Suprathermal ions in solar-wind outflows from coronal holes at 1 AU

The energy spectra and relative abundances of ³He, ⁴He, C, O, and Fe ions with energies of ~0.04–2 MeV/nucleon are studied using data from the ULEIS instrument on board the ACE spacecraft obtained during quiescent periods in 2006–2012. During the unique, prolonged minimum between cycles 23 and 24, 35 quiescent periods were distnguished, during which solar-wind flows from near-equatorial coronal holes (CHs) were detected. It is shown that the C/O and Fe/O ratios for suprathermal ions correspond to the relative abundances of the corresponding thermal ions in the fast and slow (Maxwellian) solar wind (SWICS/ACE), while the ⁴He/O ratio exceeds the corresponding ratio in the solar wind by a factor of two. The intensities of the ³He, ⁴He, C, O, and Fe suprathermal ions in outflows from CHs grow with the speed of the solar wind. This indicates that, in periods ofminimumsolar activity, suprathermal ions from CHs represent a high-temperature “tail” of the solar wind. An additional flux of suprathermal helium ions may also be contributed by other external sources.     

Decay of activity complexes and the formation of coronal holes

Analysis of long-term measurements of solar magnetic fields and the flux of UV radiation from the Sun indicates a cause-effect relationship between activity complexs, their residual magnetic fields, and coronal holes. A comparison of the background magnetic fields of the Sun and the evolution of former activity complexes reveals unipolar magnetic regions that form after the decay of these complexes. The latitude and time evolution of unipolar magnetic regions in solar cycles 21–24 is studied. A North-South asymmetry in solar activity is manifest in the distribution of unipolar regions migrating toward higher latitudes. It is shown that, when residual magnetic fields of the opposite polarity reach the polar regions, this leads to a sign change of the polar magnetic field and a decrease in the area of polar coronal holes, or even their complete disappearance. These interactions can explain the triple sign change of the polar magnetic field of the Sun in cycle 21 and the short-term polarity reversals observed in 2010 and 2011.     

Relationship between the contrast of coronal holes and parameters of the solar wind streams

It is shown that the contrast of coronal holes (CH) determines the speed of the solar wind streams to the same extent as their area does. We analyzed more than 400 images obtained in the λ284 Å channel. The time interval under examination covers about 1500 days in the declining phase of cycle 23 (from 2002 to 2006). We considered all coronal holes recorded during that interval in the absence of coronal mass ejections (CME). Comparison was also made with some other parameters of the solar wind (e.g., density, temperature, and magnetic field). A fairly high correlation (0.70–0.89) was obtained with the velocity, especially during the periods of moderate activity, which makes this method useful for everyday forecast. The ratio of CH brightness to the mean brightness of the disk in the λ284 Å channel is about 25%.     

Long-period oscillations of the line-of-sight velocities in and near sunspots at various levels in the photosphere

New observational data on long-period oscillations of the line-of-sight velocities detected via the Doppler shifts of spectral lines observed at various heights in and near sunspots are presented. The sunspots and nearby magnetic elements oscillate with periods ranging from 40 to 80 min. The oscillations in the line-of-sight velocities persist over the entire observation session (up to four hours). These results support theoretical models in which this phenomenon represents natural long-period oscillations (vertical-radial displacements) of entire magnetic elements (sunspots, pores, and magnetic knots) about some stable equilibrium positions.     

Lateral variations in shear velocity and attenuation in the upper mantle

We have used digitally recorded long period seismic data from the HGLP and SRO networks to obtain estimates of multiple ScS travel times and spectra and have used these to place constraints on the lateral variations in upper-mantle shear velocity and attenuation structure. The travel time results are consistent with our previous findings: to a first approximation, upper-mantle heterogeneity as expressed in vertical travel time differences can be correlated with surface tectonic features. A spectral stacking procedure for retrieving the attenuation operator for SH polarized multiple ScS waves has been applied to seismograms representing a variety of tectonic provinces. The spectral analysis has yielded stable estimates of the phase and amplitude response of the attenuation operator in the frequency interval 6–60 mHz. These estimates indicate that the apparent Q can also be correlated with surface tectonic regimes.     

