The Pacific Decadal Oscillation （PDO） and the Atlantic Multidecadal Variability （AMV） are the two dominant low-frequency modes in the climate system. This research focused on the response of these two modes under ...The Pacific Decadal Oscillation （PDO） and the Atlantic Multidecadal Variability （AMV） are the two dominant low-frequency modes in the climate system. This research focused on the response of these two modes under weak global warming. Observational data were derived from the Hadley Center Sea Ice and Sea Surface Temperature dataset （HadISST） and coupled model outputs from the Coupled Model Intercomparison Project Phase 5 （CMIP5）. Changes in PDO and AMV were examined using four models （bcc-csml-1, CCSM4, IPSL-CM5A-LR, and MPI- ESM-LR） with long weak global warming scenarios （RCP2.6）. These models captured the two low-frequency modes in both pre-industrial run and RCP2.6 run. Under weak global warming, the time scales of PDO and AMV significantly decreased while the amplitude only slightly decreased. Interestingly, the standard deviation of the North Pacific sea surface temperature anomaly （SSTA） decreased only in decadal time scale, and that of the North Atlantic SSTA decreased both in interannual and decadal time scales. The coupled system consists of a slow ocean component, which has a decadal time scale, and a fast atmospheric component, which is calculated by subtracting the decadal from the total. Results suggest that under global warming, PDO change is dominated by ocean dynamics, and AMV change is dominated by ocean dynamics and stochastic atmosphere forcing.展开更多
The mesoscale eddy is a typical mesoscale oceanic phenomenon that transfers ocean energy. The detection and extraction of mesoscale eddies is an important aspect of physical oceanography, and automatic mesoscale eddy ...The mesoscale eddy is a typical mesoscale oceanic phenomenon that transfers ocean energy. The detection and extraction of mesoscale eddies is an important aspect of physical oceanography, and automatic mesoscale eddy detection algorithms are the most fundamental tools for detecting and analyzing mesoscale eddies. The main data used in mesoscale eddy detection are sea level anomaly(SLA) data merged by multi-satellite altimeters' data.These data objectively describe the state of the sea surface height. The mesoscale eddy can be represented by a local equivalent region surrounded by an SLA closed contour, and the detection process requires the extraction of a stable closed contour structure from SLA maps. In consideration of the characteristics of mesoscale eddy detection based on SLA data, this paper proposes a new automatic mesoscale eddy detection algorithm based on clustering. The mesoscale eddy structure can be extracted by separating and filtering SLA data sets to separate a mesoscale eddy region and non-eddy region and then establishing relationships among eddy regions and mapping them on SLA maps. This paper overcomes the problem of the sensitivity of parameter setting that affects the traditional detection algorithm and does not require a sensitivity test. The proposed algorithm is thus more adaptable. An eddy discrimination mechanism is added to the algorithm to ensure the stability of the detected eddy structure and to improve the detection accuracy. On this basis, the paper selects the Northwest Pacific Ocean and the South China Sea to carry out a mesoscale eddy detection experiment. Experimental results show that the proposed algorithm is more efficient than the traditional algorithm and the results of the algorithm remain stable. The proposed algorithm detects not only stable single-core eddies but also stable multi-core eddy structures.展开更多
Typhoon Imbudo was a super-typhoon over the northwestern Pacific in 2003. It caused tremendous damage when it made landfalls in the Philippines and China. This paper documents observational analyses of Typhoon Imbudo ...Typhoon Imbudo was a super-typhoon over the northwestern Pacific in 2003. It caused tremendous damage when it made landfalls in the Philippines and China. This paper documents observational analyses of Typhoon Imbudo during its landfall in China. All available observations are used to study its motion, intensity changes, convection, structure and precipitation. Best-track data indicate that Imbudo moved west-northwestward until 1800 UTC 23 July and then turned northwestward. FNL (final) analysis data show that the motion of Imbudo is dominated by changes of the subtropical high. At Imbudo's mature stage, the minimum sea level pressure dropped to 910 hPa and the maximum sustained winds were as high as 67 m s 1, which is the intensity of a super-typhoon. The surface wind field exhibited asymmetric characteristics. Polar-orbiting satellite imagery also manifested convective asymmetry before Imbudo made landfall in China. Analyzed the vertical wind shear, it is shown that the convection has a downshear-left pattern. All kinds of precipitation data were used to identify the asymmetric characteristic of the rainfall associated with the Imbudo. The maximum rainfalls were located in the southern boundary area between Guangxi and Guangdong. However, the lack of in situ observations limited further analyses of this typhoon.展开更多
