Monday , May 17 2021

Why is it hot on the beach, but cold in the surf this summer

In the southern hemisphere, the sea layer moves to the left of the wind direction due to the Earth's rotation (known as the Coriolis effect). Hot summer temperatures bring a sharp north easterly breeze, and the warm top layer begins to float at right angles to the prevailing wind. It has a net effect of raising cold water rich in deep-sea nutrients that replace it. The acquired cyclic vortex is called Ekman's spiral, which was explored by the Swedish oceanographer Vagn Walfrid Ekman in 1902.

Surfers in Maroubri.

Surfers in Maroubri.Credit:Brook Mitchell

It usually takes a few days, and cold water and very warm. In the end, when they bring the lost desert, we get the genesis of the amazing seaweeds that we have recently experienced in Sydney. So when that south buster finally arrives, it has the effect of pushing hot water back to the mainland and the voil, Tahiti returns.

So Ekman's effect is not all the bad news – it's just a few days in the worst case, and it brings a lot of nutrients to the fish to sneak and bring bigger fish and whales to snoop them. Surfers instinctively learn to enter the steamship after an extended hit in the north; swimmers are advised to watch the weather meteorologist Tim Bailey every night and become the Liquors.

My personal observation, from life on the beautiful Maistrala point, is that Maroubra becomes stronger and more frequent. Is this because of climate change argument for second place, but I would not be surprised. But Ekman is not the only "bad guy" here. Sometimes in the East Australian Stream (EAC) there are gigantic whirlpools.

EAC (manned in Finding Nemo) delivers tropical hot water from Queensland and seems to be getting stronger and bringing more warmer water, resulting in some species of tropical fish and soft corals in Sydney harbor.

During 2007, the extended ice water event was caused by a giant whirlpool of Tasmania, located about 100 kilometers from Sydney, which sprang like a 10-day rotary whirlwind. In its center, the vortex caused the rise of very cold water from a depth of nearly 1000 m which turned and eventually hit the shore. We've caused some of the coolest, "water keys" we've ever known.

Murray Cook is a surfer and marine biologist.

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