共查询到20条相似文献，搜索用时 218 毫秒
1.
Hideo Kawai 《Journal of Oceanography》2003,59(2):163-172
Using natural coordinates, we have derived a criterion for the inertial instability of arbitrarily meandering currents. Such
currents, governed by the eccentrically cyclogeostrophic equation, are adopted as the basic current field for the parcel method.
We assume that any virtual displacement which is given to a water parcel moving in the basic field has no influence on this
field. From the conservation of mechanical energy for a virtual displacement we derive an inertial instability frequency ω
m
= [(f + 2u/r)Z]0.5 for the eccentrically cyclogeostrophic current, where f is the Coriolis parameter, u the velocity (always positive), r the radius of curvature of a streamline (negative for an anticyclonic meander), and Z the vertical component of absolute vorticity. If ω
m
2 is negative, the eccentrically cyclogeostrophic current becomes unstable. Although the conventional, centrifugal instability
criterion, derived from the conservation of angular momentum in a circularly symmetric current field, has a certain meaning
for a monopolar vortex, it contains a radial shear vorticity that is difficult to use in arbitrarily meandering currents.
The new criterion ω
m
2 contains a lateral shear vorticity that is applicable to arbitrarily meandering currents. Examining instabilities of concentric
rings with radii of 50–100 km, we consider reasons why the anticyclonic supersolid rotation has been very much less frequently
observed than the cyclonic supersolid rotation, despite a prediction of some common stability and a rapid change in radial
velocity gradient for the former. Classifying eccentric streamlines into the large and small curvature-gradient types, we
point out that the large-gradient curvature in anticyclonic rings is apt to be unstable.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
2.
Inertial oscillations as deep ocean response to hurricanes 总被引：1，自引：0，他引：1
We discuss the deep ocean response to passing hurricanes (aka typhoons), which are considered as generators of near-inertial, internal waves. The analysis of data collected in the northwestern
parts of the Pacific and Atlantic oceans in the hurricane season permit us to assess the deep ocean response to such a strong
atmospheric forcing. A large number of moorings (more than 100) in the northwestern Pacific have allowed us to characterize
the spatial features of the oceanic response to typhoons and the variable downward velocity of near-inertial wave propagation.
The velocity of their downward propagation varies in the range 1–10 m/hour. It is higher in the regions of low stratification
and high anticyclonic vorticity. The inertial oscillations generated by a hurricane last for 10–12 days. The mean anticyclonic
vorticity in the region increases the effective frequency of inertial oscillations by 0.001–0.004 cyc/hour. 相似文献
3.
2002年春季吕宋海峡海流:观测与改进逆模式计算 总被引：10，自引：1，他引：9
基于2002年春季航次在吕宋海峡海域锚碇测流站(20°49'57"N,120°48'12"E)200,500与800m处锚碇测流以及CTD观测,采用改进逆方法对调查海域进行海流计算.(1)主要观测的结果:1)在200m处,观测期间海流平均速度为(47.4cm/s,346°).在500m处,海流观测期间平均速度为(20.3cm/s,350°).这些都表明黑潮在吕宋海峡锚碇测流站200和500m处向西北方向入侵南海.2)在800m处,海流观测期间平均速度为(1.2cm/s,35°),它的方向为东北向.比较每层实测流结果,表明800m层海流状况与200和500m层流况不同.3)在观测期间,200,500和800m处,日平均流速在4月皆比3月时要强.4)在调查海区西部的中间区域存在一个高密、冷水中心(HDCW),其中心位置位于断面A的水文站3附近.5)在调查海区东南区域存在一个低密、暖水(LDWW)中心,其中心位置位于断面B的水文站8附近.(2)主要计算结果:1)通过断面B的偏北方向与偏南方向的流量分别为32.48×106m3/s(包括反气旋涡的流量)与3.34×106m3/s.因此通过断面B的净北向流量为29.14×106m3/s.2)通过断面A的东向与西向的流量分别为16.71×106m3/s与8.57×106m3/s(包括气旋涡的流量).因此,通过断面A的净东向流量为8.14×106m3/s.3)通过断面M北向的净流量为24.68×106m3/s.4)黑潮通过断面M后分为主流和一个支流,其主流,流量为16.54×106m3/s,流向断面C的东部分.主流通过断面C的东部分后,最后流向台湾以东海域.而其一个分支,净流量为8.14×106m3/s,在一个高密、冷水中心(HDCW)的区域以东作气旋式弯曲,然后向西北方向通过断面C的西部.因此,黑潮在断面C有两个流核.5)比较计算得到的在锚碇测流站M附近流方向与在200与500m处观测流方向为西北向,它们甚为一致.6)在断面B西侧位于550m以深水层南海水可能缓慢地从西北流向东南,通过断面B的南向流量大约为3.34×106m3/s. 相似文献
4.
