bluuebunny/crossref_metadata_2025_split huggingface dataset:
Rupture process at the beginning of the 2007 Chuetsu-oki, Niigata, Japan, earthquake
Authors: Takenaka Hiroshi , Yamamoto Yosuke , Yamasaki Hirokazu 
Published: August 2014

AbstractThe rupture process at the beginning stage of the 2007 Chuetsu-oki, Niigata, Japan, earthquake (MW6.6) is investigated by analyzingP-wave records from local strong-motion stations. TheP-wave portion of the nearsource strong-motion records shows about 2 s of small but increasing amplitude arrival (so-called “initial rupture phase”) followed by the onset of the main energy release (“main rupture phase”). Two issues are addressed in this paper: (1) where the initial rupture process occurred and (2) where the seismic energy corresponding to the main rupture phase was released at the primary stage of the main rupture. The first issue is addressed by locating the main rupture onset position, and the second issue is then approached by introducing a method for mapping the wave energy onto plausible fault planes. Eventually, the following were revealed. The rupture initiated and propagated on the NW-dipping plane, which is a nodal plane of the focal mechanism solution. At 2.1 s after rupture initiation the subsequent main rupture started at a position of approximately 4 km away, southwestward and updipward from the hypocenter. The main rupture at this stage has two possible rupture planes: the same plane as the initial rupture plane, and the conjugated plane, which shares the main rupture onset point with the initial rupture plane. Although it is difficult to determine which plane was actually ruptured at the primary stage of the main rupture, we found that the possible areas radiating strong wave energy on the two possible planes, which could correspond to the first asperity of this earthquake, are located between the hypocenter and the Kashiwazaki-Kariwa nuclear power plant.
Modeling of substorms and flares by the fast reconnection mechanism
Authors: Ugai M. , Kondoh K. , Shimizu T. 
Published: August 2014

Abstract
The 3D spontaneous fast reconnection model is applied to well-known signatures of geomagnetic substorms and solar flares. First, it is applied to the traveling compression regions (TCRs) associated with plasmoids propagating down the tail plasma sheet, known as a definite signature of geomagnetic substorms, and the in-situ satellite observations can be precisely explained, both qualitatively and quantitatively. Then, it is demonstrated that the magnetospheric current wedge drastically evolves through field-aligned currents to link the tail current to the auroral electrojet. It is also found that the well-known morphological features of two-ribbon flares can be explained by the fast reconnection model. In particular, the joule heating, associated with the flare current wedge, is shown to be important for the two-ribbon heating. Therefore, it is suggested that both solar flares and geomagnetic substorms result from the same physical mechanism, i.e., the fast reconnection mechanism.
Patchy reconnection in a Y-type current sheet
Authors: Linton M. G. , DeVore C. R. , Longcope D. W. 
Published: August 2014

Abstract
We study the evolution of the magnetic field in a Y-type current sheet subject to a brief, localized magnetic reconnection event. The reconnection produces up- and down-flowing reconnected flux tubes which rapidly decelerate when they hit the Y-lines and underlying magnetic arcade loops at the ends of the current sheet. This localized reconnection outflow followed by a rapid deceleration reproduces the observed behavior of post-CME downflowing coronal voids. These simulations support the hypothesis that these observed coronal downflows are the retraction of magnetic fields reconnected in localized patches in the high corona.
Non-thermal electrons at the Earth’s bow shock: A ‘gradual’ event
Authors: Oka M. , Terasawa T. , Fujimoto M. , Matsui H. , Kasaba Y. , Saito Y. , Kojima H. , Matsumoto H. , Mukai T. 
Published: August 2014

Abstract
The Earth’s bow shock is known to produce non-thermal electrons which are generally observed as a ‘spike’ in their flux profile. Here, in this paper, we present an analysis of electron and whistler wave properties for a quasi-perpendicular shock crossing that is supercritical, but subcritical to the so-called whistler critical Mach number, M
crit
w
, above which whistler waves cannot propagate upstream. We have found that the amplitudes of whistler waves increased exponentially as a function of time prior to the shock encounter, while the suprathermal (>2 keV) electron flux similarly increased with time, although with differing e-folding time scales. Comparison of the electron energy spectrum measured within the ramp with predictions from diffusive shock acceleration theory was poor, but the variation of pitch angle distribution showed scattering of non-thermal electrons in the upstream region. While not finding a specific mechanism to account for the electron diffusion, we suggest that the whistlers seen probably account for the differences observed between this ‘gradual’ event and the ‘spike’ events seen at shocks with no upstream whistlers.
Statistically predicting Dst without satellite data
Authors: Parnowski A. S. 
Published: August 2014

