The first confirmed Perseid lunar impact flash

The first confirmed lunar impact flash due to a non-Leonid meteoroid is reported. The observed Perseid meteoroid impact occurred at 18^h28^m27^s on August 11, 2004 (UT). The selenographic coordinates of the lunar impact flash are 48±1° N and 72±2° E, and the flash had a visual magnitude of ca. 9.5 with duration of about 1/30 s. The mass of the impactor is estimated to have been 12 g based on a nominal model with conversion efficiency from kinetic to optical energy of 2×¹⁰⁻³. Extrapolation of a power law size-frequency distribution fitting the sub-centimeter Perseid meteoric particles to large meteoroids suggests that several flashes should have been observed at this optical efficiency. The detection of only one flash may indicate that the optical efficiency for Perseid lunar impact is much lower, or that the slope of the size distribution differs between large meteoroids and typical sub-centimeter meteoric particles.     

Experimental determination of partition coefficients of ten rare earth elements and barium between clinopyroxene and liquid in the synthetic silicate system at 20 kilobar pressure

Two experiments were carried out at 20 kb pressure for the measurement of partition coefficients of ten lanthanides and barium between diopside clinopyroxene and liquid in the synthetic system diopside-enstatite-silica-H₂O. Starting materials are glass of two different compositions CaMgSi₂O₆ 56, MgSiO₃ 14, SiO₂ 30 weight % and CaMgSi₂O₆ 80, MgSiO₃ 20 weight %.In the experiment on the former composition, the partition coefficient increases regularly with decrease of ionic radii from La to Dy and decreases also regularly from Dy to Lu. In the experiment on the latter composition, stepwise shift of partition coefficient was observed between Dy and Er.The results suggest that the lanthanide cations occupy the site of 8-fold coordination in the clinopyroxene and that the partition coefficients depend on the ionic radii of lanthanide elements and also on the chemical composition of the starting material or heating process during the run.     

Trace element concentrations in the isotopically unique Allende inclusion,EK 1-4-1

Concentrations of rare-earth elements (REE), Sc, Fe, Co, Cr, Na and Ir in the bulk sample and mineral separates of the isotopically unique Allende inclusion, EK 1-4-1, were determined by instrumental neutron activation analysis. REE concentrations were also determined by mass-spectrometric isotope dilution for two density separates.The inclusion showed enrichment of light REE over heavy REE with a positive Yb anomaly, thus showing a tendency to resemble group II fine-grained inclusions in REE abundances, although EK 1-4-1 is a coarse-grained inclusion. High Cr concentrations also indicate group II affinity. However, high Ir (6 ppm) and Sc (105 ppm), and low FeO (1.80%), and Co (13.8 ppm) concentrations in the bulk sample and low Na concentrations in mineral separates show group I affinity.Between melilite and pyroxene fractions, the same samples in which mass-fractionated O isotope ratios were observed (Clayton and Mayeda, 1977), REE, Sc, Co and Fe showed distributions which are substantially different from those observed for “ordinary” Allende type B inclusions. These two minerals do not appear to be in equilibrium with respect to trace element distributions.The results indicate that the isotopically unique EK 1-4-1 is also unusual in its elemental abundances and distributions.     

Microstructural development of fine-grained quartz aggregates by syntectonic recrystallization

Experimental study of syntectonic recrystallization of fine-grained quartz aggregates was carried out in order to simulate the development of some natural microstructures of quartz tectonites and to understand their formation condition. Agate was axially compressed with a constant-strain-rate apparatus. Experiments were conducted at 4 kbar solid confining pressure, 700–1000°C and 10⁻⁴-10⁻⁶ sec⁻¹ to 10%–45% strain. In all runs, deformation has proceeded under wet condition caused by dehydration of pyrophyllite used as pressure medium.Two different types of microstructure were distinguished in the deformed specimens. One is P-type which is characterized by equant, equidimensional, and polygonal grains. The other is S-type which is characterized by the highly oblate grains with the largest dimension perpendicular to the compression axis. The P-type microstructure is developed at higher temperatures and slower strain rates, while the S-type developed at lower temperatures and faster strain rates. The transition between the S- and P-types is found to be very sharp.     

