bluuebunny/crossref_metadata_2025 huggingface dataset:
Caldera geometry determined by the depth of the magma chamber
Authors: Kusumoto Shigekazu , Takemura Keiji
Published: August 2014

The depth of the magma chamber is shown to be an important factor governing the initial type, scale, and collapse of a caldera. The collapse of the magma chamber is approximated by the contraction of a sphere in an elastic medium, and the distribution of plastic and/or rupturing area on the surface is calculated using the Coulomb failure criterion under the assumption of an elastic-perfectly plastic material. It is found that the necessary contraction for the formation of a caldera is described by fifth-power polynomial expression of the depth of the magma chamber, and that the radius and geometry of the caldera are dependent on the depth of the magma chamber.
A study of smoothed TEC precision inferred from GPS measurements
Authors: Liu Zhizhao , Gao Yang , Skone Susan
Published: August 2014

The availability of a large amount of TEC data derived from dual frequency GPS measurements observed by GPS reference networks provides a great opportunity for ionosphere studies. In order to obtain better accuracy for the derived TEC, a data smoothing technique is usually employed to take advantage of both code pseudorange and carrier phase GPS measurements. The precision of TEC data therefore is dependent on the smoothing approach. However little work has been done to evaluate the precision of the smoothed TEC data obtained from different smoothing approaches. This investigation examines the properties of two popularly used smoothing approaches and develops the closed-form formulas for estimating the precision of the smoothed TEC data. In addition, a previously proposed approximate formula for estimating TEC precision is also evaluated against its closed-form formula developed in this paper. The TEC precisions derived from the closed-form precision estimation formulas for approaches I and II are analyzed in a numerical test. The results suggest that approach II outperforms approach I and the precision of TEC data smoothed by approach II is higher than approach I. For approach I, a numerical test is also conducted to compare the precision difference between the closed-form and approximate formulas for estimating TEC precision. The comparison indicates that TEC derived from the closed-form formula have better precisions than the approximate formula. Analysis also reminds users that extra cautions should be taken when using the approximate formula in order to avoid the precision divergence phenomenon.
Understanding the concept of outlier and its relevance to the assessment of data quality: Probabilistic background theory
Authors: Monhor Davaadorjin , Takemoto Shuzo
Published: August 2014

In recent years an increasing interest in the studies on outlier can be observed, however, for the time being there exists no general definition of outlier. In the present paper we introduced a generic descriptive definition of outlier. We observed that the outlier problems had so far been treated in statistical way without paying proper attention to probabilistic-theoretic backgrounds. In view of this gap, we made an attempt to establish a probabilistic background theory. Within this framework, the large deviations are considered as probabilistic-theoretic model of outlier, and the interrelationship of the laws of large numbers, the central limit theorems and the large deviations are clarified. These considerations are specialized for the case of statistical sample, which is important from the point of view of the assessment of data quality. Some methodological and historical aspects of geodesy, geophysics and astronomy are mentioned, too. We revealed that the data analysis carried out by Kepler in the process of discovery of his famous elliptic law of planetary motion has relevance to the outlier problem. This methodologically interesting fact is a new result in the history of geosciences. We established that the accuracy of Chebyshev inequality increases as the deviation of the random variable involved from its expectation, increases. The possibility of application of Chebyshev inequality to the outlier problem is pointed out.
Three-dimensional structure of Vp, Vs and Vp/Vs in the upper crust of the Marmara region, NW Turkey
Authors: Bariş Şerif , Nakajima Junichi , Hasegawa Akira , Honkura Yoshimori , Ito Akihiko , Üçer S. Balamir
Published: August 2014

