bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sharp and seismically transparent inner core boundary region revealed by an entire network observation of near-vertical PKiKP
Authors: Kawakatsu Hitoshi 
Published: August 2014

Abstract
We present an entire network observation of near-vertical PKiKP from the Japanese seismic network, Hi-net. The record section of an intermediate depth (298 km) earthquake in Mariana (2001/07/03 13:10:43, Mw 6.5) shows remarkably clear arrivals of PKiKP in an epicentral distance range of 14–24 degrees. From more than 170 individual picks of PKiKP, we performed array analyses of PKiKP-related seismic phases to infer the structure near the inner core boundary (ICB) with unprecedented high quality. Both PKiKP and PcP showed strong similarity in waveforms up to a frequency of 2 Hz. Both amplitude and waveform analyses indicate that the ICB may be as sharp as the CMB and no thicker than 2 km. The slant stack for a 1–2 Hz frequency band, where PKiKP and PcP show energy peaks and where the background noise level is ∼3% of PKiKP, indicated no conspicuous phase other than SKiKP. We also noted that no gradual energy build-up of the inner core scattering signal was observed. Thus, this part of the inner core appears highly transparent seismically in this frequency range. In the 0.5–1.0 Hz frequency band (10–15% noise level), we observed one possible reflection phase from a slightly dipping (∼5°) reflector/discontinuity inside of the inner core around a depth of 470 km below the ICB (3% reflection). However, this phase may be due to pPKiKP water/crustal layer reverberations. Other than this, there appears to be no sharp (∼5 km thick) horizontal discontinuity in the top 400 km part of the inner core whose reflection amplitude is larger than ∼2%.
Preliminary results of rocket attitude and auroral green line emission rate in the DELTA campaign
Authors: Iwagami Naomoto , Komada Sayaka , Takahashi Takao 
Published: August 2014

Abstract
The attitude of a sounding rocket launched in the DELTA (Dynamics and Energetics of the Lower Thermosphere in Aurora) campaign was determined with IR horizon sensors and geomagnetic sensors. Since the payload was separated into two portions, two sets of attitude sensors were needed. A new IR sensor was developed for the present experiment, and found the zenith-angle of the spin-axis of the rocket with an accuracy of 2°. By combining information obtained by both type of sensors, the absolute attitudes were determined. The auroral green line emission rate was measured by a photometer on board the same rocket launched under active auroral conditions, and the energy flux of the auroral particle precipitation was estimated.
Rocket observation of energetic electrons in the low-altitude auroral ionosphere during the DELTA campaign
Authors: Ogasawara K. , Asamura K. , Takashima T. , Saito Y. , Mukai T. 
Published: August 2014

Abstract
This paper reports on properties of energetic electrons observed by the Auroral Particle Detector (APD) on board the sounding rocket S-310-35, which was launched from And/0ya Rocket Range, Norway, at 0033:00 UT on 13 December 2004 during the DELTA campaign. The APD was designed to measure energy spectra of energetic electrons in the range of 3.5 to 65 keV every 10 ms using avalanche photodiodes. The measurement was done at altitudes of 90–140 km (apogee height of the rocket flight), which corresponded to the collisional interaction region of precipitating electrons with the atmospheric constituents. The overall profile of energetic electron precipitations was consistent with auroral images taken from the ground. The downward fluxes almost always exceeded those of upward electrons, and the ratio of downward to upward fluxes increased with energy and also with altitude. This is reasonably understood in terms of the effect of collisions between the energetic electrons and the atmospheric constituents. An interesting feature in energy spectra of precipitating electrons is the existence of non-thermal electrons at higher energies, regardless of inside or outside of auroral arcs. In order to predict the incident downward spectra at the top of the atmosphere, we have applied an analytic method of Luhmann (1976) to evaluate the collisional effect on the electron spectra. As a result, most of the observed energy spectra of precipitating electrons are well expressed by kappa distributions with the thermal energy of a few hundreds of eV and kappa of 5–8, while the spectrum inside a strong arc is better fitted by the sum of a Maxwellian distribution on the lower energy side and a power law at higher energies. To the authors’ knowledge, this is the first direct and reliable measurement of energy spectra of electrons in the 10-keV energy range in the auroral ionosphere.
Dynamics and Energetics of the Lower Thermosphere in Aurora (DELTA)—Japanese sounding rocket campaign—
Authors: Abe Takumi , Kurihara Junichi , Iwagami Naomoto , Nozawa Satonori , Ogawa Yasunobu , Fujii Ryoichi , Hayakawa Hajime , Oyama Koh-ichiro 
Published: August 2014

