东卡罗琳海盆(East Caroline Basin,ECB)是太平洋经向翻转环流深层流上分支(upper deep branch of the Pacific Meridional Overturning Circulation,U-PMOC)进出西太平洋的关键通道,其深层环流特征与动力机制对理解太平洋深层环流结构...东卡罗琳海盆(East Caroline Basin,ECB)是太平洋经向翻转环流深层流上分支(upper deep branch of the Pacific Meridional Overturning Circulation,U-PMOC)进出西太平洋的关键通道,其深层环流特征与动力机制对理解太平洋深层环流结构、变化及气候效应具有重要意义。基于1993~2022年OFES高分辨率模式数据,分析了ECB深层环流(>2500 m)的气候态平均输运、空间结构及季节变化特征。研究发现,ECB深层水体主要经西南深水通道流入(年均流量2.12 Sv),沿海盆西侧北向输运形成深层西边界流,随后转向东流,最终由东北深水通道流出(年均流量-2.35 Sv,负值表示流出)。海盆内部净输运接近平衡(-0.10 Sv),整体呈现顺时针(反气旋式)环流结构。深层环流具有明显季节变化:北半球冬春季(12~6月)以输入为主,夏秋季(7~11月)以输出为主,且流出过程相对流入存在滞后,表明ECB在年周期中充当深层水团的临时储存区。从动力机制看,水体自西南向东北输运过程中,β效应使行星涡度增加,为维持位涡守恒,相对涡度相应减小,驱动形成顺时针环流;深层西边界流则通过侧向摩擦耗散负涡度异常,维持系统动力平衡。本研究系统揭示了ECB深层环流结构、季节变化与动力机制,深化了对西太平洋深层环流的认识,为全球经向翻转环流模拟与深海生物地球化学循环研究提供了科学依据。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
Studies of wave-current interactions are vital for the safe design of structures.Regular waves in the presence of uniform,linear shear,and quadratic shear currents are explored by the High-Level Green-Naghdi model in ...Studies of wave-current interactions are vital for the safe design of structures.Regular waves in the presence of uniform,linear shear,and quadratic shear currents are explored by the High-Level Green-Naghdi model in this paper.The five-point central difference method is used for spatial discretization,and the fourth-order Adams predictor-corrector scheme is employed for marching in time.The domain-decomposition method is applied for the wave-current generation and absorption.The effects of currents on the wave profile and velocity field are examined under two conditions:the same velocity of currents at the still-water level and the constant flow volume of currents.Wave profiles and velocity fields demonstrate substantial differences in three types of currents owing to the diverse vertical distribution of current velocity and vorticity.Then,loads on small-scale vertical cylinders subjected to regular waves and three types of background currents with the same flow volume are investigated.The maximum load intensity and load fluctuation amplitude in uniform,linear shear,and quadratic shear currents increase sequentially.The stretched superposition method overestimates the maximum load intensity and load fluctuation amplitude in opposing currents and underestimates these values in following currents.The stretched superposition method obtains a poor approximation for strong nonlinear waves,particularly in the case of the opposing quadratic shear current.展开更多
The study of mesoscale eddies is generally categorized in Eulerian or Lagrangian frameworks.We employed the eddy identification techniques in both frameworks in the South China Sea(SCS),examining the differential char...The study of mesoscale eddies is generally categorized in Eulerian or Lagrangian frameworks.We employed the eddy identification techniques in both frameworks in the South China Sea(SCS),examining the differential characteristics of mesoscale eddies ascertained through each approach,and attempting to identify factors influencing eddy lifetime.The findings suggest that eddies identified via the sea surface height(SSH)method in the Eulerian framework typically have larger spatial extents compared to those identified using the Lagrangian Average Vorticity Deviation(LAVD)method.The latter is characterized