Environment Counts | Unprecedented disruption in the upper equatorial atmosphere :
The quasi-biennial oscillation (QBO) is an oscillation in the upper atmosphere near the equator with a period that varies between two and three years. It is characterized by alternating prevailing eastward and westward wind-jets descending through the equatorial stratosphere from about 50 km down to about 16km in altitude. It was discovered in the 1950s and since then no disruptions in the oscillation have been observed in the atmosphere. In February 2016 an unprecedented westward jet formed within the eastward phase in the lower stratosphere. The primary cause has been ascribed to waves transporting momentum from the Northern Hemisphere.
Time series of monthly mean wind vs altitude averaged over the equatorial region showing descending eastward (yellow) and westward (blue) wind regimes for the last thirteen observed QBO cycles. The unexpected formation of a second westward layer interrupting the lower stratospheric eastward phase can be seen in early 2016.
An unexpected disruption of the atmospheric quasi-biennial oscillation, Scott M. Osprey, Neal Butchart, Jeff R. Knight, Adam A. Scaife, Kevin Hamilton, James A. Anstey, Verena Schenzinger, and Chunxi Zhang, Science 08 Sep 2016: DOI: 10.1126/science.aah4156