Abstract
Japanese sounding rocket “S-310-35” was launched from And/0ya Rocket Range in Norway on December 13, 2004 during Dynamics and Energetics of the Lower Thermosphere in Aurora (DELTA) campaign, in which the rocket-borne in-situ measurements and ground-based measurements were coordinated to carry out a comprehensive observation of the thermospheric response against the auroral energy input. The instruments on board the rocket successfully performed their measurements during the flight, and thereby the temperature and density of molecular nitrogen, auroral emission rate, and the ambient plasma parameters were derived. Simultaneous measurements by the ground-based instruments provided neutral wind, neutral temperature, the auroral images and the ionospheric parameters near the rocket trajectory. This paper introduces science objectives, experimental outline, and preliminary scientific results of the DELTA campaign and explains geophysical condition at the time of the rocket launch, while the companion papers in this special issue describe more detailed results from each instrument.
The contribution of sprites to the global atmospheric electric circuit
Authors: Füllekrug Martin , Rycroft Michael J. 
Published: August 2014

Abstract
The global static electric field in the global atmospheric electric circuit resulting from mesospheric sprite discharges is inferred from a coupled model for the global static and dynamic electric fields derived from Maxwell’s equations. It is found that the global atmospheric electric field from individual sprites is ≲ 44 mV/m, which can be measured with conventional ULF/ELF radio wave antennas at frequencies ≲ 4 Hz.
Low-frequency variability of a two-layer ocean forced by periodic winds
Authors: Sakamoto Toshihiro 
Published: August 2014

Abstract
To seek the variability of the oceanic subtropical gyre on interannual and longer time scales we have conducted numerical experiments with a two-layer quasigeostrophic model in a square basin bounded by no-slip walls. We find that when the amplitude of annually periodic wind forcing is increased, the time series of the total energy exhibit a transition to chaos in such a manner that the response frequency constitutes a quasi-devil’s staircase against the forcing amplitude; in particular, the n-cycles appear in descending order of n. The low-frequency modes may thus be produced by seasonal winds. Since, however, the power of the subharmonics is much weaker than that with the forcing frequency, their energy would be concealed by noise in the presence of stochastic wind forcing. The present result is in contrast with the case of the time-independent forcing in which we observe the intrinsic frequencies probably associated with the wave propagation, frequency locking and a cascade of period-doubling bifurcations.
Simulation study on nonlinear frequency shift of narrow band whistler-mode waves in a homogeneous magnetic field
Authors: Katoh Yuto , Omura Yoshiharu 
Published: August 2014

Abstract
We study frequency variation of a coherent whistler-mode wave in a homogeneous magnetic field by a selfconsistent simulation model. Simulation results show that an injected whistler-mode wave packet grows due to an instability driven by temperature anisotropy and the amplified wave packet triggers emissions with frequency shift during its propagation. We clarify that the resonant currents J
E and J
B due to the nonlinear wave-particle interaction play significant roles in both wave growth and frequency variation. Based on the simulation results, we show that the range of the frequency shift in a homogeneous system is quantitatively estimated by the trapping frequency V
T of trapped electrons; in a case that the original frequency of the wave packet is 0.62Ωe and V
T=4.05 × 10−2
c, the lower and upper frequencies are estimated to be 0.565Ωe and 0.685Ωe, respectively. The results of the present study reveal that the role of nonlinear trapping is significant in the elementary process of VLF triggered emissions in the equatorial region of the magnetosphere.
Identifying block rotations from remanent magnetization effect: Example from northern Central Turkey
Authors: Bilim Funda , Ates Abdullah 
Published: August 2014

