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41.
Kazuyuki Uehara Shin-Ichi Ito Hideo Miyake Ichiro Yasuda Yugo Shimizu Tomowo Watanabe 《Journal of Oceanography》2004,60(2):397-409
During November 2000–June 2002, both direct current measurements from deployment of a line of five moorings and repeated CTD
observations were conducted along the Oyashio Intensive observation line off Cape Erimo (OICE). All the moorings were installed
above the inshore-side slope of the Kuril-Kamchatka Trench. Before calculating the absolute volume transports, we compared
vertical velocity differences of relative geostrophic velocities with those of the measured velocities. Since both the vertical
velocity differences concerned with the middle three moorings were in good agreement, the flows above the continental slope
are considered to be in thermal wind balance. We therefore used the current meter data of these three moorings, selected among
all five moorings, to estimate the absolute volume transports of the Oyashio referred to the current meter data. As a result,
we estimated that the southwestward absolute volume transports in 0–1000 db are 0.5–12.8 × 106 m3/sec and the largest transport is obtained in winter, January 2001. The Oyashio absolute transports in January 2001, crossing
the OICE between 42°N and 41°15′ N from the surface to near the bottom above the continental slope, is estimated to be at
least 31 × 106 m3/sec.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
42.
Hidekazu Yasuda 《Journal of Oceanography》2004,60(3):587-596
The fundamental nature of the mass flux due to the shear effect is examined analytically in a basin with steady and oscillatory
currents to promote a better understanding of the mass transport process in coastal waters. The currents are given from solutions
of the simplified motion equation so as to be consistent with the diffusion equation. The matter concentration used is given
by an analytical solution of the diffusion equation with the settling flux term contained. Mass flux, yielding the depth-averaged
dispersion coefficient, is rather varied vertically in both steady and oscillatory currents. In the oscillatory current with
a Stokes layer in particular, the vertical profile of flux is more complicated and even negative flux is induced near the
basin floor. This negative flux does not necessarily yield a negative value of the vertically averaged dispersion coefficient.
The exact dispersion coefficient given by the flux analysis is realized only in the steady state of the matter concentration
distribution, though we can scarcely observe the steady state in the actual sea. The vertically uniform longitudinal dispersion
coefficient at the stationary stage is shown to be caused from the vertical complexity of mass flux by the action of the vertical
diffusing and the settling flux.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
43.
Hidekazu Yasuda 《Journal of Oceanography》1983,38(6):385-394
The longitudinal dispersion effect due to the boundary layer formed by a tidal oscillatory current is examined theoretically. This analysis reveals the process whereby the dispersion coefficient becomes steady after the release of the diffusing substance. Though the dispersion due to an oscillatory current has so far been investigated mostly in the case of a linear velocity profile, the following result was found by taking account of the boundary layer in the oscillatory current. The depth-averaged dispersion coefficient for the case of a current having a boundary layer can be a few times larger than in the case of a linear velocity profile when the characteristic mixing time is long; the phase lead in the boundary layer induces nearly 20 percent of the longitudinal dispersion effect. 相似文献
44.
45.
Shin-Ichi Ito Kazuyuki Uehara Takashi Miyao Hideo Miyake Ichiro Yasuda Tomowo Watanabe Yugo Shimizu 《Journal of Oceanography》2004,60(2):425-437
An observation line along the TOPEX/POSEIDON (T/P) ground track 060 was set to estimate the Oyashio transport. We call this
line the OICE (Oyashio Intensive observation line off-Cape Erimo) along which we have been conducting repeated hydrographic
observations and maintaining mooring systems. T/P derived sea surface height anomaly (SSHA) was compared with velocity and
transport on OICE. Although the decorrelation scale of SSHA was estimated at about 80–110 km in the Oyashio region, the SSHA
also contains horizontal, small-scale noise, which was eliminated using a Gaussian filter. In the comparison between the SSHA
difference across two selected points and the subsurface velocity measured by a moored Acoustic Doppler Current Profiler (ADCP),
the highest correlation (0.92) appeared when the smoothing scale was set at 30 km with the two points as near as possible.
For the transport in the Oyashio region, the geostrophic transport between 39°30′ N and 42°N was compared with the SSHA difference
across the same two points. In this case the highest correlations (0.79, 0.88 and 0.93) occurred when the smoothing scale
was set at 38, 6 and 9 km for reference levels of 1000, 2000 and 3000 db, respectively. The annual mean transport was estimated
as 9.46 Sv in the 3000 db reference case. The Oyashio transport time series was derived from the T/P SSHA data, and the transports
are smaller than that estimated from the Sverdrup balance in 1994–1996 and larger than that in 1997–2000. This difference
is consistent with baroclinic response to wind stress field.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
46.
