2011年夏季台湾海峡上升流的变化特征及其与风场的关系

根据2011年6月27日至7月4日台湾海峡航次的调查资料,结合6月1日至8月31日海表温度和风场的卫星遥感数据,分析了平潭附近海域、澎湖北部海域、东山附近海域、台湾浅滩东南部海域上升流的变化特征及其与风场的关系.以海表温度差值(SSTd)来反映上升流强度,该值负值越大,上升流强度越强,分析可知:在2011年夏季,平潭附近海域上升流的强度除了7月中、下旬和8月底外,其余时段较为稳定.SSTd值与局地沿岸风速存在滞后3 d左右的相关关系,特别是稳定持续的西南风对其强度有较大的影响.澎湖北部海域上升流的SSTd值在-1℃左右,强度相对较小,且6、7月比8月时强盛,局地风场对澎湖北部海域上升流有一定的影响,但不是主要影响因素,而是由地形和风共同作用.东山附近海域上升流的强度并不稳定,在6、7月变化较剧烈,到8月SSTd值稳定在-3℃左右,SSTd值的变化对于局地沿岸风的响应同样存在一个3 d左右的滞后时间,除此之外还与上升流中心的水平变动有关.而台湾浅滩东南部海域上升流虽有波动,但持续存在,且6、7月比8月时强盛,其变化与局地风场的关系不大,主要受海流和地形等其他因素的影响.     

琼东上升流的年际变化及长期变化趋势

全球变暖背景下沿岸上升流的年际变化是近年来的研究热点。本文基于1982—2012年的海表面温度和风场资料,分析了琼东上升流的强度和中心位置的年际变化规律以及沿岸风应力及其旋度的作用。结果显示,近30年来,琼东上升流强度总体减弱,相比于沿岸风应力,其变化与减弱的局地风应力旋度相关性更高;琼东上升流强中心位置最大概率发生在19.2°—19.3°N,与最大风应力旋度位置接近,且存在北移趋势。琼东上升流强度和位置的年际变化还存在周期约3年、5年和10年的本征模态,以3年周期变化为主。局地风应力旋度在琼东上升流的年际变化中发挥了重要作用。     

2006年夏季琼东、粤西沿岸上升流研究

利用2006年夏季广东、海南、广西近海的海洋水文调查资料和卫星遥感QuikSCAT风场资料分析琼东、粤西沿岸上升流的空间结构特征, 探讨风场、风应力旋度对上升流的影响以及上升流区水温、海流、海平面对上升流的响应。结果表明:琼东、粤西沿岸上升流区并非相互独立, 从10 m层以下已经连成一片。琼东沿岸上升流主要由夏季西南季风驱动而产生, 风应力旋度也有一定贡献。琼东沿岸上升流的强度比粤西强。琼东沿岸海域的上层海水(18 m以浅)以离岸运动为主, 中下层海水以向岸运动为主。上层的离岸流速大于中下层的向岸流速。琼东沿岸的上升流现象是间歇性的, 与沿岸风速强弱有关。琼东沿岸海域海平面的升降与上升流的强弱有良好的关系, 上升流的强弱滞后于海平面的升降约1～2 d。     

东山岛外海表层水温的亚潮频波动初步研究

本研究通过对东山岛外海浮标观测的表层水温(SST)数据进行分析,发现2016、2017年夏季东山岛外海表层水温均存在周期为5~8 d的亚潮频波动信号,最大振幅分别为3.1 ℃和2.1 ℃。结合卫星遥感SST数据以及风场数据,采用小波分析、交叉小波分析等方法对该现象进行研究分析,结果表明：2016年夏季表层水温中出现的亚潮频波动信号源自短波辐射,表层水温变化滞后短波辐射1天左右;2017年夏季的亚潮频波动源自沿岸风应力,表层水温变化滞后沿岸风应力2天左右。2016年和2017年表层水温出现的亚潮频波动均与台风有关,但信号的来源出现差异是因为2017年台风过境引起了较强的沿岸风松弛现象,在沿岸风中出现了亚潮频波动信号,沿岸风影响上升流变化,进而引起表层水温的变化;2016年由于台风过境引起的沿岸风松弛现象较弱,沿岸风中并未出现亚潮频波动信号,而表层水温中的亚潮频波动信号源自短波辐射,这可能与台风引起局地天气系统的变化有关。     

