Whitney gathers in the solar atmosphere

The structures called Whitney gathers in the catastrophe theory are not unusual among the various types of chromospheric Hα filaments and coronal helmets. They result from a projection of smooth surfaces onto a plane of the sky. The apices of the helmets can be described as gathers of the surface B _r = 0 in the corona (where B _r is the magnetic field). Near the limb, Hα filaments are frequently observed as similar types of structures. A model of the B _r = 0 surface with sources located inside the Sun (∫ Bds = 0) is constructed here in this context. Gathers and folds of this surface are shown to be possible in relatively simple fields. Our model computations are supported by the available observational data.     

On the 4-connected nets in some silica structures of Boisen,Gibbs and Bukowinski

The nets of some theoretical silica structures described by M.B. Boisen, G.V. Gibbs and M.S.T. Bukowinski [Phys Chem Minerals 21:269–284 (1994)] are identified and discussed.     

Solubility of sulfur in some magmas at 1 atmosphere

In order to understand the distribution of sulfur in igneous rooks, we determined the solubility of sulfur in volcanic rock melts (tholeiite basalt, hawaiite and rhyodacite from Hawaii) at various gas compositions and at 1250° and 1300°C and 1 atm total pressure. The solubility of sulfur in the melt passes through a minimum with change in oxygen partial pressure, if other factors are held constant. For the basaltic liquid at 1200°C, most sulfur in the melt is as dissolved sulfide (S^?2) at oxygen partial pressures below 10^?8 atm and as dissolved sulfate at oxygen partial pressures above 10^?8 atm. Based on the present solubility data, 5 per cent is inferred for volcanic gas at 1 atm total pressure in equilibrium with subaerially extruded Hawaiian tholeiite basalt (Pele's hair with 180 ppm S) at 1200°C and 10^?8 atm P_O2.     

Coherent structures in the dynamics of the large-scale solar magnetic field

Variations in the mean solar magnetic field (MSMF) are studied in both the frequency-time and longitude-time domains. A wavelet analysis of the MSMF clearly demonstrates that variations in the mean field are not stationary. Combined with longitude-time diagrams for the background solar magnetic field (BSMF), the analysis reveals the emergence of the background field, which occurs discretely at intervals of 1.5–2 years. Based on an analysis of the fine structure in MSMF variations, we develop a numerical technique to study timedependent heliographic-longitude distribution of the large-scale magnetic field. A detailed picture of the rotation of the large-scale magnetic field is derived for activity cycles 20–23. Coherent structures are detected in longitude-time diagrams obtained by deconvolving the MSMF series. These structures are related to discrete rigid-rotation modes of the large-scale magnetic fields. Various rotational modes coexist and replace one another. During the phase of activity growth, modes with periods of 27.8–28.5 days dominate, whereas a mode with a rotational period of about 27 days dominates during the decline phase. Occasionally, modes with periods of 29–30 days appear. Most structures in the longitude-time MSMF distribution correspond to similar structures in the BSMF distribution for the northern or southern hemisphere. Chronologically, the emergence of the BSMF has frequently been accompanied by changes in the solar rotational regime and has been correlated with variations in the polarity asymmetry in the course of the 11-year activity cycle.     

The magnetic-field geometry in polar ray structures of the solar corona

Variations in the positions of the intersection points of tangents to ray structures in the polar corona of the Sun during the solar cycle are considered. At first glance, the decrease in the distance q between the tangent intersection point and the center of the solar disk during activity maximum contradicts harmonic analyses that indicate that the relative weight of higher harmonics in the global field increases during this period. Indeed, the higher the harmonic number in an axisymmetric field, the closer the intersection point of the field-line tangents (the magnetic focus) to the solar surface. It is shown that q for a field composed of two harmonics with opposite polarities at the poles can be smaller than q for either of them taken alone. A simple model representing the global field using the third and seventh harmonics is analyzed; this model can reproduce quite satisfactorily the observed dynamics of magnetic foci of the polar field.     