The bimodality of the Kuroshio path is studied numerically with a barotropic inflow-outflow model. The dynamics that determines the path depends on the Rossby number,Ro (proportional to inlet velocity) and the Reynolds number (representing effects of viscosity). At lowRo (<Ro
1) only a meander path occurs, while at highRo(Ro
2) only a straight path is developed. Between these critical values (Ro
1RoRo2) either of the two paths can occur (multiple states), and the choice of path is determined by its history. Increase (decrease) inRo acrossRo
2 (Ro
1) leads to catastrophic transition from one path to the other. In the intermediate range (Ro
1RoRo2), the straight path is conditionally unstable to finite amplitude disturbances, and abrupt changes to the meander path take place. Absolute vorticity is almost conserved along the meander path, while along the straight path it is dissipated in large amount near the coast. At low Re, the flow tends to a viscous flow, and steady states are obtained. At highRe, time variations with different periods for the meander and straight paths become dominant. Intermittent transitions from one state to the other without any changes of external parameters are found at intermediateRo and at highRe. 相似文献
47.
Hidekazu Yasuda 《Journal of Oceanography》1988,44(5):244-253
Longitudinal dispersion from an instantaneous point-source in an oscillatory current with a Stoke layer is investigated theoretically using a simplified two-dimensional model. This study introduces a new definition of the variance expressing the degree of mixing at the initial stage in the point-source case, and reveals that the Stokes layer can induce a large dispersion coefficient during the initial stage in the case where the released point is at the solid boundary (bottom) producing the Stokes layer. Furthermore, this study shows that the dispersion coefficient is independent of the depth during the initial first period but is inversely proportional to the depth at the stationary stage. 相似文献
48.
Cr and Al diffusion in chromite spinel: experimental determination and its implication for diffusion creep 总被引:1,自引:0,他引:1
Diffusion coefficients of Cr and Al in chromite spinel have been determined at pressures ranging from 3 to 7 GPa and temperatures
ranging from 1,400 to 1,700°C by using the diffusion couple of natural single crystals of MgAl2O4 spinel and chromite. The interdiffusion coefficient of Cr–Al as a function of Cr# (=Cr/(Cr + Al)) was determined as D
Cr–Al = D
0 exp {−(Q′ + PV*)/RT}, where D
0 = exp{(10.3 ± 0.08) × Cr#0.54±0.02} + (1170 ± 31.2) cm2/s, Q′ = 520 ± 81 kJ/mol at 3 GPa, and V* = 1.36 ± 0.25 cm3/mol at 1,600°C, which is applicable up to Cr# = 0.8. The estimation of the self-diffusion coefficients of Cr and Al from
Cr–Al interdiffusion shows that the diffusivity of Cr is more than one order of magnitude smaller than that of Al. These results
are in agreement with patterns of multipolar Cr–Al zoning observed in natural chromite spinel samples deformed by diffusion
creep. 相似文献
49.
50.
The Loess Plateau in China constitutes an important source area for both water and sediments to the Yellow River. Thus, improved prediction techniques of rainfall may lead to better estimation of discharge and sediment content for the Yellow River. Consequently, the objective of this study was to establish better links between rainfall of the Loess Plateau in China and sea surface temperature (SST) in the Pacific Ocean. Results showed that there is a strong lagged correlation between and SST and rainfall. The SST for Micronesia and areas south of the Aleutian Islands showed significant correlations (s.f. < 0·001; 99·9%) with rainfall over the dryer region of the Loess Plateau for a lag of 4 to 6 months. The SST over the equator on the east Pacific Ocean also showed significant negative correlation with rainfall. Low and middle latitude areas (S10–20° and around 30° ) of the south‐east Pacific Ocean displayed significant positive and negative correlation with rainfall on the semiarid Loess Plateau. The differenced SST values (positive SST minus negative SST) increased these correlations with rainfall. An artificial neural network (ANN) model was used to predict summer rainfall from the differenced SST during the spring period. The correlation between predicted and observed monthly rainfall was in general larger than 0·7. This indicates that major annual rainfall (during summer season) can be predicted with good accuracy using the suggested approach. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献