The response of the mid-latitude thermospheric wind to magnetic activity     

T. Yagi  P.L. Dyson 《Planetary and Space Science》1985,33(4):461-467

Observations of the thermospheric wind at a mid-latitude station have been made using a Fabry-Perot interferometer to measure the Doppler shift of the nighttime OI emission at 630 nm. The results from 12 summer nights show that the zonal wind has a distinct feature associated with magnetic activity. The zonal wind first reverses and becomes westward. The maximum strength of the westward wind, its duration, and the maximum strength of the subsequent eastward wind all increase with increasing magnetic activity. The meridional wind is less consistent in its behaviour. It is normally equatorward but during magnetic activity it can increase, decrease, or even reverse, although it is consistently equatorward and of increased strength after 02.00 L.T. The initial reversal of the zonal wind is consistent with changes in the wind expected as a result of convective electric fields penetrating to mid-latitudes indicating that these electric fields modify the mid-latitude wind pattern before effects due to auroral heating reach mid-latitudes. The reversal of the zonal wind back to eastward may also be the result of electric field effects. The large variability of the meridional wind, to the extent that it becomes poleward at times, indicates the importance of wind sources equatorward of the observatory.  相似文献   

Satellite detection of red tide in Ariake Sound, 1998–2001     

Joji Ishizaka  Yasuhisa Kitaura  Yasuharu Touke  Hiroaki Sasaki  Akihiko Tanaka  Hiroshi Murakami  Toshikazu Suzuki  Kazumi Matsuoka  Hideaki Nakata 《Journal of Oceanography》2006,62(1):37-45

High resolution SeaWiFS data was used to detect red tide events that occurred in the Ariake Sound, Japan, a small embayment known as one of the most productive areas in Japan. SeaWiFS chlorophyll data clearly showed that a large red tide event, which damaged seaweed (Nori) cultures, started early in December 2000 in Isahaya Bay, expanded to the whole sound and persisted to the end of February 2001. The monthly average of SeaWiFS data from May 1998 to December 2001 indicated that the chlorophyll peaks appeared twice a year, in early summer and in fall, after the peaks of rain and river discharge. The SeaWiFS data showed that the red tide event during 2000–2001 winter was part of the fall bloom; however, it started later and continued significantly longer than other years. Satellite ocean color data is useful to detect the red tide; however the algorithms require improvement to accurately estimate chlorophyll in highly turbid water and in red tide areas.  相似文献   

Excess CO2 and pHexcess in the Intermediate Water Layer of the Northwestern Pacific     

Andrey Andreev  Makio Honda  Yuichiro Kumamoto  Masashi Kusakabe  Akihiko Murata 《Journal of Oceanography》2001,57(2):177-188

Excess CO₂ and pH_excess showing an increase in dissolved inorganic carbon and a decrease in pH from the beginning of the industrial epoch (middle of the 19th century) until the present time have been calculated in the intermediate water layer of the northwestern Pacific and the Okhotsk Sea. It is concluded that: (1) The Kuril Basin (Okhotsk Sea) and the Bussol' Strait areas are characterized by the greatest concentrations of excess CO₂ at isopycnal surfaces due to the processes of formation and transformation of intermediate water mass. (2) The largest difference in excess CO₂ concentration between the Okhotsk Sea and the western subarctic Pacific (about 8 µmol/kg) is found at the = 27.0. (3) The difference in excess CO₂ between the western subarctic Pacific and subtropical regions is significant only in the upper part of the intermediate water layer ( = 26.7–27.0). (4) About 10% of the excess CO₂ accumulation in the subtropical north Pacific is determined by water exchange with the subarctic Pacific and the Okhotsk Sea.  相似文献   

Distributions and upward fluxes of particulate matter near bottom in the southeastern Bering Sea Shelf     

Masahiro Kajihara  Tsutomu Morinaga  Akihiko Sekine 《Journal of Oceanography》1986,42(5):389-401

