Dynamics of the Disrupted 2015-16 Quasi-Biennial Oscillation.

A significant disruption of the Quasi-Biennial Oscillation (QBO) occurred during the Northern Hemisphere (NH) winter of 2015-16. Since the QBO is the major wind variability source in the tropical lower stratosphere and influences the rate of ascent of air entering the stratosphere, understanding the cause of this singular disruption may provide new insights into the variability and sensitivity of the global climate system. Here we examine this disruptive event using global reanalysis winds and temperatures from 1980-2016. Results reveal record maxima in tropical horizontal momentum fluxes and wave forcing of the tropical zonal mean zonal wind over the NH 2015-16 winter. The Rossby waves responsible for these record tropical values appear to originate in the NH and were focused strongly into the tropics at the 40 hPa level. Two additional NH winters, 1987-88 and 2010-11 were also found to have large, tropical lower stratosphere, momentum flux divergences; however, the QBO westerlies did not change to easterlies in those cases.