The role of faculae in wave-energy transfer to upper layers of the solar atmosphere: Observations

The properties of Doppler-velocity oscillations in solar faculae are analyzed at the photospheric level (based on Fe I 6569 ? and Fe I 8536 ? lines) and chromospheric level (based on Hα and Ca II 8542 ? lines) to search for upward propagating waves. The similarity of the averaged power spectra at 2.5–4 mHz is not found to be convincing proof of the presence of unidirectional wave-energy transfer from the photosphere to the chromosphere. Phase relations between the photospheric and chromospheric oscillations that are indicative of either upward or downward propagating waves are obtained for various areas in many faculae. This suggests that the wave energy of the five-minute oscillations returns to the photosphere, at least partially. The derived properties suggest that the role of faculae in the transfer of the five-minute oscillations to the chromosphere and overlying layers is not as obvious as could be expected. The relatively typical presence of low-frequency (0.5–2 mHz) oscillations in faculae and their possible important role in this energy transfer are noted.     

Petrological implications of some corona structures

Reactions between olivine and plagioclase, and between pyroxenes and plagioclase, commonly produce corona assemblages of lower volume and entropy. These coronas imply that assemblages representative of intermediate-and high-pressure granulite facies, and of eclogite facies (emphacite + garnet), can be produced by the cooling of dry olivine + plagioclase and pyroxene + plagioclase assemblages from igneous temperatures within the continental crust. They further imply that eclogite is a stable assemblage within the deeper parts of the continental crust; this in turn requires that dP/dT > 0 for the equilibrium curves for the relevant reactions. The general relations between T and rates of nucleation, growth and diffusion suggest that these coronas will only be formed in relatively deep-seated rocks (P > 6 kb ?). The formation of such coronasby regional or contact metamorphism, or by metasomatism, is unlikely; they are best regarded as retrograde features.     

Gamma-ray radiation with energy 2.223 MeV and the density distribution in the solar atmosphere during flares

Interactions of particles accelerated in solar flares with matter in the solar atmosphere give rise to neutrons, which are efficiently captured on hydrogen nuclei as they are slowed to thermal velocities. This capture is accompanied by the emission of a gamma-ray with energy 2.223 MeV. Observational data for the temporal profiles of the gamma-ray fluxes in this line are used to study the plasma-density distribution in the solar atmosphere during the flares of December 16, 1988, March 22, 1991, and November 6, 1997. This analysis is based on comparisons between the observations and profiles computed taking into account a number of parameters describing the generation and transport of the flare neutrons in atmospheric layers of various densities. In three cases studied, the density of the material in the photosphere below the flare region is enhanced compared to the density in an unperturbed part of the solar atmosphere at the same height. In the case of the December 16, 1988 flare, we are able for the first time to relate the profile of the 2.223 MeV line with the shape of the accelerated particle (proton) spectrum. This opens new possibilities for studies of particle acceleration on the Sun based on observations of flare gamma-ray emission.     

The effect of acoustic waves on spectral-line profiles in the solar atmosphere: Observations and theory

The fine structure of the FeI λ 532.4185-nm line of neutral iron is studied with high spatial (0.5″) and temporal (9.3 s) resolution using observations of a quiet region at the center of the solar disk. The character of the line asymmetry depends strongly on the nature of the velocity field, i.e., on whether it is due to convective or wave motions. The magnitude of the asymmetry due to acoustic waves is comparable to that due to convective motions. The propagation of acoustic waves in moving granules and intergranular lanes is studied by solving a system of hydrodynamical equations in a three-dimensional model for the solar atmosphere. The temporal variations in the bisector of the line synthesized in a non-LTE approximation agree well with the observational data.     

Characteristics of oscillatory-wave processes in solar structures with various magnetic field topology

Recognizing that waves play an important role in energy-exchange processes between layers of the solar atmosphere, and that the characteristics of propagating waves are determined by the physical conditions of the medium, and, most importantly, the magnetic-field configuration, we have carried out a comparative analysis of the properties of oscillations in solar structures with various magnetic-field topologies: sunspots, faculae, and coronal holes. Simultaneous measurements of the Doppler velocities and intensities at the photospheric and chromospheric levels were accompanied by episodic measurements of the longitudinal magnetic field. In the chromosphere, spot umbrae dominate the three-minute oscillations, while lower-frequency modes are also observed in the penumbrae and at the outer parts of spots. Clear signs of propagating waves have been observed at the bases of coronal holes and in faculae only at frequencies close to 3 mHz.     