Shocks at the bases of non-relativistic jets from young stars

A cylindrical magneto-hydrodynamical model for the transverse structures of the nonrelativisitic jets observed from young stars is proposed. The importance of the temperature terms in the equations describing one-dimensional cylindrical flows is discussed. It is shown that taking into account heating at an oblique shock at the base of the jet makes it possible to obtain physical parameters of the jet that are in good agreement with observations. In particular, the jet can be confined by an external magnetic field of the order of 10⁻⁶ G at a distance of 100 AU from the rotational axis.     

Magnetic-field variations in the active region NOAA 10486 and their relationship to X-ray flares and coronal mass ejections

SOHO/MDI magnetograms are used to analyze the time variations in the magnetic parameters of the active region (AR) NOAA 10486, which was part of a large activity complex that passed over the solar disk from October 26 to 31, 2003, during solar cycle 23. The results are compared with X-ray flares in the AR and the parameters of coronal mass ejections associated with the AR. The time variations in the distributions of themagnetic-field strengths associated with the total magnetic flux (Fa), the flux imbalance between the northern and southern polarities (Im), the complexity of the field, as a measure of the mutual overlapping of the opposite polarities (Co), and the tilt angle of the magnetic axis (An) are considered. The time variations in the free energy accumulated in current sheets of ARs were traced using a parameter introduced for this purpose (Sh). The following results were obtained. First, the parameters Fa, Im, Co, An, and Sh quantitatively describe the current state of the AR and can be used to trace and analyze the dynamical evolution of its magnetic field. Second, variations in the magnetic-field-strength distributions and the mean values of Fa, Im, Co, An, and Sh are associated with flares and coronal mass ejections, and the variations have considerable amplitudes. Third, the parameter Sh characterizing the degree to which the magnetic field is non-potential in regions adjacent to the main neutral line increases before eruptive events, and is thus particular interest for monitoring the states of ARs in real time. Fourth, the magnetic field of the AR manifests a sort of quasi-elasticity, so that the field structure is restored after active events, on average, within 1–3 h.     

Photometry of the intermediate polar 1RXS J062518.2+733433: Characteristics of its periodic brightness variations

We present the results of our photometry of the recently discovered intermediate polar 1RXS J062518.2+733433. The observations were made using the 70 cm telescope of the Astronomical Observatory of the Ural State University with a multichannel photometer, and were carried out during 13 nights in March–May 2004. Our analysis reveals brightness variations with periods of 19.788 ± 0.003 min, corresponding to the rotational period of the white dwarf, 21.273 ± 0.003 min, corresponding to the orbital sideband, and 283.3 ± 0.5 min, which is the orbital period. The variations with the white dwarf’s rotational period show a stable amplitude and a quasi-sinusoidal pulse shape persistent over a long time. In contrast, the orbital-sideband variations have an unstable amplitude and a significantly nonsinusoidal pulse shape that varies with time. Variations of the amplitude and pulse shape of the orbital-sideband variations can be related to structural changes of the accretion disk surrounding the white dwarf.     

Temporal and spatial variations in density and velocity fields of the waters of Gareloch,Scotland