We applied a 3-D seismic tomography inversion algorithm to arrival-time data obtained, during 18 years from 1985 to 2002, from local seismic networks and aftershock studies in the Marmara region, in order to better understand the upper crustal structure of the complex tectonic region. We integrated all the available data set into a common data set and relocated the events, using a 1-D velocity model. We then selected 3,949 earthquakes and obtained 92355 arrival times, in total, consisting of 59,313P-wave and 33,042S-wave arrival times. In this paper we present detailed crustal structures forV p,V sandV p/V sratios from the surface down to 15 km depth with good resolution in terms of the hit count analysis of seismic rays, the checkerboard and restoring resolution tests for the studied region. The results obtained from the inversion suggest that the western part of the North Anatolian Fault Zone shows strong lateral heterogeneity. We concluded that no clear pattern exists between the distribution of microearthquakes and aftershocks and the velocity perturbations presented in this paper. This is probably due to complex tectonic and geological structures. Large coseismic slip associated with the two recent strong earthquakes was found to correspond to higher velocity anomalies, as was often found recently. On the other hand, low velocity values correspond to the sedimentary units or the alluvium regions, as supported by the low resistivity and gravity values. Thus the results presented in this paper are quite consistent with the other data such as gravity, resistivity and magnetic anomalies, indicating that our model is reliable and efficient and it should be useful for further interpretation of tectonic and geological problems in this region. It should be pointed out, however, that the results ofS-wave perturbations andV p/V sratio could not be discussed in detail because of insufficient quality of theS-wave data and the reliability of the results is not very high. Nonetheless, the fact that recent large Izmit earthquake and moderate aftershocks that occurred in or around the high velocity zones near the low velocity region suggests that high velocity regions found in the area close to Istanbul in the Marmara Sea and also at the Iznik-Mekece fault are potential sites for strain energy accumulation and release.
A synoptic study of VLF sudden phase anomalies recorded at Visakhapatnam
Authors: Khan Ibrahim , Devi M. Indira , Arunamani T. , Madhusudhana Rao D. N.
Published: August 2014

A synoptic survey of Sudden Phase Anomalies (SPAs) observed in the phase variation measurements of 16 kHz VLF transmissions from Rugby (England) made at Visakhapatnam (India) has been carried out. These Sudden Ionospheric Disturbances caused during solar flares are examined in relation to flare time enhancements of X-ray radiation fluxes. It is found that nearly 81% of SPAs recorded have accompanying X-ray enhancements and in 80% of the cases Hα flares and microwave bursts also occur concurrently. Using SPA magnitudes and flare time X-ray flux values, the threshold level of X-ray flux to induce an SPA has been estimated as 1.5⊙×10−3 ergs/cm2/s. In majority of the events, the change in reflection height during the flare is observed to be less than 4 kms. Other SPA characteristics like onset times, growth and relaxation times etc. have also been studied. These results are consistent with those obtained for other propagation paths.
The observation of ULF emissions at Nakatsugawa in possible association with the 2004 Mid Niigata Prefecture earthquake
Authors: Ohta Kenji , Watanabe Nobuo , Hayakawa Masashi
Published: August 2014

The observation of ULF/ELF electromagnetic emissions at Nakatsugawa, Gifu, has indicated that ULF emissions in the frequency below 0.1 Hz take place about two-three weeks before the 2004 Mid Niigata Prefecture earthquakes. The most important support to this is based on the goniometric direction finding for those ULF emissions in the period of October 2–6, which indicates their azimuth being very close to the epicenters of the earthquake. So, these ULF emissions on October 2–6 are likely to be associated with the 2004 Mid Niigata Prefecture earthquake.
Local gravity from Lunar Prospector tracking data: Results for Mare Serenitatis
Authors: Goossens S. , Visser P. N. A. M. , Heki K. , Ambrosius B. A. C.
Published: August 2014

High-resolution gravity anomalies on the surface of the Moon are determined from Lunar Prospector tracking data residuals. By means of a benchmark test the recovery method is validated with respect to the orbit determination and gravity field recovery strategy. Tracking data for the entire extended mission of Lunar Prospector, during which the satellite flew at an average altitude of 30 km above the lunar surface, have been completely and independently processed and orbits have been determined. Using tracking data residuals from these precise orbits, adjustments to the a priori gravity field model have been created for Mare Serenitatis. The results for Mare Serenitatis with the local recovery are comparable to global recovery results, yet faster and more efficient with a possibility to increase the resolution.
International Geomagnetic Reference Field—the tenth generation
Authors: Macmillan Susan , Maus Stefan
Published: August 2014

