Organic carbon, total nitrogen, amino acids, sugars, and chlorophyll were determined in < 1 mm fractions of the samples collected by successive large aperture time-series sediment traps (Honjo-Mark Ⅵ ) in northern...Organic carbon, total nitrogen, amino acids, sugars, and chlorophyll were determined in < 1 mm fractions of the samples collected by successive large aperture time-series sediment traps (Honjo-Mark Ⅵ ) in northern China China Sea during September 1987 to October1988. The ratio of C/N and the relative abundance of amino acids and sugars show that organicmatter in the settling particles from northem South China Sea is derived mainly from marineplantkon (especially phytoplankton). The organic carbon fluxes in our sediment traps are lowerthan those in other sediment traps. But the relative contents of Corg/total particulate matter aregenerally similar to those in the Panama Basin, Arabian Sea and Subarctic Pacific. It is suggested that monsoon-caused changes of physical and chemical conditions in the upper euphoticlayer would contro the fluxes of organic matter as well as its composition and transport innorthern South China Sea.展开更多
Trump’s South China Sea policy is now returning to balance and rationality following the initial tough stance that caused concern.The US will continue to meddle in the disputes,but it will be more difficult to influe...Trump’s South China Sea policy is now returning to balance and rationality following the initial tough stance that caused concern.The US will continue to meddle in the disputes,but it will be more difficult to influence the situation as regional actors adjust their policy objectives.展开更多
The general situation of the South China Sea in 2017 is easing with an obvious increase of regional cooperation.However,under the apparent calmness,there are two important changes:first,the problem of the South China ...The general situation of the South China Sea in 2017 is easing with an obvious increase of regional cooperation.However,under the apparent calmness,there are two important changes:first,the problem of the South China Sea has risen from a partial sovereignty issue to a monolithic issue of maritime rights;second,conflicts in the region still exist and展开更多
On March 1,the Experts Meeting on Maritime Confidence-Building in the South China Sea was co-held by CIIS and the Centre for Humanitarian Dialogue in Beijing.CIIS President Qi Zhenhong attended the meeting and gave op...On March 1,the Experts Meeting on Maritime Confidence-Building in the South China Sea was co-held by CIIS and the Centre for Humanitarian Dialogue in Beijing.CIIS President Qi Zhenhong attended the meeting and gave opening remarks.CIIS SecretaryGeneral Yang Yi hosted the meeting.展开更多
Daily and weekly sea surface temperature data of Tropical Rainfall Measuring Mission (TRMM) Microwave Imager and Advanced Microwave Scanning Radiometer-Earth Observing System sensors are used as forcing of the underly...Daily and weekly sea surface temperature data of Tropical Rainfall Measuring Mission (TRMM) Microwave Imager and Advanced Microwave Scanning Radiometer-Earth Observing System sensors are used as forcing of the underlying sea surface in the mesoscale numerical model to simulate Typhoon Dujuan that moved across the South China Sea in 2003. The numerical results show that different SSTs near the typhoon center result in differences in the atmospheric wind field, indicating that the model has a fast and obvious response to SSTs. Different SST influences the intensity and track of Dujuan to some degree and has significant impacts on its precipitation and latent heat flux near the eye. The SST influence on Dujuan is mainly fulfilled by changing the latent heat flux between the ocean surface and the atmosphere above.展开更多
The best track data of tropical cyclones (TCs) provided by Regional Specialized Meteorological Center (RSMC) Tokyo for the South China Sea (SCS) from 1977 to 2007 are employed to study the spatiotemporal variations (f...The best track data of tropical cyclones (TCs) provided by Regional Specialized Meteorological Center (RSMC) Tokyo for the South China Sea (SCS) from 1977 to 2007 are employed to study the spatiotemporal variations (for a period of 12 hours) and the rapid (slow) intensification (RI/SI) of TCs with different intensity. The main results are as follows. (1) Over this period, the tropical storms (TSs) and severe tropical storms (STSs) mostly intensify or are steady while the typhoons (TYs) mostly weaken. The stronger a TC is initially, the more observation of its intensification and the less its variability will be; the more