Influence of a western boundary current on shelf dynamics and upwelling from repeat glider deployments

2015 ◽  
Vol 42 (1) ◽  
pp. 121-128 ◽  
Author(s):  
A. Schaeffer ◽  
M. Roughan
Keyword(s):  
Western Boundary Current ◽  
Western Boundary ◽  
Boundary Current ◽  
Shelf Dynamics

Cross-Shelf Dynamics in a Western Boundary Current Regime: Implications for Upwelling

2013 ◽  
Vol 43 (5) ◽  
pp. 1042-1059 ◽  
Author(s):  
Amandine Schaeffer ◽  
Moninya Roughan ◽  
Bradley D. Morris
Keyword(s):  
Wind Stress ◽  
Cold Water ◽  
Western Boundary Current ◽  
Separation Point ◽  
Western Boundary ◽  
Boundary Current ◽  
Geostrophic Balance ◽  
Upwelled Water ◽  
Shelf Dynamics ◽  
Weak Winds

Abstract The cross-shelf dynamics up- and downstream of the separation of the South Pacific Ocean’s Western Boundary Current (WBC) are studied using two years of high-resolution velocity and temperature measurements from mooring arrays. The shelf circulation is dominated by the East Australian Current (EAC) and its eddy field, with mean poleward depth-integrated magnitudes on the shelf break of 0.35 and 0.15 m s−1 up- and downstream of the separation point, respectively. The high cross-shelf variability is analyzed though a momentum budget, showing a dominant geostrophic balance at both locations. Among the secondary midshelf terms, the bottom stress influence is higher upstream of the separation point while the wind stress is dominant downstream. This study investigates the response of the velocity and temperature cross-shelf structure to both wind and EAC intrusions. Despite the deep water (up to 140 m), the response to a dominant along-shelf wind stress forcing is a classic two-layer Ekman structure. During weak winds, the shelf encroachment of the southward current drives an onshore Ekman flow in the bottom boundary layer. Both the bottom velocity and the resultant bottom cross-shelf temperature gradient are proportional to the magnitude of the encroaching current, with similar linear regressions up- and downstream of the WBC separation. The upwelled water is then subducted below the EAC upstream of the separation point. Such current-driven upwelling is shown to be the dominant driver of cold water uplift in the EAC-dominated region, with significant impacts expected on nutrient enrichment and thus on biological productivity.

scholarly journals Frequency-Domain Analysis of the Energy Budget in an Idealized Coupled Ocean–Atmosphere Model

2020 ◽  
Vol 33 (2) ◽  
pp. 707-726 ◽  
Author(s):  
Paige E. Martin ◽  
Brian K. Arbic ◽  
Andrew McC. Hogg ◽  
Andrew E. Kiss ◽  
James R. Munroe ◽  
...  
Keyword(s):  
Frequency Domain ◽  
Time Scales ◽  
Energy Budget ◽  
Western Boundary Current ◽  
Spectral Energy ◽  
Western Boundary ◽  
Intrinsic Variability ◽  
Boundary Current ◽  
Ocean Atmosphere ◽  
Atmosphere Model

AbstractClimate variability is investigated by identifying the energy sources and sinks in an idealized, coupled, ocean–atmosphere model, tuned to mimic the North Atlantic region. The spectral energy budget is calculated in the frequency domain to determine the processes that either deposit energy into or extract energy from each fluid, over time scales from one day up to 100 years. Nonlinear advection of kinetic energy is found to be the dominant source of low-frequency variability in both the ocean and the atmosphere, albeit in differing layers in each fluid. To understand the spatial patterns of the spectral energy budget, spatial maps of certain terms in the spectral energy budget are plotted, averaged over various frequency bands. These maps reveal three dynamically distinct regions: along the western boundary, the western boundary current separation, and the remainder of the domain. The western boundary current separation is found to be a preferred region to energize oceanic variability across a broad range of time scales (from monthly to decadal), while the western boundary itself acts as the dominant sink of energy in the domain at time scales longer than 50 days. This study paves the way for future work, using the same spectral methods, to address the question of forced versus intrinsic variability in a coupled climate system.