The mainstream depth of a return flow can be viewed as an intrinsic depth of horizontal convection. By using a theoretical tube model combined with the application of the Maximum Entropy Production Principle (MaxEPP) ...The mainstream depth of a return flow can be viewed as an intrinsic depth of horizontal convection. By using a theoretical tube model combined with the application of the Maximum Entropy Production Principle (MaxEPP) in thermodynamics, the following statements can be made. Under fixed external forcing, the system chooses a particular depth as the mainstream depth of its return flow, the depth of which not only satisfies the maximum circulation rate and the maximum heat transport, but also satisfies the maximum entropy production rate. A comparison between this intrinsic depth and the container height leads to the definition of a relative partial and full-penetration pattern of the circulation. Moreover, this intrinsic depth is found to vary with the external forcing; the regulation of this variation is related to the Modified Rayleigh number.展开更多
This study produced a statistical analysis of multicore eddy structures based on 23 years’ altimetry data in global oceans. Multicore structures were identified using a threshold-free closed-contour algorithm of sea ...This study produced a statistical analysis of multicore eddy structures based on 23 years’ altimetry data in global oceans. Multicore structures were identified using a threshold-free closed-contour algorithm of sea surface height, which was improved for this study in respect of certain technical details. Meanwhile a more accurate definition of eddy boundary was used to estimate eddy scale. Generally, multicore structures, which have two or more closed eddies of the same polarity within their boundaries, represent an important transitional stage in their lives during which the component eddies might experience splitting or merging. In comparison with global eddies, the lifetimes and propagation distances of multicore eddies were found to be much smaller because of their inherent structural instability. However, at the same latitude, the spatial scale of multicore eddies was found larger than that of single-core eddies, i.e., the eddy area could be at least twice as large. Multicore eddies were found to exhibit some features similar to global eddies. For example, multicore eddies tend to occur in the Antarctic Circumpolar Current, some western boundary currents, and mid-latitude regions around 25°N/S, the majority(70%) of eddies propagate westward while only 30% propagate eastward, and large-amplitude eddies are restricted mainly to reasonably confined regions of highly unstable currents.展开更多
A theory of tailing wavetrain generation for the precursor soliton generation in two-layer flow is presented by using averaged KdV equations (AKdV), which are derived by the authors in terms of Whitham's method of...A theory of tailing wavetrain generation for the precursor soliton generation in two-layer flow is presented by using averaged KdV equations (AKdV), which are derived by the authors in terms of Whitham's method of averaging([1,2]). From the AKdV equations, group velocities of the tailing wavetrain generation are obtained by means of generating conditions of the tailing wavetrains, furthermore an analytical solution of the tailing wavetrain generation is found theoretically. A comparison between the theoretical and numerical results is carried out in the present paper, which shows that the theoretical results are in good agreement with the numerical ones, obtained from the fKdV equation in two-layer flow with the depth of unity in the rest.展开更多
In this paper,some data observed during the Intensive Observation Period of the South China Sea Monsoon Experiment (IOP-SCSMEX) were analyzed.Based on the meteorological observation data,the sea surface heat flux is c...In this paper,some data observed during the Intensive Observation Period of the South China Sea Monsoon Experiment (IOP-SCSMEX) were analyzed.Based on the meteorological observation data,the sea surface heat flux is calculated by the iterative flux-profile method.Based on the CTD (conductivity-temperature-depth) data the thermal and dynamical features of the mixed layer and its relation with the onset of the SCS summer monsoon were also analyzed.There are the thin barrier layers in the SCS in May and June,During the onset of summer monsoon in 1998,the barrier layer became thicker (about 28 m) than before monsoon onset (its thickness is 2-5 m) in north of the SCS.During May and June 1998,the variations of the upper mixed layer temperature and depth could be divided into three stages:before the summer monsoon onset,the onset period and after onset.There is not only difference of the thermal and dynamical features in the three stages,but also difference in the north and south observation points.The numerical simulation and experiment results to use the turbulence kinetic Energy (TKE) model are introduced in the two observation points.展开更多
