An MIDAS-400 Customised Data Ac- quisition System was deployed to obtain current ve- locity and suspended sediment concentration profiles over the intertidal flat at Wanggang, on the Jiangsu coast (China). At the same...An MIDAS-400 Customised Data Ac- quisition System was deployed to obtain current ve- locity and suspended sediment concentration profiles over the intertidal flat at Wanggang, on the Jiangsu coast (China). At the same time, seawater tempera- ture, conductivity and pressure were measured. Us- ing a data sampling rate of 4 Hz, the high-frequency pressure signals in response to water surface fluc- tuations were recorded and subsequently trans- formed into wave parameters. The analytical results show that the apparent bed roughness length has a magnitude close to the height of sand ripples, which is much larger than the grain size diameter. The bot- tom shear stress associated with current-wave in- teraction is higher than the tidally-induced stress and intensified turbulent mixing and resuspension. Fur- thermore, several suspended sediment concentration peaks occurred during a tidal cycle, which can be related to strong turbulence near the bed caused by frontal tidal currents and the enhanced resuspension; advection and extreme weather conditions (e. g. storms and strong winds) also played an important role. Finally, large net suspended sediment fluxes were observed to present when the flood or ebb currents prolonged, i.e. the flow became quasi-unid- irectional during a tidal cycle. In general, the MIDAS- 400 is a suitable tool for high-resolution data collec- tion for the situations of combined current-wave ac- tion over intertidal flats; the data obtained can be used to analyze the processes and mechanisms of material transport.展开更多
本文利用2015年3月—2021年5月热带印度洋观测网(tropical Indian Ocean observation net,TIOON)在赤道80°E、85°E和93°E布设的观测潜标所获取的环流时间序列,结合BRAN2020(Bluelink Re ANalysis)环流流速数据以及JRA-55...本文利用2015年3月—2021年5月热带印度洋观测网(tropical Indian Ocean observation net,TIOON)在赤道80°E、85°E和93°E布设的观测潜标所获取的环流时间序列,结合BRAN2020(Bluelink Re ANalysis)环流流速数据以及JRA-55(Japanese 55-year Reanalysis)气象数据,研究了印度洋赤道深层环流(1200m以下)的季节内变化特征及其驱动机制。观测结果显示,深层环流流速平均值接近0,纬向流速标准偏差范围为2.5~3.1cm·s^(-1),经向流速标准偏差范围为2.6~3.1cm·s^(-1)。纬向流和经向流的季节内周期信号强度分别占各自总流动强度的88%~91%和74%~84%,揭示了深层环流中的显著季节内周期变率特征。小波分析表明,深层纬向流季节内信号主要周期为10~100d,其中80°E处的周期较长(50~90d),而93°E处的主要为50d及更高频信号,表现为蓝移现象,即环流变化的主导频率随位置靠东而变高的现象。经向流季节内信号以60d周期最显著。赤道风应力异常是深层环流季节内变率的重要驱动因素。中海盆(80°E和85°E)深层环流季节内变率主要受纬向风应力异常驱动,通过反射波动过程调制;基于低阶斜压模态,能量通过Kelvin波在东边界反射后形成的Rossby波向深层传递。东海盆(93°E)深层环流季节内变率主要受纬向和经向风应力异常驱动,通过直接波动过程调制;基于多阶斜压模态,能量通过在环流西侧由风直接驱动产生的Yanai波向深层传递。根据线性波动理论,本研究刻画了上述赤道波的能量传播射线,结果显示地形对赤道波调制深海环流的动力过程有重要影响:中海盆的平坦地形有利于向下向西传播能量的反射波动过程,而90°E海脊可能会阻碍向下向东传播能量的直接波动过程。在平坦地形区域,正压不稳定过程在经向上无显著差异且强度弱,区域平均结果显示能量主要由平均流向环流季节内变率释放;90°E海脊附近,环流季节内变率与平均流之间存在更强的非线性动力作用,表现为环流季节内变率向平均流转移能量。本研究加深了对深层环流动力学的理解,为改进深海环流模拟提供了观测依据。展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.40576040,40231010 and 40206006).
文摘An MIDAS-400 Customised Data Ac- quisition System was deployed to obtain current ve- locity and suspended sediment concentration profiles over the intertidal flat at Wanggang, on the Jiangsu coast (China). At the same time, seawater tempera- ture, conductivity and pressure were measured. Us- ing a data sampling rate of 4 Hz, the high-frequency pressure signals in response to water surface fluc- tuations were recorded and subsequently trans- formed into wave parameters. The analytical results show that the apparent bed roughness length has a magnitude close to the height of sand ripples, which is much larger than the grain size diameter. The bot- tom shear stress associated with current-wave in- teraction is higher than the tidally-induced stress and intensified turbulent mixing and resuspension. Fur- thermore, several suspended sediment concentration peaks occurred during a tidal cycle, which can be related to strong turbulence near the bed caused by frontal tidal currents and the enhanced resuspension; advection and extreme weather conditions (e. g. storms and strong winds) also played an important role. Finally, large net suspended sediment fluxes were observed to present when the flood or ebb currents prolonged, i.e. the flow became quasi-unid- irectional during a tidal cycle. In general, the MIDAS- 400 is a suitable tool for high-resolution data collec- tion for the situations of combined current-wave ac- tion over intertidal flats; the data obtained can be used to analyze the processes and mechanisms of material transport.
文摘本文利用2015年3月—2021年5月热带印度洋观测网(tropical Indian Ocean observation net,TIOON)在赤道80°E、85°E和93°E布设的观测潜标所获取的环流时间序列,结合BRAN2020(Bluelink Re ANalysis)环流流速数据以及JRA-55(Japanese 55-year Reanalysis)气象数据,研究了印度洋赤道深层环流(1200m以下)的季节内变化特征及其驱动机制。观测结果显示,深层环流流速平均值接近0,纬向流速标准偏差范围为2.5~3.1cm·s^(-1),经向流速标准偏差范围为2.6~3.1cm·s^(-1)。纬向流和经向流的季节内周期信号强度分别占各自总流动强度的88%~91%和74%~84%,揭示了深层环流中的显著季节内周期变率特征。小波分析表明,深层纬向流季节内信号主要周期为10~100d,其中80°E处的周期较长(50~90d),而93°E处的主要为50d及更高频信号,表现为蓝移现象,即环流变化的主导频率随位置靠东而变高的现象。经向流季节内信号以60d周期最显著。赤道风应力异常是深层环流季节内变率的重要驱动因素。中海盆(80°E和85°E)深层环流季节内变率主要受纬向风应力异常驱动,通过反射波动过程调制;基于低阶斜压模态,能量通过Kelvin波在东边界反射后形成的Rossby波向深层传递。东海盆(93°E)深层环流季节内变率主要受纬向和经向风应力异常驱动,通过直接波动过程调制;基于多阶斜压模态,能量通过在环流西侧由风直接驱动产生的Yanai波向深层传递。根据线性波动理论,本研究刻画了上述赤道波的能量传播射线,结果显示地形对赤道波调制深海环流的动力过程有重要影响:中海盆的平坦地形有利于向下向西传播能量的反射波动过程,而90°E海脊可能会阻碍向下向东传播能量的直接波动过程。在平坦地形区域,正压不稳定过程在经向上无显著差异且强度弱,区域平均结果显示能量主要由平均流向环流季节内变率释放;90°E海脊附近,环流季节内变率与平均流之间存在更强的非线性动力作用,表现为环流季节内变率向平均流转移能量。本研究加深了对深层环流动力学的理解,为改进深海环流模拟提供了观测依据。
