Trade Winds Story

This fascinating clip shows the island of St Vincent erupting gas and dust (brown colour) to levels in excess of 30,000 ft. Look carefully and you notice the NE Trade Wind blowing the low clouds westward past the island in a constant and steady easterly tropical breeze. The question is, why does the gas and dust, erupted from the volcano, set off in the opposite direction eastward?

St Vincent, latitude 13N, lies within the northern Hadley cell, which is the exchange of air masses between the rising air near the equator and the descending air at the tropics.

Image from Wikipedia

The Hadley Cell consists of air rising near the equator, flowing at high level toward the North and South Poles, returning to the surface of the Earth in the subtropics, and flowing back toward the equator at the surface of the Earth. This produces tropical easterly surface winds called the trade winds.

The Coriolis Effect deviates both the northward and southward flows to the right in the northern hemisphere, causing the southbound surface wind to be easterly and the northbound upper wind to be westerly, which is so starkly demonstrated in the volcano movie.

Thanks for reading this blog which is part of my retirement activity on behalf of the Reading Astronomical Society