The role of wind in the near field and midfield of a river plume

Kakoulaki, Georgia; MacDonald, Daniel G.; Horner‐Devine, Alexander R.

doi:10.1002/2014gl060606

Cited by 29 publications

(35 citation statements)

References 22 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Observations by Hickey et al () of the Columbia River plume close to the river mouth indicate that the plume may be advected north or south by corresponding winds. Similarly, drifters show that the Merrimack River plume is strongly affected in its near field and midfield by moderate wind forcing (>4 m/s), responding in the direction of the wind present (Kakoulaki et al, ).…”

Section: Introductionmentioning

confidence: 99%

“…An underlying assumption of most near‐field dynamics studies has been that the wind is relatively unimportant in this region (Chen et al, ; Kilcher et al, ; McCabe et al, ). Some studies have examined the impact of wind and wave forcing on the dynamics of plumes in the far field (Akan et al, ; Lentz & Largier, ), and many have studied wave‐driven turbulence in the open ocean (Craig & Banner, ; Gemmrich, ; Thomson et al, ); however, the effects of wind and wave forcing on near‐field plume mixing are not well understood (Kakoulaki et al, ).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

The Influence of Wind and Waves on Spreading and Mixing in the Fraser River Plume

2018

View full text Add to dashboard Cite

This study uses drifter-based observations to investigate the role of wind and waves on spreading and mixing in the Fraser River plume. Local winter wind patterns commonly result in two distinct forcing conditions, moderate winds from the southeast (SE) and strong winds from the northwest (NW). We examine how these patterns influence the spreading and mixing dynamics of the plume. Under SE winds, the plume thins, spreads, and turns to the right (north) upon exiting the river mouth. Mixing is initially intense in the region of maximum spreading, but it is short-lived. Under NW winds, which oppose the rightward tendency of the plume, the plume remains thicker, narrower, and flows directly across the Strait with a lateral front on its northern side. Mixing is initially lower than under SE forcing but persists further across the Strait. A Lagrangian stream-normal momentum balance shows that wind and interfacial stress under NW conditions compress the sea surface height anomaly formed by the river discharge and guide the flow across the Strait. This reconfiguration changes spreading and mixing dynamics of the plume; plume spreading, which drives intense mixing under SE winds, is shut down under NW winds, and mixing rates are consequently much lower. Despite the initially lower mixing rates, the region of active mixing extends further under NW winds, resulting in higher net mixing. These results highlight that the wind, which is often a primary cause of increased plume mixing, can also significantly influence mixing by changing the geometry of the plume.Plain Language Summary Rivers transport sediment, pollutants, and nutrients from inland regions to coastal seas. Where rivers meet the ocean, freshwater flows over the ambient salty seawater, forming a river plume. The quantities that the river transports into the ocean are mixed into the seawater along with the freshwater, and so it is vital to understand this mixing process. While ocean surface waves might be the most striking visual feature of the coastal ocean, at the Fraser River mouth, south of Vancouver, Canada, we find that wind is a much more important influence on river plume mixing than waves. Wind can influence mixing by changing the geometry of the plume to either favor or discourage intense mixing occurring in the system. This is a result of the wind encouraging or discouraging plume spreading, which is the primary cause of mixing close to the river mouth. Ocean surface waves, despite being a visually striking feature of this system, do not play a large role in mixing the Fraser River plume. Thus, in order to correctly predict river plume mixing, we must take into account wind conditions near the river mouth, while waves are less important.

show abstract

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The Influence of Wind and Waves on Spreading and Mixing in the Fraser River Plume

2018

View full text Add to dashboard Cite

show abstract

“…Exchange between estuarine and coastal systems represents a major link between terrestrial and marine environments. The dynamics at the estuarine outflow region (i.e., near field) are complex and controlled by a number of factors such as buoyancy, tidal flows [ Hetland and MacDonald , ; Chen , ], advection [ Avicola and Huq , ; Fong and Geyer , ], winds [ Fong and Geyer , ; Lentz , ; Hunter et al ., ; Kakoulaki et al ., ], and turbulence [ MacDonald and Geyer , ; Nash and Moum , ; Horner‐Devine et al ., ]. Away from the outflow region, however, where the coastal current is set up (i.e., far field), buoyancy, winds, and tides are the main forcing mechanisms [ Fong and Geyer , ; Whitney and Garvine , ; Shcherbina and Gawarkiewicz , ; Jurisa and Chant , ; Mazzini et al ., ].…”

