bluuebunny/crossref_metadata_2025_split huggingface dataset:
Candidate main-field models for the Definitive Geomagnetic Reference Field 1995.0 and 2000.0
Authors: Chambodut A. , Langlais B. , Mandea M. 
Published: August 2014

Abstract
Two geomagnetic main-field models for epochs 1995.0 and 2000.0 were proposed as candidate models for DGRF 1995 and DGRF 2000. A main-field model was derived for epoch 2000.0, using the high-quality data provided by the Ørsted satellite around this epoch. Since no high-quality satellite vector measurements of the magnetic field were acquired between 1980 and 1999, our approach was to extrapolate this 2000.0 accurate model back to 1995. To do this we produced a secular-variation model for the time-span 1995-2000, from ground measurements. The models obtained were incorporated into DGRF 1995 and DGRF 2000 as part of the 9th generation of the IGRF in 2003.
Enhancing comprehensive inversions using the Swarm constellation
Authors: Sabaka Terence J. , Olsen Nils 
Published: August 2014

Abstract
This paper reports on the findings of a simulation study designed to test various satellite configurations suggested for the upcoming Swarm magnetic mapping mission. The test is to see whether the mission objectives of recovering small-scale core secular variation (SV) and lithospheric magnetic signals, as well as information about mantle conductivity structure, can be met. The recovery method used in this paper is known as comprehensive inversion (CI) and involves the parameterization of all major fields followed by a co-estimation of these parameters in a least-squares sense in order to achieve proper signal separation. The advantage of coestimation over serial estimation of parameters is demonstrated by example. Synthetic data were calculated for a pool of six Swarm satellites from a model based heavily on the CM4 comprehensive model, but which has more small-scale lithospheric structure, a more complicated magnetospheric field, and an induced field reflecting a 3-D conductivity model. These data also included realistic magnetic noise from spacecraft and payload. Though the parameterization for the CI is based upon that of CM4, modifications have been made to accommodate these new magnetospheric and induced fields, in particular with orthogonality constraints defined so as to avoid covariance between slowly varying induced fields and SV. The use of these constraints is made feasible through an efficient numerical implementation. Constellations of 4, 3, 2, and 1 satellites were considered; that with 3 was able to meet the mission objectives, consistently resolving the SV to about spherical harmonic (SH) degree n = 15 and the lithosphere to a limited n < 90 due to external field leakage, while those with 2 and 1 were not; 4 was an improvement over 3, but was much less than the improvement from 2 to 3. The resolution of the magnetospheric and induced SH time-series from the 3 satellite configuration was sufficient enough to allow the detection of 3-D mantle conductivity structure in a companion study.
Ocean circulation generated magnetic signals
Authors: Manoj C. , Kuvshinov A. , Maus S. , Lühr H. 
Published: August 2014

Abstract
Conducting ocean water, as it flows through the Earth’s magnetic field, generates secondary electric and magnetic fields. An assessment of the ocean-generated magnetic fields and their detectability may be of importance for geomagnetism and oceanography. Motivated by the clear identification of ocean tidal signatures in the CHAMP magnetic field data we estimate the ocean magnetic signals of steady flow using a global 3-D EM numerical solution. The required velocity data are from the ECCO ocean circulation experiment and alternatively from the OCCAM model for higher resolution. We assume an Earth’s conductivity model with a surface thin shell of variable conductance with a realistic 1D mantle underneath. Simulations using both models predict an amplitude range of ±2 nT at Swarm altitude (430 km). However at sea level, the higher resolution simulation predicts a higher strength of the magnetic field, as compared to the ECCO simulation. Besides the expected signatures of the global circulation patterns, we find significant seasonal variability of ocean magnetic signals in the Indian and Western Pacific Oceans. Compared to seasonal variation, interannual variations produce weaker signals.
The performance of RTK-GPS for surveying under challenging environmental conditions
Authors: Lee In-Su , Ge Linlin 
Published: August 2014

