This study assesses the capability of a coarse-resolution ocean model to replicate the response of the Southern Ocean Meridional Overturning Circulation(MOC)to intensified westerlies,focusing on the role of the eddy t...This study assesses the capability of a coarse-resolution ocean model to replicate the response of the Southern Ocean Meridional Overturning Circulation(MOC)to intensified westerlies,focusing on the role of the eddy transfer coefficient().κis a parameter commonly used to represent the velocities induced by unresolved eddies.Our findings reveal that a stratification-dependent,incorporating spatiotemporal variability,leads to the most robust eddy-induced MOC response,capturing 82%of the reference eddy-resolving simulation.Decomposing the eddy-induced velocity into its vertical variation(VV)and spatial structure(SS)components unveils that the enhanced eddy compensation response primarily stems from an augmented SS term,while the introduced VV term weakens the response.Furthermore,the temporal variability of the stratification-dependentκemerges as a key factor in enhancing the eddy compensation response to intensified westerlies.The experiment with stratification-dependentκexhibits a more potent eddy compensation response compared to the constant,attributed to the structure ofκand the vertical variation of the density slope.These results underscore the critical role of accurately representingκin capturing the response of the Southern Ocean MOC and emphasize the significance of the isopycnal slope in modulating the eddy compensation mechanism.展开更多
Atlantic meridional overturning circulation(AMOC)plays an important role in transporting heat meridionally in the Earth’s climate system and is also a key metrical tool to verify oceanic general circulation models.Tw...Atlantic meridional overturning circulation(AMOC)plays an important role in transporting heat meridionally in the Earth’s climate system and is also a key metrical tool to verify oceanic general circulation models.Two OMIP(Ocean Model Intercomparison Project phase 1 and 2)simulations with LICOM3(version 3 of the LASG/IAP Climate System Ocean Model)developed at the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics(LASG),Institute of Atmospheric Physics(IAP),are compared in this study.Both simulations well reproduce the fundamental characteristics of the AMOC,but the OMIP1 simulation shows a significantly stronger AMOC than the OMIP2 simulation.Because the LICOM3 configurations are identical between these two experiments,any differences between them must be attributed to the surface forcing data.Further analysis suggests that sea surface salinity(SSS)differences should be mainly responsible for the enhanced AMOC in the OMIP1 simulation,but sea surface temperature(SST)also play an unignorable role in modulating AMOC.In the North Atlantic,where deep convection occurs,the SSS in OMIP1 is more saline than that in OMIP1.We find that in the major region of deep convection,the change of SSS has more significant effect on density than the change of SST.As a result,the SSS was more saline than that in OMIP2,leading to stronger deep convection and subsequently intensify the AMOC.We conduct a series of numerical experiments with LICOM3,and the results confirmed that the changes in SSS have more significant effect on the strength of AMOC than the changes in SST.展开更多
Rapid urbanization has led to a surge in the number of towering structures,and overturning is widely used because it can better accommodate the construction of shaped structures such as variable sections.The complexit...Rapid urbanization has led to a surge in the number of towering structures,and overturning is widely used because it can better accommodate the construction of shaped structures such as variable sections.The complexity of the construction process makes the construction risk have certain randomness,so this paper proposes a cloudbased coupled matter-element model to address the ambiguity and randomness in the safety risk assessment of overturning construction of towering structures.In the pretended model,the digital eigenvalues of the cloud model are used to replace the eigenvalues in the matter–element basic element,and calculate the cloud correlation of the risk assessment metrics through the correlation algorithm of the cloud model to build the computational model.Meanwhile,the improved hierarchical analysis method based on the cloud model is used to determine the weight of the index.The comprehensive evaluation scores of the evaluation event are then obtained through the weighted average method,and the safety risk level is determined accordingly.Through empirical analysis,(1)the improved hierarchical analysis method based on the cloud model can incorporate the data of multiple decisionmakers into the calculation formula to determine theweights,which makes the assessment resultsmore credible;(2)the evaluation results of the cloud-basedmatter-element coupledmodelmethod are basically consistent with those of the other two commonly used methods,and the confidence factor is less than 0.05,indicating that the cloudbased physical element coupled model method is reasonable and practical for towering structure overturning;(3)the cloud-based coupled element model method,which confirms the reliability of risk level by performing Spearman correlation on comprehensive assessment scores,can provide more comprehensive information of instances compared with other methods,and more comprehensively reflects the fuzzy uncertainty relationship between assessment indexes,which makes the assessment results more realistic,scientific and reliable.展开更多
In seismology and earthquake engineering,it is fundamental to identify and characterize the pulse-like features in pulse-type ground motions.To capture the pulses that dominate structural responses,this study establis...In seismology and earthquake engineering,it is fundamental to identify and characterize the pulse-like features in pulse-type ground motions.To capture the pulses that dominate structural responses,this study establishes congruence and shift relationships between response spectrum surfaces.A similarity search between spectrum surfaces,supplemented with a similarity search in time series,has been applied to characterize the pulse-like features in pulse-type ground motions.The identified pulses are tested in predicting the rocking consequences of slender rectangular blocks under the original ground motions.Generally,the prediction is promising for the majority of the ground motions where the dominant pulse is correctly identified.展开更多
