Seasonal variation of atmospheric 210Pb and Al in the western North Pacific region     

Shizuo Tsunogai  Takayoshi Kurata  Toshitaka Suzuki  Khchiro Yokota 《Journal of Atmospheric Chemistry》1988,7(4):389-407

The atmospheric concentration of ²¹⁰Pb was determined for two years at six stations in the western North Pacific region. The following results were obtained and discussed by comparing them with those of Al. The atmospheric concentration of ²¹⁰Pb varied widely from week to week, but the degree of variation was about a half that of Al. Contrary to Al, the year-to-year variation of ²¹⁰Pb was not pronounced and its seasonal variation was well expressed by a sine curve. The ²¹⁰Pb concentration did not show a marked latitudinal variation and its base-line concentration was high in the surface air over the North Pacific. These suggest that atmospheric ²¹⁰Pb has a longer residence time, due to its transportation through higher altitudes and deposits much more evenly onto the Earth's surface and the ocean, as compared with Al in mineral dust which is larger in size in the source region.  相似文献   

Full-correlation analysis of turbulent scattering layers in the mesosphere observed by the MU radar     

Mamoru Yamamoto  Toru Sato  Toshitaka Tsuda  Shoichiro Fukao  Susumu Kato 《Pure and Applied Geophysics》1989,130(2-3):605-616

We have applied a full-correlation analysis technique to the echo power fluctuations observed by the MU radar (35°N, 136°E), and analyzed the horizontal structure of the scattering pattern in the mesosphere as well as their horizontal motions. The velocity of the scattering pattern did not agree with the background wind velocity, but was associated with the horizontal propagating direction of a saturated inertia gravity wave identified in the wind field. The length of the long axis of the characteristic ellipse of the scattering pattern was approximately 50 km, and the direction was almost perpendicular to the propagating direction of the wave. The correlation time of the scattering pattern was approximately 700 s, which is much longer than the lifetime of the isolated turbulence itself. This implies that the observed scattering pattern is associated with a region where the saturated inertia gravity wave generates turbulence.  相似文献   

Diurnal variations of the planetary boundary layer observed with anL-band clear-air doppler radar     

Hiroyuki Hashiguchi  Manabu D. Yamanaka  Toshitaka Tsuda  Mamoru Yamamoto  Takuji Nakamura  Tatsuhiro Adachi  Shoichiro Fukao  Toru Sato  Daniel L. Tobing 《Boundary-Layer Meteorology》1995,74(4):419-424

Based on continuous observations of the planetary boundary layer (PBL) with anL-band (1357.5 MHz) boundary-layer radar (BLR) at a hilly location in Japan, we have discovered that on clear days, a thin enhanced echo layer corresponding to the top of the PBL (or mixed layer) appeared at about 500 m height in the morning and ascended to about 1500 m in the afternoon. Strong upward velocities were observed below the echo layer (or inside the PBL), reaching 1500 m in the afternoon.  相似文献   

Seismic Retrofit of Gravity Retaining Walls for Residential Fills Using Ground Anchors     

Aurelian Catalin Trandafir  Toshitaka Kamai  Roy Carl Sidle  Mihail Popescu 《Geotechnical and Geological Engineering》2007,25(6):679-691

Failure of several gravity retaining walls in residential areas built on reclaimed land, during the October 23, 2004 Chuetsu earthquake in Niigata Prefecture, Japan, determined the authorities to consider the seismic retrofit of the walls in order to mitigate future similar disasters in the urban environment. This study addresses the effectiveness of ground anchors in improving the seismic performance of such retaining structures through a sliding block analysis of the seismic response of an anchored gravity retaining wall supporting a dry homogeneous fill slope subject to horizontal ground shaking. Sliding failure along the base of the wall and translational failure along a planar slip surface of the active wedge within the fill material behind the wall were considered in the formulation, whereas the anchor load was taken as a line load acting on the face of the gravity retaining wall. The effects of magnitude and orientation of anchor load on the yield acceleration of the wall-backfill system and seismically induced wall displacements were examined. It was found that for the same anchor orientation, the yield acceleration increases in a quasi-linear manner with increasing the anchor load, whereas an anchor load of a given magnitude acting at various orientations produces essentially identical yield accelerations. On the other hand, the computed earthquake-induced permanent displacements of the anchored gravity retaining wall decrease exponentially with increasing magnitude of anchor load. Additionally, the influence of backfill strength properties (e.g., internal friction angle) on the seismic wall displacement appears to diminish considerably for the anchored gravity retaining wall. A dynamic displacement analysis conducted for the anchored gravity retaining wall subjected to various seismic waveforms scaled to the same peak earthquake acceleration revealed a good correlation between the calculated permanent wall displacements and the Arias intensity parameter characterizing the input accelerogram.  相似文献   

Geographical Variation of Body Size of Neocalanus cristatus, N. plumchrus and N. flemingeri in the Subarctic Pacific and Its Marginal Seas: Implications for the Origin of Large Form of N. flemingeri in the Oyashio Area     

Atsushi Tsuda  Hiroaki Saito  Hiromi Kasai 《Journal of Oceanography》2001,57(3):341-352

