Statistical characteristics of medium-latitude VLF emissions (unstructured and structured): Local time dependence and the association with geomagnetic disturbances     

M. Hayakawa  Y. Tanaka 《Planetary and Space Science》1986,34(12):1361-1372

The purpose of the paper is to present the statistical characterictics of mid-latitude VLF emissions (both unstructured hiss and structured emissions) based on the VLF data obtained at Moshiri in Japan (geomag. lat. 35°; L = 1.6) during the period January 1974–March 1984. Local time dependence of occurrence rate and the association with geomagnetic disturbances have been studied for both types of emissions. Both types (unstructured and structured) of mid-latitude VLF emissions are found to have definite correlations with geomagnetic disturbances. Then, the time delay of the emission event behind the associated geomagnetic disturbance has enabled us to estimate the resonant electron energy for VLF hiss to be 5 keV at L = 3–4 and that for structured VLF emissions to be considerably larger, such as 20 keV at L 4. Combined considerations of these estimated resonant energies, theoretical electron drift orbits and the local time dependences, allow us to construct the following model to explain the experimental results in a reasonable way. Electrons in a wide energy range are injected during disturbances around the midnight sector, followed by the eastward drift. Lower energy ( 5 keV) electrons tend to drift closer to the Earth, resulting in the dawnside enhancement of VLF hiss within the plasmasphere. Further, these lower energy electrons are allowed to enter the duskside asymmetric plasmaspheric bulge and to generate VLF hiss there. On the other hand, higher energy (20 keV) electrons tend to drift at L shells farther away from the Earth and those substorm electrons are responsible for the generation of structured VLF emissions around dawn due to an increase of plasma density from the sunlit ionosphere. However, such higher energy electrons are forbidden from entering the duskside of the magnetosphere and so we cannot expect a duskside peak in the occurrence of structured VLF emissions, which is in agreement with the experimental result.  相似文献   

Atoll island vulnerability to flooding and inundation revealed by historical reconstruction: Fongafale Islet, Funafuti Atoll, Tuvalu   总被引：1，自引：1，他引：0  

Hiroya Yamano  Hajime Kayanne  Toru Yamaguchi  Yuji Kuwahara  Hiromune Yokoki  Hiroto Shimazaki  Masashi Chikamori   《Global and Planetary Change》2007,57(3-4):407-416

The reef islands formed on coral atolls are generally small, low, and flat, with elevations of only a few meters. These islands are thus highly vulnerable to elevated sea levels caused by extreme events and global warming. Such vulnerability was recently evidenced at Fongafale Islet, the capital of Tuvalu, when it flooded during accelerated spring high tides possibly related to sea level rise caused by global warming. Many factors, not only environmental but also economic and social, determine the vulnerability of an island to sea level rise. In this study, we used data spanning 108 yrs to reconstruct changes in topography, land use/cover, population, and the distribution of buildings at Fongafale Islet. The results indicate that the vulnerability of Fongafale Islet relates to its original landform characteristics: the central part of the island was formerly dominated by swampland that flooded at high tides. Fongafale Islet experienced greater population in-migration and centralization beginning in the 1970s following the independence of Tuvalu and Kiribati. Migrants were also responding to declines in overseas mining operations and limited options for paid employment. As the population increased, construction took place in vulnerable swampland areas. Our results clearly demonstrate that examinations of global environmental issues should focus on characteristics specific to the region of interest. These characteristics should be specified using historical reconstruction to understand and address the vulnerability of an area to global environmental changes.  相似文献   

Erratum: Sunyaev–Zel'dovich distortion from early galactic winds     

Subhabrata Majumdar  Biman B. Nath  Masashi Chibaby 《Monthly notices of the Royal Astronomical Society》2001,326(3):1216-1216

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Simultaneous spaced direction-finding measurements of medium-latitude VLF/ELF emissions     

M. Hayakawa  Y. Tanaka  A. Iwai  J. Ohtsu  L.R.O. Storey  C. Béghin  T.S. Jorgensen 《Planetary and Space Science》1981,29(5):505-520

Simultaneous spaced measurements of medium-latitude VLF/ELF emissions were carried out during the three northern winters from 1976 to 1979. The experiment was making use of two different kinds of direction-finding systems (a field-analysis method and a goniometer network) at two stations in Europe, namely Brorfelde in Denmark (L = 2.9) and Chambron-la-Foret in France (L = 1.9); this enabled us to locate the ionospheric exit regions of emissions over a wide range of L-values up to and beyond 4.0, the average plasmapause location. In order to study the time delay in the temporal evolution of VLF emissions or the longitudinal drift of the emissions, observations from the Moshiri Observatory in Japan, widely separated in longitude, are also used. The overall system of the VLF equipment installed at the three stations is described. Then we present the VLF/ELF data of good quality obtained during the final year's campaign (Nov. 1978–Feb. 1979). By making use of the direction-finding data, we were able to classify the observed emissions into several categories, and some early results for some of the emissions are presented.  相似文献   

Observation of cosmic soft X-rays     

S. Hayakawa  T. Kato  T. Kohno  K. Nishimura  Y. Tanaka  K. Yamashita 《Astrophysics and Space Science》1972,17(1):30-38

Cosmic X-rays in the energy range between 0.210 keV were observed with polypropylene window proportional counters on board a sounding rocket. The field of view crossed the galactic plane in the Sgr region and reached galactic latitudes of 50° and –90°. A new soft X-ray source was found in the Aries-Taurus region. The soft X-ray flux from the direction of NGC 1275 was conspicuous, whereas that of Sgr region source were very weak. The distribution of the intensity of diffuse soft X-rays over the scanned region indicates the galactic emission of soft X-rays.  相似文献   

