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1.
Thermal fronts and cross-frontal heat flux in the southern Huanghai Sea and the East China Sea 总被引：1，自引：0，他引：1
Synoptic features in/around thermal fronts and cross-frontal heat fluxes in the southern Huanghai./Yellow Sea and East China Sea （HES） were examined using the data collected from four airborne expendable bathythermograph surveys with horizontal approxmately 35 km and vertical 1 m（from the surface to 400 m deep） spacings. Since the fronts are strongly affected by HES current system, the synoptic thermal features in/around them represent the interaction of currents with surrounding water masses. These features can not be obtained from climatological data. The identified thermal features are listed as follows ： （ 1 ） multiple boundaries of cold water, asymmetric thermocline intrusion, locally-split front by homogeneous water of approxmately 18 ℃, and mergence of the front by the Taiwan Warm Current in/around summertime southern Cheju - Changjiang/Yangtze front and Tsushima front; （2） springtime frontal eddy-like feature around Tsushima front; （3） year-round cyclonic meandering and summertime temperature-inversion at the bottom of the surface mixed layer in Cheju - Tsushima front; and （4） multistructure of Kuroshio front. In the Kuroshio front the mean variance of vertical temperature gradient is an order of degree smaller than that in other HES fronts. The southern Cheju- Changjiang front and Cheju -Tsushima front are connected with each other in the summer with comparable cross-frontal temperature gradient. However, cross-frontal heat flux and lateral eddy diffusivity are stronger in the southern Cheju - Changjiang front. The cross-frontal heat exchange is the largest in the mixing zone between the modified Huanghai Sea bottom cold water and the Tsushima Warm Current, which is attributable to enhanced thermocline intrusions. 相似文献
2.
3.
横穿黑潮锋断面的流场结构 总被引：2，自引：0，他引：2
基于一组简化了的运动方程组，在充分考虑底Ekman层作用的情况下，提出一种横穿锋面的断面上流场结构的计算方法。应用该方法对东海横穿黑潮锋的不同断面上的流场（1989－1990年资料）进行计算。结果表明，黑潮锋左侧（向岸侧）存在较强的上升流，而锋区右侧（离岸侧）表现为海水的下降运动。垂直流速为（1－20）×10－3cm／s的量级，而横穿锋面方向的水平流速为1－3cm／s，其中以夏、秋季跃层附近最强。在陆架坡折处，上升流转向陆架。同时，还分析了正压场和斜压场对这种流场的不同贡献，认为在黑潮区，正压场起主要作用;而在内陆架区，斜压场则变得重要。将计算的流场与硝酸盐的分布比较表明，两者有较好的对应关系。 相似文献
4.
Role of Kuroshio frontal eddy in exchange between shelf water and Kuroshio water in East China Sea 总被引：4，自引：0，他引：4
Basic patterns of the reversal of the Kuroshio water toward the shelf, intrusion of the shelf mixed waterinto the Kuroshio and uplifting of the near-bottom nutrient-rich water into the upper layer by the pumping of the frontal eddy are analyzed on the basis of satellite infrared images and hydrologic, chemical and biological observations. Results show that the Kuroshio frontal eddies play a very important role in the exchange between the shelf water and the Kuroshio water. The estimation of the average volume transports for three frontal eddy events indicates that the shelf mixed water entrained by an eddy into Kuroshio is 0.44×10~6 m3/s and the reversal Kuroshio water onto the shelf region only 0.04×10~6 m3/s. Along the whole shelf edge, the volume transport of the shelf mixed water entrained by the eddies into the Kuroshio is 1.8×10~6 m3/s. The nutrient (NO3-N) flux pumped to the euphotic zone and input to the continental shelf through a column with 1 m wide is 974 μmol/(s·m) when there is frontal eddy and only 79 μmol/(s·m) in the case of no frontal eddy. Yearly nutrient (NO3-N) flux input to the shelf area caused by the frontal eddy is 1.7×10~5 t/a. 相似文献
5.
