المؤلفون: Ohya, H., Suzuki, T., Tsuchiya, F., Nakata, H., Shiokawa, K.

المصدر: Radio Science; Mar2024, Vol. 59 Issue 3, p1-10, 10p

مصطلحات موضوعية: METEOROIDS, METEORS, GLOBAL Positioning System, SOUND waves, IONOSPHERE, SPEED of sound, ACOUSTIC wave propagation

مصطلحات جغرافية: HOKKAIDO (Japan), JAPAN

مستخلص: Several studies have examined ionospheric variation associated with meteorites, meteoroids, or meteors based on Global Satellite Navigation System total electron content observations. However, there have been few quantitative studies of the D‐region of the ionosphere (60–90 km), which is associated with meteoroids. We investigated variation in the D‐region during the passage of a meteoroid over northeastern Hokkaido, Japan, at 11:55:55 UT on 18 October 2018, using very low‐frequency (VLF, 3–30 kHz) and low‐frequency (LF, 30–300 kHz) signals observed by three transmitters [JJY (40 kHz), JJY (60 kHz), and JJI (22.2 kHz)], at Rikubetsu, Japan. Periodic variation of 100–200 s was observed in the VLF and LF amplitudes upon arrival of the acoustic wave. The vertical seismic velocity of Hi‐net and F‐net data also showed acoustic waves. Although the main period of the acoustic wave was 0.1–0.5 s in the seismic data, a longer period component (100–200 s) remained during propagation up to the D‐region ionosphere. The estimated velocity of the acoustic waves was ∼340 m/s on the ground according to the Hi‐net seismic data. The acoustic wave originated near the endpoint (25 km altitude) of the meteoroid trajectory. Based on the observed propagation time of the acoustic waves and ray tracing results, the acoustic waves propagated obliquely from near the endpoint of the meteoroid trajectory up to a D‐region height (about ∼90 km altitude), south of the Rikubetsu receiver. Key Points: Periodic variation of 100–200 s was observed at very low‐frequency/low‐frequency amplitudes and in seismic data at the time of acoustic wave arrivalThe acoustic wave originated near the endpoint (25 km altitude) of the meteoroid trajectoryThe disturbed ionospheric area was estimated to be south of the Rikubetsu receiver, at 90 km height [ABSTRACT FROM AUTHOR]

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المؤلفون: Ye, Hailun^1,2 (AUTHOR), Yi, Wen^1,2 (AUTHOR), Zhou, Baozhu^1,2 (AUTHOR), Wu, Jianfei^1,2,3 (AUTHOR), Yu, Bingkun⁴ (AUTHOR), Tian, Penghao^1,2 (AUTHOR), Wang, Jianyuan^1,2 (AUTHOR), Long, Chi⁵ (AUTHOR), Lu, Maolin^1,2 (AUTHOR), Xue, Xianghui^1,2,3,6,7 (AUTHOR) xuexh@ustc.edu.cn, Chen, Tingdi^1,2,3,6 (AUTHOR), Dou, Xiangkang^1,6,7 (AUTHOR)

المصدر: Remote Sensing. Feb2023, Vol. 15 Issue 4, p1160. 19p.

مصطلحات موضوعية: *MAGNETIC storms, *RADIO wave propagation, *IONOSPHERIC disturbances, *GLOBAL Positioning System, *IONOSONDES, *LATITUDE

مصطلحات جغرافية: ASIA, JAPAN

مستخلص: This study presents the observations of midlatitude plasma irregularities over Eastern Asia during a moderate magnetic storm on 16 July 2003. Multi-instrumental observations, including the ground-based ionosondes, the GNSS networks, and the CHAMP and ROCSAT-1 satellites, were utilized to investigate the occurrence and characteristics of midlatitude plasma irregularities. The midlatitude strong spread F (SSF) mainly occurred in the midnight–morning sector as observed by ionosondes over Japan during this storm. SSF was related to plasma depletions, which is also recorded by GNSS network in the form of the enhancement of the rate of total electron content (TEC) change index (ROTI). The possible mechanism for the generation of SSF is that the enhanced eastward electric fields, associated with the prompt penetration electric fields and disturbance dynamo electric fields, cause the uplift and latitudinal extension of equatorial plasma bubbles (EPBs) to generate the observed midlatitude SSF further. Meanwhile, plasma density increased significantly under the influence of this storm. In addition, other common type of spread F, frequency spread F (FSF), was observed over Japan on the non-storm day and/or at high latitude station WK545, which seems to be closely related to the coupling of medium-scale traveling ionospheric disturbances (MSTIDs) and sporadic E (Es) layer. The above results indicate that various types of midlatitude spread F can be produced by different physical mechanisms. It is found that SSF can significantly affect the performance of radio wave propagation compared with FSF. Our results show that space weather events have a significant influence on the day-to-day variability of the occurrence and characteristics of ionospheric F-region irregularities at midlatitudes. [ABSTRACT FROM AUTHOR]

المؤلفون: Tanaka, Tetsu¹, Kozono, Shigeru¹, Akeyama, Akira²

المصدر: Electronics & Communications in Japan, Part 1: Communications. Aug91, Vol. 74 Issue 8, p80-88. 9p.