Time-series measurements of temperature, salinity, suspended matter and beam attenuation coefficient () were measured at four hour intervals for about two days in June/ July 1982 in the middle shelf region and the coastal region of the southeastern Bering Sea. Current meters were also moored at the same locations.Depth-time distributions of indicated that profiles of suspended matter resulted from a combined process of resuspension of underlying sediments and sinking of suspended particles. Average-values for all measurements for particles revealed that the upward transport of particles due to resuspension formed a boundary layer, with a thickness apparently related to scalar speed. The average-profiles of the particle volume concentration were assumed to result from a balance between the sinking and diffusive flux of particles under a steady state, and the upward fluxes were calculated. Within the boundary layer, values of the upward fluxes of particulate organic matter linearly decreased with the logarithm of distance from the bottom. Fluxes of organic carbon at the upper edge of the boundary layer were 0.375 gC·m^–2·day^–1 in the middle shelf region (18 m above the bottom, bottom depth=78m) and 0.484gC·m^–2·day^–1 in the coastal region (25 m above the bottom, bottom depth=33m), and fluxes of nitrogen in both regions were 0.067 gN·m^–2·day^–1. The flux of organic carbon obtained in the middle shelf region (18 m above the bottom) agreed approximately with the flux (0.416 gC·m^–2·day^–1) calculated by substituting primary production data into the empirical equation of Suess (1980).  相似文献   

Upwelling plumes in sagami bay and adjacent water around the Izu Islands,Japan     

Masayuki Takahashi  Isao Koike  Takashi Ishimaru  Toshiro Saino  Ken Furuya  Yoshihiko Fujita  Akihiko Hattori  Shun-ei Ichimura 《Journal of Oceanography》1980,36(4):209-216

Water plumes, 20 km long or less, identified by low temperature, high salinity and high nutrient concentrations, were observed on the eastern side of Izu Islands where the Kuroshio Current or its branch flowed eastward. The T-S diagrams and the vertical profiles of oceanographic variables indicated that the water plumes resulted from the upwelling of subsurface water. A newly formed plume, characterized by a sharp temperature front and high nutrient concentrations, contained less chlorophyll than did old plumes. It is suggested that the upwelling plumes are maintained for a period long enough to allow luxuriant growth of phytoplankton.  相似文献   

Announcement     

K. Yagi  S. Akimoto 《Marine Geophysical Researches》1988,9(2):195-195

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Geological and geomorphological characteristics of landslides triggered by the 2004 Mid Niigta prefecture earthquake in Japan   总被引：8，自引：0，他引：8  

Masahiro Chigira  Hiroshi Yagi 《Engineering Geology》2006,82(4):202-221

The 2004 Mid Niigta prefecture earthquake (M_JMA 6.8) triggered more than one thousand landslides in the Miocene to Quaternary sedimentary rocks in Japan. The most common landslides were shallow disrupted landslides on steep slopes, which has been common in many previous disastrous earthquakes in the world. The Mid Niigta prefecture earthquake also triggered more than one hundred deep landslides, providing valuable information on the conditions for their occurrence. A field investigation and the interpretation of aerial photographs taken before and after the earthquake suggest that reactivation of existing landslides and undercutting of slopes are the most important factors for deep landslides to be triggered by earthquakes. In addition, planar sliding surfaces seem to be essential for the generation of catastrophic landslides triggered by this earthquake. Planar bedding–parallel sliding surfaces were formed at the boundary between the overlying permeable sandstone and underlying siltstone or along the bedding planes of alternating beds of sandstone and siltstone. Sliding surfaces along the slope-parallel oxidation front were formed in the area of black mudstone. New landslides (rockslide-avalanches) occurred with the sliding surfaces in a several-cm thick tuff interbedded in siltstone. One rockslide-avalanche occurred on a slope where buckling deformation preceded the earthquake. Gentle valley bottom sediments were mobilized in many locations, probably because they were saturated and partial liquefaction had occurred due to the earthquake shaking.  相似文献   

Slip-weakening distance in dynamic rupture of in-slab normal-faulting earthquakes   总被引：1，自引：0，他引：1  

Takeshi Mikumo  Yuji Yagi 《Geophysical Journal International》2003,155(2):443-455

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Theoretical and experimental evidence for the post-cotunnite phase transition in zirconia at high pressure     

Daisuke Nishio-Hamane  Haruhiko Dekura  Yusuke Seto  Takehiko Yagi 《Physics and Chemistry of Minerals》2015,42(5):385-392

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Subsurface nutrient maximum and submesoscale structures in the southwestern Japan Sea   总被引：1，自引：1，他引：0  

Tetsutaro Takikawa  Akihiko Morimoto  Goh Onitsuka 《Journal of Oceanography》2016,72(4):529-540

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