Inhomogeneous isothermal equatorial Poiseuille - Ekman flow

2020 ◽  
Author(s):  
A. V. Gorshkov ◽  
E. Yu. Prosviryakov
Keyword(s):  
Ekman Flow

scholarly journals Volume and Nutrient Transports Disturbed by the Typhoon Chebi (2013) in the Upwelling Zone East of Hainan Island, China

2021 ◽  
Vol 9 (3) ◽  
pp. 324
Author(s):  
Manli Zheng ◽  
Lingling Xie ◽  
Quanan Zheng ◽  
Mingming Li ◽  
Fajin Chen ◽  
...  
Keyword(s):  
South China Sea ◽  
Coastal Upwelling ◽  
Unit Area ◽  
Hainan Island ◽  
Volume Transport ◽  
Coastal Ocean ◽  
Offshore Water ◽  
Nutrient Distribution ◽  
Before And After ◽  
Ekman Flow

Using cruise observations before and after the typhoon Chebi in August 2013 and those without the typhoon in July 2012, this study investigates variations in current structure, nutrient distribution, and transports disturbed by a typhoon in a typical coastal upwelling zone east of Hainan Island in the northwestern South China Sea. The results show that along-shore northeastward flow dominates the coastal ocean with a volume transport of 0.64 × 106 m3/s in the case without the typhoon. The flow reversed southwestward, with its volume transport halved before the typhoon passage. After the typhoon passage, the flow returned back northeastward except the upper layer in waters deeper than 50 m and the total volume transport decreased to 0.10 × 106 m3/s. For the cross-shelf component, the flow kept shoreward, while transports crossing the 50 m isobath decreased from 0.25, 0.12 to 0.06 × 106 m3/s in the case without the typhoon as well as before and after typhoon passage, respectively. For the along-shore/cross-shelf nutrient transports, SiO32− has the largest value of 866.13/632.74 μmol/s per unit area, NO3− half of that, and PO43− and NO2− one order smaller in the offshore water without the typhoon. The values dramatically decreased to about one-third for SiO32−, NO3−, and PO43− after the typhoon, but changed little for NO2−. The disturbed wind field and associated Ekman flow and upwelling process may explain the variations in the current and nutrient transports after the typhoon.

Modelling Ekman flow during the ACRT process with marked particles

1998 ◽  
Vol 183 (1-2) ◽  
pp. 140-149 ◽  
Author(s):  
Liu Juncheng ◽  
Jie Wanqi
Keyword(s):  
Ekman Flow

scholarly journals Generation of Subsurface Anticyclones at Arctic Surface Fronts due to a Surface Stress

2017 ◽  
Vol 47 (11) ◽  
pp. 2653-2671 ◽  
Author(s):  
Liam Brannigan ◽  
Helen Johnson ◽  
Camille Lique ◽  
Jonas Nycander ◽  
Johan Nilsson
Keyword(s):  
Mixed Layer ◽  
Surface Stress ◽  
Ekman Transport ◽  
The Arctic ◽  
Near Surface ◽  
Geostrophic Flow ◽  
Unstable Surface ◽  
Surface Cyclone ◽  
Ekman Flow ◽  
The Right

AbstractIsolated anticyclones are frequently observed below the mixed layer in the Arctic Ocean. Some of these subsurface anticyclones are thought to originate at surface fronts. However, previous idealized simulations with no surface stress show that only cyclone–anticyclone dipoles can propagate away from baroclinically unstable surface fronts. Numerical simulations of fronts subject to a surface stress presented here show that a surface stress in the same direction as the geostrophic flow inhibits dipole propagation away from the front. On the other hand, a surface stress in the opposite direction to the geostrophic flow helps dipoles to propagate away from the front. Regardless of the surface stress at the point of dipole formation, these dipoles can be broken up on a time scale of days when a surface stress is applied in the right direction. The dipole breakup leads to the deeper anticyclonic component becoming an isolated subsurface eddy. The breakup of the dipole occurs because the cyclonic component of the dipole in the mixed layer is subject to an additional advection because of the Ekman flow. When the Ekman transport has a component oriented from the anticyclonic part of the dipole toward the cyclonic part then the cyclone is advected away from the anticyclone and the dipole is broken up. When the Ekman transport is in other directions relative to the dipole axis, it also leads to deviations in the trajectory of the dipole. A scaling is presented for the rate at which the surface cyclone is advected that holds across a range of mixed layer depths and surface stress magnitudes in these simulations. The results may be relevant to other regions of the ocean with similar near-surface stratification profiles.

scholarly journals Friction, Frontogenesis, and the Stratification of the Surface Mixed Layer

2008 ◽  
Vol 38 (11) ◽  
pp. 2501-2518 ◽  
Author(s):  
Leif Thomas ◽  
Raffaele Ferrari
Keyword(s):  
Wind Stress ◽  
Mixed Layer ◽  
Numerical Experiments ◽  
Turbulent Transport ◽  
Surface Mixed Layer ◽  
Geostrophic Shear ◽  
Frictional Forces ◽  
Ekman Flow ◽  
Differential Advection ◽  
Ocean Wind

