bluuebunny/crossref_metadata_2025_split huggingface dataset:
An improved double-difference earthquake location algorithm using s P phases: application to the foreshock and aftershock sequences of the 2004 earthquake offshore of the Kii peninsula, Japan (Mw=7.5)
Authors: Bai Ling , Kawasaki Ichiro , Zhang Tianzhong , Ishikawa Yuzo 
Published: August 2014

AbstractWe have useds Pphases to improve the hypocentral locations of the earthquakes that occurred offshore southeast of the Kii peninsula in association with the Mw=7.5 mainshock on September 5, 2004. The earthquakes were more than 100 km from the onshore seismic network and, thus, their focal depths were poorly constrained. Thes Pphases were recorded about 7–11 s after the initialPphases, with both phases having almost the same apparent velocities. The computation of ray-paths revealed that the arrival times of the laters Pphases are sensitive to focal depths. We have recalculated the hypocenters and origin times for 36 events with more than sixs Pphase identifications on seismograms recorded at the High Sensitivity Seismograph Network by includings Pphases in a double-difference earthquake location algorithm, which eliminates the errors introduced by crustal heterogeneity. The relocation results were then compared with those from the Japan Meteorological Agency based on traditional absolute location techniques.
Bubble expansion rates in viscous compressible liquid
Authors: Yamada Kou , Emori Hiroyuki , Nakazawa Kiyoshi 
Published: August 2014

Abstract
A new equation has been derived for radial expansion of a bubble in viscous liquid, taking into account the compressibility of liquid. This model is important in understanding the time-evolution of the bubble growth in a cavitating flow. We solved the equation of motion of viscous liquid and obtained the velocity field and the pressure distribution in liquid. It is found that the expansion rate of a bubble in viscous compressible liquid is governed by the friction force due to viscosity as well as the surface tension, the inertial force, and the gas pressure. Further, the bubble expansion rate is brought by the same expression to that in an incompressible liquid only in the case that the liquid is in a hydrostatic state before the bubble grows.
Equatorial electrojet as a diagnostic tool of geomagnetic field models
Authors: McCreadie Heather , Iyemori Toshihiko 
Published: August 2014

Abstract
The equatorial electrojet (EEJ) is a unique feature of the Earth’s external current systems because it must flow along the dip equator. This provides us with a tool to determine the nature of the variations imposed by competing main field models on the equatorial region. First we show that for certain regions a comparison between scalar geomagnetic measurements that use different models to remove the main field may not be reasonable. Next we found the intrinsic error in the determination of the possible location of the dip equator was ±9.8 km (0.088°) at 108 km altitude for the models shown here. Using scalar measurements from over 14,000 CHAMP satellite passes, the latitude of the maximum of the EEJ field at the satellite altitude was determined by subtracting four different models of the main field. We find that the location can be statistically determined to within ±0.5° of the dip equator (calculated at 108 km altitude) irrespective of longitude, time of the measurement, degree of magnetic activity, and subtracted model. However, variations of the latitude of the maximum EEJ field with longitude are sometimes caused by the actual model and are not always a physical phenomenon. By choosing one model, and assuming it is the best representation of the main field, we have also shown that the accuracy of determination of the position of the EEJ signal is reduced in the morning and evening hours and that a morning and evening shift in the location of the EEJ found using ground measurements is also seen here. There exists a clear annual variation in the position of the EEJ regardless of longitude: it is south of the dip equator in December which is in agreement with the findings of all previous studies.
Morphological and spectral characteristics of L-band and VHF scintillations and their impact on trans-ionospheric communications
Authors: Rama Rao P. V. S. , Tulasi Ram S. , Gopi Krishna S. , Niranjan K. , Prasad D. S. V. V. D. 
Published: August 2014