The International Geomagnetic Reference Field (IGRF) 10th Generation was adopted in 2004 by the International Association of Geomagnetism and Aeronomy (IAGA) Working Group V-MOD. It is the latest version of a standard mathematical description of the Earth’s main magnetic field and is used widely in studies of the Earth’s deep interior, its crust and its ionosphere and magnetosphere. This generation differs from the previous generation with the replacement of the secular-variation model for 2000.0–2005.0 with a main-field model at 2005.0 and a secular-variation model for 2005.0–2010.0. The IGRF is the product of a huge collaborative effort between magnetic field modellers and the institutes involved in collecting and disseminating magnetic field data from satellites and from observatories and surveys around the world. This paper lists the new coefficients and includes contour maps and pole positions.
New parameterization of external and induced fields in geomagnetic field modeling, and a candidate model for IGRF 2005
Authors: Olsen Nils , Sabaka Terence J. , Lowes Frank
Published: August 2014

When deriving spherical harmonic models of the Earth’s magnetic field, low-degree external field contributions are traditionally considered by assuming that their expansion coefficient q
1
0
varies linearly with the D
st-index, while induced contributions are considered assuming a constant ratio Q
1 of induced to external coefficients. A value of Q
1 = 0.27 was found from Magsat data and has been used by several authors when deriving recent field models from Èrsted and CHAMP data. We describe a new approach that considers external and induced field based on a separation of D
st = E
st + I
st into external (E
st) and induced (I
st) parts using a 1D model of mantle conductivity. The temporal behavior of q
1
0
and of the corresponding induced coefficient are parameterized by E
st and I
st, respectively. In addition, we account for baseline-instabilities of D
st by estimating a value of q
1
0
for each of the 67 months of Èrsted and CHAMP data that have been used. We discuss the advantage of this new parameterization of external and induced field for geomagnetic field modeling, and describe the derivation of candidate models for IGRF 2005.
NGDC/GFZ candidate models for the 10th generation International Geomagnetic Reference Field
Authors: Maus Stefan , McLean Susan , Dater David , Lühr Hermann , Rother Martin , Mai Wolfgang , Choi Sungchan
Published: August 2014

Following the call for candidates for the 10th generation IGRF, we produced and submitted three main field and three secular variation candidate models. The candidates are derived from parent models which use a standard quadratic parameterisation in time of the internal Gauss coefficients. External magnetospheric fields are represented by combined parameterisations in Solar Magnetic (SM) and in Geocentric Solar Magnetospheric (GSM) coordinates. Apart from the daily and annual variations caused by these external fields, the model also accounts for induction by Earth rotation in a non-axial external field. The uncertainties of our candidates are estimated by comparing independent models from CHAMP and Èrsted data. The root mean square errors of our main field candidates, for the internal field to spherical harmonic degree 13, are estimated to be less than 8 nT at the Earth’s surface. Our secular variation candidates are estimated to have root mean square uncertainties of 12 nT per year. A hind-cast analysis of the geomagnetic field for earlier epochs shows that our secular acceleration estimates from post-2000 satellite data are inconsistent with pre-2000 acceleration in the field. This could confirm earlier reports of a jerk around 2000.0, with a genuine change in the secular acceleration.
The IZMIRAN main magnetic field candidate model for IGRF-10, produced by a spherical harmonic-natural orthogonal component method
Authors: Golovkov Vadim P. , Zvereva Tatiana I. , Chernova Tatiana A.
Published: August 2014

A simple method is proposed for constructing a space-time model of the main magnetic field based on the high-accuracy satellite survey data. At the first stage, we expand the CHAMP daily mean data into spherical harmonics with constant coefficients. It provides us with a series of the daily mean spherical-harmonic models (DMM) over a survey interval of several years, which are, then, expanded into the natural orthogonal components (NOC). It is shown that the NOC series converges rapidly, and that the accuracy of the space-time model over the time interval under consideration is no worse than the accuracy of the traditional models.
Evaluation of candidate geomagnetic field models for the 10th generation of IGRF
Authors: Maus Stefan , Macmillan Susan , Lowes Frank , Bondar Tatjana
Published: August 2014