scholarly journals Midlatitude–Equatorial Dynamics of a Grounded Deep Western Boundary Current. Part I: Midlatitude Flow and the Transition to the Equatorial Region

2015 ◽  
Vol 45 (10) ◽  
pp. 2457-2469 ◽  
Author(s):  
Gordon E. Swaters
Keyword(s):  
Bottom Topography ◽  
Zonal Flow ◽  
Ocean Basin ◽  
Equatorial Region ◽  
Western Boundary Current ◽  
Western Boundary ◽  
Boundary Current ◽  
Qualitative Properties ◽  
Deep Western Boundary Current ◽  
The Tropics

AbstractA comprehensive theoretical study of the nonlinear hemispheric-scale midlatitude and cross-equatorial steady-state dynamics of a grounded deep western boundary current is given. The domain considered is an idealized differentially rotating, meridionally aligned basin with zonally varying parabolic bottom topography so that the model ocean shallows on both the western and eastern sides of the basin. Away from the equator, the flow is governed by nonlinear planetary geostrophic dynamics on sloping topography in which the potential vorticity equation can be explicitly solved. As the flow enters the equatorial region, it speeds up and becomes increasingly nonlinear and passes through two distinguished inertial layers referred to as the “intermediate” and “inner” inertial equatorial boundary layers, respectively. The flow in the intermediate equatorial region is shown to accelerate and turn eastward, forming a narrow equatorial jet. The qualitative properties of the solution presented are consistent with the known dynamical characteristics of the deep western boundary currents as they flow from the midlatitudes into the tropics. The predominately zonal flow across the ocean basin in the inner equatorial region (and its exit from the equatorial region) is determined in Part II of this study.

scholarly journals Characteristics and causes of Deep Western Boundary Current transport variability at 34.5° S during 2009–2014

2016 ◽  
Author(s):  
Christopher S. Meinen ◽  
Silvia L. Garzoli ◽  
Renellys C. Perez ◽  
Edmo Campos ◽  
Alberto R. Piola ◽  
...  
Keyword(s):  
Volume Transport ◽  
Horizontal Resolution ◽  
Western Boundary Current ◽  
Meridional Overturning Circulation ◽  
Time Variability ◽  
Western Boundary ◽  
Boundary Current ◽  
Meridional Heat Transport ◽  
Data Set ◽  
Deep Western Boundary Current

Abstract. The Deep Western Boundary Current (DWBC) at 34.5° S in the South Atlantic carries a significant fraction of the cold deep limb of the Meridional Overturning Circulation (MOC), and therefore its variability affects both the meridional heat transport and the regional and global climate. Nearly six years of observations from a line of pressure-equipped inverted echo sounders (PIES) have yielded an unprecedented data set for studying the characteristics of the time-varying DWBC volume transport at 34.5° S. Furthermore, the horizontal resolution of the observing array was greatly improved in December 2012 with the addition of two current-and-pressure-equipped inverted echo sounders (CPIES) at the midpoints of three of the existing sites. Regular hydrographic sections along the PIES/CPIES line confirm the presence of recently-ventilated North Atlantic Deep Water carried by the DWBC. The time-mean absolute geostrophic transport integrated within the DWBC layer, defined between 800–4800 dbar, and within longitude bounds of 51.5° W to 44.5° W is −15 Sv (1 Sv = 106 m3 s−1; negative indicates southward flow). The observed peak-to-peak range in volume transport using these integration limits is from −89 Sv to +50 Sv, and the temporal standard deviation is 23 Sv. Testing different vertical integration limits based on time-mean water-mass property levels yields small changes to these values, but no significant alteration to the character of the transport time series. The time-mean southward DWBC flow at this latitude is confined west of 49.5° W, with recirculations dominating the flow further offshore. As with other latitudes where the DWBC has been observed for multiple years, the time variability greatly exceeds the time-mean, suggesting the presence of strong coherent vortices and/or Rossby Wave-like signals propagating to the boundary from the interior.

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