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Downstream Evolution of the East Australian Current System: Mean Flow, Seasonal, and Intra‐annual Variability
Author(s) -
Kerry Colette,
Roughan Moninya
Publication year - 2020
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1029/2019jc015227
Subject(s) - eddy , annual cycle , mesoscale meteorology , rossby wave , climatology , mean flow , jet (fluid) , environmental science , middle latitudes , atmospheric sciences , latitude , current (fluid) , seasonality , geology , oceanography , turbulence , physics , meteorology , geodesy , thermodynamics , statistics , mathematics
The East Australian Current (EAC) varies on both seasonal and mesoscale eddy related timescales, with important impacts for weather, primary productivity, and fisheries. While the EAC and its eddies have been the subject of many synoptic studies, a consistent three‐dimensional picture of the current, its downstream evolution, and the associated seasonal and intra‐annual variability is lacking. We use a 22‐year model simulation to quantify the EAC's temporal and latitudinal variability, from where it flows as a mostly coherent jet (27° S) to its separation from the coast (31–33° S), its energetic eddy field in the Tasman Sea and its southern extension. We show that the current intensifies and deepens poleward toward the separation latitude; the mean poleward transport reaches a maximum of 26.8 Sv and the seasonal cycle amplitude peaks at 6.2 Sv. Over the separation region, the EAC core broadens and shallows, mean poleward transport is lower and the transport standard deviation peaks at 22.0 Sv. The meandering EAC jet is modulated at interannual timescales, while the eddy driven transport over the separation region has a strong annual modulation, related to the annual cycle in eddy kinetic energy. SSH variability at intra‐annual frequencies is described primarily by an alongshore propagating mode and an onshore propagating mode, demonstrating that mesoscale SSH variability stems from a combination of intrinsic instabilities of the EAC jet and westward propagating Rossby waves. The results provide the first holistic analysis of the EAC system along its latitudinal range.