The results obtained from both atmospheric and laboratory measurements and from LES data show that, in the stably stratified
flows of the atmospheric boundary layer, turbulent mixing occurs at gradient Richardson numbers Ri
g
that significantly exceed one: the inverse turbulent Prandtl number Pr
t
−1 decreases with an increase in the thermal flow stability. The decreasing trend of the inverse turbulent Ptandtl number is
reproduced in a stably stratified atmospheric boundary layer in agreement with measurement data with the aid of an improved
three-parameter turbulence model. In this model, a modified model that takes into account the effect of stratification in
the expression for the time scale of the scalar field is used for the pressure-scalar correlation. 相似文献
5.
1997年夏季西北太平洋环流模拟 总被引：5，自引：1，他引：5
采用1997年7月中日副热带环流合作调查资料,即“向阳红14”号、“东方红”两调查船CTD观测资料、日本TK和IK断面资料以及GTSPP同步资料,应用开边界情形的MOM2模式计算了西北太平洋21.875°～35.125°N,120.875°～137.125°E范围的环流,主要结果如下:在此期间,(1)黑潮在台湾以东并不存在东分支流向琉球群岛以东海域;(2)东海黑潮的流量约为30×106m3/s,日本以南黑潮流量最大约为70×106m3/s;(3)在21.875°～25°N之间大约有15×106m3/s的流量向西流去.速度分布与流函数分布均表明这一支向西的海流大约在冲绳岛西南分为3支,主要分支转向东北沿冲绳岛以东海域向东北流去;(4)琉球海流主要来自上述西向海流. 相似文献
6.
We used Argo float drift data to estimate average ocean currents at 1000 dbar depth from early 2000 to early 2010. Our estimates
cover the global oceans, except for marginal seas and ice-covered regions, at a resolution of 1 degree in latitude and longitude.
The estimated flow field satisfies the horizontal boundary condition of no flow through the topography, and is in geostrophic
balance. We also estimated the uncertainty in the average flow field, which had a typical magnitude of 0.03 ms−1. The uncertainty is relatively large (>0.03 ms−1 in both the zonal and meridional directions) near the Equator and in the Southern Ocean. The array bias, which is the bias
due to the horizontal gradient in the spatial density of the float data, is generally negligible, with an average magnitude
outside the equatorial region of 0.007 ms−1, becoming relatively large (>0.01 ms−1) only near the coastal regions. The measurement uncertainty is assumed to be spatially uniform and includes errors due to
the Argos positioning system, internal clock drift, unknown surface drift before submerging or after surfacing, and unknown
drifts during ascent and descent between the surface and the parking depth. We found that the overall uncertainty was not
sensitive to the assumed value of the measurement uncertainty (ɛ
m
)1/2 when (ɛ
m
)1/2 < 0.01 ms−1 but it increased with (ɛ
m
)1/2 for (ɛ
m
)1/2 > 0.01 ms−1. 相似文献
7.
I. B. Palymskii 《Izvestiya Atmospheric and Oceanic Physics》2009,45(5):646-653
The problem of the incompressible liquid convection between two horizontal planes heated on the underside is considered in
the three-dimensional statement. The horizontal boundaries are assumed to be free of tangential stresses and isothermal. The
calculated temporal spectrum of the temperature pulsations at the convection cell center at a supercriticality of 410 agrees
well with the experimental measurement result. The Bolgiano-Obukhov (BO), k
−11/5, k
−3, and k
−5, were obtain for the velocity pulsations. The Kolmogorov spectra k
−5/3 and k
−2.4 were obtained for the temperature pulsations. The presence of clearly identified spectra in the convective flow under study
allows this process to be characterized as developed turbulence. 相似文献
8.