 Spatial variations in the density and velocity fields have been observed in the Gareloch (Scotland) during surveys in 1987–1988 and 1993–1994. The variation of the density field has been analyzed on a variety of time scales from semidiurnal to seasonal in order to quantify effects caused by the forcing factors of tidal mixing, freshwater input, and wind. Initial results indicate that water density in the loch is controlled (to a major degree) by the freshwater input from runoff from the local catchment area and from freshwater entering on the flood tide from the Clyde Estuary. It is estimated that during winter periods the high freshwater flows from the rivers Leven and Clyde into the Clyde Estuary account for up to 75% of the freshwater creating the density structure in the loch. Analysis of long-term dissolved oxygen data reveals that major bottom water renewals occurred between July and January in the years 1987–1994. Major bottom water dissolved oxygen renewals have a general trend but during the year sporadic renewals can take place due to abnormal dry spells increasing the density of the water entering from the Clyde, or consistently strong winds from the north reducing stratification in the loch and producing better mixed conditions. Velocities vary spatially, with the highest velocities of up to 0.6 m s^–1 being associated with the velocity jet effect at the constriction at the sill of the loch. Observed near-surface mid-loch velocities increased as the vertical density gradients in the upper layers increased. This indicates for the observed conditions that increased stratification in the upper layers inhibits the entrainment rate and hence rate of gain of thickness of the wind-driven surface layer, resulting in increased surface velocities for a given wind speed and direction. The main flow is concentrated in the upper 10 m and velocities below 10 m are low. Observed mean spring tide surface velocities are on average 30% greater than mean neap tide surface velocities. Received: 22 May 1995 · Accepted: 23 August 1995     

Distinct variations of crustal shear wave velocity structure and radial anisotropy beneath the North China Craton and tectonic implications

This study presents the crustal shear wave velocity structure and radial anisotropy along two linear seismic arrays across the North China Craton (NCC) from ambient noise tomography. About a half to one year long ambient noise data from 87 stations were used for obtaining the inter-station surface wave empirical Green's functions (EGFs) from cross-correlation. Rayleigh and Love dispersion curves within the period band 5–30 s were measured from the EGFs of the vertical and transverse components, respectively. These dispersion data were then used to determine the crustal shear wave velocity structure (V_SV and V_SH) and radial anisotropy (2(V_SH ? V_SV) / (V_SH + V_SV)) from point-wise linear inversion with constraints from receiver function analysis. Our results reveal substantial structural variations among different parts of the NCC. The Bohai Bay Basin in the eastern NCC is underlain by a thin crust (~ 30 km) with relatively low velocities (particularly V_SV) and large positive radial anisotropy in the middle to lower crust. Such a crustal structure is no longer of a cratonic type and may have resulted from the widespread tectonic extension and intensive magmatism in this region since late Mesozoic. Beneath the Ordos Basin in the western NCC, the crust is relatively thicker (≥ 40 km) and well stratified, and presents a large-scale low velocity zone in the middle to lower crust and overall weak radial anisotropy except for a localized lower crust anomaly. The overall structural features of this region resemble those of typical Precambrian shields, in agreement with the long-term stability of the region. The crustal structure under the Trans North China Orogen (TNCO, central NCC) is more complicated and characterized by smaller scale velocity variations, strong positive radial anisotropy in the middle crust and rapid change to weak-to-negative anisotropy in the lower crust. These features may reflect complex deformations and crust–mantle interactions, probably associated with tectonic extension and magmatic underplating during the Mesozoic to Cenozoic evolution of the region. Our structural images in combination with previous seismic, geological and geochemical observations suggest that the Phanerozoic lithospheric reactivation and destruction processes may have affected the crust (especially the middle and lower crust) of the eastern NCC, and the effect probably extended to the TNCO, but may have minor influence on the crust of the western part of the craton.     

Seismicity and structural investigations of the Romanian Vrancea Region: Evidence for azimuthal variations of p-wave velocity and poisson's ratio

