A subsurface intensity index of the cold eddy in the East China Sea

The Cold Eddy in the East China Sea(CEECS) is located about 150 km southwest of Cheju Island.This region experiences a complex current system under the influences of the Yellow Sea Warm Current(YSWC),the Yellow Sea Coastal Current(YSCC),and the northward Kuroshio residual.To identify the strength of the CEECS,a simple subsurface intensity index is developed.Because the CEECS can be traced by temperature minimum,the intensity index is determined by the difference in sea temperature averaged across cores within and surrounding the region.Based on SODA,the CEECS subsurface intensity index time series can be calculated,with which the inter-annual variation of the CEECS is analyzed.

Role of Kuroshio frontal eddy in exchange between shelf water and Kuroshio water in East China Sea

Basic patterns of the reversal of the Kuroshio water toward the shelf, intrusion of the shelf mixed water into 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.

Cold event at 5500 a BP recorded in mud sediments on the inner shelf of the East China Sea

A 700-year record （1.0-1.5 a resolution） of the East Asian winter monsoon （EAWM）, based on grain-size analysis and AMSI4C dating of Core EC2005 from the inner-shelf mud wedge of the East China Sea （ECS）, was compared with the Dongge stalagmite 8180 record during the mid-Holocene. The upper muddy section of Core EC2005 has been formed mainly by suspended sediments derived from the Changjiang （Yangtze） River mouth since 7.3 ka BP. High precipitation and a strengthened EAWM might have played key roles in the high sedimentation rate （1 324-1 986 crn/ka） between 5.9-5.2 ka BP. The EAWM strengthened when the Asian summer monsoon weakened, especially around 5 500 a BE which corresponded to a worldwide cold event. The EAWM during the mid-Holocene shows statistically significant solar periodicities at 62 and 11 a. The 5 500 a BP cold event might be resulted from orbital forcing and changes in solar activity.

Study on the growth of wind wave frequency spectra generated by cold waves in the northern East China Sea

The growth of frequency spectra and spectral parameters of wind waves generated by cold waves, a kind of severe weather system, in the northern East China Sea is studied in this paper. Based on a third-generation wave action model(the Simulating WAves Nearshore model), simulations were developed to analyze the spatiotemporal characteristics of wind waves and to output spectral data. It is shown that the cold wave-induced spectra can be well described by the modified Joint North Sea Wave Project spectral form. The growth of wave spectra is comprehensively reflected by the evolution of the three characteristic parameters: peak frequency, spectral peak and wave energy. Besides, the approximations of dependences between spectral parameters and the three types of universal induced factors are obtained with the least squares method and compared systematically. Fetch and peak frequency turn out to be suitable parameters to describe the spectral parameters, while the dependences on the inverse wave age vary in different sea areas. In general, the derived relationships improve on results from previous studies for better practical application of the wind wave frequency spectrum in the northern East China Sea.

The numerical simulation of the Kuroshio frontal eddies in the East China Sea using a hybrid coordinate ocean mode

A hybrid coordinate ocean model （ltYCOM） is used to simulate the Kuroshio frontal eddies in the East China Sea （ECS）. The research area is located （20°-32°N, 120°-132°E）. Using tile simulating data, it is figured out that the Kuroshio frontal eddies occur in summer as well as in the other season in this area. The life cycle of the Kuroshio and its frontal eddies is different with the position. The life-cycle of the Kuroshio frontal eddies of the northwest Diaoyu Islands is about 14 d; and the life cycle of the Kuroshio frontal eddies of southwest Yakushima about 20 d. This result extends the in situ researching results greatly. In addition, the vertical impact depth of the Kuroshio frontal eddies is also changing with the position. On the whole, in the ECS, the maximum impact depth of the Kuroshio frontal eddies of the northwest Taiwan Islands is about 75 m; the maximum impact depth of the Kuroshio frontal eddies of the northwest Diaoyu Islands is more than 125 m, but no more than 200 m; and the maximum impact depth of the Kuroshio frontal eddies of southwest Yakushima is up to 100 m.