东海东北部春季若干重要水文结构的分析 总被引：7，自引：2，他引：7
本文主要基于韩国海洋研究所在东海沿岸海洋过程试验中收集的ＣＴＤ资料，分析了１９９５年春季出现在东海东北部的一些重要水文结构。结果表明，一种锋涡状结构出现在黑潮向东转折点附近。它不仅使邻近海域的水文结构变得更复杂，而且诱发黑潮水与陆架水间活跃的交换。在陆架坡折处观测到若干孤立的陆架水块，可能是锋涡的卷挟作用所致；该海域存在４个水团，即黑潮水、对马暖流水、陆架水和混合水。对马暖流水分为上下两层：上层水为变性黑潮水，盐度比黑潮水约低０．１，底层对马暖流水仅位于冲绳海槽区，并有着与黑潮中层水相同的温、盐特性；一种双锋结构出现在邻近黑潮的陆架边缘附近。在内陆架形成的陆架锋，由北向南伸展时，愈来愈偏向陆架边缘。而黑潮锋沿九州以西深槽的陆架边缘向北伸展。在黑潮转折点附近，两锋几乎合并为一条锋。狭窄的锋带由黑潮水及其变性水和陆架水的混合水所占据。 相似文献
6.
The temporal variation of tidal-front sharpness (i.e., the maximal gradient of sea surface temperature (SST)) in Iyo-Nada,
Japan has been investigated using SST obtained by a commercial ferryboat. Tidal-front sharpness varies in time with a period
of 15 days. A numerical model approach was also adopted to investigate the temporal variation of frontal sharpness. The numerical
model, which contains a restoring term to express the tidal front reconstructed fortnightly by tides, reproduces the tidal
front accompanied by growing and/or decaying frontal waves. The amplitude of modeled frontal sharpness agrees well with the
observation. The amplitude of sharpness is much smaller than the observed value, unless frontal waves develop along the modeled
front. This therefore implies that tidal fronts are destroyed mainly due to growing frontal waves, and are restored fortnightly
at spring tides. We quantitatively evaluated the subsurface intrusion of seawater into the stratified region from the mixed
region by conducting passive-tracer experiments. We find that the cross-frontal transport with frontal waves is 4.9 times
larger than that without frontal waves. In addition, the cross-frontal transport reaches a long distance (about 25 km) because
of heton (mushroom)-type eddies developing along the front with frontal waves. 相似文献
7.
本文利用现场观测资料和卫星遥感数据, 并结合ROMS(regional ocean modeling system)数值模拟对南海北部粤东陆架的锋面特征及其影响因素进行探讨。观测结果显示, 夏季南海北部陆架存在活跃的上升流温度锋面, 其水平尺度约为50km, 强度达到0.06℃∙km-1, 大于同时期卫星遥感观测结果, 垂向影响深度超过20m, 且具有一阶理查森数(Richardson number, Ri)的典型动力学特征。进一步的ROMS 模式诊断分析结果显示, 锋面处水平梯度增强, 且动力学上表现出一阶Ri数, 为锋面不稳定的发生提供了有利条件。高分辨率模拟结果显示, 在夏季西南风的驱动下, 沿锋面地转流方向的风应力引起的跨陆架Ekman输运将锋面处冷水向暖水运移, 导致水平浮力梯度和锋面强度增强并形成负Ertel位涡(Ertel potential vorticity, EPV)。因此, 夏季风场强迫引起的Ekman浮力通量(Ekman buoyancy flux, EBF)可能是南海北部锋面不稳定现象的主要贡献者, 对局地动力环境有重要影响。 相似文献
8.
