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11.
Mesoscale features in the eastward extension of the Kuroshio were investigated using assimilation of TOPEX/POSEIDON (T/P)
data into a three-layer quasi-geostrophic model. The T/P data exhibited an elongated state of the southern recirculation gyre
in 1993–95 and 1997, between whose two periods the gyre had a contracted state in 1995–96. A few stationary eddies were located
in the southern gyre during the contracted state. The baroclinic instability, which was indicated by the phase shift from
the uppermost-to the lowest-layer anomalies toward the downstream side, was evident near the Kuroshio Extension (KE) path.
Since the instability never appeared in the artificial model without bottom topography, the topographic barrier for the eastward
flow in the lowest layer was a necessary condition for the instability. The instability synchronized with the transition in
the western region of the KE axis from the elongated to the contracted states. This evolution was interpreted as if the baroclinic
instability played some part in the KE states and was a trigger for the transition from the elongated to the contracted states. 相似文献
12.
Mean circulation induced over bottom topography by mesoscale variabilities in the Kuroshio Extension
Circulation could be generated over bottom topography by vertical shrinking or stretching of a water parcel, in which potential
vorticity is conserved. The water parcel moves up or down over the bottom topography yielding shrinking or stretching. In
addition to a prevailing current which advects the water parcel in one direction, an oscillatory motion can also induce shrinking
and stretching, and circulation is consequently generated over the bottom topography, once it is averaged in time. A two-layer
quasi-geostrophic model has been used to reproduce mesoscale variabilities both in and under the Kuroshio Extension around
the Shatsky Rise. A combination of TOPEX and ERS altimeters provided information on an eddy field near the sea surface, while
a data assimilation method was used to reconstruct the flow field below the main thermocline. Among various mesoscale processes
associated with the Kuroshio, it is remarkable that topographic Rossby waves trapped over the Shatsky Rise are generated by
the upper-layer mesoscale variability. A persistent anticyclonic circulation is produced on the Shatsky Rise through a water
parcel moving up and down over the bottom slope, and is consistent with the observed density anomaly in the WOA94. 相似文献
13.
Climatological water-mass structures were identified in the Arctic Ocean using the geochemical dataset in the Hydrochemical Atlas of the Arctic Ocean (HAAC) as well as data on a geochemically conserved parameter, PO4*, based on phosphate and dissolved oxygen. In the upper ocean above a depth of 500 m, the HAAC was found to reliably depict the boundary between Pacific-Origin Water (P-Water) and Atlantic-Origin Water (A-Water), which is aligned 135°E–45°W near the surface but rotates counterclockwise with depth. Thus, the Arctic and Atlantic oceans exchange high-silicate P-Water and low-silicate A-Water. The PO4* field in the lower ocean below a depth of 1500 m was analyzed statistically, and the results indicated that the Eurasian Basin receives low-PO4* Nordic Seas Deep Water, which flows along the bottom from the Greenland Sea. The routes from the upper ocean to the lower ocean were determined. Only the southern portion of the Canada Basin, which receives water from the Chukchi and Beaufort Seas, has high PO4* levels; the rest of the Amerasian Basin receives low-PO4* water from the Laptev Sea and/or the Barents Sea. The Eurasian Basin receives moderate levels of PO4* from the Fram Strait and from the intermediate layer. The intermediate-layer water gradually travels up from the lower ocean and returns to the Atlantic, entraining the subsurface portion. It is likely that high-PO4* water occasionally flows down from the upper ocean along Greenland, making the Eurasian Basin heterogeneous. 相似文献
14.
A combination of a three-dimensional hydrodynamic model and in-situ measurements provides the structures of barotropic tides,
tidal circulation and their relationship with turbulent mixing in the Java Sea, which allow us to understand the impact of
the tides on material distribution. The model retains high horizontal and vertical resolutions and is forced by the boundary
conditions taken from a global model. The measurements are composed of the sea level at coastal stations and currents at moorings
embedded in Seawatch buoys, in addition to hydrographic data. The simulated tidal elevations are in good agreement with the
data for the K1 and M2 constituents. The K1 tide clearly shows the lowest mode resonance in the Java Sea with intensification around the nodal point in the central region.
