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Robert H Weisberg - One of the best experts on this subject based on the ideXlab platform.
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west florida shelf response to local Wind Forcing april 1998
Journal of Geophysical Research, 2001Co-Authors: Robert H Weisberg, Zhenjiang Li, Frank E MullerkargerAbstract:We compare west Florida shelf velocity and sea level data with a model simulation for April 1998. Responses for three upwelling and three downwelling favorable Wind events are documented. Along-shelf jets accompanied by oppositely directed upper and lower layer across-shelf flows (with connecting vertical velocity) comprise the fully three-dimensional inner shelf responses, which are sensitive to stratification. With an initial density field representative of April 1998 the model simulates velocity and sea level variations in general agreement with the observations, whereas substantial mismatches occur without stratification. Despite the Winds being the primary motive agent for the inner shelf the stratification dependence requires that model density fields be maintained through a combination of adequate initial conditions; surface, offshore, and land-derived buoyancy inputs; and data assimilation. Dynamical analyses define the inner shelf as the region where the surface and bottom boundary layers are important in the momentum balance. Kinematically, this is where surface Ekman layer divergence, fed by the bottom Ekman layer convergence, or conversely, sets up the across-shelf pressure gradient. Stratification causes a response asymmetry wherein the offshore scale and magnitude of the upwelling responses are larger than those for the downwelling responses. This asymmetry is attributed to thermal Wind effects across the bottom Ekman layer. Buoyancy torque by isopycnals bending into the bottom adds constructively (destructively) with planetary vorticity tilting under upwelling (downwelling) favorable Winds, and this may have important implications for nutrients and other material property distributions on the shelf.
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west florida shelf response to upwelling favorable Wind Forcing kinematics
Journal of Geophysical Research, 1999Co-Authors: Zhenjiang Li, Robert H WeisbergAbstract:The barotropic responses of the west Florida continental shelf to idealized upwelling favorable alongshore and offshore Wind stresses are studied using the three-dimensional, time-dependent, primitive equation Princeton Ocean Model (POM). When forced with uniform Winds, the shelf circulation evolves quickly to a quasi steady state. A southeastward alongshore Wind lowers sea level along the coast and drives a southeastward coastal jet with a relatively weak northwestward return flow farther offshore. A southwestward offshore Wind lowers sea level along the west Florida coast and raises sea level along the Panhandle coast. Two independent circulation gyres are set up in association with these regionally different sea level distributions: an anticyclonic gyre off the west Florida coast consisting of a southeastward coastal jet and a broad return flow over the middle shelf and a cyclonic gyre off the Panhandle coast consisting of a strong northwestward coastal jet and an adjacent narrow southeastward undercurrent. These gyres are separated by the Big Bend region. In both cases (alongshore and offshore Wind Forcing) the circulations are fully three-dimensional, with opposing surface and bottom boundary layer flows accounting for the across-shelf transports. The shapes of the coastline and the isobaths are important determinants of the shelf-wide responses. Several locally maximum upwelling regions are identified for geometrical reasons. These include the Panhandle coast south of Apalachicola Bay, the west Florida coast south of Tampa Bay, along the Florida Keys, and at the shelf break where topographic Rossby waves are evident.
J S Allen - One of the best experts on this subject based on the ideXlab platform.
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On open boundary conditions for a limited-area coastal model off Oregon. Part 1: Response to idealized Wind Forcing
Ocean Modelling, 2020Co-Authors: J S AllenAbstract:A two-part study focusing on the development and application of open boundary conditions (OBCs) for a limited-area high-resolution coastal ocean model off Oregon is pursued. In Part 1, the OBCs are formulated and evaluated in numerical experiments utilizing idealized Wind Forcing. In Part 2, the OBCs are applied in an experiment with Forcing by space and time variable Winds obtained from a regional mesoscale atmospheric model. The initial experiments in Part 1 involve Forcing by Winds that are constant in time and are spatially uniform. The response to both upwelling favorable (southward) and downwelling favorable (northward) Winds are examined and compared to results obtained with cyclic alongshore boundary conditions (CBCs). Additional experiments are conducted with idealized spatial variability in the Wind Forcing to include assessment of the OBC performance in situations when coastal trapped wave (CTW) dynamics play an important role in the shelf flow response. Some aspects of OBC performance with time-dependent Wind Forcing are investigated in these latter experiments by examining the response after Wind Forcing is turned off. The OBCs separate the total baroclinic solution at the open boundary into local and global components. In these applications, the local solution is obtained from an across-shore, depth and time-dependent two-dimensional submodel. The existence of inflow or outflow is determined from the global solutions using radiation conditions. During inflow, the local solution is smoothly imposed. During outflow, the global part of the solution is radiated out of the domain. Favorable, dynamically consistent performance of these OBCs is found in all experiments. (C) 2004 Elsevier Ltd. All rights reserved
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on open boundary conditions for a limited area coastal model off oregon part 1 response to idealized Wind Forcing
Ocean Modelling, 2005Co-Authors: J S AllenAbstract:Abstract A two-part study focusing on the development and application of open boundary conditions (OBCs) for a limited-area high-resolution coastal ocean model off Oregon is pursued. In Part 1, the OBCs are formulated and evaluated in numerical experiments utilizing idealized Wind Forcing. In Part 2, the OBCs are applied in an experiment with Forcing by space and time variable Winds obtained from a regional mesoscale atmospheric model. The initial experiments in Part 1 involve Forcing by Winds that are constant in time and are spatially uniform. The response to both upwelling favorable (southward) and downwelling favorable (northward) Winds are examined and compared to results obtained with cyclic alongshore boundary conditions (CBCs). Additional experiments are conducted with idealized spatial variability in the Wind Forcing to include assessment of the OBC performance in situations when coastal trapped wave (CTW) dynamics play an important role in the shelf flow response. Some aspects of OBC performance with time-dependent Wind Forcing are investigated in these latter experiments by examining the response after Wind Forcing is turned off. The OBCs separate the total baroclinic solution at the open boundary into local and global components. In these applications, the local solution is obtained from an across-shore, depth and time-dependent two-dimensional submodel. The existence of inflow or outflow is determined from the global solutions using radiation conditions. During inflow, the local solution is smoothly imposed. During outflow, the global part of the solution is radiated out of the domain. Favorable, dynamically consistent performance of these OBCs is found in all experiments.
