The Experts below are selected from a list of 249 Experts worldwide ranked by ideXlab platform
Lisa M Beal - One of the best experts on this subject based on the ideXlab platform.
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variability and coherence of the agulhas Undercurrent in a high resolution ocean general circulation model
Journal of Physical Oceanography, 2009Co-Authors: Arne Biastoch, Lisa M Beal, J R E Lutjeharms, Tânia G D CasalAbstract:Abstract The Agulhas Current system has been analyzed in a nested high-resolution ocean model and compared to observations. The model shows good performance in the western boundary current structure and the transports off the South African coast. This includes the simulation of the northward-flowing Agulhas Undercurrent. It is demonstrated that fluctuations of the Agulhas Current and Undercurrent around 50–70 days are due to Natal pulses and Mozambique eddies propagating downstream. A sensitivity experiment that excludes those upstream perturbations significantly reduces the variability as well as the mean transport of the Undercurrent. Although the model simulates Undercurrents in the Mozambique Channel and east of Madagascar, there is no direct connection between those and the Agulhas Undercurrent. Virtual float releases demonstrate that topography is effectively blocking the flow toward the north.
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a time series of agulhas Undercurrent transport
Journal of Physical Oceanography, 2009Co-Authors: Lisa M BealAbstract:Abstract A 550-day record of Agulhas Undercurrent transport between March 2003 and August 2004 is constructed from five deep moorings placed on the continental shelf off South Africa at nominally 32°S. The vertical and lateral scales of the Undercurrent are estimated to be 2000 m and 40 km, respectively, using the average of seven direct velocity sections, predominantly taken in austral autumn over a 10-yr period from 1995 to 2005. Peak speeds in the Undercurrent are some of the greatest ever seen at depth: over 90 cm s−1 at 1400 m. The Undercurrent has a transport of 4.2 ± 5.2 Sv (1 Sv = 1 × 106 m3 s−1), in close agreement with a previous estimate from a single current meter record during 1995 of 4.2 ± 2.9 Sv. Records below 1800 m, within the North Atlantic Deep Water (NADW) layer of the Undercurrent, show a higher level of coherence and less variance than those at intermediate depths. On average, 2.3 ± 3.0 Sv of NADW is carried northeastward within the Undercurrent, an amount similar to that estimated p...
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Comparison of three velocity sections of the Agulhas Current and Agulhas Undercurrent
Journal of Geophysical Research, 2000Co-Authors: Kathleen A. Donohue, Eric Firing, Lisa M BealAbstract:Lowered acoustic Doppler current profiles (LADCP) from an early March 1995 cruise across the Agulhas Current show a swift, narrow Undercurrent flowing northeast along the continental slope. Neither this Agulhas Undercurrent nor the adjacent deep extension of the Agulhas Current are evident from measurements of water properties alone, and their absence from the conventional referencing of geostrophic current estimates biases net southward transport estimates high by several sverdrups. Here we refine the original transport calculation by removing barotropic tides and by estimating instrumental and sampling errors. Two additional LADCP sections, from cruises in late March and June 1995, also show the Undercurrent and the deep extension of the Agulhas. Differences in the current structure are evident. The Agulhas Current extends throughout the water column in March, but extends only to 2300 m depth in June. Additionally, the current extends further offshore in March. Of the three available LADCP sections, only those from early March and June have sufficient sampling to calculate the net southward transport of the Agulhas Current and Undercurrent. The two estimates, 78±3 and 76±2 Sv, are nearly identical. Consideration of water properties on density surfaces shows that although the Undercurrent carries intermediate water with Red Sea Water influence northward, the bulk of this water mass is flowing southward, away from its source, in the Agulhas Current.
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observations of an agulhas Undercurrent
Deep-Sea Research Part I: Oceanographic Research Papers, 1997Co-Authors: Lisa M Beal, Harry L BrydenAbstract:An Agulhas Undercurrent has been directly measured on two occasions using a new acoustic current profiling technique (Lowered Acoustic Doppler Current Profiler, LADCP). The core of the Undercurrent is centred around a depth of 1200 m, against the continental slope and directly below the surface core of the south-westward flowing Agulhas Current. Maximum velocities of 30 cm s−1 to the north-east are observed in the Undercurrent, and its volume transport is 6 Sv (1 Sv = 106 m3 s−1), approximately one-tenth that of the Agulhas Current.
R W Hobbs - One of the best experts on this subject based on the ideXlab platform.