The three-dimensional structure and the seasonal variation of the North Pacific meridional overturning circulation (NPMOC) are analyzed based on the Simple Ocean Data Assimilation data and Argo profiling float data....The three-dimensional structure and the seasonal variation of the North Pacific meridional overturning circulation (NPMOC) are analyzed based on the Simple Ocean Data Assimilation data and Argo profiling float data. The NPMOC displays a multi-cell structure with four cells in the North Pacific altogether. The TC and the STC are a strong clockwise meridional cell in the low latitude ocean and a weaker clockwise meridional cell between 7°N and 18°N, respectively, while the DTC and the subpolar cell are a weaker anticlockwise meridional cell between 3°N and 15°N and a weakest anticlockwise meridional cell between 35°N and 50°N, respectively. The DTC, the TC and the STC are all of very strong seasonal variations. As to the DTC, the southward transport is strongest in fall and weakest in spring. For the TC, the northward transport is strongest in winter and weakest in spring, while the southward transport is strongest in fall and weakest in spring, which is associated with the strong southward fiow of the DTC in fall. As the STC, the northward transport is strongest in winter and weakest in summer, while the southward transport is strongest in summer and weakest in spring. This seasonal difference may be associated with the DTC. The zonal wind stress and the east-west slope of sea level play important roles in the seasonal variations of the TC, the STC and the DTC.展开更多
The shallow meridional overturning circulation (upper 1000 m) in the northern Indian Ocean and its interannual variability are studied, based on a global ocean circulation model (MOM2) with an integration of 10 years ...The shallow meridional overturning circulation (upper 1000 m) in the northern Indian Ocean and its interannual variability are studied, based on a global ocean circulation model (MOM2) with an integration of 10 years (1987-1996). It is shown that the shallow meridional overturning circulation has a prominent seasonal reversal characteristic. In winter, the flow is northward in the upper layer and returns southward at great depth. In summer, the deep northward inflow upwells north of the equator and returns southward in the Ekman layer. In the annual mean, the northward inflow returns through two branches: one is a southward flow in the Ekman layer, the other is a flow that sinks near 10°N and returns southward between 500 m and 1000 m. There is significant interannual variability in the shallow meridional overturning circulation, with a stronger (weaker) one in 1989 (1991) and with a period of about four years. The interannual variability of the shallow meridional overturning circulation is intimately r展开更多
The effects of ocean density vertical stratification and related ocean mixing on the transient response of the Atlantic meridional overturning circulation (AMOC) are examined in a freshwater perturbation simulation ...The effects of ocean density vertical stratification and related ocean mixing on the transient response of the Atlantic meridional overturning circulation (AMOC) are examined in a freshwater perturbation simulation using the Bergen Climate Model (BCM). The results presented here are based on the model outputs of a previous freshwater experiment: a 300-year control integration (CTRL), a freshwater integration (FW1) which started after 100 years of running the CTRL with an artificially and continuously threefold increase in the freshwater flux to the Greenland-Iceland-Norwegian (GIN) Seas and the Arctic Ocean throughout the following 150-year simulation. In FW1, the transient response of the AMOC exhibits an initial decreasing of about 6 Sv (1 Sv=106 m3 s^-1) over the first 50-year integration and followed a gradual recovery during the last 100-year integration. Our results show that the vertical density stratification as the crucial property of the interior ocean plays an important role for the transient responses of AMOC by regulating the convective and diapycnal mixings under the enhanced freshwater input to northern high latitudes in BCM in which the ocean diapycnal mixing is stratification-dependent. The possible mechanism is also investigated in this paper.展开更多
Zonal overturning circulation (ZOC) and its associated zonal heat flux (ZHF) are important components of the oceanic circulation and climate system, although these conceptions have not received adequate attentions...Zonal overturning circulation (ZOC) and its associated zonal heat flux (ZHF) are important components of the oceanic circulation and climate system, although these conceptions have not received adequate attentions. Heaving induced by inter-annual and decadal wind stress perturbations can give rise to anomalous ZOC and ZHF. Based on a simple reduced gravity model, the anomalous ZOC and ZHF induced by idealized heaving modes in the world oceans are studied. For example, in a Pacific-like model basin intensified equatorial easterly on decadal time scales can lead to a negative ZOC with a non-negligible magnitude (-0.3×10^6 m^3/s) and a considerable westward ZHF with an amplitude of -11.2 TW. Thus, anomalous ZOC and ZHF may consist of a major part of climate signals on decadal time scales and thus play an important role in the oceanic circulation and climate change.展开更多
