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Crossing the Atlantic Ocean

Catching the trade wind

about 2 months ago
Written by Ronald Toppe
Ocean education > Catching the trade wind

Catching the trade wind

about 2 months agoOcean education
Written by Ronald Toppe
Crossing the Atlantic Ocean

It was no coincidence that Statsraad Lehmkuhl sailed south to the Canary Islands before heading west and across the Atlantic Ocean.

Everyone knows that the weather varies from day to day and from place to place.

But there are large wind patterns that are surprisingly stable throughout the year. The trade winds is one of these systems; the steady wind that blows from east to west at the equator.

Rising air

The engine that drives the wind systems is the sun. The mechanism is simple, air that heats up expands, becomes lighter, and rises.

The sun is strong at the equator, so here warm air rises all year round, and flows north and south high up in the atmosphere. The rising air is replaced by air drawn in from the north and south.

Due to the earth's rotation, the direction of the incoming wind is diverged. North of the equator the wind blows from the northeast, south of the equator from the southeast. These are the trade winds, the steady and reliable winds that carried the merchant ships across the ocean, full of goods.

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

The doldrums

Above the equator the air is calm, as it is in the center of all low pressure zones.

This area is called the doldrums, and is just as scary as it sounds. If a sailing ship gets stuck in the doldrums, it risks drifting around with slack sails for weeks.

No wind.
No wind. Photo: Ingrid Wollberg

When air rises, it eventually cools down. Cool air can not hold as much water vapor as warm air. Clouds form, and it starts to rain. This is the reason we find the globe's rainforests along the equator.

The westerlies

Around 30 degrees north and south, the air that rose at the equator sinks down again. Sinking air heats up, there is room for more water vapor, and the clouds disappear. This is where the great deserts of the globe are found.

At 60 degrees north and south is a new zone of rising air. Here, the prevailing wind direction is from west to east, so the sailing routes back to Europe go further north in the Atlantic.

Monsoon

These atmospheric systems regulates the large scale wind patterns on the earth, but sailing ships have to deal with other wind systems too.

The change of seasons creates its own winds.

The monsoon is an annual guest in India and the surrounding countries. In summer, the land masses heat up faster than the sea. The air rises, drawing moist air and heavy rainfalls northeast from the Indian Ocean and inland.

In winter, the sea is warmer than land, and cold and dry air blows down from the Himalayas, over India and into the ocean. This time of year the coasts of Southeast Asia and Australia gets rain.

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