The Coriolis effect on frontogenesis in the transitional region between the inner bay and the outer ocean is studied by running
several three-dimensional numerical experiments. The aim is to clarify what external parameters, including the transverse
scale of the basin, control the phenomena. The characteristics of the front in each case are described by defining three diagnostic
quantities, namely, the sharpness of the front, the intrusion of the front, and the buoyancy difference between the minimum
buoyancy region and the surrounding part, as the existence of the minimum buoyancy region is closely related to frontogenesis.
The three quantities are shown to depend on two nondimensional numbers,R
of (=f
−1
L
−2/3
F
b
1/3
: defined as flux Rossby number) andR
ef (=ν
v
−1
L
−2/3
F
b
1-3
H
2: defined as flux Reynolds number). 相似文献
9.
合理的人工鱼礁组合可以有效改善投放水域的流场效应,提高投放水域底层与上层水体之间的扰动。通过使用并行大涡模拟模式及被动示踪物模块,并通过调整人工鱼礁布设间距,研究了在不同背景流速条件(0.1、0.5、0.6和1.0 m/s)下,在不同的横向间距(1L、2L、3L)(L表示人工鱼礁的边长)或纵向间距(1L、2L、3L、4L、5L)情况下,方型人工鱼礁对上升流体积、营养盐的抬升和垂向涡黏系数的影响。研究结果表明,在同一布置条件下,单排布置下的三块人工鱼礁形成的上升流体积大小与来流速度成正相关,体积随来流流速增加而增大6.4%～80.5%;在同一流速条件下,上升流体积大小与纵向布置的间距成正比,与横向布置的间距成反比;在横向布置条件下,当来流速度为1.0 m/s、布设间距为1L时,上升流体积参数最佳。总体来说,上升流体积参数、示踪物浓度差和垂向涡黏性系数均显示横向布置优于纵向布置,相较于布设间距,来流速度是影响上升流体积最重要的因素。 相似文献
10.
Momentum and heat flux were measured with a sonic anemometer at the Marine Observation Tower in the port of ItÔ. Under unstable conditions (T
w
-T
a
=3C4C), using the eddy correlation method, results show thatCd=(1.2±0.3)×10–3 andCh=(1.5±0.3)×10–3 at 5.5 m above mean sea level except for the case of weak winds.An unexpected relationship betweenCd and (–z/L) was observed, that is,Cd decreases as (–z/L) increases. If roughness variation over the sea is taken into account, we can explain the decrease in the range of (–z/L) less than 1, but not in the range greater than 1. This is due to a strong instability effect and the change of roughness class, from moderately rough to smooth. 相似文献
11.
The barotropic instability of a boundary jet on a beta plane is considered with emphasis on the effect of internal viscosity.
An eigenvalue problem for the disturbance equations and its inviscid version are solved by the aid of numerical methods, and
instability characteristics are determined as functions of the Reynolds numberR for various values of the beta-parameter. Typical disturbance structures (eigenfunctions) are also computed.
Numerical examples show that the minimum critical Reynolds numberR
cr
for instability is smaller than 100. At a Reynolds number of the order of hundreds, there appears a second mode of instability
in addition to the first unstable mode originating atR
cr
; a kind of ‘resonance’ between the first and second eigenvalues occurs at the particular value ofR. The neutral stability curves are accordingly multi-looped. Although each of the two unstable modes asymptotically approaches
its inviscid counterpart asR→∞, the asymptotic approach to the inviscid limit is rather slow and the effect of varyingR is conspicuous even atR∼O (104). It is thus demonstrated that the Reynolds number is an essential stability parameter for real boundary jets.
The main part of the material contained in this paper was presented at 1981-Autumn Assembly of the Oceanographical Society
of Japan. 相似文献
12.