by a greater number of vortices with smaller average values of characteristic parameters.SSH eddies exhibited more remarked seasonal variations than LAVD vortices,and the seasonal variations of their respective cyclonic and anticyclonic eddies showed opposite trends.Analysis in both frameworks indicates that eddy lifetime is positively correlated with various eddy characteristic parameters,including radius,vorticity,kinetic energy,amplitude,EKE/MKE(ratio of boundary to spatial mean kinetic energy),and U/c(max rotation speed to mean propagation speed ratio).A subsequent comparison between SSH eddies with LAVD cores(SSH eddy with LAVD vortex inside)and those without reveals a greater likelihood of extended lifetime in the former.Compared to the characteristic parameters of eddies,the presence of LAVD cores emerges as a critical factor in determining the lifetime of SSH eddies.展开更多
The subantarctic mode water(SAMW)represents a large water mass in the Southern Ocean.This body of water forms through deep convection(subduction)in winter and contributes to the uptake and storage of anthropogenic hea...The subantarctic mode water(SAMW)represents a large water mass in the Southern Ocean.This body of water forms through deep convection(subduction)in winter and contributes to the uptake and storage of anthropogenic heat.However,its longterm changes in subduction rate and volume in response to shifting climate conditions are unclear.In this study,we investigated the long-term trend of the subduction rate and volume of the South Pacific–SAMW(SPSAMW)using Simple Ocean Data Assimilation outputs during 1980–2017.The results show the overall increasing trend of the subduction rate of the SPSAMW.The increased subduction of the SPSAMW directly contributes to the volume variation in the SPSAMW.The increased subduction in the South Pacific reached(0.28±0.16)Sv-1 per year,which explains nearly 68%of the volume increase in the SPSAMW.This variability in the SPSAMW reflects alterations in the overlying atmosphere.The positive to negative phase change of the Interdecadal Pacific Oscillation(IPO)in 1980–2017 deepened the Amundsen Sea Low(ASL)via atmospheric teleconnections over the South Pacific.Further analysis reveals that the increased westerly winds during the deepening of ASL resulted in more cold water transport from the south,which deepened the winter mixed layer and thus increased subduction and volume within the SPSAMW subduction region.This finding suggests the association of the long-term trends of SPSAMW subduction and volume with the phase change of the IPO.展开更多
文摘东卡罗琳海盆(East Caroline Basin,ECB)是太平洋经向翻转环流深层流上分支(upper deep branch of the Pacific Meridional Overturning Circulation,U-PMOC)进出西太平洋的关键通道,其深层环流特征与动力机制对理解太平洋深层环流结构、变化及气候效应具有重要意义。基于1993~2022年OFES高分辨率模式数据,分析了ECB深层环流(>2500 m)的气候态平均输运、空间结构及季节变化特征。研究发现,ECB深层水体主要经西南深水通道流入(年均流量2.12 Sv),沿海盆西侧北向输运形成深层西边界流,随后转向东流,最终由东北深水通道流出(年均流量-2.35 Sv,负值表示流出)。海盆内部净输运接近平衡(-0.10 Sv),整体呈现顺时针(反气旋式)环流结构。深层环流具有明显季节变化:北半球冬春季(12~6月)以输入为主,夏秋季(7~11月)以输出为主,且流出过程相对流入存在滞后,表明ECB在年周期中充当深层水团的临时储存区。从动力机制看,水体自西南向东北输运过程中,β效应使行星涡度增加,为维持位涡守恒,相对涡度相应减小,驱动形成顺时针环流;深层西边界流则通过侧向摩擦耗散负涡度异常,维持系统动力平衡。本研究系统揭示了ECB深层环流结构、季节变化与动力机制,深化了对西太平洋深层环流的认识,为全球经向翻转环流模拟与深海生物地球化学循环研究提供了科学依据。
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。
基金Supported by the Development and Application Project of Ship CAE Software.