Abstract
In this paper we construct a regression relationship for predicting Dst 1 hour ahead. Our model uses only previous Dst values. This regression is totally unbiased and does not rely on any physical model, except for the fact that Dst somehow contains the information on the recurrent geomagnetic storms. This regression has the prediction efficiency of 0.964, linear correlation with official Dst index of 0.982, and RMS of 4.52 nT. These characteristics are inferior only to our other model, which uses satellite data and provides the prediction efficiency of 0.975, linear correlation with official Dst index of 0.986, and RMS of 3.76 nT. This makes it quite suitable for prediction purposes when satellite data are not available.
Properties of dayside nonlinear rising tone chorus emissions at large L observed by GEOTAIL
Authors: Verkhoglyadova Olga P. , Tsurutani Bruce T. , Omura Y. , Yagitani S. 
Published: August 2014

Abstract
This paper studies some wave properties of nonlinear rising tone chorus emissions in the outer regions of the dayside equatorial magnetosphere at ∼(6.3,–4.7, 0.7R
E) in GSE coordinates. We analyze data obtained with the PWI and WFC receivers on GEOTAIL associated with a substorm on April 29, 1993. Fine structure of the chorus elements and inter-element spacings are shown. Directions of propagation of the chorus elements relative to the local magnetic field lines are analyzed. Wave polarizations, intensities and spectral properties of chorus in the equatorial Earth’s magnetosphere are discussed.
The total failures of GPS functioning caused by the powerful solar radio burst on December 13, 2006
Authors: Afraimovich E. L. , Demyanov V. V. , Smolkov G. Ya. 
Published: August 2014

Abstract
We investigated failures in the GPS performance produced by extremely dense solar radio burst fluxes associated with the intense (X3.4 in GOES classification) solar flare and Halo CME recorded by SOHO/LASCO on December 13, 2006. According to substantial experimental evidence, high-precision GPS positioning on the entire sunlit side of the Earth was partially disrupted for more than 12–15 min; the high level of GPS slips resulted from the wideband solar radio noise emission. Our results are in agreement with the data obtained recently for the extreme solar radio burst on December 6, 2006, and provide a sound basis for revising the role of space weather factors in the functioning of state-of-the-art satellite systems and for taking a more thorough account of these factors in their development and operation.
Aeronomic effects of the solar flares in the topside ionosphere
Authors: Leonovich L. A. , Taschilin A. V. 
Published: August 2014

Abstract
We obtained that according to the GPS data at altitudes of the topside ionosphere (h >300 km) a flare is able to cause a decrease of the electron content. Using the theoretical model it is shown that the intense transport of O+ ions into the above-situated plasma caused by a sharp increase in the ion production rate and thermal expansion of the ionospheric plasma is a cause of the formation of the negative disturbance in the electron concentration in the topside ionosphere.
Effect of stochastic ionospheric delay modeling for GPS ambiguity resolution
Authors: Hong Chang-Ki , Grejner-Brzezinska Dorota A. , Kwon Jay Hyoun , Arslan Niyazi 
Published: August 2014

Abstract
The network-derived ionospheric delay can improve the fast and accurate determination of the long baseline in both the rapid-static and kinematic Global Positioning System (GPS) positioning mode. In this study, an interpolation of the undifferenced (UD) ionospheric delays is performed on a satellite-by-satellite and epoch-by-epoch basis, respectively, using the least-squares collocation (LSC) to provide not only ionospheric delays but also their variances. The developed method retains the simplicity of the two-dimensional (2-D) model, but it does not introduce errors due to the thin-shell assumption made in the single-layered model. Our method also provides flexibility in forming the predicted double-differenced (DD) ionospheric delays. Faster and more reliable positioning solutions can be obtained when the developed method is used to predict DD ionospheric delays. The numerical test applying the method to the Ohio Continuously Operating Reference Station network shows a 23% improvement in mean time-to-fix with the network-derived ionospheric delays.
Nonstationary ray decomposition in a homogeneous half space
Authors: Kinoshita Shigeo 
Published: August 2014

