Theory suggests sinking tropical air masses, not rising ones, lead to dead calms

Water, water, every where,

And all the boards did shrink;

Water, water, every where,

Nor any drop to drink.

So goes the plight of sailors marooned in the windless doldrums of the tropical seas, never sure when—or whether—a gust would send them home. Although Samuel Taylor Coleridge encapsulated the phenomenon in the poem quoted above, 1834’s “The Rime of the Ancient Mariner,” scientifically, doldrums have largely been ignored and the textbook explanation for them taken at face value. Now, a study turns that explanation on its head, arguing the phenomenon is caused not by rising masses of sea air, but rather by sinking ones.

The result, published recently in Geophysical Research Letters, revealed a big flaw in the conventional explanation: Averaged over long timescales of days or weeks, the doldrums appear to coincide with big rainstorms. But in reality, over short, hourlong timescales, the rain and windless episodes occur separately.

It turned out a clue had been hiding in Coleridge’s poem all along. Stranded sailors were usually dry, not wet:

Water, water, every where,

And all the boards did shrink;

Water, water, every where,

Nor any drop to drink.

That means the standing theory for the doldrums is backward.

Although rainfall generally depends on rising parcels of moist air, the doldrums are better described by sinking masses of air.