bluuebunny/crossref_metadata_2025 huggingface dataset:
Deep Impact and sample return
Authors: A’Hearn Michael F. , Belton Michael J. S. , Collins Steven M. , Farnham Tony L. , Feaga Lori M. , Groussin Olivier , Lisse Carey M. , Meech Karen J. , Schultz Peter H. , Sunshine Jessica M.
Published: August 2014

Returning a cold sample containing the ices from a cometary nucleus has long been an unachievable goal of cometary scientists. The results from the Deep Impact encounter with comet Tempel 1 suggest that the task is much easier than previously thought. Thus a cold sample return with ice becomes an achievable goal, at least from comet Tempel 1 and plausibly from other, active Jupiter-family comets.
Asteroids and the origin of life—two steps of chemical evolution on the surface of these objects
Authors: Simakov M. B.
Published: August 2014

It is now well-known that carbonaceous chondrites contain large quantities of prebiotic molecules, including amino acids, carbohydrates, and heterocyclic bases of nucleic acids. It has become evident that the chemical evolution proceeds under conditions of open space, which serves as a huge chemical reactor. The extraterrestrial origin of these prebiotic molecules has been established on the basis of diversity, molecular structure, and isotopic composition. The molecular composition of a meteorite’s organics resembles abiotic processes governed by physico-chemical processes that occurred on the parent bodies, including asteroids. The synthesis of soluble compounds in carbonaceous chondrites consists of a multi-step process in which organic precursors were formed in the interstellar cloud, incorporated with many volatiles into icy planetesimals and, upon aqueous processing produced the variety of compounds which can form complexes under space energy sources. We show experimentally that the solid mixtures of biologically significant compounds (nucleosides and amino acids) produce more complex compounds when they are exposed to either vacuum UV photons or ionizing radiation.
Performance and scientific objectives of the SELENE (KAGUYA) Multiband Imager
Authors: Ohtake Makiko , Haruyama Junichi , Matsunaga Tsuneo , Yokota Yasuhiro , Morota Tomokatsu , Honda Chikatoshi ,   LISM team
Published: August 2014

The Multiband Imager (MI) is one of the 14 instruments for the Japanese SELENE (KAGUYA) mission. Goal of the SELENE (KAGUYA) mission is to understand origin and evolution of the Moon by obtaining global element and mineral compositions, topological structure, gravity field of the whole Moon, and electromagnetic and particle environment of the Moon. MI is designed to be a high-resolution multiband imaging camera with a spatial resolution in visible bands of 20 m and a spatial resolution in near-infrared bands of 62 m from the 100 km SELENE (KAGUYA) orbit altitude. The MI flight model has been manufactured and integrated. MTF, viewing vector, over-all sensibility, sensor linearity and electrical noise level (S/N estimation test) were measured, and the results indicate that the MI will provide sufficient MTF and low-noise data, just as estimated in the MI design phase. Operation and data analyses plans have been established, and related tools and algorithms have been developed and checked. One of MI scientific objectives is to investigate small but scientifically very important areas such as crater central peaks and crater walls and to investigate magnesian anorthosites.
Numerical estimation of lunar X-ray emission for X-ray spectrometer onboard SELENE
Authors: Ogawa Kazunori , Okada Tatsuaki , Shirai Kei , Kato Manabu
Published: August 2014

We conducted a numerical estimation of lunar X-ray spectra, which is applicable for lunar X-ray fluorescence observations using an X-ray spectrometer (XRS) onboard the SELENE orbiter, with an improved simulation model. We investigated the integration times of measurements for six elements (Mg, Al, Si, Ca, Ti, and Fe) to achieve signal-to-background ratio of over 10 under various solar conditions. The results of these calculations indicate that expected along-the-track spatial resolutions of a single orbital path for Mg, Al and Si will be <90 km and 20 km under normal and active Sun conditions, respectively. Ca, Ti and Fe will be also detectable with a spatial resolution of 20 km during the periods active solar flares over M1 class happen to occur.
The possibility of studying the lunar ionosphere with the SELENE radio science experiment
Authors: Imamura Takeshi , Oyama Koh-Ichiro , Iwata Takahiro , Kono Yusuke , Matsumoto Koji , Liu Qinghui , Noda Hirotomo , Futaana Yoshifumi , Nabatov Alexander
Published: August 2014

The electron density profiles above the lunar surface will be observed by the radio occultation technique during the SELENE mission using the Vstar sub-satellite. Previous radio occultation observations have indicated the existence of an ionosphere with densities of up to 1000 cm−3 above the dayside lunar surface. The measured densities are difficult to explain theoretically when the removal of plasma by the solar wind is considered, and thus the generation mechanism of the lunar ionosphere is a major issue, with even the validity of previous observations still under debate. The SELENE radio science experiment will establish the morphology of the lunar ionosphere and will reveal its relationship with various physical conditions to provide possible clues to the mechanism.
Effects of interactions between stations on the calculation of geomagnetically induced currents in an electric power transmission system
Authors: Pirjola Risto
Published: August 2014