AbstractAmethod for decomposing anSH-wave at the surface into the instantaneous power of shearing strain associated with rays in a homogeneous half space as a function of lapse timetand depth time τ, which is the travel time for the depth direction, is demonstrated. The instantaneous power in the (t, τ) space shows local maxima at the intersections of up-coming and down-going rays, which correspond to the velocity boundaries of the real layered structure beneath the site. Thus, the proposed method provides a tool for estimating the velocity boundaries of real layered structure from only surface recordings. The estimated results obtained by applying the proposed method to strong-motion data recorded at two Kanto sediment sites are in good agreement with the velocity boundaries previously determined by means of down-hole methods.
Geographical variations of the 0S0 normal mode amplitude: predictions and observations after the Sumatra-Andaman earthquake
Authors: Rosat Severine , Watada Shingo , Sato Tadahiro 
Published: August 2014

Abstract
The radial seismic normal mode 0S0 was strongly excited by the 2004 Mw = 9.3 Sumatra-Andaman earthquake at a period of 20.5 min. In a spherically symmetric Earth model, 0S0 amplitude is the same everywhere on the Earth’s surface. However, when the ellipticity and rotation of the Earth are taken into consideration, theoretical computations predict an amplitude of 0S0 1% higher at the pole than at the equator. Based on a realistic three-dimensional heterogeneous rotating elliptic Earth model, our predictions indicate that the amplitude of 0S0 is 2% higher at the pole than at the equator. A longitude dependency of 0S0 amplitude is also shown. The analysis of 13 superconducting gravimeter (SG) records of the 2004 Sumatra-Andaman earthquake supports the predicted geographical variations of 0S0 amplitude. We have also obtained new estimates for the frequency and Q of 0S0: 0.8146566±1.6 10−6 mHz and 5506±19.
Ionospheric temporal and spatial variations during the 18 August 2003 storm over China
Authors: Wen Debao , Yuan Yunbin , Ou Jikun , Huo Xingliang , Zhang Kefei 
Published: August 2014

Abstract
The effects of the 18 August 2003 geomagnetic storm on the ionosphere over China have been first studied by combining dual-frequency Global Positioning System (GPS) observation data from the Crustal Movement Observation Network of China (CMONOC) using the computerized ionospheric tomography (CIT) technique. The temporal and spatial variations of the ionosphere are analyzed using a time series of ionospheric electron density (IED) maps, and the ionospheric storm evolution process is revealed. The tomographic results show that the main ionospheric effects of this storm over China are: (1) that positive storm phase effects usually happen in the low-latitude ionosphere, (2) that negative storm phase effects occur in the mid-latitude ionosphere, and (3) that the equatorial anomaly structure can also be found. In contrast to the quiet period of the ionosphere on 17 August 2003, the equatorial anomaly crest moved to the north in the main phase of the storm and then moved back to the original location in the recovery phase on 19 August 2003. We compared the peak density NmF2 and the peak height hmF2 obtained from the ionosonde observations at Wuhan station and those inverted by the CIT technique to confirm the reliability of the GPS-based tomographic technique. The tomographic results revealed that the GPS-based CIT technique can be used to monitor large-scale ionospheric disturbances during geomagnetic storms.
Weak interplate coupling beneath the subduction zone off Fukushima, NE Japan, inferred from GPS/acoustic seafloor geodetic observation
Authors: Matsumoto Yoshihiro , Ishikawa Tadashi , Fujita Masayuki , Sato Mariko , Saito Hiroaki , Mochizuki Masashi , Yabuki Tetsuichiro , Asada Akira 
Published: August 2014

Abstract
We have been carrying out GPS/acoustic seafloor geodetic observations at several reference points situated along the Japan Trench, a major plate boundary of subduction. A time series of horizontal coordinates of one of the seafloor reference points, located off Fukushima, obtained from seven campaign observations for the period 2002-2008, exhibits a linear trend with a scattering root mean square of about 3 cm. A linear fit to the time series gives an intraplate crustal movement velocity of 3.1 cm per year in a westerly direction, which is significantly smaller than that at the other seafloor reference point 120 km away along the trench axis. This result implies weak interplate coupling in this region.
Subsurface structures derived from receiver function analysis and relation to hypocenter distributions in the region from the eastern Shikoku to the northern Chugoku districts, Southwest Japan
Authors: Ueno Tomotake , Shibutani Takuo , Ito Kiyoshi 
Published: August 2014