Continual matter accretion into the solar system     

S. Hayakawa 《Earth, Moon, and Planets》1978,18(3):321-324

Rapid accretion of matter takes place while the solar system resides in a dark cloud of high density. The mass thus accreted may be comparable to the mass of the planetary system. Since the elemental abundances in a dark cloud are considered to be heterogeneous due to matter processed inside stars and then ejected, the continual accretion causes elemental heterogeneities in the solar system.Paper dedicated to Professor Hannes Alfvén on the occasion of his 70th birthday, 30 May 1978.  相似文献   

Joint distribution of distances to the first and the second nearest facilities     

Masashi Miyagawa 《Journal of Geographical Systems》2012,14(2):209-222

This paper derives the joint distribution of the distances to the first and the second nearest points for regular and random patterns. Distance is measured as the Euclidean and the rectilinear distances on a continuous plane. The joint distribution extends the kth nearest distance distribution of previous works. The kth nearest distance distribution only shows how the distance to the kth nearest point is distributed, whereas the joint distribution provides the relationship between the distances. An application of the joint distribution can be found in a facility location problem with non-closest facility service where the distance to the second nearest facility is also important. The joint distribution that allows us to examine the first and the second nearest distances simultaneously is useful for evaluating the reliability of facility location when some of the existing facilities are closed. The joint distribution of the road network distances is also obtained to confirm that the model on a continuous plane can be applied to actual road networks.  相似文献   

Short-term earthquake prediction: Current status of seismo-electromagnetics   总被引：3，自引：0，他引：3  

Seiya Uyeda  Toshiyasu Nagao  Masashi Kamogawa 《Tectonophysics》2009,470(3-4):205-213

Loss of human lives as a result of earthquakes is caused overwhelmingly by the collapse of buildings within less than a few minutes of main shocks. The most urgent countermeasure consists of two key elements. One is strengthening of weak structures and the other is short-term earthquake prediction. Short-term prediction needs precursors. Although some promising precursors are reported, the prevailing views in Japan and elsewhere are overly pessimistic. The pessimism largely roots in the fact that short-term precursors are generally non-seismic and tools developed for seismology are not designed to detect them. Nonetheless, nationally funded large-scale earthquake prediction programs always emphasize the need to reinforce seismometer networks. They do not take into account the views of those in the science community who point to the importance of non-seismic precursors. While there are well-founded causes to be skeptical, the situation needs to be improved. One reason for skepticism is that the observations of precursors have not yet been perfect enough and another is that some important fundamental aspects of non-seismic precursors are still unresolved. We review some of these problems.  相似文献   

Underwater observations of the giant spoon worm <Emphasis Type="Italic">Ikeda taenioides</Emphasis> (Annelida: Echiura: Ikedidae) in a subtidal soft-bottom environment in northeastern Japan,which survived tsunamis of the 2011 off the Pacific Coast of Tohoku Earthquake     

Ryutaro Goto  Shingo Sakamoto  Jun Hayakawa  Koji Seike 《Journal of Oceanography》2017,73(1):103-113

Tsunamis associated with the 2011 off the Pacific Coast of Tohoku Earthquake seriously disrupted the shallow marine ecosystem along a 2000 km stretch of the Pacific coast of Japan. The effects of the 2011 tsunamis on the soft-bottom benthic community have been relatively well studied in the intertidal zone, whereas tsunami effects on the subtidal benthos remain poorly understood. Here, we investigated populations of the world’s largest spoon worm Ikeda taenioides (Annelida: Echiura: Ikedidae) in subtidal zone of Funakoshi Bay, Tohoku District, northeastern Japan. Subtidal scuba-diving surveys at two sites in the bay showed extremely long proboscises frequently extending from small holes in the sandy seafloor shortly before and soon after the tsunami disturbances. Based on morphological and molecular identification, the proboscises were revealed to be parts of I. taenioides. On 30 November 2011, 265 days after the tsunami event, many large-sized individuals with >1 m long proboscises were observed; these individuals were probably not derived from post-tsunami larval recruitment but more likely survived the tsunami disturbances. This is surprising because other sympatric megabenthos (e.g. spatangoid echinoids and venerid bivalves) and seagrass beds were almost completely destroyed (although they later recovered) by the tsunamis in this bay. The burrows of I. taenioides are known to be very deep (70–90 cm), which may have sheltered them from the impacts of the tsunamis. Our observations suggest that the effects of the 2011 tsunamis on benthos in soft sediments may differ depending on their burrowing depth.  相似文献   

Finite‐element analysis of laminated rubber bearing of building frame under seismic excitation          下载免费PDF全文

Makoto Ohsaki  Tomoshi Miyamura  Masayuki Kohiyama  Takuzo Yamashita  Masashi Yamamoto  Naohiro Nakamura 《地震工程与结构动力学》2015,44(11):1881-1898

Finite element analysis is carried out for a building frame supported by laminated rubber bearings to simultaneously investigate global displacement and local stress responses under seismic excitation. The frame members and the rubber bearings are discretized into hexahedral solid elements with more than 3 million degrees of freedom. The material property of rubber is represented by the Ogden model, and the frame is assumed to remain in elastic range. It is shown that the time histories of non‐uniform stress distribution and rocking behavior of the rubber bearings under a frame subjected to seismic excitation can be successfully evaluated, and detailed responses of base and frame can be evaluated through large‐scale finite element analysis. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献