Abstract
Amplitude scintillations recorded at 1.5 GHz frequency during the high (1998–1999) and low (2004–2005) sunspot activity periods over a low latitude station, Waltair (17.7°N, 83.3°E) revealed that the L-band scintillations mostly occur during the post-sunset to midnight hours peaking around 21:00 hr local time with maximum occurrence during equinoxes, moderate during winter and minimum during the summer months. The occurrence, as well as the intensity of scintillations, is found to be strongly dependant on both the season of the year and the sunspot number. Strong (S4-index >0.45) and fast fading scintillations (fading rates >40 fads/min) observed during the post-sunset hours of equinoxes and winter months manifest as several short duration patches at both VHF (244 MHz) and L-band (1.5 GHz) frequencies and are found to be always associated with the range or total Spread-F on ionograms and bubbles/depletions in the Total Electron Content (TEC) measured from a colocated dual frequency GPS receiver, suggesting that these scintillations are of the Plasma Bubble Induced (PBI) type. On the other hand, relatively weak and slow fading scintillations (fading rates <8 fads/min) observed around the post-midnight hours of the summer months which appear as long-duration patches (>3 hr) at 244 MHz signal (with practically no scintillation activity at the L-band frequencies) are often found to be associated with frequency Spread-F on ionograms with no depletions in TEC. Further, the presence of Fresnel oscillations observed in the spectrum of 244 MHz suggests that the long-duration scintillations observed are due to the presence of a thin layer of irregularities in the bottom side F-region which are generally known as Bottom Side Sinusoidal (BSS) irregularities. Further, the PBI-type scintillations at L-band frequencies are often found to exceed 10 dB power levels (S4 > 0.45) even during the low sunspot activity period of 2004–2005, and cause Loss of Lock in the GPS receivers resulting in a total interruption in the received signals.
Combined ground-based optical support for the aurora (DELTA) sounding rocket campaign
Authors: Griffin Eoghan , Kosch Mike , Aruliah Anasuya , Kavanagh Andrew , McWhirter Ian , Senior Andrew , Ford Elaina , Davis Chris , Abe Takumi , Kurihara Junichi , Kauristie Kirsti , Ogawa Yasunobu 
Published: August 2014

Abstract
The Japan Aerospace Exploration Agency (JAXA) DELTA rocket experiment, successfully launched from Andøya at 0033 UT on December 13, 2004, supported by ground based optical instruments, primarily 2 Fabry- Perot Interferometers (FPIs) located at Skibotn, Norway (69.3°N, 20.4°E) and the KEOPS Site, Esrange, Kiruna, Sweden (67.8°N, 20.4°E). Both these instruments sampled the 557.7 nm lower thermosphere atomic oxygen emission and provided neutral temperatures and line-of-sight wind velocities, with deduced vector wind patterns over each site. All sky cameras allow contextual auroral information to be acquired. The proximity of the sites provided overlapping fields of view, adjacent to the trajectory of the DELTA rocket. This allowed independent verification of the absolute temperatures in the relatively quiet conditions early in the night, especially important given the context provided by co-located EISCAT ion temperature measurements which allow investigation of the likely emission altitude of the passive FPI measurements. The results demonstrate that this altitude changes from 120 km pre-midnight to 115 km post-midnight. Within this large scale context the results from the FPIs also demonstrate smaller scale structure in neutral temperatures, winds and intensities consistent with localised heating. These results present a challenge to the representation of thermospheric variability for the existing models of the region.
Sodium lidar measurements of waves and instabilities near the mesopause during the DELTA rocket campaign
Authors: Williams B. P. , Fritts D. C. , Vance J. D. , She C.-Y. , Abe T. , Thrane E. 
Published: August 2014

Abstract
The sounding rocket for the DELTA (Dynamics and Energetics of the Lower Thermosphere in Aurora) campaign was successfully launched from Andoya at 00:33 UT on Dec 13, 2004. Though it was cloudy at the time of launch, theWeber Na lidar was operating intermittently between 20:00 UT and 23:30 UT on Dec 12, observing Na density, temperature and meridional wind between 80 and 100 km. Throughout the lidar observations, we observed significant small (λz < 5 km) and medium-scale (λz ≈8–15 km) wave activity producing significant wind and temperature shears. There were unusually large (up to 10 m/s and 10 K amplitudes) perturbations of the vertical wind and temperature profiles at 21 UT with a 3 km vertical wavelength that was much stronger in the vertical beam than in the north beam. The atmosphere appeared to become more active as the launch time approached. During the last interval with data, at ∼23:20 UT, Dec. 12th, the lidar profiles revealed a gravity wave in both beams with a magnitude of 5–10 K in temperature and approximately 5 km vertical wavelength. The large background shear plus the wave perturbation produced regions with potential convective instability at multiple altitudes.
A two-dimensional simulation of thermospheric vertical winds in the vicinity of an auroral arc
Authors: Shinagawa H. , Oyama S. 
Published: August 2014