Abstract
One of the difficulties in interpreting magnetic anomaly data is the distortion caused by rock body magnetization. There have been several successful studies carried out on the estimation of body magnetization based on the correlation of the Bouguer and magnetic anomaly data. A number of other significant research projects have aimed at identifying the effect of remanent magnetization in magnetic data only. In this paper, we present a threedimensional method for determining the body magnetization direction by means of comparing the amplitude of the analytic signal with the horizontal gradient of pseudogravity of magnetic anomaly using the correlation coefficient equation. The method has been successfully applied to test cases and is applied here to the aeromagnetic anomalies located in northern Central Turkey. Anomalies displaying individual polarities were separated out and correlated with themselves using the correlation coefficient equation. Counter-clockwise rotations in the range of 3° and 174° were determined. Clockwise rotations were determined in the range of 19° and 153°. The inclination of the body magnetization directions for one of the blocks was estimated to be 68.4°, while all other blocks had a low inclination angle of body magnetization in the range of 32° to 57°. These results may imply that these blocks gained their magnetizations when Turkey was at low latitudes. Possible buried faults are also identified. The results reported here comply with the new mobilistic theory.
Ionospheric measurements during the total solar eclipse of 11 August 1999
Authors: Chandra H. , Sharma Som , Lele P. D. , Rajaram G. , Hanchinal Arun 
Published: August 2014

Abstract
A number of radio experiments were conducted at Ahmedabad (23°N, 73°E) with the aim of studying the ionospheric effects of the total solar eclipse of 11 August 1999. Rapid radio soundings from the ionosonde were made on the eclipse day and on control days. A riometer was operating at 30 MHz, and field strength measurements along the three oblique incidence paths of Colombo-Ahmedabad (11905 kHz), Bombay-Ahmedabad (558 kHz) and Rajkot-Ahmedabad (810 kHz) were also made. A reduction of about 20% was observed in the minimum frequency of reflection from the ionosonde (fmin), which indicates a reduction in D-region ionization. The critical frequency of the E-layer was not measurable beyond 1600 h IST on eclipse day due to the strong blanketing sporadic-E, but there is a 20% decrease in the critical frequency of the F1-layer. Although there was no change in the minimum virtual height of the F-layer on eclipse day, there appears to have been a decrease in the height of maximum ionization (hpF2) during the eclipse, indicating a reduction in the thickness of the F-layer. The signal strength of the Colombo-Ahmedabad path shows an initial rapid increase with the start of the eclipse (indication of a decrease in ionization in the D- and lower E-regions), but subsequently decreases until the maximum of the eclipse (excessive deviative absorption because of the wave penetrating to the E-region). The field strength measurements of the Bombay-Ahmedabad path show a large fading after sunset as the sky wave also appeared. On eclipse day the fading started about an hour earlier. Riometer recordings also show a higher signal during eclipse day, which again indicates an eclipse-associated decrease in ionization.
Modelling the disturbance caused by a dc-electrified railway to geomagnetic measurements
Authors: Pirjola Risto , Newitt Larry , Boteler David , Trichtchenko Larisa , Fernberg Peter , McKee Lorne , Danskin Donald , van Beek Gerrit Jansen 
Published: August 2014

Abstract
Magnetic fields created by a dc-electrified railway are a nuisance to the operation of a geomagnetic observatory and also disturb other electromagnetic studies. Theoretical formulas that enable quantitative estimates of the magnetic effect of a dc railway including leakage currents in the ground are presented in this paper. They are illustrated by numerical examples. The validity of the theoretical model was verified by measurements carried out in the vicinity of a nearly north-south railway in Calgary, Canada. The earth structure in that area is approximately layered, which is an assumption included in the theoretical model. The agreement between the measured magnetic fields due to trains and the theoretical values is good. Numerical computations indicate that magnetic fields larger than the maximum allowable noise level (assumed to be about 10 pT) at today’s magnetic observatories may extend to distances of tens of kilometres from a railway. We have prepared computer programs based on the theoretical formulas in the MatLab, Octave, FORTRAN and IDL languages, in which the locations (i.e. the latitudes and the longitudes) of the point of observation, of the feeding substations and of the trains, together with the feeding and leakage currents and the heights of the feeding lines, can be given as inputs.
Generation mechanism of Z-mode waves in the equatorial plasmasphere
Authors: Nishimura Y. , Ono T. , Iizima M. , Shinbori A. , Kumamoto A. 
Published: August 2014

