On the divergence of the ionospheric electric field around the westward travelling surge     

Naoko Hori  Takashi Yamamoto 《Planetary and Space Science》1987,35(12):1489-1500

The pattern of the ionospheric electric field around the westward travelling surge (WTS) is theoretically studied. This is obtained by solving the current continuity equation at the ionospheric altitude for temporal and spatial development of the field-aligned current density modelled as the WTS phenomenon. The results show that the divergence of the ionospheric electric field is significantly changed depending on the dawn-to-dusk convection electric field E₀ because of non-uniformity in the ionospheric conductivity: the ionospheric electric field diverges in the upward current region (around the head of the WTS) when a westward electric field E₀ of 10 mV m⁻¹ is uniformly applied. On the other hand, the ionospheric electric field converges without E₀. From the observational inference that the ionospheric electric field converges around the head of the WTS, it is suggested that the WTS phenomenon may not be accounted for by the discharging process in the presence of the enhanced dawn-to-dusk convection electric field and non-uniform conductivity as was studied by previous authors.  相似文献   

Non-local memory effects of the electromotive force by fluid motion with helicity and two-dimensional periodicity     

Kumiko Hori  Shigeo Yoshida 《地球物理与天体物理流体动力学》2013,107(6):601-632

In mean-field dynamo theory, the electromotive force term 〈u′ × B′〉 due to small-scale fields connects the small-scale magnetic field with the large-scale field. This term is usually approximated as the α-effect, assumed to be instantaneous in time and local in space. However, the approximation is valid only when the magnetic Reynolds number Rm is much less than unity, and is inappropriate when Rm ? 1, which is the condition satisfied in the Earth's core or solar convection zone. We introduce a function φ _qr as a non-local and non-instantaneous generalization of the usual α-effect and examine its behaviour as a function of Rm in the range 1/64 ≤ Rm ≤ 10 for a kinematic dynamo model. We use the flow of G.O. Roberts 1972 Roberts, GO. 1972. Dynamo action of fluid motions with two-dimensional periodicity. Phil. Trans. Roy. Soc. London Ser. A, 271: 411–454. [Crossref], [Web of Science ®] , [Google Scholar] (Phil, Trans. Roy. Soc. London Ser. A, 1972, 271, 411–454), which is steady and has non-zero helicities and two-dimensional periodicity. As a result, we identify three regions in Rm space according to the behaviour of the function φ _qr : (i) Rm ? 1/4, where the function φ _qr is local and instantaneous and can be approximated by the traditional α and β effects, (ii) 1/4 ? Rm ? 4, where the deviation from the traditional α and β effects increases and non-localness and non-instantaneousness increase, and (iii) Rm ? 4, where boundary layers develop fully and non-localness and non-instantaneousness are prominent. We show that the non-local memory effect for Rm ? 4 strongly affects the dynamo action and explains an observed augmentation of the growth rate in the dispersion relation. The results imply that the non-local memory effect of the electromotive force should be important in the geodynamo or the solar dynamo.  相似文献   

An integrated analysis platform merging SuperDARN data within the THEMIS tool developed by ERG-Science Center (ERG-SC)     

Tomoaki Hori  Nozomu Nishitani  Yoshizumi Miyoshi  Yukinaga Miyashita  Kanako Seki  Tomonori Segawa  Keisuke Hosokawa 《极地研究(英文版)》2013,24(1)

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Comprehensive numerical analysis of fault‐structure systems – Computation of the large‐scale seismic structural response to a given earthquake scenario –     

T. Ichimura  M. Hori  P. E. Quinay  M. L. L. Wijerathne  T. Suzuki  S. Noguchi 《地震工程与结构动力学》2012,41(4):795-811

The seismic structural response is affected by temporal and spatial variations in strong ground motion. It can be evaluated through the fault‐structure system: the fault mechanism, wave propagation through the crust, amplification near the surface, and soil‐structure interaction. To analyze this system at high resolution and accuracy, we previously proposed a new multiscale analysis method and numerically verified its validity. However, the problem of the extremely large computation cost of constructing a three‐dimensional numerical model and solving the discretized governing equations still remains. Here, we introduce a new method to resolve these difficulties. By combining this new method with our multiscale analysis, we developed a tool for fault‐structure system analysis. The accuracy of this tool is verified by comparing it to a Green's function solution. Finally, we demonstrate the potential utility of the method by estimating the seismic response of a large and complex underground highway junction in a given earthquake scenario. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Geochemical and hydrological controls on biannual lamination of tufa deposits     

Tatsuya Kawai  Akihiro Kano  Masako Hori 《Sedimentary Geology》2009,213(1-2):41-50

Fluvial tufa deposits in southwest Japan commonly develop biannual lamination consisting of dense summer layers and porous winter layers, and the clearness of the laminae varies among the sites. The laminae have been largely attributed to a seasonally variable inorganic precipitation rate of calcite. This rate-controlled hypothesis was examined by using quantitative data for calcite packing-density (CPD) and the precipitation rate of calcite (PWP rate) calculated from water chemistry. The results for four tufa-depositing sites in SW Japan show that a positive correlation between CPD and PWP rate becomes less certain with increasing PWP rate. In the temperature realm of SW Japan, tufas develop regular distinct seasonal change in CPD when deposited in water containing Ca values less than 65 mg/l, which results in a relatively low precipitation rate. The CPD of tufa deposits rarely exceeds 65%, owing to pore space between fine-grained calcite crystals and to porosity derived from decomposed cyanobacteria and other microorganisms. By increasing the Ca content to more than 65 mg/l, the CPD often attains an upper limit and becomes insensitive to seasonal changes in the PWP rate. Therefore, seasonal variations in CPD at sites with a higher Ca content are unclear, as seen in two examples from tropical islands in southern Japan and in one locality in a temperate climate. The flow rate and microbial density on the tufa surface are subordinate factors with respect to the CPD. Seasonal changes in these two factors often enhance the porous/dense contrast of biannual lamination in SW Japan.  相似文献   