The recent satellite magnetic missions, combined with high quality ground observatory measurements, have provided excellent data for main field modelling. Four different groups submitted seven main-field and eight secular-variation candidate models for IGRF-10. These candidate models were evaluated using several different strategies. Comparing models with independent data was found to be difficult. Valuable information was gained by mapping model differences, computing root mean square differences between all pairs of models and between models and the common mean, and by studying power spectra and azimuthal distributions of coefficient power. The resulting adopted IGRF main-field model for 2005.0, an average of three selected candidate models, is estimated to have a formal root mean square error over the Earth’s surface of only 5 nT, though it is likely that the actual error is somewhat larger than this. Due to the inherent uncertainty in secular variation forecasts, the corresponding error of the adopted secular-variation model for 2005.0–2010.0, an average of four selected candidate models, is estimated at 20 nT/a.
Outline of vertical displacement of the 2004 and 2005 Sumatra earthquakes revealed by satellite radar imagery
Authors: Tobita Mikio , Suito Hisashi , Imakiire Tetsuro , Kato Min , Fujiwara Satoshi , Murakami Makoto
Published: August 2014

Analyses of satellite radar imagery before and after the 2004 and 2005 Sumatra earthquakes reveal an overview of the uplift and submergence pattern of islands along the subduction zone and provide an outline of the regions that experienced coseismic vertical deformation. We find evidence of crustal deformation from the northern tip of the Andaman Islands to Nias Island. A line 145 km east of the trench separates western uplifted zone from eastern subsided zone. Agreement with the field observation demonstrates the feasibility of our method. We find that radar imagery analysis is more efficient for investigating vertical displacements than similar techniques using optical sensors.
Aeromagnetic constraits on the subsurface structure of the Unzen Graben, Kyushu, Japan
Authors: Okubo Ayako , Nakatsuka Tadashi , Tanaka Yoshikazu , Kagiyama Tsuneomi , Utsugi Mitsuru
Published: August 2014

Aeromagnetic analyses have been conducted in and around the Unzen Volcano, Kyushu, Japan, in order to reveal the subsurface structure of the Unzen graben. First, we applied a magnetization intensity mapping method to analyze the aeromagnetic anomalies of the central part of the Shimabara peninsula. Magnetization highs and lows correspond to the Older Unzen (0.15–0.5 Ma) and the Younger Unzen (<0.15 Ma), respectively. However, the Mayu-Yama volcano is exceptionally high in the Younger Unzen. Moreover, it turns out that the Pre-Unzen (>0.5 Ma) or localized hydrothermally altered areas show magnetization lows. Next, magnetic models were constructed from aeromagnetic anomalies, drilling data and the result of magnetization intensity mapping. Finally, similar to the results of other geophysical data, it turns out that the Unzen graben has the features of a half-graben, with the northern fault (the Chijiwa fault) down in the western Unzen region and the southern fault (the Futsu and Fukae fault) down in the eastern Unzen region. Moreover, it clarified that the layers of low magnetization extend to the near-surface beneath Shimo-Dake, Kami-Dake, and the Unzen hot spring. These layers of low magnetization reflect the fractured or hydrothermally altered zones caused by the upflow of geothermal convection that exists in the central part in the graben.
Rupture process of the 2005 West Off Fukuoka Prefecture earthquake obtained from strong motion data of K-NET and KiK-net
Authors: Sekiguchi Haruko , Aoi Shin , Honda Ryou , Morikawa Nobuyuki , Kunugi Takashi , Fujiwara Hiroyuki
Published: August 2014

