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• 1. [Article] Coastal Wind-Driven Circulation in the Vicinity of a Bank. Part II: Modeling Flow over the Heceta Bank Complex on the Oregon Coast

  This study investigates wind-driven circulation in the vicinity of the Heceta Bank complex along the Oregon shelf. Numerical experiments forced with steady winds (0.1 Pa) are conducted; upwelling and downwelling ...

  Citation × Citation Citation Abstract Copy Title: Coastal Wind-Driven Circulation in the Vicinity of a Bank. Part II: Modeling Flow over the Heceta Bank Complex on the Oregon Coast Author: Whitney, Michael M., Allen, J. S. This study investigates wind-driven circulation in the vicinity of the Heceta Bank complex along the Oregon shelf. Numerical experiments forced with steady winds (0.1 Pa) are conducted; upwelling and downwelling cases are compared. The asymmetric bank bathymetry is the only configurational difference from the symmetric bank runs analyzed in Part I (Whitney and Allen). Upwelling-favorable winds generate an upwelling front and southward baroclinic jet. Model results indicate the upwelling jet is centered on the 100-m isobath along the straight shelf. The jet follows this isobath offshore around the northern part of the bank but separates from sharply turning isobaths in the southern half and flows over deeper waters. The jet turns back toward the coast farther downstream. Inshore of the main jet, currents reverse and flow back onto the bank. These reversed currents turn southward again (at the bank center) and join a secondary southward coastal upwelling jet. This secondary coastal jet converges with the stronger main jet farther downstream. Upwelling is intense at the northern bank edge near the coast, where a dense water tongue is advected over the bank. Upwelling also is strong on the southern bank half where the flow turns and reverses. Other areas of the bank have reduced upwelling or even downwelling during upwelling-favorable winds. Downwelling-favorable winds drive a near-bottom density front and a northward jet. The slower downwelling jet flows along the 130-m isobath over the straight shelf. The jet departs from isobaths over the southern bank half and follows a straighter path over shallower waters. There are no reversed currents over the bank. The bank is an area of reduced downwelling. Some of the differences in the evolution of the current and density fields are linked to fundamental differences between the upwelling and downwelling regimes; these are anticipated by the symmetric bank results of Part I. Other differences arise because of the bank asymmetry and opposite flow directions over the bank. The lowest-order depth-averaged across-stream momentum balance remains geostrophic over the bank. Advection, ageostrophic pressure gradients, wind stress, and bottom stress all are important in the depth-averaged alongstream momentum balance over the Heceta Bank complex. Both across-shelf and alongshelf density advection are important. Barotropic potential vorticity is not conserved over the bank, but the tendency for relative vorticity changes and depth changes to partially counter each other influences the different paths of the upwelling and downwelling jets. There are several regions of active upwelling and downwelling over the bank. In these areas, vertical velocities at the top of the bottom boundary layer are linked to topographic upwelling and downwelling and Ekman pumping. There is considerable spatial variability in the currents, densities, and dynamics over the Heceta Bank complex. Title: Coastal Wind-Driven Circulation in the Vicinity of a Bank. Part II: Modeling Flow over the Heceta Bank Complex on the Oregon Coast Author: Whitney, Michael M., Allen, J. S. This study investigates wind-driven circulation in the vicinity of the Heceta Bank complex along the Oregon shelf. Numerical experiments forced with steady winds (0.1 Pa) are conducted; upwelling and downwelling cases are compared. The asymmetric bank bathymetry is the only configurational difference from the symmetric bank runs analyzed in Part I (Whitney and Allen). Upwelling-favorable winds generate an upwelling front and southward baroclinic jet. Model results indicate the upwelling jet is centered on the 100-m isobath along the straight shelf. The jet follows this isobath offshore around the northern part of the bank but separates from sharply turning isobaths in the southern half and flows over deeper waters. The jet turns back toward the coast farther downstream. Inshore of the main jet, currents reverse and flow back onto the bank. These reversed currents turn southward again (at the bank center) and join a secondary southward coastal upwelling jet. This secondary coastal jet converges with the stronger main jet farther downstream. Upwelling is intense at the northern bank edge near the coast, where a dense water tongue is advected over the bank. Upwelling also is strong on the southern bank half where the flow turns and reverses. Other areas of the bank have reduced upwelling or even downwelling during upwelling-favorable winds. Downwelling-favorable winds drive a near-bottom density front and a northward jet. The slower downwelling jet flows along the 130-m isobath over the straight shelf. The jet departs from isobaths over the southern bank half and follows a straighter path over shallower waters. There are no reversed currents over the bank. The bank is an area of reduced downwelling. Some of the differences in the evolution of the current and density fields are linked to fundamental differences between the upwelling and downwelling regimes; these are anticipated by the symmetric bank results of Part I. Other differences arise because of the bank asymmetry and opposite flow directions over the bank. The lowest-order depth-averaged across-stream momentum balance remains geostrophic over the bank. Advection, ageostrophic pressure gradients, wind stress, and bottom stress all are important in the depth-averaged alongstream momentum balance over the Heceta Bank complex. Both across-shelf and alongshelf density advection are important. Barotropic potential vorticity is not conserved over the bank, but the tendency for relative vorticity changes and depth changes to partially counter each other influences the different paths of the upwelling and downwelling jets. There are several regions of active upwelling and downwelling over the bank. In these areas, vertical velocities at the top of the bottom boundary layer are linked to topographic upwelling and downwelling and Ekman pumping. There is considerable spatial variability in the currents, densities, and dynamics over the Heceta Bank complex. Close

• 2. [Article] Coastal Wind-Driven Circulation in the Vicinity of a Bank. Part I: Modeling Flow over Idealized Symmetric Banks

  This study examines how coastal banks influence wind-driven circulation along stratified continental shelves. Numerical experiments are conducted for idealized symmetric banks; the standard bank (200 km ...

