Geoeffectiveness of the interplanetary manifestations of coronal mass ejections and solar-wind stream–stream interactions

Coronal mass ejections and high-speed streams from the Sun, and related structures formed and evolved in interplanetary space, i.e. interplanetary manifestations of CMEs (ICMEs) and stream interaction regions (SIRs)/corotating interaction regions (CIRs), are mainly responsible for geomagnetic disturbances in the Earth’s magnetic environment. However, the presence or absence of associated/finer structures of ICMEs (e.g., shock/sheath, magnetic cloud) and SIRs/CIRs (forward and reverse shocks, stream interface) might influence their geoeffectiveness as these features within large-scale structures of ICMEs and SIRs display different and varying plasma and field characteristics. In this work, we analyze the solar-wind plasma and field parameters (plasma velocity, density and pressure, magnetic field, its north-south component and electric field) together with geomagnetic activity parameters (kp and Dst), applying the method of superposed epoch analysis. By systematically changing the time of passage of different features as epochs, e.g. discontinuities/shocks, CMEs/magnetic clouds in ICMEs and discontinuities/forward shocks in SIRs/CIRs, we study the relative geoeffectiveness of not only the large-scale structures (ICMEs/SIRs/CIRs), but of their finer features also. We critically analyze the differences in geoeffectiveness due to different structures and features, with distinct plasma/field characteristics, and we utilize these results to understand the mechanism during their interaction with geospace.     

The evolution of two types of pulsars

We have discussed the evolution of two pulsar types suggested by Huanget al. (1985). Starting from the formulae given by them, we find that these two types of pulsars follow different evolutionary tracks, different structures, different average ages; and they are going to different graveyards. From these differences we may infer that the two pulsar types may have different progenitors.     

Simultaneous observations of second and sub-second time structures in H α , radio and hard X-ray data due to the periodical particle acceleration and MHD waves in the November 1, 2004 flare

Second and sub-second structures were simultaneously detected in optical, radio and hard X-ray (HXR) band, respectively by the GanYu Station of Purple Mountain Observatory, Nobeyama Radio Observatory, and RHESSI satellite in the November 1, 2004 flare (Ji et al., in Astrophys. J. 636:L173, 2006), which may be contributed to the energy transport of the continuous heat flux from the hot corona or chromosphere evaporation and of the accelerated electrons. The linear correlations between the amplitudes of these fluctuations and their flare emissions, and those between the cross-correlation coefficients of the fluctuations at two H _α kernels, or two radio frequencies, or two X-ray energies and their flare emissions may support the causal relationship of the flare and these time structures. While, the cross-correlations of the fluctuations at three different bands suggest that the fluctuations are caused by the common thermal or nonthermal processes in the flare. Moreover, some new features of the fluctuations are reported in the flare: (1) The sub-second fluctuations in radio and HXR bands have a same timescale, which is evidently larger than that in H-alpha band. The difference may be explained by the downward movements of nonthermal electrons or the upward motion of chromosphere evaporation. (2) The power-law distributions of the amplitudes of the second and the sub-second structures are obtained at optical, radio and HXR bands with different indices. (3) The peak-to-peak correspondence of Stokes I and V components in the sub-second structures at radio band suggests that they may be resulted from a periodical particle acceleration and particle injection in this event. However, the second structures may be caused by the modulations of Alfvén waves with an upward speed of 10³ km/s.     

Storm-intensity criteria for several classes of the driving interplanetary structures

In this paper we discuss the main-phase evolution of intense magnetic storms, associated with the passage of different interplanetary magnetic structures. It is shown that their evolution, driven by intense magnetic fields in the sheath region just behind interplanetary shocks, evolves faster (implying physically different magnetospheric configurations) than that associated with intense magnetic fields in the ejecta itself and in corotating streams. The estimated ring-current injection rate for the main phase of intense magnetic storms caused by sheath fields is ∼10 times greater than the estimated injection rate for N–S magnetic clouds. Based on these results, we propose storm-intensity criteria for several classes of the driving interplanetary structures. The time necessary to reach a Dst/SYM index threshold level is an important parameter for a space weather forecast.     

