bluuebunny/crossref_metadata_2025_split huggingface dataset:
Observations of the lower thermospheric neutral temperature and density in the DELTA campaign
Authors: Kurihara Junichi , Abe Takumi , Oyama Koh-Ichiro , Griffin Eoghan , Kosch Mike , Aruliah Anasuya , Kauristie Kirsti , Ogawa Yasunobu , Komada Sayaka , Iwagami Naomoto 
Published: August 2014

Abstract
The rotational temperature and number density of molecular nitrogen (N2) in the lower thermosphere were measured by the N2 temperature instrument onboard the S-310-35 sounding rocket, which was launched from Andøya at 0:33 UT on 13 December 2004, during the Dynamics and Energetics of the Lower Thermosphere in Aurora (DELTA) campaign. The rotational temperature measured at altitudes between 95 and 140 km, which is expected to be equal to neutral temperature, is much higher than neutral temperature from the Mass Spectrometer Incoherent Scatter (MSIS) model. Neutral temperatures in the lower thermosphere were observed using the auroral green line at 557.7 nm by two Fabry-Perot Interferometers (FPIs) at Skibotn and the Kiruna Esrange Optical Platform System site. The neutral temperatures derived from the look directions closest to the rocket correspond to the rotational temperature measured at an altitude of 120 km. In addition, a combination of the all-sky camera images at 557.7 nm observed at two stations, Kilpisjärvi and Muonio, suggests that the effective altitude of the auroral arcs at the time of the launch is about 120 km. The FPI temperature observations are consistent with the in situ rocket observations rather than the MSIS model.
Electron density measurement under the influence of auroral precipitation and electron beam injection during the DELTA campaign
Authors: Wakabayashi M. , Ono T. 
Published: August 2014

Abstract
The direct observation of electron number density was successfully carried out using an impedance probe onboard the S310-35 sounding rocket during the DELTA (Dynamics and Energetics of the Lower Thermosphere in Aurora) campaign, which provided the altitude profile along the rocket trajectory in a diffuse aurora. The plasma density profile showed clear density enhancements due to the auroral precipitation as well as artificial ionizations induced by the electron beam injection. The enhanced ionization due to the electron beam experiment was too high to be determined by means of the detection of the UHR (Upper Hybrid Resonance) frequencies. To overcome this difficulty, SHR (Sheath Resonance) frequency and sheath capacitance values were used to deduce the plasma density in the artificially ionized region. Based on the SHR analysis method, we were able to determine the maximum density to be 2·106 cm−3 at the altitude of 98.9 km; this measurement was ascribed to the artificial ionization by the 1-keV electron beam in comparison with the results of particle detector instrument on-board the S310-35. The data analysis of the sheath capacitance was able to distinguish the natural ionization region from the artificial one. The impedance probe measurement was able to evaluate the ionospheric conductivities which have important properties for evaluating the Joule heating process in the thermosphere. Both Pedersen and Hall conductivities showed distinctive enhancement around an altitude of 128 km which were due to the auroral particle precipitation.
Seismic velocity variations on the San Andreas fault caused by the 2004 M6 Parkfield Earthquake and their implications
Authors: Li Yong-Gang , Chen Po , Cochran Elizabeth S. , Vidale John E. 
Published: August 2014