Under strong seismic excitation, a rigid block will uplift from its support and undergo rocking oscillations which may lead to (complete) overturning. Numerical and analytical solutions to this highly nonlinear vibr...Under strong seismic excitation, a rigid block will uplift from its support and undergo rocking oscillations which may lead to (complete) overturning. Numerical and analytical solutions to this highly nonlinear vibration problem are first highlighted in the paper and then utilized to demonstrate how sensitive the overturning behavior is not only to the intensity and frequency content of the base motion, but also to thc presence of strong pulses, to their detailed sequence, and even to their asymnletry. Five idealised pulses capable of representing "rupture-directivity" and "fling" affected ground motions near the fault, are utilized to this end : the one-cycle sinus, the one-cycle cosinus, the Ricker wavelet, the truncated (T)-Ricker wavelet, and the rectangular pulse "Overturning-Acceleration Amplification" and "Rotation" spectra are introduced and presented. Artificial neural network modeling is then developed as an alternative numerical solution. The neural network analysis leads to closed-form expressions for predicting the overturning failure or survival of a rigid block, as a function of its geometric properties and the characteristics of the excitation time history. The capability of the developed neural network modeling is validated through comparisons with the numerical solution. The derived analytical expressions could also serve as a tool for assessing the destructiveness of near-fault ground motions, for structures sensitive to rocking with foundation uplift.展开更多
The structure of the annual-mean shallow meridional overturning circulation (SMOC) in the South China Sea (SCS) and the related water movement are investigated, using simple ocean data assimilation (SODA) output...The structure of the annual-mean shallow meridional overturning circulation (SMOC) in the South China Sea (SCS) and the related water movement are investigated, using simple ocean data assimilation (SODA) outputs. The distinct clockwise SMOC is present above 400 m in the SCS on the climatologically annual-mean scale, which consists of downwelling in the northern SCS, a southward subsurface branch supplying upwelling at around 10°N and a northward surface flow, with a strength of about 1x 108 ma/s. The formation mechanisms of its branches are studied separately. The zonal component of the annual-mean wind stress is predominantly westward and causes northward Ekman transport above 50 m. The annual-mean Ekman transport across 18°N is about 1.2×106 m^3/s. An annual-mean subduction rate is calculated by estimating the net volume flux entering the thermocline from the mixed layer in a Lagrangian framework. An annual subduction rate of about 0.66×106 ma/s is obtained between 17° and 20°N, of which 87% is due to vertical pumping and 13% is due to lateral induction. The subduction rate implies that the subdution contributes significantly to the downwelling branch. The pathways of traced parcels released at the base of the February mixed layer show that after subduction water moves southward to as far as 1 I^N within the western boundary current before returning northward. The velocity field at the base of mixed layer and a meridional velocity section in winter also confirm that the southward flow in the subsurface layer is mainly by strong western boundary currents. Significant upwelling mainly occurs off the Vietnam coast in the southern SCS. An upper bound for the annual-mean net upwelfing rate between 10° and 15°N is 0.7×108 ma/s, of which a large portion is contributed by summer upwelling, with both the alongshore component of the southwest wind and its offshore increase causing great upwelling.展开更多
The mechanisms involved in the variability of Atlantic Meridional Overturning Circulation (AMOC) are studied using a 2000-yr control simulation of the coupled Fast Ocean-Atmosphere Model (FOAM).This study identifi...The mechanisms involved in the variability of Atlantic Meridional Overturning Circulation (AMOC) are studied using a 2000-yr control simulation of the coupled Fast Ocean-Atmosphere Model (FOAM).This study identifies a coupled mode between SST and surface heat flux in the North Atlantic at the decadal timescale,as well as a forcing mode of surface heat flux at the interannual timescale.The coupled mode is regulated by AMOC through meridional heat transport.The increase in surface heating in the North Atlantic weakens the AMOC approximately 10 yr later,and the weakened AMOC in turn decreases SST and sea surface salinity.The decreased SST results in an increase in surface heating in the North Atlantic,thus forming a positive feedback loop.Meanwhile,the weakened AMOC weakens northward heat transport and therefore lowers subsurface temperature approximately 19 yr later,which prevents the AMOC from weakening.In the forcing mode,the surface heat flux leads AMOC by approximately 4 yr.展开更多
The low-frequency variability of the shallow meridional overturning circulation(MOC) in the South China Sea(SCS) is investigated using a Simple Ocean Data Assimilation(SODA) product for the period of 1900-2010. ...The low-frequency variability of the shallow meridional overturning circulation(MOC) in the South China Sea(SCS) is investigated using a Simple Ocean Data Assimilation(SODA) product for the period of 1900-2010. A dynamical decomposition method is used in which the MOC is decomposed into the Ekman, external mode, and vertical shear components. Results show that all the three dynamical components contribute to the formation of the seasonal and annual mean shallow MOC in the SCS. The shallow MOC in the SCS consists of two cells: a clockwise cell in the south and an anticlockwise cell in the north; the former is controlled by the Ekman flow and the latter is dominated by the external barotropic flow, with the contribution of the vertical shear being to reduce the magnitude of both cells. In addition, the strength of the MOC in the south is found to have a falling trend over the past century, due mainly to a weakening of the Luzon Strait transport(LST) that reduces the transport of the external component. Further analysis suggests that the weakening of the LST is closely related to a weakening of the westerly wind anomalies over the equatorial Pacific, which leads to a southward shift of the North Equatorial Current(NEC) bifurcation and thus a stronger transport of the Kuroshio east of Luzon.展开更多
