Summer gone as swimmers feel the chill

A Swedish physicist called V. Walfrid Ekman has come back to haunt the Illawarra's early morning swimmers, with the ocean effect that takes his name making summer seem a long time gone.

The temperature in ocean pools - and in the ocean - has dropped by several degrees since last weekend, courtesy of water movement called the Ekman Transport.

Ekman's research showed that several days of a northerly or northeasterly wind has the effect of pushing the surface water away at 90 degrees to the direction of the wind.

On the east coast of Australia, this means the surface water is pushed out to sea, producing an "upwelling" where the cooler water rises from below to take its place.

And for the Illawarra's early morning swimmers, the aftermath of last weekend's turbulent weather means some very sharp intakes of breath as they ease themselves into the water in the favourite pool.

Brian Cummins, 64, swims every morning at the Austinmer Beach ocean pool and measures the temperature each morning.

"Last Saturday we measured it was about 24 degrees . . . that's when the really big surf was on," he said. "On Monday it was down to 21, then Tuesday straight down to 17."

Yesterday the temperature dropped below 17 degrees.

"We're hanging out for the southerly to come again ... it will be strong enough to blow the warm water back."

University of Wollongong climate scientist Dr Helen McGregor said the Ekman Transport was a somewhat "odd" phenomenon but not an uncommon one.

"When you get coastal winds, even though they're pushing along the coast, the surface current is directed out to sea," she said.

The water was also influenced by the Coriolis effect, Dr McGregor said.

"It's like a turning force that the earth's rotation puts on things that are moving.

"For ocean currents, we see instead of the ocean going in the same direction as the wind, it actually directed to the left in the Southern hemisphere, because of the earth's rotation," Dr McGregor said.

Ekman made his discovery after allowing his ship to become caught in ice so he could see where it drifted.

Illawarra swimmers will be hoping it doesn't come to that this weekend.

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