Based on monthly mean Simple Ocean Data Assimilation （SODA） products from 1958 to 2007, this study analyzes the seasonal and interannual variability of the North Equatorial Current （NEC） bifurcation latitude and t...Based on monthly mean Simple Ocean Data Assimilation （SODA） products from 1958 to 2007, this study analyzes the seasonal and interannual variability of the North Equatorial Current （NEC） bifurcation latitude and the Indonesian Throughflow （ITF） volume transport. Further, Empirical Mode Decomposition （EMD） method and lag-correlation analysis are employed to reveal the relationships between the NEC bifurcation location, NEC and ITF volume transport and ENSO events. The analysis results of the seasonal variability show that the annual mean location of NEC bifurcation in upper layer occurs at 14.33°N and ITF volume transport has a maximum value in summer, a minimum value in winter and an annual mean transport of 7.75×10^6 m^3/s. The interannual variability analysis indicates that the variability of NEC bifurcation location can be treated as a precursor of El Nino. The correlation coefficient between the two reaches the maximum of 0.53 with a time lag of 2 months. The ITF volume transport is positively related with E1 Nifio events with a maximum coefficient of 0.60 by 3 months. The NEC bifurcation location is positively correlated with the ITF volume transport with a correlation coefficient of 0.43.展开更多
Fluorescence-based maximal photochemical efficiency, Fv/Fm, is widely used as an indicator to photosynthetic competence in marine systems. It has been considered a useful parameter diagnosing the nutrient stress on ph...Fluorescence-based maximal photochemical efficiency, Fv/Fm, is widely used as an indicator to photosynthetic competence in marine systems. It has been considered a useful parameter diagnosing the nutrient stress on phytoplankton photosynthesis, but many studies argue its usefulness. In the present study, we try to find a temporal relationship between Fv/Fm and nitrogen concentration, and provide a possible explanation on the controversy. We continuously measured Fv/Fm and nitrogen concentration once every 10 days from September 2003 to March 2004 at two stations in Jiaozhou Bay, northern China. It was found that Fv/ffm did not significantly correlate to synchronous nitrogen concentration, but the variation （i.e. the change between two adjacent cruises） of nitrogen concentration of the previous cruise and the variation ofFv/Fm of the current cruise were strongly correlated. This result indicates that a time lag exists between the variation of nutrient status and the subsequent Fv/Fm response. Length of the time lag seems just matched the interval of our measurements （10 days）. In the field, direct dependence of Fv/Fm on nitrogen concentration may not be found because of the lagged response of Fv/Fm to nitrogen concentration variations or physiological acclimation. Our results provide a possible way to explain the previously reported conflicting results on the relationship between Fv/Fm and nutrient status. To give a more-accurate estimate about the length of the time lag, an investigation that includes more frequent measurements is needed.展开更多
Unsteady flow characteristics of a normal shock wave,a lambda foot,and a separated turbulent boundary layer are investigated within a unique test section with supersonic inlet flow.The supersonic wind tunnel facility,...Unsteady flow characteristics of a normal shock wave,a lambda foot,and a separated turbulent boundary layer are investigated within a unique test section with supersonic inlet flow.The supersonic wind tunnel facility,containing this test section,provides a Mach number of approximately 1.54 at the test section entrance.Digitized shadowgraph flow visualization data are employed to visualize shock wave structure within the test section.These data are analyzed to determine shock wave unsteadiness characteristics,including grayscale spectral energy variations with frequency,as well as time and space correlations,which give coherence and time lag properties associated with perturbations associated with different flow regions.Results illustrate the complexity and unsteadiness of shock-wave-boundary-layerinteractions,including event frequencies from grayscale spectral energy distributions determined using a Lagrangian approach applied to shock wave location,and by grayscale spectral energy distributions determined using ensemble-averaging applied to multiple closely-located stationary pixel locations.Auto-correlation function results and two-point correlation functions(in the form of magnitude squared coherence)quantify the time-scales of periodic events,as well as the coherence of flow perturbations associated with different locations,over a range of frequencies.Associated time lag data provide information on the originating location of perturbation events,as well as the propagation direction and event sequence associated with different flow locations.Additional insight into spatial variations of time lag and flow coherence is provided by application of magnitude squared coherence analysis to multiple locations,relative to a single location associated with the normal shock wave.展开更多
以长江三角洲地区为研究区,利用2005年全年的MODIS地表温度产品和气象观测资料,定量分析了地表温度年内变化规律与气候因子之间的时滞响应关系。首先,通过谐波分析方法(Harmonic Analysis of Time Series,HANTS)消除地表温度数据中云的...以长江三角洲地区为研究区,利用2005年全年的MODIS地表温度产品和气象观测资料,定量分析了地表温度年内变化规律与气候因子之间的时滞响应关系。首先,通过谐波分析方法(Harmonic Analysis of Time Series,HANTS)消除地表温度数据中云的影响,提取地表温度时间序列谐波(即周期变化规律),重建地表温度无云时间序列;然后,利用DEM和纬度数据计算了研究区太阳辐射的空间分布,并将其与地表温度的年内变化进行时滞相关分析。0.991 6的相关系数表明:太阳辐射是地表温度年周期变化的主要控制因素,地表温度峰值出现的时间相对于太阳辐射时间而言滞后20 d左右;时滞相关分析表明,地表温度和气温之间的年内变化规律呈极显著相关,气温的变化相对于地表温度存在约5 d左右的滞后响应。展开更多
基金The National Natural Science Foundation of China under contract No.41476025the National Natural Science Foundation of China-Shandong Joint Fund for Marine Science Research Centers under contract No.U1406404+3 种基金the National High Technology Research and Development Program(863 Program) of China under contract No.2013AA09A506the National Program on Global Change and Air-Sea Interaction under contract No.GASI-03-01-01-04the International Cooperation Program of State Oceanic Administration of China under contract No.QY0213022the "Strategic Priority Research Program" of the Chinese Academy of Sciences under contract No.XDA11010301
文摘Based on monthly mean Simple Ocean Data Assimilation （SODA） products from 1958 to 2007, this study analyzes the seasonal and interannual variability of the North Equatorial Current （NEC） bifurcation latitude and the Indonesian Throughflow （ITF） volume transport. Further, Empirical Mode Decomposition （EMD） method and lag-correlation analysis are employed to reveal the relationships between the NEC bifurcation location, NEC and ITF volume transport and ENSO events. The analysis results of the seasonal variability show that the annual mean location of NEC bifurcation in upper layer occurs at 14.33°N and ITF volume transport has a maximum value in summer, a minimum value in winter and an annual mean transport of 7.75×10^6 m^3/s. The interannual variability analysis indicates that the variability of NEC bifurcation location can be treated as a precursor of El Nino. The correlation coefficient between the two reaches the maximum of 0.53 with a time lag of 2 months. The ITF volume transport is positively related with E1 Nifio events with a maximum coefficient of 0.60 by 3 months. The NEC bifurcation location is positively correlated with the ITF volume transport with a correlation coefficient of 0.43.