Zhenjiang Li - One of the best experts on this subject based on the ideXlab platform.
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west florida shelf response to local Wind Forcing april 1998
Journal of Geophysical Research, 2001Co-Authors: Robert H Weisberg, Zhenjiang Li, Frank E MullerkargerAbstract:We compare west Florida shelf velocity and sea level data with a model simulation for April 1998. Responses for three upwelling and three downwelling favorable Wind events are documented. Along-shelf jets accompanied by oppositely directed upper and lower layer across-shelf flows (with connecting vertical velocity) comprise the fully three-dimensional inner shelf responses, which are sensitive to stratification. With an initial density field representative of April 1998 the model simulates velocity and sea level variations in general agreement with the observations, whereas substantial mismatches occur without stratification. Despite the Winds being the primary motive agent for the inner shelf the stratification dependence requires that model density fields be maintained through a combination of adequate initial conditions; surface, offshore, and land-derived buoyancy inputs; and data assimilation. Dynamical analyses define the inner shelf as the region where the surface and bottom boundary layers are important in the momentum balance. Kinematically, this is where surface Ekman layer divergence, fed by the bottom Ekman layer convergence, or conversely, sets up the across-shelf pressure gradient. Stratification causes a response asymmetry wherein the offshore scale and magnitude of the upwelling responses are larger than those for the downwelling responses. This asymmetry is attributed to thermal Wind effects across the bottom Ekman layer. Buoyancy torque by isopycnals bending into the bottom adds constructively (destructively) with planetary vorticity tilting under upwelling (downwelling) favorable Winds, and this may have important implications for nutrients and other material property distributions on the shelf.
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west florida shelf response to upwelling favorable Wind Forcing kinematics
Journal of Geophysical Research, 1999Co-Authors: Zhenjiang Li, Robert H WeisbergAbstract:The barotropic responses of the west Florida continental shelf to idealized upwelling favorable alongshore and offshore Wind stresses are studied using the three-dimensional, time-dependent, primitive equation Princeton Ocean Model (POM). When forced with uniform Winds, the shelf circulation evolves quickly to a quasi steady state. A southeastward alongshore Wind lowers sea level along the coast and drives a southeastward coastal jet with a relatively weak northwestward return flow farther offshore. A southwestward offshore Wind lowers sea level along the west Florida coast and raises sea level along the Panhandle coast. Two independent circulation gyres are set up in association with these regionally different sea level distributions: an anticyclonic gyre off the west Florida coast consisting of a southeastward coastal jet and a broad return flow over the middle shelf and a cyclonic gyre off the Panhandle coast consisting of a strong northwestward coastal jet and an adjacent narrow southeastward undercurrent. These gyres are separated by the Big Bend region. In both cases (alongshore and offshore Wind Forcing) the circulations are fully three-dimensional, with opposing surface and bottom boundary layer flows accounting for the across-shelf transports. The shapes of the coastline and the isobaths are important determinants of the shelf-wide responses. Several locally maximum upwelling regions are identified for geometrical reasons. These include the Panhandle coast south of Apalachicola Bay, the west Florida coast south of Tampa Bay, along the Florida Keys, and at the shelf break where topographic Rossby waves are evident.
Dimitris Menemenlis - One of the best experts on this subject based on the ideXlab platform.
