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Southern Ocean bathymetry constrains the path of the Antarctic Circumpolar Current (ACC), but the bathymetric influence on the coupled ocean–atmosphere system is poorly understood. Here, we investigate this impact by respectively flattening large topographic barriers around the Kerguelen Plateau, Campbell Plateau, Mid-Atlantic Ridge, and Drake Passage in four simulations in a coupled climate model. The barriers impact both the wind and buoyancy forcing of the ACC transport, which increases by between 4% and 14% when barriers are removed individually and by 56% when all barriers are removed simultaneously. The removal of Kerguelen Plateau bathymetry increases convection south of the plateau and the removal of Drake Passage bathymetry reduces convection upstream in the Ross Sea. When the barriers are removed, zonal flattening of the currents leads to sea surface temperature (SST) anomalies that strongly correlate to precipitation anomalies, with correlation coefficients ranging between r = 0.92 and r = 0.97 in the four experiments. The SST anomalies correlate to the surface winds too in some locations. However, they also generate circumpolar waves of sea level pressure (SLP) anomalies, which induce remote wind speed changes that are unconnected to the underlying SST field. The meridional variability in the wind stress curl contours over the Mid-Atlantic Ridge, the Kerguelen Plateau, and the Campbell Plateau disappears when these barriers are removed, confirming the impact of bathymetry on surface winds. However, bathymetry-induced wind changes are too small to affect the overall wave-3 asymmetry in the Southern Hemisphere westerlies. Removal of Southern Hemisphere orography is also inconsequential to the wave-3 pattern.

Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 52(6), (2022): 1233-1244, https://doi.org/10.1175/jpo-d-21-0223.1., The Sverdrup relation is the backbone of wind-driven circulation theory; it is a simple relation between the meridional transport of the wind-driven circulation in the upper ocean and the wind stress curl. However, the relation is valid for steady circulation only. In this study, a time-dependent Sverdrup relation is postulated, in which the meridional transport in a time-dependent circulation is the sum of the local wind stress curl term and a time-delayed term representing the effect of the eastern boundary condition. As an example, this time-dependent Sverdrup relation is evaluated through its application to the equatorial circulation in the Indian Ocean, using reanalysis data and a reduced gravity model. Close examination reveals that the southward Somali Current occurring during boreal winter is due to the combination of the local wind stress curl in the Arabian Sea and delayed signals representing the time change of layer thickness at the eastern boundary., This work is supported by NSFC (41822602, 41976016, 42005035, 42076021), the Strategic Priority Research Program of Chinese Academy of Sciences (XDB42000000, XDA 20060502), Key Special Project for Introduced Talents Team of Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou) (GML2019ZD0306), Guangdong Basic and Applied Basic Research Foundation (2021A1515011534), Youth Innovation Promotion Association CAS, ISEE2021ZD01, and LTOZZ2002. The numerical simulation is supported by the High-Performance Computing Division in the South China Sea Institute of Oceanology., 2022-11-27

Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 52(6), (2022): 1233-1244, https://doi.org/10.1175/jpo-d-21-0223.1., The Sverdrup relation is the backbone of wind-driven circulation theory; it is a simple relation between the meridional transport of the wind-driven circulation in the upper ocean and the wind stress curl. However, the relation is valid for steady circulation only. In this study, a time-dependent Sverdrup relation is postulated, in which the meridional transport in a time-dependent circulation is the sum of the local wind stress curl term and a time-delayed term representing the effect of the eastern boundary condition. As an example, this time-dependent Sverdrup relation is evaluated through its application to the equatorial circulation in the Indian Ocean, using reanalysis data and a reduced gravity model. Close examination reveals that the southward Somali Current occurring during boreal winter is due to the combination of the local wind stress curl in the Arabian Sea and delayed signals representing the time change of layer thickness at the eastern boundary., This work is supported by NSFC (41822602, 41976016, 42005035, 42076021), the Strategic Priority Research Program of Chinese Academy of Sciences (XDB42000000, XDA 20060502), Key Special Project for Introduced Talents Team of Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou) (GML2019ZD0306), Guangdong Basic and Applied Basic Research Foundation (2021A1515011534), Youth Innovation Promotion Association CAS, ISEE2021ZD01, and LTOZZ2002. The numerical simulation is supported by the High-Performance Computing Division in the South China Sea Institute of Oceanology., 2022-11-27

The Indonesian throughflow (ITF) transports a significant amount of warm freshwater from the Pacific to the Indian Ocean, making it critical to the global climate system. This study examines decadal ITF variations using ocean reanalysis data as well as climate model simulations from the Coupled Model Inter-comparison Project Phase 5 (CMIP5). While the observed annual cycle of ITF transport is known to be correlated with the annual cycle of sea surface height (SSH) difference between the Pacific and Indian Oceans, ocean reanalysis data (1959-2015) show that the Pacific Ocean SSH variability controls more than 85% of ITF variation on decadal timescales. In contrast, the Indian Ocean SSH variability contributes less than 15%. While those observed contributions are mostly reproduced in the CMIP5 historical simulations, an analysis of future climate projections shows a 25-30% increase in the Indian Ocean SSH variability to decadal ITF variations and a corresponding decrease in the Pacific contribution. These projected changes in the Indian Ocean SSH variability are associated with a 23% increase in the amplitudes of negative zonal wind stress anomalies over the equatorial Indian Ocean, along with a 12º eastward shift in the center of action in these anomalies. This combined effect of the increased amplitude and eastward shift in the zonal wind stress increases the SSHA variance over the Indian Ocean, increasing its contribution to the ITF variation. The decadal ITF changes discussed in this study will be crucial in understanding the future global climate variability, strongly coupled to Indo-Pacific interactions.

The southwestern tropical Atlantic is a region of complex ocean dynamic where originates the strong western boundary current system composed of North Brazil current and North Brazil undercurrent. The region includes a variety of features including the Atoll das Rocas (AR) and Fernando de Noronha (FN) ridge that may favour mesoscale eddy dynamics. However, origin, occurrence and characteristics of mesoscale eddies were still not described in the region. Using satellite altimetry data from 1993 to 2018 off Northeast Brazil (37-25°W; 13-1°S), we reconstruct eddy trajectories and analyse the main eddy surface characteristics (e.g., size, amplitude, polarity) and their spatiotemporal variations. The study reveals two distinct dynamic regions before quantifying mesoscale eddies characteristics. Approximately 2000 mesoscale eddies crossed the region during the study period, among which 76% were generated inside the region, with amplitudes and radii ranging between 1 and 2 cm and 25 and 205 km, respectively. Eddies are preferentially formed between August and September and propagate westward. In the region around the FN Archipelago (36-26°W; 6-1°S), the formation of cyclonic eddies is likely favoured by barotropic instabilities of surface currents and the wind stress curl. On the other hand, in the south of the region (36-26°W; 12-8°S), eddies formation is likely associated with the barotropic instabilities, wind stress curl and the meandering of surface currents. Based on vertical temperature and salinity profiles from Argo floats’ data, we determined that in average, the core of cyclonic eddies is centred at ~ 130 m (140 m) in the northern (southern) region while the core of anticyclonic eddies is centred at ~90 m (125 m) in the northern (southern) region. Moreover, mesoscale eddies formed in the tropical Atlantic do not connect the eastern tropical Atlantic and northeast Brazil.

The Indonesian throughflow (ITF) transports a significant amount of warm freshwater from the Pacific to the Indian Ocean, making it critical to the global climate system. This study examines decadal ITF variations using ocean reanalysis data as well as climate model simulations from the Coupled Model Inter-comparison Project Phase 5 (CMIP5). While the observed annual cycle of ITF transport is known to be correlated with the annual cycle of sea surface height (SSH) difference between the Pacific and Indian Oceans, ocean reanalysis data (1959-2015) show that the Pacific Ocean SSH variability controls more than 85% of ITF variation on decadal timescales. In contrast, the Indian Ocean SSH variability contributes less than 15%. While those observed contributions are mostly reproduced in the CMIP5 historical simulations, an analysis of future climate projections shows a 25-30% increase in the Indian Ocean SSH variability to decadal ITF variations and a corresponding decrease in the Pacific contribution. These projected changes in the Indian Ocean SSH variability are associated with a 23% increase in the amplitudes of negative zonal wind stress anomalies over the equatorial Indian Ocean, along with a 12º eastward shift in the center of action in these anomalies. This combined effect of the increased amplitude and eastward shift in the zonal wind stress increases the SSHA variance over the Indian Ocean, increasing its contribution to the ITF variation. The decadal ITF changes discussed in this study will be crucial in understanding the future global climate variability, strongly coupled to Indo-Pacific interactions.