Fast Segmentation of Solar Extreme Ultraviolet Images

A segmentation scheme for identifying large-scale structures (coronal holes, active regions, etc.) in solar extreme ultraviolet images, is presented. Unlike standard approaches, both the image intensity and the relative contribution of different wavelengths are used. Spectral information is important for compensating luminosity changes. The approach is illustrated with images taken in the extreme ultraviolet by the EIT telescope onboard SOHO. This supervised segmentation scheme, which incorporates a Bayesian classifier, is computationally simple, and can easily be used to track in near-real time structures, such as coronal holes.     

CME Classification Based on Wavelet Spectra

We study the internal structure of coronal mass ejections (CMEs) using wavelet analysis. We derive wavelet spectra, spatially integrated over regions of interest within LASCO C2 white-light coronographic images. These spectra show an inflection point, which we use to characterize each spectrum. In a diagram of flux vs. spatial scale of the inflection point, we find that the analyzed structures fall into two, distinct groups: a low-flux, small-spatial-scale group (which we call the “homogeneous” type), and a high-flux, larger-spatial-scale group (the “collimated” type). Interestingly, if we study different regions of a given image, all of the structures fall into one of the two groups described above. From a qualitative comparison with the images, it is clear that the two groups identified by the wavelet analysis correspond to two types of morphologies, which are seen as either more-homogeneous or more-collimated structures.     

A Multiscale Vision Model applied to analyze EIT images of the solar corona

The large dynamic range provided by the SOHO/EIT CCD (1 : 5000) is needed to observe the large EUV zoom of coronal structures from coronal homes up to flares. Histograms show that often a wide dynamic range is present in each image. Extracting hidden structures in the background level requires specific techniques such as the use of the Multiscale Vision Model (MVM, Bijaoui et al., 1998). This method, based on wavelet transformations optimizes detection of various size objects, however complex they may be. Bijaoui et al. built the Multiscale Vision Model to extract small dynamical structures from noise, mainly for studying galaxies. In this paper, we describe requirements for the use of this method with SOHO/EIT images (calibration, size of the image, dynamics of the subimage, etc.). Two different areas were studied revealing hidden structures: (1) classical coronal mass ejection (CME) formation and (2) a complex group of active regions with its evolution. The aim of this paper is to define carefully the constraints for this new method of imaging the solar corona with SOHO/EIT. Physical analysis derived from multi-wavelength observations will later complete these first results. Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1017579625208 with J.P. Delaboudinière P.I.     

Signatures of recent star formation in ring S0 galaxies

We present a study of the stellar populations of ring and/or arm-like structures in a sample of S0 galaxies using GALEX far- and near-ultraviolet imaging and SDSS optical data. Such structures are prominent in the UV and reveal recent star formation. We quantitatively characterize these rejuvenation events, estimating the average age and stellar mass of the ring structures, as well as of the entire galaxy. The mass fraction of the UV-bright rings is a few percent of the total galaxy mass, although the UV ring luminosity reaches 70% of the galaxy luminosity. The integrated colors of these S0s locates them in the red sequence (NGC 2962) and in the so-called green valley. We suggest that the star formation episodes may be induced by different triggering mechanisms, such as the inner secular evolution driven by bars, and interaction episodes.     

Examining Periodic Solar-Wind Density Structures Observed in the SECCHI <Emphasis Type="Italic">Heliospheric Imagers</Emphasis>

We present an analysis of small-scale, periodic, solar-wind density enhancements (length scales as small as ≈ 1000 Mm) observed in images from the Heliospheric Imager (HI) aboard STEREO-A. We discuss their possible relationship to periodic fluctuations of the proton density that have been identified at 1 AU using in-situ plasma measurements. Specifically, Viall, Kepko, and Spence (J. Geophys. Res. 113, A07101, 2008) examined 11 years of in-situ solar-wind density measurements at 1 AU and demonstrated that not only turbulent structures, but also nonturbulent, periodic density structures exist in the solar wind with scale sizes of hundreds to one thousand Mm. In a subsequent paper, Viall, Spence, and Kasper (Geophys. Res. Lett. 36, L23102, 2009) analyzed the α-to-proton solar-wind abundance ratio measured during one such event of periodic density structures, demonstrating that the plasma behavior was highly suggestive that either temporally or spatially varying coronal source plasma created those density structures. Large periodic density structures observed at 1 AU, which were generated in the corona, can be observable in coronal and heliospheric white-light images if they possess sufficiently high density contrast. Indeed, we identify such periodic density structures as they enter the HI field of view and follow them as they advect with the solar wind through the images. The smaller, periodic density structures that we identify in the images are comparable in size to the larger structures analyzed in-situ at 1 AU, yielding further evidence that periodic density enhancements are a consequence of coronal activity as the solar wind is formed.     

