QBO

The Quasi Biennial Oscillation - is a regular variation in the direction of winds high in the stratosphere above the Equator. The winds change direction from easterly to westerly (or vice versa) approximately every 14 months. The (easterly or westerly) phase of the QBO has indirect effects on the wider atmospheric circulation, including the strength of the jet stream. When the QBO is in its easterly phase, it tends to weaken the jet stream and can increase the chance of a Sudden Stratospheric Warming (SSW) which, in turn, can make cold outbreaks more likely across parts of the mid latitudes.