The Indonesian throughflow (ITF) transports a significant amount of warm freshwater from the Pacific to the Indian Ocean, making it critical to the global climate system. This study examines decadal ITF variations using ocean reanalysis data as well as climate model simulations from the Coupled Model Inter-comparison Project Phase 5 (CMIP5). While the observed annual cycle of ITF transport is known to be correlated with the annual cycle of sea surface height (SSH) difference between the Pacific and Indian Oceans, ocean reanalysis data (1959-2015) show that the Pacific Ocean SSH variability controls more than 85% of ITF variation on decadal timescales. In contrast, the Indian Ocean SSH variability contributes less than 15%. While those observed contributions are mostly reproduced in the CMIP5 historical simulations, an analysis of future climate projections shows a 25-30% increase in the Indian Ocean SSH variability to decadal ITF variations and a corresponding decrease in the Pacific contribution. These projected changes in the Indian Ocean SSH variability are associated with a 23% increase in the amplitudes of negative zonal wind stress anomalies over the equatorial Indian Ocean, along with a 12º eastward shift in the center of action in these anomalies. This combined effect of the increased amplitude and eastward shift in the zonal wind stress increases the SSHA variance over the Indian Ocean, increasing its contribution to the ITF variation. The decadal ITF changes discussed in this study will be crucial in understanding the future global climate variability, strongly coupled to Indo-Pacific interactions.

The southwestern tropical Atlantic is a region of complex ocean dynamic where originates the strong western boundary current system composed of North Brazil current and North Brazil undercurrent. The region includes a variety of features including the Atoll das Rocas (AR) and Fernando de Noronha (FN) ridge that may favour mesoscale eddy dynamics. However, origin, occurrence and characteristics of mesoscale eddies were still not described in the region. Using satellite altimetry data from 1993 to 2018 off Northeast Brazil (37-25°W; 13-1°S), we reconstruct eddy trajectories and analyse the main eddy surface characteristics (e.g., size, amplitude, polarity) and their spatiotemporal variations. The study reveals two distinct dynamic regions before quantifying mesoscale eddies characteristics. Approximately 2000 mesoscale eddies crossed the region during the study period, among which 76% were generated inside the region, with amplitudes and radii ranging between 1 and 2 cm and 25 and 205 km, respectively. Eddies are preferentially formed between August and September and propagate westward. In the region around the FN Archipelago (36-26°W; 6-1°S), the formation of cyclonic eddies is likely favoured by barotropic instabilities of surface currents and the wind stress curl. On the other hand, in the south of the region (36-26°W; 12-8°S), eddies formation is likely associated with the barotropic instabilities, wind stress curl and the meandering of surface currents. Based on vertical temperature and salinity profiles from Argo floats’ data, we determined that in average, the core of cyclonic eddies is centred at ~ 130 m (140 m) in the northern (southern) region while the core of anticyclonic eddies is centred at ~90 m (125 m) in the northern (southern) region. Moreover, mesoscale eddies formed in the tropical Atlantic do not connect the eastern tropical Atlantic and northeast Brazil.

The Indonesian throughflow (ITF) transports a significant amount of warm freshwater from the Pacific to the Indian Ocean, making it critical to the global climate system. This study examines decadal ITF variations using ocean reanalysis data as well as climate model simulations from the Coupled Model Inter-comparison Project Phase 5 (CMIP5). While the observed annual cycle of ITF transport is known to be correlated with the annual cycle of sea surface height (SSH) difference between the Pacific and Indian Oceans, ocean reanalysis data (1959-2015) show that the Pacific Ocean SSH variability controls more than 85% of ITF variation on decadal timescales. In contrast, the Indian Ocean SSH variability contributes less than 15%. While those observed contributions are mostly reproduced in the CMIP5 historical simulations, an analysis of future climate projections shows a 25-30% increase in the Indian Ocean SSH variability to decadal ITF variations and a corresponding decrease in the Pacific contribution. These projected changes in the Indian Ocean SSH variability are associated with a 23% increase in the amplitudes of negative zonal wind stress anomalies over the equatorial Indian Ocean, along with a 12º eastward shift in the center of action in these anomalies. This combined effect of the increased amplitude and eastward shift in the zonal wind stress increases the SSHA variance over the Indian Ocean, increasing its contribution to the ITF variation. The decadal ITF changes discussed in this study will be crucial in understanding the future global climate variability, strongly coupled to Indo-Pacific interactions.

This study examines the modifications of air-sea coupling processes by dust-radiation-cloud interactions over the North Atlantic Ocean using a high-resolution coupled atmosphere-wave-ocean-dust (AWOD) regional model. The dust-induced mechanisms that are responsible for changes of sea surface temperature (SST) and latent and sensible heat fluxes (LHF/SHF) are also examined. Two 3-month numerical experiments are conducted, and they differ only in the activation and deactivation of dust-radiation-cloud interactions. Model results show that the dust significantly reduces surface downward radiation fluxes (SDRF) over the ocean with the maximum change of 20-30 W m-2. Over the dust plume region, the dust effect creates a low-pressure anomaly and a cyclonic circulation anomaly, which drives a positive wind stress curl anomaly, thereby reducing sea surface height and mixed layer depth. However, the SST change by dust, ranging from -0.5 to 0.5 K, has a great spatial variation which differs from the dust plume shape. Dust cools SST around the West African coast, except under the maximum dust plume ridge, and extends westward asymmetrically along the northern and southern edges of the dust plume. Dust unexpectedly warms SST over a large area of the western tropical North Atlantic and north of the dust plume. These SST changes are controlled by different mechanisms. Unlike the SST change pattern, the LHF and SHF changes are mostly reduced underneath the dust plume region, though they are different in detail due to different dominant factors, and increased south of the dust plume over the tropic.

This study examines the modifications of air-sea coupling processes by dust-radiation-cloud interactions over the North Atlantic Ocean using a high-resolution coupled atmosphere-wave-ocean-dust (AWOD) regional model. The dust-induced mechanisms that are responsible for changes of sea surface temperature (SST) and latent and sensible heat fluxes (LHF/SHF) are also examined. Two 3-month numerical experiments are conducted, and they differ only in the activation and deactivation of dust-radiation-cloud interactions. Model results show that the dust significantly reduces surface downward radiation fluxes (SDRF) over the ocean with the maximum change of 20-30 W m-2. Over the dust plume region, the dust effect creates a low-pressure anomaly and a cyclonic circulation anomaly, which drives a positive wind stress curl anomaly, thereby reducing sea surface height and mixed layer depth. However, the SST change by dust, ranging from -0.5 to 0.5 K, has a great spatial variation which differs from the dust plume shape. Dust cools SST around the West African coast, except under the maximum dust plume ridge, and extends westward asymmetrically along the northern and southern edges of the dust plume. Dust unexpectedly warms SST over a large area of the western tropical North Atlantic and north of the dust plume. These SST changes are controlled by different mechanisms. Unlike the SST change pattern, the LHF and SHF changes are mostly reduced underneath the dust plume region, though they are different in detail due to different dominant factors, and increased south of the dust plume over the tropic.

The Agulhas Current plays a significant role in both local and global ocean circulation and climate regulation, yet the mechanisms that determine the seasonal cycle of the current remain unclear, with discrepancies between ocean models and observations. Observations from moorings across the current and a 22 year proxy of Agulhas Current volume transport reveal that the current is over 25% stronger in austral summer than in winter. We hypothesize that winds over the Southern Indian Ocean play a critical role in determining this seasonal phasing through barotropic and first baroclinic mode adjustments and communication to the western boundary via Rossby waves. Our hypothesis is explored using single layer and one‐and‐a‐half layer models. We find that the barotropic contribution to seasonal phasing is small, with the majority of the seasonal signal deflected offshore and along the Mozambique Ridge. The summertime maximum and wintertime minimum can, however, be reproduced by a one‐and‐a‐half layer reduced gravity model in which adjustment time to wind forcing via Rossby waves is in line with observations from satellite altimetry. Additionally, near‐field winds (to the west of 35° E) are shown to have a controlling influence on the seasonal phasing, as signals from farther afield dissipate through destructive interference with overlying winds before reaching the western boundary. These results suggest a critical role for a baroclinic adjustment to near‐field winds in setting the summertime maximum in Agulhas Current transport. Plain Language Summary The Agulhas Current flows along the east coast of South Africa, transporting warm Indian Ocean water southwards, acting as a vital limb of the global ocean conveyor‐belt and influencing local rainfall and climate. This study looks at the seasonal cycle of the Agulhas Current and uses idealized models to explore how winds over the Southern Indian Ocean may influence this seasonality. The current is 25% stronger in summertime