AbstractWe carried out receiver function imaging to estimate detailed configurations of the Philippine Sea (PHS) slab beneath the Shikoku and Chugoku districts and crustal structures in the region. We used two temporary seismic arrays with an average station spacing of about 10 km in the Chugoku district. Beneath Shikoku a clear northward dipping discontinuity at about 20–40 km depth was found, with other discontinuities below. We present a new interpretation that the clear boundary corresponds to the under surface of a low velocity layer in the upper part of the PHS slab. We also found a discontinuity at about 60 km depth beneath the Chugoku district, which is thought to be the aseismic PHS slab. Small scale discontinuities were found in the crust beneath the source area of the 2000 western Tottori Earthquake and around the Median Tectonic Line. The discontinuities might relate to the occurrence of large inland earthquakes.
Planetary wave oscillations in sporadic E layer occurrence at Wuhan
Authors: Zuo Xiaomin , Wan Weixing 
Published: August 2014

Abstract
Quasi 6-day oscillations in E
s occurrence were observed to occur in relation with planetary wave activity at Wuhan, China (30.6°N, 114.5°E). Wavelet analysis of E
s occurrence time series revealed that a strong 5- to 7-day oscillation was present during the period from about day 120 to 137 of 2003. The same quasi 6-day planetary wave oscillation was also found to dominate the spectrum of concurrent wind data measured in the 80- to 100-km region by a meteor radar, in agreement with the E
s occurrence. There is also a great deal of similarity between the 5- to 7-day band-pass filtered waveforms of E
s occurrence and the wind data. By estimating the wave phase changes with altitude, the quasi 6-day PW in the zonal wind was found to be in phase with the sporadic E layer critical frequency, f
o
E
s, at about 115 km, close to the observed E
s height. The quasi 6-day PW modulation was also present in the amplitude of the 12-h and 24-h periodicities which existed in the f
o
E
s time series. The present results provide new evidence in favor of a planetary wave indirect role on E
s formation through the modulation of tides, which in line with previous studies by Haldoupis and Pancheva (2002), and Pancheva et al. (2003).
Coseismic deformation of the 2007 Chuetsu-oki earthquake derived from PALSAR/InSAR and its fault model
Authors: Ozawa Taku 
Published: August 2014

AbstractThe 2007 Chuetsu-oki earthquake (Mj6.8) occurred offshore of Niigata Prefecture, northeast Japan, on 16 July 2007. I applied PALSAR/InSAR to detect coseismic deformation associated with the earthquake. The interferogram generated from descending data revealed a slant-range shortening exceeding 20 cm in the coastal area of Kashiwazaki adjacent to the epicenter and a maximum slant range extension of approximately 15 cm southeast of the slant-range shortening pattern. The interferogram generated from descending data is consistent with GPS displacements, but the non-crustal deformation component was large in the interferogram generated from ascending data. Based on a fault plane dipping to the southeast, a fault-slip distribution was estimated from the descending interferogram and GPS displacements. The largest fault-slip was located in the southwestern deeper part of the mainshock hypocenter. In the northern part of the focal region, the fault-slip was dominant at depths of 5–15 km, but it was limited to shallower depths in the southern part of the focal region. Such fault-slip distribution is consistent with the aftershock distribution. This consistency supports the assumption that the fault rupture in the mainshock has primarily occurred in the nodal plane dipping to the southeast.
Local time variation of the amplitude of geomagnetic sudden commencements (SC) and SC-associated polar cap potential
Authors: Araki T. , Tsunomura S. , Kikuchi T. 
Published: August 2014

Abstract
Local time (LT) variations of the averaged H-component amplitude of geomagnetic sudden commencements (SCs) observed at Memambetsu (geomagnetic latitude 35.4°) are derived separately for the summer and winter season. The amplitude was found to be higher at nighttime than daytime in both seasons, and the LT variations showed a good agreement with calculated LT variations of the resultant magnetic field due to a pair of fieldaligned currents (FACs) and ionospheric currents produced by the FACs. The DL- and DP-component of the disturbance field of SC can be separated based on a comparison of the observed and calculated LT variations. A method is introduced by which we can estimate the potential voltage difference associated with the FACs in the polar cap.
Possible influence of ultra-fast Kelvin wave on the equatorial ionosphere evening uplifting
Authors: Takahashi H. , Abdu M. A. , Wrasse C. M. , Fechine J. , Batista I. S. , Pancheva D. , Lima L. M. , Batista P. P. , Clemesha B. R. , Shiokawa K. , Gobbi D. , Mlynczak M. G. , Russell J. M. 
Published: August 2014