涡旋对海洋中的能量传递和物质交换有重要作用。黑海西北部陆坡边缘是长生命周期涡旋经常发生的海域,但涡旋引起的陆架和海盆之间水交换通量的季节性特征,以及海盆边缘环流对跨陆架水交换的作用等方面的研究还不是很充分。本文对黑海西北部陆架区与深海盆区间的跨陆架水交换进行了研究,利用高分辨率三维原始方程模式模拟的温、盐、流等资料,结合涡旋自动探测方法,统计了黑海西北部海域的涡旋活动,研究了涡致跨陆架水交换的季节性特征,计算对比了2002年到2010年间海盆边缘环流与涡旋对跨陆架水交换通量的各自贡献。结果表明:黑海西北部地区海盆边缘环流强度与跨陆架进、出通量的相关系数分别为0.57和0.67,海盆边缘环流位置与跨陆架交换量的相关系数为0.52;海盆边缘环流强度与位置的季节性变化导致了黑海西北部跨陆架通量的季节性变化。黑海西北部地区表层3月到8月之间涡旋所引起跨陆架交换量约占了跨陆架交换总量的16%~31%;涡致跨陆架通量也具有季节性特征。文中对单个涡旋进行了详细研究:2005年5月5日到2005年7月20日之间在黑海西北部存在一个直径最大值时达到120 km的反气旋式涡旋,涡旋存在期间完成了从陆架区向深海区的水体传输,相当于黑海西北陆架区水体积的30.9%。 相似文献
9.
Michael S. Dinniman John M. Klinck Walker O. Smith Jr. 《Deep Sea Research Part II: Topical Studies in Oceanography》2003,50(22-26):3103
Transport of warm, nutrient-rich Circumpolar Deep Water (CDW) onto Antarctic continental shelves and coastal seas has important effects on physical and biological processes. The present study investigates the locations of this transport and its dynamics in the Ross Sea with a high-resolution three-dimensional numerical model. The model circulation is forced by daily wind stress along with heat and salt fluxes calculated from atmospheric climatologies by bulk formulae. All surface fluxes are modified by an imposed climatological ice cover. Waters under the Ross Ice Shelf are not included explicitly, but their effect on temperature and salinity is imposed in a buffer zone at the southern end of the model domain. A simple nutrient uptake is calculated based on the climatological chlorophyll distribution and Monod uptake kinetics.Model circulation is strongly affected by bottom topography, due to weak stratification, and agrees with schematics of the general flow and long-term current measurements except near the southern boundary. The sea-surface temperature is similar to satellite estimates except that the warmest simulated temperatures are slightly higher than observations. There is a significant correlation between the curvature of the shelf break and the transport across the shelf break. A momentum term balance shows that momentum advection helps to force flow across the shelf break in specific locations due to the curvature of the bathymetry (that is, the isobaths curve in front of the flow). For the model to create a strong intrusion of CDW onto the shelf, it appears two mechanisms are necessary. First, CDW is driven onto the shelf at least partially due to momentum advection and the curvature of the shelf break; then, the general circulation on the shelf takes the CDW into the interior. 相似文献
10.
The generation and propagation mechanisms of a Kyucho and a bottom intrusion in the Bungo Channel, Japan, have been studied
numerically using the hydrostatic primitive equations by assuming density stratification during summer. The experiments are
designed to generate a Kuroshio small meander in Hyuga-Nada, which acts as a trigger for these disturbances. After the current
speed of the Kuroshio is changed, a small meander is generated. At the head of the small meander, warm Kuroshio water is engulfed,
and encounters the southwest coast of Shikoku. However, convergence of heat flux on the bump off Cape Ashizuri suppresses
the generation of a warm disturbance, if the current speed is large. As the cold eddy associated with the small meander approaches
Cape Ashizuri, the heat flux diverges on the bump. This heat source forces a warm disturbance, which intrudes along the east
coast of the Bungo Channel as a baroclinic Kelvin wave (a Kyucho). After the cold eddy passes off Cape Ashizuri, the Kuroshio
approaches the bump again. Strong convergence of heat flux then occurs on the bump, which forces a cold disturbance. This
disturbance propagates as a topographic Rossby wave along the shelf break at the mouth of the channel. After the topographic
wave reaches the west end of the shelf break, it intrudes along the bottom layer of the channel as a density current (a bottom
intrusion). These results suggest that a Kyucho and a bottom intrusion are successive events associated with the propagation
of the small meander. 相似文献
11.
