scholarly journals Enhancement of Alongshore Freshwater Transport in Surface-Advected River Plumes by Tides

2014 ◽  
Vol 44 (11) ◽  
pp. 2951-2971 ◽  
Author(s):  
Shih-Nan Chen
Keyword(s):  
Numerical Study ◽  
Incident Angle ◽  
Ocean Modeling ◽  
Positive Pressure ◽  
Coastal Current ◽  
Current Transport ◽  
Coastal Currents ◽  
Regional Ocean Modeling System ◽  
Tidal Forcing ◽  
Freshwater Transport

Abstract A recent numerical study by Isobe showed that imposing alongshore tidal forcing on buoyant coastal discharge enhances the net freshwater transport in the coastal currents. The mechanisms for this transport enhancement are studied using a three-dimensional, primitive equation ocean model [Regional Ocean Modeling System (ROMS)]. Lagrangian drifters are used to trace the freshwater transport paths. It is found that the river plume bulge circulation largely follows the rigid-body motion (i.e., constant vorticity). The buoyant fluid near the bulge’s outer edge is thinner and faster, behaving as a baroclinic jet. The bulge currents then split after impinging on the coast. The outer fluid feeds the downshelf-flowing coastal currents, while the inner fluid recirculates to form the bulge. The coastal current transport estimated from the present and prior studies corresponds well to a baroclinic jet theory, with the incident angle of bulge currents at the coast being a key parameter. Without tides, the bulge is approximately circular. The incident angle measured with respect to the cross-shore axis is small. With tides, the convergence of tidal momentum fluxes near the upshelf plume front leads to a positive pressure anomaly, which acts to compress the bulge shoreward. As a result, the incident angle increases, which in turn enhances the downshelf momentum input, thus increasing the freshwater transport in the coastal currents. Finally, the parameter space for coastal current transport in the presence of tidal forcing is explored with a conceptual model. A few observational examples are given.

scholarly journals An estimate of the Sunda Shelf and the Strait of Malacca transports: a numerical study

2015 ◽  
Vol 12 (1) ◽  
pp. 275-313 ◽  
Author(s):  
F. Daryabor ◽  
A. A. Samah ◽  
S. H. Ooi ◽  
S. N. Chenoli
Keyword(s):  
Numerical Study ◽  
Ocean Modeling ◽  
Sea Surface Salinity ◽  
Andaman Sea ◽  
Regional Ocean Modeling System ◽  
Sunda Shelf ◽  
Surface Salinity ◽  
Volume Heat ◽  
Ocean Data Assimilation ◽  
Strait Of Malacca

Abstract. Using the Regional Ocean Modeling System (ROMS), this study aims to provide an estimate of the volume, freshwater, heat, and salt transports through the Sunda Shelf and the Strait of Malacca in the southern region of the South China Sea (SSCS). The modeling system is configured with two one-way nested domains representing parent and child with resolutions of 1/2 and 1/12°, respectively. The simulated currents, sea surface salinity, temperature and various transports (e.g., volume, heat, etc) agree well with the observed values as well as those estimated from the Simple Ocean Data Assimilation (SODA) re-analysis product. The ROMS estimated seasonal and mean annual transports are in accord with those calculated from SODA and those of limited observations. The ROMS estimates of mean annual volume, freshwater, heat and salt transports through the Sunda Shelf into the Java Sea are 0.32Sv (1 Sv = 106 m3 s−1), 0.023 Sv, 0.032 PW (1 PW = 1015 j s−1), and 0.010 × 109 kg s−1 respectively. The corresponding ROMS estimates for mean annual transports through the Strait of Malacca into Andaman Sea are 0.14, 0.009 Sv, 0.014 PW, and 0.0043 × 109 kg s−1 respectively. The relative percentages of mean annual transports computed individually from those of volume, heat, salinity, and freshwater between the Strait of Malacca and the Sunda Shelf range from 39 to 43.8%. This reflects that the Strait of Malacca plays an equally significant role in the annual transports from the SSCS into the Andaman Sea.

scholarly journals Impact of Shelf Valleys on the Spread of Surface Trapped River Plumes

2020 ◽  
Author(s):  
Canbo Xiao ◽  
Weifeng (Gordon) Zhang ◽  
Ying Chen
Keyword(s):  
Incident Angle ◽  
Coastal Current ◽  
Current Sensitivity ◽  
Coriolis Parameter ◽  
River Plumes ◽  
Estuary Mouth ◽  
Freshwater Transport ◽  
Bulge Region ◽  
Freshwater Plumes ◽  
Topographic Influence