We have investigated the rupture process of the 2005 West Off Fukuoka Prefecture earthquake by the multitime- window linear waveform inversion method using the strong ground motion data recorded at 11 K-NET and KiK-net stations. From the waveforms of the P-wave portion, it is indicated that the energy release in the first few seconds was markedly lower than the subsequent part, and this causes difficulty in identifying onset of the S-wave. To decide an appropriate time window for the waveform inversion, we estimate the S-wave onset using aftershock records. The inverted slip distribution shows a single asperity of 8 km × 6 km and its center located 8 km to the southeast and 6 km above the hypocenter. The asperity explains most of the large-amplitude signals in the observed waveforms. The turning point from the initial low-energy-release rupture to the main high-energyrelease rupture is estimated from the spatial variation of the observed initial rupture phase. It is found 3.3 s after the initiation of the rupture at about 4 km to the southeast of the hypocenter. Stress drop during the initial rupture is estimated to be in the same order of those of moderate size aftershocks, which indicates that the initial rupture is an ordinary dynamic rupture.
Off-fault aftershocks of the 2005 West Off Fukuoka Prefecture Earthquake: Reactivation of a structural boundary?
Authors: Imanishi Kazutoshi , Kuwahara Yasuto , Haryu Yoshikatsu
Published: August 2014

After the occurrence of the 20 March 2005 West Off Fukuoka Prefecture Earthquake (Mj7.0), off-fault aftershocks occurred in and around Hakata bay adjacent to the main fault of the earthquake. The locations of the activity seem to coincide with the Ishido-Uminonakamichi fault (I-U fault), which is a structural boundary and not considered as an active fault. In order to elucidate relations between these off-fault aftershocks and the I-U fault, we determine the double-difference earthquake locations and focal mechanism solutions. Results of the present study show that the off-fault aftershocks are aligned in a sense of left-lateral faulting striking 120° from the north and in that of their conjugate right-lateral fault structures striking 30? from the north. Comparing the trends of these aligned structures with the orientation of the I-U fault, we conclude that earthquakes in and around the Hakata bay occurred along these aligned structures, not along a fault plane inferred from the surface trace of the I-U fault. The analysis of Coulomb failure stress due to the mainshock also supports this conclusion. Stress tensor inversion shows that the stress field in and around the Hakata bay is characterized by a strike-slip faulting. The angles between the fault trends and the maximum principal stress suggest that the aligned structures found in this study are favorably oriented, while the fault plane inferred from the surface trace of the I-U fault is unfavorably oriented.
Source model of the 2005 west off Fukuoka prefecture earthquake estimated from the empirical Green’s function simulation of broadband strong motions
Authors: Suzuki Wataru , Iwata Tomotaka
Published: August 2014

We estimated strong motion generation area (SMGA) source model which is responsible for broadband (0.2, 0.3–10 Hz) strong motions of the 2005 west off Fukuoka prefecture earthquake and its largest aftershock using the empirical Green’s function (EGF) method. The estimated SMGAs are almost corresponding to the large slip area deduced by kinematic waveform inversion. The SMGA rupture for the mainshock propagated mainly upward and toward the northwest with rupture velocity of 3.15 km/s. The size of the SMGA follows the self-similar empirical formula of the asperity size derived by Somervilleet al.(1999). The stress drop of the mainshock SMGA is calculated to be 10.7 MPa, which is larger than those of the largest aftershock SMGA and the aftershocks used as EGF.
Multi-step prediction of Dst index using singular spectrum analysis and locally linear neurofuzzy modeling
Authors: Sharifi Javad , Araabi Babak N. , Lucas Caro
Published: August 2014

Even one-step prediction of natural time series without delay especially in main phase of storm is difficult for many complicated time series such as Dst index. In this study, with a new method based on singular spectrum analysis, we extract the main components of the time series, model each component with a locally linear neurofuzzy network, and utilize the trained networks for multi-step ahead prediction of a validation set of data, and finally combine the predicted patterns for construction of general prediction. Our methods are compared with several previous studies for Dst index prediction. Several solar geomagnetic extreme events are predicted well with our state-of-the-art method; such as extreme events in 14 March 1989 that led to power black-out in Quebec, as well as other extreme storms.
Deriving main field and secular variation models from synthetic Swarm satellite and observatory data
Authors: Lesur Vincent , Macmillan Susan , Thomson Alan
Published: August 2014

