Dynamics of Interannual Eddy Kinetic Energy Modulations in a Western Boundary Current. Issue 19 (9th October 2021)

• Record Type: Journal Article
• Authors: Li, Junde; Roughan, Moninya; Kerry, Colette
• Is Part Of: Geophysical research letters. Volume 48:Issue 19(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-10-09
• Subjects: East Australian Current -- mesoscale eddies -- eddy kinetic energy -- eddy‐mean flow interactions -- volume transport; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2021GL094115
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: Among Western Boundary Currents, the East Australian Current (EAC) has a more energetic eddy field relative to its mean flow, however, the relationship between upstream transport and downstream eddy kinetic energy (EKE) is still unclear. We investigate the modulation of downstream EKE in the EAC's typical separation region (Tasman EKE Box) (33. 1 ° S–36. 6 ° S) based on a long‐term (22‐year), high‐resolution (2.5–6 km) model simulation and satellite altimeter observations from 1994 to 2016. Our results show that the poleward EAC transport at 28 ° S leads the EKE in the Tasman EKE Box by 93–118 days. Barotropic instabilities are the primary source of EKE, and they control EKE variability in the EAC system. Anticyclonic eddies shed from the EAC dominate from 33 ° S– 36 ° S during high‐EKE periods, but in low‐EKE periods anticyclonic eddies penetrate even further south by ∼ 2 ° . Plain Language Summary: The East Australian Current (EAC) mean flow is typically coherent from ∼ 27 ° S– 32 ° S (upstream), but eddies form after it separates from the coast typically at ∼ 32 ° S, associated with high eddy variability downstream. However, we know little about what drives changes in the downstream eddies and the correlation with transport upstream. Here, we use both satellite observations and model simulations to investigate the interannual variability in the eddy field. We find that the transport upstream of separation is well correlated with the variability of sea surface height within the typical EAC separation region. An anomalously higher EAC transport at 28 ° S corresponds to an anomalously higher sea surface height within the typical EAC separation region. The reverse is true when the EAC transport is weaker, but the current separates from the coast further to the south. We also show that the energy converted from the mean flow to the eddy fields is mainly through mean kinetic energy to eddy kinetic energy. Key Points: Barotropic instabilities dominate eddy shedding and control variability of eddy kinetic energy (EKE) in the East Australian Current There is a clear (inverse) relationship between poleward transport at 28 ° S and the latitude that anticyclonic eddies are shed Transport at 28 ° S and sea level anomalies at ∼ 27 ° S– 29 ° S (upstream) are significantly correlated with EKE at ∼ 33.1 ° S–36. 6 ° S (downstream)