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Jonathan Gagnon - One of the best experts on this subject based on the ideXlab platform.
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Wind‐driven upwelling around grounded tabular icebergs
Journal of Geophysical Research: Oceans, 2015Co-Authors: A. A. Stern, Till J. W. Wagner, Keith W Nicholls, Eric S Johnson, David M Holland, Peter Wadhams, Richard Bates, Anna J Crawford, E. Povl Abrahamsen, Jonathan GagnonAbstract:Temperature and salinity data collected around grounded tabular icebergs in Baffin Bay in 2011, 2012, and 2013 indicate wind-induced upwelling at certain locations around the icebergs. These data suggest that along one side of the iceberg, wind forcing leads to Ekman Transport away from the iceberg, which causes upwelling of the cool saline water from below. The upwelling water mixes with the water above the thermocline, causing the mixed layer to become cooler and more saline. Along the opposite side of the iceberg, the surface Ekman Transport moves towards the iceberg, which causes a sharpening of the thermocline as warm fresh water is trapped near the surface. This results in higher mixed layer temperatures and lower mixed layer salinities on this side of the iceberg. Based on these in situ measurements, we hypothesize that the asymmetries in water properties around the iceberg, caused by the opposing effects of upwelling and sharpening of the thermocline, lead to differential deterioration around the iceberg. Analysis of satellite imagery around iceberg PII-B-1 reveals differential decay around the iceberg, in agreement with this mechanism.
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wind driven upwelling around grounded tabular icebergs
Journal of Geophysical Research, 2015Co-Authors: A. A. Stern, Till J. W. Wagner, Keith W Nicholls, Eric S Johnson, David M Holland, Peter Wadhams, Richard Bates, Povl E Abrahamsen, Anna J Crawford, Jonathan GagnonAbstract:Temperature and salinity data collected around grounded tabular icebergs in Baffin Bay in 2011, 2012, and 2013 indicate wind-induced upwelling at certain locations around the icebergs. These data suggest that along one side of the iceberg, wind forcing leads to Ekman Transport away from the iceberg, which causes upwelling of the cool saline water from below. The upwelling water mixes with the water above the thermocline, causing the mixed layer to become cooler and more saline. Along the opposite side of the iceberg, the surface Ekman Transport moves towards the iceberg, which causes a sharpening of the thermocline as warm fresh water is trapped near the surface. This results in higher mixed layer temperatures and lower mixed layer salinities on this side of the iceberg. Based on these in situ measurements, we hypothesize that the asymmetries in water properties around the iceberg, caused by the opposing effects of upwelling and sharpening of the thermocline, lead to differential deterioration around the iceberg. Analysis of satellite imagery around iceberg PII-B-1 reveals differential decay around the iceberg, in agreement with this mechanism.
John A. Barth - One of the best experts on this subject based on the ideXlab platform.
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Time-Varying Across-Shelf Ekman Transport and Vertical Eddy Viscosity on the Inner Shelf
Journal of Physical Oceanography, 2009Co-Authors: Anthony R. Kirincich, John A. BarthAbstract:Abstract The event-scale variability of across-shelf Transport was investigated using observations made in 15 m of water on the central Oregon inner shelf. In a study area with intermittently upwelling-favorable winds and significant density stratification, hydrographic and velocity observations show rapid across-shelf movement of water masses over event time scales of 2–7 days. To understand the time variability of across-shelf exchange, an inverse calculation was used to estimate eddy viscosity and the vertical turbulent diffusion of momentum from velocity profiles and wind forcing. Depth-averaged eddy viscosity varied over a large dynamic range, but averaged 1.3 × 10−3 m2 s−1 during upwelling winds and 2.1 × 10−3 m2 s−1 during downwelling winds. The fraction of full Ekman Transport present in the surface layer, a measure of the efficiency of across-shelf exchange at this water depth, was a strong function of eddy viscosity and wind forcing, but not stratification. Transport fractions ranged from 60%, d...
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upwelling around cabo frio brazil the importance of wind stress curl
Geophysical Research Letters, 2006Co-Authors: Renato M Castelao, John A. BarthAbstract:[1] Data from the SeaWinds scatterometer on the QuikSCAT satellite are used to estimate upwelling around Cabo Frio, Brazil, due to Ekman Transport and Ekman pumping. The region close to shore (up to 200 km from the coast) is characterized by negative wind stress curl (upwelling favorable) year-round, with maximum values during summer, and minimum values during fall. Integrated values from Sao Sebastiao Island to Vitoria reveal that during summer, Ekman pumping and Ekman Transport are of the same magnitude in the region. Estimates of Ekman Transport are relatively uniform along the coast during summer. Ekman pumping, on the other hand, is strongly enhanced between Sao Sebastiao Island and Vitoria, the region where the coldest water on satellite images is frequently found. This suggests that wind stress curl-driven upwelling is a major contributor to the coldest surface water being found near Cabo Frio.
