Seasonal Variation of the Quasi‐Biennial Oscillation Descent
Lawrence Coy, Paul A. Newman, S. E. Strahan, Steven Pawson
Abstract
Abstract This study examines variations through the year in the rate of descent of the quasi‐biennial oscillation (QBO) wind in the tropical lower stratosphere. The work is based on the Modern‐Era Retrospective analysis for Research and Applications, Version 2 (MERRA‐2) multiyear global reanalysis. A 10‐member ensemble of free‐running atmospheric simulations using the Global Earth Observing System (GEOS) atmospheric general circulation model is also examined. The QBO winds are decomposed into two orthogonal modes that describe amplitude and phase propagation. This reveals a semiannual signal in descent rate, with slow descent at times of large middle‐latitude planetary wave activity, suggesting that this wave activity influences equatorial vertical velocity. This result also explains the suppression of QBO wind transitions during active wave times. Results also show a variation in descent speed when plotted against QBO phase. These results provide a baseline of QBO behavior for future QBO modeling.