Giant ocean eddy shadows Sydney
The giant ocean eddy that cooled Sydney's shores a year ago has been superseded by another 300 km diameter giant.
CSIRO Wealth from Oceans National Research Flagship scientist, Dr David Griffin, says the 鈥榖irth鈥� of the eddy has been traced to last August.
鈥淔rom satellite maps of sea-level we can see that it had been loitering this side of Lord Howe Island for some time and began approaching the NSW coast near Christmas,鈥� Dr Griffin says.
鈥淚t remained stationary during January and simply grew larger but, because it remained offshore, less people would have noticed its impacts on water temperatures.鈥�
The cold water at the new eddy鈥檚 centre has welled up about 500m from the ocean depths.
鈥淚n the southern hemisphere, a cold eddy has to rotate clockwise,鈥� Dr Griffin says. 鈥淭his one completes a full revolution every 10 days and the sea level at its centre is reduced by nearly 1m, which is how researchers can tell where the eddy is.鈥�
Four people who definitely noticed the eddy were the crew who rowed across the Tasman Sea from New Zealand in late December. Skirting its southern boundary, they received a homeward boost of 3km/h or more.
鈥淭he eddy appears to be on the wane now and the question of interest for oceanographers is what have been the factors that influenced its development and led to its evolution into an ocean feature approaching the size of Tasmania,鈥� Dr Griffin says.
Instruments that detect the height of the world鈥檚 oceans are carried by satellites such as Jason-1 (Jet Propulsion Laboratory-NASA and the French Space Agency CNES) and the European Space Agency鈥檚 Envisat. These are valuable aids to scientists developing ocean forecasting systems such as Australia鈥檚 BlueLINK.
Source: CSIRO
