The Weather Notebook: The trades

The trades
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Dave Thurlow, Host

Hi, I'm Dave Thurlow for The Weather Notebook and today on the show, I'm going to talk about wind and the old sailing days.

GOES-8 Satellite Derived Winds and Analyses
If you wanted to sail across the Atlantic from Europe to America, an east wind would be the wind of choice. Learning by trial and error, many of the early traders making the journey from the old to the new world, found an area of persistent east winds blowing across the Atlantic, a few hundred kilometers north of the equator. This made the westward part of the trip pretty much a piece of cake as the winds were steady, predictable, not too light and not too strong. Because all of the sailors who were dealing in commercial trade used these winds to whisk across the Atlantic, they became called the trade winds, or just simply the trades.

In a simplified view of the atmosphere, the air immediately over the equator rises because it's so hot. This means that the wind doesn't blow very much, making for lousy sailing. This area, sailors called the doldrums. The air that rises over the equator sinks back down about 20 degrees north (and south) of the equator. The sinking air makes for very little wind and another lousy place to sail.

So lousy in fact was this zone that when traders were bobbing about, going nowhere, they would try to lighten the ship's load by throwing horses overboard, so the area came to be called the horse latitudes. As the sinking air of the horse latitudes replaces the rising air of the doldrums it makes a zone of northeast to east winds; the sailor-friendly trade winds, which have been steering ships across the Atlantic for centuries.

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