Based on the 50-year Simple Ocean Data Assimilation (SODA) reanalysis data, we investigated the basic characteristics and seasonal changes of the meridional heat transport carried by the North Pacific Meridional Overt...Based on the 50-year Simple Ocean Data Assimilation (SODA) reanalysis data, we investigated the basic characteristics and seasonal changes of the meridional heat transport carried by the North Pacific Meridional Overturning Circulation. And we also examined the dynamical and thermodynamic mechanisms responsible for these heat transport variability at the seasonal time scale. Among four cells, the tropical cell (TC) is strongest with a northward heat transport (NHT) of (1.75±0.30) PW (1 PW=1.0×10^15 W) and a southward heat transport (SHT) of (-1.69±0.55) PW, the subtropical cell (STC) is second with a NHT of (0.71±0.65) PW and SHT of (-0.63±0.53) PW, the deep tropical cell (DTC) is third with a NHT of (0.18±0.03) PW and SHT of (-0.18±0.11) PW, while the subpolar cell (SPC) is weakest with a NHT of (0.09±0.05) PW and SHT of (-0.07±0.09) PW. These four cells all have diff erent seasonal changes in their NHT and SHT. Of all, the TC has stronger change in its SHT than in its NHT, so do both the DTC and SPC, but the seasonal change in the STC SHT is weaker than that in its NHT. Therefore, their dynamical and thermodynamic mechanisms are diff erent each other. The local zonal wind stress and net surface heat flux are mainly responsible for the seasonal changes in the TC and STC NHTs and SPC SHT, while the local thermocline circulations and sea temperature are primarily responsible for the seasonal changes of the TC, STC and DTC SHTs and SPC NHT.展开更多
The climatologies of dissolved oxygen concentration in the ocean simulated by nine Earth system models(ESMs) from the historical emission driven experiment of CMIP5(Phase 5 of the Climate Model Intercomparison Project...The climatologies of dissolved oxygen concentration in the ocean simulated by nine Earth system models(ESMs) from the historical emission driven experiment of CMIP5(Phase 5 of the Climate Model Intercomparison Project) are quantitatively evaluated by comparing the simulated oxygen to the WOA09 observation based on common statistical metrics. At the sea surface, distribution of dissolved oxygen is well simulated by all nine ESMs due to well-simulated sea surface temperature(SST), with both globally-averaged error and root mean square error(RMSE) close to zero, and both correlation coefficients and normalized standard deviation close to 1. However, the model performance differs from each other at the intermediate depth and deep ocean where important water masses exist. At the depth of 500 to 1 000 m where the oxygen minimum zones(OMZs) exist, all ESMs show a maximum of globally-averaged error and RMSE, and a minimum of the spatial correlation coefficient. In the ocean interior, the reason for model biases is complicated, and both the meridional overturning circulation(MOC) and the particulate organic carbon flux contribute to the biases of dissolved oxygen distribution. Analysis results show the physical bias contributes more. Simulation bias of important water masses such as North Atlantic Deep Water(NADW), Antarctic Bottom Water(AABW) and North Pacific Intermediate Water(NPIW) indicated by distributions of MOCs greatly affects the distributions of oxygen in north Atlantic, Southern Ocean and north Pacific, respectively.Although the model simulations of oxygen differ greatly from each other in the ocean interior, the multi-model mean shows a better agreement with the observation.展开更多
The lunar volcanic glasses and Mg-suite rocks represent the early enigmatic episodes of lunar magmatism.Due to the gravitational instability of the Fe-Ti enriched(±KREEP)layer,which is formed at the later stage o...The lunar volcanic glasses and Mg-suite rocks represent the early enigmatic episodes of lunar magmatism.Due to the gravitational instability of the Fe-Ti enriched(±KREEP)layer,which is formed at the later stage of fractional crystallization,a post-magma-ocean cumulate overturn occurred contemporaneously or near-contemporaneously with the lunar magma ocean(LMO)solidification.The radioactive elements within the KREEP layer were transferred downward and provided continuous energy for the partial melting of the Moon’s interior.The melt from the Moon’s interior and those from decompression melting,in turn,provide source magma for the origin of lunar volcanic glasses and Mg-suite.However,experimental and theoretical studies on the formation process of lunar volcanic glasses and Mg-suite show that the origin of their parental magma is poorly constrained,which largely depends on the initial depth and composition of the LMO.This review examines the mineralogy,petrogenesis,and distribution of lunar volcanic glasses and Mg-suite.Combining with existing models,we constrain the degree,distribution,and timescale of lunar mantle overturn and explore their relationship with later stages of LMO differentiation.We propose an updated chemical composition of the lunar interior,which provides a useful reference for estimating the bulk composition and early differentiation of the Moon and the early Earth.展开更多
An increasing amount of freshwater has been observed to enter the Arctic Ocean from the six largest Eurasian rivers over the past several decades. The increasing trend is projected to continue in the twenty-first cent...An increasing amount of freshwater has been observed to enter the Arctic Ocean from the six largest Eurasian rivers over the past several decades. The increasing trend is projected to continue in the twenty-first century according to Coupled Model Intercomparison Project Phase 5 (CMIP5) coupled models. The present study found that water flux from rivers to the Arctic Ocean at the end of the century will be 1.4 times that in 1950 according to CMIP5 projection results under Representative Concentration Pathway 8.5. The effect of increasing Arctic river runoff on the Atlantic meridional overturning circulation (AMOC) was investigated using an ocean-ice coupled model. Results obtained from two numerical experiments show that 100, 150 and 200 years after the start of an increase in the Arctic river runoff at a rate of 0.22%/a, the AMOC will weaken by 0.6 (3%), 1.2 (7%) and 1.8 (11%) Sv. AMOC weakening is mainly caused by freshwater transported from increasing Arctic river runoff inhibiting the formation of North Atlantic Deep Water (NADW). As the AMOC weakens, the deep seawater age will become older throughout the Atlantic Basin owing to the increasing of Arctic runoff.展开更多
基金supported by the National Key R&D Program for Developing Basic Sciences(2022YFC3104802)the National Natural Science Foundation of China(Nos.42306219 and 42106020)+3 种基金the Tai Shan Scholar Pro-gram(Grant No.tstp20231237)Part of computing resources are financially supported by Laoshan Laboratory(No.LSKJ202300301)Dr.Eric P.CHASSIGNET is supported by the CAS President’s International Fellowship Initiative(PIFI)NOAA Climate Program Office MAPP Program(Award NA15OAR4310088).