东海沿岸海区垂直环流及其温盐结构动力过程研究Ⅰ.环流的基本特征

利用三维斜压流体动力学模型,通过对东海沿岸海区冬、夏季的斜压环流及其温盐结构的数值研究,揭示研究海区垂直环流及其温盐结构的动力过程及其成因。垂直环流的模拟结果表明：冬季,沿岸海区的垂直环流以逆时针流动,近表层为向岸流,沿岸为下降流,近表层以下为离岸流,其在外海有明显的上升趋势,沿岸下降流自表层至底层逐渐由强变弱;夏季,沿岸海区的垂直环流以顺时针流动,近表层以下为向岸流,沿岸为上升流,近表层为离岸流,其在外海有明显的下降趋势,沿岸上升流自底层至表层逐渐由弱变强。就整个沿岸海区而论,冬季沿岸下降流和夏季沿岸上升流的强度都随着岸界地形坡度、风速及风向与岸线偏角的变化而变化。沿岸下降流形成的主要原因是由于冬季东北风与岸界地形的耦合效应及海区温盐分布不均匀所致,而沿岸上升流形成的主要原因则是由于夏季西南风与岸界地形的耦合效应及海区温盐分布不均匀所致。     

东海沿岸海区垂直环流及其温盐结构动力过程研究I．环流的基本特征

利用三维斜压流体动力学模型 ,通过对东海沿岸海区冬、夏季的斜压环流及其温盐结构的数值研究 ,揭示研究海区垂直环流及其温盐结构的动力过程及其成因。垂直环流的模拟结果表明 :冬季 ,沿岸海区的垂直环流以逆时针流动 ,近表层为向岸流 ,沿岸为下降流 ,近表层以下为离岸流 ,其在外海有明显的上升趋势 ,沿岸下降流自表层至底层逐渐由强变弱 ;夏季 ,沿岸海区的垂直环流以顺时针流动 ,近表层以下为向岸流 ,沿岸为上升流 ,近表层为离岸流 ,其在外海有明显的下降趋势 ,沿岸上升流自底层至表层逐渐由弱变强。就整个沿岸海区而论 ,冬季沿岸下降流和夏季沿岸上升流的强度都随着岸界地形坡度、风速及风向与岸线偏角的变化而变化。沿岸下降流形成的主要原因是由于冬季东北风与岸界地形的耦合效应及海区温盐分布不均匀所致 ,而沿岸上升流形成的主要原因则是由于夏季西南风与岸界地形的耦合效应及海区温盐分布不均匀所致。     

ENSO发展期琼东上升流的动力过程响应差异

上升流是海洋中最重要的海洋现象之一,通过ROMS数值模型模拟并研究了2000—2013年间琼东上升流对ENSO信号(2002和2009年作为典型El Nio年; 2008和2010年作为典型La Nia年)的响应。结果表明,琼东上升流对ENSO气候事件有明显的响应。在El Nio信号较强时琼东上升流减弱,近岸海域水温升高;而在La Nia信号较强时琼东上升流加强,沿岸海域水温降低。对海面风场以及琼东海域沿岸流的分析表明,ENSO信号通过局地海面风场以及沿岸流对琼东上升流产生影响,并且风和沿岸流对琼东上升流的影响是协同的,在El Nio期间均不利于上升流的发展,而在La Nia期间二者的变化均有助于上升流的强化。     

