A statistical study of the post-impulsive-phase acceleration of flare-associated coronal mass ejections

It is now generally accepted that the impulsive acceleration of a coronal mass ejection (CME) in the inner corona is closely correlated in time with the main energy release of the associated solar flare. In this paper, we examine in detail the post-impulsive-phase acceleration of a CME in the outer corona, which is the phase of evolution immediately following the main impulsive acceleration of the CME; this phase is believed to correspond to the decay phase of the associated flare. This observational study is based on a statistical sample of 247 CMEs that are associated with M- and X-class GOES soft X-ray flares from 1996 to 2006. We find that, from many examples of events, the CMEs associated with flares with long-decay time (or so-called long-duration flares) tend to have positive post-impulsive-phase acceleration, even though some of them have already obtained a high speed at the end of the impulsive acceleration but do not show a deceleration expected from the aerodynamic dragging of the background solar wind. On the other hand, the CMEs associated with flares of short-decay time tend to have significant deceleration. In the scattering plot of all events, there is a weak correlation between CME post-impulsive-phase acceleration and flare decay time. The CMEs deviated from the general trend are mostly slow or weak ones associated with flares of short-decay time; the deviation is caused by the relatively stronger solar wind dragging force for these events. The implications of our results on CME dynamics and CME-flare relations are discussed.Comment: 32 pages, 9 figures, accepted for publication in Ap

Solar and Interplanetary Sources of Major Geomagnetic Storms (Dst less than or equal to -100 nT) During 1996 - 2005

We present the results of an investigation of the sequence of events from the Sun to the Earth that ultimately led to the 88 major geomagnetic storms (defined by minimum Dst less than or equal to -100 nT) that occurred during 1996 - 2005. The results are achieved through cooperative efforts that originated at the Living with a Star (LWS) Coordinated Data- Analysis Workshop (CDAW) held at George Mason University in March 2005. Based on careful examination of the complete array of solar and in-situ solar wind observations, we have identified and characterized, for each major geomagnetic storm, the overall solar-interplanetary (solar-IP) source type, the time, velocity and angular width of the source coronal mass ejection (CME), the type and heliographic location of the solar source region, the structure of the transient solar wind flow with the storm-driving component specified, the arrival time of shock/disturbance, and the start and ending times of the corresponding IP CME (ICME). The storm-driving component, which possesses a prolonged and enhanced southward magnetic field (B(sub s)) may be an ICME, the sheath of shocked plasma (SH) upstream of an ICME, a corotating interaction region (CIR), or a combination of these structures. We classify the Solar-IP sources into three broad types: (1) S-type, in which the storm is associated with a single ICME and a single CME at the Sun; (2) M-type, in which the storm is associated with a complex solar wind flow produced by multiple interacting ICMEs arising from multiple halo CMEs launched from the Sun in a short period; (3) C-type, in which the storm is associated with a CIR formed at the leading edge of a high speed stream originating from a solar coronal hole (CH). For the 88 major storms, the S-type, M-type and C-type events number 53 (60%): 24 (27%) and 11 (13%), respectively. For the 85 events for which the surface source regions could be investigated, 54 (63%) of the storms originated in solar active regions, 10 (12%) in quiet Sun regions associated with quiescent filaments or filament channels, and 11 (13%) were associated with coronal holes. Remarkably, 10 (12%) CME-driven events showed no sign of eruptive features on the surface (e.g., no flare, no coronal dimming, and no loop arcade, etc), even though all the available solar observation in a suitable time period were carefully examined. Thus, while it is generally true that a major geomagnetic storm is more likely to be driven by a front-side fast halo CME associated with a major flare, our study indicates a broad distribution of source properties. The implications of the results for space weather forecasting are briefly discussed

Using "ghost front" to predict the arrival time and speed of CMEs at Venus and Earth

