### Abstract

Flow splitting occurs when part of a gravity current becomes neutrally buoyant and separates from the bottom-trapped plume as an interflow. This phenomenon has been previously observed in laboratory experiments, small-scale water bodies (e.g., lakes) and numerical studies of small-scale systems. Here, the potential for flow splitting in oceanic gravity currents is investigated using high-resolution (Δx = Δz = 5 m) two-dimensional numerical simulations of gravity flows into linearly stratified environments. The model is configured to solve the non-hydrostatic Boussinesq equations without rotation. A set of experiments is conducted by varying the initial buoyancy number B_{0}=Q_{0}N^{3}/g^{′2} (where Q_{0} is the volume flux of the dense water flow per unit width, N is the ambient stratification and g′ is the reduced gravity), the bottom slope (α) and the turbulent Prandtl number (Pr). Regardless of α or Pr, when B_{0} ≤ 0.002 the outflow always reaches the deep ocean forming an underflow. Similarly, when B_{0} ≥ 0.13 the outflow always equilibrates at intermediate depths, forming an interflow. However, when B_{0} ∼ 0.016, flow splitting always occurs when Pr ≥ 10, while interflows always occur for Pr = 1. An important characteristic of simulations that result in flow splitting is the development of Holmboe-like interfacial instabilities and flow transition from a supercritical condition, where the Froude number (Fr) is greater than one, to a slower and more uniform subcritical condition (Fr < 1). This transition is associated with an internal hydraulic jump and consequent mixing enhancement. Although our experiments do not take into account three-dimensionality and rotation, which are likely to influence mixing and the transition between flow regimes, a comparison between our results and oceanic observations suggests that flow splitting may occur in dense-water outflows with weak ambient stratification, such as Antarctic outflows.

Original language | English (US) |
---|---|

Pages (from-to) | 66-84 |

Number of pages | 19 |

Journal | Ocean Modelling |

Volume | 113 |

DOIs | |

State | Published - May 1 2017 |

### Fingerprint

### Keywords

- Gravity currents
- Intermediate and bottom water formation
- Internal hydraulic jump
- Overflows

### ASJC Scopus subject areas

- Oceanography
- Computer Science (miscellaneous)
- Geotechnical Engineering and Engineering Geology
- Atmospheric Science

### Cite this

*Ocean Modelling*,

*113*, 66-84. https://doi.org/10.1016/j.ocemod.2017.03.011

**Flow splitting in numerical simulations of oceanic dense-water outflows.** / Marques, Gustavo M.; Wells, Mathew G.; Padman, Laurie; Ozgokmen, Tamay M.

Research output: Contribution to journal › Article

*Ocean Modelling*, vol. 113, pp. 66-84. https://doi.org/10.1016/j.ocemod.2017.03.011

}

TY - JOUR

T1 - Flow splitting in numerical simulations of oceanic dense-water outflows

AU - Marques, Gustavo M.

AU - Wells, Mathew G.

AU - Padman, Laurie

AU - Ozgokmen, Tamay M

PY - 2017/5/1

Y1 - 2017/5/1

N2 - Flow splitting occurs when part of a gravity current becomes neutrally buoyant and separates from the bottom-trapped plume as an interflow. This phenomenon has been previously observed in laboratory experiments, small-scale water bodies (e.g., lakes) and numerical studies of small-scale systems. Here, the potential for flow splitting in oceanic gravity currents is investigated using high-resolution (Δx = Δz = 5 m) two-dimensional numerical simulations of gravity flows into linearly stratified environments. The model is configured to solve the non-hydrostatic Boussinesq equations without rotation. A set of experiments is conducted by varying the initial buoyancy number B0=Q0N3/g′2 (where Q0 is the volume flux of the dense water flow per unit width, N is the ambient stratification and g′ is the reduced gravity), the bottom slope (α) and the turbulent Prandtl number (Pr). Regardless of α or Pr, when B0 ≤ 0.002 the outflow always reaches the deep ocean forming an underflow. Similarly, when B0 ≥ 0.13 the outflow always equilibrates at intermediate depths, forming an interflow. However, when B0 ∼ 0.016, flow splitting always occurs when Pr ≥ 10, while interflows always occur for Pr = 1. An important characteristic of simulations that result in flow splitting is the development of Holmboe-like interfacial instabilities and flow transition from a supercritical condition, where the Froude number (Fr) is greater than one, to a slower and more uniform subcritical condition (Fr < 1). This transition is associated with an internal hydraulic jump and consequent mixing enhancement. Although our experiments do not take into account three-dimensionality and rotation, which are likely to influence mixing and the transition between flow regimes, a comparison between our results and oceanic observations suggests that flow splitting may occur in dense-water outflows with weak ambient stratification, such as Antarctic outflows.

AB - Flow splitting occurs when part of a gravity current becomes neutrally buoyant and separates from the bottom-trapped plume as an interflow. This phenomenon has been previously observed in laboratory experiments, small-scale water bodies (e.g., lakes) and numerical studies of small-scale systems. Here, the potential for flow splitting in oceanic gravity currents is investigated using high-resolution (Δx = Δz = 5 m) two-dimensional numerical simulations of gravity flows into linearly stratified environments. The model is configured to solve the non-hydrostatic Boussinesq equations without rotation. A set of experiments is conducted by varying the initial buoyancy number B0=Q0N3/g′2 (where Q0 is the volume flux of the dense water flow per unit width, N is the ambient stratification and g′ is the reduced gravity), the bottom slope (α) and the turbulent Prandtl number (Pr). Regardless of α or Pr, when B0 ≤ 0.002 the outflow always reaches the deep ocean forming an underflow. Similarly, when B0 ≥ 0.13 the outflow always equilibrates at intermediate depths, forming an interflow. However, when B0 ∼ 0.016, flow splitting always occurs when Pr ≥ 10, while interflows always occur for Pr = 1. An important characteristic of simulations that result in flow splitting is the development of Holmboe-like interfacial instabilities and flow transition from a supercritical condition, where the Froude number (Fr) is greater than one, to a slower and more uniform subcritical condition (Fr < 1). This transition is associated with an internal hydraulic jump and consequent mixing enhancement. Although our experiments do not take into account three-dimensionality and rotation, which are likely to influence mixing and the transition between flow regimes, a comparison between our results and oceanic observations suggests that flow splitting may occur in dense-water outflows with weak ambient stratification, such as Antarctic outflows.

KW - Gravity currents

KW - Intermediate and bottom water formation

KW - Internal hydraulic jump

KW - Overflows

UR - http://www.scopus.com/inward/record.url?scp=85016409173&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85016409173&partnerID=8YFLogxK

U2 - 10.1016/j.ocemod.2017.03.011

DO - 10.1016/j.ocemod.2017.03.011

M3 - Article

VL - 113

SP - 66

EP - 84

JO - Ocean Modelling

JF - Ocean Modelling

SN - 1463-5003

ER -