No abstract

Extratropical cyclones (ETCs) are the primary driver of large-scale episodic beach erosion along coastlines in temperate regions. However, key drivers of the magnitude and regional variability in rapid morphological changes caused by ETCs at the coast remain poorly understood. Here we analyze an unprecedented dataset of high-resolution regional-scale morphological response to an ETC that impacted southeast Australia, and evaluate the new observations within the context of an existing long-term coastal monitoring program. This ETC was characterized by moderate intensity (for this regional setting) deepwater wave heights, but an anomalous wave direction approximately 45 degrees more counter-clockwise than average. The magnitude of measured beach volume change was the largest in four decades at the long-term monitoring site and, at the regional scale, commensurate with that observed due to extreme North Atlantic hurricanes. Spatial variability in morphological response across the study region was predominantly controlled by alongshore gradients in storm wave energy flux and local coastline alignment relative to storm wave direction. We attribute the severity of coastal erosion observed due to this ETC primarily to its anomalous wave direction, and call for greater research on the impacts of changing storm wave directionality in addition to projected future changes in wave heights.

[1] Observations from an intensive oceanographic field program which took place in 1998-1999 about the separation point of the East Australian Current (EAC) show significant spatial and temporal variability of the EAC. Upstream of the separation point, southward flowing currents are strong, with subinertial velocities of up to 130 cm s À1 in the near-surface waters, whereas downstream currents are highly variable in both strength (1-70 cm s À1 ) and direction. Upwelling is observed to occur through both wind-driven and current-driven processes, with wind effects playing a lesser role. By contrast, the encroachment of the EAC upon the coast has a profound effect on the coastal waters, accelerating the southward (alongshore) currents and decreasing the temperature in the bottom boundary layer (BBL) by up to 5°C. As the axis of the jet moves onshore, negative vorticity increases in association with an increase in nonlinear acceleration. During this time, bottom friction is increased, the Burger number is reduced, and the BBL shut-down time lengthens. The observed upwelling is attributed to enhanced onshore Ekman pumping through the BBL resulting from increased bottom stress as the southerly flow accelerates when the EAC encroaches across the continental shelf.INDEX TERMS: 4279

No abstract

No abstract