The Agulhas Current plays a significant role in both local and global ocean circulation and climate regulation, yet the mechanisms that determine the seasonal cycle of the current remain unclear, with discrepancies between ocean models and observations. Observations from moorings across the current and a 22 year proxy of Agulhas Current volume transport reveal that the current is over 25% stronger in austral summer than in winter. We hypothesize that winds over the Southern Indian Ocean play a critical role in determining this seasonal phasing through barotropic and first baroclinic mode adjustments and communication to the western boundary via Rossby waves. Our hypothesis is explored using single layer and one‐and‐a‐half layer models. We find that the barotropic contribution to seasonal phasing is small, with the majority of the seasonal signal deflected offshore and along the Mozambique Ridge. The summertime maximum and wintertime minimum can, however, be reproduced by a one‐and‐a‐half layer reduced gravity model in which adjustment time to wind forcing via Rossby waves is in line with observations from satellite altimetry. Additionally, near‐field winds (to the west of 35° E) are shown to have a controlling influence on the seasonal phasing, as signals from farther afield dissipate through destructive interference with overlying winds before reaching the western boundary. These results suggest a critical role for a baroclinic adjustment to near‐field winds in setting the summertime maximum in Agulhas Current transport. Plain Language Summary The Agulhas Current flows along the east coast of South Africa, transporting warm Indian Ocean water southwards, acting as a vital limb of the global ocean conveyor‐belt and influencing local rainfall and climate. This study looks at the seasonal cycle of the Agulhas Current and uses idealized models to explore how winds over the Southern Indian Ocean may influence this seasonality. The current is 25% stronger in summertime

The Agulhas Current plays a significant role in both local and global ocean circulation and climate regulation, yet the mechanisms that determine the seasonal cycle of the current remain unclear, with discrepancies between ocean models and observations. Observations from moorings across the current and a 22 year proxy of Agulhas Current volume transport reveal that the current is over 25% stronger in austral summer than in winter. We hypothesize that winds over the Southern Indian Ocean play a critical role in determining this seasonal phasing through barotropic and first baroclinic mode adjustments and communication to the western boundary via Rossby waves. Our hypothesis is explored using single layer and one‐and‐a‐half layer models. We find that the barotropic contribution to seasonal phasing is small, with the majority of the seasonal signal deflected offshore and along the Mozambique Ridge. The summertime maximum and wintertime minimum can, however, be reproduced by a one‐and‐a‐half layer reduced gravity model in which adjustment time to wind forcing via Rossby waves is in line with observations from satellite altimetry. Additionally, near‐field winds (to the west of 35° E) are shown to have a controlling influence on the seasonal phasing, as signals from farther afield dissipate through destructive interference with overlying winds before reaching the western boundary. These results suggest a critical role for a baroclinic adjustment to near‐field winds in setting the summertime maximum in Agulhas Current transport. Plain Language Summary The Agulhas Current flows along the east coast of South Africa, transporting warm Indian Ocean water southwards, acting as a vital limb of the global ocean conveyor‐belt and influencing local rainfall and climate. This study looks at the seasonal cycle of the Agulhas Current and uses idealized models to explore how winds over the Southern Indian Ocean may influence this seasonality. The current is 25% stronger in summertime

The Agulhas Current plays a significant role in both local and global ocean circulation and climate regulation, yet the mechanisms that determine the seasonal cycle of the current remain unclear, with discrepancies between ocean models and observations. Observations from moorings across the current and a 22 year proxy of Agulhas Current volume transport reveal that the current is over 25% stronger in austral summer than in winter. We hypothesize that winds over the Southern Indian Ocean play a critical role in determining this seasonal phasing through barotropic and first baroclinic mode adjustments and communication to the western boundary via Rossby waves. Our hypothesis is explored using single layer and one‐and‐a‐half layer models. We find that the barotropic contribution to seasonal phasing is small, with the majority of the seasonal signal deflected offshore and along the Mozambique Ridge. The summertime maximum and wintertime minimum can, however, be reproduced by a one‐and‐a‐half layer reduced gravity model in which adjustment time to wind forcing via Rossby waves is in line with observations from satellite altimetry. Additionally, near‐field winds (to the west of 35° E) are shown to have a controlling influence on the seasonal phasing, as signals from farther afield dissipate through destructive interference with overlying winds before reaching the western boundary. These results suggest a critical role for a baroclinic adjustment to near‐field winds in setting the summertime maximum in Agulhas Current transport. Plain Language Summary The Agulhas Current flows along the east coast of South Africa, transporting warm Indian Ocean water southwards, acting as a vital limb of the global ocean conveyor‐belt and influencing local rainfall and climate. This study looks at the seasonal cycle of the Agulhas Current and uses idealized models to explore how winds over the Southern Indian Ocean may influence this seasonality. The current is 25% stronger in summertime

This study investigated the eastern Pacific Intertropical Convergence Zone (ITCZ) as an atmospheric forcing to the ocean by using various observed and reanalysis data sets over 29 years. Climatologically, a zonal band of positive wind stress curl (WSC) with a 10° meridional width was exhibited along the ITCZ. A southward shift of the positive WSC band during the El Niño phase induced a negative (positive) WSC anomaly along the northern (southern) portion of the ITCZ, and vice versa during the La Niña phase. This meridional dipole accounted for more than 25 % of interannual variances of the WSC anomalies (WSCAs), based on analysis of the period 1993–2008. The negative (positive) WSCA in the northern portion of the ITCZ during the El Niño (La Niña) phase was collocated with a positive (negative) sea surface height anomaly (SSHA) that propagated westward as a Rossby wave all the way to the western North Pacific. This finding indicates that this off-equatorial Rossby wave is induced by the WSCA around the ITCZ. Our analysis of a 1.5-layer reduced gravity model revealed that the Rossby waves are mostly explained by wind stress forcing, rather than by reflection of an equatorial Kelvin wave on the eastern coastal boundary. The off-equatorial Rossby wave had the same SSHA polarity as the equatorial Kelvin wave, and generation of a phase-preserving Rossby wave without the Kelvin wave reflection was explained by meridional movement of the ITCZ. Thus, the ITCZ acts as an atmospheric bridge that connects the equatorial and off-equatorial oceanic waves.

This study investigated the eastern Pacific Intertropical Convergence Zone (ITCZ) as an atmospheric forcing to the ocean by using various observed and reanalysis data sets over 29 years. Climatologically, a zonal band of positive wind stress curl (WSC) with a 10° meridional width was exhibited along the ITCZ. A southward shift of the positive WSC band during the El Niño phase induced a negative (positive) WSC anomaly along the northern (southern) portion of the ITCZ, and vice versa during the La Niña phase. This meridional dipole accounted for more than 25 % of interannual variances of the WSC anomalies (WSCAs), based on analysis of the period 1993–2008. The negative (positive) WSCA in the northern portion of the ITCZ during the El Niño (La Niña) phase was collocated with a positive (negative) sea surface height anomaly (SSHA) that propagated westward as a Rossby wave all the way to the western North Pacific. This finding indicates that this off-equatorial Rossby wave is induced by the WSCA around the ITCZ. Our analysis of a 1.5-layer reduced gravity model revealed that the Rossby waves are mostly explained by wind stress forcing, rather than by reflection of an equatorial Kelvin wave on the eastern coastal boundary. The off-equatorial Rossby wave had the same SSHA polarity as the equatorial Kelvin wave, and generation of a phase-preserving Rossby wave without the Kelvin wave reflection was explained by meridional movement of the ITCZ. Thus, the ITCZ acts as an atmospheric bridge that connects the equatorial and off-equatorial oceanic waves.

This study investigated the eastern Pacific Intertropical Convergence Zone (ITCZ) as an atmospheric forcing to the ocean by using various observed and reanalysis data sets over 29 years. Climatologically, a zonal band of positive wind stress curl (WSC) with a 10° meridional width was exhibited along the ITCZ. A southward shift of the positive WSC band during the El Niño phase induced a negative (positive) WSC anomaly along the northern (southern) portion of the ITCZ, and vice versa during the La Niña phase. This meridional dipole accounted for more than 25 % of interannual variances of the WSC anomalies (WSCAs), based on analysis of the period 1993–2008. The negative (positive) WSCA in the northern portion of the ITCZ during the El Niño (La Niña) phase was collocated with a positive (negative) sea surface height anomaly (SSHA) that propagated westward as a Rossby wave all the way to the western North Pacific. This finding indicates that this off-equatorial Rossby wave is induced by the WSCA around the ITCZ. Our analysis of a 1.5-layer reduced gravity model revealed that the Rossby waves are mostly explained by wind stress forcing, rather than by reflection of an equatorial Kelvin wave on the eastern coastal boundary. The off-equatorial Rossby wave had the same SSHA polarity as the equatorial Kelvin wave, and generation of a phase-preserving Rossby wave without the Kelvin wave reflection was explained by meridional movement of the ITCZ. Thus, the ITCZ acts as an atmospheric bridge that connects the equatorial and off-equatorial oceanic waves.

