CHARACTERISING COASTAL SHELF WAVES ALONG THE NSW COAST

New South Wales (NSW) often experiences periods of coastal inundation and estuarine flooding. One of the causal mechanisms of these episodes are coastal shelf waves (CSW), generated by synoptic disturbances (Church et al., 2006). CSWs in Australia often result from wind stress, mostly along mid-latitudes (e.g., the Great Australian Bight) and propagate anticlockwise (Woodham et al., 2013). However, there are no tools available for identifying and characterising CSWs and as such there is very little information on the magnitude, frequency, duration, and spatiotemporal variability. This paper aims to: (1) develop a method to identify and track CSWs using the existing ocean tide gauge network, (2) identify patterns in the frequency, duration, and magnitude of CSW, and (3) assess the factors that affect the frequency, duration, and magnitude of CSWs along the NSW coast.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/oigzYIKFBmA

Coastal Trapped Waves and other subinertial variability along the Southeast Greenland Coast in a realistic numerical simulation

Ocean currents along the Southeast Greenland Coast play an important role in the climate system. They carry dense water over the Denmark Strait sill, fresh water from the Arctic and the Greenland Ice Sheet into the subpolar ocean, and warm Atlantic water into Greenland’s fjords, where it can interact with outlet glaciers. Observational evidence from moorings shows that the circulation in this region displays substantial subinertial variability (typically with periods of several days). For the dense water flowing over the Denmark Strait sill, this variability augments the time-mean transport. It has been suggested that the subinertial variability found in observations is associated with Coastal Trapped Waves, whose properties depend on bathymetry, stratification, and the mean flow. Here, we use the output of a high-resolution realistic simulation to diagnose and characterize subinertial variability in sea surface height and velocity along the coast. The results show that the subinertial signals are coherent over hundreds of kilometers along the shelf. We find Coastal Trapped Waves on the shelf and along the shelf break in two subinertial frequency bands—at periods of 1–3 days and 5–18 days—that are consistent with a combination of Mode I waves and higher modes. Furthermore, we find that northeasterly barrier winds may trigger the 5–18 day shelf waves, whereas the 1–3 day variability is linked to high wind speeds over Sermilik Deep.

Stokes Drift in Topographic Waves over an Enclosed Basin Shelf

The effect of the continental shelf wave on the flow field over the southern shelf of the Caspian Sea (CS) as the largest enclosed basin of the world, is investigated. Considerable currents with subinertial time scales are observed over the continental shelf in the southern CS. For variations in the surface layer with typical periods of 1 day, local episodic wind events appear to be the driving force. For longer time scales, it is suggested that the observed currents are due to passing continental shelf waves. Measurements over the continental shelf and shelf slope, showing periods of 2–6 days, indicate the presence of such waves. Combined with theory and numerical modeling, the amplitude of the continental shelf wave modes at the coast is assessed from current meter observations. It is demonstrated that the mean drift velocity (the Stokes drift) for long continental shelf waves is determined entirely by the shelf geometry. For the actual shelf mode, it is shown that the associated Stokes drift constitute a nonnegligible mean current along the shelf. This current should be taken into account when assessing the transport of biological material and neutral tracers along the southern coast of the CS.

Leaky Slope Waves and Sea Level: Unusual Consequences of the Beta Effect along Western Boundaries with Bottom Topography and Dissipation

ABSTRACTCoastal trapped waves (CTWs) carry the ocean’s response to changes in forcing along boundaries and are important mechanisms in the context of coastal sea level and the meridional overturning circulation. Motivated by the western boundary response to high-latitude and open-ocean variability, we use a linear, barotropic model to investigate how the latitude dependence of the Coriolis parameter (β effect), bottom topography, and bottom friction modify the evolution of western boundary CTWs and sea level. For annual and longer period waves, the boundary response is characterized by modified shelf waves and a new class of leaky slope waves that propagate alongshore, typically at an order slower than shelf waves, and radiate short Rossby waves into the interior. Energy is not only transmitted equatorward along the slope, but also eastward into the interior, leading to the dissipation of energy locally and offshore. The β effect and friction result in shelf and slope waves that decay alongshore in the direction of the equator, decreasing the extent to which high-latitude variability affects lower latitudes and increasing the penetration of open-ocean variability onto the shelf—narrower continental shelves and larger friction coefficients increase this penetration. The theory is compared with observations of sea level along the North American east coast and qualitatively reproduces the southward displacement and amplitude attenuation of coastal sea level relative to the open ocean. The implications are that the β effect, topography, and friction are important in determining where along the coast sea level variability hot spots occur.