Abstract
The observations made by Fabry-Perot interferometers (FPIs), radars, and satellites have indicated that large vertical motion in the polar region is occasionally generated in the thermosphere associated with auroral activities. However, the behavior of the vertical wind is often very complicated, and the cause of the vertical wind has not been explained by auroral heating or by ion-neutral drag alone. It has been pointed out that a background horizontal flow is likely to significantly alter the dynamics of the neutral atmosphere near an auroral arc. Recent observations have also suggested that strong downward motion is generated in the vicinity of an auroral arc. To study the thermospheric dynamics near a local heating region embedded in a large-scale horizontal flow, a two-dimensional numerical simulation of the thermospheric dynamics has been performed. It is found that interaction of local heating and strong horizontal flow could play an important role in generating vertical motion near an auroral arc. The simulation results indicate that for a horizontal wind speed larger than about 300 m/s, a steady wave-like structure of the neutral wind is formed within and downstream of the heated region. For a horizontal wind speed less than about 300 m/s, on the other hand, no significant vertical motion is generated outside the heated region. This process might account for at least some of the observed features of vertical motion within and outside an auroral arc.
Kinetic effects on the parametric decays of Alfvén waves in relativistic pair plasmas
Authors: Muñoz V. , Hada T. , Matsukiyo S. 
Published: August 2014

Abstract
Parametric decays of a circularly polarized wave propagating along a constant magnetic field in an electronpositron plasma are studied. Fully relativistic effects on the particle velocity in the wave field are considered, as well as kinetic effects in the parallel direction, by means of a one-dimensional relativistic Vlasov equation. In this approximation, a dispersion relation is found for the parametric decays which describes the coupling between normal modes of the system, namely electromagnetic sideband modes and Langmuir waves.
Automatic scaling of F2-layer parameters from ionograms based on the empirical orthogonal function (EOF) analysis of ionospheric electron density
Authors: Ding Zonghua , Ning Baiqi , Wan Weixing , Liu Libo 
Published: August 2014

Abstract
In this paper we apply a method based on empirical orthogonal function (EOF) analysis to automatically scale the F2-layer parameters obtained from ionograms. For a given location, the F layer’s height profiles of ionospheric electron density are represented as an EOF series with adjustable coefficients derived from the EOF analysis of electron density profiles obtained from the International Reference Ionosphere (IRI-2001) model or measured ionograms. By adjusting the coefficients of the series and combining image matching technique, we were able to construct a calculated trace that approximates as close as possible the observed ionogram F2 trace. The corresponding parameters are then known, including the critical frequency (foF2), peak height (hmF2) and maximum usable frequency [MUF(3000)F2] of the F2 layer. Polarization information is unnecessary; only an amplitude array is essential. Consequently, this method is universal and can be applied to many kinds of ionograms (even the film ionograms after an appropriate conversion of the information to the digital form from the film ionogram). To evaluate the acceptability of the obtained parameters, large numbers of foF2, hmF2 and MUF(3000)F2 values from the manually scaled ionograms at Wuhan (114.4°E, 30.5°N), China are compared with those from automatically scaled ionograms by the Automatic Real Time Ionogram Scaler with True height (ARTIST) and our method. The results indicate that the scaled parameters are acceptable and stable.
Evaluation of ozone column amount from the solar backscattering spectra measured with a spectrograph onboard an aircraft
Authors: Nakata Toshimi , Kita Kazuyuki , Suzuki Makoto , Shiomi Kei , Okumura Shin-ichiro , Ogawa Toshihiro 
Published: August 2014