文摘This study assesses the capability of a coarse-resolution ocean model to replicate the response of the Southern Ocean Meridional Overturning Circulation(MOC)to intensified westerlies,focusing on the role of the eddy transfer coefficient().κis a parameter commonly used to represent the velocities induced by unresolved eddies.Our findings reveal that a stratification-dependent,incorporating spatiotemporal variability,leads to the most robust eddy-induced MOC response,capturing 82%of the reference eddy-resolving simulation.Decomposing the eddy-induced velocity into its vertical variation(VV)and spatial structure(SS)components unveils that the enhanced eddy compensation response primarily stems from an augmented SS term,while the introduced VV term weakens the response.Furthermore,the temporal variability of the stratification-dependentκemerges as a key factor in enhancing the eddy compensation response to intensified westerlies.The experiment with stratification-dependentκexhibits a more potent eddy compensation response compared to the constant,attributed to the structure ofκand the vertical variation of the density slope.These results underscore the critical role of accurately representingκin capturing the response of the Southern Ocean MOC and emphasize the significance of the isopycnal slope in modulating the eddy compensation mechanism.
基金Supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDA19060102)the National Natural Science Foundation of China(Nos.91958201,42130608)the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDB42000000)。
文摘Atlantic meridional overturning circulation(AMOC)plays an important role in transporting heat meridionally in the Earth’s climate system and is also a key metrical tool to verify oceanic general circulation models.Two OMIP(Ocean Model Intercomparison Project phase 1 and 2)simulations with LICOM3(version 3 of the LASG/IAP Climate System Ocean Model)developed at the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics(LASG),Institute of Atmospheric Physics(IAP),are compared in this study.Both simulations well reproduce the fundamental characteristics of the AMOC,but the OMIP1 simulation shows a significantly stronger AMOC than the OMIP2 simulation.Because the LICOM3 configurations are identical between these two experiments,any differences between them must be attributed to the surface forcing data.Further analysis suggests that sea surface salinity(SSS)differences should be mainly responsible for the enhanced AMOC in the OMIP1 simulation,but sea surface temperature(SST)also play an unignorable role in modulating AMOC.In the North Atlantic,where deep convection occurs,the SSS in OMIP1 is more saline than that in OMIP1.We find that in the major region of deep convection,the change of SSS has more significant effect on density than the change of SST.As a result,the SSS was more saline than that in OMIP2,leading to stronger deep convection and subsequently intensify the AMOC.We conduct a series of numerical experiments with LICOM3,and the results confirmed that the changes in SSS have more significant effect on the strength of AMOC than the changes in SST.
基金funded by China Railway No.21 Bureau Group No.1 Engineering Co.,Ltd.,Grant No.202209140002.
文摘Rapid urbanization has led to a surge in the number of towering structures,and overturning is widely used because it can better accommodate the construction of shaped structures such as variable sections.The complexity of the construction process makes the construction risk have certain randomness,so this paper proposes a cloudbased coupled matter-element model to address the ambiguity and randomness in the safety risk assessment of overturning construction of towering structures.In the pretended model,the digital eigenvalues of the cloud model are used to replace the eigenvalues in the matter–element basic element,and calculate the cloud correlation of the risk assessment metrics through the correlation algorithm of the cloud model to build the computational model.Meanwhile,the improved hierarchical analysis method based on the cloud model is used to determine the weight of the index.The comprehensive evaluation scores of the evaluation event are then obtained through the weighted average method,and the safety risk level is determined accordingly.Through empirical analysis,(1)the improved hierarchical analysis method based on the cloud model can incorporate the data of multiple decisionmakers into the calculation formula to determine theweights,which makes the assessment resultsmore credible;(2)the evaluation results of the cloud-basedmatter-element coupledmodelmethod are basically consistent with those of the other two commonly used methods,and the confidence factor is less than 0.05,indicating that the cloudbased physical element coupled model method is reasonable and practical for towering structure overturning;(3)the cloud-based coupled element model method,which confirms the reliability of risk level by performing Spearman correlation on comprehensive assessment scores,can provide more comprehensive information of instances compared with other methods,and more comprehensively reflects the fuzzy uncertainty relationship between assessment indexes,which makes the assessment results more realistic,scientific and reliable.
基金National Key Research and Development Program,Ministry of Science and Technology of China under Grant No.2022YFC3803004the National Natural Science Foundation of China under Grant No.51838004。
文摘In seismology and earthquake engineering,it is fundamental to identify and characterize the pulse-like features in pulse-type ground motions.To capture the pulses that dominate structural responses,this study establishes congruence and shift relationships between response spectrum surfaces.A similarity search between spectrum surfaces,supplemented with a similarity search in time series,has been applied to characterize the pulse-like features in pulse-type ground motions.The identified pulses are tested in predicting the rocking consequences of slender rectangular blocks under the original ground motions.Generally,the prediction is promising for the majority of the ground motions where the dominant pulse is correctly identified.