We investigate how well the core field component of the underlying model used in the Swarm End-to-End simulator can be recovered when relatively simple geomagnetic field models are fitted to synthetic Swarm satellite and observatory data. In particular we demonstrate the potential benefits of Swarm by deriving models without these data. From two years of observatory data, the underlying secular variation model is recovered up to about spherical harmonic degree 8. This maximum degree is higher than was expected but increases to 10 when satellite data are also used. The constant part of the geomagnetic field model is recovered to at least degree 17. These results improve when a better statistical treatment of the data errors is made, a slightly more complex field model is fitted, or when five years of data are used.
Determining dislocation Love numbers using satellite gravity mission observations
Authors: Sun Wenke , Okubo Shuhei , Sugano Takayuki
Published: August 2014

This paper presents a new approach to calculate dislocation Love numbers using observations of a satellite gravity mission (e.g. GRACE). The necessary condition is that the co-seismic potential change be sufficiently large to be detected by the gravity mission. Co-seismic deformations for each spherical harmonic degree n are decoupled. Therefore, dislocation Love numbers of degree n can be determined independently. The determinable maximum harmonic degree n depends on the seismic size, source type, magnitude, and the accuracy of a satellite gravity mission. For an arbitrary seismic source, all four types of dislocation Love numbers can be determined using data from only one seismic event because all deformation components are involved together. Only the concerned dislocation Love numbers can be computed for any one of the four types of sources. To prove the validity of the method proposed in this study, a simulation test is carried out by considering a similar case to the 2004 Sumatra earthquake (Mw 9.1). Results show that the method works well and guarantee the accuracy.
Behavior of fluorine and chlorine in volcanic ash of Sakurajima volcano, Japan in the sequence of its eruptive activity
Authors: Nogami Kenji , Iguchi Masato , Ishihara Kazuhiro , Hirabayashi Jun-ichi , Miki Daisuke
Published: August 2014

At Sakurajima volcano, strombolian eruptions forerun vulcanian explosions, and volcanian explosions are often followed by continuous ash eruptions. Change in the mode of its eruptive activity is drastic and release of volatiles from magma corresponding to its eruptive activity is examined by determination of fluorine and chlorine in volcanic ash. The F contents of all the ash samples are markedly higher than the arithmetic mean value of Japanese volcanic rocks (ca. 300 μg/g). Further, the water-soluble Cl contents of almost all the ash samples are also extremely higher than those of Japanese volcanic rocks (less than 50 μg/g). This is attributed to fixation of F and Cl in hot gas onto the volcanic ash particles in the crater and/or eruption plumes. The differences in those contents among the “strombolian eruption”-, “vulcanian explosion”- and “continuous ash eruption” groups are significant, which implies that hot gas rich in F and Cl are issued during strombolian eruptions, while those halogens are less concentrated in hot gas after strombolian eruptions. The water-insoluble Cl content of the “strombolian eruption” group is significantly higher than those of the other groups. This result implies that Cl and the other volatiles are intensely released from magma during the doming period before vulcanian eruptions.

Yet, it is inferred that continuous ash eruption is the final phase of vulcanian one.
A significant mass density increase during a large magnetic storm in October 2003 obtained by ground-based ULF observations at L ≈ 1.4
Authors: Takasaki Satoko , Kawano Hideaki , Tanaka Yoshimasa , Yoshikawa Akimasa , Seto Masahiro , Iizima Masahide , Obana Yuki , Sato Natsuo , Yumoto Kiyohumi
Published: August 2014

