Gary Brassington (Centre for Australian Weather and Climate Research, Bureau of Meteorology)
Stratified vortex merger in the Tasman Sea - observed by drifting buoys, Argo et al
During 2007-2009 a drifting buoy campaign was undertaken to deploy pairs of NOAA buoys into the East Australian Current system to achieve a number of objectives including: increase the sampling of the EAC/Tasman Sea a low density region for drifting buoys, observe the characteristics of the EAC and intercompare and interpret with the observing system and model based analyses. An overview of the design, the campaign and results will be given.
One of the buoy pairs were deployed into a newly formed EAC eddy and remained within an anticyclonic eddy (~150 km diameter) completing 9 orbits over a period of 60 days. A new technique was developed to reconstruct the boundary of the material surface occupied by each of the drifting buoys from which properties of the divergence/vertical transport, secondary rotation and eddy speed were derived. Using this information as well as observations from Argo, satellite altimetry, satellite SST together with eddy-resolved model analyses the evolution of the eddy was interpreted to have undergone a stratified vortex merger. Stratified vortex mergers have been previously observed in the Tasman Sea and analyses of model analyses suggest this process is common. Such complexity in the eddy field poses significant challenges for the observing system in the Tasman Sea as well as ocean model analyses.