AbstractThis study focuses on mechanisms of shelf valley bathymetry affecting the spread of riverine freshwater in the nearshore region. In the context of Changjiang River, a numerical model is used with different no-tide idealized configurations to simulate development of unforced river plumes over a sloping bottom, with and without a shelf valley off the estuary mouth. All simulated freshwater plumes are surface-trapped with continuously growing bulges near the estuary mouth and narrow coastal currents downstream. The simulations indicate that a shelf valley tends to compress the bulge along the direction of the valley long axis and modify the incident angle of the bulge flow impinging toward the coast, which then affects the strength of the coastal current. The bulge compression results from geostrophic adjustment and isobath-following tendency of the depth-averaged flow in the bulge region. Generally, the resulting change in the direction of the bulge impinging flow enhances down-shelf momentum advection and freshwater delivery into the coastal current. Sensitivity simulations with altered river discharges (Q), Coriolis parameter, shelf bottom slope, valley geometry, and ambient stratification show that enhancement of down-shelf freshwater transport in the coastal current, ΔQc, increases with increasing valley depth within the bulge region and decreasing slope Burger number of the ambient shelf. Assuming potential vorticity conservation, a scaling formula of ΔQc?Q is developed, and it agrees well with results of the sensitivity simulations. Mechanisms of valley influences on unforced river plumes revealed here will help future studies of topographic influence on river plumes under more realistic conditions.

scholarly journals Modelling the response of ice shelf basal melting to different ocean cavity environmental regimes

2016 ◽  
Vol 57 (73) ◽  
pp. 131-141 ◽  
Author(s):  
David E. Gwyther ◽  
Eva A. Cougnon ◽  
Benjamin K. Galton-Fenzi ◽  
Jason L. Roberts ◽  
John R. Hunter ◽  
...  
Keyword(s):  
Molecular Diffusion ◽  
Ocean Modeling ◽  
Regional Ocean Modeling System ◽  
Ice Shelf ◽  
Tidal Forcing ◽  
Environmental Regimes ◽  
Order Of Magnitude ◽  
Basal Melting ◽  
Cold Cavity ◽  
Present Simulation

ABSTRACTWe present simulation results from a version of the Regional Ocean Modeling System modified for ice shelf/ocean interaction, including the parameterisation of basal melting by molecular diffusion alone. Simulations investigate the differences in melting for an idealised ice shelf experiencing a range of cold to hot ocean cavity conditions. Both the pattern of melt and the location of maximum melt shift due to changes in the buoyancy-driven circulation, in a different way to previous studies. Tidal forcing increases both the circulation strength and melting, with the strongest impact on the cold cavity case. Our results highlight the importance of including a complete melt parameterisation and tidal forcing. In response to the 2.4°C ocean warming initially applied to a cold cavity ice shelf, we find that melting will increase by about an order of magnitude (24 × with tides and 41 × without tides).

scholarly journals Meanders and eddy formation by a buoyant coastal current flowing over a sloping topography

Ocean Science ◽  
2017 ◽  
Vol 13 (6) ◽  
pp. 905-923 ◽  
Author(s):  
Laura Cimoli ◽  
Alexandre Stegner ◽  
Guillaume Roullet
Keyword(s):  
Linear Instability ◽  
Ocean Modeling ◽  
Coastal Current ◽  
Regional Ocean Modeling System ◽  
Non Linear ◽  
Dynamical Regimes ◽  
The Cross ◽  
Linear Instability Analysis ◽  
Channel Configuration ◽  
Sloping Topography

Abstract. This study investigates the linear and non-linear instability of a buoyant coastal current flowing along a sloping topography. In fact, the bathymetry strongly impacts the formation of meanders or eddies and leads to different dynamical regimes that can both enhance or prevent the cross-shore transport. We use the Regional Ocean Modeling System (ROMS) to run simulations in an idealized channel configuration, using a fixed coastal current structure and testing its unstable evolution for various depths and topographic slopes. The experiments are integrated beyond the linear stage of the instability, since our focus is on the non-linear end state, namely the formation of coastal eddies or meanders, to classify the dynamical regimes. We find three non-linear end states, whose properties cannot be deduced solely from the linear instability analysis. They correspond to a quasi-stable coastal current, the propagation of coastal meanders, and the formation of coherent eddies. We show that the topographic parameter Tp, defined as the ratio of the topographic Rossby wave speed over the current speed, plays a key role in controlling the amplitude of the unstable cross-shore perturbations. This result emphasizes the limitations of linear stability analysis to predict the formation of coastal eddies, because it does not account for the non-linear saturation of the cross-shore perturbations, which is predominant for large negative Tp values. We show that a second dimensionless parameter, the vertical aspect ratio γ, controls the transition from meanders to coherent eddies. We suggest the use of the parameter space (Tp, γ) to describe the emergence of coastal eddies or meanders from an unstable buoyant current. By knowing the values of Tp and γ for an observed flow, which can be calculated from hydrological sections, we can identify which non-linear end state characterizes that flow – namely if it is quasi-stable, meanders, or forms eddies.

scholarly journals The Evolution of a Buoyant River Plume in Response to a Pulse of High Discharge from a Small Midlatitude River

2020 ◽  
Vol 50 (7) ◽  
pp. 1915-1935
Author(s):  
Emily Lemagie ◽  
James Lerczak
Keyword(s):  
Pulse Duration ◽  
River Mouth ◽  
Coastal Ocean ◽  
Ocean Modeling ◽  
Rain Event ◽  
Kelvin Wave ◽  
Regional Ocean Modeling System ◽  
Transport Pathways ◽  
Freshwater Transport ◽  
The Impact