Intrusion of less saline shelf water into the Kuroshio subsurface layer in the East China Sea 总被引：7，自引：0，他引：7
The possible origin and cause of the less saline shelf water detected in the Kuroshio subsurface layer around the shelf edge
of the East China Sea are investigated using observational results obtained in May 1998–2001 in conjunction with a dataset
archived by Japan Oceanographic Data Center and a numerical model. The observations show that subsurface intrusions of less
saline water are always detected in May in layers above 24.5σθ isopycnal surface, and that salinity inversions (i.e., areas
in which the less saline water lies beneath the saline water) are detected around the trough of the Kuroshio frontal eddy
(or wave). Analyses of the archived dataset reveal that the isopycnal surface of 24.5σθ is the deepest layer of the Kuroshio
pycnocline outcropping to the sea surface on the shallow shelf in early spring. Outcropping isopycnals above 24.5σθ encounter
a less saline water plume originating from the Changjiang, especially in the western East China Sea. Thereafter, the less
saline water moves along isopycnal layers and reaches the Kuroshio front around the shelf edge. Numerical models demonstrate
that, when the frontal wave captures the less saline water, the shelf water takes the form of a salinity inversion in the
trough because isohalines in the frontal wave have a phase lag between the upper and lower layers in consequence of the baroclinic
instability. 相似文献
12.
Through a simple analytical model, we examine the shear dispersion associated with oscillatory winds in an unstratified coastal ocean. As noted previously in the tidal regime, the vertical-integrated (total) horizontal diffusivity has a maximum where the water depth equals the diffusive depth – defined as the reach of the vertical diffusion during one forcing cycle. Due principally to the long synoptic timescale that characterizes the wind forcing, this depth lies over the outer shelf. When combined with effective mixing of the slope water by meso-scale eddies, the total diffusivity exhibits a minimum around the shelf break, thus facilitating frontogenesis. Due again to the long forcing period, the bottom Ekman flow is well developed at the diffusive depth, which would accentuate the gradient enhancement of the front over the inshore water, which however is bounded above by doubling.Calculations from a primitive-equation numerical model are carried out for both unstratified and stratified oceans. From an initially uniform property gradient, a front is seen to emerge around the shelf break after an oscillating wind is switched on, in a visual demonstration of the proposed frontogenesis. The unstratified solution closely agrees with the analytical solution, and although the front is not particularly sharp, it is comparable to that observed. The stratified solution renders a more realistic simulation of the observed front, but it retains the basic features, suggesting the dominance of the proposed mechanism even in the presence of the cross-frontal circulation. 相似文献
13.
南海西部风驱离岸急流次中尺度锋面的动力学分析 总被引：1，自引：0，他引：1
本文利用卫星观测资料和500 m分辨率数值模拟结果，结合理论分析，对南海西部夏季风场驱动的离岸急流海域次中尺度锋面及其不稳定对背景流场的动力学影响进行了研究。卫星观测和模拟结果表明，南海西部（WSCS）存在侧向尺度为O（1-10）km的次中尺度锋面，在地转和非地转运动的共同作用下，次中尺度密度锋面具有一阶Rossby（Ro）和Richardson（Ri）数。锋面诊断结果显示，沿锋面急流方向的风场强迫引起了显著的跨锋面Ekman净输送，有效地在跨锋面方向将表层冷水平流输送至暖水侧，导致海表浮力损失。减弱的垂向层结和增强的水平浮力梯度使得锋面海域出现负Ertel位涡（PV），表明该密度锋面易受次中尺度对称不稳定（SI）的影响。次中尺度锋面不稳定引起的跨锋面次级环流能够显著增强垂向速度，其最大值可达100 m·d-1。能量评估结果表明，次中尺度湍流的两个主要能量源，即地转剪切项（GSP）和垂向浮力通量（BFLUX）在锋面海域显著增强表明在沿锋面急流方向的风场强迫作用下，大尺度地转流的地转剪切动能和锋面有效位能能有效地通过锋面不稳定向次中尺度过程传递。因此，次中尺度锋面及其不稳定有助于增强局地垂向交换和正向串级地转能量，可以为夏季WSCS高叶绿素浓度的相干结构和锋面地转能量的正向传递提供新的动力解释。 相似文献
14.