Abstract
In order to clarify the generation mechanism of Z-mode waves observed in the equatorial plasmasphere, the growth rate of Z-mode electromagnetic waves has been calculated under the higher-order cyclotron interaction process. Z-mode waves can interact with some tens of keV electrons with large pitch angles even in the dense cold background, and the amplitude is consistent with the Akebono plasma wave measurements. UHR and whistler mode waves are also excited by the same electron distribution, and this is also consistent with observations. The origin of these energetic electrons are identified as the ring current electrons injected into the plasmasphere by the intense large-scale electric field during geomagnetic storms, accelerated perpendicular to the ambient magnetic field and confined around the geomagnetic equator conserving the first and second adiabatic invariants. Since the intensity of Z-mode and UHR waves is associated with the development and decay of the ring current, ring current particles are most possible candidate for the free energy source of these waves.
Mapping absolute migration of global mid-ocean ridges since 80 Ma to Present
Authors: Masalu Desiderius C. P. 
Published: August 2014

Abstract
We have computed and mapped the absolute migration of global mid-ocean ridges in the past 80 m.y. and found that ridges have migrated substantially during that period. Presently, the faster-migrating ridges are Pacific-Antarctic, Central Indian, Southeast Indian, Juan de Fuca, Pacific-Nazca, Antarctic-Nazca and Australia- Antarctic ridges which migrate between 3.3 and 5.5 cm/yr. The slower-migrating ridges are Mid-Atlantic and Southwest Indian ridges which migrate between 0.3 and 2.0 cm/yr. Comparing these results with mantle tomography and geochemistry suggests that slower-migrating ridges have deeper depth of origin than faster-migrating ridges, implying a correlation between migration velocity and depth of origin of ridges. The reconstructed Southwestern Indian ridge (near 44°E) between 60 Ma and Present, lies atop reconstructed Central Indian ridge between 80 and 50 Ma, and the present-day Antarctic-Nazca or (Chile) ridge lies atop the reconstructed East Pacific Rise at 70 Ma. Furthermore, the South Mid Atlantic Ridge and the East Pacific Rise near 10?S appear to have been stationary relative to the mantle for the last 80 m.y. These observations suggest that different portions of the mantle have undergone different recycling history, and may explain the origin of mantle heterogeneities.
Gravity basement of the Guinsaugon landslide along the Philippine Fault Zone
Authors: Makino Masahiko , Mandanas Allan A. , Catane Sandra G. 
Published: August 2014

Abstract
A gravity survey was conducted in Guinsaugon, St. Bernard, Southern Leyte, Philippines, to determine the subsurface structure of the Leyte segment of the Philippine Fault Zone (PFZ), where a massive landslide killed 1119 villagers on 17 February 2006. The landslide started on top of a 780-m-high ridge linked with the PFZ. The build-up of pore pressure in the slope due to saturation and possible earthquake-triggered ground shaking along the PFZ, may have initiated the landslide. A two-dimensional structure using homogeneous density models was applied to interpret the gravity anomalies in the Guinsaugon landslide. The most suitable model depicts a deep, narrow graben filled with low-density sediments. The graben is 1.5 km wide and 2 km deep and has a density contrast of -0.4 g/cm3. The western boundary of the graben is steep and coincides with the terminus (southern) Leyte segment of the PFZ. The existence of a deep-seated seismically active fault at the foot of the steep slopes and the soft sediments in the narrow graben are important factors in understanding the trigger and failure mechanisms of the landslide and in the assessment of hazards and risks due to landslides and earthquakes.
Effect of elastic inhomogeneity on the surface displacements in the northeastern Japan: Based on three-dimensional numerical modeling
Authors: Sato Kachishige , Minagawa Naoya , Hyodo Mamoru , Baba Toshitaka , Hori Takane , Kaneda Yoshiyuki 
Published: August 2014