Using in-situ measurements and remote-sensing observations, we study two Coronal Mass Ejections (CMEs) that left the Sun on 13-14 June 2012 and impacted both Venus and Earth while the planets were in close radial alignment. The two CMEs generate multiple fronts in STEREO/HI images, which can also be observed in ‘J-map’ as bifurcated features. We present the ‘ghost front’ model to combine remote observations from STEREO/SECCHI and in-situ observations from the Wind and VEX spacecraft, and to derive the kinematics and propagation directions of the CMEs. By fitting the observations of multiple fronts to a kinematically evolving flux rope (KEFR) model and assuming the CMEs undergo deceleration through frictional drag with a steady-state solar wind, we confirm that the outer and inner fronts of the CMEs as detected in HI images are consistent with peaks in Thomson scattered light returned from the flank and nose of a single front for each CME. An interaction takes place between the CME-1 and CME-2 that can be observed in the HI-1 field of view before CME-1 encounters Venus. The multi-point in-situ observations of the shock-CME interaction event serve as further evidence of the interaction between CMEs. The arrival times calculated from the ghost-front model are within 2.5 hours of those observed at VEX and Wind. Our analysis indicates that ghost fronts could provide information about the longitudinally-extended shape of the CME in the field of view of HI-1, which can be used to improve the forecast of ICME arrival time at Earth

A Helicity-Based Method to Infer the CME Magnetic Field Magnitude in Sun and Geospace: Generalization and Extension to Sun-Like and M-Dwarf Stars and Implications for Exoplanet Habitability

Patsourakos et al. (Astrophys. J. 817, 14, 2016) and Patsourakos and Georgoulis (Astron. Astrophys. 595, A121, 2016) introduced a method to infer the axial magnetic field in flux-rope coronal mass ejections (CMEs) in the solar corona and farther away in the interplanetary medium. The method, based on the conservation principle of magnetic helicity, uses the relative magnetic helicity of the solar source region as input estimates, along with the radius and length of the corresponding CME flux rope. The method was initially applied to cylindrical force-free flux ropes, with encouraging results. We hereby extend our framework along two distinct lines. First, we generalize our formalism to several possible flux-rope configurations (linear and nonlinear force-free, non-force-free, spheromak, and torus) to investigate the dependence of the resulting CME axial magnetic field on input parameters and the employed flux-rope configuration. Second, we generalize our framework to both Sun-like and active M-dwarf stars hosting superflares. In a qualitative sense, we find that Earth may not experience severe atmosphere-eroding magnetospheric compression even for eruptive solar superflares with energies ~ 10^4 times higher than those of the largest Geostationary Operational Environmental Satellite (GOES) X-class flares currently observed. In addition, the two recently discovered exoplanets with the highest Earth-similarity index, Kepler 438b and Proxima b, seem to lie in the prohibitive zone of atmospheric erosion due to interplanetary CMEs (ICMEs), except when they possess planetary magnetic fields that are much higher than that of Earth.Comment: http://adsabs.harvard.edu/abs/2017SoPh..292...89

Virosome and ISCOM vaccines against Newcastle disease: preparation, characterization and immunogenicity

The purpose of this study was to prepare and characterize virosomes and ISCOMs containing envelope proteins of Newcastle disease virus (NDV) and to evaluate their immunogenicity in target animals (chickens). Virosomes were prepared by solubilization of virus with either Triton X-100 or octyl glucoside (OG) followed by detergent removal. Biochemical analysis revealed that these virosomes contained both the haemagglutinin-neuraminidase protein (HN) and the fusion protein (F), with preserved biological activity. Acidic environment triggered the fusion between virosomes and chicken erythrocyte ghosts. Formation of ISCOMs was achieved by solubilizing phospholipids, cholesterol, envelope protein antigen and Quil A in Triton X-100. The ISCOM particles were formed by removal of the detergent. In each formulation the relative HN content correlated with the capability to agglutinate red blood cells. The immunogenicity of these lipid-based subunit vaccines was determined in chickens after subcutaneous immunization. The relative HN content of the subunit vaccines correlated with the haemagglutination-inhibition (HI) antibody titres. Virosomes prepared with Triton X-100 and ISCOMs offered high clinical protection (> 80%) upon challenge with virulent NDV. Virosomes prepared with OG yielded lower clinical protection despite high HI antibody titres. Virosomes with reduced antigen density showed poor immunogenicity and protection. In conclusion, ND virosomes and ISCOMs were found to be immunogenic and provided good protection