“Geomagnetically induced currents” (GIC) in ground-based technological networks are a manifestation of space weather. GIC are a potential source of problems to the systems and therefore important in practice. GIC in a power system (or in principle in any other discretely-earthed system) can be calculated conveniently by using matrix equations presented earlier. Since temporal variations associated with GIC are slow compared to the 50/60 Hz frequency used in power transmission, a dc treatment is acceptable. An essential quantity in calculations of GIC in a power grid is the earthing impedance matrix, which is the transfer function coupling GIC flowing to (from) the Earth with the voltages between the earthing points, called nodes or (sub)stations, and a remote earth. The diagonal elements of the matrix equal the earthing resistances of the nodes whereas an off-diagonal element expresses how much GIC at one earthing point affects the voltage at another node. In GIC calculations, except for some special treatments of individual sites, the off-diagonal elements are usually neglected by saying simply that the earthing points (are assumed to) lie distantly enough. In this paper, we examine the effects of off-diagonal elements of the earthing impedance matrix, i.e. the effects of interactions between different stations, on GIC calculations in greater detail and more quantitatively than before. We consider a fictitious system that represents a high-voltage power grid and a simple “network” consisting of two stations with a line connecting them. For both systems, the conclusion can be drawn that the off-diagonal elements do not play a major role in practice. Modelling them only approximately, or even ignoring them, is not of great significance compared to other shortcomings involved in GIC calculations. This is particularly true when looking at a power grid as a whole although at some individual stations the neglect may lead to larger errors in GIC values.
A detector telescope’s pitch angle sampling of magnetospheric particles
Authors: Adel Miah M.
Published: August 2014

A geometrical method developed for a particle detector can be extended for application to the determination of the pitch angle sampling capability of the particle telescope of any orientation and for the parent satellite of any orbital orientation. A unit vector tangent to a dipole geomagnetic field line has been calculated from the dipole magnetic field equations in the geomagnetic coordinate system. Rotation matrices have been used, step-by-step, to align the geomagnetic coordinate frame with the detector coordinate frame. The detector selected in this work has its axis tilted with the local zenith direction. The component of the unit vector in the detector coordinate system is found at an observation point characterized by longitude, latitude, and the geocentric radial distance. Pitch angles are measured with respect to the guiding field direction. The pitch angle sampling factor is used in the calculation of detector response functions to particles of different pitch angles. The sampling efficiency functions are useful to make an absolute comparison of magnetospheric particle fluxes measured by particle telescopes under different solar conditions pertaining to different epochs.
A simple model for mantle-driven flow at the top of Earth’s core
Authors: Amit Hagay , Aubert Julien , Hulot Gauthier , Olson Peter
Published: August 2014

We derive a model for the steady fluid flow at the top of Earth’s core driven by thermal coupling with the heterogeneous lower mantle. The model uses a thermal wind balance for the core flow, and assumes a proportionality between the horizontal density gradients at the top of the core and horizontal gradients in seismic shear velocity in the lowermost mantle. It also assumes a proportionality between the core fluid velocity and its radial shear. This last assumption is validated by comparison with numerical models of mantle-driven core flow, including self-sustaining dynamo (supercritical) models and non-magnetic convection (subcritical) models. The numerical dynamo models show that thermal winds with correlated velocity and radial shear dominate the boundary-driven large-scale flow at the top of the core. We then compare the thermal wind flow predicted by mantle heterogeneity with the 150 year time-average flow obtained from inverting the historical geomagnetic secular variation, focusing on the non-zonal components of the flows because of their sensitivity to the boundary heterogeneity. Comparing magnitudes provides an estimate of the ratio of lower mantle seismic anomalies to core density anomalies. Comparing patterns shows that the thermal wind model and the time-average geomagnetic flow have comparable length scales and exhibit some important similarities, including an anticlockwise vortex below the southern Indian and Atlantic Oceans, and another anticlockwise vortex below Asia, suggesting these parts of the non-zonal core flow could be thermally controlled by the mantle. In other regions, however, the two flows do not match well, and some possible reasons for the dissimilarity between the predicted and observed core flow are identified. We propose that better agreement could be obtained using core flows derived from geomagnetic secular variation over longer time periods.
Depth estimation of fumarolic gas source deduced by fume pressure measurement
Authors: Mori Takehiko , Suzuki Takashi , Hirabayashi Jun’ichi , Nogami Kenji , Ohwada Michiko , Yoshikawa Shin
Published: August 2014

The origin of fumarolic gas is hydrothermal boiling in the active fumarolic area and magma degassing in the active volcano where high temperature gas is discharged. The determination of the fumarolic gas source is important for understanding the geothermal activity or the eruption process. However, it is difficult to determine the gas source by geophysical prospecting using seismic or geomagnetic techniques due to the resolution limitation of these techniques. New measurement tools are therefore necessary. The aim of this study was to determine the conduit length—i.e., the depth of the fumarolic gas source—by measuring the fume pressure, which in turn facilitates the determination of the pressure oscillation of a conduit generated by acoustic resonance. We initially assembled the measuring device and measured the fume pressure at an active fumarole in Kusatsu-Shirane volcano, Japan. Our measuring device succeeded in measuring the pressure oscillation generated by acoustic resonance, revealing that the fumarolic gas source at Kusatsu-Shirane volcano has a depth of approximately 40 m. We propose that the use of an acoustic resonance is an effective approach for deducing the fumarolic gas source.
Paleomagnetic directions of the Gauss-Matuyama polarity transition recorded in drift sediments (IODP Site U1314) in the North Atlantic
Authors: Ohno Masao , Murakami Fumi , Komatsu Fumiki , Guyodo Yohan , Acton Gary , Kanamatsu Toshiya , Evans Helen F. , Nanayama Futoshi
Published: August 2014

