (MCs), where a magnetic flux rope can be identified. The main conclusions are the following ones. First, we obtain theoretical expressions showing that the observed velocity gradient within an ICME is not a direct characteristic of its expansion, but that it depends also on other physical quantities such as its global velocity and acceleration. The derived equations quantify these dependencies for the three components of the velocity. Second, using three different types of data we show that the global acceleration of ICMEs has, at most, a small contribution to the in situ measurements of the velocity. This eliminates practically one contribution to the observed velocity gradient within ICMEs. Third, we provide a method to quantify the expansion rate from velocity data. We apply it to a set of 26 MCs observed by Wind or ACE spacecrafts. They are typical MCs, and their main physical parameters cover the typical range observed in MCs in previous statistical studies. Though the velocity difference between their front and back includes a broad range of values, we find a narrow range for the determined dimensionless expansion rate. This implies that MCs are expanding at a comparable rate, independently of their size or field strength, despite very different magnitudes in their velocity profiles. Furthermore, the equations derived provide a base to further analyze the dynamics of MCs/ICMEs.     

Magnetic Properties of Metric Noise Storms Associated with Coronal Mass Ejections

Using Nancay Radioheliograph (NRH) imaging observations, combined with SOHO/Michelson Doppler Imager (MDI) magnetogram observations and coronal magnetic field extrapolation, we studied the magnetic nature of metric noise storms that are associated with coronal mass ejections (CMEs). Four events are selected: the events of 2000 July 14, 2001 April 26, 2002 August 16 and 2001 March 28. The identified noise storm sources cover or partially cover the active regions (ARs), but the centers of storm sources are offset from the ARs. Using extrapolated magnetic field lines, we find that the noise storm sources trace the boundary between the open and closed field lines. We demonstrate that the disappearance of noise storm source is followed by the appearance of the burst source. The burst sources spread on the solar disk and their distributions correspond to the extent of the CME in LASCO C2 field of view. All the SOHO/Extreme Ultraviolet Imaging Telescope (EIT) dimmings associ- ated with noise storm sources are located at the periphery of noise storms where the magnetic lines of force were previously closed and low-lying. When the closed field becomes partially or fully open, the basic configurations of noise storm sources are changed, then the noise storm sources are no longer observed. These observations provide the information that the variations of noise storms manifest the restructuring or reconfiguring of the coronal magnetic field.     

Is the Asymmetric Cone Model for Halo Coronal Mass Ejections Correct?

A set of 106 limb CMEs which are wide and could be possible halo events, when directed towards Earth, are used to check the accuracy of the asymmetric cone model. For this purpose characteristics of CMEs (widths and radial speeds) measured for the possible halo CMEs are compared with these obtained for halo CMEs using the asymmetric cone model (Michalek, Solar Phys. 237, 101, 2006). It was shown that the width and speed distributions for both datasets are very similar and with a probability of p>0.93 (using the Kolmogorov – Smirnov test) were drawn from the same distribution of events. We also determined the accurate relationship between radial (V _rad) and expansion (V _exp) speeds of halo CMEs. This relation for the halo CMEs is simply V _rad=V _exp and could be very useful for space weather application.     

Rotational Quasi-Periodicities and the Sun – Heliosphere Connection

Mutual quasi-periodicities near the solar-rotation period appear in time series based on the Earth’s magnetic field, the interplanetary magnetic field, and signed solar-magnetic fields. Dominant among these is one at 27.03±0.02 days that has been highlighted by Neugebauer et al. (J. Geophys. Res. 105, 2315, 2000). Extension of their study in time and to different data reveals decadal epochs during which the ≈ 27.0 days, or a ≈ 28.3 days, or other quasi-periods dominate the signal. Space-time eigenvalue analyses of time series in 30 solar latitude bands, based on synoptic maps of unsigned photospheric fields, lead to two maximally independent modes that account for almost 30% of the data variance. One mode spans 45° of latitude in the northern hemisphere and the other one in the southern. The modes rotate around the Sun rigidly, not differentially, suggesting connection with the subsurface dynamo. Spectral analyses yield familiar dominant quasi-periods 27.04±0.03 days in the North and at 28.24±0.03 days in the South. These are replaced during cycle 23 by one at 26.45±0.03 days in the North. The modes show no tendency for preferred longitudes separated by ≈ 180°.     

Latitudinal Distribution of Solar Flares and Their Association with Coronal Mass Ejections

Major solar flare events have been utilised to study the latitudinal frequency distribution of solar flares in northern and southern hemispheres for the period of 1986 to 2003. A statistical analysis has been performed to obtain the correlation between Coronal Mass Ejections (CMEs) and Forbush decrease (Fds) of cosmic ray intensity. Almost the same flares distribution in both hemispheres is found in association with CMEs. In a further analysis, it is noted that a larger number of CME-associated solar flares located in the northern hemisphere are found to be more effective in producing Forbush decreases.     

