A tale of two eddies in the EAC: introducing Murphy and Freddy.

Researchers in a recent study have contrasted two eddies, Murphy and Freddy, that had formed in the Eastern Australian Current, whilst on board the Marine National Facility RV Investigator.


The study, led by Associate Professor Moninya Roughan at the University of New South Wales, was published in the Journal of Geophysical Research Oceans, and presents the first depth observations of a small (~35 km in diameter) cold core eddy (“Freddy”) which formed along the landward front of the East Australian Current (EAC). The researchers contrast the observations with a typical larger (~160 km in diameter) cold core eddy (“Murphy”).

The in-situ observations were collected from a dedicated research voyage in 2015 aboard the Marine National Facility RV Investigator, the study also made use of satellite remote-sensed observations of AVHRR and MODIS sea surface temperature (SST) and ocean color on cloud-free days, processed and served through the IMOS OceanCurrent website.

Observational data sets depicting the 3-D structure of eddies are rare, and to date the dynamics of frontal eddies have primarily been diagnosed through modeling studies. The comprehensive data set revealing the 3-D structure and dynamics of two contrasting cyclonic eddies shows that not all cyclonic eddies are created equal, i.e., the smaller frontal eddy, Freddy, is significantly more energetic, and productive than the mesoscale cyclone, Murphy, despite its small size and short life. Freddy was a very dynamic feature. It rotated rapidly, extended to more than 1000 m in depth and was highly productive. The researchers believe these features make a significant contribution to the productivity of the Tasman Sea region.


To read the full paper:

Roughan, M., S. R. Keating, A. Schaeffer, P. Cetina Heredia, C. Rocha, D. Griffin, R. Robertson, and I. M. Suthers (2017), A tale of two eddies: The biophysical characteristics of two contrasting cyclonic eddies in the East Australian Current System, J. Geophys. Res. Oceans, 122, 2494–2518, doi:10.1002/2016JC012241.

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(a) Three day composite SST and geostrophic velocities derived from SSH centered on 7 June 2016. (b) MODIS SST and (c) Ocean Color for Murphy (5 June 2015), top and Freddy (9 June 2015) bottom. Solid black lines indicate the location of the ADCP and Triaxus lines in subsequent figures. (d) and (e) are zoom insets (as indicated in Figures 1b and 1c) of cruise track colored by SST from the underway thermosalinograph, velocities at 30 m depth as measured by the shipboard ADCP, and the location of CTD casts (numbered circles). Bathymetric contours are 4000, 2000, 200, 100 m from east to west. Figure from the paper published in J.Geophys. Res. Oceans.