A study of the shallow and intermediate depth seismicity of the Romanian Vrancea region in the period 1964–1981 has been performed. The seismic events have been relocated by a standard location procedure using a regional velocity model. From the temporal and spatial distribution of the seismic activity, aspects of the seismicity before the large March 4, 1977 earthquake are treated, in particular the seismic gap in space and time prior to this event, found by Mârze (1979), which is critically discussed and revised. The concept of the precursor time/magnitude relationships of different authors is applied and its validity to the Vrancea region assessed. The hypocentral distribution shows that the intermediate depth seismic activity is confined to a small volume with dimensions of only some tens of kilometers. The results are interpreted in terms of the tectonics of the region. From an analysis of the travel-time residuals at different local stations, evidence for lateral velocity heterogeneities beneath the region is obtained e.g. a high velocity zone southeastwards of the Carpathian chain. Finally mean ratios, (i.e. Poisson's ratios), for various stations are calculated from P- and S-wave travel times. They show azimuthal variations of up to 6% for stations within the area where the intermediate seismic activity occurs in comparison with the station Focsani, situated eastwards in the Carpathian foredeeps. All these results are compatible with the plate tectonic concept for the Vrancea region, that is the subduction of an oceanic lithospheric slab under the Carpathian mountain arc, giving rise to such a highly active seismic zone.     

Parameters of the turbulent magnetic field in the solar photosphere: Power spectrum of the line-of-sight field

Ground-based (Big Bear Solar Observatory) and extra-atmospheric (SOHO/MDI) measurements of the photospheric line-of-sight magnetic field of one active and two quiet regions are used to calculate power spectra of the field, taking into account the characteristic function for the diffraction limit of the telescope resolution. At high frequencies, the physically meaningful linear interval in the spectrum extends to a wave number of k=4.6 Mm^?1 (spatial scale l=1.4 Mm) for the quiet regions and k=3.35 Mm^?1 (l=1.9 Mm) for the active region. A high-frequency spectral break at k≥3 Mm^?1 is associated with the characteristic telescope function; the position of the break and the spectral slope beyond the break do not reflect the turbulent state of the field. As the field recording improves, the break shifts toward higher frequencies. The spectral indices in the physically meaningful linear interval are substantially different for the active and quiet regions: in the active region (NOAA 8375), the spectrum behaves as E(k)≈k ^?1.7 (very close to the Kolmogorov index, ?5/3) in the interval 0.78≤k≤3.35 Mm^?1, while in the quiet regions E(k)≈k ^?1.3 for 0.77≤k≤4.57 Mm^?1. This difference can be explained by the additional effect of a small-scale turbulent dynamo in the unperturbed photosphere. In this case, this mechanism can generate at least 6% of the magnetic energy of the photospheric line-of-sight field in quiet regions.     

Field examples of variations in fault patterns at different scales

Three field examples are presented which show changes in fault patterns at different scales. Normal faults in Jurassic limestones in Somerset consist of zones of sub-parallel segments at the exposure-scale, but contain complex zones of brecciation at the decimetre-scale. Normal faults in chalk at Flamborough Head consist of a complex network of small faults which accommodate strain between a set of large faults. The different-sized faults at Flamborough Head have different geometries and histories, with the larger faults showing a phase of reverse reactivation. The faulting in the Sydney Basin, Australia, can be explained in terms of the evolution and reactivation of transfer zones between overstepping faults. These transfer zones can cause the deformation to appear to be more complex as the analysis becomes more detailed.
Much recent work on the scaling relationslups of faults assumes that self-similar fault patterns occur over a wide range of scales. The data presented in this paper, however, suggest that there are problems in using the deformation pattern at one scale to infer deformation at other scales. Ideally, any analysis should involve the study of a wide range of scales to overcome these problems.     

Non-radial coronal streamers in the course of the solar cycle

Equatorward deviations of coronal streamers at solar minima and poleward deviations at solar maxima are interpreted as the effects of changes in the general topology of the global solar magnetic field. The streamer axis is located on the neutral surface of the radial magnetic field B _r = 0, and the neutral surfaces deviate toward the field null points. The magnetic configuration with a null point (line) located at the equator is typical for the solar minima, while the null points are located on the rotational axis of the Sun at the solar maxima.     

