The Agulhas Current is a major western boundary current flowing polewards on the southeast coast of South Africa.This analysis assesses its characteristics and suitability to generate power as a source of clean renewa...The Agulhas Current is a major western boundary current flowing polewards on the southeast coast of South Africa.This analysis assesses its characteristics and suitability to generate power as a source of clean renewable energy.On a section of coastline some 400 km long,over a period spanning more than 5 years an extensive set of current measurements was obtained.These data confirmed that south-westward currents with a speed greater than 1.2 m s^(-1)occurred over more than 60%of the recorded time;such ocean current speeds compare very favourably to winds required for energy generation.These currents occurred at the continental shelf break in water depths around 100 m,in the upper 50 m of the water column.Occasional current slowdowns and reversals did occur,with the major influence coming from‘Natal Pulses’,which are large-scale meanders in the Current that temporarily reversed the currents at the measurement sites.However,because of the surface temperature structure of the relevant water masses,such meanders can be identified in satellite imagery giving a few days advance warning of such current reversals.The characteristics of western boundary currents have been known for many years,but at Present,there is no operational system where this source of power is being utilised.It has tremendous potential for renewable energy generation,but is symptomatic of the many engineering challenges that still have to be solved to make such generation economically viable.展开更多
The Agulhas system is the strongest western boundary current system in the Southern Hemisphere and plays an important role in modulating the Indian-to-Atlantic Ocean water exchange by the Agulhas leakage.It is difficu...The Agulhas system is the strongest western boundary current system in the Southern Hemisphere and plays an important role in modulating the Indian-to-Atlantic Ocean water exchange by the Agulhas leakage.It is difficult to measure in situ transport of the Agulhas leakage as well as the Agulhas retroflection position due to their intermittent nature.In this study,an innovative kinematic algorithm was designed and applied to the gridded altimeter observational data,to ascertain the longitudinal position of Agulhas retroflection,the stability of Agulhas jet stream,as well as its strength.The results show that the east-west shift of retroflection is related neither to the strength of Agulhas current nor to its stability.Further analysis uncovers the connection between the westward extension of Agulhas jet stream and an anomalous cyclonic circulation at its northern side,which is likely attributed to the local wind stress curl anomaly.To confirm the effect of local wind forcing on the east-west shift of retroflection,numerical sensitivity experiments were conducted.The results show that the local wind stress can induce a similar longitudinal shift of the retroflection as altimetry observations.Further statistical and case study indicates that whether an Agulhas ring can continuously migrate westward to the Atlantic Ocean or re-merge into the main flow depends on the retroflection position.Therefore,the westward retroflection may contribute to a stronger Agulhas leakage than the eastward retroflection.展开更多
South Africa strengthens its efforts in polar and ocean research Under the command of Ashley Johnson,the iron gate on the starboard side of the S.A.Agulhas II vessel opened slowly,and the paired bongo nets,supported b...South Africa strengthens its efforts in polar and ocean research Under the command of Ashley Johnson,the iron gate on the starboard side of the S.A.Agulhas II vessel opened slowly,and the paired bongo nets,supported by a mechanised framework,gradually sank 100 metres into the sea.After being towed for a while,they were retrieved,and scientists on board sampled the plankton collected for analysis.Simultaneously,the bongo nets also gathered data on temperature,salinity,conductivity,and depth.Following this,the scientists deployed Niskin bottles to collect water samples from various depths.展开更多
In studies of upwelling,usually data from infrared and optical sensors is used which provides information on the sea surface temperature(SST)and the chlorophyll-a(Chl-a)concentration.In this paper,we show that also sy...In studies of upwelling,usually data from infrared and optical sensors is used which provides information on the sea surface temperature(SST)and the chlorophyll-a(Chl-a)concentration.In this paper,we show that also synthetic aperture radars(SAR)images can give valuable contribution to such studies.Upwelling regions become detectable by SAR because they are associated with a reduction of the radar backscatter due to(1)the change of the stability of the air-sea interface or/and(2)the presence of biogenic slicks.Furthermore,the boundary of upwelling regions consists of a line of increased radar backscatter due to the presence of convergent surface flow.展开更多