Statistical properties of polarized radio continuum emission and effects of data processing

Polarized intensity and polarization angles are calculated from Stokes parameters Q and U in a nonlinear way. The statistical properties of polarized emission hold information about the structure of magnetic fields in a large range of scales, but the contributions of different stages of data processing to the statistical properties should first be understood. We use 1.4 GHz polarization data from the Effelsberg 100‐m telescope of emission in the Galactic plane, near the plane and far out of the plane. We analyze the probability distribution function and the wavelet spectrum of the original maps in Stokes parameters Q, U and corresponding PI. Then we apply absolute calibration (i.e. adding the large‐scale emission to the maps in Q and U), subtraction of polarized sources and subtraction of the positive bias in PI due to noise (“denoising”). We show how each procedure affects the statistical properties of the data. We find a complex behavior of the statistical properties for the different regions analyzed which depends largely on the intensity level of polarized emission. Absolute calibration changes the morphology of the polarized structures. The statistical properties change in a complex way: Compact sources in the field flatten the wavelet spectrum over a substantial range. Adding large‐scale emission does not change the spectral slopes in Q and U at small scales, but changes the PI spectrum in a complex way. “Denoising” significantly changes the p.d.f. of PI and raises the entire spectrum. The final spectra are flat in the Galactic plane due to magnetic structures in the ISM, but steeper at high Galactic latitude and in the anticenter. For a reliable study of the statistical properties of magnetic fields and turbulence in the ISM based on radio polarization observations, absolute calibration and source subtraction are required. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Tectonic Structure,Classification, and Evolution of Arachnoids on Venus: Preliminary Results

An analysis has been done of the topography and geologic structure of arachnoids—specific radial/concentric volcannic-tectonic structures on the surface of Venus. A representative sample (53 arachnoids) from 265 structures of this type, which are listed in the catalog of volcanic structures of the surface of Venus (Crumpler and Aubele, 2000), has been studied. The overwhelming majority of arachnoids are shown to be depressions that are commonly outlined by concentric extensional structures. Following Head et al. (1992) and Aittola and Kostama (2001), the assumption is confirmed and substantiated that arachnoids are formed by gravitational relaxation of small magmatic diapirs. Several types of arachnoids are identified on the basis of an analysis of structural patterns characteristic of such structures. It is also shown that the formation of different types of arachnoids depends on the depth of the magmatic diapir under the surface, on the thickness and reologic properties of the structures superposed on the evolving magmatic diapir, and on the character of regional stress fields that arise in the process of formation of such structures. The conclusion is drawn that most of the arachnoids were formed due to the gravitational relaxation of magmatic diapirs within the brittle part of the lithosphere, and some of them appeared as a result of the gravitational relaxation of radially fractured centers—novae. It is also shown that arachnoids are long-lived and multistep structures. At least some of them began to evolve before the formation of regional plains with wrinkle ridges, and their development ended after this event.     

Alfvén wave heating and acceleration of plasmas in the solar transition region producing jet-like eruptive activity

We present an analysis of observations and theory of selected transition-region phenomena, concentrating on small scale jet-like structures known as spicules and macrospicules. We examine a number of mechanisms that may be responsible for their formation and conclude that Alfvén waves could provide the necessary acceleration through the ponderomotive force and dissipation for heating forming a beam or jet like structure. In applying the Alfvén wave model we make no fundamental distinction between spicules and macrospicules. In this respect we consider them to be manifestations of the same phenomenon on different scales. We predict that the most effective Alfvén waves have frequencies around 1 Hz and amplitudes of 1 V m^–1. The resulting plasma jet sets up plasma conditions suitable for creating rotating structures which are also observed.     