The geomagnetic field direction during the Gauss-Matuyama (G-M) polarity transition was investigated from a high-accumulation-rate (≥10 cm/kyr) sediment core drilled in the Gardar drift in the North Atlantic at Site U1314 during Expedition 306 of the Integrated Ocean Drilling Program (IODP). A well-defined characteristic remanent magnetization was generally obtained by alternating field demagnetization. The consistency of the results with records from Icelandic lavas confirms that the North Atlantic drift sediments contain a high-fidelity record of the geomagnetic field change. During the G-M transition, the virtual geomagnetic pole (VGP) latitude shows north-south-north-south rebounding, with the three VGP paths falling within different longitudinal bands. Two of the three paths are close to or within the preferred bands in which transitional VGPs are suggested to be longitudinally confined. Three additional loops occur that approach mid-to-low latitudes from the North or South pole regions. In addition, the VGPs show rapid movement (directional jumps) between VGP clusters.
Decreased b-value prior to the M 6.2 Northern Miyagi, Japan, earthquake of 26 July 2003
Authors: Tsukakoshi Yoshiki , Shimazaki Kunihiko
Published: August 2014

We developed a method to map and investigate temporal changes in theb-value using the signed Akaike information criterion (AIC) value and seismicity rate before the 2003 September 26–27 Northern Miyagi earthquake sequence. We studied the seismicity within a radius of 30 km around the epicenter of the largest shock, which wasM6.4, by three approaches: an analysis of all the events listed in the catalog; an analysis of only background events, but on data extracted by two different methods. We found that the change in theb-value of the clustered activities and background activities are different. Theb-value of all events decreased from 1.2 to 0.7 and that of background event decreased even more. We empirically modeled the precursory temporal variation of theb-value and searched similar patterns among 971 areas chosen sequentially from inland Japan. The precursory pattern was both rare and significant; the AIC value was the second most significant factor among the more than 3000 tests conducted on 971 areas, each with four time windows. If the catalog was not declustered, the AIC of the precursory pattern became lower.
Interaction of Alfven waves with a turbulent layer
Authors: Pilipenko V. , Fedorov E. , Engebretson M. J.
Published: August 2014

We consider the interaction of Alfven waves with a resistive turbulent layer with anomalous conductivity. High-frequency turbulence causes the occurrence of both field-aligned and transverse resistivity. The correct dispersion relationship for Alfven waves in a turbulent medium with anisotropic conductivities has been derived. Alfven waves may partially reflect from a resistive layer, be absorbed in it, or be transmitted through it. When field-aligned resistivity dominates, the relative effectiveness of these processes critically depends on the wave transverse scale. For a thin layer as compared with the wave field-aligned length, the characteristic parameter that controls the effectiveness of the wave interaction with a layer is the resistive Alfven scale λA, determined by the field-aligned resistance and Alfven velocity above the layer. Comparison of energy losses estimated from analytical relationships for a “thin” layer and from numerical calculations for a finite width layer shows that the thin layer approximation provides a reasonable estimate over a wide range of wave scales, not only very small. Estimation of the effective damping scale of the Pc1 waves in a turbulent cusp shows that the cusp proper cannot be a conduit of Pc1 wave energy from the magnetosheath to the ground. The “thin” layer model has been applied to the interpretation of the results of early studies of transient ULF wave (Pi2 pulsations) damping during substorm onset, which showed that the damping rate increased for accompanying magnetic bays stronger than ∼100 nT. Our estimates confirm that this additional damping can be caused by the occurrence of anomalous transverse resistance when magnetospheric current exceeds the threshold necessary for the excitation of highfrequency plasma turbulence.
Learning from dynamic triggering of low-frequency tremor in subduction zones
Authors: Miyazawa Masatoshi , Brodsky Emily E. , Mori Jim
Published: August 2014

Remote triggering of small low-frequency seismic tremor (non-volcanic tremor) near the seismic-aseismic transition zone of subduction zones, by surface waves from large distant earthquakes, has been reported in southwest Japan and the Cascadia region. Recent observed triggering in southwest Japan from three large earthquakes (2003 Tokachi-oki, 2007 Solomon, and 2008 Wenchuan) covering wide azimuthal information provides strong evidence for the influence of fluids in the source area. The Coulomb failure stress analyses suggest the effective friction coefficient is large for southwest Japan and small for the Cascadia region, which could be related to the amount of fluid in the source regions of the low-frequency tremor.
Frequency and field dependent susceptibility of magnetite at low temperature
Authors: Özdemir Özden , Dunlop David J. , Jackson Michael
Published: August 2014