文摘The Pacific Decadal Oscillation （PDO） and the Atlantic Multidecadal Variability （AMV） are the two dominant low-frequency modes in the climate system. This research focused on the response of these two modes under weak global warming. Observational data were derived from the Hadley Center Sea Ice and Sea Surface Temperature dataset （HadISST） and coupled model outputs from the Coupled Model Intercomparison Project Phase 5 （CMIP5）. Changes in PDO and AMV were examined using four models （bcc-csml-1, CCSM4, IPSL-CM5A-LR, and MPI- ESM-LR） with long weak global warming scenarios （RCP2.6）. These models captured the two low-frequency modes in both pre-industrial run and RCP2.6 run. Under weak global warming, the time scales of PDO and AMV significantly decreased while the amplitude only slightly decreased. Interestingly, the standard deviation of the North Pacific sea surface temperature anomaly （SSTA） decreased only in decadal time scale, and that of the North Atlantic SSTA decreased both in interannual and decadal time scales. The coupled system consists of a slow ocean component, which has a decadal time scale, and a fast atmospheric component, which is calculated by subtracting the decadal from the total. Results suggest that under global warming, PDO change is dominated by ocean dynamics, and AMV change is dominated by ocean dynamics and stochastic atmosphere forcing.
基金The National Key R&D Program of China under contract No.2016YFC1401800the National Natural Science Foundation of China under contract No.41576176the National Programme on Global Change and Air-Sea Interaction under contract Nos GASI-02-PAC-YGST2-04,GASI-02-IND-YGST2-04 and GASI-02-SCS-YGST2-04
文摘The mesoscale eddy is a typical mesoscale oceanic phenomenon that transfers ocean energy. The detection and extraction of mesoscale eddies is an important aspect of physical oceanography, and automatic mesoscale eddy detection algorithms are the most fundamental tools for detecting and analyzing mesoscale eddies. The main data used in mesoscale eddy detection are sea level anomaly(SLA) data merged by multi-satellite altimeters' data.These data objectively describe the state of the sea surface height. The mesoscale eddy can be represented by a local equivalent region surrounded by an SLA closed contour, and the detection process requires the extraction of a stable closed contour structure from SLA maps. In consideration of the characteristics of mesoscale eddy detection based on SLA data, this paper proposes a new automatic mesoscale eddy detection algorithm based on clustering. The mesoscale eddy structure can be extracted by separating and filtering SLA data sets to separate a mesoscale eddy region and non-eddy region and then establishing relationships among eddy regions and mapping them on SLA maps. This paper overcomes the problem of the sensitivity of parameter setting that affects the traditional detection algorithm and does not require a sensitivity test. The proposed algorithm is thus more adaptable. An eddy discrimination mechanism is added to the algorithm to ensure the stability of the detected eddy structure and to improve the detection accuracy. On this basis, the paper selects the Northwest Pacific Ocean and the South China Sea to carry out a mesoscale eddy detection experiment. Experimental results show that the proposed algorithm is more efficient than the traditional algorithm and the results of the algorithm remain stable. The proposed algorithm detects not only stable single-core eddies but also stable multi-core eddy structures.
基金This work was partly supported by the National Nature Science Foundation of China under the grant numbers of 40275033 and 40240420564the open project of the Shanghai Hphoon Institute.
文摘Typhoon Imbudo was a super-typhoon over the northwestern Pacific in 2003. It caused tremendous damage when it made landfalls in the Philippines and China. This paper documents observational analyses of Typhoon Imbudo during its landfall in China. All available observations are used to study its motion, intensity changes, convection, structure and precipitation. Best-track data indicate that Imbudo moved west-northwestward until 1800 UTC 23 July and then turned northwestward. FNL (final) analysis data show that the motion of Imbudo is dominated by changes of the subtropical high. At Imbudo's mature stage, the minimum sea level pressure dropped to 910 hPa and the maximum sustained winds were as high as 67 m s 1, which is the intensity of a super-typhoon. The surface wind field exhibited asymmetric characteristics. Polar-orbiting satellite imagery also manifested convective asymmetry before Imbudo made landfall in China. Analyzed the vertical wind shear, it is shown that the convection has a downshear-left pattern. All kinds of precipitation data were used to identify the asymmetric characteristic of the rainfall associated with the Imbudo. The maximum rainfalls were located in the southern boundary area between Guangxi and Guangdong. However, the lack of in situ observations limited further analyses of this typhoon.
