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1.
Norihisa Imasato Shinzou Fujio Qian Zhang Toshiyuki Awaji Kazunori Akitomo 《Journal of Oceanography》1994,50(2):119-139
We have investigated the three-dimensional Lagrangian motion of water particles related with tidal exchange between two basins with a constant depth connected through a narrow strait and the effects of density stratification on the exchange processes by tracking a number of the labeled particles. Tide-induced transient eddies (TITEs), which are similar to those in two-dimensional basin, are generated behind the headlands. Upwelling appears around the center of the eddy and sinking around the boundary. When the basins are filled with homogeneous water, a pair of vortices are produced in the vertical cross section of the strait due to bottom stress, with upwellings along the side walls of the strait and sinking in the center of the strait. These circulations form the horizontally convergent field in the cross-strait direction in the upper layers while the horizontal divergence takes place in the bottom layer. These vertical water-motions produce the three-dimensional distribution of velocity shear and phase lag of the tidal current around the strait, and the Lagrangian drifts of water particles become large. As a result, water exchange through the strait is greatly enhanced: The water exchange rate reaches 94.1% which is much larger than that obtained in the vertically integrated two-dimensional model. When the basins are stratified, the stable stratification suppresses the vertical motion so that a pair of vertical vortices are confined in the lower layers. This leads to a decrease in the exchange rate, down to 88.6%. Our numerical results show that the three-dimensional structure of tidal currents should be taken into account in tidal exchange through a narrow strait. 相似文献
2.
By using the Euler-Lagrangian method, we examine water movements within the layer of minimum oxygen concentration and estimate local oxygen consumption rates for 15 regions of the global ocean. To do this, a number of labeled particles (which represent water parcels) are deployed at the center of a grid with 15 depth levels and tracked backward in time for 50 years in a three-dimensional velocity field. We assume that a particle picks up oxygen when it encounters the point of maximum oxygen concentration along the 50 years segment of its path. We introduce a contribution rate from waters distributed throughout the global ocean to the oxygen concentration of a local layer under consideration. Water parcels which are assumed to pick up oxygen within the oxygen minimum layer of an oceanic region under consideration make a very small contribution to the overall oxygen concentration of this layer. In addition, these parcels move out of the layer and water parcels from the upper layers take their place. The averaged Lagrangian local oxygen consumption rate is 0.033 ml/l/yr for the depth of the oxygen minimum layer, 0.20 ml/l/yr at 100 m depth (euphotic layer), 0.043 ml/l/yr for layers from 150 m to 800 m depth and 0.012 ml/l/yr for deep layers from 800 m to 3000 m. The present Lagrangian numerical experiment produces a maximum difference between observed and calculated concentrations of oxygen and, therefore, a maximum oxygen consumption rate. Although the present method has an ambiguity as to how oxygen is picked up, we nevertheless were able to identify regions in which the water parcels pick up oxygen of maximum concentration. We found that the South Equatorial Current (SEC) transports oxygen of higher concentration to the middle latitude regions of both the North Atlantic and the North Pacific across the equator. 相似文献
3.
Tomonori Naya Yoshihiro Tanimura Yutaka Kanai Fujio Kumon Kazuo Amano 《Journal of Paleolimnology》2007,37(4):547-563
In order to assess the recent anthropogenic environmental changes in Lake Kitaura, central Japan, changes during the past
few centuries were reconstructed from results of radiometric and tephrochlonological age determination, magnetic susceptibility
measurements, total organic carbon analyses, total nitrogen analyses and fossil diatom analyses on a sediment core from the
lake. A total of six major and sub-zones are recognized according to the diatom fossil assemblages, and we discuss aquatic
environmental change in Lake Kitaura mainly based on these diatom assemblage change. Zone Ia and Zone Ib (older than AD 1707)
are marine to brackish. In Zone IIa (AD␣1707–AD 1836), most of the brackish diatoms disappeared, and were replaced by freshwater
species indicating a decrease in salinity. We interpret the salinity decrease in Zone I–IIa as a sea-level fall during the
Little Ice Age. The salinity of the lake decreased to near freshwater conditions in Zone IIb (AD 1836–AD 1970), which could
arise from alteration in River Tone or development of a sandspit in the mouth of River Tone in addition to sea-level change.
In Zone IIIa (AD 1970–AD 1987), the diatom assemblage indicates a freshwater environment, and sedimentation rates increase
rapidly. These changes reflect sedimentary environment change and an ecosystem transition due to the construction of the tide
gate. In Zone IIIb (AD 1987–AD 2002), the diatom flux (valves cm−2 y−1) increased and species composition changed. The changes in Zone IIIb show a good agreement with limnological monitoring data
gathered from the lake. These paleolimnological data suggest that the recent human-induced changes of the aquatic environment
of the lake after the 1970s exceed rates during the period concerned in this study. 相似文献
4.