  Citation × Citation Citation Abstract Copy Title: Coastal Wind-Driven Circulation in the Vicinity of a Bank. Part I: Modeling Flow over Idealized Symmetric Banks Author: Whitney, Michael M., Allen, J. S. This study examines how coastal banks influence wind-driven circulation along stratified continental shelves. Numerical experiments are conducted for idealized symmetric banks; the standard bank (200 km long and 50 km wide) has dimensions similar to the Heceta Bank complex along the Oregon shelf. Model runs are forced with 10 days of steady winds (0.1 Pa); upwelling and downwelling cases are compared. The bank introduces significant alongshelf variability in the currents and density fields. Upwelling-favorable winds create an upwelling front and a baroclinic jet (flowing opposite coastal-trapped wave propagation) that bend around the standard bank, approximately centered on the 90-m isobath. The upwelling jet is strongest over the upstream bank half, where it advects a tongue of dense water over the bank. There is a current reversal shoreward of the main jet at the bank center. Upwelling is most intense over the upstream part of the bank, while there is reduced upwelling and even downwelling over other bank sections. Downwelling-favorable winds create a near-bottom density front and a baroclinic jet (flowing in the direction of coastal-trapped wave propagation) that bend around the standard bank; the jet core moves from the 150-m isobath to the 100-m isobath and back over the bank. The downwelling jet is slowest and widest over the bank; there are no current reversals. Results over the bank are more similar to 2D results (that preclude alongshelf variability) than in the upwelling case. Downwelling is weakened over the bank. The density field evolution over the bank is fundamentally different from the upwelling case. Most model results for banks with different dimensions are qualitatively similar to the standard run. The exceptions are banks having a radius of curvature smaller than the inertial radius; the main jet remains detached from the coast far downstream from these banks. The lowest-order across-stream momentum balance indicates that the depth-averaged flow is geostrophic. Advection, ageostrophic pressure gradients, wind stress, and bottom stress are all important in the depth-averaged alongstream momentum balance over the bank. There is considerable variability in alongstream momentum balances over different bank sections. Across-shelf and alongshelf advection both change the density field over the bank. Barotropic potential vorticity is not conserved, but the tendency for relative vorticity changes and depth changes to partially counter each other results in differences between the upwelling and downwelling jet paths over the bank. Only certain areas of the bank have significant vertical velocities. In these areas of active upwelling and downwelling, vertical velocities at the top of the bottom boundary layer are due to either the jet crossing isobaths or bottom Ekman pumping Title: Coastal Wind-Driven Circulation in the Vicinity of a Bank. Part I: Modeling Flow over Idealized Symmetric Banks Author: Whitney, Michael M., Allen, J. S. This study examines how coastal banks influence wind-driven circulation along stratified continental shelves. Numerical experiments are conducted for idealized symmetric banks; the standard bank (200 km long and 50 km wide) has dimensions similar to the Heceta Bank complex along the Oregon shelf. Model runs are forced with 10 days of steady winds (0.1 Pa); upwelling and downwelling cases are compared. The bank introduces significant alongshelf variability in the currents and density fields. Upwelling-favorable winds create an upwelling front and a baroclinic jet (flowing opposite coastal-trapped wave propagation) that bend around the standard bank, approximately centered on the 90-m isobath. The upwelling jet is strongest over the upstream bank half, where it advects a tongue of dense water over the bank. There is a current reversal shoreward of the main jet at the bank center. Upwelling is most intense over the upstream part of the bank, while there is reduced upwelling and even downwelling over other bank sections. Downwelling-favorable winds create a near-bottom density front and a baroclinic jet (flowing in the direction of coastal-trapped wave propagation) that bend around the standard bank; the jet core moves from the 150-m isobath to the 100-m isobath and back over the bank. The downwelling jet is slowest and widest over the bank; there are no current reversals. Results over the bank are more similar to 2D results (that preclude alongshelf variability) than in the upwelling case. Downwelling is weakened over the bank. The density field evolution over the bank is fundamentally different from the upwelling case. Most model results for banks with different dimensions are qualitatively similar to the standard run. The exceptions are banks having a radius of curvature smaller than the inertial radius; the main jet remains detached from the coast far downstream from these banks. The lowest-order across-stream momentum balance indicates that the depth-averaged flow is geostrophic. Advection, ageostrophic pressure gradients, wind stress, and bottom stress are all important in the depth-averaged alongstream momentum balance over the bank. There is considerable variability in alongstream momentum balances over different bank sections. Across-shelf and alongshelf advection both change the density field over the bank. Barotropic potential vorticity is not conserved, but the tendency for relative vorticity changes and depth changes to partially counter each other results in differences between the upwelling and downwelling jet paths over the bank. Only certain areas of the bank have significant vertical velocities. In these areas of active upwelling and downwelling, vertical velocities at the top of the bottom boundary layer are due to either the jet crossing isobaths or bottom Ekman pumping Close