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Wind-driven inner-shelf circulation off central Oregon during summer : Wind-driven circulation and Ecosystem Response off the Oregon Coast: Results from the coastal ocean advances in shelf Transport (COAST) program
Journal of Geophysical Research, 2005Co-Authors: Anthony R. Kirincich, John A. Barth, Brian A. Grantham, Bruce A. Menge, Jane LubchencoAbstract:Velocity measurements from 17 deployments of moored acoustic Doppler current profilers obtained during four summer upwelling seasons are used to describe the cross-shelf divergence of Ekman Transport in the inner shelf off Oregon. For each deployment the measured surface and bottom cross-shelf Transports were compared with estimates of the theoretical Ekman Transports to find the fraction of full theoretical Ekman Transport present. In general, in 15 m of water at 1-2 km offshore, measured Transport was 25% of the full Ekman Transport. Measured Transports reached full Ekman Transport 5-6 km offshore in 50 m of water. This result indicates that the region of active upwelling marked by the divergence of Ekman Transport was limited to a narrow region along the coast. With small wind stress curl and no major headlands in the region, no along-shelf trends in the Transport fractions were observed. Average Transport fractions at each station were similar from year to year with one exception. The interannual variability seen at this particular site was most likely a result of local along-shelf bathymetric features. In addition, a weak linear relationship was found between the ambient stratification and the fraction of full Ekman Transport. Reduced cross-shelf Transport occurred at times of decreased stratification. This type of shutdown of the inner-shelf cross-shelf circulation has significant biological implications, sequestering production in the nearshore and reducing larval cross-shelf Transport.
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Wind-driven inner-shelf circulation off central Oregon during summer
Journal of Geophysical Research, 2005Co-Authors: Anthony R. Kirincich, John A. Barth, Brian A. Grantham, Bruce A. Menge, Jane LubchencoAbstract:[1] Velocity measurements from 17 deployments of moored acoustic Doppler current profilers obtained during four summer upwelling seasons are used to describe the cross-shelf divergence of Ekman Transport in the inner shelf off Oregon. For each deployment the measured surface and bottom cross-shelf Transports were compared with estimates of the theoretical Ekman Transports to find the fraction of full theoretical Ekman Transport present. In general, in 15 m of water at 1–2 km offshore, measured Transport was 25% of the full Ekman Transport. Measured Transports reached full Ekman Transport 5–6 km offshore in 50 m of water. This result indicates that the region of active upwelling marked by the divergence of Ekman Transport was limited to a narrow region along the coast. With small wind stress curl and no major headlands in the region, no along-shelf trends in the Transport fractions were observed. Average Transport fractions at each station were similar from year to year with one exception. The interannual variability seen at this particular site was most likely a result of local along-shelf bathymetric features. In addition, a weak linear relationship was found between the ambient stratification and the fraction of full Ekman Transport. Reduced cross-shelf Transport occurred at times of decreased stratification. This type of “shutdown” of the inner-shelf cross-shelf circulation has significant biological implications, sequestering production in the nearshore and reducing larval cross-shelf Transport.
Bo Qiu - One of the best experts on this subject based on the ideXlab platform.
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Heat Flux Estimates for the Western North Atlantic. Part II: The Upper-Ocean Heat Balance
Journal of Physical Oceanography, 1995Co-Authors: Kathryn A. Kelly, Bo QiuAbstract:Abstract The assimilation of temperature and altimetric velocity into a numerical model of the upper-ocean mixed layer in Part I allowed an analysis of the upper ocean heat budget for the western North Atlantic Ocean over the 2.5-year period of the Geosat Exact Repeat Mission (November 1986–April 1989). The balance of terms varied regionally: south of the Gulf Stream advection was relatively unimportant in the heat budget, and the ocean responded passively to changes in surface flux. Within the Gulf Stream and to the north of it, cooling of the upper ocean by advection was as large as 0.15°C/day for periods of several weeks. An analysis of the advection term showed that cooling by Ekman Transport was opposed by warming from the geostrophic currents of the Gulf Stream, with cooling typically stronger by a factor of 2 because nonuniform Ekman Transport disrupted the normal alignment between isotherms and sea surface height contours. There is a complex ocean-atmosphere coupling in this region: in addition to...
Robert L. Molinari - One of the best experts on this subject based on the ideXlab platform.
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Ageostrophic Transport in the upper layers of the tropical Atlantic Ocean
Geophysical Research Letters, 2001Co-Authors: Silvia L. Garzoli, Robert L. MolinariAbstract:A test of the theoretical Ekman relation in the tropical Atlantic Ocean is performed by comparing estimated Ekman Transport with observations collected along two transects symmetric about equator (6°N and 6°S). Ekman Transport is calculated theoretically using ship winds and climatological data. Total ageostrophic Transport is obtained by subtracting the observed geostrophic Transports from the measured total Transports using the data collected along the two transects. Along 6°S, both the zonal mean ageostrophic Transport and it's variability with longitude can be accounted for by the theoretical Ekman Transport. Along 6°N, the total ageostrophic and Ekman Transports agree, but significant differences are found in the cumulative Transport curves between the African coast and about 40°W. These departures from theory may be related to the effect of advective terms in the Ekman relation and/or other ageostrophic motion at the reference depth for the comparisons. Begin typing abstract here.