AbstractRepeated earthquakes and explosions recorded at the San Andreas fault (SAF) near Parkfield before and after the 2004M6 Parkfield earthquake show large seismic velocity variations within an approximately 200- m-wide zone along the fault to depths of approximately 6 km. The seismic arrays were co-sited in the two experiments and located in the middle of a high-slip part of the surface rupture. Waveform cross-correlations of microearthquakes recorded in 2002 and subsequent repeated events recorded a week after the 2004M6 mainshock show a peak of an approximately 2.5% decrease in seismic velocity at stations within the fault zone, most likely due to the co-seismic damage of fault-zone rocks during dynamic rupture of this earthquake. The damage zone is not symmetric; instead, it extends farther on the southwest side of the main fault trace. Seismic velocities within the fault zone measured for later repeated aftershocks in the following 3–4 months show an approximate 1.2% increase at seismogenic depths, indicating that the rock damaged in the mainshock recovers rigidity—or heals—through time. The healing rate was not constant but was largest in the earliest post-mainshock stage. The magnitude of fault damage and healing varies across and along the rupture zone, indicating that the greater damage was inflicted and thus greater healing is observed in regions with larger slip in the mainshock. Observations of rock damage during the mainshock and healing soon thereafter are consistent with our interpretation of the low-velocity waveguide on the SAF being at least partially softened in the 2004M6 mainshock, with additional cumulative effects due to recurrent rupture.
Initial studies of high latitude magnetic field data during different magnetospheric conditions
Authors: Cersosimo D. O. , Wanliss J. A. 
Published: August 2014

Abstract
We investigate the statistical properties of high-latitude magnetometer data for differing geomagnetic activity. This is achieved by characterizing changes in the nonlinear statistics of the geomagnetic field, by means of the Hurst exponent, measured from a single ground-based magnetometer station. The long-range statistical nature of the geomagnetic field at a local observation site can be described as a multifractional Brownian motion, thus suggesting the statistical structure required of mathematical models of magnetospheric activity. We also find that, in general, the average Hurst exponent for quiet magnetospheric intervals is smaller than that for more active intervals.
Detecting horizontal gradient of sound speed in ocean
Authors: Kido Motoyuki 
Published: August 2014

Abstract
We propose a new approach to monitor the horizontal gradient of sound speed in ocean for its correction on seafloor positioning using the GPS/acoustic technique. The new method requires five seafloor transponders to solve five parameters: δx, horizontal position of a transponder array; δt, a common delay in traveltimes due to the stratified component of sound speed; ∇
t, the gradient of traveltime delays among the transponders associated with the sound speed gradient. We also numerically evaluate the geometrical strength of the five transponders’ layout and observation point to avoid possible trade-off among the parameters.
Polarization analysis of a Pi2 pulsation using continuous wavelet transform
Authors: Kulesh M. , Nosé M. , Holschneider M. , Yumoto K. 
Published: August 2014

AbstractIn this contribution, we extend a series of previous works focused on an investigation of signal’s polarization attributes using the continuous wavelet transform, where we proposed a method to map instantaneous polarization attributes of multicomponent signals in the wavelet domain and explicitly relate these attributes with the wavelet transform coefficients of the analyzed signal. In this work, we applied our polarization method to an examination of characteristics of Pi2 pulsations. We have shown some merits of the use of the continuous wavelet transform for the Pi2 pulsations’ analysis. First, we used our polarization method for the geomagnetic field data from the MSR, KAK, GUA, SMA, BLM and LAQ observatories and showed some correlations between the polarization parameters of pulsation and the station’s position (nightside or dayside). Secondly, we considered the signal’s north components of a pair of stations and demonstrated a time-frequency variations of the phase difference between two stations during the pulsation.
Rayleigh-Taylor instability after giant impacts: Imperfect equilibration of the Hf-W system and its effect on the core formation age
Authors: Sasaki Takanori , Abe Yutaka 
Published: August 2014

Abstract
Hf-W chronometry provides constraints on the timing of planetary accretion and differentiation, as the segregation of a metal core from silicates should induce strong fractionation of Hf from W. In most previous studies, it was assumed that a giant impact would perfectly reset the Hf-W chronometer. Here, we show the difficulty of achieving perfect equilibration of the Hf-W system. Perfect equilibration requires iron to split into small droplets. However, since the sedimentation velocities of small droplets are low, the Rayleigh-Taylor instability between the upper metal-containing and lower metal-free layers results in quick overturning of the layers, unless iron droplets were uniformly distributed in the entire mantle. Therefore, the lower metal-free layers cannot be equilibrated. We calculated the isotopic evolution of the Hf-W system, taking into account the partial resetting of this chronometer. Our study led to three conclusions: (1) collision conditions and the number of giant impact events affect the age estimation of core formation, (2) the Earth’sWisotope ratio indicates that more than two-tenths of the volume of the protoearth’s mantle must have been equilibrated at each giant impact, and (3) Mars should have experienced a late, extensive equilibration event; it could have been a single giant impact.
A compound linear discriminant method for small-magnitude seismic events and its application to the North Korea seismic event of October 9, 2006
Authors: Che Il-Young , Jun Myung-Soon , Jeon Jeong-Soo 
Published: August 2014