Abstract
The aim of this paper was to assess the availability of RTK GPS (Real-Time Kinematic Global Positioning Systems) under some challenging environmental conditions. Testing was performed under two of these conditions, i.e. a small tree-covered garden and a pylon for high-voltage electricity supply. The increase in the number of satellites had many benefits for the integer ambiguity resolution, but no significant contribution to the accuracy of RTK positions and PDOP (Precision Dilution of Position). The results of RTK testing were compared against results from Total Station surveying as a further quality check. The results indicate that integrating RTK GPS system with Total Station is favoured for surveying in urban environments.
Strain accumulation in South Korea inferred from GPS measurements
Authors: Jin Shuanggen , Park Pil-Ho 
Published: August 2014

AbstractMonitoring the variation of the crustal strain is a key issue to understand the physical process of crustal tectonic activities. In this paper, GPS data for the period from March 2000 to February 2004 were analyzed to quantitatively investigate the plate deformation patterns and distributions in the South Korean peninsula. The results show two anomalous rates of strain accumulation in South Korea, a W-E compression accumulation of crustal strain in the East and West parts, and a N-S extension strain accumulation in the middle part along the longitude of about 127.5°E. In addition, the GPS-derived seismic moment accumulation rate is significant and consistent with recent historic earthquakes and fault zones in South Korea. The most anomalous seismic moment rates are in the middle part (about 127.3°E, 35.5°N), North edge (about 128.0°E, 38.0°N) and Northeast part (about 128.5°E, 37.3°N) of South Korea, indicating a high earthquake risk.
A Virtual Global Magnetic Observatory Network: VGMO.NET
Authors: Papitashvili Vladimir O. , Petrov Valeriy G. , Saxena Anshuman B. , Clauer C. Robert , Papitashvili Natalia E. 
Published: August 2014

Abstract
Since the mid-1990s, many geomagnetic datasets began appearing on the World Wide Web. Often these data were not submitted to the World Data Centers as recommended since the International Geophysical Year (1957- 58). As a result, existing data become naturally distributed creating an urgent need for more sophisticated search engines capable of identifying and retrieving the data from Web for scientific analyses. We introduce a Virtual Global Magnetic Observatory concept for “pulling” geomagnetic data distributed worldwide. The VGMO moves information exchange from simple file transfers to a higher level of abstraction, forming the distributed databases through establishment of self-organizing data nodes. We present the first working VGMO prototype: an “on-demand” objects-building Internet application that is transparent in its internal data management to the external users/clients. The VGMO server continuously builds data-objects only from client requests by going through a pre-set list of Web-based data nodes (including WDCs). As the retrieved data are added to the server (or node) database, future requests of the same interval would not force a new Web search. Furthermore, new nodes can be made available to others through the VGMO network, building the worldwide geomagnetic data “fabric” in a platform-independent and location-neutral environment of newly “webbed“ digital data. Application is on a server at http://mist.engin.umich.edu.
Inferred long term trends in lightning activity over Africa
Authors: Price Colin , Asfur Mustafa 
Published: August 2014

Abstract
Global warming is becoming a reality, with growing evidence that anthropogenic activity on our planet is starting to influence our climate (IPCC, 2001). Due to the increase in significant weather-related disasters in recent years, it is important to investigate the role of global warming on such changes. In this paper we attempt to estimate the long term trends in lightning activity over tropical Africa during the past 50 years, using upper tropospheric water vapor as a proxy for regional lightning activity. We use the NCAR/NCEP reanalysis product available for the period 1948 to the present to estimate the long term trends in lightning activity. Similarity between the long term African lightning variability and observed rainfall and river discharge variability are demonstrated. Since 1950 the inferred lightning activity over Africa shows significant variability, reaching a maximum during the 1960s, followed by a decrease in activity during the following 30 years.
Parallel electric field structures associated with the low-frequency oscillations in the auroral plasma
Authors: Reddy R. V. , Singh S. V. , Lakhina G. S. , Bharuthram R. 
Published: August 2014