observation of its weakening is, the larger its variability will be. (2) The TC intensifies the fastest at 0000 UTC while weakening the fastest at 1200 UTC. (3) In the intensifying state, TSs, STSs, and TYs are mainly active in the northeastern, central-eastern, and central SCS respectively. The weakening cases mainly distribute over waters east off Hainan Island and Vietnam and west off the Philippines. Some cases of TSs and STSs weaken over the central SCS. (4) The RI cases form farther south in contrast to the SI cases. The RI cases are observed in regions where there are weaker vertical shear and easterly components at 200 hPa. The RI cases also have stronger mid-and lower-level warm-core structure and smaller radii of 15.4 m/s winds. The SI cases have slightly higher SST.展开更多
Features of atmospheric circulation and thermal structures are discussed using the NCAR/NCEP data to reveal the reasons for the late onset and anomalous southward persistence of the South China Sea Summer Monsoon(SCSS...Features of atmospheric circulation and thermal structures are discussed using the NCAR/NCEP data to reveal the reasons for the late onset and anomalous southward persistence of the South China Sea Summer Monsoon(SCSSM) in 2005.The results show that three factors are crucial.First,a strong Arabian High overlaps with a high-latitude blocking high and channels strong cold air to southern Asia.Second,the Tibetan Plateau has a bigger snow cover than usual in spring and the melting of snow cools down the surface.Third,the Somali Jet breaks out at a much later date,being not conducive to convection over Indochina.The former two factors restrict atmospheric sensible heating over the Tibetan Plateau and nearby regions while the third one limits latent heating over Indochina.All of the factors slow down atmospheric warming and postpone the onset of SCSSM.Long after the onset of SCSSM,strong cold air over India advances the Southwest Monsoon northward slowly,resulting in weaker convection and latent heating over the Tibetan Plateau and nearby areas.The negative feedback conversely inhibits further northward movement of Southwest Monsoon.展开更多
The relationship between the intensity of the South China Sea summer monsoon （SCSSM） and the Nino3.4 index and anomalous atmospheric circulation patterns associated with a strong and weak SCSSM are investigated usin...The relationship between the intensity of the South China Sea summer monsoon （SCSSM） and the Nino3.4 index and anomalous atmospheric circulation patterns associated with a strong and weak SCSSM are investigated using the NCEP/NCAR reanalysis data, Extended Reconstructed Sea Surface Temperature （ERSST） data and Climate Prediction Center Merged Analysis of Precipitation （CMAP） data. The SCSSM is significantly positively correlated with the Nino3.4 index in the succeeding northern autumn and winter. In the strong minus weak SCSSM composite, a positive East Asia-Pacific teleconnection （EAP） pattern and a negative Europe-Asian-Pacific teleconnection （EUP） pattern appear in the 500 hPa height difference field; low-level cross-equatorial flows are strengthened over the Maritime Continent （MC） region; positive （negative） precipitation anomalies occur in the South China Sea and western north Pacific （MC）. A possible mechanism through which SCSSM affects ENSO is proposed. A strong （weak） SCSSM strengthens （weakens） cross-equatorial flows over the MC. The anomalous cross-equatorial flows cool （warm） the SST around the MC through enhanced （reduced） surface latent heat fluxes. The cooling （warming） further leads to suppressed （enhanced） convection over the MC, and causes the anomalous westerly （easterly） in the equatorial western Pacific, which favors the onset of E1 Nino （La Nina） through modulating the positive air-sea feedback process.展开更多
The northern slope region of the South China Sea(SCS) is a biological hot spot characterized by high primary productivity and biomasses transported by cross-shelf currents, which support the spawning and growth of com...The northern slope region of the South China Sea(SCS) is a biological hot spot characterized by high primary productivity and biomasses transported by cross-shelf currents, which support the spawning and growth of commercially and ecologically important fish species. To understand the physical and biogeochemical processes that promote the high primary production of this region, we conducted a cruise from June 10 and July 2, 2015. In this study, we used fuzzy cluster analysis and optimum multiparameter analysis methods to analyze the hydrographic data collected during the cruise to