The Southern Ocean Subtropical Front (STF) is thought to play a key role in the global climate system. Theory suggests that the latitude of the STF regulates the volume of saline Agulhas Leakage into the Atlantic Ocean from the Indian. Here we use satellite sea surface temperature (SST) and sea surface height (SSH) data to study the physical characteristics of the STF water mass boundary. We find that the strong currents in this region do not align with the surface water mass boundary. Therefore, we provide a new climatology for these currents which we define as the Dynamical STF (DSTF). The DSTF is the eastward extension of the western boundary current in each basin and is characterized by strong SST and SSH gradients and no seasonal cycle. At the center of each basin it merges with the Sub-Antarctic Front. On the eastern side of basins, the STF surface water mass boundary coincides with a separate region of multiple SST fronts. We call this the Subtropical Frontal Zone (STFZ). The fronts in the STFZ have a large seasonal cycle and no SSH signature. Despite lying close to the same water mass boundary, the DSTF and STFZ are completely unrelated. We therefore suggest the term STF only be used when referring to the surface water mass boundary. When studying the strong currents on the western side of basins the term DSTF is more relevant and, similarly, the term STFZ better describes the region of enhanced SST gradients towards the east., AuthorCount: 2

In recent years the latitudinal position of the Subtropical Front (STF) has emerged as a key parameter in the global climate. A poleward positioned front is thought to allow a greater salt flux from the Indian to the Atlantic Ocean and so drive a stronger Atlantic Meridional Overturning Circulation. Here the common view that the STF aligns with the zero wind stress curl (WSC) is challenged. Based on the STF climatologies of Orsi et al. (1995), Belkin and Gordon (1996), Graham and De Boer (2013), and on satellite scatterometry winds, we find that the zero WSC contour lies on average ∼10°, ∼8°, and ∼5° poleward of the front for the three climatologies, respectively. The circulation in the region between the Subtropical Gyres and the zero WSC contour is not forced by the WSC but rather by the strong bottom pressure torque that is a result of the interaction of the Antarctic Circumpolar Current with the ocean floor topography. The actual control of the position of the STF is crucially dependent on whether the front is regarded as simply a surface water mass boundary or a dynamical front. For the Agulhas Leakage problem, the southern boundary of the so-called Super Gyre may be the most relevant property but this cannot easily be identified in observations., AuthorCount: 4

In recent years the latitudinal position of the Subtropical Front (STF) has emerged as a key parameter in the global climate. A poleward positioned front is thought to allow a greater salt flux from the Indian to the Atlantic Ocean and so drive a stronger Atlantic Meridional Overturning Circulation. Here the common view that the STF aligns with the zero wind stress curl (WSC) is challenged. Based on the STF climatologies of Orsi et al. (1995), Belkin and Gordon (1996), Graham and De Boer (2013), and on satellite scatterometry winds, we find that the zero WSC contour lies on average ∼10°, ∼8°, and ∼5° poleward of the front for the three climatologies, respectively. The circulation in the region between the Subtropical Gyres and the zero WSC contour is not forced by the WSC but rather by the strong bottom pressure torque that is a result of the interaction of the Antarctic Circumpolar Current with the ocean floor topography. The actual control of the position of the STF is crucially dependent on whether the front is regarded as simply a surface water mass boundary or a dynamical front. For the Agulhas Leakage problem, the southern boundary of the so-called Super Gyre may be the most relevant property but this cannot easily be identified in observations., AuthorCount: 4

The Southern Ocean Subtropical Front (STF) is thought to play a key role in the global climate system. Theory suggests that the latitude of the STF regulates the volume of saline Agulhas Leakage into the Atlantic Ocean from the Indian. Here we use satellite sea surface temperature (SST) and sea surface height (SSH) data to study the physical characteristics of the STF water mass boundary. We find that the strong currents in this region do not align with the surface water mass boundary. Therefore, we provide a new climatology for these currents which we define as the Dynamical STF (DSTF). The DSTF is the eastward extension of the western boundary current in each basin and is characterized by strong SST and SSH gradients and no seasonal cycle. At the center of each basin it merges with the Sub-Antarctic Front. On the eastern side of basins, the STF surface water mass boundary coincides with a separate region of multiple SST fronts. We call this the Subtropical Frontal Zone (STFZ). The fronts in the STFZ have a large seasonal cycle and no SSH signature. Despite lying close to the same water mass boundary, the DSTF and STFZ are completely unrelated. We therefore suggest the term STF only be used when referring to the surface water mass boundary. When studying the strong currents on the western side of basins the term DSTF is more relevant and, similarly, the term STFZ better describes the region of enhanced SST gradients towards the east., AuthorCount: 2

In recent years the latitudinal position of the Subtropical Front (STF) has emerged as a key parameter in the global climate. A poleward positioned front is thought to allow a greater salt flux from the Indian to the Atlantic Ocean and so drive a stronger Atlantic Meridional Overturning Circulation. Here the common view that the STF aligns with the zero wind stress curl (WSC) is challenged. Based on the STF climatologies of Orsi et al. (1995), Belkin and Gordon (1996), Graham and De Boer (2013), and on satellite scatterometry winds, we find that the zero WSC contour lies on average approximate to 10 degrees, approximate to 8 degrees, and approximate to 5 degrees poleward of the front for the three climatologies, respectively. The circulation in the region between the Subtropical Gyres and the zero WSC contour is not forced by the WSC but rather by the strong bottom pressure torque that is a result of the interaction of the Antarctic Circumpolar Current with the ocean floor topography. The actual control of the position of the STF is crucially dependent on whether the front is regarded as simply a surface water mass boundary or a dynamical front. For the Agulhas Leakage problem, the southern boundary of the so-called Super Gyre may be the most relevant property but this cannot easily be identified in observations.

In recent years the latitudinal position of the Subtropical Front (STF) has emerged as a key parameter in the global climate. A poleward positioned front is thought to allow a greater salt flux from the Indian to the Atlantic Ocean and so drive a stronger Atlantic Meridional Overturning Circulation. Here the common view that the STF aligns with the zero wind stress curl (WSC) is challenged. Based on the STF climatologies of Orsi et al. (1995), Belkin and Gordon (1996), Graham and De Boer (2013), and on satellite scatterometry winds, we find that the zero WSC contour lies on average ∼10°, ∼8°, and ∼5° poleward of the front for the three climatologies, respectively. The circulation in the region between the Subtropical Gyres and the zero WSC contour is not forced by the WSC but rather by the strong bottom pressure torque that is a result of the interaction of the Antarctic Circumpolar Current with the ocean floor topography. The actual control of the position of the STF is crucially dependent on whether the front is regarded as simply a surface water mass boundary or a dynamical front. For the Agulhas Leakage problem, the southern boundary of the so-called Super Gyre may be the most relevant property but this cannot easily be identified in observations., AuthorCount: 4

The Southern Ocean Subtropical Front (STF) is thought to play a key role in the global climate system. Theory suggests that the latitude of the STF regulates the volume of saline Agulhas Leakage into the Atlantic Ocean from the Indian. Here we use satellite sea surface temperature (SST) and sea surface height (SSH) data to study the physical characteristics of the STF water mass boundary. We find that the strong currents in this region do not align with the surface water mass boundary. Therefore, we provide a new climatology for these currents which we define as the Dynamical STF (DSTF). The DSTF is the eastward extension of the western boundary current in each basin and is characterized by strong SST and SSH gradients and no seasonal cycle. At the center of each basin it merges with the Sub-Antarctic Front. On the eastern side of basins, the STF surface water mass boundary coincides with a separate region of multiple SST fronts. We call this the Subtropical Frontal Zone (STFZ). The fronts in the STFZ have a large seasonal cycle and no SSH signature. Despite lying close to the same water mass boundary, the DSTF and STFZ are completely unrelated. We therefore suggest the term STF only be used when referring to the surface water mass boundary. When studying the strong currents on the western side of basins the term DSTF is more relevant and, similarly, the term STFZ better describes the region of enhanced SST gradients towards the east., AuthorCount: 2

The Hawaiian Lee Countercurrent (HLCC) is an eastward surface current flowing against the broad westward flow of the North Pacific subtropical circulation. Analyses of satellite altimeter data over 16 years revealed that the HLCC is characterized by strong interannual variations. The strength and meridional location of the HLCC axis varied significantly year by year. The eastward velocity of the HLCC was higher when the location of the axis was stable. Mechanisms for the interannual variations were explored by analyses of the altimeter data and results from a simple baroclinic model. The interannual variations in the strength of the HLCC did not correlate with those of the wind stress curl (WSC) dipole formed on the leeward side of the Hawaii Islands, although the WSC dipole has been recognized as the generation mechanism of the HLCC. Meridional gradients of the sea surface height anomaly (SSHA) across the HLCC generated by baroclinic Rossby waves propagating westward from the east of the Hawaii Islands were suggested as a possible mechanism for the interannual variations in the HLCC. The spatial patterns in the observed SSHAs were reproduced by a linear baroclinic Rossby wave model forced by wind fields from a numerical weather prediction model. Further analysis of the wind data suggested that positive and negative anomalies of WSC associated with changes in the trade winds in the area east of the Hawaii Islands are a major forcing for generating SSHAs that lead to the HLCC variations with a time lag of about 1 year.

