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Inside "The roaring forties"

2 months ago
Written by Ronald Toppe
Ocean education > Inside "The roaring forties"

Inside "The roaring forties"

2 months agoOcean education
Written by Ronald Toppe
Photo: Hanna Thevik

Statsraad Lehmkuhl is now 45 degrees south, off the coast of South America, inside one of the "highways" of the old sailing ships.

In his report for March 13, Captain Marcus Seidl sounds almost a little disappointed.

- Now that we are approaching latitude 45 South, we are in a wind pattern known as the “Roaring Forties”. Although we have gone clear of the depressions associated with the name so far, our weather charts are showing stronger winds to the south of us.

On the map below you can see where the ship was when he wrote his report. The strong wind south of them is easy to spot.

Wind and wave height. Map: Earth Nullschool
Wind and wave height. Map: Earth Nullschool

Fun fact: The map above shows that the wind is blowing clockwise around low pressures, and counterclockwise around high pressures. The opposite of in the northern hemisphere.

The highway

"The roaring forties" does not sound like a stretch of water you would like to visit, but this was the "highway" the sailing ships took on their way between Europe, Asia, Australia and back.

You could rely on strong winds blowing from west to east, winds that a ship could ride all the way around the globe. On their way out, the ships sailed straight south in the Atlantic until they reached 40 degrees south, and the wind that took them south of the Cape of Good Hope and Africa, and on to Australia - if they did not set their course out of the wind belt and north towards India and Asia.

On their way home from Australia, the ships sailed east, across the Pacific Ocean towards South Africa and around Cape Horn, and then north towards Europe. The Dutchman Hendrik Brouwer was the one who discovered this route, in 1611, and the "motorway" now has his name, the Brouwer route.

The sun

The sun is the engine setting up "The roaring forties". The air heated above the equator expands, becomes lighter, and rises. High up in the atmosphere the air flows north and south. At sea-level, the air that rises up is replaced by air that is drawn in from the north and south.

The large scale atmospheric circulation. Source: earth.nullschool / Wikipedia
The large scale atmospheric circulation. Source: Earth.nullschool / Wikipedia

The earth's rotation shifts the wind direction. North of the equator it blows from the northeast, south of the equator from the southeast. These are the trade winds. At 60 degrees north and south, there is a new area of ​​air rising in the atmosphere, also powered by differences in temperature. This is where we find "The roaring forties", with winds blowing from west to east.

Apart from the tip of South America, there are no large areas of land that can affect the wind, and it often gets very strong. Nice for sailing ship captains short of time, perhaps not as nice for the passengers.

Further south, the wind is even stronger, "The furious fifties". It is a good reason that sailing past Cape Horn at 55 degrees south is regarded as quite a rite of passage for sailors.

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