Strengthening effect of super typhoon Rammasun(2014)on upwelling and cold eddies in the South China Sea

Typhoon is one of the frequent natural disasters in coastal regions of China.As shown in many studies,the impact of typhoons on the South China Sea(SCS)should not be overlooked.Super typhoon Rammasun(2014)was studied that formed in the northwestern Pacific,passed through the SCS,then landed in the Leizhou Peninsula.Remote sensing data and model products were used to analyze the spatiotemporal variations of the cold eddies,upwelling,sea surface temperature,mixed layer depth,rainfall,sea surface salinity,suspended sediment concentration,and surface-level anomaly.Results confirm the constant presence of upwelling and cold eddies in the southeast of Hainan(north of the Zhongsha Islands)and the southeast of Vietnam in July.In addition,we found the strengthening effect of super typhoon Rammasun on the upwelling and cold eddies in the SCS.The major reasons for the continuous decrease in sea surface temperature and the slow regaining of seawater temperature were the enhanced upwelling and vertical mixing caused by the typhoon.The increasing of the surface runoff in the Indochina Peninsula was mainly affected by the typhoon,with some contribution for the southeast of Vietnam’s cold eddy and upwelling.

Submesoscale eddies in the East China Sea detected from SAR images

Seven-year(2005-2011)Synthetic Aperture Radar(SAR)images are applied to study oceanic eddies in the East China Sea.It is found that most of these eddies detected from the SAR images are less than 10 km,which are submesoscale eddies.Seasonal differences are evident in the distribution of eddies,with the highest and the lowest number of eddies noted in summer and winter,respectively.Since slick streaks in SAR images look dark,an eddy identified due to the slicks is referred to as“black eddy”.As a result of wave-current interactions in the zones of current shear,it can be seen that an eddy exhibits a bright curve,the eddy is called“white eddy”.During the seven years,95 black eddies and 50 white eddies are identified in the study area.Black eddies are found in the whole study area while white eddies are mainly distributed in the vicinity of the Kuroshio Current.This study suggests that the distribution of the white eddy is denser around the Kuroshio because of the strong shear in the Kuroshio region.In terms of the eddy sizes,white eddies are generally smaller than black eddies.

Regional Characteristics of Typhoon-Induced Ocean Eddies in the East China Sea

The asymmetrical structure of typhoon-induced ocean eddies（TIOEs） in the East China Sea（including the Yellow Sea）and the accompanying air–sea interaction are studied using reanalysis products. Thirteen TIOEs are analyzed and divided into three groups with the k-prototype method： Group A with typhoons passing through the central Yellow Sea; Group B with typhoons re-entering the sea from the western Yellow Sea after landing on continental China; and Group C with typhoons occurring across the eastern Yellow Sea near to the Korean Peninsula. The study region is divided into three zones（Zones Ⅰ, Ⅱ and Ⅲ） according to water depth and the Kuroshio position. The TIOEs in Group A are the strongest and could reverse part of the Kuroshio stream, while TIOEs in the other two groups are easily deformed by topography. The strong currents of the TIOEs impact on the latent heat flux distribution and upward transport, which facilitates the typhoon development. The strong divergence within the TIOEs favors an upwelling-induced cooling. A typical TIOE analysis shows that the intensity of the upwelling of TIOEs is proportional to the water depth, but its magnitude is weaker than the upwelling induced by the topography. In Zones Ⅰ and Ⅱ, the vertical dimensions of TIOEs and their strong currents are much less than the water depths.In shallow water Zone Ⅲ, a reversed circulation appears in the lower layer. The strong currents can lead to a greater, faster,and deeper energy transfer downwards than at the center of TIOEs.