We report the temperature dependence of in-phase and quadrature susceptibilities, k′ and k″, between 20 K and 300 K for a stoichiometric natural single crystal of magnetite. Measurements were made for amplitudes of the AC driving field ranging from H = 30 A/m to 2 kA/m and frequencies ranging from f = 40 Hz to 4 kHz. In cubic magnetite above the Verwey transition, TV = 120 K, k′ is limited by self-demagnetization and does not vary greatly with T, H or f. As the crystal cools through TV and transforms to monoclinic structure, k′ decreases by about a factor 2, with a further more gradual decrease of 10-20% in cooling from 40 to 20 K. Saturation remanence also drops sharply at T
V but shows no further change in cooling below 40 K. Thus it appears that domain walls remain pinned throughout the 20-40 K range but small segments undergo reversible oscillations in an AC field, the amplitude of oscillation decreasing steadily with cooling below 40 K. In this same range, k″ reaches a peak, while the temperature at which k′ decreases most rapidly changes with frequency. Both observations indicate that domain wall oscillations lag appreciably behind the driving field at very low temperature. Both k′ and k″ increase markedly with increasing AC field amplitude below TV. The field dependence is particularly strong below 40 K. Analysis of the k′(f) data between 20 and 40 K based on an Arrhenius thermal activation equation gives a pre-exponential frequency factor f
o ≈ 2.5 × 108 s-1 and an activation energy ΔE = 0.035 eV. The ΔE is appropriate for electron hopping but f
o suggests an indirect mechanism for wall mobility related to changes in electron ordering within walls.
Formation of magnetite in Magnetospirillum gryphiswaldense studied with FORC diagrams
Authors: Carvallo Claire , Hickey Stanislawa , Faivre Damien , Menguy Nicolas
Published: August 2014

In order to study the formation of magnetite in magnetotactic bacteria, FORC diagrams were measured on a set of cultured Magnetospirillum gryphiswaldense, following an assay in which the iron uptake is used only for magnetite formation and not for cell growth. This enabled us to follow the magnetite formation independently of growth. The FORC diagrams showed a clear evolution from a size-distribution with a majority of superparamagnetic grains, to a distribution dominated by stable, single-domain grains, but still containing some superparamagnetic particles. TEM observations confirm this evolution. According to the saturation isothermal remanent magnetization cooling and warming curves, the Verwey transition can only be seen in the most mature samples, and slightly below 120 K. This suggests that the samples may have suffered from some partial oxidation.
New palaeomagnetic results from Late Paleozoic volcanic units along the western Gondwana margin in La Pampa, Argentina
Authors: Tomezzoli Renata Nela , Pierre Teresa Saint , Valenzuela Claudia
Published: August 2014

Preliminary palaeomagnetic results from the Paleozoic volcanic units along the Gondwana margin in Argentina are presented. Even though we are still working on the palaeomagnetic data of the sampled section, these data are consistent with data from former studies carried out in the area. More than 90 specimens were measured from the Sierra Chica locality (37°52′S; 65°27′W) computed in 11 sites (Sc1-Sc11). These rocks are carriers of a characteristic remanence magnetization with reverse polarity, acquired during the Early Permian and assigned to the Kiaman Superchron. The resulting palaeomagnetic pole (PP) is Lat.: 64°S; Long.: 017°E, A95 = 15°, K = 12, N = 10. Others interpretations are also possible if the directions of two sites (SC9 and SC10) are considered to have a different magnetic field record. In that case, the PP calculated for sites Sc1-Sc7 is Lat.: 65°S; Long.: 44°E, A95 = 8°, K = 54, N = 7, and the virtual geomagnetic pole (VGP) calculated for sites Sc9 and Sc10 is Lat.: 48.5°S; Long.: 315°E, A
95 = 8°, N = 2. The last possibility to consider Sc9 and Sc10 after structural correction, and the resulting PP position is Lat.: 66.5°S; Long.: 034°E, A
95 = 8°, K = 41, N = 9. This deformation episode could be related to the San Rafaelic orogenic phase, found for the first time in La Pampa province, but previously observed in other neighboring areas during Permian time. However, more detailed palaeomagnetic sampling, rock magnetism studies, and age dating are necessary to complete the palaeomagnetic study of this area.
Geophysical investigation of seamounts near the Ogasawara Fracture Zone, western Pacific
Authors: Lee Tae-Gook , Lee Kiehwa , Hein James R. , Moon Jai-Woon
Published: August 2014

This paper provides an analysis of multi-channel seismic data obtained during 2000–2001 on seamounts near the Ogasawara Fracture Zone (OFZ) northwest of the Marshall Islands in the western Pacific. The OFZ is unique in that it is a wide rift zone that includes many seamounts. Seven units are delineated on the basis of acoustic characteristics and depth: three units (I, II, and III) on the summit of seamounts and four units (IV, V, VI, and VII) in basins. Acoustic characteristics of layers on the summit of guyots and dredged samples indicate that the seamounts had been built above sea level by volcanism. This was followed by reef growth along the summit margin, which enabled deposition of shallow-water carbonates on the summit, and finally by subsidence of the edifices. The subsidence depth of the seamounts, estimated from the lower boundary of unit II, ranges between 1,550 and 2,040 m. The thick unit I of the southern seamounts is correlated with proximity to the equatorial high productivity zone, whereas local currents may have strongly affected the distribution of unit I on northern seamounts. A seismic profile in the basin around the Ita Mai Tai and OSM4 seamounts shows an unconformity between units IV and V, which is widespread from the East Mariana Basin to the Pigafetta Basin.
Timing of substorm related auroral oscillations
Authors: Martin P. , Turner N. E. , Wanliss J.
Published: August 2014