On the stability of a coupled ocean atmosphere system in the presence of wave-CISK

The stability of a simple coupled ocean-atmosphere system similar to the one studied by Hirst with general ocean thermodynamics is investigated in which the atmospheric heating is determined by sea surface temperature anomalies as well as the convergence feedback (low level moisture convergence by the waves themselves). It is shown that the unstable coupled mode found by Hirst (UH mode) is profoundly modified by the convergence feedback. The feedback increases the unstable range of the UH mode and can increase its growth rate several folds. The maximally growing UH mode can become westward propagating for certain strength of convergence feedback. If the convergence feedback strength exceeds a critical value, several new unstable intraseasonal modes are also introduced. These modes are basically ‘advective’ modes. For relatively weak strengths of the convergence feedback the growth rates of these modes are smaller than that of the UH mode. As the atmosphere approaches ‘moist neutral’ state, the growth rates of these modes could become comparable or even larger than that of the UH mode. It is argued that these results explain why the El Nino and Southern Oscillation (ENSO) signal is clear in the eastern Pacific but not so in the western Pacific and they may also explain some of the differences between individual ENSO events. Our results also explain the aperiodic behaviour of some coupled numerical models. Importance of this process in explaining the observed aperiodicity of the ENSO phenomenon is indicated.     

Evidence for the prolonged existence of >100 MeV solar protons in coronal structures

Solar proton events (SPEs) of 1989–1992 accompanied by ground-level enhancements of the cosmic-ray intensity are analyzed. A diffusive-propagation model can well approximate the solar proton intensity at energies of 84–200 MeV measured on board the GOES-7 satellite during the first 15–20 hours of the development of an SPE, assuming several episodes of proton injection into interplanetary space over some hours. The detection of π⁰-decay gamma-ray emission during the flares of June 11 and 15, 1991 on board the CGRO and GAMMA-1 space observatories is the sole experimental evidence for the existence of protons with energies >100 MeV near the Sun over such extended times. The number of protons in the source is estimated for various times based on the propagation model. Moreover, this value is in qualitative and quantitative agreement with the number of protons required to generate the observed gamma-ray emission for the June 15, 1991 event (and in qualitative agreement for the June 11, 1991 event). This provides evidence that processes of prolonged trapping and/or acceleration of protons in coronal structures may be possible in other such events.     

On some future tsunamis in the Pacific Ocean

Possible tsunamis in the Pacific Ocean, especially in its northeastern part, are discussed in relation to a predicted major earthquake in the Shumagin Seismic Gap (located in the eastern part of the Aleutian Island Chain) and to a major eruption of the St. Augustine volcano in Cook Inlet, Alaska. The deep-water propagation of the tsunami generated in the Shumagin Gap is simulated through the use of a spherical polar coordinate grid of the approximate size of 14km. The tsunami generated by the St. Augustine volcano is studied through the fine mesh grid confined to the Cook Inlet only. The numerical models were calibrated against historical tsunami data. The properties of the tsunami signal are described by the maximum amplitude which occurs in the tsunami record. This allows us to single out the direction along which a maximum tsunami is to be expected.Presented at the International Conference on Natural and Man-Made Hazards in Coastal Zones, held in Ensenada, Mexico, August 1988.     

Corotating structures in the solar wind from 111-MHz observations of interplanetary scintillations at large elongations

Results of continuous 111 MHz observations of interplanetary scintillations of the strong radio source 3C 48 at elongations larger than 80? out on the Large Phased Array (LPA) of the Lebedev Physical Institute are reported. The data were taken during a four-year interval, from 2012 to 2015, near the maximum of the 24th solar-activity cycle. The averaged elongation dependence of the scintillation index and similar dependences for individual years during the approach and recession phases suggest the presence of a periodic modulation with a 26-day period, which is masked by day-to-day variations. This periodic modulation can be explained by the existence of a long-lived region of enhanced plasma density adjacent to the solar equator during the solar-activity maximum. It is shown that the scintillation timescale increases in the transition to elongations exceeding 90?.     