5.
A Simple Single-Layer Urban Canopy Model For Atmospheric Models: Comparison With Multi-Layer And Slab Models 总被引：26，自引：7，他引：26
Hiroyuki Kusaka Hiroaki Kondo Yokihiro Kikegawa Fujio Kimura 《Boundary-Layer Meteorology》2001,101(3):329-358
We developed a simple, single-layer urban canopy model, and comparedit to both multi-layer and slab models. Our single-layer model has thefollowing features: (a) It is a column model of energy and momentumexchange between an urban surface and the atmosphere, (b) it includesthe influence of street canyons, which are parameterized to representthe urban geometry, (c) it includes shadowing from buildings andreflection of radiation, and (d) it estimates both the surfacetemperatures of, and heat fluxes from, three surface types: roof, wall,and road. In the simulation of the single-layer model, the roof washottest during the daytime, but coolest from midnight to early morning.This is consistent with output from the multi-layer model and fieldobservations at a residential area on a clear, summer day. The diurnalvariation of the energy budget from the single-layer model agrees wellwith that from the multi-layer model. Our single-layer model'sperformance is nearly that of a multi-layer model for studyingmesoscale heat islands. Nevertheless, it is simply parameterized,and thus easily included in larger-scale atmospheric models. The slabmodel has the largest nighttime cooling rate of the three models. Toovercome this, it needs more adjustments than for the canopy models. 相似文献
6.
Compilation method for 1 km grid data of monthly mean air temperature for quantitative assessments of climate change impacts 总被引：1，自引：0，他引：1
Hideki Ueyama Sachiho Adachi Fujio Kimura 《Theoretical and Applied Climatology》2010,101(3-4):421-431
A new method is proposed to compile 1 km grid data of monthly mean air temperature by dynamically downscaling general circulation model (GCM) data with a regional climate model (RCM). The downscaling method used is a technique referred to as the pseudoglobal warming method to reduce GCM bias. For the grid data, RCM data were corrected with data from an existing meteorological network. The correction model for the RCM bias was developed by stepwise multiple regression analysis using the difference in the monthly mean air temperatures between the observation and RCM output as a dependent variable and the geographical factors as independent variables. Our method corrected the RCM bias from 1.69°C to 0.58°C for the month of August in the 1990s (1990–1999). 相似文献
7.
Hydrographic data show that the meridional deep current at 47°N is weak and southward in northeastern North Pacific; the strong
northward current expected for an upwelling in a flat-bottom ocean is absent. This may imply that the eastward-rising bottom
slope in the Northeast Pacific Basin contributes to the overturning circulation. After analysis of observational data, we
examine the bottom-slope effect using models in which deep water enters the lower deep layer, upwells to the upper deep layer,
and exits laterally. The analytical model is based on geostrophic hydrostatic balance, Sverdrup relation, and vertical advection–diffusion
balance of density, and incorporates a small bottom slope and an eastward-increasing upwelling. Due to the sloping bottom,
current in the lower deep layer intensifies bottomward, and the intensification is weaker for larger vertical eddy diffusivity
(K
V), weaker stratification, and smaller eastward increase in upwelling. Varying the value of K
V changes the vertical structure and direction of the current; the current is more barotropic and flows further eastward as
K
V increases. The eastward current is reproduced with the numerical model that incorporates the realistic bottom-slope gradient
and includes boundary currents. The interior current flows eastward primarily, runs up the bottom slope, and produces an upwelling.
The eastward current has a realistic volume transport that is similar to the net inflow, unlike the large northward current
for a flat bottom. The upwelling water in the upper deep layer flows southward and then westward in the southern region, although
it may partly upwell further into the intermediate layer. 相似文献
8.
Pacific ocean circulation based on observation 总被引：2，自引：1，他引：1
A thorough understanding of the Pacific Ocean circulation is a necessity to solve global climate and environmental problems.