In recent years the latitudinal position of the Subtropical Front (STF) has emerged as a key parameter in the global climate. A poleward positioned front is thought to allow a greater salt flux from the Indian to the Atlantic Ocean and so drive a stronger Atlantic Meridional Overturning Circulation. Here the common view that the STF aligns with the zero wind stress curl (WSC) is challenged. Based on the STF climatologies of Orsi et al. (1995), Belkin and Gordon (1996), Graham and De Boer (2013), and on satellite scatterometry winds, we find that the zero WSC contour lies on average approximate to 10 degrees, approximate to 8 degrees, and approximate to 5 degrees poleward of the front for the three climatologies, respectively. The circulation in the region between the Subtropical Gyres and the zero WSC contour is not forced by the WSC but rather by the strong bottom pressure torque that is a result of the interaction of the Antarctic Circumpolar Current with the ocean floor topography. The actual control of the position of the STF is crucially dependent on whether the front is regarded as simply a surface water mass boundary or a dynamical front. For the Agulhas Leakage problem, the southern boundary of the so-called Super Gyre may be the most relevant property but this cannot easily be identified in observations.

The Hawaiian Lee Countercurrent (HLCC) is an eastward surface current flowing against the broad westward flow of the North Pacific subtropical circulation. Analyses of satellite altimeter data over 16 years revealed that the HLCC is characterized by strong interannual variations. The strength and meridional location of the HLCC axis varied significantly year by year. The eastward velocity of the HLCC was higher when the location of the axis was stable. Mechanisms for the interannual variations were explored by analyses of the altimeter data and results from a simple baroclinic model. The interannual variations in the strength of the HLCC did not correlate with those of the wind stress curl (WSC) dipole formed on the leeward side of the Hawaii Islands, although the WSC dipole has been recognized as the generation mechanism of the HLCC. Meridional gradients of the sea surface height anomaly (SSHA) across the HLCC generated by baroclinic Rossby waves propagating westward from the east of the Hawaii Islands were suggested as a possible mechanism for the interannual variations in the HLCC. The spatial patterns in the observed SSHAs were reproduced by a linear baroclinic Rossby wave model forced by wind fields from a numerical weather prediction model. Further analysis of the wind data suggested that positive and negative anomalies of WSC associated with changes in the trade winds in the area east of the Hawaii Islands are a major forcing for generating SSHAs that lead to the HLCC variations with a time lag of about 1 year.

In recent years the latitudinal position of the Subtropical Front (STF) has emerged as a key parameter in the global climate. A poleward positioned front is thought to allow a greater salt flux from the Indian to the Atlantic Ocean and so drive a stronger Atlantic Meridional Overturning Circulation. Here the common view that the STF aligns with the zero wind stress curl (WSC) is challenged. Based on the STF climatologies of Orsi et al. (1995), Belkin and Gordon (1996), Graham and De Boer (2013), and on satellite scatterometry winds, we find that the zero WSC contour lies on average approximate to 10 degrees, approximate to 8 degrees, and approximate to 5 degrees poleward of the front for the three climatologies, respectively. The circulation in the region between the Subtropical Gyres and the zero WSC contour is not forced by the WSC but rather by the strong bottom pressure torque that is a result of the interaction of the Antarctic Circumpolar Current with the ocean floor topography. The actual control of the position of the STF is crucially dependent on whether the front is regarded as simply a surface water mass boundary or a dynamical front. For the Agulhas Leakage problem, the southern boundary of the so-called Super Gyre may be the most relevant property but this cannot easily be identified in observations.

The Hawaiian Lee Countercurrent (HLCC) is an eastward surface current flowing against the broad westward flow of the North Pacific subtropical circulation. Analyses of satellite altimeter data over 16 years revealed that the HLCC is characterized by strong interannual variations. The strength and meridional location of the HLCC axis varied significantly year by year. The eastward velocity of the HLCC was higher when the location of the axis was stable. Mechanisms for the interannual variations were explored by analyses of the altimeter data and results from a simple baroclinic model. The interannual variations in the strength of the HLCC did not correlate with those of the wind stress curl (WSC) dipole formed on the leeward side of the Hawaii Islands, although the WSC dipole has been recognized as the generation mechanism of the HLCC. Meridional gradients of the sea surface height anomaly (SSHA) across the HLCC generated by baroclinic Rossby waves propagating westward from the east of the Hawaii Islands were suggested as a possible mechanism for the interannual variations in the HLCC. The spatial patterns in the observed SSHAs were reproduced by a linear baroclinic Rossby wave model forced by wind fields from a numerical weather prediction model. Further analysis of the wind data suggested that positive and negative anomalies of WSC associated with changes in the trade winds in the area east of the Hawaii Islands are a major forcing for generating SSHAs that lead to the HLCC variations with a time lag of about 1 year.

The Southern Ocean Subtropical Front (STF) is thought to play a key role in the global climate system. Theory suggests that the latitude of the STF regulates the volume of saline Agulhas Leakage into the Atlantic Ocean from the Indian. Here we use satellite sea surface temperature (SST) and sea surface height (SSH) data to study the physical characteristics of the STF water mass boundary. We find that the strong currents in this region do not align with the surface water mass boundary. Therefore, we provide a new climatology for these currents which we define as the Dynamical STF (DSTF). The DSTF is the eastward extension of the western boundary current in each basin and is characterized by strong SST and SSH gradients and no seasonal cycle. At the center of each basin it merges with the Sub-Antarctic Front. On the eastern side of basins, the STF surface water mass boundary coincides with a separate region of multiple SST fronts. We call this the Subtropical Frontal Zone (STFZ). The fronts in the STFZ have a large seasonal cycle and no SSH signature. Despite lying close to the same water mass boundary, the DSTF and STFZ are completely unrelated. We therefore suggest the term STF only be used when referring to the surface water mass boundary. When studying the strong currents on the western side of basins the term DSTF is more relevant and, similarly, the term STFZ better describes the region of enhanced SST gradients towards the east., AuthorCount: 2

In recent years the latitudinal position of the Subtropical Front (STF) has emerged as a key parameter in the global climate. A poleward positioned front is thought to allow a greater salt flux from the Indian to the Atlantic Ocean and so drive a stronger Atlantic Meridional Overturning Circulation. Here the common view that the STF aligns with the zero wind stress curl (WSC) is challenged. Based on the STF climatologies of Orsi et al. (1995), Belkin and Gordon (1996), Graham and De Boer (2013), and on satellite scatterometry winds, we find that the zero WSC contour lies on average ∼10°, ∼8°, and ∼5° poleward of the front for the three climatologies, respectively. The circulation in the region between the Subtropical Gyres and the zero WSC contour is not forced by the WSC but rather by the strong bottom pressure torque that is a result of the interaction of the Antarctic Circumpolar Current with the ocean floor topography. The actual control of the position of the STF is crucially dependent on whether the front is regarded as simply a surface water mass boundary or a dynamical front. For the Agulhas Leakage problem, the southern boundary of the so-called Super Gyre may be the most relevant property but this cannot easily be identified in observations., AuthorCount: 4

The Southern Ocean Subtropical Front (STF) is thought to play a key role in the global climate system. Theory suggests that the latitude of the STF regulates the volume of saline Agulhas Leakage into the Atlantic Ocean from the Indian. Here we use satellite sea surface temperature (SST) and sea surface height (SSH) data to study the physical characteristics of the STF water mass boundary. We find that the strong currents in this region do not align with the surface water mass boundary. Therefore, we provide a new climatology for these currents which we define as the Dynamical STF (DSTF). The DSTF is the eastward extension of the western boundary current in each basin and is characterized by strong SST and SSH gradients and no seasonal cycle. At the center of each basin it merges with the Sub-Antarctic Front. On the eastern side of basins, the STF surface water mass boundary coincides with a separate region of multiple SST fronts. We call this the Subtropical Frontal Zone (STFZ). The fronts in the STFZ have a large seasonal cycle and no SSH signature. Despite lying close to the same water mass boundary, the DSTF and STFZ are completely unrelated. We therefore suggest the term STF only be used when referring to the surface water mass boundary. When studying the strong currents on the western side of basins the term DSTF is more relevant and, similarly, the term STFZ better describes the region of enhanced SST gradients towards the east., AuthorCount: 2

In recent years the latitudinal position of the Subtropical Front (STF) has emerged as a key parameter in the global climate. A poleward positioned front is thought to allow a greater salt flux from the Indian to the Atlantic Ocean and so drive a stronger Atlantic Meridional Overturning Circulation. Here the common view that the STF aligns with the zero wind stress curl (WSC) is challenged. Based on the STF climatologies of Orsi et al. (1995), Belkin and Gordon (1996), Graham and De Boer (2013), and on satellite scatterometry winds, we find that the zero WSC contour lies on average ∼10°, ∼8°, and ∼5° poleward of the front for the three climatologies, respectively. The circulation in the region between the Subtropical Gyres and the zero WSC contour is not forced by the WSC but rather by the strong bottom pressure torque that is a result of the interaction of the Antarctic Circumpolar Current with the ocean floor topography. The actual control of the position of the STF is crucially dependent on whether the front is regarded as simply a surface water mass boundary or a dynamical front. For the Agulhas Leakage problem, the southern boundary of the so-called Super Gyre may be the most relevant property but this cannot easily be identified in observations., AuthorCount: 4