Abstract
Equatorial 3.5-day ultra-fast Kelvin wave was observed in the MLT zonal wind measured by meteor radar at Cariri (7.4°S, 36.5°W, geomag. 8°S) and in the stratosphere-mesosphere temperature structures from the TIMED/SABER data. The ionospheric F-layer bottom-side virtual height hT’F and the critical frequency f
o
F
2 observed at Fortaleza (3.9°S, 38.4°W, geomag. 5°S) also showed similar oscillation structures, indicating an influence of the Kelvin wave in the F region height and modulation of E × B uplifting during the evening period. Consequently the ionospheric spread F onset time was also modulated in the same period, around 4 days.
Propagation characteristics of nighttime mesospheric and thermospheric waves observed by optical mesosphere thermosphere imagers at middle and low latitudes
Authors: Shiokawa K. , Otsuka Y. , Ogawa T. 
Published: August 2014

Abstract
We review measurements of nighttime atmospheric/ionospheric waves in the upper atmosphere in Japan, Indonesia, and Australia, using all-sky airglow imagers of optical mesosphere thermosphere imagers (OMTIs). The imagers observe two-dimensional patterns of airglow emissions from oxygen (wavelength: 557.7 nm) and hydroxyl (OH) (near-infrared band) in the mesopause region (80–100 km) and from oxygen (630.0 nm) in the thermosphere/ionosphere (200–300 km). Several statistical studies were done to investigate propagation characteristics of small-scale (less than 100 km) gravity waves in the mesopause region and medium-scale traveling ionospheric disturbances (MSTIDs, ∼100–1,000 km) in the thermosphere/ionosphere. Clear seasonal variations of occurrence and propagation directions were reported for these waves. The propagation directions in the mesopause region are controlled by wind filtering, ducting processes and relative location to the wave sources in the troposphere. Poleward-propagating waves tend to be observed in the summer in the mesopause region at several stations, suggesting that mesospheric gravity waves are generated by intense convective activity in the equatorial troposphere. On the other hand, systematic equatorward and westward motions were observed for all seasons for nighttime MSTIDs in the midlatitude ionosphere with geomagnetic conjugacy between the northern and southern hemispheres. Ionospheric instabilities may play important role for the generation and propagation of these MSTIDs. We also give an example of simultaneous observation of quasi-periodic southward-moving waves in the mesopause region and in the thermosphere at the geographic equator. From these results, we discuss mean wind acceleration by mesospheric gravity waves and penetration of gravity waves from the mesosphere to the thermosphere.
Surface fair-weather potential gradient measurements from a small tropical island station Suva, Fiji
Authors: Kumar Vickal V. , Ramachandran V. , Buadromo V. , Prakash J. 
Published: August 2014

Abstract
Systematic analysis of the surface fair-weather potential gradient (PG) measured for 13 months (July 2005–July 2006) at 10 s resolution over a small tropical island station Suva (18.08°S, 178.45°E), Fiji is presented. Based on the solar radiation (>800 W m−2) and surface wind speed (<4.5 m s−1) conditions, 63 fair-weather days were selected. After sorting the data into a range of 0–1000 V m−1, the average PG was ∼139 V m−1. The measured fair-weather PG had a semi-diurnal structure, with a more pronounced peak at 0730 LT (1930 UT) and a reduced peak at 2200 LT (1000 UT). The time of occurrence of the morning peak and the noontime minima agreed well with the Carnegie curve. However, the variation about the global mean in the measured PG was 150% whereas for the Carnegie curve it was only 35%. The effects of the local meteorological parameters on the PG measurements were found to be small. On average, the PG during the dry season (May–October) was always greater than in the wet season (November–April). In contrast, analysis of regional (0–60°S and 100°E–160°W) lightning activity on fair-weather days showed a peak at ∼2000 LT and higher lightning activity during the wet season. These results indicate that the regional thunderstorm activity has no direct connection with the local fair-weather PG at the site.