Previous studies have shown that auroral luminosity oscillations are often associated with substorms. Here we examine photometer data for the magnetospheric substorm on April 1, 2000 (expansive phase onset at 0525 UT) to study the detailed timing of the auroral oscillations relative to onset. Accurate timing information for the periodicities in the photometer data were determined using the wavelet transform. We find that the oscillations occur primarily during the recovery phase.
Investigation of ionospheric gradients for GAGAN application
Authors: Chandra K. Ravi , Srinivas V. Satya , Sarma A. D.
Published: August 2014

To cater to the needs of aviation applications, GPS Aided GEO Augmented Navigation (GAGAN) system is being implemented over the Indian region. The most prominent parameter affecting the navigation accuracy of GAGAN is ionospheric delay which is a function of TEC. In the equatorial and low latitude regions such as India, TEC is often quite high with large spatial gradients. Carrier phase data from the GAGAN network of Indian TEC Stations is used for estimating ionospheric gradients in multiple viewing directions. Rate of TEC (ROT) and Rate of TEC Index (ROTI) are calculated to identify the ionospheric gradients. Among the satellite signals arriving in multiple directions, the signals which suffer from severe ionospheric gradients are identified and avoided for improving GAGAN positional accuracy. The outcome of this paper will be helpful for improving GAGAN system performance.
Modification of the Network-MT method and its first application in imaging the deep conductivity structure beneath the Kii Peninsula, southwestern Japan
Authors: Yamaguchi Satoru , Uyeshima Makoto , Murakami Hideki , Sutoh Sirou , Tanigawa Daichi , Ogawa Tsutomu , Oshiman Naoto , Yoshimura Ryokei , Aizawa Koki , Shiozaki Ichiro , Kasaya Takafumi
Published: August 2014

The Network-Magnetotelluric (NMT) method is well-suited for investigating deep and large-scale conductivity structure; however, application of the method is strongly dependent on the availability of telecommunication facilities (specifically, metallic transmission cables). To overcome the problem posed by the progressive replacement of metallic transmission cables with fiber cables, we developed a modified NMT (modified NMT) method consisting of purpose-built electrodes, making use of local metallic telecommunication lines, without a transmission cable. We first applied this modified NMT method over the Kii Peninsula, southwestern Japan, undertaking two-dimensional conductivity modeling along a transect across the central part of the peninsula. The model is characterized by a large (∼20 km wide and depths of 10–60 km) and highly conductive (< 10 Ω m) zone in the central part of the peninsula between the Conrad discontinuity and the upper surface of the Philippine Sea slab. This zone contains the hypocenters of many deep low-frequency tremors but regular earthquakes are rare. The zone also corresponds to a high-V

p
/V

s
area. The presence of fluid in the zone plays a key role in the absence of regular earthquakes, occurrence of deep low-frequency tremors, and elevated V

p
/V

s
values, as well as enhancing conductivity.
Argon retentivity of carbonaceous materials: feasibility of kerogen as a carrier phase of Q-noble gases in primitive meteorites
Authors: Osawa Takahito , Hirao Norie , Takeda Nobuyori , Baba Yuji
Published: August 2014

Extremely large amounts of heavy noble gases are concentrated in phase Q, which seems to be a carbonaceous phase analogous to terrestrial Type III kerogen. Phase Q must have very high noble gas retentivity based on the presence of such extremely large amounts of heavy noble gases in a very minor fraction of the meteorite. To verify that kerogen is a carrier phase of Q-noble gases, X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) using synchrotron radiation were carried on for kerogens (coals) and carbon allotropes that had been bombarded by 3-keV Ar ions, and the Ar retentivities of the two materials were compared. This comparison of the estimated Ar concentrations in the target materials revealed that carbon allotropes (graphite, fullerene, carbon nanotube, and diamond) have a much higher Ar retentivity than kerogens. This unexpected result clearly shows that the terrestrial kerogens tested in our study are not suitable as a carrier phase of Ar and, consequently, that phase Q may not be similar to the terrestrial kerogen tested. If heavy noble gases are really concentrated in carbonaceous components of primitive meteorites, phase Q may have a more ordered structure than terrestrial kerogen based on the fact that the greatest difference between terrestrial kerogen and carbon allotropes is the degree of order of the molecular structure.
Seismicity in source regions of large interplate earthquakes around Japan and the characteristic earthquake model
Authors: Ishibe Takeo , Shimazaki Kunihiko
Published: August 2014