AbstractOn October 9, 2006, a seismic event (mb3.9) occurred in North Korea, which was later announced as a nuclear test. We studied the seismic event from the viewpoint of seismological discrimination withouta prioriinformation of the source. This paper presents a compound discriminant method that enhances the ability to distinguish between earthquakes and explosions on the Korean Peninsula. The method includes four single discriminants based on seismic spectral amplitude ratios. These discriminants are used as single variables in a multivariate statistical analysis to derive a compound linear discriminant function that optimally separates the two populations. Short-period vertical component seismograms recorded by seismo-acoustic array (CHNAR) are used for the method. Combining the mutually complementary discrimination abilities of the single methods improves the discriminant power and lowers the probability of misclassification to 1.7% for the data sets. Using this compound method, we were able to identify the North Korea seismic event as explosion-induced. This discrimination technique can be applied automatically to new observations and extended to other seismic arrays or networks. The combination of these seismic discriminants with infrasound observations will increase our ability to detect surface explosions on the Korean Peninsula.
Numerical study of electrostatic electron cyclotron harmonic waves due to Maxwellian ring velocity distributions
Authors: Umeda Takayuki 
Published: August 2014

Abstract
Excitation of electrostatic electron cyclotron harmonic (ECH) waves is studied by performing linear dispersion analysis and particle-in-cell computer simulation. The ECH wave emissions can be excited by a positive slope in a velocity distribution function perpendicular to the ambient magnetic field, such as that due to a loss cone or ring velocity distribution. However, there exists no analytic expression for integration of Maxwellian ring velocity distribution functions. Here we present a method to solve the linear dispersion relations of Maxwellian ring velocity distribution functions with numerical integration. The obtained dispersion relations are confirmed by particle-in-cell simulation.
Occurrence of quasi-periodic slow-slip off the east coast of the Boso peninsula, Central Japan
Authors: Ozawa Shinzaburo , Suito Hisashi , Tobita Mikio 
Published: August 2014

Abstract
An analysis of Global Positioning System (GPS) data revealed south-southeastward transient deformation caused by the expected slow-slip near the Boso peninsula, central Japan, approximately 5 years after a similar event in 2002. An area of aseismic slip with a moment magnitude of 6.6 was estimated off the Boso peninsula, adjacent to the area of associated seismic activity. The 2007 aseismic slip started from around August 10, expanded slightly to the north, and gradually ceased activity over a period of about 10 days. This rupture process is different from those of the last two events in which the slow-slip area moved from north to south. However, the three slow-slip events detected by the GPS array verify the hypothesis that the Boso slow-slips occur quasi-periodically in a certain area, accompanied by seismic swarms. The factors causing the slight differences in the rupture process, magnitude, recurrence time, and slip area among the observed slow-slip events remain unclear.
Horizontal deformation in South Korea from permanent GPS network data, 2000–2003
Authors: Hamdy Ahmed M. , Park Pil-Ho , Lim Hyung-Chul 
Published: August 2014