Abstract
The nonlinear evolution of low-frequency electrostatic oscillations in a magnetized plasma consisting of protons, electrons and oxygen ion beams has been studied. The fluid equations have been used for the oxygen beam, whereas the Boltzmann distributions are used for the protons and electrons. The coupled system of equations are reduced to a single nonlinear differential equation in the rest frame of the propagating wave for any direction of propagation with respect to the ambient magnetic field. This nonlinear differential equation is solved numerically for the parameters charateristic of the auroral acceleration region. Depending on the wave Mach number, proton and oxygen ion concentrations, and driving electric field, the numerical solutions show a range of periodic solutions varying from sinusoidal to sawtooth and highly spiky waveforms. The effects of the plasma parameters, in particular the oxygen ion concentration and the proton temperature on the evolution of the nonlinear waves are examined. The results from the model are compared with satellite observations.
Simultaneous DMSP, all-sky camera, and IMAGE FUV observations of the brightening arc at a substorm pseudo-breakup
Authors: Yago K. , Shiokawa K. , Yumoto K. , Baishev D. G. , Solovyev S. I. , Rich F. J. 
Published: August 2014

Abstract
Auroral particles, field-aligned currents, and plasma convections in the vicinity of the brightening arc at substorm onset are still not well understood, since it is very rare to have conjugate satellite measurements above the brightening arc. In this paper, we investigate the characteristics of auroral particles and fields associated with the brightening arc at a pseudo-onset of substorm on October 31, 2000, using ground all-sky TV images, IMAGE FUV auroral images, and particle, magnetic field, and plasma flow data obtained by the DMSP F12 satellite. The arc brightening at Tixie (66.0°MLAT), Russia, occurred at 1004 UT (18.75 MLT) coincident with a coherent Pi 2 pulsation at midlatitudes and with the DMSP crossing above the arc. The brightening arc did not develop on a global scale, indicating that this event is a pseudo auroral breakup, which occurred ≈16 min before the major substorm expansion onset. IMAGE auroral images indicate that the longitude of the brightening center was ≈2.5 h nightside of Tixie. The DMSP data show that the precipitating particles associated with the brightening arc correspond to an electron inverted-V structure at the equatorward edge of the electron precipitation region. The arc was located in the energetic (>1 keV) ion precipitation region, near the equatorward boundary of the upward region 1 field-aligned current, and at the peak of the sunward convection velocity. These facts indicate that the brightening arc at duskside of the onset local time was located in the inner plasma sheet at the inner edge of the region 1 current source in the sunward convection region.
A note on the semidiurnal non-migrating tide at polar latitudes
Authors: Aso Takehiko 
Published: August 2014

Abstract
In the Antarctic upper mesosphere and lower thermosphere around 90 km, meteor radar observations at the South Pole have detected a significant semidiurnal wind component in summer which is found to be non-migrating with zonal wavenumber s = 1. It has been surmised that this component might possibly be excited through the non-linear interaction of the migrating semidiurnal tide with stationary planetary waves with zonal wavenumber s = 1 prevailing at stratospheric heights. The Kyushu University GCM has been successful in elucidating very unambiguously this conjecture. In the present paper, linearized steady tidal modeling is carried out in this connection to reproduce, by a fairly simplified but explicit model, trans-equatorial propagation of non-migrating semidiurnal tide forced in the opposite winter hemisphere and to compare latitudinal structures of migrating and non-linearly excited intermittent tides in view of polar latitudes where non-migrating tide tends to dominate over migrating tide. It is also shown that the re-analysis meteorological data for almost 10 years clearly supports the well-known N-S asymmetry in stationary planetary wave activity in winter polar stratospheric regions, possibly due to the difference in surface topography between two hemispheres. We suggest that there might be significant asymmetry in the summertime enhancement of semidiurnal non-migrating tide between both polar regions. This phenomenon may be in a context similar with the N-S asymmetry of gravity wave activity in the polar regions, possibly giving rise to N-S disparity of cold summertime mesopause temperature. Clarification awaits intensive bi-polar studies by coordinated radar and optical observations which are running both in the Arctic and Antarctic regions.
Determination of ground conductivity and system parameters for optimal modeling of geomagnetically induced current flow in technological systems
Authors: Pulkkinen Antti , Pirjola Risto , Viljanen Ari 
Published: August 2014