地形斜坡对东海黑潮陆架坡折锋稳定性影响研究 总被引：1，自引：1，他引：0
为了研究地形斜坡对东海黑潮陆架坡折锋稳定性的影响,利用简化的线性原始方程,在一定背景流的情况下,主要从增长率、相速度、空间结构和能量方面分析海底地形斜坡变化对坡折锋稳定性的影响。模式结果表明,平底地形时,扰动的强度大且扰动区域广,但有地形斜坡时,扰动区域变窄,强度变弱,地形对坡折锋起稳定性作用。通过能量分析得出东海黑潮陆架坡折锋是正压和斜压的混合不稳定,其中斜压不稳定占主导地位。实验分析得出,地形对东海黑潮陆架坡折锋起稳定作用,斜坡增大,斜压不稳定和正压不稳定均减弱,斜压不稳定减弱更明显。 相似文献
15.
作为中尺度过程与小尺度过程中的过渡,次中尺度过程[空间尺度为O(1～10)km,时间尺度为O(1)天]是海洋动力过程中重要的一环。海洋次中尺度过程具有明显的非地转特征,从而促进垂向热量和物质的输运,因此在海洋上层热量与物质垂直交换中肩负着极为重要的作用。黑潮作为全球最强的西边界流之一,是海洋能量的重要聚集区。针对黑潮流区大尺度环流和中尺度涡旋等动力过程的研究,受到海洋和气象学者的广泛关注,但对黑潮流区次中尺度过程的相关研究相对较少。本文基于高分辨率ROMS数值模式(空间分辨率为1公里),针对黑潮流区(25.5°～29.4°N, 124.4°～131°E)次中尺度过程的空间分布特征及其诱导的热量输运特征进行了研究。模拟结果表明,黑潮流区存在着十分活跃的次中尺度过程,尤其是在黑潮流区及岛屿周边等地形变化剧烈的海区。相对涡度和垂直流速的分布特征表明,次中尺度相对涡度和垂向流速上表现出了明显的不对称性,正相对涡度强于负相对涡度,向下垂向流速强于向上垂向流速,而这主要是由惯性不稳定所导致。通过计算次中尺度引起的热量输运,结果表明次中尺度的水平热量通量为东北方向,从较低纬度朝较高纬度输运,这意味着次中尺度可以促进不同纬度的热量交换;而垂向热量通量则表现出向上输运的特征,即由深层往表层输运,这意味着次中尺度过程可以导致热量在垂直方向上的再分配,从而使得海洋趋于再分层。 相似文献
16.
17.
《African Journal of Marine Science》2013,35(1):35-49
Mesoscale circulation features have been shown to play an important role in the cross-frontal mixing of upwelling cells, their frontal morphology and in their interaction with oceanic water masses. With three years of detailed thermal infra-red satellite information on the South-East Atlantic upwelling system available, it proved possible to present a preliminary study of four prevalent frontal features intrinsic to the short-term behaviour of upwelling in this area. Upwelling filaments are shown to extend between 50 and 600 km seawards of the main front and are found, as are upwelling plumes, predominantly off the recognized major upwelling cells. Frontal eddies have a range of diameters and are found distributed over the full area of upwelling and on both sides of the main upwelling front. Warm filaments of Agulhas Current origin are advected preferentially along the western border of the Agulhas Bank and follow closely the front of the southernmost upwelling cells, where they may play a catalytic role in the creation of frontal turbulence. 相似文献
18.
Kazunori Akitomo 《Journal of Oceanography》1988,44(4):171-188
We numerically investigated the physical process of water exchange caused by fluctuations of the front. This front is formed
in a vertically two-dimensional NH-model (non-hydrostatic model) under steady forcing and simulates well the front observed
during winter in the Kii Channel, Japan. The velocity field in the model has two kinds of oscillations. The first has a period
of 6∼12 hr and is caused by intermittent gravitational convection in the frontal zone. The period and the intensity of intermittent
convection are determined by buoyancy flux through the side boundaries as well as surface cooling. The other is associated
with large scale circulation driven at the side boundaries and is controlled by the Coriolis force and the bottom stress.
Its period of 3∼4 days is determined by the sum of the inertial period and the spin down time for the baroclinic mode of the
along-front velocity component. These oscillations make the position of the front fluctuate with the same periods.
