2013 Volume 91 Issue 3 Pages 243-256
Data from the Japanese 25-yr reanalysis/Japan Meteorological Agency Climate Data Assimilation System (JRA-25/JCDAS) and the chemistry climate model (CCM) of the Meteorological Research Institute (MRI) were used in this study to investigate the annual synchronization tendency of the quasi-biennial oscillation (QBO) in the equatorial stratosphere. The annual synchronization refers to phase transitions of the QBO that tend to occur for specific seasons.
The JRA-25/JCDAS reanalysis data exhibit similar features of the annual synchronization. The present diagnosis based on the transformed-Eulerian mean zonal momentum equation shows that zonal wind accelerations for the annual synchronization are largely unexplained by explicitly calculated terms, with a small contribution from resolved wave driving and a strong canceling effect from vertical advection.
The CCM does not simulate the annual synchronization as observed, although it does simulate general features of the QBO, as well as annual variation in equatorial upwelling with some differences. The absence of the annual synchronization is related to an almost seasonally uniform distribution of parameterized gravity wave forcing.
It is speculated from these results collectively that seasonal variation of convection and gravity waves plays a key role in inducing the annual synchronization tendency of the QBO under actual conditions.