Abstract
In this work, methods to determine technological system parameters and the ground conductivity structure from different sets of geomagnetically induced current (GIC), magnetic field and geoelectric field observations are explored. The goal of the work is to enable optimal modeling of induced currents in any technological system experiencing GIC. As an additional product, the introduced methods can also be applied to utilize GIC observations in the imaging of the subsurface geological structures. Here a robust processing scheme and Occam’s inversion technique familiar from magnetotelluric (MT) studies are applied to the determination of the ground conductivity structure. The application of the methods to GIC data from the Finnish pipeline for a storm period of October 24-November 1, 2003 demonstrate that optimal system parameters and ground conductivity structure can be obtained using time series comprising only 8 days worth of data. Importantly, the obtained ground model is in agreement with models obtained in earlier MT studies. Furthermore, it is shown that although in an ideal case the magnetic field data used should be obtained from the immediate vicinity of the GIC observation site, some spatial separation (200–300 km) between the sites can be tolerated.
Formation process of recent fumarolic gases at the Mt. Mihara summit peak of the Izu-Oshima volcano, Japan
Authors: Ohba Takeshi 
Published: August 2014

Abstract
We have investigated the chemical and isotopic composition of recently formed gases emitted by three fumaroles on the Mt. Mihara summit peak of the Izu-Oshima volcano in order to assess the formation process of these gases. The CO2/H2O ratio of these gases varied greatly, with the σD and σ18O of the H2O being as low as a vapor phase equilibrated with the local meteoric water. These features are explained by a mixing of the vapor equilibrated with local meteoric groundwater and primary steam, which is a vapor phase generated by the mixing of magmatic gas and a cold meteoric groundwater. We concluded that there was no direct mixing between the magmatic vapor and a vapor phase of meteoric origin in the processes involved in fumarolic gas formation.
Shock-induced anisotropy of magnetic susceptibility: impact experiment on basaltic andesite
Authors: Nishioka Itoyuki , Funaki Minoru , Sekine Toshimori 
Published: August 2014

Abstract
Changes in the anisotropy of the low-field magnetic susceptibility (AMS) of basaltic andesite were induced by decaying stress waves and subsequently quantified. An initial shock pressure of 5 GPa was generated in a block of the target rock through impacting with a cylindrical projectile. Following the impact, the maximum or minimum principal susceptibility axes of the target were reoriented toward the shock direction at low (0.5–3 GPa) or high (>3 GPa) estimated shock pressures, respectively. Subtraction of the initial AMS demonstrated a parallelism between the induced susceptibility axes and the shock direction. These results suggest a potential application of AMS as an indicator of the propagation directions of stress waves generated in rocks at terrestrial impact structures.
The seismological and geodetical roles of strain seismogram suggested from the 2004 off the Kii peninsula earthquakes
Authors: Okubo Makoto , Asai Yasuhiro , Aoki Harumi , Ishii Hiroshi 
Published: August 2014

Abstract
Dynamic strain seismograms obtained by high-speed sampling include not only long-period changes, such as ‘strain-step’, step change in strain, but also short period variations, such as body waves. We studied dynamic strain variations caused by the 2004 off the Kii peninsula earthquakes. Using such strain seismograms, we clarified the relation between dynamic strain and velocity. Our results will contribute greatly to seismology. We also clarified the strain-step formation process. This result and the concept of dynamic strain will bring more information to geodetics.
Estimation of local site effects in Ojiya city using aftershock records of the 2004 Mid Niigata Prefecture earthquake and microtremors
Authors: Yamanaka Hiroaki , Motoki Kentaro , Fukumoto Shun’ichi , Takahashi Toshiyuki , Yamada Nobuyuki , Asano Kimiyuki 
Published: August 2014

