2002 Vol. 21, No. 2
Display Method:
2002, (2): 157-163.
Abstract:
A P-vector method is optimized using the variational data assimilation technique(VDAT).The absolute geostrophic velocity fields in the vicinity of the Luzon Strait (LS) are calculated,the spatial structures and seasonal variations of the absolute geostrophic velocity field are investigated.Our results show that the Kuroshio enters the South China Sea (SCS) in the south and middle of the Luzon Strait and flows out in the north,so the Kuroshio makes a slight clockwise curve in the Luzon Strait,and the curve is strong in winter and weak in summer.During the winter,a westward current appears in the surface,and locates at the west of the Luzon Strait.It is the north part of a cyclonic gyre which exits in the northeast of the SCS; an anticyclonic gyre occurs on the intermediate level,and it exits in the northeast of the SCS,and an eastward current exits in the southeast of the anti-cyclonic gyre.
A P-vector method is optimized using the variational data assimilation technique(VDAT).The absolute geostrophic velocity fields in the vicinity of the Luzon Strait (LS) are calculated,the spatial structures and seasonal variations of the absolute geostrophic velocity field are investigated.Our results show that the Kuroshio enters the South China Sea (SCS) in the south and middle of the Luzon Strait and flows out in the north,so the Kuroshio makes a slight clockwise curve in the Luzon Strait,and the curve is strong in winter and weak in summer.During the winter,a westward current appears in the surface,and locates at the west of the Luzon Strait.It is the north part of a cyclonic gyre which exits in the northeast of the SCS; an anticyclonic gyre occurs on the intermediate level,and it exits in the northeast of the SCS,and an eastward current exits in the southeast of the anti-cyclonic gyre.
2002, (2): 165-173.
Abstract:
Using Morlet wavelet transform and harmonic analysis the multiscale variability of subsurface temperature in the South China Sea is studied by analyzing one-year (from April 1998 to April 1999) ATLAS mooring data.By wavelet transform,annual and semi-annual cycle as well as intrasea-sonal variations are found,with different dominance,in subsurface temperature.For annual harmonic cycle,both the downward net surface heat flux and thermocline vertical movement partially control the subsurface temperature variability.For semi-annual cycle and intraseasonal variability,the subsurface temperature variability is mainly linked to the vertical displacement of thermocline.
Using Morlet wavelet transform and harmonic analysis the multiscale variability of subsurface temperature in the South China Sea is studied by analyzing one-year (from April 1998 to April 1999) ATLAS mooring data.By wavelet transform,annual and semi-annual cycle as well as intrasea-sonal variations are found,with different dominance,in subsurface temperature.For annual harmonic cycle,both the downward net surface heat flux and thermocline vertical movement partially control the subsurface temperature variability.For semi-annual cycle and intraseasonal variability,the subsurface temperature variability is mainly linked to the vertical displacement of thermocline.
2002, (2): 175-185.
Abstract:
An analysis of historical oxygen data provides evidence on the water exchange between the South China Sea (SCS) and the Pacific Ocean (PO).In the vicinity of the Luzon Strait (LS),the dissolved oxygen concentration of sea water is found to be lower on the Pacific side than on the SCS side at depths between 700 and 1500 m (intermediate layer),while the situation is reversed above 700 m (upper layer) and below 1 500 m (deep layer).The evidence suggests that water exits the SCS in the intermediate layer but enters it from the Pacific in both the upper and the deep layers,supporting the earlier speculation that the Luzon Strait transport has a sandwiched structure in the vertical.Within the SCS basin,the oxygen distribution indicates widespread vertical movement,including the upwelling in the intermediate layer and the downwelling in the deep layer.
An analysis of historical oxygen data provides evidence on the water exchange between the South China Sea (SCS) and the Pacific Ocean (PO).In the vicinity of the Luzon Strait (LS),the dissolved oxygen concentration of sea water is found to be lower on the Pacific side than on the SCS side at depths between 700 and 1500 m (intermediate layer),while the situation is reversed above 700 m (upper layer) and below 1 500 m (deep layer).The evidence suggests that water exits the SCS in the intermediate layer but enters it from the Pacific in both the upper and the deep layers,supporting the earlier speculation that the Luzon Strait transport has a sandwiched structure in the vertical.Within the SCS basin,the oxygen distribution indicates widespread vertical movement,including the upwelling in the intermediate layer and the downwelling in the deep layer.
2002, (2): 187-202.
