Abstract
AbstractWater in the ocean is generally carried with the mean flow, mixed by eddies, or transported westward by coherent eddies at speeds close to the long baroclinic Rossby wave speed. Modons (dipole eddy pairs) are a theoretically predicted exception to this behavior, which can carry water to the east or west at speeds much larger than the Rossby wave speed, leading to unusual transports of heat, nutrients, and carbon. We provide the first observational evidence of such rapidly moving modons propagating over large distances. These modons are found in the midlatitude oceans around Australia, with one also seen in the South Atlantic west of the Agulhas region. They can travel at more than 10 times the Rossby wave speed of 1–2 cm s−1 and typically persist for about 6 months carrying their unusual water mass properties with them, before splitting into individual vortices, which can persist for many months longer.
Highlights
A recent census of mesoscale sea level anomaly propagation [Chelton et al, 2011] has shown that, be they wave-like or eddy-like, almost all anomalies propagate to the west at close to the long baroclinic Rossby wave speed
Water in the ocean is generally carried with the mean flow, mixed by eddies, or transported westward by coherent eddies at speeds close to the long baroclinic Rossby wave speed
Where they propagate to the east, they are in eastward-flowing currents which are faster than the Rossby wave speed, and are still propagating to the west relative to the flow
Summary
Supplementary information consists of a table of modon vortex positions, and four movies showing the propagation of nine modons, and more detail for modon E.
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