Abstract
In geodetic inversions such as estimation of coseismic slip and/or afterslip distribution on faults, the displacements on the surface calculated under an assumption of homogeneous elastic half space have been mostly used as the Green’s functions (GF’s). However, this seems not adequate for better estimations of such slip distribution, because the subsurface structures are more or less inhomogeneous, especially those in and around Japan where the structure must be much complicated. In this study, to examine how much the inhomogeneous subsurface structure affects on the surface displacements, we conduct some 3-D finite element calculations with a grid for the region of 1400 km (EW) × 1200 km (NS) × 200 km (depth) including the Tohoku and Hokkaido, northeastern Japan. Assuming homogeneous and inhomogeneous elastic models with various values for the Young’s modulus and Poisson’s ratio, we calculated the surface displacements due to a dip-slip type dislocation of 1 m on many cell-like subfaults assumed on the interface between the Pacific and land side plates. Comparing the results, we find a large discrepancy in the surface displacements between the homogeneous and inhomogeneous elastic models and less dependency of the surface displacements on the Poisson’s ratio. The discrepancy is found to be more than 20% and can be as large as ~40% in some cases. Such a large discrepancy indicates that the surface displacements calculated for inhomogeneous elastic medium with realistic subsurface structure, unlike as in usual cases, should be used as the GF’s for better geodetic inversions.
Sporadic aurora from Spain
Authors: Vaquero J. M. , Trigo R. M. , Gallego M. C. 
Published: August 2014

Abstract
Some authors have shown recently that “sporadic auroras” have occurred at relatively low latitude when the geomagnetic activity is quiet or moderate. Here we present and analyze a case of “sporadic aurora” observed from Spain on the 29 December 1845 and compare its low geomagnetic activity with other three aurorae also observed in Spain in mid-19th century.
Tectonomagnetic study in the eastern part of Hokkaido, NE Japan (II): Magnetic fields related with the 2003 Tokachi-oki earthquake and the 2004 Kushiro-oki earthquake
Authors: Nishida Yasunori , Utsugi Mitsuru , Mogi Toru 
Published: August 2014

Abstract
We examined short-term geomagnetic changes related with the 2003 Tokachi-oki earthquake (M 8.0) and the 2004 Kushiro-oki earthquake (M 7.1) in Hokkaido, Japan. However, we could not find the precursory and co-seismic signals above several nT at a magnetic station whose epicentral distances were about 120 km and 50 km, respectively. Model calculations showed that co-seismic piezomagnetic fields did not amount to 1 nT at the station in both cases when we assumed the relevant fault parameters, in-situ Curie temperature depth, subsurface magnetic structure and stress sensitivity of rocks. Therefore, it may be reasonable that we could not detect the piezomagnetic signals at the station. We also made model calculations to forecast the piezomagnetic amplitudes caused by M 7.9 and M 8.5 earthquakes which have been expected to occur along the southern Kurile trench in the future. The model calculations reveal the piezomagnetic fields up to about −4 nT and −7 nT are expected in the eastern part of the Hokkaido island for the M 7.9 and M 8.5 earthquakes respectively, encouraging magnetic observations hereafter.
Quality control of Ebro magnetic observatory using momentary values
Authors: Curto J. J. , Marsal S. 
Published: August 2014

Abstract
Intercomparison of momentary values from observatories across Europe can be used as a test of reliability for a particular magnetic station in this area, as well as the whole network. The method presented by Voppel at the IAGA Assembly of Grenoble (1975) and developed by Schulz and Voppel at the IAGA Assembly of Edinburgh (1981) is based on simultaneous measurements taken at 02:00 UT, which coincides with the period least disturbed by Sq associated currents on central European longitudes. A selected list of ten least disturbed days per month is provided by the Niemegk (initially Wingst) Geomagnetic Observatory which gathers the corresponding momentary values from the collaborating institutions. This method can be applied to detect fluctuations or jumps in geomagnetic standards. Independent techniques, like linear regression and axial intercept of the standard deviation of the mutual differences of monthly mean values, have been applied to the magnetic elements of Ebro Observatory (EBR) for the period 1997–2001. These tools give results in good agreement amongst them, and most of the coefficients are similar to those obtained for the most significant observatories of the network. No jumps or trends in data are observed, indicating excellent performance of EBR.