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A transatlantic section at 14.5N: Meridional volume and heat fluxes
Journal of Marine Research, 1995Co-Authors: Birgit Klein, Robert L. Molinari, Thomas J. Müller, Gerold SiedlerAbstract:Two high-resolution hydrographic sections occupied during February, March 1989 in the western and eastern basins of the North Atlantic at 14.5N are combined to study the water mass structure and meridional mass and heat Transports. Absolute velocities were determined using these data and an earlier section at 8N in a linear inverse analysis. Mass balance for several layers representing the main water masses in the region and a zero net divergence for the sum of geostrophic and Ekman Transport between the two sections are assumed. Using the annual mean of Ekman Transports (13.6 Sv, 14.5N), (15.2 Sv, 8N) based on the climatology by Isemer and Hasse (1985) the annual average fluxes for the sections at 8N and 14.5N have been calculated. For the annual mean the strength of the meridional overturning cell at 14.5N amounts to 15.9 Sv with an associated heat Transport of 1.22 PW. A similar value can be obtained at 8N where the annual mean heat Transport reaches 1.18 PW and the overturning cell measures 15 Sv. The total northward heat Transport is strongly dominated by the wind-driven Ekman heat Transport. 'In-situ' values of heat Transport using the actual wind-driven Transports for the respective months yield even higher estimates. Heat Transport at 14.5N rises to 1.37 +/- 0.42 PW (February) and the maximum is now at the 8N section, 1.69 +/- 0.52 PW (May). Comparisons of our results with another tropical section at 11N occupied concurrently demonstrate the large variability in heat Transport related to changes in the wind field. Due to extremely weak winds in the eastern Atlantic and a resulting low Ekman Transport, the 'in-situ' value of heat Transport through this section ranged between 0.30 +/- 0.18 PW and 0.59 +/- 0.18 PW depending on the value chosen for the Ekman Transport. The lower of the two heat Transport estimates results from calculations with the actual observed winds and the other using a monthly climatological mean. That even the computations with the climatological monthly mean give such a low heat Transport points to additional changes in the baroclinic structures between 11N and 14.5N.
Matthew H. England - One of the best experts on this subject based on the ideXlab platform.
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Ekman Transport dominates local air sea fluxes in driving variability of subantarctic mode water
Journal of Physical Oceanography, 2002Co-Authors: Stephen R. Rintoul, Matthew H. EnglandAbstract:Subantarctic Mode Water (SAMW) is formed by deep convection in winter on the equatorward side of the Antarctic Circumpolar Current. Observations south of Australia show that the SAMW temperature (T) and salinity (S) vary significantly from year to year. The magnitude and density-compensating nature of the temperature and salinity changes cannot be explained by variations in air-sea exchange of heat and freshwater in the subantarctic zone where SAMW is formed. Rather, the T and S variability reflects variations in the equatorward Ekman Transport of cool, low salinity water across the subantarctic front. Experiments with a coupled climate model suggest that the observations south of Australia are typical of the subantarctic zone. The model changes in SAMW properties are correlated significantly (at 99% level) with changes in wind stress and northward Ekman Transport of cool low- salinity water. In contrast, air-sea heat flux anomalies are mostly a response to changes in SST, and anomalies in precipitation minus evaporation in the subantarctic zone are too small to account for the model SAMW salinity variations. Mode waters provide significant reservoirs of heat and freshwater that extend below the depth of the seasonal thermocline and, hence, can persist from year to year. The fact that wind stress variations can drive changes in mode water properties therefore has implications for climate variability.
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Ekman Transport Dominates Local Air–Sea Fluxes in Driving Variability of Subantarctic Mode Water
Journal of Physical Oceanography, 2002Co-Authors: Stephen R. Rintoul, Matthew H. EnglandAbstract:Subantarctic Mode Water (SAMW) is formed by deep convection in winter on the equatorward side of the Antarctic Circumpolar Current. Observations south of Australia show that the SAMW temperature (T) and salinity (S) vary significantly from year to year. The magnitude and density-compensating nature of the temperature and salinity changes cannot be explained by variations in air-sea exchange of heat and freshwater in the subantarctic zone where SAMW is formed. Rather, the T and S variability reflects variations in the equatorward Ekman Transport of cool, low salinity water across the subantarctic front. Experiments with a coupled climate model suggest that the observations south of Australia are typical of the subantarctic zone. The model changes in SAMW properties are correlated significantly (at 99% level) with changes in wind stress and northward Ekman Transport of cool low- salinity water. In contrast, air-sea heat flux anomalies are mostly a response to changes in SST, and anomalies in precipitation minus evaporation in the subantarctic zone are too small to account for the model SAMW salinity variations. Mode waters provide significant reservoirs of heat and freshwater that extend below the depth of the seasonal thermocline and, hence, can persist from year to year. The fact that wind stress variations can drive changes in mode water properties therefore has implications for climate variability.