AbstractA unique feature of small mountainous rivers is that discharge can be elevated by an order of magnitude during a large rain event. The impact of time-varying discharge on freshwater transport pathways and alongshore propagation rates in the coastal ocean is not well understood. A suite of simulations in an idealized coastal ocean domain using the Regional Ocean Modeling System (ROMS) with varying steady background discharge conditions (25–100 m3 s−1), pulse amplitude (200–800 m3 s−1), pulse duration (1–6 days), and steady downwelling-favorable winds (0–4 m s−1) are compared to investigate the downstream freshwater transport along the coast (in the direction of Kelvin wave propagation) following a discharge pulse from the river. The nose of the pulse propagates rapidly alongshore at 0.04–0.32 m s−1 (faster propagation corresponds with larger pulse volume and faster winds) transporting 13%–66% of the discharge. The remainder of the discharge volume initially accumulates in the bulge near the river mouth, with lower retention for longer pulse duration and stronger winds. Following the pulse, the bulge eddy disconnects from the river mouth and is advected downstream at 0–0.1 m s−1, equal to the depth-averaged wind-driven ambient water velocity. As it transits alongshore, it sheds freshwater volume farther downstream and the alongshore freshwater transport stays elevated between the nose and the transient bulge eddy. The evolution of freshwater transport at a plume cross section can be described by the background discharge, the passage of the pulse nose, and a slow exponential return to background conditions.

scholarly journals Meanders and eddies formation by a buoyant coastal current flowing over a sloping topography

2017 ◽  
Author(s):  
Laura Cimoli ◽  
Alexandre Stegner ◽  
Guillaume Roullet
Keyword(s):  
Linear Instability ◽  
Ocean Modeling ◽  
Coastal Current ◽  
Regional Ocean Modeling System ◽  
Non Linear ◽  
Dynamical Regimes ◽  
The Cross ◽  
Linear Instability Analysis ◽  
Channel Configuration ◽  
Sloping Topography

Abstract. This study investigates the linear and non-linear instability of a buoyant coastal current flowing along a sloping topography. In fact, the bathymetry strongly impacts the formation of meanders or eddies and leads to different dynamical regimes that can both enhance or prevent the cross-shore transport. We use the Regional Ocean Modeling System (ROMS) to run simulations in an idealized channel configuration, using a fixed coastal current structure and testing its unstable evolution for various depths and topographic slopes. The experiments are integrated beyond the linear stage of the instability, since our focus is on the non-linear end state, namely the formation of coastal eddies or meanders, to classify the dynamical regimes. We find three non-linear end states, whose properties cannot be deduced solely from the linear instability analysis. They correspond to a quasi-stable coastal current, the propagation of coastal meanders, and the formation of coherent eddies. We show that the topographic parameter, Tp, defined as the ratio of the topographic Rossby wave speed over the current speed, plays a key role in controlling the amplitude of the unstable cross-shore perturbations. This result emphasizes the limitations of linear stability analysis to predict the formation of coastal eddies, because it does not account for the non-linear saturation of the cross-shore perturbations, which is predominant for large negative Tp values. We show that a second dimensionless parameter, the vertical aspect ratio γ, controls the transition from meanders to coherent eddies. We suggest the use of the parameter space (Tp, γ) to describe the emergence of coastal eddies or meanders from an unstable buoyant current. By knowing the values of Tp and γ for an observed flow, which can be calculated from hydrological sections, we can identify which non-linear end states characterizes that flow, namely if it is quasi-stable, meanders, or forms eddies.

scholarly journals A Numerical Study on the Impact of High-Frequency Winds on the Peru Upwelling System during 2014–2016

2019 ◽  
Vol 7 (5) ◽  
pp. 161
Author(s):  
Linhui Wang ◽  
Huiwang Gao ◽  
Jie Shi ◽  
Lian Xie
Keyword(s):  
High Frequency ◽  
Numerical Study ◽  
Heat Budget ◽  
Vertical Mixing ◽  
Ocean Modeling ◽  
Wind Forcing ◽  
Regional Ocean Modeling System ◽  
Upwelling System ◽  
Budget Analysis ◽  
The Impact

The contribution of high-frequency wind to the Peruvian upwelling system during 2014–2016 was studied using the Regional Ocean Modeling System (ROMS), forced by four different temporal resolution (six-hourly, daily, weekly, and monthly) wind forcing. A major effect of the high-frequency wind is its warming of the water at all depths along the Peruvian coast. The mechanism for the temperature changes induced by high-frequency wind forcing was analyzed through heat budget analysis, which indicated a three-layer structure. Vertical advection plays a leading role in the warming of the mixed layer (0–25 m), and enhanced vertical mixing balances the warming effect. Analysis suggests that around the depths of 25–60 m, vertical mixing warms the water by bringing heat from the surface to deeper depths. In waters deeper than 60 m, the effect of vertical mixing is negligible. The differences among the oceanic responses in the sensitivity experiments suggest that wind forcing containing variabilities at higher than synoptic frequencies must be included in the atmospheric forcing in order to properly simulate the Peru upwelling system.

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