Author Posting. © American Geophysical Union, 2012. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 117 (2012): C08012, doi:10.1029/2012JC008016., Analysis of sea surface temperature (SST) from coastal buoys suggests that the summertime over-shelf water temperature off the U.S. West Coast has been declining during the past 30 years at an average rate of −0.19°C decade−1. This cooling trend manifests itself more strongly off south-central California than off Oregon and northern California. The variability and trend in the upwelling north of off San Francisco are positively correlated with those of the equatorward wind, indicating a role of offshore Ekman transport in the north. In contrast, Ekman pumping associated with wind stress curls better explains the stronger and statistically more significant cooling trend in the south. While the coast-wide variability and trend in SST are strongly correlated with those of large-scale modes of climate variability, they in general fail to explain the southward intensification of the trend in SST and wind stress curl. This result suggests that the local wind stress curl, often topographically forced, may have played a role in the upwelling trend pattern., H.S. acknowledges the WHOI supports from the Coastal Research Fund in Support of Scientific Staff, the Penzance Endowed Fund in Support of Assistant Scientists, and the Andrew W. Mellon Foundation Endowed Fund for Innovative Research. K.B. and C.E. acknowledge support by the National Science Foundation through grants OCE-1059632 and OCE 1061434., 2013-03-09

Author Posting. © American Geophysical Union, 2012. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 117 (2012): C08012, doi:10.1029/2012JC008016., Analysis of sea surface temperature (SST) from coastal buoys suggests that the summertime over-shelf water temperature off the U.S. West Coast has been declining during the past 30 years at an average rate of −0.19°C decade−1. This cooling trend manifests itself more strongly off south-central California than off Oregon and northern California. The variability and trend in the upwelling north of off San Francisco are positively correlated with those of the equatorward wind, indicating a role of offshore Ekman transport in the north. In contrast, Ekman pumping associated with wind stress curls better explains the stronger and statistically more significant cooling trend in the south. While the coast-wide variability and trend in SST are strongly correlated with those of large-scale modes of climate variability, they in general fail to explain the southward intensification of the trend in SST and wind stress curl. This result suggests that the local wind stress curl, often topographically forced, may have played a role in the upwelling trend pattern., H.S. acknowledges the WHOI supports from the Coastal Research Fund in Support of Scientific Staff, the Penzance Endowed Fund in Support of Assistant Scientists, and the Andrew W. Mellon Foundation Endowed Fund for Innovative Research. K.B. and C.E. acknowledge support by the National Science Foundation through grants OCE-1059632 and OCE 1061434., 2013-03-09

Fourteen acoustic Doppler current profilers (ADCPs) were deployed on the shelf and slope for 1 year just west of the DeSoto Canyon in the Northeastern Gulf of Mexico by the Naval Research Laboratory (NRL) as part of its Slope to Shelf Energetics and Exchange Dynamics (SEED) project. The winter and spring observations are discussed here in regards to the low-frequency current variability and its relation to wind and eddy forcing. Empirical orthogonal function (EOF) analyses showed that two modes described most of the current variability. Wind-forced variability of the along-shelf flow was the main contributor in Mode 1 while eddies contributed much of the variability in Mode 2. Wind-stress controlled currents on the shelf and slope at time scales of about a week. On longer time scales, variations in the currents on both the outer shelf and slope appear to be related to seasonal variations in the time-cumulated wind stress curl. Winds were dominant in driving the along-shelf transports, particularly along the slope. However, the effective wind stress component was found to be aligned with the west Florida shelf direction rather than the local shelf direction. Eddy intrusions, which were more numerous in winter and spring than in summer and fall, and winds were found to contribute significantly to cross-shelf exchange processes., The original document contains color images. All DTIC reproductions will be in black and white. Published in Continental Shelf Research, v28 p399-423, 2008.

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution January, 1972, The method used by N. P. Fofonoff for estimating wind stress curl from surface atmospheric pressure maps is developed for use with the National Meterological Center analysis grid. A formula is developed relating the wind stress curl directly to geometrically apparent features of the surface pressure analyses. The sensitivity of the formula to small deviations in the basic pressure field is estimated. Some statistical properties of the resulting formula as applied to actual pressure analyses are investigated. In particular, the geostrophic wind estimated for two finite difference grids is compared to observed winds from an independent anemometer located at W.H.O.L site "D". The statistical distribution of wind stress curl estimates is found to be non-Gaussian. The difficulty in estimating a mean value from such distributions is discussed. The root mean square values of wind stress curl are found to be approximately 10 times the mean values. Means are estimated and found to be inadequate to drive the mean transports in the Gulf Stream and Kuroshio. The formula is applied at Bermuda and the results compared to the record from the tide gauge located there. A significant relation between wind stress curl and sea level is found after tidal and inverted barometer effects are suppressed. The formula is applied to time dependent motions of the Labrador Current as evidenced by iceberg drifts for the 1959 ice season. Agreement is found between calculated and observed iceberg motions on the eastern slope of the Grand Banks using static Sverdrup dynamics., Supported by the Office of Naval Research under Contract N00014-66-C0241; NR 083-004, and the U. S. Coast Guard contract DOT-CG- 10618-A.

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution January, 1972, The method used by N. P. Fofonoff for estimating wind stress curl from surface atmospheric pressure maps is developed for use with the National Meterological Center analysis grid. A formula is developed relating the wind stress curl directly to geometrically apparent features of the surface pressure analyses. The sensitivity of the formula to small deviations in the basic pressure field is estimated. Some statistical properties of the resulting formula as applied to actual pressure analyses are investigated. In particular, the geostrophic wind estimated for two finite difference grids is compared to observed winds from an independent anemometer located at W.H.O.L site "D". The statistical distribution of wind stress curl estimates is found to be non-Gaussian. The difficulty in estimating a mean value from such distributions is discussed. The root mean square values of wind stress curl are found to be approximately 10 times the mean values. Means are estimated and found to be inadequate to drive the mean transports in the Gulf Stream and Kuroshio. The formula is applied at Bermuda and the results compared to the record from the tide gauge located there. A significant relation between wind stress curl and sea level is found after tidal and inverted barometer effects are suppressed. The formula is applied to time dependent motions of the Labrador Current as evidenced by iceberg drifts for the 1959 ice season. Agreement is found between calculated and observed iceberg motions on the eastern slope of the Grand Banks using static Sverdrup dynamics., Supported by the Office of Naval Research under Contract N00014-66-C0241; NR 083-004, and the U. S. Coast Guard contract DOT-CG- 10618-A.

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution January, 1972, The method used by N. P. Fofonoff for estimating wind stress curl from surface atmospheric pressure maps is developed for use with the National Meterological Center analysis grid. A formula is developed relating the wind stress curl directly to geometrically apparent features of the surface pressure analyses. The sensitivity of the formula to small deviations in the basic pressure field is estimated. Some statistical properties of the resulting formula as applied to actual pressure analyses are investigated. In particular, the geostrophic wind estimated for two finite difference grids is compared to observed winds from an independent anemometer located at W.H.O.L site "D". The statistical distribution of wind stress curl estimates is found to be non-Gaussian. The difficulty in estimating a mean value from such distributions is discussed. The root mean square values of wind stress curl are found to be approximately 10 times the mean values. Means are estimated and found to be inadequate to drive the mean transports in the Gulf Stream and Kuroshio. The formula is applied at Bermuda and the results compared to the record from the tide gauge located there. A significant relation between wind stress curl and sea level is found after tidal and inverted barometer effects are suppressed. The formula is applied to time dependent motions of the Labrador Current as evidenced by iceberg drifts for the 1959 ice season. Agreement is found between calculated and observed iceberg motions on the eastern slope of the Grand Banks using static Sverdrup dynamics., Supported by the Office of Naval Research under Contract N00014-66-C0241; NR 083-004, and the U. S. Coast Guard contract DOT-CG- 10618-A.