determine the compositions of the upper 55-m water masses on the SCS northern slope and thereby elucidate the cross-slope transport of shelf water(SHW) and the intrusions of Kuroshio water(KW). We also analyzed the geostrophic currents derived from acoustic Doppler current profiler measurements and satellite data. The results reveal the surface waters on the northern slope of the SCS to be primarily composed of waters originating from South China Sea water(SCSW), KW, and SHW. The SCSW dominated a majority of the study region at percentages ranging between 60% and 100%. We found a strong cross-slope current with speeds greater than 50 cms^(-1) to have carried SHW into and through the surveyed slope area, and KW to have intruded onto the slope via mesoscale eddies, thereby dominating the southwestern section of the study area.展开更多
The Global and Regional Assimilation and Prediction System (GRAPES), a limited-area regional model, was used to simulate the onset of South China Sea summer monsoon. In view of the relatively insufficient information ...The Global and Regional Assimilation and Prediction System (GRAPES), a limited-area regional model, was used to simulate the onset of South China Sea summer monsoon. In view of the relatively insufficient information about the initial field in simulation predictions, the Advanced Microwave Sounding Unit-B (AMSU-B) data from a NOAA satellite were introduced to improve the initial values. By directly using the 3-dimensional variational data assimilation system of GRAPES, two schemes for assimilation tests were designed. In the design, Test 1 (T1) assimilates both sounding and AMSU-B data, and Test 2 (T2) assimilates only the conventional sounding data, before applying the model in simulation forecasts. Comparative experiments showed that the model was very sensitive to initial fields and successful in reproducing the monsoon onset, allocation of high- and low-level wind fields during the pentad of onset, and the northward advancement of the monsoon and monsoon rain bands. The scheme, however, simulated rainfall and the location of the subtropical high with deviations from observations. The simulated location of the subtropical high was more westward and northward and the simulated rainfall for the South China Sea was larger and covered a broader area.展开更多
Natural hydrocarbon seeps in the marine environment are important contributors to greenhouse gases in the atmosphere. Such gases include methane, which plays a significant role in global carbon cycling and climate cha...Natural hydrocarbon seeps in the marine environment are important contributors to greenhouse gases in the atmosphere. Such gases include methane, which plays a significant role in global carbon cycling and climate change. To accurately quantify the methane flux from hydrocarbon seeps on the seafloor, a specialized in situ and online gas flux measuring(GFM) device was designed to obtain high-resolution time course gas fluxes using the process of equal volume exchange. The device consists of a 1.0-m diameter, 0.9-m tall, inverted conical tent and a GFM instrument that contains a solenoid valve, level transducer, and gas collection chamber. Rising gas bubbles from seeps were measured by laboratory-calibrated GFM instruments attached to the top of the tent. According to the experimental data, the optimal anti-shake time interval was 5 s. The measurement range of the device was 0–15 L min^(-1), and the relative error was ± 1.0%. The device was initially deployed at an active seep site in the Lingtou Promontory seep field in South China Sea. The amount of gas released from a single gas vent was 30.5 m^3 during the measurement period, and the gas flow rate ranged from 22 to 72 Lh^(-1), depending on tidal period, and was strongly negatively correlated with water depth. The measurement results strongly suggest that oceanic tides and swells had a significant forcing effect on gas flux. Low flow rates were associated with high tides and vice versa. The changes in gas volume escaping from the seafloor seeps could be attributed to the hydrostatic pressure induced by water depth. Our findings suggest that in the marine environment, especially in the shallow shelf area, sea level variation may play an important role in controlling methane release into the ocean. Such releases probably also affect atmospheric methane levels.展开更多