On the binder of some ancient mortars

Summary About 90 samples of mortars from historical buildings in Pisa have been analysed and compared with some samples of ancient mortars characterized by pozzolanic aggregates. Chemical (XRF), mineralogical (XRD) and petrographical (optical microscopy) data have been collected on bulk samples. An X-ray energy-dispersive system (EDS) attached to a SEM was used to determine the chemical compositions of binder, clots and pozzolanic grains (whenever present). The binder components which could not be directly assessed (CO₂, H₂O+) have been indirectly derived through a computation method.Data collected suggest that the main stock of analysed samples (i.e., mortars from Pisa monuments) contains two principal types of binder: the first type corresponds to a common carbonated lime; the second type is a hydraulic lime, where the carbonate component is associated with an important silicate fraction, which constitutes 13 to 89 wt% of the total binder (on average 47%). This hydraulic type had a widespread application in the construction of ancient monuments in Pisa; for example, it was constantly employed in the building of the famous Leaning Tower. This study shows that the silicate fraction of such hydraulic mortar, which is amorphous to X-ray diffraction, is made up by a hydrated calcium alumino-silicate having a very low Al₂O₃/SiO₂ ratio (on average 0.125). On the basis of chemical and optical characteristics of hydraulic mortar binders from Pisa and the results of laboratory tests, as well as through comparison with the characteristics of ancient hydraulic mortars having pozzolanic aggregates, it is concluded that such mortars were prepared most likely by mixing slaked lime with a reactive, highly siliceous material such as a diatomaceous earth.

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Über Bindemittel in antiken Mörteln

Zusammenfassung Etwa 90 Mörtelproben von historischen Gebäuden in Pisa wurden analysiert und mit Proben von antiken Mörteln, die durch pozzolanische Aggregate charakterisert sind, verglichen. Chemische (XRF), mineralogische (XRD) und petrographische (optische Mikroskopie) Daten wurden an den Gesamtproben ermittelt. Ein an ein SEM angeschlossenes energiedispersives System (EDS) wurde für die Bestimmung der chemischen Zusammensetzung des Bindemittels, der Mörtelklümpchen und der pozzolanischen Körner (sofern vorhanden) verwendet. Die Komponenten des Bindemittels, die nicht direkt gemessen werden konnten (CO₂, H₂O⁺) wurden indirekt durch ein Berechnungsverfahren ermittelt.Die gesammelten Daten belegen, dass die meisten untersuchten Proben (i.e. Mörtel von Monumenten aus Pisa) zwei Typen von Bindemittel enthalten: Der erste Typ entspricht einem gewöhnlichen karbonatisierten Kalk. Der zweite Typ ist ein hydraulischer Kalk, in dem die Karbonatkomponente mit einer mengenmäßig bedeutenden Silikatfraktion assoziiert ist, die 13–89 Gew.% des gesamten Bindemittels ausmachen kann (durchschnittlich 47%). Dieser zweite Typ wurde häufig beim Bau alter Monumente in Pisa verwendet, z.B. wurde er ständig beim Bau des Schiefen Turms herangezogen. Diese Studie zeigt, dass die Silikatfraktion dieses hydraulischen Mörtels, die röntgenamorph ist, aus einem hydratisierten Aluminosilikat mit einem niedrigen Al₂O₃/SiO₂ Verhältnis (im Durchschnitt 0.125) besteht.Auf Basis der chemischen und optischen Charakteristika des hydraulischen Mörtel, die pozzolanische Aggregate führen, schließen wir, dass diese Mörtel höchstwahrschein lich durch Mischung von Löschkalk mit sehr reaktivem, silikatischen Material, wie etwa Diatomeenerde hergestellt wurden.