Abstract:
A fine-resolution MOM code is used to study the South China Sea basin-scale circulation and its relation to the mass transport through the Luzon Strait.The modal domain includes the South China Sea,part of the East China Sea,and part of the Philippine Sea so that the currents in the vicinity of the Luzon Strait are free to evolve.In addition,all channels between the South China,Sea and the Indonesian seas are closed so that the focus is on the Luzon Strait transport.The model is driven by specified Philippine Sea currents and by surface heat and salt flux conditions.For simplicity,no windstress is applied at the surface.
The simulated Luzon Strait transport and the South China Sea circulation feature a sandwich vertical structure from the surface to the bottom.The Philippine Sea water is simulated to enter the South China Sea at the surface and in the deep ocean and is carried to the southern basin by western boundary currents.At the intermediate depth,the net Luzon Strait transport is out of the South China Sea and is fed by a western boundary current flowing to the north at the base of the thermocline.Corresponding to the western boundary currents,the basin circulation of the South China Sea is cyclonic gyres at the surface and in the abyss but an anticyclonic gyre at the intermediate depth.The vorticity balance of the gyre circulation is between the vortex stretching and the meridional change of the planetary vorticity.Based on these facts,it is hypothesized that the Luzon Strait transports are determined by the diapycnal mixing inside the entire South China Sea.The South China Sea plays the role of a "mixing mill" that mixes the surface and deep waters to return them to the Luzon Strait at the intermediate depth.The gyre structures are consistent with the Stommel and Arons theory (1960),which suggests that the mixlng-induced circulation inside the South China Sea should be cyclonic gyres at the surface and at the bottom but an anti-cyclonic gyre at the intermediate depth.The simulated gyre circulation at the intermediate depth has been confirmed by the dynamic height calculation based on the Levitns hydrography data.The sandwich transports in the Luzon Strait are consistent with recent hydrographic,al observations.
Model results suggest that the Kuroshio tends to form a loop current in the northeastern South China Sea.The simulated Kuroshio Loop Current is generated by the pressure head at the Pacific side of the Luzon Strait and is enhanced by the β-plane effects.The β-plane appears to be of paramount importance to the South China Sea circulation and to the Luzon Strait translports.Without the β-plane,the Luzon Strait transports would be greatly reduced and the South China Sea circulation would be complete-ly different.
A fine-resolution MOM code is used to study the South China Sea basin-scale circulation and its relation to the mass transport through the Luzon Strait.The modal domain includes the South China Sea,part of the East China Sea,and part of the Philippine Sea so that the currents in the vicinity of the Luzon Strait are free to evolve.In addition,all channels between the South China,Sea and the Indonesian seas are closed so that the focus is on the Luzon Strait transport.The model is driven by specified Philippine Sea currents and by surface heat and salt flux conditions.For simplicity,no windstress is applied at the surface.
The simulated Luzon Strait transport and the South China Sea circulation feature a sandwich vertical structure from the surface to the bottom.The Philippine Sea water is simulated to enter the South China Sea at the surface and in the deep ocean and is carried to the southern basin by western boundary currents.At the intermediate depth,the net Luzon Strait transport is out of the South China Sea and is fed by a western boundary current flowing to the north at the base of the thermocline.Corresponding to the western boundary currents,the basin circulation of the South China Sea is cyclonic gyres at the surface and in the abyss but an anticyclonic gyre at the intermediate depth.The vorticity balance of the gyre circulation is between the vortex stretching and the meridional change of the planetary vorticity.Based on these facts,it is hypothesized that the Luzon Strait transports are determined by the diapycnal mixing inside the entire South China Sea.The South China Sea plays the role of a "mixing mill" that mixes the surface and deep waters to return them to the Luzon Strait at the intermediate depth.The gyre structures are consistent with the Stommel and Arons theory (1960),which suggests that the mixlng-induced circulation inside the South China Sea should be cyclonic gyres at the surface and at the bottom but an anti-cyclonic gyre at the intermediate depth.The simulated gyre circulation at the intermediate depth has been confirmed by the dynamic height calculation based on the Levitns hydrography data.The sandwich transports in the Luzon Strait are consistent with recent hydrographic,al observations.
Model results suggest that the Kuroshio tends to form a loop current in the northeastern South China Sea.The simulated Kuroshio Loop Current is generated by the pressure head at the Pacific side of the Luzon Strait and is enhanced by the β-plane effects.The β-plane appears to be of paramount importance to the South China Sea circulation and to the Luzon Strait translports.Without the β-plane,the Luzon Strait transports would be greatly reduced and the South China Sea circulation would be complete-ly different.
2002, (2): 203-216.