Numerical Simulation of Wintertime Mesoscale Eddies in the East China Sea

A POM based three dimension baroclinic prognostic model in σ coordinate was established to simulate the eddies in the East China Seas wintertime circulation, considering the topography, inflow and outflow on the open boundary, Changjiang runoff, heat, flux, and wind stress on the sea surface. The model results showed that three branches separate from the Kuroshio flow toward the interior of the Yellow Sea, and form three eddies respectively. The middle eddy is centered at 124°37′E,37°00′N,the southern eddy is centered at 124°00′E,35°30′N. The large cyclonic eddy centered at 125°06′E,30°30′N and located southwest of Cheju Island is a closed structure formed by the northeastward flowing Taiwan Warm Current, northwestward flowing Yellow Sea Warm Current and southward flowing coastal current. The Kuroshio intrusion engenders an eddy west of Kyushu Island of Japan. The branching of the Kuroshio is the direct dynamic cause of the formation of this large eddy. Moreover, both the topographic influence and the northward wind prevailing in winter affect the eddy’s formation obviously.

Holocene Temperature Records from the East China Sea Mud Area Southwest of the Cheju Island Reconstructed by theU_(37)~K~' and TEX_(86) Paleothermometers

As an important marginal sea under the influences of both the Changjiang River and the Kuroshio, the East China Sea （ECS） environment is sensitive to both continental and oceanic forcing. Paleoenvironmental records are essential for understanding the long-term environmental evolution of the ECS and adjacent areas. However, paleo-temperature records from the ECS shelf are currently very limited. In this study, the U^K_37 and TEX86 paleothermometers were used to reconstruct surface and subsurface temperature changes of the mud area southwest of the Cheju Island （Site F10B） in the ECS during the Holocene. The results indicate that temperature changes of F 10B during the early Holocene （11.6-6.2 kyr） are associated with global climate change. During the period of 6.2-2.5 kyr, the similar variability trends of smoothing average of AT （the difference between surface and subsurface temperature） of Site F10B and the strength of the Kuroshio suggest that the Kuroshio influence on the site started around 6.2kyr when the Kuroshio entered the Yellow Sea and continued to 2.5 kyr. During the late Holocene （2.5-1.45 kyr）, apparent decreases of U^K_37 sea surface temperature （SST） and AT imply that the direct influence of the Kuroshio was reduced while cold eddy induced by the Kuroshio gradually controlled hydrological conditions of this region around 2.5 kyr.

Thermal fronts and cross-frontal heat flux in the southern Huanghai Sea and the East China Sea

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.

The circulation in the southern Huanghai Sea and northern East China Sea in June 1999

On the basis of hydrographic data and current measurement (the mooring system, vessel-mounted ADCP and toward ADCP) data obtained in June 1999, the circulations in the southern Huanghai Sea (HS) and northern East China Sea (ECS) are computed by using the modified inverse method. The Kuroshio flows northeastward through eastern part of the investigated region and has the main core at Section PN, a northward flow at the easternmost part of Section PN, a weaker anti-cyclonic eddy between these two northward flows, and a weak cyclonic eddy at the western part of Section PN. The above current structure is one type of the current structures at Section PN in ECS. The net northward volume transport (VT) of the Kuroshio and the offshore branch of Taiwan Warm Current (TWCOB) through Section PN is about 26.2 x 10(6) m(3)/s in June 1999. The VT of the inshore branch of Taiwan Warm Current (TWCIB) through the investigated region is about 0.4 x 10(6) m(3)/s. The Taiwan Warm Current (TWC) has much effect on the currents over the continental shelf. The Huanghai Sea Coastal Current (HSCC) flows southeastward and enters into the northwestern part of investigated region, and flows to turn cyclonically, and then it flows northeastward, due to the influences of the Taiwan Warm Current and topography. There is a cyclonic eddy south of Cheju Island where the Huanghai Sea Coastal Current flows to turn cyclonically. It has the feature of high dense and cold water. The uniform and cold water is occurred in the layer from about 30 m level to the bottom between Stations C306 and C311 at the northernmost Section C3. It is a southern part of the Huanghai Sea Cold Water Mass (HSCWM).