The occurrence rate of the characteristic earthquake (CE) was compared with seismicity in nine source regions of interplate earthquake (i.e., the regions off Shikotan Island, off Nemuro, off Tokachi, off Northern Sanriku, off Miyagi, far off Miyagi, and the Tonankai, Nankai, and Kanto regions) by combining instrumental data and the recurrence interval of CEs evaluated by the Headquarters for Earthquake Research Promotion (HERP) in Japan. The recurrence interval of the Nankai earthquake was estimated on the basis of long historical records and found to be one of the least uncertain ones. We used the unified catalog of earthquakes obtained by the Japan Meteorological Agency (JMA) on the basis of a recently improved seismic network, together with the old JMA catalog. Seismicity of all the interplate source regions indicated that the number of observed events was much less than the number of events predicted from the Gutenberg-Richter (G-R) relation and the occurrence rate of the CE. In all regions except for far off Miyagi, the CEs occurred during the interval of the earthquake catalog. Thus, our data set included the highest seismicity period during an earthquake cycle. In the region off Tokachi where the 1952 and 2003 Tokachi-Oki earthquakes occurred, the magnitude frequency distribution (MFD) during one seismic cycle exhibited a magnitude gap of 1.1 between the CE and the other events. Therefore, our results favored the CE model. Moreover, we conversely estimated an average recurrence interval of the CEs in each region, based on the assumption that the G-R relation holds. Most estimated recurrence intervals were far longer than the evaluation given by HERP.
Characteristics of discrete VLF falling-tone chorus emissions observed at low latitude ground station Jammu
Authors: Singh Ashutosh K. , Patel R. P. , Singh R. , Singh K. K. , Singh A. K.
Published: August 2014

The discrete VLF chorus emissions recorded at low latitude ground station Jammu (geomag. lat. = 22°26′N, L = 1.17) are reported and their characteristics based on spectral analysis have been carried out. These discrete chorus emissions are falling tone emissions which are rarely observed at low latitude ground stations. These discrete chorus emissions are generated during a strong geomagnetic storm period of 2–7 May, 1998. We have computed the frequency sweep rate, repetition period and source region of the individual chorus elements. It is observed that the sweep rate increases with time.
Mantle-driven geodynamo features—effects of post-Perovskite phase transition
Authors: Amit Hagay , Choblet Gaël
Published: August 2014

Exploring the impact of the heterogeneous lower mantle on the geodynamo requires knowledge of the heat flux anomaly across the core-mantle boundary. Most studies so far used a purely thermal interpretation of seismic shear wave anomalies to assign heterogeneous heat flux boundary conditions on numerical dynamo models, ignoring phase transition or compositional origins. A recent study of mantle convection (Nakagawa and Tackley, 2008) provides guidelines to include such non-thermal effects. Here we construct maps of heat flux across the core-mantle boundary based on a lower mantle tomography model (Masters et al, 2000) with a combined thermal and post-Perovskite phase transition interpretation. We impose these patterns as outer boundary conditions on numerical dynamo simulations and study the impact of accounting for post-Perovskite effects on the long-term time-average properties of the dynamo. We then compare our results with geophysical observations. We find in all cases that surface downwellings associated with cyclones concentrate intense non-axisymmetric magnetic flux at high-latitudes, the surface flow contains a large anticlockwise vortex at mid-latitudes of the southern hemisphere, and the inner boundary buoyancy flux is dominated by a Y
2
0
pattern. Boundary-driven time-average surface flow with some equatorial asymmetry is organized in the shell by quasi-axial convective rolls that extract more buoyancy from low-latitudes of the inner-boundary. These positive inner boundary buoyancy flux structures are found at low-latitudes of the northern hemisphere, in some places due to cyclonic flow at mid-latitudes of the southern hemisphere connecting with higher latitude cyclonic flow in the northern hemisphere. Accounting for post-Perovskite effects improves the recovery of several geodynamo observations, including the Atlantic/Pacific hemispherical dichotomy in core flow activity, the single intense paleomagnetic field structure in the southern hemisphere, and possibly the m = 1 dominant mode of inner-core seismic heterogeneity.
Continuous thermal monitoring of the 2008 eruptions at Showa crater of Sakurajima volcano, Japan
Authors: Yokoo Akihiko
Published: August 2014

An infrared thermal monitoring system installed 3.5 km from the Showa crater of Sakurajima volcano, Japan, enabled the capture of continuous thermal waveform data at 1 Hz during two recent episodes of eruptive activity. The eruptions were characterized by a sudden increase in volcanic cloud temperature in the first 2–5 s, followed by gradual cooling over a few minutes. The maximum cloud temperature varied widely between individual events with a range of more than 180°C. A positive relation between the maximum temperature and the exit velocity of the cloud has also been established. At higher temperatures and faster exit velocities of the volcanic cloud, the eruptions tend to be accompanied by pyroclastic density currents. However, no strong correlation was observed in a 6-month period of 2008 between temporal changes in surface manifestation of eruptive activity and the change of cloud temperatures. Identification of factors that control such observed apparent temperatures of volcanic cloud would lead to a better understanding of the thermodynamics of the eruption itself.
Geomagnetic sudden commencement at the dawn-time dip equator
Authors: Han De-Sheng , Li Qi
Published: August 2014