Abstract
Analysis of continuous GPS data 2000–2003 at 50 stations of the Korean GPS Network (KGN) suggests that the southern part of the Korean peninsula is tectonically more stable than other regions in the Eastern Asia. The average velocity was ∼1.5 mm/yr and the average overall strain rate was around −0.3 × 10−9str/yr. The obtained velocity field indicates the presence of anticlockwise rotation of the whole region with respect to Daejeon station (DAEJ), in the central part of South Korea. It also showed that KM-OB (Kyonggi Massif and the Okchon Basin) and YM-TB (Yeongnam Massif and Taebaeksan Basin) have left-lateral shearing movements. Both movements were confirmed by the deformation analysis of the KGN horizontal velocity field using the infinitesimal plate theory. The results show that South Korea moves toward the WNW direction with a velocity of 0.9 mm/yr with a slow anticlockwise rotation. The strain field in South Korea indicates the existence of both compression and tension. The compression and extension axes have WSW-EWE and NNW-SSE directions, respectively.
A simulation study of effects of GRACE orbit decay on the gravity field recovery
Authors: Yamamoto Keiko , Otsubo Toshimichi , Kubo-oka Toshihiro , Fukuda Yoichi 
Published: August 2014

Abstract
The effects of satellite ground track changes of GRACE on monthly gravity field recoveries are investigated. In the case of a gravity field recovery using a relatively short period of a month or so, the variation of ground tracks affects the precision of the gravity field solutions. It is a serious problem when the solutions are employed for detecting temporal gravity changes which are almost at their detection limits. In this study, the recoveries of four-weekly gravity fields are simulated and the relation between the recovery precision and the ground track is investigated. The result shows that the GRACE ground track of the year 2003 was in good condition for four-week gravity field recovery, but it will sometimes appear as worse cases as the orbit altitude decays. In those cases, the global standard deviations of geoid height errors will be about one order worse than the best case. From our simulation, ground tracks of around altitudes of 473, 448, 399, 350 and 337 km give insufficient spatial resolutions, even for gravity field recovery up to degree 30.
Very low frequency earthquakes excited by the 2004 off the Kii peninsula earthquakes: A dynamic deformation process in the large accretionary prism
Authors: Obara Kazushige , Ito Yoshihiro 
Published: August 2014

Abstract
Anomalous seismic events were observed after the occurrence of the foreshock (Mw=7.2) and the main shock (Mw=7.5) of the 2004 off the Kii peninsula earthquakes. These anomalous events are characterized by very low-frequency energy of around 10 seconds with almost no higher-frequency energy and are considered the same as the very low-frequency (VLF) earthquakes discovered by Ishihara (2003) in some places along the Nankai trough, southwest Japan. The VLF seismic activity is mainly coincident with the aftershock area of the 2004 off the Kii peninsula earthquakes; however a minor activity was also excited in the southern Kii channel area. The VLF seismograms sometimes include higher-frequency wave trains with amplitudes much smaller than that of regular aftershocks. This indicates that VLF earthquakes have different source properties from the regular earthquakes. The centroid moment tensor analysis for one of the larger events suggests that the source depth is very shallow and the focal mechanism is the reverse faulting. These features suggest that the event occurs on the well-developed reverse fault system in the large accretionary prism near the Nankai trough. The swarm activity of VLF earthquakes might be considered as a chain-like occurrence of slips on the reverse fault system and thus the signature of a dynamic deformation process in the accretionary prism.
Urgent aftershock observation of the 2004 off the Kii Peninsula earthquake using ocean bottom seismometers
Authors: Sakai Shin’ichi , Yamada Tomoaki , Shinohara Masanao , Hagiwara Hiroko , Kanazawa Toshihiko , Obana Koichiro , Kodaira Shuichi , Kaneda Yoshiyuki 
Published: August 2014