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trends in arctic sea ice drift and role of Wind Forcing 1992 2009
Geophysical Research Letters, 2011Co-Authors: Gunnar Spreen, R Kwok, Dimitris MenemenlisAbstract:[1] We examine the spatial trends in Arctic sea ice drift speed from satellite data and the role of Wind Forcing for the winter months of October through May. Between 1992 and 2009, the spatially averaged trend in drift speed within the Arctic Basin is 10.6% ± 0.9%/decade, and ranges between −4% and 16%/decade depending on the location. The mean trend is dominated by the second half of the period. In fact, for the five years after a clear break point in March 2004, the average trend increased to 46% ± 5%/decade. Over the 1992–2009 period, averaged trends of Wind speed from four atmospheric reanalyses are only 1% to 2%/decade. Regionally, positive trends in Wind speed (of up to 9%/decade) are seen over a large fraction of the Central Arctic, where the trends in drift speeds are highest. Spatial correlations between the basin-wide trends in Wind and drift speeds are moderate (between 0.40 and 0.52). Our results suggest that changes in Wind speed explain a fraction of the observed increase in drift speeds in the Central Arctic but not over the entire basin. In other regions thinning of the ice cover is a more likely cause of the increase in ice drift speed.
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simulated response of the arctic freshwater budget to extreme nao Wind Forcing
Journal of Climate, 2009Co-Authors: Alan Condron, Peter Winsor, Chris Hill, Dimitris MenemenlisAbstract:Abstract The authors investigate the response of the Arctic Ocean freshwater budget to changes in the North Atlantic Oscillation (NAO) using a regional-ocean configuration of the Massachusetts Institute of Technology GCM (MITgcm) and carry out several different 10-yr and 30-yr integrations. At 1/6° (∼18 km) resolution the model resolves the major Arctic transport pathways, including Bering Strait and the Canadian Archipelago. Two main calculations are performed by repeating the Wind fields of two contrasting NAO years in each run for the extreme negative and positive NAO phases of 1969 and 1989, respectively. These calculations are compared both with a control run and the compiled observationally based freshwater budget estimate of Serreze et al. The results show a clear response in the Arctic freshwater budget to NAO Forcing, that is, repeat NAO negative Wind Forcing results in virtually all freshwater being retained in the Arctic, with the bulk of the freshwater content being pooled in the Beaufort gyre...
Steven J Lentz - One of the best experts on this subject based on the ideXlab platform.
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the influence of Wind Forcing on the chesapeake bay buoyant coastal current
Journal of Physical Oceanography, 2006Co-Authors: Steven J Lentz, John L LargierAbstract:Observations of the buoyant coastal current that flows southward from Chesapeake Bay are used to describe how the thickness, width, and propagation speed vary in response to changes in the along-shelf Wind stress. Three basic regimes were observed depending on the strength of the Wind. For weak Wind stresses (from 0.02 to 0.02 Pa), the buoyant coastal current was relatively thin, the front slope was not steep, and the width was variable (1–20 km). For moderate downwelling (southward) Wind stresses (0.02– 0.07 Pa), Wind-driven cross-shelf advection steepened the front, causing the plume to narrow and thicken. For stronger downwelling Wind stresses (greater than 0.07 Pa), vertical mixing dominated, bulk Richardson numbers were approximately 0.25, isopycnals were nearly vertical, and the plume front widened but the plume width did not change. Plume thickness and width were normalized by the theoretical plume scales in the absence of Wind Forcing. Normalized plume thickness increased linearly from 1 to 2 as downwelling Wind stresses increased from 0 to 0.2 Pa. Normalized plume widths were approximately 1 for downwelling Wind stresses from 0.02 to 0.2 Pa. The observed along-shelf propagation speed of the plume was roughly equal to the sum of the theoretical propagation speed and the Wind-driven along-shelf flow.
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the amazon river plume during amasseds subtidal current variability and the importance of Wind Forcing
Journal of Geophysical Research, 1995Co-Authors: Steven J LentzAbstract:Current variability over the north Brazilian shelf, particularly within the Amazon Plume, is characterized using observations from a moored array deployed about 300 km north of the Amazon River mouth from February to June 1990 as part of A Multidisciplinary Amazon Shelf SEDiment Study (AMASSEDS). The moored array consisted of a transect perpendicular to the coast with inner shelf (18 m depth) and midshelf (65 m) moorings and a third mooring near the shelf break, in 100 m of water. To our knowledge, the AMASSEDS moored array includes the first long-term (2 months) moored observations made within the Amazon Plume. The current variability is dominated by two components, semidiurnal cross-shelf currents with peak velocities of 50 to 200 cm/s and vertically sheared subtidal (timescales days to weeks) along-shelf currents. This study focuses on the subtidal flow within the Amazon Plume which is strong and variable with along-shelf currents ranging from −50 cm/s to over 150 cm/s. The variability in the along-shelf current within the plume is Wind driven. The relatively weak (<0.5 dyn/cm2) along-shelf Wind stresses in this region drive strong along-shelf current variability because the Amazon Plume is thin and the interfacial drag is weak. However, in the absence of an along-shelf Wind stress the plume flow is northwestward at 40 to 80 cm/s, indicating that direct Wind Forcing does not account for the mean northwestward flow of the Amazon Plume. In the cross-plume direction there is a tendency for the onshore Wind stress due to the persistent trade Winds to balance the typically offshore buoyancy force and the Coriolis force associated with the Wind-driven along-shelf flow. Thus the Wind stress is a key factor influencing variability in both the flow and cross-shelf structure of the Amazon Plume in the vicinity of the moored array.