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution January, 1972, The method used by N. P. Fofonoff for estimating wind stress curl from surface atmospheric pressure maps is developed for use with the National Meterological Center analysis grid. A formula is developed relating the wind stress curl directly to geometrically apparent features of the surface pressure analyses. The sensitivity of the formula to small deviations in the basic pressure field is estimated. Some statistical properties of the resulting formula as applied to actual pressure analyses are investigated. In particular, the geostrophic wind estimated for two finite difference grids is compared to observed winds from an independent anemometer located at W.H.O.L site "D". The statistical distribution of wind stress curl estimates is found to be non-Gaussian. The difficulty in estimating a mean value from such distributions is discussed. The root mean square values of wind stress curl are found to be approximately 10 times the mean values. Means are estimated and found to be inadequate to drive the mean transports in the Gulf Stream and Kuroshio. The formula is applied at Bermuda and the results compared to the record from the tide gauge located there. A significant relation between wind stress curl and sea level is found after tidal and inverted barometer effects are suppressed. The formula is applied to time dependent motions of the Labrador Current as evidenced by iceberg drifts for the 1959 ice season. Agreement is found between calculated and observed iceberg motions on the eastern slope of the Grand Banks using static Sverdrup dynamics., Supported by the Office of Naval Research under Contract N00014-66-C0241; NR 083-004, and the U. S. Coast Guard contract DOT-CG- 10618-A.

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution January, 1972, The method used by N. P. Fofonoff for estimating wind stress curl from surface atmospheric pressure maps is developed for use with the National Meterological Center analysis grid. A formula is developed relating the wind stress curl directly to geometrically apparent features of the surface pressure analyses. The sensitivity of the formula to small deviations in the basic pressure field is estimated. Some statistical properties of the resulting formula as applied to actual pressure analyses are investigated. In particular, the geostrophic wind estimated for two finite difference grids is compared to observed winds from an independent anemometer located at W.H.O.L site "D". The statistical distribution of wind stress curl estimates is found to be non-Gaussian. The difficulty in estimating a mean value from such distributions is discussed. The root mean square values of wind stress curl are found to be approximately 10 times the mean values. Means are estimated and found to be inadequate to drive the mean transports in the Gulf Stream and Kuroshio. The formula is applied at Bermuda and the results compared to the record from the tide gauge located there. A significant relation between wind stress curl and sea level is found after tidal and inverted barometer effects are suppressed. The formula is applied to time dependent motions of the Labrador Current as evidenced by iceberg drifts for the 1959 ice season. Agreement is found between calculated and observed iceberg motions on the eastern slope of the Grand Banks using static Sverdrup dynamics., Supported by the Office of Naval Research under Contract N00014-66-C0241; NR 083-004, and the U. S. Coast Guard contract DOT-CG- 10618-A.

Sea surface elevation in the South China Sea is examined in the Topex/Poseidon altimeter data from 1992 to 1995. Sea level anomalies are smoothed along satellite tracks and in time with tidal errors reduced by harmonic analysis. The smoothed data are sampled every ten days with an along-track separation of about 40 km. The data reveal significant annual variations in sea level. In winter, low sea level is over the entire deep basin with two local lows centred off Luzon and the Sunda Shelf. In summer, sea level is high off Luzon and off the Sunda Shelf, and a low off Vietnam separates the two highs. The boundary between the Vietnam low and Sunda high coincides with the location of a jet leaving the coast of Vietnam described in earlier studies. Principal component analysis shows that the sea level variation consists mainly of two modes, corresponding well to the first two modes of the wind stress curl. Mode 1 represents the oscillation in the southern basin and shows little inter-annual variation. The mode 2 oscillation is weak in the southern basin and is strongest off central Vietnam. During the winters of 1992-1993 and 1994-1995 and the following summers, the wind stress curl is weak, and the mode 2 sea level variation in the northern basin is reduced, resulting in weaker winter and summer gyres. Weakening of the Vietnam low in summer implies diminishing of the eastward jet leaving the coast of Vietnam. The results are consistent with model simulations., Les variations du niveau de la mer de Chine méridionale sont examinées à partir des données Topex/Poseidon pour la période 1992–1995. Les anomalies de niveau de la mer sont lissées le long des traces des satellites, à la fois dans le temps et dans l'espace, et en réduisant les erreurs dues à la marée par une analyse harmonique. Les données lissées sont échantillonnées tous les 10 j avec une distance entre les traces d'environ 40 km. Les variations annuelles du niveau de la mer sont significatives. En hiver, le niveau est bas dans la région où le bassin est profond, avec deux minima marqués près de Luzon et du plateau de la Sonde. En été, la situation est inverse avec deux maxima au large de Luzon et du plateau de la Sonde séparés par un minimum au large du Vietnam. La limite entre le creux au large du Vietnam et la bosse au large du plateau de la Sonde coïncide avec un jet partant de la côte du Vietnam et déjà décrit antérieurement. Dans la variabilité annuelle, l'analyse en composantes principales des séries temporelles met en évidence deux modes principaux qui peuvent être directement reliés aux deux premiers modes du rotationnel du vent. Le mode 1 représente l'oscillation dans le bassin méridional et montre peu de variabilité interannuelle. Le mode 2 a une amplitude faible dans la partie sud du bassin et forte au large du Vietnam. Pendant les hivers 1992–1993 et 1994–1995 et les étés suivants, le rotationnel du vent est faible et le mode 2 est réduit dans la partie nord du bassin, ce qui affaiblit les circulations hivernales et estivales. L'atténuation du creux au large du Vietnam en été diminue l'intensité du jet dirigé vers l'est à partir de la côte du Vietnam. Les résultats sont en bon accord avec les simulations.

Sea surface elevation in the South China Sea is examined in the Topex/Poseidon altimeter data from 1992 to 1995. Sea level anomalies are smoothed along satellite tracks and in time with tidal errors reduced by harmonic analysis. The smoothed data are sampled every ten days with an along-track separation of about 40 km. The data reveal significant annual variations in sea level. In winter, low sea level is over the entire deep basin with two local lows centred off Luzon and the Sunda Shelf. In summer, sea level is high off Luzon and off the Sunda Shelf, and a low off Vietnam separates the two highs. The boundary between the Vietnam low and Sunda high coincides with the location of a jet leaving the coast of Vietnam described in earlier studies. Principal component analysis shows that the sea level variation consists mainly of two modes, corresponding well to the first two modes of the wind stress curl. Mode 1 represents the oscillation in the southern basin and shows little inter-annual variation. The mode 2 oscillation is weak in the southern basin and is strongest off central Vietnam. During the winters of 1992-1993 and 1994-1995 and the following summers, the wind stress curl is weak, and the mode 2 sea level variation in the northern basin is reduced, resulting in weaker winter and summer gyres. Weakening of the Vietnam low in summer implies diminishing of the eastward jet leaving the coast of Vietnam. The results are consistent with model simulations., Les variations du niveau de la mer de Chine méridionale sont examinées à partir des données Topex/Poseidon pour la période 1992–1995. Les anomalies de niveau de la mer sont lissées le long des traces des satellites, à la fois dans le temps et dans l'espace, et en réduisant les erreurs dues à la marée par une analyse harmonique. Les données lissées sont échantillonnées tous les 10 j avec une distance entre les traces d'environ 40 km. Les variations annuelles du niveau de la mer sont significatives. En hiver, le niveau est bas dans la région où le bassin est profond, avec deux minima marqués près de Luzon et du plateau de la Sonde. En été, la situation est inverse avec deux maxima au large de Luzon et du plateau de la Sonde séparés par un minimum au large du Vietnam. La limite entre le creux au large du Vietnam et la bosse au large du plateau de la Sonde coïncide avec un jet partant de la côte du Vietnam et déjà décrit antérieurement. Dans la variabilité annuelle, l'analyse en composantes principales des séries temporelles met en évidence deux modes principaux qui peuvent être directement reliés aux deux premiers modes du rotationnel du vent. Le mode 1 représente l'oscillation dans le bassin méridional et montre peu de variabilité interannuelle. Le mode 2 a une amplitude faible dans la partie sud du bassin et forte au large du Vietnam. Pendant les hivers 1992–1993 et 1994–1995 et les étés suivants, le rotationnel du vent est faible et le mode 2 est réduit dans la partie nord du bassin, ce qui affaiblit les circulations hivernales et estivales. L'atténuation du creux au large du Vietnam en été diminue l'intensité du jet dirigé vers l'est à partir de la côte du Vietnam. Les résultats sont en bon accord avec les simulations.