Abstract
The 2004 off the Kii Peninsula earthquake occurred on September 5, 2004. Knowing the precise aftershock distribution is important for understanding the mechanism of this earthquake. However, the hypocenter of the main shock was located more than 100 km offshore from the nearest station of the land observation network. In the three days after the main shock, we started ocean bottom seismometer (OBS) observation in order to determine the precise distribution of the aftershocks. We assumed a seismic velocity structure for the hypocenter calculation, based on the results of previous seismic refraction study. The station corrections were incorporated to locate the hypocenter precisely. The hypocenters located within an area covered by five OBSs show relatively small errors. It is found that the OBS-located hypocenters are located about 5.5 km east-southeast from those by JMA and the depth range of the aftershocks is about 5–25 km just beneath the Nankai trough axis. The aftershock hypocenters can be grouped into two clusters at different depths of about 10 km and about 20 km. It is inferred that the main shock also has a depth of 5–25 km. Since this extent of the main shock was larger than one of the oceanic crust of the Philippine Sea plate, the fault plane of the main shock extended at the upper most mantle of the Philippine Sea plate. Although we cannot assign the actual fault plane of the main shock form our observation results, it is clarified that intra-plate earthquakes occurred near the trench region. Our OBS result supports that the main shock was the earthquake not at the plate boundary but within the bending Philippine Sea plate near the trough axis.
Temporal changes in seismic velocity of the crust around Iwate volcano, Japan, as inferred from analyses of repeated active seismic experiment data from 1998 to 2003
Authors: Nishimura Takeshi , Tanaka Satoru , Yamawaki Teruo , Yamamoto Hidekazu , Sano Takashi , Sato Minemori , Nakahara Hisashi , Uchida Naoki , Hori Shuichiro , Sato Haruo 
Published: August 2014

AbstractWe have examined temporal changes in seismic velocity of the crust through repeated active seismic experiments at Iwate volcano, Japan, where a significant volcanic activity and an M6.1 earthquake were observed in 1998. We apply a cross spectrum moving window technique to seismic data recorded at eight stations for the six explosions detonated from1998 to 2003. The seismic velocity at the frequency range of 3-9 Hz decreased by about 1% during the three months including the occurrence of M6.1 earthquake. The seismic velocity gradually increased, and about one third of the decrease was recovered by 2002. Then, the seismic velocity decreased again in 2003. Spatio-temporal changes in the volumetric strains predicted from the M6.1 fault mechanism and the volcanic pressure sources are well correlated with the seismic velocity changes observed in 1998. However, the predicted stress fields are not completely matched with the observed velocity changes from 1998 to 2003. This inconsistency may be due to unknown regional tectonic stress field and/or localized stress fields induced by volcanic pressure sources. It should be noted that the observed velocity changes indicate frequency dependent characteristics although the mechanism is not yet understood.
A simulation analysis to optimize orbits for a tropical GPS radio occultation mission
Authors: Mousa Ashraf , Aoyama Yuichi , Tsuda Toshitaka 
Published: August 2014

Abstract
Space-based Radio Occultation (RO) measurements using a GPS receiver on a low Earth orbiter (LEO) provide accurate atmospheric refractivity profiles. EQUatorial Atmospheric Research Satellite (EQUARS) is a planned satellite mission carrying a GPS receiver for RO measurements, whose main focus is to study the vertical coupling process in the equatorial atmosphere and ionosphere through upward propagating atmospheric waves. This paper presents a model simulation to determine the best practical orbital parameters of a LEO satellite for GPS occultation, which provides dense occultation coverage from 20°S to 20°N and sparser coverage extending to 30°S and 30°N. Constellations of 29 GPS satellites are computed every 10 sec using the six Keplerian parameters based on real almanac data, while various orbits of LEO satellite are computed by varying orbital parameters, especially orbital altitude and inclination. Then, the occultation events are simulated under the assumption that the ray path between the occulting GPS and LEO satellites is a straight line. The simulation analysis shows that altitude and inclination angle of orbit are considered as principal parameters among the Keplerian parameters to accomplish the RO measurements in the equatorial region. Taking into account the long-lived mission, an avoidance of ionospheric F-layer influences, and practical antenna field of view, the best practical orbit for RO measurement in the equatorial region has an altitude of 750 km and an inclination of 20°. LEO on this orbit is expected to provide 530 RO events per day. The analysis also shows that three LEOs in that orbit with 120° separation can provide atmospheric profiles at least once every 6 h within 1000 km from an arbitrary station in the equator.