Heliospheric Observations of STEREO-Directed Coronal Mass Ejections in 2008?–?2010: Lessons for Future Observations of Earth-Directed CMEs

We present a study of coronal mass ejections (CMEs) which impacted one of the STEREO spacecraft between January 2008 and early 2010. We focus our study on 20 CMEs which were observed remotely by the Heliospheric Imagers (HIs) onboard the other STEREO spacecraft up to large heliocentric distances. We compare the predictions of the Fixed-?? and Harmonic Mean (HM) fitting methods, which only differ by the assumed geometry of the CME. It is possible to use these techniques to determine from remote-sensing observations the CME direction of propagation, arrival time and final speed which are compared to in-situ measurements. We find evidence that for large viewing angles, the HM fitting method predicts the CME direction better. However, this may be due to the fact that only wide CMEs can be successfully observed when the CME propagates more than 100^° from the observing spacecraft. Overall eight CMEs, originating from behind the limb as seen by one of the STEREO spacecraft can be tracked and their arrival time at the other STEREO spacecraft can be successfully predicted. This includes CMEs, such as the events on 4 December 2009 and 9 April 2010, which were viewed 130^° away from their direction of propagation. Therefore, we predict that some Earth-directed CMEs will be observed by the HIs until early 2013, when the separation between Earth and one of the STEREO spacecraft will be similar to the separation of the two STEREO spacecraft in 2009??C?2010.     

Solar Flares and Coronal Mass Ejections: A Statistically Determined Flare Flux – CME Mass Correlation

In an effort to examine the relationship between flare flux and corresponding CME mass, we temporally and spatially correlate all X-ray flares and CMEs in the LASCO and GOES archives from 1996 to 2006. We cross-reference 6733 CMEs having well-measured masses against 12 050 X-ray flares having position information as determined from their optical counterparts. For a given flare, we search in time for CMEs which occur 10 – 80 minutes afterward, and we further require the flare and CME to occur within ± 45° in position angle on the solar disk. There are 826 CME/flare pairs which fit these criteria. Comparing the flare fluxes with CME masses of these paired events, we find CME mass increases with flare flux, following an approximately log-linear, broken relationship: in the limit of lower flare fluxes, log (CME mass)∝0.68×log (flare flux), and in the limit of higher flare fluxes, log (CME mass)∝0.33×log (flare flux). We show that this broken power-law, and in particular the flatter slope at higher flare fluxes, may be due to an observational bias against CMEs associated with the most energetic flares: halo CMEs. Correcting for this bias yields a single power-law relationship of the form log (CME mass)∝0.70×log (flare flux). This function describes the relationship between CME mass and flare flux over at least 3 dex in flare flux, from ≈ 10⁻⁷ – 10⁻⁴ W m⁻².     

Extension of fast periodic transfer orbits from the Earth–Moon RTBP to the Sun–Earth–Moon Quasi-Bicircular Problem

Starting from 80 families of low-energy fast periodic transfer orbits in the Earth–Moon planar circular Restricted Three Body Problem (RTBP), we obtain by analytical continuation 11 periodic orbits and 25 periodic arcs with similar properties in the Sun–Earth–Moon Quasi-Bicircular Problem (QBCP). A novel and very simple procedure is introduced giving the solar phases at which to attempt continuation. Detailed numerical results for each periodic orbit and arc found are given, including their stability parameters and minimal distances to the Earth and Moon. The periods of these orbits are between 2.5 and 5 synodic months, their energies are among the lowest possible to achieve an Earth–Moon transfer, and they show a diversity of circumlunar trajectories, making them good candidates for missions requiring repeated passages around the Earth and the Moon with close approaches to the last.     

Galactic Cosmic Ray Intensity Response to Interplanetary Coronal Mass Ejections/Magnetic Clouds in 1995 – 2009

We summarize the response of the galactic cosmic ray (CGR) intensity to the passage of the more than 300 interplanetary coronal mass ejections (ICMEs) and their associated shocks that passed the Earth during 1995 – 2009, a period that encompasses the whole of Solar Cycle 23. In ∼ 80% of cases, the GCR intensity decreased during the passage of these structures, i.e., a “Forbush decrease” occurred, while in ∼ 10% there was no significant change. In the remaining cases, the GCR intensity increased. Where there was an intensity decrease, minimum intensity was observed inside the ICME in ∼ 90% of these events. The observations confirm the role of both post-shock regions and ICMEs in the generation of these decreases, consistent with many previous studies, but contrary to the conclusion of Reames, Kahler, and Tylka (Astrophys. J. Lett. 700, L199, 2009) who, from examining a subset of ICMEs with flux-rope-like magnetic fields (magnetic clouds) argued that these are “open structures” that allow free access of particles including GCRs to their interior. In fact, we find that magnetic clouds are more likely to participate in the deepest GCR decreases than ICMEs that are not magnetic clouds.     

Spatial Structures of the North–South Asymmetry in the Green Coronal Line and Magnetic Fields

Astronomy Letters - The spatial distribution of the north–south (N–S) asymmetry over 1977–2001 is studied. A comparison of the distributions and time variations of the asymmetry...     

Hybrid Reconstruction to Derive 3D Height – Time Evolution for Coronal Mass Ejections

We present a hybrid combination of forward and inverse reconstruction methods using multiple observations of a coronal mass ejection (CME) to derive the three-dimensional (3D) “true” height?–?time plots for individual CME components. We apply this hybrid method to the components of the 31 December 2007 CME. This CME, observed clearly in both the STEREO A and STEREO B COR2 white-light coronagraphs, evolves asymmetrically across the 15-solar-radius field of view within a span of three hours. The method has two reconstruction steps. We fit a boundary envelope for the potential 3D CME shape using a flux-rope-type model oriented to best match the observations. Using this forward model as a constraining envelope, we then run an inverse reconstruction, solving for the simplest underlying 3D electron density distribution that can, when rendered, reproduce the observed coronagraph data frames. We produce plots for each segment to establish the 3D or “true” height?–?time plots for each center of mass as well as for the bulk CME motion, and we use these plots along with our derived density profiles to estimate the CME’s asymmetric expansion rate.