Section: Introductionmentioning

confidence: 99%

Two‐dimensional circulation and mixing in the far field of a surface‐advected river plume

Mazzini

Chant

2016

JGR Oceans

View full text Add to dashboard Cite

Field observations of the Hudson River plume are presented to discuss circulation and mixing in the far field of this coastally trapped buoyant flow. The plume was surface advected and propagated downshelf near the internal wave speed. The plume outflow was characterized by a two‐layer bulge‐like feature but became continuously stratified and vertically sheared in the far field, where Richardson numbers are generally below 0.5. High‐frequency velocity and backscatter data from a moored ADCP revealed strong vertical and horizontal oscillatory motions at the front with a wavelength approximately 7–8 times the plume thickness, consistent with Kelvin‐Helmholtz instabilities. These motions quickly died out after 2–3 cycles. The combination of vertical shear and stratification in the plume leads to a buoyancy flux toward the nose of the plume, which competes with mixing. However, the continued salinity increase of the plume as it propagated downshelf indicates that mixing overcomes this delivery of freshwater to the plume front. A simple 2‐D model is developed, which relates the time rate‐of‐change of the plume salinity to: (1) salt entrainment due to vertical mixing, and (2) freshwater flux and salt removal due to the vertical shear of the stratified plume. Estimates of an entrainment coefficient from this model are consistent with previous estimates from the near field of a river outflow. A scaling of the plume width is obtained by assuming that vertical shears are controlled by both thermal wind and a critical Richardson number. This scaling yields plume widths that are consistent with previous laboratory studies.

show abstract

“…The midfield is the transition area where the energetic freshwater jet (near-field) transforms into a coastal current or far-field plume. It is expected that in this region, the wind and the Coriolis force start influencing the evolution of the river plume and its dynamics (Kakoulaki et al 2014).…”

mentioning

confidence: 99%

Calculating lateral plume spreading with surface Lagrangian drifters

Kakoulaki

MacDonald

Whitney

2020

Limnology & Ocean Methods

Self Cite

View full text Add to dashboard Cite

This work provides a rare quantification of lateral spreading from Lagrangian measurements in a buoyant river plume by comparing four methods. Drifter motions, including along‐stream shear and rotation, can be incorrectly interpreted as lateral spreading. This work aims to improve estimates of lateral spreading by identifying additional motions in drifter trajectories. The techniques applied are first evaluated and compared using an idealized group of drifters undergoing specific types of motion, and then applied to in situ data from 27 surface Lagrangian drifters released in the Merrimack River plume (Massachusetts) under a variety of different environmental conditions. The techniques tested include two methods using the standard deviation of drifter position with respect to various interpretations of mean drifter direction and two methods using a rotating elliptical coordinate reference frame. The idealized trajectories are modeled analytically with each type of motion (i.e., spreading, rotation, and shear) separately, then in different combinations, to identify the method that best resolves and isolates lateral spreading. The idealized experiments demonstrate that three of the methods are sensitive to shear and rotational motion in various combinations. The most robust method resolving lateral spreading is the “time‐step” method, which applies a reference frame that follows the mean flow at each time step, calculated as the average direction of the drifters between two time steps. This method also successfully identifies lateral spreading in observations, which is maximized in classic bulge‐shaped plume deployments. This work is applicable to other river plume systems as well as other propagating oceanographic phenomena.

show abstract

The role of wind in the near field and midfield of a river plume

Cited by 29 publications

References 22 publications

The Influence of Wind and Waves on Spreading and Mixing in the Fraser River Plume

The Influence of Wind and Waves on Spreading and Mixing in the Fraser River Plume

Two‐dimensional circulation and mixing in the far field of a surface‐advected river plume

Calculating lateral plume spreading with surface Lagrangian drifters

Contact Info

Product

Resources

About