鲁海丰海洋牧场流场特征分析

根据海底有缆观测系统连续观测得到的3个半月的海水流矢量资料,利用功率谱分析、调和分析、旋转谱分析和相关分析等方法研究了鲁海丰海洋牧场海域海流的时间变化规律和空间结构特征。主要结论如下:在整个水体厚度上,西北向流占优,呈现出向岸流的特点,且由表及底,西向流减弱,北向流增强;潮流类型为正规半日潮,M2分潮流为主,各层主要分潮流均表现为以逆时针方向旋转为主的往复运动,总体上观测点的日周期波动只由全日潮流引起,不受当地惯性流影响。此外观测点处的流还表现出更高频的波动周期;鲁海丰海洋牧场的表层余流主要由海面风场驱动,同时也受到山东半岛沿岸流的影响。     

粤东至闽南沿岸海域夏季上升流的调查研究

利用2001、2002、2006和2009年夏季6个航次的温盐深(conductivity-temperature-depth,CTD)调查资料,揭示粤东至闽南沿岸海域上升流空间结构和强度的年际差异;并利用卫星遥感风场资料、海床基的海流和底层水温资料、广东南澳海洋站表层水温资料探讨海面风场、热带气旋对上升流的影响,上升流强度的时空特征,上升流的短期变化、生消过程及上升流的水体来源。结果表明,粤东至闽南沿岸海域上升流的范围和强度存在年际差异。上升流涌升至表层只出现在2009年7~8月航次。闽粤交界区沿岸海域,2006年7~8月航次,上升流范围较窄,且偏东北;2009年7~8月航次,范围较宽;2001年7~8月航次,范围偏西南。粤东沿岸海域,2006年7~8月航次上升流涌升高度较低,其他航次较高。研究海域2002年7~8月航次上升流强度较强,其他航次较弱。热带气旋使得上升流区海水垂向混合强烈,中下层冷水与表层暖水混合后迅速升温,上升流被破坏。粤东沿岸海域上升流强度强于闽南沿岸,出现时间也早于闽南沿岸。7月初至7月中旬,上升流开始形成,但不稳定;7月中旬至8月上旬,上升流处于强盛阶段;8月中旬至9月上旬,上升流减弱;9月上旬至9月中旬,上升流迅速消亡。粤东至闽南沿岸海域上升流的水体来源于粤东沿岸外海深层冷水。     

冬季黄、东海中国沿岸水位的低频波动

本文选用黄、东海中国沿岸9个水位站的水位、气压、风速资料分析冬季水位变化的基本特征,结果表明黄海及东海北部沿岸水位的变化主要与NNW-SSE向的风有关,该方向大体同黄海海槽的伸展方向一致;东海南部沿岸水位的低频变化同E-W向风有关,这一方向同该海域的岸线约有60°的交角。水位低频波动的主要周期是2,3和5天左右,东海还有6—7天的波动。水位变化的振幅为北部大、南部小,西海岸大、东海岸及岛链地区小。水位波动自北向南传播,其波速在黄海北部沿岸约为18—20km/h,东海北部沿岸逐渐增至30—40km/h。东海南部的低频波速几乎是频率的线性函数。水位对风的响应时间尺度约13—28小时,自北向南逐步增加。中国沿岸还存在周期约为2,3和5天的自由波动向南传播,其波速约为30—60km/h。     

A study of cross-shore maximum upwelling intensity along the Northwest Africa coast

Satellite images of sea surface temperature (SST) show that the location of cross-shore SST minimum (LCSM) stretches along the isobaths in the Northwest Africa Upwelling System. To understand and interpret these observations better, we set up a two-dimensional analytical model that takes into account the surface and bottom Ekman transport and the alongshore geostrophic current, as well as bottom friction and variations in bottom topography. The structure of vertical velocity with a realistic topography clearly illustrates the variations of SST drop in a sample cross-shore section. Some idealized theoretical model experiments are carried out to examine the effects of eddy viscosity, Coriolis force, and cross-shore wind on the location of the cross-shore maximum upwelling intensity. The results show that the cross-shore wind largely impacts on the location where the coldest water outcrops to the surface through an adjustment of the cross-shore pressure gradient. This is also verified by the remotely sensed data, which indicate that the maximum correlation coefficient between cross-shore wind stress and the depth of LCSM is ?0.65 with a lag of approximately 1 day.     