本文基于2016年长江口海域(舟山绿华山)的连续观测数据,分析了该海域水文环境要素分布,并估算了溶解氧跨跃层垂向输运。本次观测发现,水体的温度、盐度和溶解氧剖面具有明显的分层结构,三者跃层具有相同的变化趋势且主要受潮流变化影响。通过计算,得到跃层浮性频率的平方(N2)在10–3—10–2/s2之间,剪切的平方(S2)介于10–5—10–2/s2。潮流活动会激发水体剪切不稳定促进水体中溶解氧的垂向交换。最后,采用简化的一维溶解氧垂向输运模型,得到观测周期内跨跃层输运的溶解氧的含量为4.75mmol/(m2·d),佐证层化是长江口海域出现氧亏损现象的主要原因之一。 相似文献
13.
Hourly fluctuations of vertical velocity in relation to components of flow and wind and temperature oscillations at a morring site in the shelf waters off the west coast of India are discussed. The vertical velocities were computed from a time series of vertical temperature profiles assuming that horizontal advection of temperature is negligible. The computed values at a depth of 40 m during the 72-h period of observation were of the order of 10−1 to 10−2cm s−1, with a mean value of −2·77 × 10−2 cm s−1 indicating a net upward movement of water. The computed vertical velocity showed fluctuations of about 2–3 h, in addition to weaker signals of about 12 h. Based on the spectral estimates, we speculate that these fluctuations of 2–3 h in the vertical velocity may be caused by the fluctuations in the along-shore wind. The oscillations of isotherms found in the temperaturedepth time series and the spectral estimates of temperature and cross-shore flow component showed a periodicity of about 12 h, which indicated the presence of semi-diurnal internal waves. The fact that these internal wave troughs were associated with the measured onshore flow suggested that the waves were propagating offshore. The computed stability parameters showed little evidence of instability or mixing. It was found that the isotherm troughs in the temperaturedepth time series at about 12-h period coincided with high vertical shear in the cross-shore direction and low values of Brunt Vaisälä frequency. 相似文献
14.
O. A. Druzhinin 《Izvestiya Atmospheric and Oceanic Physics》2008,44(6):768-780
The onset of a three-dimensional jet flow in a stratified fluid is studied with the aid of a direct numerical simulation. An initially cylindrical jet with a Gaussian velocity profile is considered in a fluid with stable linear density stratification. The results indicate that, if an initial small perturbation of the velocity field has a wide spectrum, an exponential growth of the isolated quasi-two-dimensional mode occurs and its spectral maximum is shifted toward smaller wave numbers in comparison with the maximum of the helical mode of the instability of a nonstratified jet. The growth rate is proportional to Ri0.5, where Ri is the global Richardson number. The onset of the instability leads to the formation of the flow’s vortex structure, which consists of a collection of different-polarity quasi-two-dimensional vortices located in a horizontal plane near the longitudinal axis of the jet. At sufficiently long times (Nt > 100, where N is the buoyancy frequency and t is time), the growth of instability reaches the saturation stage and further fluctuations in velocity and density decay under the effect of viscous diffusion. At this stage, the flow becomes self-similar and the time dependences of the transverse and vertical widths of the jet are consistent with the asymptotic behaviors of integral parameters of the flow that are observed experimentally in the far stratified wake. The results suggest that the onset of the instability of a quasitwo-dimensional mode can play the determining role in the dynamics of flow in the far stratified wake. 相似文献
15.
The spectral analyses of moored current velocities in the central Luzon Strait reveal northward (i.e., downstream of the Kuroshio)
propagation of a frontal wave with a five-day period, with wave amplitude increasing northward. Estimated from both curve
fitting and frequency domain Empirical Orthogonal Function methods, the characteristics of five-day variations have wave speeds
ranging from 32 to 40 cm s−1, wavelengths ranging from 130 to 150 km, and e-folding time scales for growth ranging from 0.8 to 3 days. An analytical two-layer model used to explore linear stability
characteristics indicates that bottom topography (two meridional ridges) is important for the Kuroshio stability characteristics
in the Luzon Strait. In the two-layer model with the two ridges, the flow is stabilized for the long-wave mode but destabilized
for the short-wave mode (due to increasing vertical shear in the horizontal velocity). The analytical model produces wavelengths
and phase speeds for the most unstable mode which is similar to the observation, but the growth rate is underestimated. However,
a spectral numerical model applied with a more realistic stratification and velocity structure does obtain faster growth rates
comparable to the observations. Parameter sensitivity tests were conducted using the analytical model. The characteristics
of the most unstable mode are most sensitive to the surface front location relative to the bottom topography but not sensitive
to varying the density difference and thickness of the upper layer. 相似文献
16.