During 28–31 October, 2003, a series of coronal mass ejections hit the magnetosphere and triggered two consecutive large storms. Three ground magnetometers at L = 1.32–1.41 recorded field-line resonances (FLRs) during this interval. The FLR frequencies decreased from 0600 LT on 31 October 2003 during the main phase of the second storm until 12 LT when the recovery phase of this storm began. After the decrease, the FLR frequencies returned to its pre-storm value (at 0600 LT on 31 Oct.) in a few hours. The measured decrease in the FLR frequency suggests a relative increase in mass density along the field lines during the magnetic storm. On the other hand, the total electron content (TEC) data suggest that the ionospheric plasma number density during this storm was similar to that during quiet times. A possible explanation for the increase in mass density would be an outflow of the heavy ions (e.g., O+) from the ionosphere to the plasmasphere.
Influence of the interplanetary magnetic field on the ring current injection rate
Authors: Aoki Takao
Published: August 2014

In order to check the validity of Akasofu’s ε parameter and of the Vasyliunas et al. (1982) general formula, we examine the dependence of the ring current injection rate, calculated from the Dst index for the period of 1965–1990, on the interplanetary magnetic field (IMF). We compare the influence of the Bz component with the influence of the combination of sin(θ/2), where θ is the IMF clock angle, and the IMF magnitude, B, (or the transverse component of the IMF, BT = (By2 + Bz2)1/2) by using the regression analysis in a power law form. The main results are as follows: (1) the exponent for Bz shows higher consistency than that for sin(θ/2); (2) we never obtain B
2 sin4(θ/2) or B
T
2 sin4(θ/2), which is the IMF dependence expected from the ε parameter; and (3) the ring current injection rate has a very low correlation with the Alfven Mach number, from which the IMF dependence of the Vasyliunas et al. general formula is assumed to arise. On the basis of the above results we conclude that the ε parameter and the Vasyliunas et al. general formula are less appropriate than a function of Bz, and that the energy coupling function between the solar wind and the Earth’s magnetosphere is described better by Bz than by the combination of B (or B
T) and sin(θ/2). The above results and conclusions are the same as those obtained by Aoki (2005) through the analysis of the AL index.
Longitudinal dependence of characteristics of low-latitude Pi2 pulsations observed at Kakioka and Hermanus
Authors: Nosé M. , Liou K. , Sutcliffe P. R.
Published: August 2014

We statistically investigated longitudinal dependence of characteristics of low-latitude Pi2 pulsations to find the longitudinal structure of the plasmaspheric cavity mode. We used the geomagnetic field data from two ground stations, Kakioka (27.2° geomagnetic latitude, 208.5° geomagnetic longitude) and Hermanus (—33.9° geomagnetic latitude, 82.2° geomagnetic longitude), and auroral image data acquired by the ultraviolet imager onboard the Polar satellite for the period of December 4, 1996 to March 3, 1997. Our findings include the following: (1) Pi2 amplitude is the largest around the magnetic local time of the auroral breakup site and decreases away from it; (2) when a nightside Pi2 pulsation has large amplitude, a dayside Pi2 pulsation can be observed with a similar waveform; (3) Pi2 pulsations generally have no clear phase differences (mean phase difference of 3.3°) between Kakioka and Hermanus, except for some events; and (4) the phase difference is independent on AMLT (difference of magnetic local time between a station and the auroral breakup). These observations suggest that the plasmaspheric cavity mode can be excited globally with a very small value of the azimuthal wave number(m≈0).
Annual and semi-annual variations of the geomagnetic field components analysed by the multi-taper method
Authors: Wardinski I. , Mandea M.
Published: August 2014

Monthly means of three geomagnetic components (X-northern, Y-eastern and Z-vertical downward) from 154 observatories over the interval 1960-2002 have been analysed to determine the annual and semi-annual variations. The method applied is a multi-taper analysis, which gives a robust estimate of the power spectral density of the temporal variation of the field components. The main objective is to investigate the geographic dependence of the annual and semi-annual variations. Surprisingly, these variations in the vertical downward component are not homogeneously distributed all over the globe, having mainly a longitudinal dependency. The results of the analysis are briefly discussed with regard to possible mechanisms responsible for these variations and to mantle conductivity.
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

We 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

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

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

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

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

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

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

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

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

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.