Waveform of geomagnetic sudden commencement (SC) on the ground depends on both latitude and local time (LT). Using high-resolution (1 s) geomagnetic field measurements obtained at Jicamarca (JIC, MAGLAT = 0.0°) from 1998 to 2005, we examined the waveforms of 188 SC events and found that some of the SCs observed at nighttime (approx. 22-05 LT) and dawn time (approx. 05-07 LT) had a common observational feature, i.e., a positive impulse always appeared at the beginning of the main impulse of the SC, which led to these events show preliminary positive impulse (PPI) or ‘Stepwise’ structure in the waveforms. In particular, the occurrence rate of the PPI/Stepwise events at the dawn time was clearly higher than that at the nighttime. This is the first complete report of this observational feature for the SCs observed at the dip equator. Based on a comparison of our observations with the previously proposed model calculation of Kikuchi et al. (2001), we suggest that the PPI/Stepwise events observed at the dawn-time dip equator reflect the effects of the ionospheric currents (ICs) and field-aligned currents (FACs). We therefore argue that this observational result provides evidence for the validity of the model calculation.
Tracking F-region plasma depletion bands using GPS-TEC, incoherent scatter radar, and all-sky imaging at Arecibo
Authors: Seker Ilgin , Livneh Dorey J. , Makela Jonathan J. , Mathews John D.
Published: August 2014

F-region plasma dynamics has been one of the main foci of the ionospheric research community for decades. The mid-latitude F-region has been considered to be relatively calm; however recent observations using highly sensitive CCD imaging systems and Global Positioning System (GPS) receivers have revealed that mid-latitude F-region mesoscale electrodynamics are more complex and this region is more active than usually assumed. Here we report combined incoherent scatter radar (ISR), imager, and GPS observations of F-region Medium-Scale Traveling Ionospheric Disturbance (MSTID) structures over the Arecibo Observatory in Puerto Rico. In particular, the plasma structures seen in the narrow-beam ISR cannot be understood fully without the all-sky images, which provide the context for the radar results—specifically, the spatial and temporal properties of the mesoscale structure. The GPS-derived total electron content (TEC) data provide additional information on the intensity of the MSTIDs. Here we present analysis of two specific plasma depletion events, which we prefer to call “MSTID bands”. Important results on the 3D geometry of these structures were found using a newly developed observation technique. For the first time, it is shown that the southern part of MSTID bands reaches higher altitudes than the northern part (vertically tilted by 12° towards magnetic south). These results give a much broader perspective on nighttime, mid-latitude F-region structure and point to new ways of interpreting these structures and how they appear in ISR results.
Time-evolution of bubble formation in a viscous liquid
Authors: Yamada Kou , Emori Hiroyuki , Nakazawa Kiyoshi
Published: August 2014

Time-evolutions of bubble vesiculation in viscous liquid are characterized by two stages, i.e., the bubble formation stage and the bubble coalescence stage. We have focused on the former stage of bubble vesiculation and investigated numerically bubble formation in decompressed viscous liquid. Bubble formation consists of nucleation and growth of bubbles due to the exsolution of volatile elements from liquid. In order to describe the bubble formation processes, we have developed a theoretical model, taking into account the bubble size distribution and the viscosity of liquid, on the base of the model proposed by Toramaru (J. Geophys. Res., 100, 1913–1931, 1995). Numerical solutions show that the feature of bubble nucleation is significantly varied according to the magnitude of the liquid viscosity. In low viscosity cases, the growth of bubbles is mainly controlled by the diffusive flux of volatile molecules to bubbles. The number density of bubbles is sensitive to the diffusivity of volatile element in liquid. On the other hand, bubbles hardly grow in the case of the extremely high viscosity. Therefore, bubbles continue to be formed in order to reduce the volatile oversaturation of liquid. In the case of the intermediate viscosity, bubbles grow to the large size slowly by the viscous resistance. After the nucleation of bubbles ceases, the Ostwald ripening occurs and leads to the dissolution of small bubbles. The number density of bubbles varies greatly with time. The time-evolutions of the bubble size distribution have been also caluclated. In the case of the low and extreme high viscosity, the bubble size distribution evolves as an unimodal size distribution. In the case of the moderate viscosity, the size distribution of bubbles shows the distribution with a wider dispersion. These characteristic time-evolutions of the number density and size distribution of bubbles would be useful in evaluating material quantities such as the diffusivity, the viscosity, and the surface tension of liquid from experimental results. Furthermore our results provide the number density and size distribution of bubbles just before bubble coalescence occurs.
Probability distribution of orbital crossing times in a protoplanetary system
Authors: Emori Hiroyuki , Nakazawa Kiyoshi , Iwasaki Kazunori
Published: August 2014

Long term behavior of five protoplanets was studied under the same conditions as those used in Chambers et al. (1996). One major difference was the number of calculations carried out for one parameter set of initial orbital distance. We reconfirmed their result for the orbital crossing times among five protoplanets starting from circular and co-planar orbits with an equal distance of their semi major axes. For each distance, the distribution of orbital crossing times was calculated from 500 sets of azimuthal positions of protoplanets randomly chosen. The distribution of the times around the average value resembles each other for almost all orbital distance cases. Based on a statistical certification we conclude that the fluctuations in orbital crossing times take “the log normal function”. The dispersion of the log normal distribution function is equal to 0.2. This means that 70% of the events of orbital crossing occurs in the range between 10−0.2 times earlier and 100.2 times later than the average orbital crossing time.
Efficient GPS receiver DCB estimation for ionosphere modeling using satellite-receiver geometry changes
Authors: Hong Chang-Ki , Grejner-Brzezinska Dorota A. , Kwon Jay Hyoun
Published: August 2014