Abstract:
A pair of remarkable meso-scale anticyclonic vortices,one formed closely to another,in the northern part of the South China Sea during the period from the later August to early September of 1994 were documented by the in situ observation data.Their spatial structures were examined in detail from the horizontal and two nearly perpendicular/vertical angles of view.It was shown that the horizontal scales of these two vortices were around 100,50 km,and their vertical scales were about 500,1000 m,respectively.Two "warm core" structures associated with these two vortices were found in their horizontal and vertical analyses.The closer spacing of these two vortices (namely,60 km),which was smaller than the Rossby radius of deformation,suggested that they might merge with each other during their next evolution stages and form into a larger vortex eventually.
A pair of remarkable meso-scale anticyclonic vortices,one formed closely to another,in the northern part of the South China Sea during the period from the later August to early September of 1994 were documented by the in situ observation data.Their spatial structures were examined in detail from the horizontal and two nearly perpendicular/vertical angles of view.It was shown that the horizontal scales of these two vortices were around 100,50 km,and their vertical scales were about 500,1000 m,respectively.Two "warm core" structures associated with these two vortices were found in their horizontal and vertical analyses.The closer spacing of these two vortices (namely,60 km),which was smaller than the Rossby radius of deformation,suggested that they might merge with each other during their next evolution stages and form into a larger vortex eventually.
2002, (2): 217-226.
Abstract:
A data-based hypothesis on the role of the South China Sea (SCS) in ENSO cycle is proposed:during El Niño,there are westerly wind anomaly over the western equatorial Pacific and positive SST anomaly in the eastern equatorial Pacific.Meanwhile anomalous convection moves to the central Pacific with anomalous sinking over Indonesian Archipelago.The latter can cause southerly wind anomaly over the north of South China Sea (NSCS) and makes the NSCS warmer.The warm NSCS can attract the anomalous convection to it in some degree.This attraction is in favor for producing easterly wind anomaly over the western equatorial Pacific,so it helps to form a cycle.
A data-based hypothesis on the role of the South China Sea (SCS) in ENSO cycle is proposed:during El Niño,there are westerly wind anomaly over the western equatorial Pacific and positive SST anomaly in the eastern equatorial Pacific.Meanwhile anomalous convection moves to the central Pacific with anomalous sinking over Indonesian Archipelago.The latter can cause southerly wind anomaly over the north of South China Sea (NSCS) and makes the NSCS warmer.The warm NSCS can attract the anomalous convection to it in some degree.This attraction is in favor for producing easterly wind anomaly over the western equatorial Pacific,so it helps to form a cycle.
2002, (2): 227-261.
Abstract:
In this study,we used the Navy's Master Oceanographic Observation Data Set (MOODS),consisting of 116 019 temperature and 9 617 salinity profiles,during 1968~1984 to investigate the temporal and spatial variabilities of South China Sea thermohaline structures and circulation.For temperature,profiles were binned into 204 monthly data sets from 1968 to 1984 (17 years).For salinity,profiles were binned into 12 climatological monthly data sets due to the data paucity.A twoscale optimal interpolation method was used to establish a three-dimensional monthly-varying gridded data set from MOODS,covering the area of 5°~25°N and 105°~125°E and the depth from the surface to 400 m.After the gridded data set had been established,both composite analysis and the Empirical Orthogonal Function (EOF) analysis (for temperature only) were used to identify the major thermohaline fratures including annual mean,monthly anomalies,and interarmual thermal variabilities.The inverted monthly circulation pattern using the P-vector method is also discussed.
In this study,we used the Navy's Master Oceanographic Observation Data Set (MOODS),consisting of 116 019 temperature and 9 617 salinity profiles,during 1968~1984 to investigate the temporal and spatial variabilities of South China Sea thermohaline structures and circulation.For temperature,profiles were binned into 204 monthly data sets from 1968 to 1984 (17 years).For salinity,profiles were binned into 12 climatological monthly data sets due to the data paucity.A twoscale optimal interpolation method was used to establish a three-dimensional monthly-varying gridded data set from MOODS,covering the area of 5°~25°N and 105°~125°E and the depth from the surface to 400 m.After the gridded data set had been established,both composite analysis and the Empirical Orthogonal Function (EOF) analysis (for temperature only) were used to identify the major thermohaline fratures including annual mean,monthly anomalies,and interarmual thermal variabilities.The inverted monthly circulation pattern using the P-vector method is also discussed.
2002, (2): 275-304.