基金Supported by the National Basic Research Development Program of China(973 Program)under contract Nos 2007CB816002,2007CB816005the innovative key project of Chinese Academy of Sciences under contract No.KZCXZ-YW-201
文摘The three-dimensional structure and the seasonal variation of the North Pacific meridional overturning circulation (NPMOC) are analyzed based on the Simple Ocean Data Assimilation data and Argo profiling float data. The NPMOC displays a multi-cell structure with four cells in the North Pacific altogether. The TC and the STC are a strong clockwise meridional cell in the low latitude ocean and a weaker clockwise meridional cell between 7°N and 18°N, respectively, while the DTC and the subpolar cell are a weaker anticlockwise meridional cell between 3°N and 15°N and a weakest anticlockwise meridional cell between 35°N and 50°N, respectively. The DTC, the TC and the STC are all of very strong seasonal variations. As to the DTC, the southward transport is strongest in fall and weakest in spring. For the TC, the northward transport is strongest in winter and weakest in spring, while the southward transport is strongest in fall and weakest in spring, which is associated with the strong southward fiow of the DTC in fall. As the STC, the northward transport is strongest in winter and weakest in summer, while the southward transport is strongest in summer and weakest in spring. This seasonal difference may be associated with the DTC. The zonal wind stress and the east-west slope of sea level play important roles in the seasonal variations of the TC, the STC and the DTC.
基金This study was supported by National Natural Science Foundation of China(NSFC)under Grant No.40233033.
文摘The shallow meridional overturning circulation (upper 1000 m) in the northern Indian Ocean and its interannual variability are studied, based on a global ocean circulation model (MOM2) with an integration of 10 years (1987-1996). It is shown that the shallow meridional overturning circulation has a prominent seasonal reversal characteristic. In winter, the flow is northward in the upper layer and returns southward at great depth. In summer, the deep northward inflow upwells north of the equator and returns southward in the Ekman layer. In the annual mean, the northward inflow returns through two branches: one is a southward flow in the Ekman layer, the other is a flow that sinks near 10°N and returns southward between 500 m and 1000 m. There is significant interannual variability in the shallow meridional overturning circulation, with a stronger (weaker) one in 1989 (1991) and with a period of about four years. The interannual variability of the shallow meridional overturning circulation is intimately r
文摘The effects of ocean density vertical stratification and related ocean mixing on the transient response of the Atlantic meridional overturning circulation (AMOC) are examined in a freshwater perturbation simulation using the Bergen Climate Model (BCM). The results presented here are based on the model outputs of a previous freshwater experiment: a 300-year control integration (CTRL), a freshwater integration (FW1) which started after 100 years of running the CTRL with an artificially and continuously threefold increase in the freshwater flux to the Greenland-Iceland-Norwegian (GIN) Seas and the Arctic Ocean throughout the following 150-year simulation. In FW1, the transient response of the AMOC exhibits an initial decreasing of about 6 Sv (1 Sv=106 m3 s^-1) over the first 50-year integration and followed a gradual recovery during the last 100-year integration. Our results show that the vertical density stratification as the crucial property of the interior ocean plays an important role for the transient responses of AMOC by regulating the convective and diapycnal mixings under the enhanced freshwater input to northern high latitudes in BCM in which the ocean diapycnal mixing is stratification-dependent. The possible mechanism is also investigated in this paper.
基金The CAS/SAFEA International Partnership Program for Creative Research Teams of Chinese Academy of Sciencesthe National Natural Science Foundation of China under contract Nos 41422601,41376024 and 41376025
文摘Zonal overturning circulation (ZOC) and its associated zonal heat flux (ZHF) are important components of the oceanic circulation and climate system, although these conceptions have not received adequate attentions. Heaving induced by inter-annual and decadal wind stress perturbations can give rise to anomalous ZOC and ZHF. Based on a simple reduced gravity model, the anomalous ZOC and ZHF induced by idealized heaving modes in the world oceans are studied. For example, in a Pacific-like model basin intensified equatorial easterly on decadal time scales can lead to a negative ZOC with a non-negligible magnitude (-0.3×10^6 m^3/s) and a considerable westward ZHF with an amplitude of -11.2 TW. Thus, anomalous ZOC and ZHF may consist of a major part of climate signals on decadal time scales and thus play an important role in the oceanic circulation and climate change.
文摘Under strong seismic excitation, a rigid block will uplift from its support and undergo rocking oscillations which may lead to (complete) overturning. Numerical and analytical solutions to this highly nonlinear vibration problem are first highlighted in the paper and then utilized to demonstrate how sensitive the overturning behavior is not only to the intensity and frequency content of the base motion, but also to thc presence of strong pulses, to their detailed sequence, and even to their asymnletry. Five idealised pulses capable of representing "rupture-directivity" and "fling" affected ground motions near the fault, are utilized to this end : the one-cycle sinus, the one-cycle cosinus, the Ricker wavelet, the truncated (T)-Ricker wavelet, and the rectangular pulse "Overturning-Acceleration Amplification" and "Rotation" spectra are introduced and presented. Artificial neural network modeling is then developed as an alternative numerical solution. The neural network analysis leads to closed-form expressions for predicting the overturning failure or survival of a rigid block, as a function of its geometric properties and the characteristics of the excitation time history. The capability of the developed neural network modeling is validated through comparisons with the numerical solution. The derived analytical expressions could also serve as a tool for assessing the destructiveness of near-fault ground motions, for structures sensitive to rocking with foundation uplift.