مصطلحات موضوعية: *MOBILE communication systems, *DIGITAL communications, RADIO wave propagation, CITIES & towns, BUILDINGS

مصطلحات جغرافية: JAPAN

مستخلص: In this paper, propagation delay measurements were carried out in Tokyo (metropolitan urban area) where high rises and other buildings are concentrated on a plane and in Kofu (urban area adjacent to mountains) surrounded by tall mountains. The delay characteristics such as delay spread and wave numbers were found. The principal results obtained in these areas are as follows: (1) In a metropolitan urban area, i.e., Tokyo, (a) the average delay spread in a high-density residential district is less than about 1 µs and the delay profile consists of a group of direct waves arriving directly from the base station; and (b) the average delay spread in a location with high-rise buildings is also less than 1 µs and the average number of arriving waves is about five with the delay profile consisting of a direct wave group and a reflected wave group from reflecting object. (2) In an urban area adjacent to mountains, i.e., Kofu, the average delay spread is less than about 2 µs and the average number of arriving waves is four. The delay profile consists of a direct wave group and a reflected wave group. The level of the reflected wave group decreases exponentially with the delay time in the case of reflection from buildings, while the level is almost constant within a certain range of delay time and is of a spread shape (rectangular) in the case of reflection from mountains. From these measured results, a simple propagation model consisting of a direct wave group and a reflected wave group is proposed. It is shown that the distance dependence of the delay spread has a peak between the base station and a reflecting object. [ABSTRACT FROM AUTHOR]

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المؤلفون: Kumar De, Barin¹, Sundar De, Syam² de_syam_sundar@yahoo.co.in, Bandyopadhyay, Bijoy², Pal, Pinaki³, Ali, Rousan^1,4, Paul, Suman², Goswami, Prabir Kanta²

المصدر: Terrestrial, Atmospheric & Oceanic Sciences. Aug2011, Vol. 22 Issue 4, p435-442. 8p.

مصطلحات موضوعية: *VLF radio wave propagation, *SOLAR eclipses, *IONOSPHERE, *ATMOSPHERICS, *ABSORPTION, *ATMOSPHERIC ionization, *EARTH (Planet)

مصطلحات جغرافية: TRIPURA (India), INDIA, JAPAN

مستخلص: The results from the measurements of some of the fundamental parameters (amplitude of sferics and transmitted signal, conductivity of lower ionosphere) of the ionospheric responses to the 22 July 2009 solar eclipse (partial: 91.7%) are shown. This study summarizes our results from sferics signals at 81 kHz and subionospheric transmitted signals at 19.8 and 40 kHz recorded at Agartala, Tripura (latitude: 23°N, longitude: 91.4°E). We observed significant absorption in amplitude of these signals during the eclipse period compared to their ambient values for the same period during the adjacent 7 days. The signal strength along their propagation paths was controlled by the eclipse associated decrease in ionization in the D-region of the ionosphere. Waveguide mode theory calculations show that the elevation of the height of lower ionosphere boundary of the Earth-ionosphere waveguide to a value where the conductivity parameter was 1010 unit. The absorption in 81 kHz sferics amplitude is high compared to the absorption in the amplitude of 40 kHz signal transmitted from Japan. The simultaneous changes in the amplitudes of sferics and in the amplitude of transmitted signals assert some sort of coupling between the upper atmosphere and the Earth's near-surface atmosphere prevailing clouds during solar eclipse. [ABSTRACT FROM AUTHOR]

المؤلفون: Prants, S.¹, Uleysky, M.¹, Budyansky, M.¹

المصدر: Doklady Earth Sciences. Aug2011, Vol. 439 Issue 2, p1179-1182. 4p. 3 Maps.

