It was the three days, 15-17 Feb, when the cyclone slowed and intensified, that it made a deeper, long-lasting impression on the ocean. The extensive cooling can be seen in the SST anomaly after Oma moved on and the clouds cleared. The cyclone also generated a cold-core eddy which is evident in the satellite altimetry forming directly under the centre of the cyclone (Figure 1).
Ocean eddies, unhindered by a land barrier, propagate westward and TC Oma’s cold-core eddy has travelled over 1600km across the Coral Sea in the five months since it formed. Its surface temperature signal has almost disappeared but it is still evident in the altimetry although weaker and smaller. By chance it came in just south of the Coral Sea Islands and north of Marion Reef, and was corralled into a relatively narrow, shoaling ocean channel. The currents associated with the eddy as it crossed the Coral Sea were quite strong for this part of the ocean, over 0.5m/s at the surface, and appear to have had an unexpected effect on temperatures on the Great Barrier Reef (GBR). The southward current on the eastern side of the eddy as it approached the outer shelf appears to have advected anomalously warm Coral Sea water not only onto Marion Reef (Figure 2) but also to the outer reefs of the southern GBR.
This news item was originally published on our IMOS OceanCurrent website, which provides ready access to quick-look graphics of Australian ocean conditions, including sea surface temperature and ocean colour, overlaid with sea level contours and surface current velocities.