基金The Strategic Priority Research Program of the Chinese Academy of Sciences under contract No.XDA11010302the National Natural Science Foundation of China under contract Nos 41276011,41521091 and U1406401the Research Project of Ministry of Education of China under contract No.113041A
文摘The structure of the annual-mean shallow meridional overturning circulation (SMOC) in the South China Sea (SCS) and the related water movement are investigated, using simple ocean data assimilation (SODA) outputs. The distinct clockwise SMOC is present above 400 m in the SCS on the climatologically annual-mean scale, which consists of downwelling in the northern SCS, a southward subsurface branch supplying upwelling at around 10°N and a northward surface flow, with a strength of about 1x 108 ma/s. The formation mechanisms of its branches are studied separately. The zonal component of the annual-mean wind stress is predominantly westward and causes northward Ekman transport above 50 m. The annual-mean Ekman transport across 18°N is about 1.2×106 m^3/s. An annual-mean subduction rate is calculated by estimating the net volume flux entering the thermocline from the mixed layer in a Lagrangian framework. An annual subduction rate of about 0.66×106 ma/s is obtained between 17° and 20°N, of which 87% is due to vertical pumping and 13% is due to lateral induction. The subduction rate implies that the subdution contributes significantly to the downwelling branch. The pathways of traced parcels released at the base of the February mixed layer show that after subduction water moves southward to as far as 1 I^N within the western boundary current before returning northward. The velocity field at the base of mixed layer and a meridional velocity section in winter also confirm that the southward flow in the subsurface layer is mainly by strong western boundary currents. Significant upwelling mainly occurs off the Vietnam coast in the southern SCS. An upper bound for the annual-mean net upwelfing rate between 10° and 15°N is 0.7×108 ma/s, of which a large portion is contributed by summer upwelling, with both the alongshore component of the southwest wind and its offshore increase causing great upwelling.
基金supported by the National Natural Science Foundation of China (No. 41176002)
文摘The mechanisms involved in the variability of Atlantic Meridional Overturning Circulation (AMOC) are studied using a 2000-yr control simulation of the coupled Fast Ocean-Atmosphere Model (FOAM).This study identifies a coupled mode between SST and surface heat flux in the North Atlantic at the decadal timescale,as well as a forcing mode of surface heat flux at the interannual timescale.The coupled mode is regulated by AMOC through meridional heat transport.The increase in surface heating in the North Atlantic weakens the AMOC approximately 10 yr later,and the weakened AMOC in turn decreases SST and sea surface salinity.The decreased SST results in an increase in surface heating in the North Atlantic,thus forming a positive feedback loop.Meanwhile,the weakened AMOC weakens northward heat transport and therefore lowers subsurface temperature approximately 19 yr later,which prevents the AMOC from weakening.In the forcing mode,the surface heat flux leads AMOC by approximately 4 yr.
基金The Strategic Priority Research Program of the Chinese Academy of Sciences under contract No.XDA11010302the National Natural Science Foundation of China under contract No.41376009the Joint Program of Shandong Province and National Natural Science Foundation of China under contract No.U1406401
文摘The low-frequency variability of the shallow meridional overturning circulation(MOC) in the South China Sea(SCS) is investigated using a Simple Ocean Data Assimilation(SODA) product for the period of 1900-2010. A dynamical decomposition method is used in which the MOC is decomposed into the Ekman, external mode, and vertical shear components. Results show that all the three dynamical components contribute to the formation of the seasonal and annual mean shallow MOC in the SCS. The shallow MOC in the SCS consists of two cells: a clockwise cell in the south and an anticlockwise cell in the north; the former is controlled by the Ekman flow and the latter is dominated by the external barotropic flow, with the contribution of the vertical shear being to reduce the magnitude of both cells. In addition, the strength of the MOC in the south is found to have a falling trend over the past century, due mainly to a weakening of the Luzon Strait transport(LST) that reduces the transport of the external component. Further analysis suggests that the weakening of the LST is closely related to a weakening of the westerly wind anomalies over the equatorial Pacific, which leads to a southward shift of the North Equatorial Current(NEC) bifurcation and thus a stronger transport of the Kuroshio east of Luzon.
基金Supported by the National Natural Science Foundation of China(Nos.41406012,41576060)the Open Fund of State Key Laboratory of Satellite Ocean Environment Dynamics(Second Institute of Oceanography)(No.SOED1613)+1 种基金the Open Fund of Key Laboratory of Global Change and Marine-Atmospheric Chemistry,State Oceanic Administration,China(No.GCMAC1501)the NSFC-Shandong Joint Fund for Marine Science Research Centers(No.U1406401)
文摘Based on the 50-year Simple Ocean Data Assimilation (SODA) reanalysis data, we investigated the basic characteristics and seasonal changes of the meridional heat transport carried by the North Pacific Meridional Overturning Circulation. And we also examined the dynamical and thermodynamic mechanisms responsible for these heat transport variability at the seasonal time scale. Among four cells, the tropical cell (TC) is strongest with a northward heat transport (NHT) of (1.75±0.30) PW (1 PW=1.0×10^15 W) and a southward heat transport (SHT) of (-1.69±0.55) PW, the subtropical cell (STC) is second with a NHT of (0.71±0.65) PW and SHT of (-0.63±0.53) PW, the deep tropical cell (DTC) is third with a NHT of (0.18±0.03) PW and SHT of (-0.18±0.11) PW, while the subpolar cell (SPC) is weakest with a NHT of (0.09±0.05) PW and SHT of (-0.07±0.09) PW. These four cells all have diff erent seasonal changes in their NHT and SHT. Of all, the TC has stronger change in its SHT than in its NHT, so do both the DTC and SPC, but the seasonal change in the STC SHT is weaker than that in its NHT. Therefore, their dynamical and thermodynamic mechanisms are diff erent each other. The local zonal wind stress and net surface heat flux are mainly responsible for the seasonal changes in the TC and STC NHTs and SPC SHT, while the local thermocline circulations and sea temperature are primarily responsible for the seasonal changes of the TC, STC and DTC SHTs and SPC NHT.