مصطلحات موضوعية: *COMPUTER simulation, *RADIO wave propagation, *RADIOACTIVE pollution, *RADIOISOTOPES, *METEOROLOGICAL precipitation

مصطلحات جغرافية: JAPAN

الشركة/الكيان: FUKUSHIMA Daiichi Nuclear Power Plant (Japan)

مستخلص: Numerical simulation of the large-scale horizontal mixing and transport of radioactive water from the Fukushima Dai-ichi nuclear power plant (NPP) (141°02′ E, 37°27′ N, east coast of Honshu Island, Japan) and the use of the satellite altimetric velocity field in the northwestern Pacific allowed us to obtain the following results. The patch of radioactive water dumped from the NPP propagated eastwards as jets of an extension of the Kuroshio Current. The discovered phenomenon of trapping the radionuclides by stable and unstable manifolds of local synoptic eddies may be harmful for living organisms. If one assumes that pollution of considerable areas of coastal waters near Honshu Island took place due to fallout of radioactive precipitation with rain, then a part of the radioactive water may be subjected to north-bound advection and is mixing under the impact of stable and unstable manifolds of the triple-eddy system to the north of the NPP. No radionuclide flux from the Tsugaru strait into the Sea of Japan has been found in the surface layer. Nevertheless, there is a small likelihood of their penetration there with a deep counter current and/or due to wind drift. [ABSTRACT FROM AUTHOR]

المؤلفون: Potirakis, Stelios M., Asano, Tomokazu, Hayakawa, Masashi

المصدر: Entropy; Mar2018, Vol. 20 Issue 3, p199, 17p

مصطلحات موضوعية: EARTHQUAKES, LOWER ionosphere, ELECTROMAGNETIC wave propagation, PERTURBATION theory, LITHOSPHERE

مصطلحات جغرافية: KUMAMOTO-ken (Japan), JAPAN

مستخلص: The perturbations of the ionosphere which are observed prior to significant earthquakes (EQs) have long been investigated and could be considered promising for short-term EQ prediction. One way to monitor ionospheric perturbations is by studying VLF/LF electromagnetic wave propagation through the lower ionosphere between specific transmitters and receivers. For this purpose, a network of eight receivers has been deployed throughout Japan which receive subionospheric signals from different transmitters located both in the same and other countries. In this study we analyze, in terms of the recently proposed natural time analysis, the data recorded by the above-mentioned network prior to the catastrophic 2016 Kumamoto fault-type EQs, which were as huge as the former 1995 Kobe EQ. These EQs occurred within a two-day period (14 April: MW = 6.2 and MW = 6.0, 15 April: MW = 7.0) at shallow depths (~10 km), while their epicenters were adjacent. Our results show that lower ionospheric perturbations present critical dynamics from two weeks up to two days before the main shock occurrence. The results are compared to those by the conventional nighttime fluctuation method obtained for the same dataset and exhibit consistency. Finally, the temporal evolutions of criticality in ionospheric parameters and those in the lithosphere as seen from the ULF electromagnetic emissions are discussed in the context of the lithosphere-atmosphere-ionosphere coupling. [ABSTRACT FROM AUTHOR]

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المؤلفون: Hairoud, Siham, Combeau, Pierre, Cailbault, Jean-François, Pousset, Yannis, Cocheril, Yann, Berbineau, Marion

المساهمون: SIC, XLIM (XLIM), Université de Limoges (UNILIM)-Centre National de la Recherche Scientifique (CNRS)-Université de Limoges (UNILIM)-Centre National de la Recherche Scientifique (CNRS)-Université de Poitiers = University of Poitiers (UP), Laboratoire Électronique Ondes et Signaux pour les Transports (IFSTTAR/LEOST), Institut Français des Sciences et Technologies des Transports, de l'Aménagement et des Réseaux (IFSTTAR)-PRES Université Lille Nord de France, SYSCOM, LEOST

المصدر: Proceedings of IEEE ITST ; 10th International Conference on ITS (Intelligent Transport Systems) Telecommunications ; https://hal.science/hal-00745498Test ; 10th International Conference on ITS (Intelligent Transport Systems) Telecommunications, Nov 2010, Tokyo, Japan. 5 p

مصطلحات موضوعية: radio wave propagation simulator, channel modeling, computation time optimization, 5 pages, [SPI.ELEC]Engineering Sciences [physics]/Electromagnetism

جغرافية الموضوع: Tokyo, Japan

الوصف: International audience ; The 3D ray tracing method requires a detailed description of the environment and antenna characteristics. Thus, it allows us to consider all the paths between receivers and transmitters for a fixed number of electromagnetic interactions. However, the computational complexity of this method is directly connected to the number of scatterers and the electromagnetic environment interactions. Thus we proposed an optimization method allowing reducing the computation time of a railway tunnel simulation. It consists in modifying the modeling environment, by eliminating non-significant faces. The aim of our method is, in this case, to provide estimated results close to those obtained with a complete environment modeling, but in fewer computation time.

العلاقة: hal-00745498; https://hal.science/hal-00745498Test; https://hal.science/hal-00745498/documentTest; https://hal.science/hal-00745498/file/ITST2010tem.pdfTest

الإتاحة: https://hal.science/hal-00745498Test
https://hal.science/hal-00745498/documentTest
https://hal.science/hal-00745498/file/ITST2010tem.pdfTest

المؤلفون: Guha, A., De, B. K., Saha, A., Das, T. K.