Structure Properties of Supergranulation and Granulation

We investigate spatial dislocation ordering of the solar structures associated with supergranulation and granulation scales. The supergranular and granular structures are automatically segmented from time-distance divergence maps and from broad-band images, respectively. The spatial dislocation ordering analysis is accomplished by applying the statistical method of Pair Correlation Function, g ₂(r), to segmented features in the solar fields. We compare the computed g ₂(r) functions obtained from both single and persistent, i.e., time-averaged, fields associated with supergranulation and granulation. We conclude that supergranulation and granulation patterns present a different topological order both in single and persistent fields. The analysis carried out on single fields suggests that the granulation behaves as an essentially random distribution of soft plasma features with a very broad distribution in size, while supergranulation behaves as a random distribution of close packed, coherent stiff features with a rather defined mean size.     

The impact cratering record of Fennoscandia

The current database of craterform structures in Fennoscandia contains 22 structures of impact origin and about fifty other structures which lack sufficient evidence for impact. The discovery rate of new structures has been one or two per year during the past ten years. The proven impact structures are located in southern Fennoscandia and the majority have been found in Proterozoic target rocks. The age of the structures varies from prehistoric to 1000 Ma and their diameters (D) from 0.04 km to 55 km. Nine of the structures contain impact melt. A characteristic feature of the Fennoscandian impact record is a relatively large number of small ( 5 km) but old (> 200 Ma) structures: this is a result of success of geophysical methods to discover small but old impact structures in an eroded shield covered with relatively thin overburden. Some of the large circular structures in satellite images and/or in geophysical maps may represent deeply eroded scars of very old impacts, but due to the lack of shock metamorphic features, impact-generated rocks or identified ejecta layers, they cannot yet be classified as impact sites. Two huge structures are proposed here as possible impact sites on the basis of circular satellite images and distinct geophysical anomalies: the Lycksele structure in northern Sweden (D ~ 120 km, see also Witschard, 1984) and the Valga structure in Latvia/Estonia (D ~ 180 km). However, endogeneous explanations, like buried granites, basement domings, or fault-bounded blocks are also possible for these structures. Hints, such as distal ejecta layers or impact produced breccia dykes, of an Archaean or Early Proterozoic impact structure have not been found in Fennoscandia so far. New ways of searching for these structures are proposed with particular emphasis on high-resolution integrated geophysical methods. The impact cratering rate in Fennoscandia is ~ 2.0 · 10^–14 km^–2 a^–1 (for craters with D > 3 km) corresponding to about two events per every 100 Ma for the last 700 Ma. Due to erosion, this is a minimal estimate but is higher than the global rate probably due to strong research activity for finding impact structures in Fennoscandia.     

Fine structures of chromospheric magnetic field and material flow in a solar active region

In this paper, we analyze the relations between photospheric vector magnetic fields, chromospheric longitudinal magnetic fields and velocity fields in a solar active region. Agreements between the photospheric and chromospheric magnetograms can be found in large-scale structures or in the stronger magnetic structures, but differences also can be found in the fine structures or in other places, which reflect the variation of the magnetic force lines from the photosphere to the chromosphere. The chromospheric superpenumbral magnetic field, measured by the Hline, presents a spoke-like structure. It consists of thick magnetic fibrils which are different from photospheric penumbral magnetic fibrils. The outer superpenumbral magnetic field is almost horizontal. The direction of the chromospheric magnetic fibrils is generally parallel to the transverse components of the photospheric vector magnetic fields. The chromospheric material flow is coupled with the magnetic field structure. The structures of the H chromospheric magnetic fibrils in the network are similar to H dark fibrils, and the feet of the magnetic fibrils are located at the photospheric magnetic elements.     

