Mafic magma batches at Vesuvius: a glass inclusion approach to the modalities of feeding stratovolcanoes

Glass inclusions in olivine and diopside phenocrysts from pyroclasts of various eruptions of Vesuvius are representative of the magmas that supplied the volcano in the last 4–5000 years. During this interval the volcano alternated between open conduit activity (e.g. 1944 and 1906 eruptions) with long pauses interupted by Plinian and sub-Plinian eruptions (e.g. 3360 B.P. Avellino, A.D. 79 Pompei, A.D. 472 Pollena). The eruptive behaviour was conditioned in all cases by the presence of shallow reservoirs: two cases are distinguished: (1) small and very shallow, 1906-type; (2) large and deeper Plinian-sub-Plinian magma chamber. Lapilli of 1906 lava fountains contain olivine (Fo_89.5–90.4) including Cr-spinel [Cr/(Cr+Al)] (Cr#>75) and volatile-K-rich tephritic glasses, which represent the first recognized Vesuvius primary magmas. Mg-poorer olivine (Fo_83–89) also occurs in 1906 and 1944 products; it formed within the shallow reservoir, together with pyroxene and leucite, between 1200 and 1130°C, from K-tephritic melts (MgO=6–8 wt%). The Plinian and sub-Plinian pumices contain diopside, phlogopite and minor olivine (Fo_85–87) representing adcumulates wrenched from the chamber walls. Glass inclusions in diopside (and some olivine) range from K-basalt to K-tephrite (MgO=6–8 wt%), with homogenization temperature of 1130–1170°C. They have been regarded as representative of the magmas supplying the Plinian-sub-Plinian chamber(s). The Avellino glass inclusions have K-basaltic compositions, contrasting with the mostly K-tephritic Pompei and Pollena inclusions. They display lower C1 and P contents with respect to the younger tephritic melts, and these variations should reflect primary features of the mantle-derived magmas. The primary and the near-primary Vesuvius magmas, as illustrated by melt inclusions, emphasize high K, P and volatile (H₂O, Cl, F, S) contents, with high K₂O/H₂O (2–2.5), Cl/F (2.5) and Cl/S (2–3) ratios, consistent with a metasomatized mantle source, and distinguishing the Vesuvius potassic primary magmas from those of the northern part of the Roman Province.     

A topological approach to understand a multiple-loop solar flare

We analyze the UV and X-ray data obtained by the SMM satellite for the flare starting at 02:36 UT on November 12, 1980 in AR 2779. From a detailed revision of the Ov emission, we find that the observations are compatible with energy being released in a zone above the magnetic inversion line of the AR intermediate bipole. This energy is then transported mainly by conduction towards the two distant kernels located in the AR main bipole. One of these kernels is first identified in this paper. Accelerated particles contribute to the energy transport only during the impulsive phase.We model the observed longitudinal magnetic field by means of a discrete number of subphotospheric magnetic poles, and derive the magnetic field overall topology. As in previous studies of chromospheric flares, the Ov kernels are located along the intersection of the computed separatrices with the photosphere. Especially where the field-line linkage changes discontinuously, these kernels can be linked in pairs by lines that extend along separatrices. Our results agree with the hypothesis of magnetic energy released by magnetic reconnection occurring on separatrices.     

Circumstellar dust and circumstellar extinction curves

We have calculated the circumstellar extinction curves produced by dust grains which absorb and scatter the stellar radiation in the shells of pre-main-sequence stars. A Monte Carlo method was used to model the radiative transfer in non-spherical shells. The dependence on the particle size distribution and the dust shell parameters has been examined.The application of the theoretical results to explain the extinction and polarization of the Herbig Be star HD 45677 shows that the dust shell is not disk-like and that very small grains are absent in it.     

Flare loops heated by thermal conduction

A flare observed with the Hard X-Ray Imaging Spectrometer (HXIS) was studied during its rise to maximum temperature and X-ray emission rate. Two proximate flare loops, of lengths 2.8 × 10⁹ cm and 1.1 × 10¹⁰ cm, rose to temperatures of 21.5 × 10⁶ K and 30 × 10⁶ K, respectively, in 30 s. Assuming equal heat flux F into each loop from a thermal source at the point where they met, we derive a simple relationship between temperature T and loop length , which gives a loop temperture ratio of 0.68, in close agreement with the observed ratio of 0.72. The observations imply that heating in each loop was maintained by a thermal flux of 5 × 10⁹ ergs cm^-2 s^-1. It is suggested that conductive heating adequately describes the rise and maximum phase emissions in the loops and that long flare loops reach higher temperatures than short loops during the impulsive phase because of an equipartition of energy between them at their point of interaction.     

Large,solid particles in the clouds of Venus: Do they exist?

The discovery of large, solid particles in the clouds of Venus is one of the most significant findings of Pioneer Venus because it means that a substantial mass of the clouds is composed of a material other than sulfuric acid. The evidence which suggests that solid particles form a distinctive size mode is reexamined. The mode is defined by a discontinuity between two size ranges of the Pioneer Venus particle size spectrometer. This discontinuity could represent a real size mode. However, it could also be an artifact of the measurement technique. R. G. Knollenberg (1984) discusses several possible instrumental effects which might have caused this discontinuity. It is hypothesized herein that such effects did occur and that the large particles are really the tail of the mode 2 sulfuric acid particle size distribution and are not a separate mode of solid particles. Using such a revised size distribution, it is shown that all of the Pioneer Venus and Venera optical data from the lower clouds can be explained with sulfuric acid droplets without introducing any solid particles. As a by-product of this analysis, it is also found that the upper clouds of Venus must contain a material with a higher refractive index than sulfuric acid. A small quantity of sulfur could account for this observation.     

On the discrepancy between the magnetic D-component and the overhead horizontal current at high-latitudes

The discrepancy between the overhead E-region current and the magnetic D-component is studied using data obtained by the Chatanika incoherent scatter radar (L = 5.6). The F-region horizontal current is estimated to be too small to cause the observed D-deflection. Also, the assumption that the magnetic effects of the Pedersen and field-aligned currents cancel each other on the ground is shown to be inadequate to solve the problem. The significance of the inclination angle in the data analysis and the importance of the field-aligned current sheets are discussed.     

A relation in families of periodic solutions

We show the existence of a general relation between the parameters of periodic solutions in dynamical systems with ignorable coordinates. In particular, for time-independent systems with an axis of symmetry, the relation takes the form T/A=–/E, whereT is the period,A is the angular momentum, is the angle through which the system has rotated after one period, andE is the energy.     

The north-south distribution of major solar flare events,sunspot magnetic classes and sunspot areas (1955–1974)

The north-south incidence has been studied of 31 white-light flares observed since 1859 and of 1669 events meeting the criteria for major flares of Dodson and Hedeman (1971) for the period 1955–1974. The asymmetry in favor of the northern hemisphere increases strikingly with the importance of the events. Similarly, magnetically complex sunspot groups (Mt. Wilson classes, and) display a more pronounced asymmetry in favor of the north than non-complex groups for 1962–1970. Contrary to the flare asymmetry, the spottedness asymmetry is independent of the size of sunspots.     

Thermoluminescence of the lunar surface

Observations of the lunar luminescence are reported for a dozen of specific Moon features using the line-depth method with a high resolution spectroscopic technique. The data indicate a variation of the Moon proper emission as a function of the phase angle which is interpreted as a proof of the thermoluminescent origin of this emission.