Quasi Biennial Oscillation

The Quasi-Biennial Oscillation is a regular variation of the winds that blow high above the equator. Strong winds in the stratosphere travel in a belt around the planet, and every 14 months or so, these winds completely change direction. This means a full cycle takes roughly 28 months, making it the most regular slow variation in the atmosphere after the cycle of the seasons.

The alternating wind regimes develop at the top of the lower stratosphere and propagate downwards at the tropical tropopause. Downward motion of the easterlies is usually more irregular than that of westerlies. The easterlies phase amplitude is about twice as strong as that of the westerly phase. At the top of QBO domain easterlies dominates, while at the bottom westerlies are more likely to be found.

Effects of QBO :-

• The speed of winds in the jet streams decreased and increased as per the QBO directions.
• When the QBO is easterly, the chance of a weak jet stream, sudden stratospheric warming events and colder winters in Northern Europe is increased.
• When the QBO is westerly, the chance of a strong jet, a mild winter, winter storms and heavy rainfall increases.