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seismic reflection along the path of the mediterranean Undercurrent
Continental Shelf Research, 2009Co-Authors: Grant Buffett, Berta Biescas, Josep Lluis Pelegri, Francisco Machin, Valenti Sallares, Ramon Carbonell, Dirk Klaeschen, R W HobbsAbstract:Seismic reflection profiling is applied to the study of large scale physical oceanographic processes in the Gulf of C� adiz and western Iberian coast, coinciding with the path of the Mediterranean Undercurrent. The multi-channel seismic reflection method provides clear images of thermohaline fine structure with a horizontal resolution approximately two orders of magnitude higher than CTD casting. The seismic data are compared with co-located historical oceanographic data. Three seismic reflectivity zones are identified: North Atlantic Central Water, Mediterranean Water and North Atlantic Deep Water. Seismic evidence for the path of the Mediterranean Undercurrent is found in the near-slope reflectivity patterns, with rising reflectors between about 500 and 1500 m. However, the core of the Undercurrent is largely transparent. Seismic images show that central and, particularly, intermediate Mediterranean Waters have fine structure coherent over horizontal distances of several tens of kilometers. However, the intensity of the reflectors, and their horizontal coherence, decreases downstream. This change in seismic reflectivity is probably the result of diminished vertical thermohaline contrasts between adjacent water masses, so that double-diffusion processes become unable to sustain temperature and salinity staircases. Comparison of root-mean-square seismic amplitudes with temperature and salinity differences between the Mediterranean Undercurrent and the overlying central waters suggests a causal relationship between observed thermohaline fine structure and true seismic amplitudes. We estimate that, within this intermediate water stratum, impedance contrasts are mainly controlled by sound speed contrasts (a factor between 3.5 and 10 times larger than density contrasts), which are mainly controlled by temperature contrasts (a factor between 1.5 and 5 times larger than salinity contrasts).
Joseph E Metzger - One of the best experts on this subject based on the ideXlab platform.
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an Undercurrent off the east coast of sri lanka
Ocean Science, 2017Co-Authors: Arachaporn Anutaliya, Uwe Send, Julie L Mcclean, Janet Sprintall, Luc Rainville, S Priyantha U Jinadasa, Alan J Wallcraft, Joseph E MetzgerAbstract:Abstract. The existence of a seasonally varying Undercurrent along 8° N off the east coast of Sri Lanka is inferred from shipboard hydrography, Argo floats, glider measurements, and two ocean general circulation model simulations. Together, they reveal an Undercurrent below 100–200 m flowing in the opposite direction to the surface current, which is most pronounced during boreal spring and summer and switches direction between these two seasons. The volume transport of the Undercurrent (200–1000 m layer) can be more than 10 Sv in either direction, exceeding the transport of 1–6 Sv carried by the surface current (0–200 m layer). The Undercurrent transports relatively fresher water southward during spring, while it advects more saline water northward along the east coast of Sri Lanka during summer. Although the Undercurrent is potentially a pathway of salt exchange between the Arabian Sea and the Bay of Bengal, the observations and the ocean general circulation models suggest that the salinity contrast between seasons and between the boundary current and interior is less than 0.09 in the subsurface layer, suggesting a small salt transport by the Undercurrent of less than 4 % of the salinity deficit in the Bay of Bengal.
Dunxin Hu - One of the best experts on this subject based on the ideXlab platform.
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the equatorial Undercurrent and its origin in the region between mindanao and new guinea
Journal of Geophysical Research, 2019Co-Authors: Qingye Wang, Linlin Zhang, Fujun Wang, Shijian Hu, Junqiao Feng, Dunxin HuAbstract:Herein, the spatial characteristics of the Equatorial Undercurrent (EUC) in the region between Mindanao and New Guinea and the origins of the EUC and the North Equatorial Countercurrent (NECC) were investigated using a combination of high-resolution Argo hydrographic data and numerical modeling. The Mindanao Current (MC) results in the formation of a strong EUC-depth eastward current that splits into two branches near the Halmahera Eddy west of 132 degrees E, with one branch directly flowing eastward without experiencing the Halmahera Eddy rotation effect, and the other branch flowing southwestward and then turning northeastward. The EUC and NECC were difficult to distinguish between 132 degrees E and 136 degrees E, since the former combined with the latter to form a continuous equator-tilted current. At similar to 137 degrees E, the EUC axis started turning toward the equator, and an isolated EUC core was observed at 143 degrees E and similar to 200-m depth. The Pacific EUC was shown to originate at similar to 130 degrees E, where it featured an isolated current core with a maximum velocity of 5-10cm/s at similar to 1 degrees N and 200- to 400-m depth. The EUC and NECC in the western tropical Pacific were found to have the same water sources, namely, the MC and the New Guinea Coastal Undercurrent, with the shallow parts (centered at similar to 100-m depth) of MC and New Guinea Coastal Undercurrent finally reaching the NECC and their deeper parts (centered at similar to 200-m depth) finally reaching the EUC.