     

Laminated cyanobacterial mats in sediments of solar salt works: some sedimentological implications

Formation of microlaminated sediments in solar salt works along the Mediterranean coast in southern France only occurs within a restricted salinity range of 60–150 gl^?1. These salinities are associated with development of a laminated cyanobacterial mat composed primarily of the filamentous cyanobacteria Microcoleus chthonoplastes interbedded with detrital laminae. Transplants of the cyanobacterial mat to a less saline zone (36–60 gl^?1) indicated that the cyanobacterial mats failed to colonize the less saline waters due to herbivorous snails and competition for light from floating algal masses of Cladophora and Enteromorpha. Neither the snails nor the Cladophora and Enteromorpha masses are tolerant of salinities above 60 gl^?1, and therefore the Microcoleus mats are restricted to those areas of the solar salt works with these higher salinities. Analyses of salinity, conductivity, dissolved oxygen and pH in shallow salt pans (with salinities of 60–150 gl^?1) established a relationship between the daily development of oxygen supersaturation and cyanobacterial photosynthesis. Sediments are unlaminated in those portions of the solar salt works where there are no cyanobacterial mats. These mats are frequently drained of their overlying water, and thus desiccation cracks divide them into polygonal plates. The development and translocation of these plates is enhanced by gas bubbles which form under the surface of the mats. No correlation between the microlaminae in sections from two cores located approximately 1 m apart was observed. This was consistent with the hypothesis that the surface of the desiccation crack polygons can be removed by currents and redeposited on the top of other cyanobacterial mat polygons. This process results in a ‘patchwork quilt’of young and old cyanobacterial mat polygons with an irregular microlamination pattern. The presence of such an irregular pattern of laminae permits an important distinction to be made between sediments associated with stromatolite formation and those associated with the very fine and horizontal varved sediments of stratified (meromictic) water bodies. The sedimentological significance of these observations is reviewed in relation to the processes of stromatolite genesis.     

Infrared spectroscopic study of the silicate anionic structures of some magmatic silicate melts

Summary The relation between the species of silicate anions in a silicate melt and their infrared characteristic frequency is discussed. A simple relation approximated with a quadratic equation is established between the ratio of non-bridging oxygens to silicon atoms of a silicate anion and the characteristic frequency. Based on this relation, the silicate anions in some magmatic silicate melts were estimated. The results obtained in the present study agreed well qualitatively with those estimated by some researchers on the basis of other spectroscopic methods.The constituent silicate segments and the distribution of AlO₄ tetrahedra in fully polymerized melts, albite, jadeite and anorthite, have been investigated. The polymerization degree of the silicate segments in the network seemed to decrease with the increase of AlO₄ tetrahedron. It is also suggested, that AlO₄ in the albite melt distributed more randomly, while those in anorthite melt had a tendency to form an aluminous segment.

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Infrarot-spektroskopische Untersuchungen der Silikatanionen-Strukturen einiger magmatischer Silikatschmelzen

Zusammenfassung Die Beziehungen zwischen den Spezies der Silikatanionen in den Silikatschmelzen und ihrer charakteristischen Infrarot-Frequenz wurde untersucht. Es gibt eine einfache Beziehung zwischen dem Verhältnis nicht brückenbildender Sauerstoffatome zu Si-Atomen der Silikatanionen und der charakteristischen Frequenz, die mit einer quadratischen Gleichung beschrieben werden kann. Auf Grund dieser Beziehung werden die Silikatanionen in einigen magmatischen Schmelzen abgeschätzt. Das Ergebnis dieser Untersuchung stimmt qualitativ mit den Werten überein, die von einigen Forschern durch andere spektroskopische Methoden erhalten wurden.Die Silikatsegmente und die Verteilung der AlO₄-Tetraeder in vollkommen polymerisierten Schmelzen, in Albit, Jadeit und Anorthit wurden untersucht. Der Polymerisationsgrad der Silikatsegmente in den Netzwerken scheint mit der Zunahme der AlO₄-Tetraeder geringer zu werden. Die Untersuchungläßt erkennen, daß AlO₄-Tetraeder in Albit unregelmäßig verteilt sind, und in Anorthit die Neigung haben, ein Al-Segment zu bilden.

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With 6 Figures