Systematic variations in seismic velocity and reflection in the crust of Cathaysia: New constraints on intraplate orogeny in the South China continent

The South China continent has a Mesozoic intraplate orogeny in its interior and an oceanward younging in postorogenic magmatic activity. In order to determine the constraints afforded by deep structure on the formation of these characteristics, we reevaluate the distribution of crustal velocities and wide-angle seismic reflections in a 400 km-long wide-angle seismic profile between Lianxian, near Hunan Province, and Gangkou Island, near Guangzhou City, South China. The results demonstrate that to the east of the Chenzhou-Linwu Fault (CLF) (the southern segment of the Jiangshan–Shaoxing Fault), the thickness and average P-wave velocity both of the sedimentary layer and the crystalline basement display abrupt lateral variations, in contrast to layering to the west of the fault. This suggests that the deformation is well developed in the whole of the crust beneath the Cathaysia block, in agreement with seismic evidence on the eastwards migration of the orogeny and the development of a vast magmatic province. Further evidence of this phenomenon is provided in the systematic increases in seismic reflection strength from the Moho eastwards away from the boundary of the CLF, as revealed by multi-filtered (with band-pass frequency range of 1–4, 1–8, 1–12 and 1–16 Hz) wide-angle seismic images through pre-stack migration in the depth domain, and in the P-wave velocity model obtained by travel time fitting. The CLF itself penetrates with a dip angle of about 22° to the bottom of the middle part of the crust, and then penetrates with a dip angle of less than 17° in the lower crust. The systematic variation in seismic velocity, reflection strength and discrepancy of extensional factors between the crust and the lithosphere, are interpreted to be the seismic signature of the magmatic activity in the interest area, most likely caused by the intrusion of magma into the deep crust by lithospheric extension or mantle extrusion.     

Magnetic mineral variations of South Caspian Sea sediments at laminae scale

The 998-cm long sediment core was collected from the South basin of the Caspian Sea. Sediments from the lower, Late Pleistocene part of the core (998-90 cm) are marked by laminations, which rapidly disappear under oxidising conditions. TEM/EDS analyses of magnetic extracts, done at laminae scale, show the presence of iron monosulphide (greigite Fe₃S₄) in grey and black laminae. There are also small amounts of magnetite. Magnetic hysteresis parameters Mrs/Ms and Bcr/Bc, presented on a Day plot, cluster near SD/PSD boundary, with smaller particles for black laminae. This tendency is due to a higher content of greigite, relative to coarser grained detrital magnetite in black laminae, and to a lower relative content of greigite in grey laminae. Analyses of Ca/Mg carbonates, grain size of the bulk sediment, feldspars/quartz ratios and water content show that these parameters do not vary at laminae scale. These results suggest that the laminae are of early diagenetic rather than detrital origin, reflecting rhythmic, subtle variations in the geochemical environment during laminae formation.     

Solar magnetic fields and the intensity of the green coronal line

Synoptic maps of the intensity of the λ530.5 nm FeXIV green coronal line and maps of computed coronal magnetic fields for the period 1977–2001 are compared. For quantitative comparisons, the correlation coefficients r for the correlation between these two parameters at corresponding points of the synoptic maps are calculated. This coefficient exhibits cyclic variations in the spot-formation zone, ±30° and the zone above 30° and is in antiphase in these two zones. In the low-latitude zone, the correlation coefficient is always positive, reaches its maximum at activity minimum, and strongly decreases by activity maximum. Above 30°, r reaches maximum positive values at activity maximum and then gradually decreases, passing through zero near the beginning of the phase of activity minimum and becoming negative during this phase. A Fourier analysis of r as a function of time reveals a wavelike variation with a period close to 1.3 yr (known also from helioseismological data for the tachoclinic region of magnetic-field generation), as well as a pronounced wave with a period of about 5 yr. The latitude dependence of r seems to be related to variations in the contributions from local, large-scale, and global fields. Our analysis suggests an approach to studying the complex problem of mechanisms for coronal heating.