Steerable wavelet analysis of CMB structures alignment

This paper reviews the application of a novel methodology for analysing the isotropy of the universe by probing the alignment of local structures in the CMB. The strength of the proposed methodology relies on the steerable wavelet filtering of the CMB signal. One the one hand, the filter steerability renders the computation of the local orientation of the CMB features affordable in terms of computation time. On the other hand, the scale-space nature of the wavelet filtering allows to explore the alignment of the local structures at different scales, probing possible different phenomena. We present the WMAP first-year data analysis recently performed by the same authors (Wiaux et al.), where an extremely significant anisotropy was found. In particular, a preferred plane was detected, having a normal direction with a northern end position at (θ, ) = (34°, 331°), close to the northern end of the CMB dipole axis. In addition, a most preferred direction was found in that plane, with a northern end direction at (θ, ) = (71°, 91°), very close to the north ecliptic pole. This result synthesised for the first time previously reported anomalies identified in the direction of the dipole and the ecliptic poles axes. In a forthcoming paper (Vielva et al.), we have extended our analysis to the study of individual frequency maps finding first indications for discarding foregrounds as the origin of the anomaly. We have also tested that the preferred orientations are defined by structures homogeneously distributed in the sky, rather than from localised regions. We have also analysed the WMAP 3-year data, finding the same anomaly pattern, although at a slightly lower significance level.     

Asymptotic orbits and terminations of families in the Copenhagen problem

The physico-chemical origin of the hydrogenated carbon clusters (cumulenes, PAHs, graphite or amorphous carbon) in space is still an open question. We have worked out a numerical simulation code in order to build up planar (graphite-like) carbon clusters. We assume that hydrogen atoms can fix on the carbon skeleton following a random process allowing forH ₂ formation. The structures we have found are very complex. In a given cluster, several molecular entities can simultaneously be present: (sp ²) carbon chains, rings or compact formations (aromatic structures or small PAHs). We argue that these very contorted hydrogenated structures could be ubiquitous in the interstellar medium, in carbon-rich circumstellar regions and PNe.     

Wave propagation in a magnetically structured atmosphere

The propagation of waves in a magnetic slab embedded in a magnetic environment is investigated. The possible modes of propagation are examined from the general dispersion relation, both analytically and numerically, for disturbances which are evanescent in the environment. Approximate dispersion relations governing propagation in a slender slab of field are derived both from the general dispersion relation and from an application of the slender flux tube approximation.Several different situations, representative of both photospheric and coronal conditions, are considered. In general, the structures are found to support both fast and slow, body and surface, waves. Under coronal conditions, for two dimensional propagation, disturbances propagate as fast and slow body waves. The fast body waves are analogous to the ducted shear waves of seismology (Love waves).     

Multifractal Properties of Evolving Active Regions

Magnetohydrodynamic turbulence is thought to be responsible for producing complex, multiscale magnetic field distributions in solar active regions. Here we explore the multiscale properties of a number of evolving active regions using magnetograms from the Michelson Doppler Imager (MDI) on the Solar and Heliospheric Observatory (SOHO). The multifractal spectrum was obtained by using a modified box-counting method to study the relationship between magnetic-field multifractality and region evolution and activity. The initial emergence of each active region was found to be accompanied by characteristic changes in the multifractal spectrum. Specifically, the range of multifractal structures (D _div) was found to increase during emergence, as was their significance or support (C _div). Following this, a decrease in the range in multifractal structures occurred as the regions evolved to become large-scale, coherent structures. From the small sample considered, evidence was found for a direct relationship between the multifractal properties of the flaring regions and their flaring rate.     

Sunspots and large-scale magnetic fields at various heights

Height variation of the magnetic field structure over groups of sunspots for heights ranging from the photosphere to the source surface (R = 2.5 Ro, where Ro is the radius of the Sun) is examined. For all heights, starting from the photospheric level, groups of sunspot are shown as being independent of long-lived boundaries of large-scale structures rotating with a period shorter than the Carrington period. At heights of 1–1.5 Ro, there is a clear relation between sunspot groups and boundaries separating the head and tail sunspots in the groups (the Hale boundaries). The rotation periods of these structures are close to the Carrington period, their lifespan being less than three to five rotations. The maximal intensity of the solar magnetic field drops by two orders when height increases from H = 1 to H = 1.1 Ro. Further decrease in intensity proceeds gradually (dropping by one order from H = 1.1 to 2.5 Ro). The results obtained can be considered as evidence that large-scale magnetic field structures and long-lived boundries between them (the lines dividing polarities of the magnetic field or zero lines) all exist irrespective of sunspot fields being generated by other sources than sunspots. At the photospheric level, active regions fields are superimposed on these structures.