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Atsuki Shinbori Tomoaki Hori Yoshimasa Tanaka Yukinobu Koyama Takashi Kikuchi Tsutomu Nagatsuma 《极地研究(英文版)》2013,(4):296-314
To investigate temporal and spatial evolution of global geomagnetic field variations from high-latitude to the equator during geomagnetic storms, we analyzed ground geomagnetic field disturbances from high latitudes to the magnetic equator. The daytime ionospheric equivalent current during the storm main phase showed that twin-vortex ionospheric currents driven by the Region 1 field-aligned currents （R1 FACs） are intensified significantly and expand to the low-latitude region of-30~ magnetic latitude. Centers of the currents were located around 70~ and 65~ in the morning and afternoon, respectively. Corresponding to intensification of the R1 FACs, an enhancement of the eastward/westward equatorial electrojet occurred at the daytime/nighttime dip equator. This signature suggests that the enhanced convection electric field penetrates to both the daytime and nighttime equa- tor. During the recovery phase, the daytime equivalent current showed that two new pairs of twin vortices, which are different from two-cell ionospheric currents driven by the R1 FACs, appear in the polar cap and mid latitude. The former led to enhanced north- ward Bz （NBZ） FACs driven by lobe reconnection tailward of the cusps, owing to the northward interplanetary magnetic field （IMF）. The latter was generated by enhanced Region 2 field-aligned currents （R2 FACs）. Associated with these magnetic field variations in the mid-latitudes and polar cap, the equatorial magnetic field variation showed a strongly negative signature, produced by the westward equatorial electrojet current caused by the dusk-to-dawn electric field. 相似文献
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We estimated the stress fields of the aftershocks of the 2000 western Tottori earthquake (Mw 6.6) and the northern Hyogo swarm (max Mw 5.2) by a stress tensor inversion of moment tensor solutions reported from the National Research Institute for Earth Science and Disaster Prevention (Japan). The maximum principal stress direction of the western Tottori sequence was estimated as N107°E with a strike–slip regime. In the northern Hyogo swarm, the orientations of the principal stress directions could not be well constrained by the observed data, but after examining the detailed characteristics of the solution, we obtained a most probable solution of N113°E for the σ1 direction. These solutions are consistent with the maximum horizontal directions roughly estimated from the strike directions of large earthquakes occurring geographically between these two seismic activities. We measured the angle between each fault–slip direction and maximum principal stress direction to investigate the frictional properties of earthquakes. The distribution of the angles was forward modeled to estimate the coefficient of friction and the stress ratio, assuming uniformly distributed fault orientations. For the western Tottori sequence, a homogeneous stress field with a coefficient of friction less than 0.4 was estimated. A high stress level was also suggested because very little change occurred in the stress field during the mainshock. For the northern Hyogo sequence, the coefficient of friction was estimated to be between 0.5 and 1.0. 相似文献
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NIED seismic moment tensor catalogue for regional earthquakes around Japan: quality test and application 总被引：4，自引：0，他引：4
We have examined the quality of the National Research Institute for Earth Science and Disaster Prevention (NIED) seismic moment tensor (MT) catalogue obtained using a regional broadband seismic network (FREESIA). First, we examined using synthetic waveforms the robustness of the solutions with regard to data noise as well as to errors in the velocity structure and focal location. Then, to estimate the reliability, robustness and validity of the catalogue, we compared it with the Harvard centroid moment tensor (CMT) catalogue as well as the Japan Meteorological Agency (JMA) focal mechanism catalogue. We found out that the NIED catalogue is consistent with Harvard and JMA catalogues within the uncertainty of 0.1 in moment magnitude, 10 km in depth, and 15° in direction of the stress axes. The NIED MT catalogue succeeded in reducing to 3.5 the lower limit of moment magnitude above which the moment tensor could be reliably estimated. Finally, we estimated the stress tensors in several different regions by using the NIED MT catalogue. This enables us to elucidate the stress/deformation field in and around the Japanese islands to understand the mode of deformation and applied stress. Moreover, we identified a region of abnormal stress in a swarm area from stress tensor estimates. 相似文献
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Yoshimasa Tanaka Atsuki Shinbori Tomoaki Hori Yukinobu Koyama Shuji Abe Norio Umemura Yuka Sato Manabu Yagi Satoru UeNo Akiyo Yatagai Yasunobu Ogawa Yoshizumi Miyoshi 《极地研究(英文版)》2013,(4):231-240
To comprehensively understand the Arctic and Antarctic upper atmosphere, it is often crucial to analyze various data that are obtained from many regions. Infrastructure that promotes such interdisciplinary studies on the upper atmosphere has been developed by a Japanese inter-university project called the Inter-university Upper atmosphere Global Observation Network （1UGONET）. The objective of this paper is to describe the infrastructure and tools developed by IUGONET. We focus on the data analysis software. It is written in Interactive Data Language （IDL） and is a plug-in for the THEMIS Data Analysis Software suite （TDAS）, which is a set of IDL libraries used to visualize and analyze satellite- and ground-based data. We present plots of upper atmospheric data provided by IUGONET as examples of applications, and verify the usefulness of the software in the study of polar science. We discuss IUGONET＇s new and unique developments, i.e., an executable file of TDAS that can run on the IDL Virtual Machine, IDL routines to retrieve metadata from the IUGONET database, and an archive of 3-D simulation data that uses the Common Data Format so that it can easily be used with TDAS. 相似文献
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Nicholas Williamson Atsuki Komiya Shigenao Maruyama Masud Behnia Steve W. Armfield 《Journal of Oceanography》2009,65(3):349-359
The transport of nutrient-rich, deep sea water from an artificial upwelling pipe has been simulated. A numerical model has
been built within a commercial Computational Fluid Dynamics (CFD) package. The model considers the flow of the deep sea water
after it is ejected from the pipe outlet in a negatively buoyant plume (densimetric Froude number = −2.6), within a stably
stratified ocean environment subject to strong ocean current cross flow. Two cross-flow profiles were tested with momentum
flux ratios equal to 0.92 and 3.7. The standard k-ε turbulence model has been employed and a range of turbulent Schmidt and Prandtl numbers tested. In all cases the results
show that the rapid diffusion of heat and salinity at the pipe outlet causes the plume to attain neutral buoyancy very rapidly,
preventing strong fountain-like behavior. At the higher momentum flux ratio fountain-like behavior is more pronounced close
to the pipe outlet. The strong cross-current makes horizontal advection the dominant transport process downstream. The nutrient
plume trajectory remains largely within one relatively thin stratified layer, making any ocean cross-flow profile less important.
Very little unsteady behavior was observed. The results show that the nutrient is reduced to less than 2% of its inlet concentration
10 meters downstream of the inlet and this result is largely independent of turbulent Prandtl or Schmidt number. Initial results
would suggest that if such an artificial upwelling were to be viable for an ocean farming project, a large number of upwelling
pipes would be necessary. Further work will have to determine the minimum nutrient concentration required to sustain a viable
phytoplankton population and the required spacing between upwelling pipes. 相似文献
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