Here we present a new picture of the circulation by integrating observational results. Lower and Upper Circumpolar Deep Waters
(LCDW, UCDW) and Antarctic Intermediate Water (AAIW) of 12, 7, and 5 Sv (106 m3s−1) in the lower and upper deep layers and the surface/intermediate layer, respectively, are transported to the North Pacific
from the Antarctic Circumpolar Current (ACC). The flow of LCDW separates in the Central Pacific Basin into the western (4
Sv) and eastern (8 Sv) branches, and nearly half of the latter branch is further separated to flow eastward south of the Hawaiian
Ridge into the Northeast Pacific Basin (NEPB). A large portion of LCDW on this southern route (4 Sv) upwells in the southern
and mid-latitude eastern regions of the NEPB. The remaining eastern branch joins nearly half of the western branch; the confluence
flows northward and enters the NEPB along the Aleutian Trench. Most of the LCDW on this northern route (5 Sv) upwells to the
upper deep layer in the northern (in particular northeastern) region of the NEPB and is transformed into North Pacific Deep
Water (NPDW). NPDW shifts southward in the upper deep layer and is modified by mixing with UCDW around the Hawaiian Islands.
The modified NPDW of 13 Sv returns to the ACC. The remaining volume in the North Pacific (11 Sv) flows out to the Indian and
Arctic Oceans in the surface/intermediate layer. 相似文献
9.
Masaki Kawabe Shinzou Fujio Daigo Yanagimoto Kiyoshi Tanaka 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(10):1675-1687
We conducted full-depth hydrographic observations in the southwestern region of the Northwest Pacific Basin in September 2004 and November 2005. Deep-circulation currents crossed the observation line between the East Mariana Ridge and the Shatsky Rise, carrying Lower Circumpolar Deep Water westward in the lower deep layer (θ<1.2 °C) and Upper Circumpolar Deep Water (UCDW) and North Pacific Deep Water (NPDW) eastward in the upper deep layer (1.3–2.2 °C). In the lower deep layer at depths greater than approximately 3500 m, the eastern branch current of the deep circulation was located south of the Shatsky Rise at 30°24′–30°59′N with volume transport of 3.9 Sv (1 Sv=106 m3 s−1) in 2004 and at 30°06′–31°15′N with 1.6 Sv in 2005. The western branch current of the deep circulation was located north of the Ogasawara Plateau at 26°27′–27°03′N with almost 2.1 Sv in 2004 and at 26°27′–26°45′N with 2.7 Sv in 2005. Integrating past and present results, volume transport southwest of the Shatsky Rise is concluded to be a little less than 4 Sv for the eastern branch current and a little more than 2 Sv for the western branch current. In the upper deep layer at depths of approximately 2000–3500 m, UCDW and NPDW, characterized by high and low dissolved oxygen, respectively, were carried eastward at the observation line by the return flow of the deep circulation composing meridional overturning circulation. UCDW was confined between the East Mariana Ridge and the Ogasawara Plateau (22°03′–25°33′N) in 2004, whereas it extended to 26°45′N north of the Ogasawara Plateau in 2005. NPDW existed over the foot and slope of the Shatsky Rise from 29°48′N in 2004 and 30°06′N in 2005 to at least 32°30′N at the top of the Shatsky Rise. Volume transport of UCDW was estimated to be 4.6 Sv in 2004, whereas that of NPDW was 1.4 Sv in 2004 and 2.6 Sv in 2005, although the values for NPDW may be slightly underestimated, because they do not include the component north of the top of the Shatsky Rise. Volume transport of UCDW and NPDW southwest of the Shatsky Rise is concluded to be approximately 5 and 3 Sv, respectively. The pathways of UCDW and NPDW are new findings and suggest a correction for the past view of the deep circulation in the Pacific Ocean. 相似文献
10.
Tomoharu?SenjyuEmail author Yutaka?Isoda Takafumi?Aramaki Shigeyoshi?Otosaka Shinzo?Fujio Daigo?Yanagimoto Takashi?Suzuki Kenshi?Kuma Kosuke?Mori 《Journal of Oceanography》2005,61(6):1047-1058
Hydrographic observations have revealed detailed structure of the Bottom Water in the Japan Sea. The Yamato Basin Bottom Water
(YBBW) exhibits higher temperatures and lower dissolved oxygen concentrations than those found in the Japan Basin Bottom Water
(JBBW). Both Bottom Waters meet around the boundary region between the Yamato and the Japan Basins, forming a clear benthic
front. The structure of the benthic front suggests an estuary-like water exchange between both Basins, with the inflow from
the Japan Basin passing under the outflow from the Yamato Basin. It is inferred from the property distributions that the JBBW
flowing into the Yamato Basin is entrained by the cyclonic circulation in the basin, and modified to become the YBBW. Vertical
diffusion and thermal balance in the YBBW are examined using a box model. The results show that the effect of geothermal heating
has about 70% of the magnitude of the vertical thermal diffusion and both terms cancel the advection term of the cold JBBW
from the Japan Basin. The box model also estimates the turnover time and vertical diffusivity for the YBBW as 9.1 years and
3.4 × 10−3 m2s− 1, respectively. 相似文献