Coherent and incoherent internal tides(CITs and ICITs) in the southern South China Sea were investigated from two sets of _18-month mooring current records. The CITs were mainly composed of diurnal Q _1, O _1, P _1 an...Coherent and incoherent internal tides(CITs and ICITs) in the southern South China Sea were investigated from two sets of _18-month mooring current records. The CITs were mainly composed of diurnal Q _1, O _1, P _1 and K _1 and semidiurnal M_2. The observed diurnal internal tides(ITs) were more coherent than the semidiurnal constituents. Coherent diurnal variance accounted for approximately 58% of the diurnal motion, whereas semidiurnal tides contained a much smaller fraction(35%) of coherent motion. The ICITs mainly consisted of motion at non-tidal harmonic frequencies around the tidal frequency, and showed clear intermittency. The modal decomposition of CITs and ICITs showed that CITs were dominated by mode-1, whereas mode-1 and higher modes in ICITs signals showed comparable amplitudes. CITs and ICITs accounted for approximately 64% and 36% of the total kinetic energy of internal tides, respectively.展开更多
In this paper,we utilize the variational limiting equilibrium(LE) procedure to theoretically determine the slope stability of homogeneous coral sand in the South China Sea.By establishing a reasonable functional and c...In this paper,we utilize the variational limiting equilibrium(LE) procedure to theoretically determine the slope stability of homogeneous coral sand in the South China Sea.By establishing a reasonable functional and calculating its extremum,we can deduce the stability factor of a coral reef identical to that obtained by upper bound analysis.To determine the accuracy of the results obtained using the variational LE procedure,we present some classical examples of homogeneous sand slopes without a hard shell and compare our results with those obtained by the upper bound theorem of plasticity.A series of extensive calculations and comparisons reveal that the results obtained by our proposed analysis method and those obtained using classical methods are slightly different,but the variational results are believable.On the other hand,our method solves some stability factors for reef slopes covered with a hard shell,which indicates that the existence of a hard reef shell may significantly enhance the stability of a reef slope,and that there is strong nonlinear relationship between reef stability and the mechanical characteristics of the reef shell,such as its thickness and strength.Finally,based on the variational results presented in this paper,we present a useful chart that offers a convenient and straightforward way to determine the maximum stability factor of reef slopes.Taking into account the influence of the hard reef shell,we found that,in some limit equilibrium cases,the limit stability factor and critical height of a coral slope could be improved significantly.Therefore,this issue deserves careful attention in engineering practice.展开更多
文摘Organic carbon, total nitrogen, amino acids, sugars, and chlorophyll were determined in < 1 mm fractions of the samples collected by successive large aperture time-series sediment traps (Honjo-Mark Ⅵ ) in northern China China Sea during September 1987 to October1988. The ratio of C/N and the relative abundance of amino acids and sugars show that organicmatter in the settling particles from northem South China Sea is derived mainly from marineplantkon (especially phytoplankton). The organic carbon fluxes in our sediment traps are lowerthan those in other sediment traps. But the relative contents of Corg/total particulate matter aregenerally similar to those in the Panama Basin, Arabian Sea and Subarctic Pacific. It is suggested that monsoon-caused changes of physical and chemical conditions in the upper euphoticlayer would contro the fluxes of organic matter as well as its composition and transport innorthern South China Sea.
文摘Trump’s South China Sea policy is now returning to balance and rationality following the initial tough stance that caused concern.The US will continue to meddle in the disputes,but it will be more difficult to influence the situation as regional actors adjust their policy objectives.
文摘The general situation of the South China Sea in 2017 is easing with an obvious increase of regional cooperation.However,under the apparent calmness,there are two important changes:first,the problem of the South China Sea has risen from a partial sovereignty issue to a monolithic issue of maritime rights;second,conflicts in the region still exist and
文摘On March 1,the Experts Meeting on Maritime Confidence-Building in the South China Sea was co-held by CIIS and the Centre for Humanitarian Dialogue in Beijing.CIIS President Qi Zhenhong attended the meeting and gave opening remarks.CIIS SecretaryGeneral Yang Yi hosted the meeting.