The M2 tide is secondary and propagates westward from the eastern open boundary, along with a counterclockwise amphidromic point
in the western part. The K1 tide produces a major component of tidal energy, which flows westward and dissipates through the node region near the Karimata
Strait. Meanwhile, the M2 tide dissipates in the entire Java Sea. However, the residual currents are mainly induced by the M2 tide, which flows westward following the M2 tidal wave propagation. The tidal mixing is mainly caused by K1 tide which peaks at the central region and is consistent with the uniform temperature and salinity along the vertical dimension.
This mixing is expected to play an important role in the vertical exchange of nutrients and control of biological productivity. 相似文献
15.
16.
西北太平洋黑潮主轴区浮游有孔虫的垂直分布及其古海洋学意义 总被引:5,自引:0,他引:5
我们对位于西北太平洋黑潮主轴区MTD-02站的11个不同深度进行水平浮游拖网,并将采集到的活体浮游有孔虫(>125μm)进行定量分析。结果表明,绝大多数活体浮游有孔虫生存于100~200m以上的水体中,并集中分布于75m以上的水体。本站位8月份的最主要属种为:Globigerinoidesruber,G.sacculifer,Neogloboquadrtnadutertrei和Globigerinitaglutinata.次主要属种为Globigerinella aequilateralis, globigerinabulloides,Pulleniatinaobliquiloculata,Globorotaliatruncatulinoides,Orbulinauniversa和G.conglobatua.这些种在不同的深度其产出量大不相同,但绝大多数均在叶绿素最为丰富的25m处显示出最大值。这表明食物来源是控制浮游有孔虫在MTD-02站垂直分布的最主要因素。 相似文献
17.
A unique sapphirine + orthopyroxene + quartz granulite from Mt. Riiser-Larsen in the Tula Mountains of Enderby Land, East
Antarctica, preserves two generations of coarse and texturally equilibrated orthopyroxene and sapphirine coexisting with quartz.
Initial subhedral orthopyroxene porphyroblasts retain core compositions enriched in Al2O3 (12.2 ± 0.5 wt%) compared with their rims and finer orthopyroxene (9.6 ± 0.5 wt% Al2O3) that forms granoblastic textures with sapphirine. Sapphirine and quartz also form symplectites on and along cleavage planes
within orthopyroxene. These compositional and textural features are consistent with the reaction [2MgAl2SiO6=Mg2Al4 SiO10 + SiO2] leading to the formation of sapphirine + quartz at the expense of aluminous orthopyroxene. Calculations in the MAS and FMAS
systems and theoretical considerations involving the phases enstatite, sapphirine, sillimanite, quartz and cordierite indicate
that the reaction above progresses from left to right with decreasing temperature in the orthopyroxene + sapphirine + quartz
field, at pressures of ca. 8–10 kbar. The temperature difference required to account for the ca. 2.5–3 wt% decrease in Al2O3 in orthopyroxene is at least 60–80 °C, and implies peak temperatures for the initial assemblage of at least 1120 °C if the
second granoblastic assemblage equilibrated at 1040 °C, the P–T conditions required by the sapphirine + quartz association
and other P–T-sensitive assemblage indicators in the Napier Complex. It is not possible to distinguish whether the two assemblages
are simply related by cooling and re-equilibration or reflect a polyphase evolution involving the superposition of a second
UHT event on an earlier, even higher temperature, UHT metamorphism. Preliminary thermodynamic modelling of the reaction above
incorporating the observed range in orthopyroxene Al2O3 zoning indicates that present estimates for the entropy of high-temperature sapphirine are potentially too high by 15–18%
compared with sapphirine entropy estimates that are consistent with MAS system experiments. The Mt. Riiser-Larsen sapphirine–quartz
rocks preserve the first definitive record of regional metamorphic temperatures in excess of 1120 °C in the Napier Complex,
or indeed any UHT granulite terrain worldwide. Similarly high peak temperatures may be retrieved from detailed studies of
sapphirine–quartz granulites from other regions, further expanding the thermal realm of crustal metamorphism, but progress
will critically depend on the experimental acquisition of new entropy data for sapphirine.
Received: 3 September 1998 / Accepted: 8 November 1999 相似文献
18.