基金The National Natural Science Foundation of China under contract No.41306029the Basic Scientific Fund for National Public Research Institutes of China under contract Nos 2013T01 and 2014G25
文摘The climatologies of dissolved oxygen concentration in the ocean simulated by nine Earth system models(ESMs) from the historical emission driven experiment of CMIP5(Phase 5 of the Climate Model Intercomparison Project) are quantitatively evaluated by comparing the simulated oxygen to the WOA09 observation based on common statistical metrics. At the sea surface, distribution of dissolved oxygen is well simulated by all nine ESMs due to well-simulated sea surface temperature(SST), with both globally-averaged error and root mean square error(RMSE) close to zero, and both correlation coefficients and normalized standard deviation close to 1. However, the model performance differs from each other at the intermediate depth and deep ocean where important water masses exist. At the depth of 500 to 1 000 m where the oxygen minimum zones(OMZs) exist, all ESMs show a maximum of globally-averaged error and RMSE, and a minimum of the spatial correlation coefficient. In the ocean interior, the reason for model biases is complicated, and both the meridional overturning circulation(MOC) and the particulate organic carbon flux contribute to the biases of dissolved oxygen distribution. Analysis results show the physical bias contributes more. Simulation bias of important water masses such as North Atlantic Deep Water(NADW), Antarctic Bottom Water(AABW) and North Pacific Intermediate Water(NPIW) indicated by distributions of MOCs greatly affects the distributions of oxygen in north Atlantic, Southern Ocean and north Pacific, respectively.Although the model simulations of oxygen differ greatly from each other in the ocean interior, the multi-model mean shows a better agreement with the observation.
基金funded by the Strategic Priority Research Program of the Chinese Academy of Sciences(XDB 41000000)the National Natural Science Foundation of China(41773052,41973058,41603067,and 42003054)+1 种基金Key Research Program of Frontier Sciences,CAS(ZDBS-SSW-JSC007-10)Technical Support Talent Program of Chinese Academy of Sciences,2021。
文摘The lunar volcanic glasses and Mg-suite rocks represent the early enigmatic episodes of lunar magmatism.Due to the gravitational instability of the Fe-Ti enriched(±KREEP)layer,which is formed at the later stage of fractional crystallization,a post-magma-ocean cumulate overturn occurred contemporaneously or near-contemporaneously with the lunar magma ocean(LMO)solidification.The radioactive elements within the KREEP layer were transferred downward and provided continuous energy for the partial melting of the Moon’s interior.The melt from the Moon’s interior and those from decompression melting,in turn,provide source magma for the origin of lunar volcanic glasses and Mg-suite.However,experimental and theoretical studies on the formation process of lunar volcanic glasses and Mg-suite show that the origin of their parental magma is poorly constrained,which largely depends on the initial depth and composition of the LMO.This review examines the mineralogy,petrogenesis,and distribution of lunar volcanic glasses and Mg-suite.Combining with existing models,we constrain the degree,distribution,and timescale of lunar mantle overturn and explore their relationship with later stages of LMO differentiation.We propose an updated chemical composition of the lunar interior,which provides a useful reference for estimating the bulk composition and early differentiation of the Moon and the early Earth.
基金The Project of Comprehensive Evaluation of Polar Areas on Global and Regional Climate Changes under contract No.CHINARE2016-04-04the National Natural Science Foundation of China under contract No.41406027+1 种基金the NSFC-Shandong Joint Fund for Marine Science Research Centers under contract No.U1406404the Basic Research Operating Funds of The First Institute of Oceanography,State Oceanic Administration of China under contract Nos 2015P03 and 2015P01
文摘An increasing amount of freshwater has been observed to enter the Arctic Ocean from the six largest Eurasian rivers over the past several decades. The increasing trend is projected to continue in the twenty-first century according to Coupled Model Intercomparison Project Phase 5 (CMIP5) coupled models. The present study found that water flux from rivers to the Arctic Ocean at the end of the century will be 1.4 times that in 1950 according to CMIP5 projection results under Representative Concentration Pathway 8.5. The effect of increasing Arctic river runoff on the Atlantic meridional overturning circulation (AMOC) was investigated using an ocean-ice coupled model. Results obtained from two numerical experiments show that 100, 150 and 200 years after the start of an increase in the Arctic river runoff at a rate of 0.22%/a, the AMOC will weaken by 0.6 (3%), 1.2 (7%) and 1.8 (11%) Sv. AMOC weakening is mainly caused by freshwater transported from increasing Arctic river runoff inhibiting the formation of North Atlantic Deep Water (NADW). As the AMOC weakens, the deep seawater age will become older throughout the Atlantic Basin owing to the increasing of Arctic runoff.