基金Natural Science Foundation of China (U0733002, 40876009)Natural Science Foundation of Guangdong Province (8351030101000002)+1 种基金Science and Technology Planning Project of Guangdong Province (2008B030303025)Tropical Marine Meteorology Science Research Project
文摘Daily and weekly sea surface temperature data of Tropical Rainfall Measuring Mission (TRMM) Microwave Imager and Advanced Microwave Scanning Radiometer-Earth Observing System sensors are used as forcing of the underlying sea surface in the mesoscale numerical model to simulate Typhoon Dujuan that moved across the South China Sea in 2003. The numerical results show that different SSTs near the typhoon center result in differences in the atmospheric wind field, indicating that the model has a fast and obvious response to SSTs. Different SST influences the intensity and track of Dujuan to some degree and has significant impacts on its precipitation and latent heat flux near the eye. The SST influence on Dujuan is mainly fulfilled by changing the latent heat flux between the ocean surface and the atmosphere above.
基金Specialized Project for Forecasters, China Meteorological Administration 2011(CMAYBY2011-041)
文摘The best track data of tropical cyclones (TCs) provided by Regional Specialized Meteorological Center (RSMC) Tokyo for the South China Sea (SCS) from 1977 to 2007 are employed to study the spatiotemporal variations (for a period of 12 hours) and the rapid (slow) intensification (RI/SI) of TCs with different intensity. The main results are as follows. (1) Over this period, the tropical storms (TSs) and severe tropical storms (STSs) mostly intensify or are steady while the typhoons (TYs) mostly weaken. The stronger a TC is initially, the more observation of its intensification and the less its variability will be; the more observation of its weakening is, the larger its variability will be. (2) The TC intensifies the fastest at 0000 UTC while weakening the fastest at 1200 UTC. (3) In the intensifying state, TSs, STSs, and TYs are mainly active in the northeastern, central-eastern, and central SCS respectively. The weakening cases mainly distribute over waters east off Hainan Island and Vietnam and west off the Philippines. Some cases of TSs and STSs weaken over the central SCS. (4) The RI cases form farther south in contrast to the SI cases. The RI cases are observed in regions where there are weaker vertical shear and easterly components at 200 hPa. The RI cases also have stronger mid-and lower-level warm-core structure and smaller radii of 15.4 m/s winds. The SI cases have slightly higher SST.
基金National Key Fundamental Research Development Project (2004CB418302)
文摘Features of atmospheric circulation and thermal structures are discussed using the NCAR/NCEP data to reveal the reasons for the late onset and anomalous southward persistence of the South China Sea Summer Monsoon(SCSSM) in 2005.The results show that three factors are crucial.First,a strong Arabian High overlaps with a high-latitude blocking high and channels strong cold air to southern Asia.Second,the Tibetan Plateau has a bigger snow cover than usual in spring and the melting of snow cools down the surface.Third,the Somali Jet breaks out at a much later date,being not conducive to convection over Indochina.The former two factors restrict atmospheric sensible heating over the Tibetan Plateau and nearby regions while the third one limits latent heating over Indochina.All of the factors slow down atmospheric warming and postpone the onset of SCSSM.Long after the onset of SCSSM,strong cold air over India advances the Southwest Monsoon northward slowly,resulting in weaker convection and latent heating over the Tibetan Plateau and nearby areas.The negative feedback conversely inhibits further northward movement of Southwest Monsoon.