Notes on extended–range atmospheric prediction in the Northern Hemisphere winter

We examined the characteristic feature and predictability of low frequency variability (LFV) of the atmosphere in the Northern Hemisphere winter (January and February) by using the empirical orthogonal functions (EOFs) of the geopotential height at 500 hPa. In the discussion, we used the EOFs for geostrophic zonal wind (Uznl) and the height deviation from the zonal mean (Zeddy). The set of EOFs for Uznl and Zeddy was denoted as Uznl-1. Uznl-2, …, Zeddy-1, Zeddy-2…, respectively. We used the data samples of 396 pentads derived from 33 years of NMC, ECMWF and JMA analyses, from January 1963 to 1995. From the calculated scores for Uznl-1, Uznl-2, Zeddy-1, Zeddy-2 and so on we found that Uznl-1 and Zeddy-1 were statistically stable and their scores were more persistent than those of the other EOFs. A close relationship existed between the scores of Uznl-1 and those of Zeddy-1 30-day forecast experiments were carried out with the medium resolution version of JMA global spectral model for 20 cases in January and February for the period of 1984-1992. Results showed that Zeddy-1 was more predicta?ble than the other EOFs for Zeddy Considering these results, we argued that prediction of the Zeddy-1 was to be one of the main target of extended range forecasting     

On the local equilibrium of winds and wind-waves in relation to surface drag

Local equilibrium of winds and wind-waves is discussed as a basis for research of the drag coefficient of the water surface as well as for the spectral growth of wind-waves. This hypothesis assumes, in a narrow sense, that statistical properties are determined from four physical quantities, which represent winds and wind-waves: the friction velocityu _*, the gravitational accelerationg, the powerE of the surface displacement, and the peak frequency _p of a wind-wave spectrum. Then one has only one nondimensionalcontrol parameter, which may be either the wave age or wave nonlinearity (slope) of dominant waves. In a wide-sense, one can take into account viscosity and surface tension in terms of one more additional parameter by virtue of the virtual invariance of those material constants; that parameter describes the scale ratio between dominant waves and the short waves for which viscosity or surface tension is important. A unified expression for the roughness height according to this hypothesis turns out to include Charnock's and Toba's formulas as special cases. On the basis of a preliminary analysis of the experimental data, a new empirical formula is proposed.     

Thermohaline staircases in the Warm-Core Ring off Cape Erimo,Hokkaido and their fluxes due to salt finger

Thermohaline staircases off Cape Erimo, Hokkaido are described and their physical properties are compared with those in other seas. The mean fluxes for heat and salt across the interface induced by salt finger were estimated as 105 cal cm^–2d^–1, and 0.03 g cm^–2d^–1, respectively. These values were in the same order as those in Caribbean Sea. The effective eddy diffusivities were also in the same order as the Caribbean ones. This suggests that the double-diffusive convection plays on important role on the water mass conversions occurring in the interfrontal zone between the Oyashio and the Kuroshio Waters.     

On the Solar Origins of Intense Geomagnetic Storms Observed During 6–11 March 1993

Intense geomagnetic storms with DST index -100 nT were recorded on 9 March and 11 March 1993 associated with solar activity on 6 March and 9-10 March, respectively. In this paper, we discuss the characteristic features of the solar origins of the two events that gave rise to coronal and interplanetary disturbances and as a consequence produced strong geomagnetic activity at the Earth. The source of the activity in one case is attributed to a major 3M7.0 flare that occurred on 6 March 1993 and in the other case, to two large filament disruptions on the disk during 9-10 March, 1993. Both these sources were found to be located near changing or varying low-latitude coronal holes. They were also located close to the heliospheric currents sheets. Distinct X-ray activity was observed for both the events as observed by the Yohkoh SXT telescope. The detailed evolution and a comparison of these events on the basis of Yohkoh soft X-ray observations are presented here.     

The runaway instability of self-gravitating tori with non-constant specific angular momentum around black holes

We discuss the runaway instability of axisymmetric tori with non-constant specific angular momentum around black holes, taking into account self-gravity of the tori. The distribution of specific angular momentum of the tori is assumed to be a positive power law with respect to the distance from the rotational axis. By employing the pseudo-Newtonian potential for the gravity of the spherical black hole, we have found that self-gravity of the tori causes a runaway instability if the amount of the mass which is transferred from the torus to the black hole exceeds a critical value, i.e. 3 per cent of the mass of the torus. This has been shown by two different approaches: (1) by using equilibrium models and (2) by dynamical simulations. In particular, dynamical simulations using an SPH code have been carried out for both self-gravitating and non-self-gravitating tori. For non-self-gravitating models, all tori are runaway stable. Therefore we come to the conclusion that self-gravity of the tori has a stronger destabilizing effect than the stabilizing effect of the positive power-law distribution of the angular momentum.