Abstract The generation and destruction of stratification in the surface mixed layer of the ocean is understood to result from vertical turbulent transport of buoyancy and momentum driven by air–sea fluxes and stresses. In this paper, it is shown that the magnitude and penetration of vertical fluxes are strongly modified by horizontal gradients in buoyancy and momentum. A classic example is the strong restratification resulting from frontogenesis in regions of confluent flow. Frictional forces acting on a baroclinic current either imposed externally by a wind stress or caused by the spindown of the current itself also modify the stratification by driving Ekman flows that differentially advect density. Ekman flow induced during spindown always tends to restratify the fluid, while wind-driven Ekman currents will restratify or destratify the mixed layer if the wind stress has a component up or down front (i.e., directed against or with the geostrophic shear), respectively. Scalings are constructed for the relative importance of friction versus frontogenesis in the restratification of the mixed layer and are tested using numerical experiments of mixed layer fronts forced by both winds and a strain field. The scalings suggest and the numerical experiments confirm that for wind stress magnitudes, mixed layer depths, and cross-front density gradients typical of the ocean, wind-induced friction often dominates frontogenesis in the modification of the stratification of the upper ocean. The experiments reveal that wind-induced destratification is weaker in magnitude than restratification because the stratification generated by up-front winds confines the turbulent stress to a depth shallower than the Ekman layer, which enhances the frictional force, Ekman flow, and differential advection of density. Frictional destratification is further reduced over restratification because the stress associated with the geostrophic shear at the surface tends to compensate a down-front wind stress.

Regimes of Thermocline Scaling: The Interaction of Wind Stress and Surface Buoyancy

2007 ◽  
Vol 37 (8) ◽  
pp. 2009-2021 ◽  
Author(s):  
Paola Cessi
Keyword(s):  
Potential Energy ◽  
Surface Temperature ◽  
Heat Transport ◽  
Wind Stress ◽  
Wind Stress Curl ◽  
Available Potential Energy ◽  
Ekman Flow ◽  
Diapycnal Diffusivity ◽  
Surface Buoyancy

Abstract The role of the relative geometry of mechanical forcing (wind stress) and buoyancy forcing (prescribed surface temperature) in the maintenance of the main thermocline is explored. In particular, the role of the wind stress curl in enhancing or suppressing the generation of baroclinic eddies is studied in simplified domains. The dependence of key quantities, such as the depth of the thermocline and the maximum heat transport, on the external parameters such as diapycnal mixing and dissipation rate is examined. Qualitatively different regimes are found depending on the relative phase of the wind stress and surface buoyancy distribution. The most efficient arrangement for eddy generation has Ekman pumping (suction) in conjunction with high (low) surface buoyancy. This corresponds to the situation found in the midlatitudes, where the surface Ekman flow carries heat toward the warmer region (i.e., upgradient of the surface temperature). In this case, strong eddy fluxes are generated in order to counteract the upgradient heat transport by the Ekman cell. The result is a thermocline whose depth is independent of the diapycnal diffusivity. However, the competition between these opposing heat fluxes leads to a weak net heat transport, proportional to the diffusivity responsible for the diabatic forcing. This arrangement of wind stress provides a large source of available potential energy on which eddies can grow, so the mechanical energy balance for the eddies is consistent with a substantial eddy heat flux. When the same surface temperature distribution is paired with the opposite wind stress curl, the mean flow produces a sink, rather than a source, of available potential energy and eddies are suppressed. With this arrangement, typical of low latitudes and the subpolar regions, the Ekman overturning cell carries heat downgradient of the surface temperature. Thus, the net heat transport is almost entirely due to the Ekman flow and is independent of the diapycnal diffusivity. At the same time the thermocline is a thin, diffusive boundary layer. Quantitative scalings for the thermocline depth and the poleward heat transport in these two limiting cases are contrasted and successfully compared with eddy-resolving computations.

scholarly journals Aegean Surface Circulation from a Satellite-Tracked Drifter Array

2007 ◽  
Vol 37 (7) ◽  
pp. 1898-1917 ◽  
Author(s):  
Donald B. Olson ◽  
Vassiliki H. Kourafalou ◽  
William E. Johns ◽  
Geoff Samuels ◽  
Milena Veneziani
Keyword(s):  
Mesoscale Eddy ◽  
Aegean Sea ◽  
Mesoscale Dynamics ◽  
The North ◽  
Rapid Sampling ◽  
Surface Circulation ◽  
Basin Topography ◽  
Salinity Water ◽  
Ekman Flow ◽  
Eddy Field

Abstract A pilot experiment using an array of 45 drifters to explore the circulation in the north and central Aegean Sea is described. The global positioning system drifters with holey-sock drogues provide positions every hour with data recovery through the Argos system. The drifters were launched in four separate deployments over a 1-yr period. The resulting trajectories confirm the existence of a current around the rim of the basin consistent with a buoyancy plume created by the outflow of Black Sea waters through the Dardanelles (Strait of Çanakkale in Turkish). The degree to which this is augmented by an Ekman response to the dominant northerly winds is not obvious in the dataset owing to mesoscale dynamics that obscure the existence of any westward Ekman flow. The mesoscale eddy field involves anticylonic eddies in the current around the rim of the basin consistent with eddies with low-salinity-water cores. Cyclones are also seen, with the most prominent forming over deep regions in the basin topography. The array also documents the interaction of the currents with the straits through the Sporades and Cyclades island groups. These interactions are complicated by the nature of the mesoscale flow and in some trajectories suggest a Bernouilli acceleration in straits; in others the flow through the island groups appears to be more diffusive and involves deceleration and eddy motions. The rapid sampling by the drifters reveals an extremely nonlinear submesoscale eddy field in the basin with length scales less than 4 km and Rossby numbers of order 1. A better understanding of the dynamics of these features is of importance for understanding the circulation of the basin.

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