Ken Sasaki 《Journal of Oceanography》1971,27(4):137-141
The rotational instability of a thermally stratified, viscous, conducting, rotating fluid is investigated by means of linearized perturbation equations. It is assumed that the basic horizontal flow is vertically uniform and that the horizontal shear is confined in a thin layer. By solving a simplified boundary value problem as a model of rotational instability in the sea, we have shown that the vertical wave length of the neutral disturbance is of order 10 times as large as the laminar Ekman layer thickness, and that this scale is proportional to (L/N)1/3, whereL is the width of the shear layer andN is the Brunt-Vaisala frequency. 相似文献
17.
过氧化氢(H2O2)等活性氧(ROS)物质因具有绿色高效的特点,在废水处理、杀菌消毒等领域受到研究者广泛关注。利用电催化生成H2O2是一种实时提供活性氧物质的有用方法。然而,目前报道的大多数高性能催化材料都是粉体形式,不便于在实际场景中的应用。因此,制备可直接应用的电极材料显得尤为重要。本研究利用喷涂-热解的制备方法,制备了高活性氧催化活性的氧化炭黑(O−CB)/多孔碳毡电极,通过聚四氟乙烯(PTFE)的修饰优化电极表面的氧气传质,成功制备氧掺杂碳气体扩散电极。研究结果表明,O−CB/PTFE-5 wt%电极具有最高的催化性能,其合成H2O2的速率达27.19 mg·L-1(mg catalyst)-1·cm-1·h-1。海洋典型污损微生物假单胞菌(Pseudomonas sp.)的抗菌实验表明,该电极电催化作用60 min产生的活性氧对Pseudomonas sp.的杀菌率可达到97.69%,作用120 min的杀菌率可达到99.99%。 相似文献
18.
John E. Hughes Clarke 《Geo-Marine Letters》1990,10(2):69-79
Small volume (<15 km3) debris flows which were triggered by the 1929 earthquake postdate the period of high velocity turbidity current flow resulting
from that earthquake. They thus could not have contributed sediment to the 1929 cable-breaking turbidity currents.
Both the proposed “Grand Banks Slump” and another large scale debris flow also attributed to the 1929 event, are shown to
be autochthonous.
In light of the limited volume and late-stage timing of mass wasting on the upper Laurentian Fan in 1929, an additional mechanism
must have existed which supplied further sediment to the turbidity current in 1929. 相似文献
19.
Atsushi Kubokawa 《Journal of Oceanography》1986,42(5):373-380
Stability of a one-layer density-driven coastal current with a surface front whose potential vorticity is uniformly zero is examined, and it is shown that such a current can be unstable if the stability condition derived by Paldor (1983) is not satisfied,i.e., the current width,L, is larger than 2/3U/f, wheref is the Coriolis parameter andU is the current velocity at the front. This instability is caused by the coalescence of a frontal trapped and coastal trapped waves. The energetics of this instability and the effect of potential vorticity gradient are also discussed. 相似文献
20.
Concentration and stable isotopic compositions (δ
18O) of dissolved O2 were measured in seawater samples collected from the Philippine Sea in June 2006. The in-situ O2 consumption rate and the isotopic fractionation factor (α
r
) during dissolved O2 consumption were obtained from field observations by applying a vertical one-dimensional advection diffusion model to the
deep water mass of about 1000–4000 m. The average O2 consumption rate and α
r
were, respectively, 0.11 ± 0.07 μmol kg−1yr−1 and 0.990 ± 0.001. These estimated values agree well with values from earlier estimations of Pacific deep water. The in-situ O2 consumption rates are two or more times higher north of 20°N, although the value of α
r
was not significantly different between the north and south. Its levels varied rapidly in the water mass of less about 2000
m depth. These results suggest that organic matter from the continent imparts a meaningful contribution to the upper water
in the northern part of the area; it might produce the strong O2 minimum that is evident in the water mass from about 1000–2000 m in the northern part of the Philippine Sea. 相似文献