We next examined water exchange across the fluctuating front by numerically tracking a number of labelled particles. Intermittent
convection induces exchange of particles in the frontal zone and large scale circulations transport the exchanged particles
toward offshore or onshore through the lower layer. The exchange rate and the dispersion coefficient are calculated in the
NH-model as 0.85 and 2.3×103 cm2 sec−1, respectively. On the other hand, in the H-model (hydrostatic model) parameterizing gravitational convections with a convective
adjustment method, these values are reduced to 0.68 and 3.2×102 cm2 sec−1, respectively. This result implies that intermittent convections in the frontal zone have a large effect on water exchange
across the front, and that no little water is exchanged across the fluctuating front in an actual shallow sea, such as observed
in the Kii Channel. 相似文献
19.
A two-dimensional numerical model is constructed to study the interaction between the coastal upwelling and the coastal front off Zhejiang coast in summer. In the f-plane model, the shelf topography, continuous stratification, and Richardson number-dependent eddy coefficients are considered. The results show that the coastal up-welling off Zhejiang in summer can be divided into two regions, the nearshore one (Region A) and the offshore one (Region B). In Region A, the alongshore wind stress has more important effect on the coastal upwelling while in Region B, the upwelling is mainly induced by the Taiwan Warm Current. The results also suggest that the formation of coastal front off Zhejiang in summer is closely related to the strength of the coastal upwelling in Region A. 相似文献
20.
Mikhail V. Flint Irina N. Sukhanova Alexander I. Kopylov Sergei G. Poyarkov Terry E. Whitledge 《Deep Sea Research Part II: Topical Studies in Oceanography》2002,49(26)
We studied the effect of four types of fronts, the coastal front, the middle front, the shelf partition front and the shelf break front on the quantitative distribution and the composition of plankton communities in the Pribilof area of the eastern Bering Sea shelf in late spring and summer of 1993 and 1994. The coastal fronts near St. Paul and St. George Islands and the coastal domains encircled by the fronts featured specific taxonomic composition of planktonic algae, high abundance and production of phytoplankton, as well as large numbers of heterotrophic nanoplankton. The coastal fronts also were characterized by high values of total mesozooplankton biomass, high concentrations of Calanus marshallae, as well as relatively high abundances of Parasagitta setosa and Euphausiacea compared to surrounding shelf waters. We hypothesize that wind-induced erosion of a weak thermocline in the inner part of the coastal front as well as transfrontal water exchange in subthermocline layers result in nutrient enrichment of the euphotic layer in the coastal fronts and coastal domains in summer time. This leads to prolonged high primary production and high phytoplankton biomass. In this paper a new type of front—the shelf partition front located 45–55 km to the north-east off St. Paul Island—is described, which is assumed to be formed by the flux of oceanic domain waters onto the shelf. This front features a high abundance of phytoplankton and a high level of primary production compared to the adjacent middle shelf. Near the southwestern periphery of the front a mesozooplankton peak occurred, composed of C. marshallae, with biomass in the subthermocline layer, reaching values typical for the shelf break front and the highest for the area. High abundance of phyto- and zooplankton as well as heterotrophic nanoplankton and elevated primary production were most often observed in the area adjacent to the shelf break front at its oceanic side. The phyto- and mesozooplankton peaks here were formed by oceanic community species. The summer levels of phytoplankton numbers, biomass and primary production in the shelf break frontal area were similar to those reported for the outer and middle shelf during the spring bloom and the coastal domains and coastal fronts in summer. In the environment with a narrow shelf to the south of St. George Island, the mesozooplankton peak was observed at the inner side of the shelf break front as close as 20 km from the island shore and was comprised of a “mixed” community of shelf and oceanic species. The biomass in the peak reached the highest values for the Pribilof area at 2.5 g mean wet weight m−3 in the 0–100 m layer. Details of the taxonomic composition and the numbers and production of phytoplankton hint at the similarity of processes that affect the phytoplankton summer community in the coastal domains of the islands, at the coastal fronts, and at the oceanic side of the shelf break front. The middle front was the only one that had no effect on plankton composition or its quantitative characteristics in June and July. Location of a variety of frontal productive areas within 100 km of the Pribilof Islands creates favorable foraging habitat for higher trophic level organisms, including sea birds and marine mammals, populating the islands. 相似文献