Tide-Induced Mixing in the Bottom Boundary Layer in the Western East China Sea

The East China Sea(ECS)boasts a vast continental shelf,where strong tidal motions play an important role in the substance transport and energy budget.In this study,the tide-induced mixing in the bottom boundary layer in the western ECS is analyzed based on records measured by moored acoustic Doppler current profilers from June to October 2014.Results show that the M_(2) tide is strong and shows a barotropic feature,whereas the O_(1) tide is much weaker.Based on the M_(2) tidal currents,the eddy viscosity in the bottom Ekman boundary layer is estimated with three schemes.The estimated eddy viscosity values vary within 10^(-4)–10^(-2)m^(2) s^(−1),reaching a maximum at approximately 5 m height from the bottom and decreasing exponentially with the height at all three stations.Moreover,the shear production of turbulent kinetic energy is calculated to quantify the mixing induced by different tidal constituents.The results show that the shear production of the M_(2) tide is much stronger than that of the O_(1) tide and shows a bottom intensified feature.

南海北部冷涡增强混合的个例研究

海洋作为一个多尺度非线性系统,中尺度能量可以通过小尺度的湍流混合耗散,明晰中尺度涡对湍流混合的影响对于提高对跨尺度能量传递的认识和改进气候模式模拟具有重要作用。基于Thorpe-scale和细尺度参数化方法,利用2015年水下滑翔机在南海观测的水文数据对湍流混合空间结构进行重建与分析。结果表明,在冷涡边缘、冷暖涡交汇和暖涡区域出现混合增强现象,冷涡(暖涡)的扩散系数最高可达O(10^(-3) m^(2)/s)[O(10-4 m^(2)/s)],平均扩散系数约为9.0×10^(-5) m^(2)/s(6.2×10^(-5) m^(2)/s),是无涡状态下的4(2.8)倍。冷涡边缘、冷暖涡交汇处和暖涡区域出现理查森数小于0.25的海水水团,表明该处发生剪切不稳定有利于增强湍流混合。并且较小的理查森数大量出现在冷涡及冷暖涡交汇处,这也是冷涡处的扩散系数比暖涡处大的原因。

南黄海及东海北部夏季若干水文特征和环流的分析

利用“中韩黄海水循环动力学合作研究”1 997年 7月航次和“黄海综合环境调查”1 998年 8月航次观测所得的CTD资料 ,对南黄海及东海北部夏季的水文特征和特大洪水年长江冲淡水扩展特征进行探讨。同时还根据夏季所施放的卫星跟踪漂流浮标的轨迹、底层人工水母的漂移路径及等密面深度的分布对夏季环流作了阐述 ,提出夏季南黄海环流并非单一的气旋式系统 ,其内部还存在着气旋、反气旋的多个较小的环流 ;东海北部交替出现气旋、反气旋涡旋。

黄海和东海分界线附近水文、化学特征的季节性演替

分析和探讨了黄、东海交界海域32.3°N断面化学水文学精细化特征的季节性演替,结果显示:化学、水文学要素的空间区域化分布与该断面上环流场的布局及其季节转换存在良好的对应关系,水团配置对各要素含量及分布起着控制性作用;冬、春和秋季,在黄海西部沿岸流影响范围内出现的浊度和悬浮物浓度高值区多与营养盐浓度高值区和pH低值区相共存,可能是受东海北部气旋式涡旋所产生的辐聚效应的影响,此高值区中的悬浮物趋于向该海域的底层冷涡区沉积,夏季此特征则不明显,从而证实该海域悬浮物沉积作用具有"冬强夏弱"的特征;夏季123.5°—124.25°E范围海域内存在海水下沉现象,上层水体中的长江冲淡水可被携带至下层,导致在夏季长江冲淡水东北向扩展过程中一部分冲淡水从其主体中分离出来;夏季台湾暖流的阻隔作用使得悬浮物的影响范围远没有长江冲淡水的大,促使水体和物质输运发生分离。同时,根据水文和化学各要素分布之间的对应关系,初步勾勒出了32.3°N断面4季的水团配置状况,并通过分析东海北部冷水域典型站位的温、盐度垂直结构,在一定程度上印证了该冷水的形成过程。