Abstract
Slant column amounts of ozone were evaluated from the solar backscattered spectra measured with a simple spectrograph onboard an aircraft over the Pacific Ocean south of Japan in January 2002. A least-squares fitting method optimized on the basis of Bayesian statistics was developed to evaluate them, and the random error in the fitting was about 2.4%. The evaluated slant column amounts of ozone were compared with those calculated from the total ozone data measured with the Total Ozone Mapping Spectrometer (TOMS) on the same day. The differences between the two ranged from a few percent points to more than 20%, and they increased when a small wavelength deviation in the spectrograph occurred due to the aircraft vibration. Excluding the error due to this wavelength deviation, instrumental and systematic errors were estimated to be less than 10%, demonstrating that this airborne measurement with the spectrograph and the developed fitting method could evaluate the ozone column amount with a good accuracy.
Azimuthally small-scale Alfvén waves in magnetosphere excited by the source of finite duration
Authors: Klimushkin Dmitri Yu. , Podshibyakin Ivan Yu. , Cao Jin Bin 
Published: August 2014

Abstract
In this paper the spatial structure of azimuthally small-scale Alfvén waves in magnetosphere excited by the impulse source is studied. The source is suddenly switched on at a definite moment and works as e−i
ω
0
t during the finite time interval. The influence of factors which lead to the difference of toroidal and poloidal eigenfrequencies (like curvature of field lines and finite plasma pressure) is taken into account. Due to these factors, a radial component of the group velocity of Alfvén wave appears. An important value is the time moment, t
0, when a wave front moving with radial component of wave group velocity from the poloidal surface (a magnetic surface where the source frequency ω
0 coincides with the poloidal frequency) passes the given magnetic shell with the radial coordinate x. The temporal evolution at all the points, where the front has not come yet, is determined by the phase mixing of the initial disturbance. At the points through which the wave front has already passed, the wave field structure almost coincides with the structure of monochromatic wave. The region where the front propagates is bounded by the interval between the poloidal surface and the toroidal one (that is, the Alfvén resonance surface). For this reason, outside this region the evolution is always determined by the phase mixing, which leads to much smaller amplitudes than between poloidal and toroidal surfaces. After the source turned off, a back wave front is formed, which comes through the given point in direction from the poloidal surface to the toroidal one. After the back front has come, the monochromatic wave structure disappears and there is only a weak disturbance, which steadily disappears because of the phase mixing and the final conductivity of ionosphere.
Simulations of superrotation using a GCM for Venus’ middle atmosphere
Authors: Yamamoto Masaru , Takahashi Masaaki 
Published: August 2014

Abstract
A superrotation is simulated in a T10L100 general circulation model for Venus’ middle atmosphere (VMAGCM), in which the radiative effects of aerosols are calculated. The simulation in a domain of 30–100 km is conducted under the condition of a bottom zonal flow with a velocity of 50 m s−1 at the equator. Thermal tides contribute to the maintenance of the cloud-top superrotation together with meridional circulation and vertically propagating gravity waves. The meridional circulation and wave activity are sensitive to the vertical eddy diffusion. Although the equatorial zonal flow has a velocity of about 70 m s−1 when the vertical eddy diffusion coefficient (K
V) is set at 5.0 m s−2, it has a velocity of <100 m s−1 when K
V = 2.5 m s−2. The fully developed equatorial jet for the small K
V case is enhanced at 65 km by small-scale gravity waves emitted from the cloud top.
A study on correction equations for the effect of seafloor topography on ocean bottom magnetotelluric data
Authors: Matsuno Tetsuo , Seama Nobukazu , Baba Kiyoshi 
Published: August 2014

