Wind effects on dense shelf water cascades in south-west Australia

Mahjabin, Tanziha; Pattiaratchi, Charitha; Hetzel, Yasha

doi:10.1016/j.csr.2019.103975

Cited by 9 publications

(19 citation statements)

References 60 publications

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“…Here, we show that the combined data sets, especially at the boundaries of the two domains, have the potential to greatly increase the capabilities of coastal observing networks, in general, and along the southwestern Western Australia (SWWA) coastal region, in particular. Previous research used WERA HFR data to focus on the smaller domain in the Rottnest Shelf [4,5], and neglected the area to the North, which has proven to be important for the mesoscale eddy field. The merged SeaSonde-WERA surface current data, mapped onto a 6 km grid, provided robust and consistent current measurements with negligible differences at the diurnal, seasonal and inter-annual time scales.…”

Section: Discussionmentioning

confidence: 99%

“…Seasonally averaged HFR and SST data indicated the typical mean circulation structures in the region with the relatively warmer LC as a southward current and the CC as a weaker, colder coastal current (Figures 4-6). The presence of colder water adjacent to the coast during the autumn and winter months (Figures 4c, 5c and 6c) is due to heat loss [5]. In general, the LC was stronger (mean speeds up to 0.50 ms −1 ), during autumn/winter and weaker during spring/summer.…”

Section: Seasonal and Inter-annual Variabilitymentioning

confidence: 93%

“…The eastern margins of all other ocean basins comprise equatorward cold water currents associated with upwelling. The anomalous ocean currents together with diurnal tides with low range [2], strong sea breezes [3], resonance at the critical latitude [4], currents together with diurnal tides with low range [2], strong sea breezes [3], resonance at the critical latitude [4], high air-sea heat and freshwater fluxes [5] provide a unique environment. In addition, the LC is associated with elevated levels of mesoscale eddy activity compared with other eastern boundary current regions [6,7].…”

Section: Introductionmentioning

confidence: 99%

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High-Frequency Radar Observations of Surface Circulation Features along the South-Western Australian Coast

Cosoli

Pattiaratchi

Hetzel

2020

JMSE

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A new merged high-frequency radar (HFR) data set collected using SeaSonde and WERA (WEllen RAdar) systems was used to examine the ocean surface circulation at diurnal, seasonal and inter-annual time scales along the south-west coast of Australia (SWWA), between 29°–32° S. Merging was performed after resampling WERA data on the coarser SeaSonde HFR grid and averaging data from the two HFR systems in the area of common overlap. Direct comparisons between WERA and SeaSonde vectors in their overlapping areas provided scalar and vector correlation values in the range Ru = [0.24, 0.76]; Rv = [0.39, 0.83]; ρ = [0.44, 0.75], with mean bias between velocity components in the range [−0.02, 0.28] ms−1, [−0.16, 0.16] ms−1 for the U, V components, respectively. The lower agreement between vectors was obtained in general at the boundaries of the HFR domains, where the combined effects of the bearing errors, geometrical constraints, and the limited angular field of view were predominant. The combined data set allowed for a novel characterization of the dominant features in the region, such as the warmer poleward-flowing Leeuwin Current (LC), the colder Capes Current (CC) and its northward extensions, the presence of sub-mesoscale to mesoscale eddies and their generation and aggregation areas, along with the extent offshore of the inertial-diurnal signal. The contribution of tides was weak within the entire HFR domain (<10% total variance), whilst signatures of significant inertial- and diurnal-period currents were present due to diurnal–inertial resonance. A clear discontinuity in energy and variance distribution occurred at the shelf break, which separates the continental shelf and deeper offshore regions, and defined the core of the LC. Confined between the LC and the coastline, the narrower and colder CC current was a feature during the summer months. Persistent (lifespan greater than 1 day) sub-mesoscale eddies (Rossby number O (1)) were observed at two main regions, north and south of 31.5° S, offshore of the 200 m depth contour. The majority of these eddies had diameters in the range 10–20 km with 50% more counter clockwise rotating (CCW) eddies compared to clockwise (CW) rotating eddies. The northern region was dominated by CCW eddies that were present throughout the year whilst CW eddies were prevalent in the south with lower numbers during the summer months.