基金National Science Foundation of China under contract (4067505440505019)China Meteorological Administration (CMATG2006L03)
文摘The relationship between the intensity of the South China Sea summer monsoon （SCSSM） and the Nino3.4 index and anomalous atmospheric circulation patterns associated with a strong and weak SCSSM are investigated using the NCEP/NCAR reanalysis data, Extended Reconstructed Sea Surface Temperature （ERSST） data and Climate Prediction Center Merged Analysis of Precipitation （CMAP） data. The SCSSM is significantly positively correlated with the Nino3.4 index in the succeeding northern autumn and winter. In the strong minus weak SCSSM composite, a positive East Asia-Pacific teleconnection （EAP） pattern and a negative Europe-Asian-Pacific teleconnection （EUP） pattern appear in the 500 hPa height difference field; low-level cross-equatorial flows are strengthened over the Maritime Continent （MC） region; positive （negative） precipitation anomalies occur in the South China Sea and western north Pacific （MC）. A possible mechanism through which SCSSM affects ENSO is proposed. A strong （weak） SCSSM strengthens （weakens） cross-equatorial flows over the MC. The anomalous cross-equatorial flows cool （warm） the SST around the MC through enhanced （reduced） surface latent heat fluxes. The cooling （warming） further leads to suppressed （enhanced） convection over the MC, and causes the anomalous westerly （easterly） in the equatorial western Pacific, which favors the onset of E1 Nino （La Nina） through modulating the positive air-sea feedback process.
基金supported by the National Basic Research Program of China (No. 2014CB441500)the National Natural Science Foundation of China (No. 41406021)
文摘The northern slope region of the South China Sea(SCS) is a biological hot spot characterized by high primary productivity and biomasses transported by cross-shelf currents, which support the spawning and growth of commercially and ecologically important fish species. To understand the physical and biogeochemical processes that promote the high primary production of this region, we conducted a cruise from June 10 and July 2, 2015. In this study, we used fuzzy cluster analysis and optimum multiparameter analysis methods to analyze the hydrographic data collected during the cruise to determine the compositions of the upper 55-m water masses on the SCS northern slope and thereby elucidate the cross-slope transport of shelf water(SHW) and the intrusions of Kuroshio water(KW). We also analyzed the geostrophic currents derived from acoustic Doppler current profiler measurements and satellite data. The results reveal the surface waters on the northern slope of the SCS to be primarily composed of waters originating from South China Sea water(SCSW), KW, and SHW. The SCSW dominated a majority of the study region at percentages ranging between 60% and 100%. We found a strong cross-slope current with speeds greater than 50 cms^(-1) to have carried SHW into and through the surveyed slope area, and KW to have intruded onto the slope via mesoscale eddies, thereby dominating the southwestern section of the study area.
基金National 863 Special Project (2006AA01A123)Research on Interpretation Techniques for High-Resolution Numerical Prediction of Hunan ProvinceResearch on Rainstorm Forecast System with GRAPES and Its Application and Accessment in Hunan and Key Project of Science in Hunan (2008FJ1006)
文摘The Global and Regional Assimilation and Prediction System (GRAPES), a limited-area regional model, was used to simulate the onset of South China Sea summer monsoon. In view of the relatively insufficient information about the initial field in simulation predictions, the Advanced Microwave Sounding Unit-B (AMSU-B) data from a NOAA satellite were introduced to improve the initial values. By directly using the 3-dimensional variational data assimilation system of GRAPES, two schemes for assimilation tests were designed. In the design, Test 1 (T1) assimilates both sounding and AMSU-B data, and Test 2 (T2) assimilates only the conventional sounding data, before applying the model in simulation forecasts. Comparative experiments showed that the model was very sensitive to initial fields and successful in reproducing the monsoon onset, allocation of high- and low-level wind fields during the pentad of onset, and the northward advancement of the monsoon and monsoon rain bands. The scheme, however, simulated rainfall and the location of the subtropical high with deviations from observations. The simulated location of the subtropical high was more westward and northward and the simulated rainfall for the South China Sea was larger and covered a broader area.