المصدر: AIP Conference Proceedings; 2007, Vol. 923 Issue 1, p165-168, 4p, 1 Diagram, 1 Chart, 2 Graphs

مصطلحات موضوعية: SUNRISE & sunset, DIURNAL variations of rainfall, RADIO wave propagation, DISTANCES, RADIO wave attenuation

مصطلحات جغرافية: JAPAN, INDIA

مستخلص: The sunrise effect, sunset effect, the diurnal and seasonal variations are the characteristic feature of low frequency (LF) radio wave propagated over a large distance. The normal character has been found to be perturbed during rainy days. The amplitude of 40 kHz signal transmitted from Miyakoji station, Japan and received in North-East India is remarkably attenuated after the commencement of rain. On the basis of nature of attenuation the observed records have been classified into two different forms viz., F1 and F2. An analysis in this regard is represented in this paper. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

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المؤلفون: Katz, D., Blaunstein, N., Hayakawa, M., Kishiki, Y. Sanoh

المصدر: IEEE Antennas & Propagation Magazine; Oct2009, Vol. 51 Issue 5, p200-208, 9p

مصطلحات موضوعية: MAPS, RADIO wave propagation, STOCHASTIC models, RAY tracing algorithms

مصطلحات جغرافية: TOKYO (Japan), JAPAN

مستخلص: This study is related to the investigation of two popular planning tools based on different approaches. The first is a stochastic model as a combination of a statistical description of features of rough built-up terrain (with arrays of buildings inside it), and the stochastic description of radio propagation above such a terrain, accounting for multiple reflection, scattering, and diffraction. The second is a deterministic ray-tracing model using direct computations of numerous rays arriving at the receiver from each point of the obstructions placed in the terrain. Both models are used to explain the propagation phenomena occurring inside urban communication links, and to design radio maps of areas of service in the space domain, for various elevations of the base-station antenna with respect to the buildings' overlay profiles. A comparison of two such theoretical predictors is done for an experimental site in Tokyo. It is shown that both proposed predictors are in good agreement with each other. At the same time, simple engineering formulas obtained from the stochastic model, taking into account shadowing effects caused by diffraction from buildings having non-regular overlay profiles with respect to the base- station antenna's elevation, have a vivid physical and mathematical form, usually converted into the "straight line" equations obtained from the proposed stochastic model. The general trend is predicted by this stochastic model, and the deterministic ray tracing provides us with fine structures superimposed on such a trend. [ABSTRACT FROM AUTHOR]

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المؤلفون: Hayakawa, M., Horie, T., Yoshida, M., Kasahara, Y., Muto, F., Ohta, K., Nakamura, T.

المصدر: Natural Hazards & Earth System Sciences; 2008, Vol. 8 Issue 3, p573-576, 4p, 2 Graphs

مصطلحات موضوعية: IONOSPHERIC research, ECOLOGICAL disturbances, EARTHQUAKES, VLF emissions, IONOSPHERIC radio wave propagation, RADIO meteorology, METEOROLOGICAL instruments, NATURAL disasters

مصطلحات جغرافية: JAPAN

مستخلص: In order to investigate any precursory effect of ionospheric perturbations associated with the large 2007 Niigata Chuetsu-oki earthquake (16 July 2007) (magnitude, 6.8), we have made full use of our VLF/LF network observation in Japan by examing the four propagation paths; JJI transmitter (Kyusyu, Ebino)-MSR (Moshiri, Hokkaido), JJY transmitter (Fukushima)-MSR, JJY-KOC (Kochi) and JJICBA (Tateyama, Chiba). For the former two paths of JJIMSR and JJY-MSR, we have observed significant propagation anomalies (both a decrease in nighttime average amplitude and an enhancement in nighttime amplitude fluctuation both satisfying the 2σ (σ: standard deviation) criteria) on 8- 9 July, about one week before the earthquake. However, the lack of observation for the path from JJY-KOC, has enabled us to make no conclusion for this path. On the other hand, the path from JJI-CBA does not seem to be perturbed. Although this earthquake is very big and shallow, the amount of VLF anomaly for this earthquake is not so pronounced as expected, probably because the epicenter is not unfortunately located within the sensitive areas of any propagation paths. These observational facts suggest that the lower ionosphere above the epicenter is perturbed definitely prior to the earthquake, with radius of a few hundred kilometers. [ABSTRACT FROM AUTHOR]

: Copyright of Natural Hazards & Earth System Sciences is the property of Copernicus Gesellschaft mbH and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)