Sea surface elevation in the South China Sea is examined in the Topex/Poseidon altimeter data from 1992 to 1995. Sea level anomalies are smoothed along satellite tracks and in time with tidal errors reduced by harmonic analysis. The smoothed data are sampled every ten days with an along-track separation of about 40 km. The data reveal significant annual variations in sea level. In winter, low sea level is over the entire deep basin with two local lows centred off Luzon and the Sunda Shelf. In summer, sea level is high off Luzon and off the Sunda Shelf, and a low off Vietnam separates the two highs. The boundary between the Vietnam low and Sunda high coincides with the location of a jet leaving the coast of Vietnam described in earlier studies. Principal component analysis shows that the sea level variation consists mainly of two modes, corresponding well to the first two modes of the wind stress curl. Mode 1 represents the oscillation in the southern basin and shows little inter-annual variation. The mode 2 oscillation is weak in the southern basin and is strongest off central Vietnam. During the winters of 1992-1993 and 1994-1995 and the following summers, the wind stress curl is weak, and the mode 2 sea level variation in the northern basin is reduced, resulting in weaker winter and summer gyres. Weakening of the Vietnam low in summer implies diminishing of the eastward jet leaving the coast of Vietnam. The results are consistent with model simulations., Les variations du niveau de la mer de Chine méridionale sont examinées à partir des données Topex/Poseidon pour la période 1992–1995. Les anomalies de niveau de la mer sont lissées le long des traces des satellites, à la fois dans le temps et dans l'espace, et en réduisant les erreurs dues à la marée par une analyse harmonique. Les données lissées sont échantillonnées tous les 10 j avec une distance entre les traces d'environ 40 km. Les variations annuelles du niveau de la mer sont significatives. En hiver, le niveau est bas dans la région où le bassin est profond, avec deux minima marqués près de Luzon et du plateau de la Sonde. En été, la situation est inverse avec deux maxima au large de Luzon et du plateau de la Sonde séparés par un minimum au large du Vietnam. La limite entre le creux au large du Vietnam et la bosse au large du plateau de la Sonde coïncide avec un jet partant de la côte du Vietnam et déjà décrit antérieurement. Dans la variabilité annuelle, l'analyse en composantes principales des séries temporelles met en évidence deux modes principaux qui peuvent être directement reliés aux deux premiers modes du rotationnel du vent. Le mode 1 représente l'oscillation dans le bassin méridional et montre peu de variabilité interannuelle. Le mode 2 a une amplitude faible dans la partie sud du bassin et forte au large du Vietnam. Pendant les hivers 1992–1993 et 1994–1995 et les étés suivants, le rotationnel du vent est faible et le mode 2 est réduit dans la partie nord du bassin, ce qui affaiblit les circulations hivernales et estivales. L'atténuation du creux au large du Vietnam en été diminue l'intensité du jet dirigé vers l'est à partir de la côte du Vietnam. Les résultats sont en bon accord avec les simulations.

Sea surface elevation in the South China Sea is examined in the Topex/Poseidon altimeter data from 1992 to 1995. Sea level anomalies are smoothed along satellite tracks and in time with tidal errors reduced by harmonic analysis. The smoothed data are sampled every ten days with an along-track separation of about 40 km. The data reveal significant annual variations in sea level. In winter, low sea level is over the entire deep basin with two local lows centred off Luzon and the Sunda Shelf. In summer, sea level is high off Luzon and off the Sunda Shelf, and a low off Vietnam separates the two highs. The boundary between the Vietnam low and Sunda high coincides with the location of a jet leaving the coast of Vietnam described in earlier studies. Principal component analysis shows that the sea level variation consists mainly of two modes, corresponding well to the first two modes of the wind stress curl. Mode 1 represents the oscillation in the southern basin and shows little inter-annual variation. The mode 2 oscillation is weak in the southern basin and is strongest off central Vietnam. During the winters of 1992-1993 and 1994-1995 and the following summers, the wind stress curl is weak, and the mode 2 sea level variation in the northern basin is reduced, resulting in weaker winter and summer gyres. Weakening of the Vietnam low in summer implies diminishing of the eastward jet leaving the coast of Vietnam. The results are consistent with model simulations., Les variations du niveau de la mer de Chine méridionale sont examinées à partir des données Topex/Poseidon pour la période 1992–1995. Les anomalies de niveau de la mer sont lissées le long des traces des satellites, à la fois dans le temps et dans l'espace, et en réduisant les erreurs dues à la marée par une analyse harmonique. Les données lissées sont échantillonnées tous les 10 j avec une distance entre les traces d'environ 40 km. Les variations annuelles du niveau de la mer sont significatives. En hiver, le niveau est bas dans la région où le bassin est profond, avec deux minima marqués près de Luzon et du plateau de la Sonde. En été, la situation est inverse avec deux maxima au large de Luzon et du plateau de la Sonde séparés par un minimum au large du Vietnam. La limite entre le creux au large du Vietnam et la bosse au large du plateau de la Sonde coïncide avec un jet partant de la côte du Vietnam et déjà décrit antérieurement. Dans la variabilité annuelle, l'analyse en composantes principales des séries temporelles met en évidence deux modes principaux qui peuvent être directement reliés aux deux premiers modes du rotationnel du vent. Le mode 1 représente l'oscillation dans le bassin méridional et montre peu de variabilité interannuelle. Le mode 2 a une amplitude faible dans la partie sud du bassin et forte au large du Vietnam. Pendant les hivers 1992–1993 et 1994–1995 et les étés suivants, le rotationnel du vent est faible et le mode 2 est réduit dans la partie nord du bassin, ce qui affaiblit les circulations hivernales et estivales. L'atténuation du creux au large du Vietnam en été diminue l'intensité du jet dirigé vers l'est à partir de la côte du Vietnam. Les résultats sont en bon accord avec les simulations.

A high-resolution, multi-level, primitive equation ocean model is used to examine the response of an idealized, flat-bottom, oceanic regime off northern California to steady, equatorward, local wind-forcing during the upwelling season. The model has open boundaries on all but the eastern coastal boundary on which either free-slip or zero-slip boundary conditions are imposed. Time-invariant winds, either with or without a component of wind stress curl, are used as model forcing to spin-up a classical two-dimensional, upwelling-induced coastal jet and undercurrent. Since no eddies are generated, a stability analysis of the mean flow is conducted which explores both the necessary conditions of mixed (barotropic and baroclinic) instability, through calculations of potential vorticity, and the sufficient conditions for baroclinic instability, through an application of a simple two-layer stability model. Comparisons of model results with observations of the coastal jet in the California Current System indicate that the location and the horizontal and vertical current shear associated with the model coastal jet compare favorably with observations; however the modeled jet is stronger, deeper and wider than the observed jet. Finally, the inclusion of wind stress curl and the zero-slip boundary condition are demonstrated to be important elements in model simulations of the coastal jet.

The 1982 Mixed-Layer Experiment is described in detail and the data are presented in ways designed to illustrate the spatial and temporal variability of the surface and deeper layers of the central western Mediterranean Sea during the autumn transition period. The surface mixed-layer is seen to cool and to deepen due to convection and mechanical stirring induced by passing storms. The predominating motions observed are the near inertial internal waves propagating horizontally and vertically from the mixed layer into the pycnocline. Possible generation mechanisms for the vertical oscillations are discussed. These may originate to the north, in the Golfe du Lion where a high amplitude, inertially oscillating, Ekman mass-flux divergence can be expected due to the high values of wind-stress curl in that region. Data are, in some cases, fairly extensively worked up to produce a variety of contour plots for temperature, salinity, density and dynamic anomaly and a variety of composite time-series for both the thermistor-chain data and current-meter array vectors.

Better wind field information is needed over the open ocean, especially as a forcing function for ocean circulation models. Microwave scatterometry, as a means of remotely sensing surface wind information, was developed in response to this requirement for a surface wind field with global coverage and improved spatial and temporal resolution and this led to the 1978 deployment of the SEASAT Satellite Scatterometer (SASS). Evaluations of the three months of SEASAT data established the consistency of SASS winds with high quality surface wind data from field experiments over limited areas and time periods. Directional ambiguity of the original SASS vectors has been removed by Atlas et al. (1987) for the entire data set, and the resulting SASS winds from conventional sources. This thesis compares a 1-month (12 Aug - 9 Sep 1978) subset of these dealiased winds, in the western North Atlantic, with a conventional, pressure-derived wind field from the 6-hourly surface wind analyses of the Fleet Numerical Oceanographic Center (FNOC). Through an objective mapping procedure, the irregularly spaced SASS winds are regridded to a latitude-longitude grid, facilitating statistical comparisons with the regularly spaced FNOC wind vectors and wind stress curl calculations. The study includes qualitative comparisons to synoptic weather maps, calculations of field statistics and boxed mean differences; scatter plots of wind speed, direction, and standard deviation; statistical descriptions of the SASS-FNOC difference field, and wind stress curl calculations., Prepared in cooperation with Massachusetts Institute of Technology, Cambridge.

A high-resolution, multi-level, primitive equation ocean model is used to examine the response to wind forcing of an idealized flatbottomed oceanic regime along an eastern ocean boundary. A band of steady winds, either with or without a curl, is used as forcing on both an f-plane and a beta-plane. In addition, a stability analysis is made to determine if the necessary and sufficient conditions for instability processes to occur are satisfied. It is seen that when the wind driven coastal jet and undercurrent are unstable (which occurs in the cases of wind with no curl), eddies and jets are generated. In the case of wind with curl, since the Davidson Current develops rather than the coastal jet and undercurrent, no eddies develop. A comparison of model results with available observations shows that both the time-averaged and instantaneous model simulations of the coastal jet, undercurrent and eddies are consistent with available observational data. Study results support the hypothesis that wind forcing can be an important eddy generation mechanism for the California Current System.