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structure and variability of the north equatorial current Undercurrent from mooring measurements at 130 e in the western pacific
Scientific Reports, 2017Co-Authors: Linlin Zhang, Fujun Wang, Qingye Wang, Shijian Hu, Fan Wang, Dunxin HuAbstract:The mean structure and variability of the North Equatorial Current/Undercurrent (NEC/NEUC) are investigated with one-year Acoustic Doppler Current Profilers measurements from 4 subsurface moorings deployed at 10.5°N, 13°N, 15.5°N, and 18°N along 130°E in the western Pacific. The strong westward flowing NEC ranges from the sea surface down to 400 m, and the mean zonal velocity of the NEC at 10.5°N is around −30 cm/s at the depth of 70 m. Eastward flowing NEUC jets are detected below the NEC at 10.5°N and 13°N, and the depth of the NEUC could reach at least 900 m. The mean velocity of the NEUC is around 4.2 cm/s at 800 m. No eastward Undercurrents are observed at 15°N and 18°N. The mooring measurements also reveal a strong intraseasonal variability of the currents at all 4 mooring sites, and the period is around 70–120 days. The vertical structure of this intraseasonal variability varies at different latitudes. The variability of the NEUC jets at 10.5°N and 13°N appears to be dominated by subthermocline signals, while the variability of the currents at 15.5°N and 18°N is dominated by surface-intensified signals.
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ORIGIN OF THE LUZON Undercurrent
Bulletin of Marine Science, 2012Co-Authors: Qingye Wang, Dunxin HuAbstract:The origin of the Luzon Undercurrent (LUC) was studied by a climatological simulation using a high-resolution quasi-global HYbrid Coordinate Ocean Model, configured with climatological European Centre for Medium-Range Weather Forecasts wind and heat forcing. Lagrangian trajectory analysis suggests that the LUC generally originates from the confluence region of the Kuroshio and Oyashio, with its shallow, middle, and deep parts originating from corresponding parts of the North Pacific Intermediate Water (NPIW). About 86.0% (77%-93% = 95% confidence interval) of the LUC at 18 degrees N conveys low-salinity NPIW southward. The LUC plays an important role in the southward intrusion of NPIW into the tropical Pacific.
Arachaporn Anutaliya - One of the best experts on this subject based on the ideXlab platform.
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an Undercurrent off the east coast of sri lanka
Ocean Science, 2017Co-Authors: Arachaporn Anutaliya, Uwe Send, Julie L Mcclean, Janet Sprintall, Luc Rainville, S Priyantha U Jinadasa, Alan J Wallcraft, Joseph E MetzgerAbstract:Abstract. The existence of a seasonally varying Undercurrent along 8° N off the east coast of Sri Lanka is inferred from shipboard hydrography, Argo floats, glider measurements, and two ocean general circulation model simulations. Together, they reveal an Undercurrent below 100–200 m flowing in the opposite direction to the surface current, which is most pronounced during boreal spring and summer and switches direction between these two seasons. The volume transport of the Undercurrent (200–1000 m layer) can be more than 10 Sv in either direction, exceeding the transport of 1–6 Sv carried by the surface current (0–200 m layer). The Undercurrent transports relatively fresher water southward during spring, while it advects more saline water northward along the east coast of Sri Lanka during summer. Although the Undercurrent is potentially a pathway of salt exchange between the Arabian Sea and the Bay of Bengal, the observations and the ocean general circulation models suggest that the salinity contrast between seasons and between the boundary current and interior is less than 0.09 in the subsurface layer, suggesting a small salt transport by the Undercurrent of less than 4 % of the salinity deficit in the Bay of Bengal.
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An Undercurrent off the East Coast of Sri Lanka
2017Co-Authors: Arachaporn Anutaliya, Uwe Send, Julie L Mcclean, Janet Sprintall, Luc Rainville, S Priyantha U Jinadasa, Alan J Wallcraft, E. Joseph MetzgerAbstract:Abstract. The existence of a seasonally varying Undercurrent along 8° N off the east coast of Sri Lanka is inferred from Conductivity-Temperature-Depth profiles, Argo floats, glider measurements, and Ocean General Circulation Model outputs. Together, they reveal an Undercurrent below 200 m that is approximately 140 km wide and can reach a maximum speed of 45 cm s−1 that hitherto has not been observed. The Undercurrent, flowing in the opposite direction to the surface current, is most pronounced during boreal spring and summer and switches direction between these two seasons. The Undercurrent transports relatively fresh water southward during spring, while it advects more saline water northward along the east coast of Sri Lanka during summer. This suggests a pathway, independent of the surface circulation, whereby freshwater is removed and saline water is injected into the Bay of Bengal.