Abstract:
The Zhujiang (Pearl River) Estuary is a complex water system whose catchments basin coveers a very large part of southern China.The large quantity of fresh water carried by the river system flows into the northern coast of the South China Sea through its eight inlets.The Zhujiang River Delta has experienced the fastest economic growth in China during the past two decades.Rapid population expansion and increased industrial development coupled with insufficient waste management turned the Zhujiang Estuary into waste disposal channels just before entering the coastal waters.The water quality of the estuaries and the coastal oceans has become polluted.Dttfing the past two years,an intensive study and monitoring efforts of the pollutions of these waters have been made.A systematic and integrated monitoring task including shore-based measurements,shipboard in-situ measurements,and satellite and radar remote sensing surveys has been completed.Conprehensive collection of physical,chemical and biological parameters has been accomplished and a database has been established.Unlike the previous large scale-monitoring task in which the various pollutant concentrations were the objective,the present study aims to understand the process of the pollution from their initial disposal to their final states.The understanding of the processes makes it possible to evaluate the severity of the pollution with respect to the sustainability.Also the objective is to incorporate these processes into the mathematical models from which a predictive capability of the pollution situation can be realized.The present presentation will describe the planning,methodology and the results of this effort.
The Zhujiang (Pearl River) Estuary is a complex water system whose catchments basin coveers a very large part of southern China.The large quantity of fresh water carried by the river system flows into the northern coast of the South China Sea through its eight inlets.The Zhujiang River Delta has experienced the fastest economic growth in China during the past two decades.Rapid population expansion and increased industrial development coupled with insufficient waste management turned the Zhujiang Estuary into waste disposal channels just before entering the coastal waters.The water quality of the estuaries and the coastal oceans has become polluted.Dttfing the past two years,an intensive study and monitoring efforts of the pollutions of these waters have been made.A systematic and integrated monitoring task including shore-based measurements,shipboard in-situ measurements,and satellite and radar remote sensing surveys has been completed.Conprehensive collection of physical,chemical and biological parameters has been accomplished and a database has been established.Unlike the previous large scale-monitoring task in which the various pollutant concentrations were the objective,the present study aims to understand the process of the pollution from their initial disposal to their final states.The understanding of the processes makes it possible to evaluate the severity of the pollution with respect to the sustainability.Also the objective is to incorporate these processes into the mathematical models from which a predictive capability of the pollution situation can be realized.The present presentation will describe the planning,methodology and the results of this effort.
2002, (2): 305-314.
Abstract:
The features of eddy kinetic energy (EKE) and the variations of upper circulation in the South China Sea (SCS) are discussed in this paper using geostrophic currents estimated from Maps of Sea Level Anomalies of the TOPEX/Poseidon altimetry data.A high EKE center is identified in the southeast,of Viemam coast with the highest energy level 1400 cm2·s-2 in both summer and autumn.This high EKE center is caused by the instability of the current axis leaving the coast of Vietnam in summer and the transition of seasonal circulation patterns in autumn.There exists another high EKE region in the northeastern SCS,southwest to Taiwan Island in winter.This high EKE region is generated from the eddy activities caused by the Kuroshio intrusion and accumulates more'than one third of the annual EKE,which confirms that the eddies are most active in winter.The transition of upper circulation patterns is also evidenced by the directions of the major axises of velocity variance ellipses between 10°and 14.5°N,which supports the model results reported before.
The features of eddy kinetic energy (EKE) and the variations of upper circulation in the South China Sea (SCS) are discussed in this paper using geostrophic currents estimated from Maps of Sea Level Anomalies of the TOPEX/Poseidon altimetry data.A high EKE center is identified in the southeast,of Viemam coast with the highest energy level 1400 cm2·s-2 in both summer and autumn.This high EKE center is caused by the instability of the current axis leaving the coast of Vietnam in summer and the transition of seasonal circulation patterns in autumn.There exists another high EKE region in the northeastern SCS,southwest to Taiwan Island in winter.This high EKE region is generated from the eddy activities caused by the Kuroshio intrusion and accumulates more'than one third of the annual EKE,which confirms that the eddies are most active in winter.The transition of upper circulation patterns is also evidenced by the directions of the major axises of velocity variance ellipses between 10°and 14.5°N,which supports the model results reported before.
2002, (2): 263-273.
Abstract:
By using remote sensing (ERS) data,FSU data,COADS data and Hellerman & Rosenstein objective analysis data to analyze the sea surface wind stress in the South China Sea,it is found that the remote sensing data have higher resolution and more reasonable values.Therefore we suggest that remote sensing data be chosen in the study of climatological features of sea surface wind stress and its seasonal variability in the South China Sea,especially in the study of small and middle scale eddies.
By using remote sensing (ERS) data,FSU data,COADS data and Hellerman & Rosenstein objective analysis data to analyze the sea surface wind stress in the South China Sea,it is found that the remote sensing data have higher resolution and more reasonable values.Therefore we suggest that remote sensing data be chosen in the study of climatological features of sea surface wind stress and its seasonal variability in the South China Sea,especially in the study of small and middle scale eddies.
