Distinct Upward Propagation of the Westerly QBO in Winter 2015/16 and Its Relationship With Brewer‐Dobson Circulation.

A westerly phase of the quasi‐biennial oscillation (QBO) was disrupted in 2015/16. Previous studies have primarily focused on the cause of the localized negative momentum forcing, initiating the QBO disruption. However, the upward displacement of the westerly QBO followed by the negative momentum forcing, clearly observed in 2015/16, has received less attention. This study shows that the distinct upward propagation of the westerly winds during the 2015/16 QBO disruption was contributed by the strong Brewer‐Dobson circulation (BDC). Strong Rossby waves with wavenumber 1 propagating from the troposphere mainly drove the strong BDC. Potential contributions of El Niño and Barents–Kara sea ice reduction to Rossby waves are also discussed. Plain Language Summary: The quasi‐biennial oscillation (QBO), describing alternate easterly and westerly winds in the tropical stratosphere, generally shows downward phase propagation with time. However, downward‐propagating westerly winds were split into two in February 2016, with one propagating upward and the other propagating downward. It is found that the upward propagation of the westerly winds was contributed from the stronger upwelling in the tropical stratosphere, mainly attributed to the strong planetary‐wave activity in the midlatitude troposphere. Key Points: Strong Brewer‐Dobson circulation contributed to the distinct upward propagation of the westerly QBO during the 2015/16 QBO disruptionMidlatitude Rossby waves with wavenumber 1 mainly induced the strong Brewer‐Dobson circulation in 2015/16 [ABSTRACT FROM AUTHOR]