A new and efficient algorithm using the geometry conditions between satellite and tracking receivers is proposed to determine the receiver differential code bias (DCB) using permanent reference stations. This method does not require a traditional single-layer ionosphere model and can be used for estimating DCBs of receivers in a regional network as long as one of the receiver DCBs is already known. The main underlying rationale for this algorithm is that the magnitude of the signal delay caused by the ionosphere is, under normal conditions, highly dependent on the geometric range between the satellite and the receiver. The proposed algorithm was tested with the Ohio Continuously Operating Reference Stations (CORS) sub-network data. The results show that quality comparable to the traditional DCB estimation method is obtainable by implementing this simple algorithm.
Well-resolved hypocenter distribution using the double-difference relocation method in the region of the 2007 Chuetsu-oki Earthquake
Authors: Yukutake Yohei , Takeda Tetsuya , Obara Kazushige
Published: August 2014

The 2007 Chuetsu-oki Earthquake (Mj= 6.8) occurred in the eastern margin of the Japan Sea where high strain rates have been observed and many large earthquakes have occurred. The main shock was located near the Western Nagaoka Basin active fault system dipping in the westward direction. We estimated the well-resolved hypocenter location around the main shock rupture zone from the differential arrival times obtained by both manual picking and waveform cross-correlation analysis. From the relocated aftershock distributions, we successfully resolved the detailed fault structures activated by the main shock. The estimated fault model resolves four individual fault segments. The fault model suggests that the main shock predominantly ruptured the southeastward dipping fault planes. On the other hand, the aftershocks around the hypocenter of the main shock occurred on both the northwestward and southeastward dipping fault planes. Both fault planes around the hypocenter of the main shock may have been nearly coincidentally ruptured during the main shock.
Precise aftershock distribution of the 2007 Chuetsu-oki Earthquake obtained by using an ocean bottom seismometer network
Authors: Shinohara Masanao , Kanazawa Toshihiko , Yamada Tomoaki , Nakahigashi Kazuo , Sakai Shin’ichi , Hino Ryota , Murai Yoshio , Yamazaki Akira , Obana Koichiro , Ito Yoshihiro , Iwakiri Kazuhiro , Miura Ryo , Machida Yuya , Mochizuki Kimihiro , Uehira Kenji , Tahara Michitaka , Kuwano Asako , Amamiya Shin’ichiro , Kodaira Shuichi , Takanami Tetsuo , Kaneda Yoshiyuki , Iwasaki Takaya
Published: August 2014

The Chuetsu-Oki Earthquake occurred on July 16, 2007. To understand the mechanism of earthquake generation, it is important to obtain a detailed seismic activity. Since the source region of the 2007 Chuetsu-oki Earthquake lies mainly offshore of Chuetsu region, a central part of Niigata Prefecture, it is difficult to estimate the geometry of faults using only the land seismic network data. A precise aftershock distribution is essential to determine the fault geometry of the mainshock. To obtain the detailed aftershock distribution of the 2007 Chuetsu-oki Earthquake, 32 Ocean Bottom Seismometers (OBSs) were deployed from July 25 to August 28 in and around the source region of the mainshock. In addition, a seismic survey using airguns and OBSs was carried out during the observation to obtain a seismic velocity structure below the observation area for precise hypocenter determination. Seven hundred and four aftershocks were recorded with high spatial resolution during the observation period using OBSs, temporally installed land seismic stations, and telemetered seismic land stations and were located using the double-difference method. Most of the aftershocks occurred in a depth range of 6–15 km, which corresponds to the 6-km/s layer. From the depth distribution of the hypocenters, the aftershocks occurred along a plane dipping to the southeast in the whole aftershock region. The dip angle of this plane is approximately 40°. This single plane with a dip to the southeast is considered to represent the fault plane of the mainshock. The regions where few aftershocks occurred are related to the asperities where large slip is estimated from the data of the mainshock. The OBS observation is indispensable to determine the precise depths of events which occur in offshore regions even close to a coast.
Global distribution of the thermospheric disturbances produced by effects from the upper and lower regions: simulations by a whole atmosphere GCM
Authors: Fujiwara Hitoshi , Miyoshi Yasunobu
Published: August 2014

It is well-known that low-latitude ionospheric/thermospheric disturbances are sometimes generated in association with the passage of traveling ionospheric/atmospheric disturbances (TIDs/TADs) produced in the high-latitude region and that the low-latitude ionosphere/thermosphere should be strongly coupled with the lower atmosphere. These facts suggest that the appearance of thermospheric disturbances with complex structures in the low-latitude region are the result of a superposition of disturbances which have different origins. We have investigated the lower atmospheric effects on the morphology of the thermospheric disturbances in response to changes in the geomagnetic activity by using a whole atmosphere general circulation model (GCM). In order to suppress the lower atmospheric effects, we set the global mean temperature and zero-wind below about 80-km altitude in the GCM. The simulation results show that the lower atmospheric effects can produce latitudinal and longitudinal structures in the low-latitude thermosphere. These lower atmospheric effects also modulate the amplitudes and structures of TADs propagating from the high- to low-latitude regions. Our results suggest that the lower atmospheric effects can produce variability in the TIDs/TADs, which in turn would create conditions conducive to plasma instabilities in the low-latitude ionosphere.