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Section: Discussionmentioning

confidence: 99%

Section: Seasonal and Inter-annual Variabilitymentioning

confidence: 93%

Section: Introductionmentioning

confidence: 99%

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High-Frequency Radar Observations of Surface Circulation Features along the South-Western Australian Coast

Cosoli

Pattiaratchi

Hetzel

2020

JMSE

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“…Consider an initially homogeneous water body on a continental shelf with a sloping bathymetry subject to uniform surface cooling (or heating). Here, the shallower water cools (heats) more rapidly compared to those in deeper water ('differential heating/cooling') that results in the formation of a cross-shelf density gradient 30 . The density gradient provides the buoyancy input that drives the DSWC.…”

Section: ( )mentioning

confidence: 99%

“…The third term defines the buoyancy flux through the advection of higher density water due to the cross-shelf density gradient. N Z is the vertical eddy viscosity coefficient assumed to be 1~ 17 × 10 -5 m 2 s −1 (see also Mahjabin et al 30 ). When the change in potential energy anomaly (φ) over time is positive (dφ/dt > 0), the water column is stable and stratified, and when dφ/dt < 0 the water column is vertically mixed and when φ = 0, it is vertically homogeneous with the input of buoyancy exactly balanced by vertical mixing.…”

Section: ( )mentioning

confidence: 99%

Occurrence and seasonal variability of Dense Shelf Water Cascades along Australian continental shelves

Mahjabin

Pattiaratchi

Hetzel

2020

Sci Rep

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occurrence and seasonal variability of Dense Shelf Water cascades along Australian continental shelves tanziha Mahjabin ✉ , charitha pattiaratchi & Yasha Hetzel transport of water between the coast and the deeper ocean, across the continental shelf, is an important process for the distribution of biota, nutrients, suspended and dissolved material on the shelf. presence of denser water on the inner continental shelf results in a cross-shelf density gradient that drives a gravitational circulation with offshore transport of denser water along the sea bed that is defined as Dense Shelf Water Cascade (DSWC). Analysis of field data, collected from multiple ocean glider data missions around Australia, confirmed that under a range of wind and tidal conditions, DSWC was a regular occurrence during autumn and winter months over a coastline spanning > 10,000 km. It is shown that even in the presence of relatively high wind-and tidal-induced vertical mixing, DSWcs were present due to the strength of the cross-shelf density gradient. the occurrence of DSWc around Australia is unique with continental scale forcing through air-sea fluxes that overcome local wind and tidal forcing. it is shown that DSWc acts as a conduit to transport suspended material across the continental shelf and is a critical process that influences water quality on the inner continental shelf. Globally, the coastal ocean is the receiving basin for input of suspended and dissolved matter that includes nutrients, biota and pollutants and represents an important component of the ocean environment, connecting the terrestrial system to the deeper ocean 1. Transport processes that contribute to the exchange of water between the coast and deeper regions: cross-shelf exchange, has been defined as one of the central problems in coastal physical oceanography 2. Majority of inputs to the coastal zone are through fresh water sources such as rivers and anthropogenic discharges. As these inputs are usually buoyant, they are transported along the ocean surface layer subject to the prevailing hydrodynamic regime and are easily identified in the field and in satellite imagery. If the spatial scale is unrestricted by coastal features and under relatively low mixing conditions, river plumes can influence the hydrodynamics to hundreds of kilometres from the source region 3,4. These systems have been subject to many investigations over the past decades being defined as river plumes or Regions of Freshwater Influence (ROFI) where the hydrodynamic regime is governed by the positive density gradient between lower salinity riverine water and higher salinity oceanic water 3. In ROFI, buoyancy input from freshwater sources exceeds that from changes in heat and freshwater fluxes across the ocean surface. Regions that experience a Mediterranean climate (dry hot summers, mild cooler winters and low precipitation) are subject to high rates of evaporation and negligible river input resulting in a net loss of fresh water from the coastal region. Therefore, coastal water bodies become mo...

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Flushing the Lake Littoral Region: The Interaction of Differential Cooling and Mild Winds

Ramón

Ulloa

Doda

et al. 2021

Preprint

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Wind effects on dense shelf water cascades in south-west Australia

Cited by 9 publications

References 60 publications

High-Frequency Radar Observations of Surface Circulation Features along the South-Western Australian Coast

High-Frequency Radar Observations of Surface Circulation Features along the South-Western Australian Coast

Occurrence and seasonal variability of Dense Shelf Water Cascades along Australian continental shelves

Flushing the Lake Littoral Region: The Interaction of Differential Cooling and Mild Winds

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