台湾东北海域冷涡-上升流系统冬、夏季温度三维结构

利用美国国家海洋大气管理局(NOAA)2007年发布的全球海域温度多年月平均数据库资料(WOA 05),研发计算机数值分析和图形可视技术,对台湾东北海域冬、夏季的温度分布进行数值分析,展示台湾东北海域冷涡-上升流系统冬、夏季温度分布的三维结构,分析黑潮、台湾暖流以及东海陆架水的影响,得出以下结论。(1)夏季(8月)冷涡主要存在于13—100m深度以及138—150m深度;冬季(2月)冷涡主要存在于109—150m深度之间。(2)夏季(8月)上升流的拱形结构从表层向下都存在,其中由于台湾暖流与东海陆架底层水的影响,造成在深度100—138m之间的等温线不闭合;冬季(2月)上升流的拱形结构主要存在于100m水深以下。(3)在黑潮向西北方向入侵东海陆架的区域,冷涡-上升流系统消失。在冷涡-上升流系统作用的区域,黑潮向东北方向入侵东海陆架的程度越强,冷涡-上升流系统的势力也越强。

冬季东中国海环流中的中尺度涡旋数值模拟

采用高精度的POM模式 ,考虑了海底地形、外来流、长江径流、海面风应力、海面热通量等多方面因素的影响 ,模拟了冬季东中国海环流结构。模拟结果显示 :在黄海东部很可能存在两个涡 ,中心分别在124°37′E ,37°N ,124°E ,35°30′N ;东海北部存在一个大型的气旋式涡旋 ,其中心位置在125.1°E ,30.5°N附近 ,该涡旋是由东北向的台湾暖流、西北向的黄海暖流及南下的沿岸流组成的封闭结构 ;日本九州以西黑潮入侵分支形成一涡旋 ,黑潮分支是形成此涡旋的直接动力因素 ,另外地形和冬季盛行的偏北风也对该涡旋的形成有一定正面影响。

中国近海及其附近海域若干涡旋研究综述 Ⅰ.南海和台湾以东海域

综述了南海和台湾以东海域若干气旋型和反气旋型涡旋研究.在南海存在着许多活跃的中尺度涡,我们分别对南海中、南部海域和南海北部海域中尺度涡作了评述.在南海北部海域,目前最感兴趣的问题为:南海水与西菲律宾海通过吕宋海峡的交换的物理过程,以及黑潮是否以反气旋流套形式进入南海.这些问题目前尚不清楚,尤其是这些问题的机理.这些问题必须通过今后深入和细致的、长时间的海流和水文观测,以及长时间卫星遥感观测资料的论证才能逐渐认识清楚.台湾以东海域,黑潮两侧经常出现中尺度涡,而且变化较大而复杂.文中着重讨论兰屿冷涡和台湾东北的气旋式冷涡.

南海上层水温分布的季节特征

为对南海上层水温分布特征有一总体认识，利用气候平均的1°×1°网格的Levitus资料，分析了南海0－200m层共10个等深面上的季平均温度分布状况。结果表明，南海上层水温分布的季节变化明显，季风和太阳辐射对水温分布有显著影响，四季平均水温分布与平均环流状况对应较好。冬、春两季在吕宋岛西北海域有一冷涡（即吕宋冷涡），夏、秋季在越南沿岸出现另一冷涡（即越南冷涡）。这两个冷涡均对应着本海区尺度较小的气旋式环流和正的风应力旋度。吕宋冷涡还与黑潮在吕宋海峡的形变有关，越南冷涡则与局地强上升流有联系。