文摘Studies of wave-current interactions are vital for the safe design of structures.Regular waves in the presence of uniform,linear shear,and quadratic shear currents are explored by the High-Level Green-Naghdi model in this paper.The five-point central difference method is used for spatial discretization,and the fourth-order Adams predictor-corrector scheme is employed for marching in time.The domain-decomposition method is applied for the wave-current generation and absorption.The effects of currents on the wave profile and velocity field are examined under two conditions:the same velocity of currents at the still-water level and the constant flow volume of currents.Wave profiles and velocity fields demonstrate substantial differences in three types of currents owing to the diverse vertical distribution of current velocity and vorticity.Then,loads on small-scale vertical cylinders subjected to regular waves and three types of background currents with the same flow volume are investigated.The maximum load intensity and load fluctuation amplitude in uniform,linear shear,and quadratic shear currents increase sequentially.The stretched superposition method overestimates the maximum load intensity and load fluctuation amplitude in opposing currents and underestimates these values in following currents.The stretched superposition method obtains a poor approximation for strong nonlinear waves,particularly in the case of the opposing quadratic shear current.
基金Supported by the National Natural Science Foundation of China(No.41906021)the Guangdong Ocean University Scientific Research Start-up Fund(No.060302112312)。
文摘The study of mesoscale eddies is generally categorized in Eulerian or Lagrangian frameworks.We employed the eddy identification techniques in both frameworks in the South China Sea(SCS),examining the differential characteristics of mesoscale eddies ascertained through each approach,and attempting to identify factors influencing eddy lifetime.The findings suggest that eddies identified via the sea surface height(SSH)method in the Eulerian framework typically have larger spatial extents compared to those identified using the Lagrangian Average Vorticity Deviation(LAVD)method.The latter is characterized by a greater number of vortices with smaller average values of characteristic parameters.SSH eddies exhibited more remarked seasonal variations than LAVD vortices,and the seasonal variations of their respective cyclonic and anticyclonic eddies showed opposite trends.Analysis in both frameworks indicates that eddy lifetime is positively correlated with various eddy characteristic parameters,including radius,vorticity,kinetic energy,amplitude,EKE/MKE(ratio of boundary to spatial mean kinetic energy),and U/c(max rotation speed to mean propagation speed ratio).A subsequent comparison between SSH eddies with LAVD cores(SSH eddy with LAVD vortex inside)and those without reveals a greater likelihood of extended lifetime in the former.Compared to the characteristic parameters of eddies,the presence of LAVD cores emerges as a critical factor in determining the lifetime of SSH eddies.
基金supported by the National Natural Science Foundation of China(Nos.42406256,42376034,and 42430402)the Qingdao Postdoctoral Application Research Project(No.QDBSH20220202152)+1 种基金the National Key R&D Program of China(No.2018YFA0605701)the Chinese Arctic and Antarctic Administration(No.IRASCC2020-2022-02-01-03)。
文摘The subantarctic mode water(SAMW)represents a large water mass in the Southern Ocean.This body of water forms through deep convection(subduction)in winter and contributes to the uptake and storage of anthropogenic heat.However,its longterm changes in subduction rate and volume in response to shifting climate conditions are unclear.In this study,we investigated the long-term trend of the subduction rate and volume of the South Pacific–SAMW(SPSAMW)using Simple Ocean Data Assimilation outputs during 1980–2017.The results show the overall increasing trend of the subduction rate of the SPSAMW.The increased subduction of the SPSAMW directly contributes to the volume variation in the SPSAMW.The increased subduction in the South Pacific reached(0.28±0.16)Sv-1 per year,which explains nearly 68%of the volume increase in the SPSAMW.This variability in the SPSAMW reflects alterations in the overlying atmosphere.The positive to negative phase change of the Interdecadal Pacific Oscillation(IPO)in 1980–2017 deepened the Amundsen Sea Low(ASL)via atmospheric teleconnections over the South Pacific.Further analysis reveals that the increased westerly winds during the deepening of ASL resulted in more cold water transport from the south,which deepened the winter mixed layer and thus increased subduction and volume within the SPSAMW subduction region.This finding suggests the association of the long-term trends of SPSAMW subduction and volume with the phase change of the IPO.