黑潮近岸分支流在2017年9月与2019年9月差异的研究

通过对比2017年9月和2019年9月的温盐大面观测数据,发现东海陆架上黑潮近岸分支流的路径在两次观测中存在显著差异.2019年9月黑潮近岸分支流中上游的路径相较2017年9月明显的东向偏移,造成黑潮次表层水入侵东海近岸海域的强度较弱.为了探究黑潮近岸分支流的上述显著年际差异的原因,利用卫星高度计数据和再分析风场数据,...     

风对福建中部沿岸春、夏季水文结构和上升流的影响

本文对台湾海峡西侧海坛岛附近海域风情与附近岸站的风情进行了对比分析,结果表明,海上风情和岸站风情变化基本上是一致的;在不同季风的作用下,海域温、盐度呈现不同类型的分布。风情的短期变化对上升流的强弱变化有一定影响。     

Coastal upwelling in the Gelendzhik area of the Black Sea: Effect of wind and dynamics

Long series data of a thermistor chain in the Black Sea coastal zone near Gelendzhik were analyzed. A thermistor chain installed 1 km offshore and at a depth of 22 m. There are full and incomplete upwelling events observed. The study of upwelling genesis based on: wind speed data from the NCEP/CFSR reanalysis and Gelendzhik weather station, velocity and direction of coastal currents measured by ADCP profiler moored on the bottom near the thermistor chain. Over the whole observation period (warm seasons of 2013–2015), more than 40 events of upwelling were registered four of them were full upwellings, when presence of under-thermocline water was observed near the sea surface. For every upwelling event, conditions prior to the changes in thermic structure, were analyzed. It is found that full upwelling generally occur under synergistic wind and current forcing. Fairly strong forcing of one of these factors is sufficient for partial upwelling to occur.     

Internal wave band kinetic energy production: flat vs. sloping bottom

Velocity and temperature measurements obtained with acoustic Doppler current profilers and thermistor strings are used to evaluate the production of internal wave band kinetic energy mainly in the frequency band σ>15 cpd. Results from a flat 19 m deep, vigorous tidal environment in a shelf sea are compared with energy production in a bottom boundary layer above a continental slope. In the tidal environment, maximum production occurs in the near-bottom and near-surface layers. A distinct mid-depth maximum in KE production occurs during a period when wind speeds exceed 10 m s⁻¹ and significant wave height ∼2 m. At the same time, no significant changes in the along-shore current speed take place but the cross-shore current, generated by strong stratification, is weakened. This suggests a direct energy input from the wind via surface waves into the water column turbulence. Maximum kinetic energy production in the frequency band σ>1.9 cpd, thus including the semidiurnal tide, occurs at mid-depth when strong stratification is present. The overall magnitude of internal wave band kinetic energy production agrees well with independent dissipation estimates obtained from microstructure profilers. Above the sloping bottom, KE production is somewhat larger than observed in the shallow tidal environment, despite rms currents being ∼50% smaller and wind effects being small. Above the sloping bottom KE shear production was comparable to buoyancy production. The latter was negligible at the shelf sea site.     