基金Supported by the Public Science and Technology Research Funds of Ocean(No.200905019)the Science Foundation of Young Scientist,SOA(No.2011129)+1 种基金the Outstanding Young & Middle Scientist of Shandong Province(No.BS2010HZ018)the Taishan Scholar Fund of Aquatic Animal Nutrition and Feed to ZHANG Limin
文摘Fluorescence-based maximal photochemical efficiency, Fv/Fm, is widely used as an indicator to photosynthetic competence in marine systems. It has been considered a useful parameter diagnosing the nutrient stress on phytoplankton photosynthesis, but many studies argue its usefulness. In the present study, we try to find a temporal relationship between Fv/Fm and nitrogen concentration, and provide a possible explanation on the controversy. We continuously measured Fv/Fm and nitrogen concentration once every 10 days from September 2003 to March 2004 at two stations in Jiaozhou Bay, northern China. It was found that Fv/ffm did not significantly correlate to synchronous nitrogen concentration, but the variation （i.e. the change between two adjacent cruises） of nitrogen concentration of the previous cruise and the variation ofFv/Fm of the current cruise were strongly correlated. This result indicates that a time lag exists between the variation of nutrient status and the subsequent Fv/Fm response. Length of the time lag seems just matched the interval of our measurements （10 days）. In the field, direct dependence of Fv/Fm on nitrogen concentration may not be found because of the lagged response of Fv/Fm to nitrogen concentration variations or physiological acclimation. Our results provide a possible way to explain the previously reported conflicting results on the relationship between Fv/Fm and nutrient status. To give a more-accurate estimate about the length of the time lag, an investigation that includes more frequent measurements is needed.
基金The Alabama Innovation Fund(Contract ID No.61070000002)the University of Alabama Endowment Fund,and the Office of the Vice President for Research and Economic Development of the University of Alabama in Huntsville are acknowledged for financial support for the research which is reported within the present paper.
文摘Unsteady flow characteristics of a normal shock wave,a lambda foot,and a separated turbulent boundary layer are investigated within a unique test section with supersonic inlet flow.The supersonic wind tunnel facility,containing this test section,provides a Mach number of approximately 1.54 at the test section entrance.Digitized shadowgraph flow visualization data are employed to visualize shock wave structure within the test section.These data are analyzed to determine shock wave unsteadiness characteristics,including grayscale spectral energy variations with frequency,as well as time and space correlations,which give coherence and time lag properties associated with perturbations associated with different flow regions.Results illustrate the complexity and unsteadiness of shock-wave-boundary-layerinteractions,including event frequencies from grayscale spectral energy distributions determined using a Lagrangian approach applied to shock wave location,and by grayscale spectral energy distributions determined using ensemble-averaging applied to multiple closely-located stationary pixel locations.Auto-correlation function results and two-point correlation functions(in the form of magnitude squared coherence)quantify the time-scales of periodic events,as well as the coherence of flow perturbations associated with different locations,over a range of frequencies.Associated time lag data provide information on the originating location of perturbation events,as well as the propagation direction and event sequence associated with different flow locations.Additional insight into spatial variations of time lag and flow coherence is provided by application of magnitude squared coherence analysis to multiple locations,relative to a single location associated with the normal shock wave.
文摘以长江三角洲地区为研究区,利用2005年全年的MODIS地表温度产品和气象观测资料,定量分析了地表温度年内变化规律与气候因子之间的时滞响应关系。首先,通过谐波分析方法(Harmonic Analysis of Time Series,HANTS)消除地表温度数据中云的影响,提取地表温度时间序列谐波(即周期变化规律),重建地表温度无云时间序列;然后,利用DEM和纬度数据计算了研究区太阳辐射的空间分布,并将其与地表温度的年内变化进行时滞相关分析。0.991 6的相关系数表明:太阳辐射是地表温度年周期变化的主要控制因素,地表温度峰值出现的时间相对于太阳辐射时间而言滞后20 d左右;时滞相关分析表明,地表温度和气温之间的年内变化规律呈极显著相关,气温的变化相对于地表温度存在约5 d左右的滞后响应。
