Abstract

Have you ever noticed that the clouds above you are moving very fast, even though you don’t feel any wind where you are standing on the ground? That’s because the wind blows at different speeds and directions at different altitudes in the atmosphere. The quasi-biennial oscillation is a slow change in wind direction from eastward to westward which occurs high in the atmosphere above the tropics (the latitudes close to the equator). Over about a two-year period, the wind direction switches from westward to eastward, then back again starting from the middle of the stratosphere, then working its way down. 

Or at least that’s how it usually works! This past winter, we noticed a curious change in this normal downward progression of the quasi-biennial oscillation. Instead of the eastward blowing winds slowly moving down through the atmosphere, the westward blowing winds suddenly started moving upward! This has never been observed before!