Size distributions of Neocalanus cristatus, N. flemingeri and N. plumchrus were investigated in the eastern and the western subarctic gyres and three marginal seas of the North Pacific during the diapause period to examine the geographical variation in body size of Neocalanus species and to clarify the origin of the large biennial N. flemingeri which has been observed in the Oyashio region. There were significant among region variations in body sizes for all three species of Neocalanus. Generally, the body sizes of the copepods were larger in the marginal seas and marginal areas of the open ocean. In the open ocean, the body sizes increased westward. These patterns of variation in the body sizes roughly correlated with local food availability. Distribution of biennial N. flemingeri was restricted to the Sea of Japan, the Okhotsk Sea and the Oyashio region. The large-sized biennial N. flemingeri were abundantly observed in the Okhotsk Sea, and the medium-sized biennial individuals were observed in the Sea of Japan. These facts strongly suggest that the large biennial N. flemingeri in the Oyashio region are advected from the Okhotsk Sea.  相似文献   

Abyssal circulation in the Japan Sea     

Gamo  Toshitaka  Horibe  Yoshio 《Journal of Oceanography》1983,39(5):220-230

Journal of Oceanography - The water below a depth of 1,000 m in the Japan Sea was found to consist of two water masses, the upper layer (the Deep Water) and the lower layer (the Bottom Water). The...  相似文献   

An in situ iron-enrichment experiment in the western subarctic Pacific (SEEDS): Introduction and summary   总被引：2，自引：1，他引：2  

Shigenobu Takeda  Atsushi Tsuda 《Progress in Oceanography》2005,64(2-4):95

To test the iron hypothesis in the subarctic Pacific Ocean, an in situ iron-enrichment experiment (SEEDS) was performed in the western subarctic gyre in July–August 2001. About 350 kg of iron (as acidic iron sulfate) and 0.48 mol of the inert chemical tracer sulfur hexafluoride were introduced into a 10-m deep surface mixed layer over an 80 km² area. This single iron infusion raised dissolved iron levels to 2.9 nM initially. Dissolved iron concentrations rapidly decreased after the infusion, but levels remained close to 0.15 nM even at the end of the 14-day experimental period. During SEEDS there were iron-mediated increases in chlorophyll a concentrations (up to 20 μg l⁻¹), primary production rates, biomass and photosynthetic energy conversion efficiency relative to waters outside the iron-enriched patch. The rapid and very high accumulation of phytoplankton biomass in response to the iron addition appeared to be partly attributable to shallow mixed-layer depth and moderate water temperature in the western subarctic Pacific. However, the main reason was a floristic shift to fast-growing centric diatom Chaetoceros debilis, unlike the previous iron-enrichment experiments in the equatorial Pacific and the Southern Ocean, in both of which iron stimulated the growth of pennate diatoms. The iron-mediated blooming of diatoms resulted in a marked consumption of macronutrients and drawdown of pCO₂. Biological and physiological measurements indicate that phytoplankton growth in the patch became both light- and iron-limited, making phytoplankton biomass relatively constant after day 9. The increase in microzooplankton grazing rate after day 9 also influenced the net growth rate of phytoplankton. There was no significant increase in the export flux of carbon to depth during the 14-day occupation of the experimental site. The export flux between day 4 and day 13 was estimated to be only 13% of the integrated primary production in the iron-enriched patch. The major part of the carbon fixed by the diatom bloom remained in the surface mixed layer as biogenic particulate matter. Our findings support the hypothesis that iron limits phytoplankton growth and biomass in a ‘bottom up’ manner in this area, but the fate of algal carbon remains unknown.  相似文献   

Seasonal and areal variation of continental aerosol in the surface air over the western North Pacific region   总被引：1，自引：0，他引：1  

Shizuo Tsunogai  Toshitaka Suzuki  Takayoshi Kurata  Mitsuo Uematsu 《Journal of Oceanography》1985,41(6):427-434

Weekly aerosol samples were collected for two years from 1981 at six stations in the western North Pacific region. The samples were analyzed for aluminum to determine the mineral dust concentration in the air. By combining our data with observations in the central and eastern North Pacific by a US research group, the following results and conclusions have been obtained. Spring peaks in atmospheric mineral dust were observed at all the stations accompanied byKosa episodes (hazes due to mineral dust of Chinese origin). The spring peaks, however, varied from year to year. The mean concentration of mineral dust depends not only on the distance from the Asian coast but also on the latitude of the sampling station. The half-decrease distance of the atmospheric mineral dust turned out to be 500–600 km for all latitudes in the western North Pacific. This indicates that the rate of deposition of mineral dust in the western North Pacific is much larger than that in the central and eastern North Pacific.  相似文献   

Fractal distribution of an oceanic copepodNeocalanus cristatus in the subarctic pacific     

Atsushi Tsuda 《Journal of Oceanography》1995,51(3):261-266

Horizontal distribution of the copepodNeocalanus cristatus was shown to be fractal on the scale between tens of meters and over 100 km. The fractal dimensions ranged between 1.68–1.89, significantly higher than those of oceanic turbulence and phytoplankton distribution.  相似文献   

Impact of the 2011 Tohoku earthquake tsunami on zooplankton community in Otsuchi Bay,northeastern Japan     

Yuichiro Nishibe  Hiroshi Isami  Hideki Fukuda  Shuhei Nishida  Toshi Nagata  Aiko Tachibana  Atsushi Tsuda 《Journal of Oceanography》2016,72(1):77-90

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