Influence of interaction between small asperities on various types of slow earthquakes in a 3-D simulation for a subduction plate boundary   总被引：3，自引：1，他引：2  

Keisuke Ariyoshi  Takane Hori  Jean-Paul Ampuero  Yoshiyuki Kaneda  Toru Matsuzawa  Ryota Hino  Akira Hasegawa 《Gondwana Research》2009,16(3-4):534-544

Recently, the occurrence of slow earthquakes such as low-frequency earthquakes and very low-frequency earthquakes have been recognized at depths of about 30 km in southwest Japan and Cascadia. These slow earthquakes occur sometimes in isolation and sometimes break into chain-reaction, producing tremor that migrates at a speed of about 5–15 km/day and suggesting a strong interaction among nearby small asperities. In this study, we formulate a 3-D subduction plate boundary model with two types of small asperities chained along the trench at the depth of 30 km. Our simulation succeeds in representing various types of slow earthquakes including low-frequency earthquakes and rapid slip velocity in the same asperity, and indicates that interaction between asperities may cause the very low-frequency earthquakes. Our simulation also shows chain reaction along trench with propagation speed that can be made consistent with observations by adjusting model parameters, which suggests that the interactions also explain the observed migration of slow earthquakes.  相似文献   

Monothalamous Soft-Shelled Foraminifera at an Abyssal Site in the North Pacific: A Preliminary Report     

Andrew J. Gooday  Hiroshi Kitazato  Saori Hori  Takashi Toyofuku 《Journal of Oceanography》2001,57(3):377-384

Soft-shelled monothalamous foraminifera, including species belonging to the suborders Allogromiida and Astrorhizida (families Saccamminidae and Psammosphaeridae), are an abundant and diverse component of the meiofauna in the deep NE Atlantic but have never been systematically documented in the Pacific Ocean. We examined the 32–63 µm and >63 µm fractions of a sample (0–1 cm layer, surface area 52.8 cm²) from an abyssal plain in the subarctic North Pacific, close to the Aleutian Trench (48°05.43 N, 176°55.06 E; 5289 m water depth). The residues yielded an estimated 2876 stained foraminifera (=545 per 10 cm²) of which >75% occurred in the upper 0.5 cm layer and almost half in the 32–63 µm fraction. Rather less than a third (30.5%) of individuals, and about half of the morphospecies (56 out of 121), were soft-shelled monothalamous forms. Many of these, particularly the saccamminids, were tiny, <120 µm in maximum dimension. Based on our analysis of this sample, and previous results in the North Atlantic and NW Indian Oceans, we suggest that these poorly known taxa are a consistently important component of the abyssal meiofauna in well-oxygenated areas.  相似文献   

Drag and Bulk Transfer Coefficients Over Water Surfaces in Light Winds     

Zhongwang Wei  Aiko Miyano  Michiaki Sugita 《Boundary-Layer Meteorology》2016,160(2):319-346

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Estimation of field irrigation water demand based on lumped kinematic wave model considering soil moisture balance     

Tomoharu Hori  Takeyuki Sugimoto  Yutaka Ichikawa 《Physics and Chemistry of the Earth》2008,33(5):376-381

An estimation model of farm field irrigation water demand is developed. The model is based on the lumped kinematic wave model considering soil water balance. The lumped model approach reduces the computational load in rainfall-runoff analysis and allows application to large river basins. Evapotranspiration is estimated on hourly basis by the improvement of FAO’s method. Not only water volume necessary for farm field irrigation but also the number of the water charge and its interval can be estimated by the combined use of the lumped runoff model and the hourly evapotranspiration model.  相似文献   

Nutrient and Phytoplankton Dynamics in Harima-Nada, Eastern Seto Inland Sea, Japan During a 35-Year Period from 1973 to 2007     

Tetsuya Nishikawa  Yutaka Hori  Satoshi Nagai  Kazutaka Miyahara  Yukinobu Nakamura  Kazuhiro Harada  Minoru Tanda  Takehiko Manabe  Kuninao Tada 《Estuaries and Coasts》2010,33(2):417-427

Long-term monitoring of water quality and phytoplankton was conducted at 19 sampling stations in Harima-Nada, eastern Seto Inland Sea, Japan for 35 years from 1973 to 2007. There were two significant long-term changes, an increase in winter water temperatures of 0.042°C year^?1, and a decrease in dissolved inorganic nitrogen (DIN) from about 10 μM in the 1970s to ~5 μM in the late 1990s due to the reduction in nutrient inputs. DIN concentrations and total phytoplankton cell density were both higher during the 1970s to the early 1980s and then exhibited a significant decrease in the mid 1980s and remained relatively constant thereafter. Diatoms were the dominant phytoplankton group (>90%) over the 35-year period, and there was a dramatic shift from Skeletonema dominance (~70%) to Chaetoceros in the mid 1980s. This shift in diatom species may be attributed to differences in the life cycle of Skeletonema and Chaetoceros and the response to the decrease in DIN concentration.  相似文献