Sea Level Variations Associated with Upwelling/ Downwelling Along the West Coast of India

A three-dimensional numerical model is developed and used to study the coastal upwelling processes and corresponding seasonal changes in the sea level along the west coast of India. The upwelling and associated sea level variations are seen as a response of coastal ocean to pure wind stress forcing. The model is designed to represent coastal ocean physics by resolving surface and bottom Ekman layers as realistically as possible. The prognostic variables are the three components of the velocity field, temperature, salinity and turbulent energy. The governing equations together with their boundary conditions are solved by finite-difference techniques. Experiments are performed to investigate sea level fluctuations associated with the thermal response and alongshore currents of the coastal waters. The model is forced with mean monthly wind stress forcing of January, May, July and September representing northeast monsoon and different phases of the southwest monsoon. It is known from the observational study that the upwelling process reaches to the surface waters by May along the coastal waters of the extreme southwest peninsular region. The process is more intense in July compared to May and September and its strength decreases from south to north. However, during the northeast monsoon season, which is represented by January wind stress forcing in the model, downwelling is simulated along the coast. The model simulations of the coastal response are compared with the observations and are found to be in good agreement. The maximum computed vertical velocity of about 2.0 ×10 -3 cm s -1 is predicted in July in the southern region off the coast.     

Cross-shore separation of adult and juvenile euphausiids in a shelf-break alongshore current

Euphausiids are an important component of the zooplankton in boundary current upwelling regions, including the Pacific Northwest continental margin. Many aspects of euphausiid distribution and ecology in this region are well known. However, some features of their spatial and temporal distribution are less understood:

• How and why euphausiids aggregate near the shelf-break upwelling center.

• How and why there is (within an alongshore band of high abundance of all stages) spatial segregation of adults and larvae.

• Why, despite spatial association with upwelling, euphausiid abundance off Vancouver Island is weakly or negatively correlated at interannual time scales with upwelling intensity.

To address these, we made km-resolution surveys of adult, juvenile, and larval euphausiid horizontal distributions, water properties, and currents across the Vancouver Island shelf break in mid-to-late spring of two successive years. Survey timing was before (1997) and after (1998) the spring transition to upwelling conditions, and near the annual spring reproductive peak. In both years, early developmental stages occupied an alongshore band that was offset from the late juveniles and adults. The direction of the offset differed between the two surveys. Early life history stages (larvae and early juveniles) were shoreward of adults in April 1997 (downwelling-conditions), but seaward of adults in May 1998 (upwelling-conditions). Separation distance (order 5–10 km) was consistent with expected differences in cumulative wind-driven (and vertically-sheared) cross-shore transport of surface-dwelling larvae and early juveniles vs. transport of diel migratory late juveniles and adults. Separation direction was consistent with recent history of winds and Ekman transport—shoreward during poleward winds, and seaward into blue water (and usually into a strong equatorward current) during equatorward winds.     

Observation of the bottom boundary layer off the Soya Warm Current

A mooring observation of current velocity, temperature and bottom pressure was carried out approximately 30 km off the coast of Monbetsu, between August 7 and September 2, 2005, to investigate the characteristics of bottom boundary layer (BBL) off the Soya Warm Current (SWC). We succeeded in measuring the Ekman veering and bottom Ekman transport in the BBL. On comparing the observed current velocity with that represented by the classical theoretical equation, the observed alongshore current velocity in BBL disagreed with that represented by the classical theoretical equation, but the cross-shore one agreed well. However after applying a linear extrapolation for the alongshore current velocity to estimate the alongshore geostrophic current velocity above the bottom, we could explain the alongshore current velocity by that represented in the classical theoretical equation. Consequently, our observations strongly support one of the proposed formation mechanisms of the cold-water belt observed off the SWC, that is, the convergence of bottom Ekman transport. The volume transport of vertical pumping velocity was estimated to be (0.12–0.25) Sv. In addition, the vertical profile of average temperature in all observation periods shows that slightly warmer water lies beneath the homogenous temperature layer, in the BBL. The result is considered to imply that the down-slope advection due to bottom Ekman transport supplies the SWC water in BBL and the eddy diffusivity of order of 10⁻³ m²s⁻¹ maintains the oceanic structure in the bottom mixed layer.