基金provided by the National Scientific Foundation of China (Nos. 41676046 and 41306045)the Knowledge Innovation Project of the Chinese Academy of Sciences (Nos. SIDSSE-201208 and SQ201110)+1 种基金the 'Hundred Talents Program' of the Chinese Academy of Sciencesfinancial support from China Scholarship Council
文摘Natural hydrocarbon seeps in the marine environment are important contributors to greenhouse gases in the atmosphere. Such gases include methane, which plays a significant role in global carbon cycling and climate change. To accurately quantify the methane flux from hydrocarbon seeps on the seafloor, a specialized in situ and online gas flux measuring(GFM) device was designed to obtain high-resolution time course gas fluxes using the process of equal volume exchange. The device consists of a 1.0-m diameter, 0.9-m tall, inverted conical tent and a GFM instrument that contains a solenoid valve, level transducer, and gas collection chamber. Rising gas bubbles from seeps were measured by laboratory-calibrated GFM instruments attached to the top of the tent. According to the experimental data, the optimal anti-shake time interval was 5 s. The measurement range of the device was 0–15 L min^(-1), and the relative error was ± 1.0%. The device was initially deployed at an active seep site in the Lingtou Promontory seep field in South China Sea. The amount of gas released from a single gas vent was 30.5 m^3 during the measurement period, and the gas flow rate ranged from 22 to 72 Lh^(-1), depending on tidal period, and was strongly negatively correlated with water depth. The measurement results strongly suggest that oceanic tides and swells had a significant forcing effect on gas flux. Low flow rates were associated with high tides and vice versa. The changes in gas volume escaping from the seafloor seeps could be attributed to the hydrostatic pressure induced by water depth. Our findings suggest that in the marine environment, especially in the shallow shelf area, sea level variation may play an important role in controlling methane release into the ocean. Such releases probably also affect atmospheric methane levels.
基金Supported by the Special Fund of the Strategic Priority Research Program of Chinese Academy of Sciences(No.XDA11010202)the National Basic Research Program of China(973 Program)(No.2013CB430303)+1 种基金the National Natural Science Foundation of China(NSFC)(Nos.41376022,41276021)the CAS/SAFEA International Partnership Program for Creative Research Teams
文摘Coherent and incoherent internal tides(CITs and ICITs) in the southern South China Sea were investigated from two sets of _18-month mooring current records. The CITs were mainly composed of diurnal Q _1, O _1, P _1 and K _1 and semidiurnal M_2. The observed diurnal internal tides(ITs) were more coherent than the semidiurnal constituents. Coherent diurnal variance accounted for approximately 58% of the diurnal motion, whereas semidiurnal tides contained a much smaller fraction(35%) of coherent motion. The ICITs mainly consisted of motion at non-tidal harmonic frequencies around the tidal frequency, and showed clear intermittency. The modal decomposition of CITs and ICITs showed that CITs were dominated by mode-1, whereas mode-1 and higher modes in ICITs signals showed comparable amplitudes. CITs and ICITs accounted for approximately 64% and 36% of the total kinetic energy of internal tides, respectively.
基金supported by the National Science and Technology Ministry(No.2014BAB16B03)the National Natural Science Foundation of China(No.5167 9224)
文摘In this paper,we utilize the variational limiting equilibrium(LE) procedure to theoretically determine the slope stability of homogeneous coral sand in the South China Sea.By establishing a reasonable functional and calculating its extremum,we can deduce the stability factor of a coral reef identical to that obtained by upper bound analysis.To determine the accuracy of the results obtained using the variational LE procedure,we present some classical examples of homogeneous sand slopes without a hard shell and compare our results with those obtained by the upper bound theorem of plasticity.A series of extensive calculations and comparisons reveal that the results obtained by our proposed analysis method and those obtained using classical methods are slightly different,but the variational results are believable.On the other hand,our method solves some stability factors for reef slopes covered with a hard shell,which indicates that the existence of a hard reef shell may significantly enhance the stability of a reef slope,and that there is strong nonlinear relationship between reef stability and the mechanical characteristics of the reef shell,such as its thickness and strength.Finally,based on the variational results presented in this paper,we present a useful chart that offers a convenient and straightforward way to determine the maximum stability factor of reef slopes.Taking into account the influence of the hard reef shell,we found that,in some limit equilibrium cases,the limit stability factor and critical height of a coral slope could be improved significantly.Therefore,this issue deserves careful attention in engineering practice.