Nieke J. Aoki T. Tanikawa T. Motoyoshi H. Hori M. 《Geoscience and Remote Sensing Letters, IEEE》2004,1(3):215-219
Recently, the Advanced Earth Observing Satellite 2 (ADEOS-2) was launched (December 14, 2002) successfully, and the Global Imager (GLI) onboard the ADEOS-2 satellite became operational in April 2003. In a first calibration checkup, the radiometric performance of GLI was compared relatively to that of other sensors on different satellites with different calibration backgrounds. As a calibration site, a large snowfield near Barrow, Alaska, was used, where space sensors in polar orbits view the same ground target on the same day with small differences in the local crossing times. This is why GLI, the Moderate Resolution Imaging Spectroradiometer (Terra, Aqua), the Sea-viewing Wide Field-of-view Sensor, the Advanced Very High Resolution Radiometer (N16, N17), the Medium Resolution Imaging Spectrometer, and the Advanced Along Track Scanning Radiometer datasets were selected for the following clear-sky condition days: April 14 and 26, 2003. At the same time, ground-truth experiments (e.g., measurements of ground reflectance, bidirectional reflectance distribution function, aerosol optical thickness) were carried out. Thereinafter, top-of-atmosphere (TOA) radiance/reflectance was forward calculated by means of radiative transfer code for each sensor, each band, and each day. Finally, the vicariously retrieved TOA signal was compared to TOA sensor Level 1B data. As a result, GLI's performance is encouraging at that time of the mission. GLI and the other seven sensors deliver similar sensor output in the range of about 5% to 7% around the expected vicariously calculated TOA signal. 相似文献
19.
Sensitivity of the Interannual Kuroshio Transport Variation South of Japan to Wind Dataset in OGCM Calculation 总被引:1,自引:2,他引:1
Hiroshi Yoshinari Motoyoshi Ikeda Kiyoshi Tanaka Yukio Masumoto 《Journal of Oceanography》2004,60(2):341-350
Numerical experiments were carried out using OGCM (Ocean General Circulation Model), MOM2.2 (Modular Ocean Model Ver. 2.2),
over realistic topography data, ETOPO5 (Earth Topography - 5 Minute), to investigate the interannual variability of the Kuroshio
transport in 1960–2000 south of Japan; 1) the PN line located off the East China Sea, and 2) the ASUKA (Affiliated Surveys
of the Kuroshio off Cape Ashizuri) line located off Cape Ashizuri. We adopted two wind datasets as driving forces of the OGCM:
1) the NCEP/NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research) reanalysis monthly
mean wind stress data, and 2) the ECMWF (European Centre for Medium-range Weather Forecasts) daily wind data. In the ECMWF
experiments we replaced the NCEP/NCAR data only in 1979–1993 because of the availability of the data. The OGCMs and observation
basically agree on the temporal variation patterns of the transports until 1986 on the PN line with correlation coefficients
of about 0.6. During the 1990s, when data were collected on the ASUKA line, the NCEP/NCAR experiments give lower correlation
coefficients (less than 0.3), on both PN and ASUKA lines, while the ECMWF experiments have a higher value on the ASUKA line
(0.5). One of the reasons for the disagreement between the observations and OGCMs during the 1990s might arise from the NCEP/NCAR
data. An additional analysis of a wind-driven circulation was performed to examine the sensitivity of integrated Sverdrup
transport along the western boundary to the propagation speed of a baroclinic Rossby wave, which is varied by stratification.
A variation of the stratification, which might be induced by variability of air-sea heat and freshwater fluxes, cannot be
a main cause of the disagreement.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
20.
Gleb Panteleev Motoyoshi Ikeda Alex Grotov Dmitri Nechaev Max Yaremchuk 《Journal of Oceanography》2004,60(3):613-623
Standard hydrological section data, collected in the eastern Barents Sea in September 1997, have been analyzed using a variational
data assimilation technique. This method allows us to obtain temperature, salinity and velocity fields that are consistent
with observations and dynamically balanced within the framework of a steady-state model describing large-scale nearly geostrophic
circulation. Error bars of the optimized fields are computed by explicit inversion of the Hessian matrix. The optimized velocity
field is in agreement with independent velocity observations derived from surface drifter trajectories in the southwestern
part of the Barents Sea. Optimized fields provide the following estimates of integral characteristics of the circulation in
the region: i) the North Cape current transport is 2.12 ± 0.25 Sv; ii) the Karskie Vorota Strait throughflow is 0.7 ± 0.06
Sv; iii) heat flux with Atlantic water is 4.7 ± 0.16⋅1011 W; iv) salt import from the Atlantic Ocean is 7.41 ± 0.46⋅103 kg/s. The imbalance of the heat budget in the eastern part of the Barents Sea indicates the presence of statistically insignificant
surface heat fluxes which are less than 1 W/m2.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献