文摘The Agulhas Current is a major western boundary current flowing polewards on the southeast coast of South Africa.This analysis assesses its characteristics and suitability to generate power as a source of clean renewable energy.On a section of coastline some 400 km long,over a period spanning more than 5 years an extensive set of current measurements was obtained.These data confirmed that south-westward currents with a speed greater than 1.2 m s^(-1)occurred over more than 60%of the recorded time;such ocean current speeds compare very favourably to winds required for energy generation.These currents occurred at the continental shelf break in water depths around 100 m,in the upper 50 m of the water column.Occasional current slowdowns and reversals did occur,with the major influence coming from‘Natal Pulses’,which are large-scale meanders in the Current that temporarily reversed the currents at the measurement sites.However,because of the surface temperature structure of the relevant water masses,such meanders can be identified in satellite imagery giving a few days advance warning of such current reversals.The characteristics of western boundary currents have been known for many years,but at Present,there is no operational system where this source of power is being utilised.It has tremendous potential for renewable energy generation,but is symptomatic of the many engineering challenges that still have to be solved to make such generation economically viable.
基金The National Key R&D Program of China under contract No.2019YFA0606702the National Natural Science Foundation of China under contract Nos 42176222,91858202,41630963,and 41776003+1 种基金the National Science Foundation under contract No.NSF-IIS-2123264the fund suported by the National Aeronautics and Space Administration under contract No.NASA-80NSSC20M0220.
文摘The Agulhas system is the strongest western boundary current system in the Southern Hemisphere and plays an important role in modulating the Indian-to-Atlantic Ocean water exchange by the Agulhas leakage.It is difficult to measure in situ transport of the Agulhas leakage as well as the Agulhas retroflection position due to their intermittent nature.In this study,an innovative kinematic algorithm was designed and applied to the gridded altimeter observational data,to ascertain the longitudinal position of Agulhas retroflection,the stability of Agulhas jet stream,as well as its strength.The results show that the east-west shift of retroflection is related neither to the strength of Agulhas current nor to its stability.Further analysis uncovers the connection between the westward extension of Agulhas jet stream and an anomalous cyclonic circulation at its northern side,which is likely attributed to the local wind stress curl anomaly.To confirm the effect of local wind forcing on the east-west shift of retroflection,numerical sensitivity experiments were conducted.The results show that the local wind stress can induce a similar longitudinal shift of the retroflection as altimetry observations.Further statistical and case study indicates that whether an Agulhas ring can continuously migrate westward to the Atlantic Ocean or re-merge into the main flow depends on the retroflection position.Therefore,the westward retroflection may contribute to a stronger Agulhas leakage than the eastward retroflection.
文摘South Africa strengthens its efforts in polar and ocean research Under the command of Ashley Johnson,the iron gate on the starboard side of the S.A.Agulhas II vessel opened slowly,and the paired bongo nets,supported by a mechanised framework,gradually sank 100 metres into the sea.After being towed for a while,they were retrieved,and scientists on board sampled the plankton collected for analysis.Simultaneously,the bongo nets also gathered data on temperature,salinity,conductivity,and depth.Following this,the scientists deployed Niskin bottles to collect water samples from various depths.
基金Fundation of Ocean University of China(No.201965003)。
文摘In studies of upwelling,usually data from infrared and optical sensors is used which provides information on the sea surface temperature(SST)and the chlorophyll-a(Chl-a)concentration.In this paper,we show that also synthetic aperture radars(SAR)images can give valuable contribution to such studies.Upwelling regions become detectable by SAR because they are associated with a reduction of the radar backscatter due to(1)the change of the stability of the air-sea interface or/and(2)the presence of biogenic slicks.Furthermore,the boundary of upwelling regions consists of a line of increased radar backscatter due to the presence of convergent surface flow.