AbstractAftershock observations of the 2004 Mid Niigata Prefecture earthquake were conducted in the central part of Ojiya city, the Niigata prefecture, central Japan, to investigate local site effects. We installed eight accelerographs in the vicinity of the K-NET and JMA stations in the area. The stations of the aftershock observations are situated under different geological conditions including one installed in a mountainous area on Tertiary layers to serve as a reference site. We examined the ground-motion characteristics of the records for a Mj 6.1 aftershock focusing on local site effects. The amplification, at a period of less than 1 sec, is the largest in the vicinity of the K-NET station. The amplification at periods longer than 2 sec is larger in the western part of the city than those in the east. We estimated theS-wave velocity structure in the sediments above the basement with anS-wave velocity of 3.4 km/sec from the inversion of phase velocities measured by the array observations of vertical microtremors. We discuss the amplification factors using theS-wave velocity profile and show that shallow soils over the layer with anS-wave velocity of 0.49 km/sec are responsible for the amplification at periods shorter than 0.4 sec. Deeper sedimentary layers are needed to explain amplification at periods of 1 sec.
Correlation between gravity and magnetic anomalies of Western Anatolia and its relation to tectonic structures
Authors: Düzgit Z. , Hisarli Z. M. , Sayin N. , Orbay N. 
Published: August 2014

Abstract
In this paper, we apply for the first time the moving-windows application of the Poisson’s theorem to the synthetic gravity and magnetic data, followed by calculations of the correlations of the Bouguer gravity and aeromagnetic data of Western Anatolia. The correlation coefficient, slope and intercept parameters were generated from the internal correlations existing between the gravity and magnetic anomalies. Relative negative correlation values of positive gravity and negative magnetic anomalies were found on the Menderes Massif and in the southern part of the Marmara sea. Higher heat flow values were also obtained from these regions. The negative correlation values can be seen on a profile taken along the 28°E longitude and are sourced from a large graben system which has been generated as a result of lithospheric extension in Western Anatolia since the Early Miocene. The grabens were filled up by approximately 2000-m-thick sediments. The negative correlation coefficients and high heat flow values correspond to relative uplift of the asthenosphere in these regions.
Possible TCRM acquisition of the Kilauea 1960 lava, Hawaii: failure of the Thellier paleointensity determination inferred from equilibrium temperature of the Fe−Ti oxide
Authors: Yamamoto Yuhji 
Published: August 2014

Abstract
Natural rock samples may not always be the ideal material for the Thellier-type method as they occasionally result in high paleointensities. The Kilauea 1960 lava, Hawaii, is one such example. Several previous studies have suggested that one of the possible causes for this undesirable behavior is an acquisition of thermochemical remanent magnetization (TCRM) during lava formation. In order to examine this possibility quantitatively, equilibrium temperatures of titanomagnetite grains, which are associated with samples previously subjected to Thellier experiments, are estimated by a Fe−Ti oxide geothermometer. The results show that two specimens from the rock magnetic group giving relatively ideal Thellier paleointensities have clustered equilibrium temperatures of about 800–900 and 700–800°C. In contrast, two swarmed temperatures around 300 and 700°C were observed for the specimen from a group yielding high paleointensities. Although these are semi-quantitative estimates, when the time scales of Fe−Ti interdiffusion and lava cooling are taken into consideration, the last specimen could have acquired the TCRM during its formation. For such specimens, simple calculation predicts that TCRM/TRM (thermoremanent magnetization) ratios could be 1.19–1.72 for the blocking temperature range of 400–480°C, assuming a grain-growth model. The extent of this overestimation (20–70%) is comparable to the magnitude of the observations. It is therefore suggested that attention be paid to titanomagnetite grains with well-developed ilmenite lamellae, as these could be potential sources of overestimations of Thellier paleointensities of up to a few tenths of percentage points.