Quantitative Mapping of the East Australian Current Encroachment Using Time Series Himawari‐8 Sea Surface Temperature Data

Abstract

AbstractThe East Australian Current (EAC) is a highly dynamic western boundary current that exerts significant influences on the marine ecosystem off southeast margin of Australia. For the first time, a quantitative mapping of the EAC system was conducted using Himawari‐8 sea surface temperature data and a Topographic Position Index (TPI)‐based image processing technique. The validation using Bluelink ReANalysis data suggested good reliability of our mapping results. Subsequent quantitative examination provides new insights into the EAC's cross‐shelf movement which is a driving force of adjacent slope‐shelf circulations. Along the coast of New South Wales (NSW), large‐scale and high‐frequency EAC encroachment was observed, being every 60–80 days upstream (30–32°S) and every 90–100 days downstream (33–35°S), which is associated with the EAC's intrinsic oscillation and eddy shedding. Downstream, the EAC encroachment exhibits a 20‐day longer period and a double amplitude. Such dephasing is most likely due to the abrupt change of regime at the EAC separation point (32–33°S). Upstream, the EAC encroachment also exhibits seasonality, being 10–15 km closer to the coast in austral summer, which is due to the seasonal EAC broadening. Higher‐frequency (16–32 days) and smaller‐magnitude EAC intrusion was observed along the entire NSW coast (28–37°S), which is possibly associated with EAC's meanders and frontal eddies. In the extension zone (37.30–44°S), we observed maximum EAC encroachment in summer, which is an expression of the seasonal boundary flow off eastern Tasmania. A data set of EAC encroachment (2015–2017) is available (see Data Availability Statement).