基金Supported by the The National Basic Research Program (973 Program) (Nos. 2007CB816004, 2005CB422302)the National Outstanding Youth Natural Science Foundation of China (No. 40725017)
文摘The mainstream depth of a return flow can be viewed as an intrinsic depth of horizontal convection. By using a theoretical tube model combined with the application of the Maximum Entropy Production Principle (MaxEPP) in thermodynamics, the following statements can be made. Under fixed external forcing, the system chooses a particular depth as the mainstream depth of its return flow, the depth of which not only satisfies the maximum circulation rate and the maximum heat transport, but also satisfies the maximum entropy production rate. A comparison between this intrinsic depth and the container height leads to the definition of a relative partial and full-penetration pattern of the circulation. Moreover, this intrinsic depth is found to vary with the external forcing; the regulation of this variation is related to the Modified Rayleigh number.
基金The National Key Reasearch and Development Program of China under contract No.2016YFC1401800the National Natural Science Foundation of China under contract No.41576176+1 种基金the National Programme on Global Change and Air-Sea InteractionDragon 4 Project under contract No.32292
文摘This study produced a statistical analysis of multicore eddy structures based on 23 years’ altimetry data in global oceans. Multicore structures were identified using a threshold-free closed-contour algorithm of sea surface height, which was improved for this study in respect of certain technical details. Meanwhile a more accurate definition of eddy boundary was used to estimate eddy scale. Generally, multicore structures, which have two or more closed eddies of the same polarity within their boundaries, represent an important transitional stage in their lives during which the component eddies might experience splitting or merging. In comparison with global eddies, the lifetimes and propagation distances of multicore eddies were found to be much smaller because of their inherent structural instability. However, at the same latitude, the spatial scale of multicore eddies was found larger than that of single-core eddies, i.e., the eddy area could be at least twice as large. Multicore eddies were found to exhibit some features similar to global eddies. For example, multicore eddies tend to occur in the Antarctic Circumpolar Current, some western boundary currents, and mid-latitude regions around 25°N/S, the majority(70%) of eddies propagate westward while only 30% propagate eastward, and large-amplitude eddies are restricted mainly to reasonably confined regions of highly unstable currents.
基金The project is supported by the National Natural Science Foundation of China(No.49776284)
文摘A theory of tailing wavetrain generation for the precursor soliton generation in two-layer flow is presented by using averaged KdV equations (AKdV), which are derived by the authors in terms of Whitham's method of averaging([1,2]). From the AKdV equations, group velocities of the tailing wavetrain generation are obtained by means of generating conditions of the tailing wavetrains, furthermore an analytical solution of the tailing wavetrain generation is found theoretically. A comparison between the theoretical and numerical results is carried out in the present paper, which shows that the theoretical results are in good agreement with the numerical ones, obtained from the fKdV equation in two-layer flow with the depth of unity in the rest.
基金the SCSMEX of the Climbing Program Athe National Key Program for Developing Basic Science (G19992043807) under the Ministry of Science and Technology
文摘In this paper,some data observed during the Intensive Observation Period of the South China Sea Monsoon Experiment (IOP-SCSMEX) were analyzed.Based on the meteorological observation data,the sea surface heat flux is calculated by the iterative flux-profile method.Based on the CTD (conductivity-temperature-depth) data the thermal and dynamical features of the mixed layer and its relation with the onset of the SCS summer monsoon were also analyzed.There are the thin barrier layers in the SCS in May and June,During the onset of summer monsoon in 1998,the barrier layer became thicker (about 28 m) than before monsoon onset (its thickness is 2-5 m) in north of the SCS.During May and June 1998,the variations of the upper mixed layer temperature and depth could be divided into three stages:before the summer monsoon onset,the onset period and after onset.There is not only difference of the thermal and dynamical features in the three stages,but also difference in the north and south observation points.The numerical simulation and experiment results to use the turbulence kinetic Energy (TKE) model are introduced in the two observation points.