Abstract
Consideration of the effect of seafloor topography on ocean bottom magnetotelluric data is needed to estimate a reliable resistivity structure. Selection of the correction equation which precisely takes account of distortions is important when we correct the effect of seafloor topography with forward modeling. Corrections of synthetic data based on three different correction equations are carried out, and the corrected responses and the true response are compared to investigate which correction equation is the best in application to distorted magnetotelluric data on the seafloor. Differences in the corrected responses are remarkable at periods shorter than several thousands seconds. These differences are caused by differences in treatment of the distortions of magnetic field and in robustness of the correction equation to a resistivity structure assumed for the topographic correction. The results suggest that the correction equation of Nolasco et al. (1998) should be used because it better accommodates the estimation of unknown resistivity structures. We apply the correction equation of Nolasco et al. (1998) to a response observed in the Mariana area. The one-dimensional resistivity structure estimated from the corrected response explains almost all the components of the observed response.
A measurement of the lunar semidiurnal tide at Wuhan (30°40′N, 114°30′E)
Authors: Niu X. J. , Xiong J. G. , Wan W. X. , Ning B. Q. , Liu L. B. 
Published: August 2014

Abstract
Upper atmospheric winds have been measured at heights from 80 to 100 km overWuhan (30°40N, 114°30′E), China with a meteor radar from 2002 to 2005. The variations of lunar semidiurnal tidal amplitudes and phases with both seasons and heights are studied in detail to reveal the properties of the lunar semidiurnal tide. It is shown that the lunar semidiurnal tide is stronger in January than other months, and its second peak appears near August. For most months the eastward maximum is 3 ± 1 lunar hours later than the northward maximum, as classical theory predicts for a northern hemisphere tide. The observed seasonal and height variations are also compared with the Global Scale Wave Model (GSWM). The phases do not agree well with those of the GSWM model. The maximum amplitude occurs in a different month in the model. There are about 5 lunar hours phase difference between the observed and the model at 90 and 96 km in eastward and northward components. A comparison of the lunar and solar semidiurnal tides is also shown in this paper. The behavior of these two tides in season is different, especially for the month of appearance of maximum amplitude.
Propagation characteristics of bedrock waves traveling from pre-Tertiary basement to engineering bedrock
Authors: Kinoshita Shigeo 
Published: August 2014

AbstractThis study uses borehole array recordings to measure the propagation characteristics of bedrock waves traveling from pre-Tertiary basement (seismic bedrock) to engineering bedrock with anS-wave velocity of approximately 0.5–0.8 km/s. To avoid the destructive interference of surface-reflected down-going waves and incidence waves in seismic and engineering bedrock, borehole data recorded at sufficient depth levels are used in this study. This is the most important aspect of the fundamental basis of this study. The propagation characteristics, i.e., the transfer function, of bedrock motions for S-waves are well represented by a Butterworth-type low-pass filter model with a high corner frequency in excess of 15 Hz and a low decay rate of —3 power of frequency. The use of such a filter model is based on the concise representation of the transfer function from an engineering viewpoint. Simple one-dimensional ray theory with a plane wave approximation explains the characteristics of the model filter at low frequencies of less than approximately 5 Hz; however, one-dimensional ray theory with a plane wave approximation at high frequencies in excess of 5 Hz requires the unusual frequency characteristics ofQS−1(f), which increases with increasing frequency, to explain the frequency characteristics of the model filter. These facts imply that the filter gain can be determined using the impedance ratio of seismic bedrock to engineering bedrock and the attenuation characteristics of the intervening media at low frequencies less than 5 Hz. However, the cutoff frequency and decay rate of the filter must be determined from observational data.
Temporal changes in state of stress in the Tokachi Oki area after the 2003 Tokachi Oki Earthquake
Authors: Ghimire Subesh , Katsumata Kei , Kasahara Minoru 
Published: August 2014

Abstract
A stress tensor inversion was carried out in the aftershock area of the 2003 Tokachi Oki earthquake for a comparative study on the preseismic and postseismic stress state. The inversion technique was adopted from Gephart (1990) to pursue the study with earthquake focal mechanism data from National Research Institute for Earth Science and Disaster Prevention (NIED). Results of the inversion revealed significant change in stress field before and after the main shock of the 2003 event. The preseismic uniaxial compression in strike slip stress regime was changed to a transition from transpressional to a radial compression in a compressional regime.