Graphical Abstract

Yamashita, Y., H. Akiyoshi, T. G. Shepherd, and M. Takahashi, 2015: The combined influences of westerly phase of the Quasi-Biennial Oscillation and 11-year solar maximum conditions on the Northern Hemisphere extratropical winter circulation. J. Meteor. Soc. Japan, 93, 629-644.
Special Edition on Contributions to Asia Oceania Atmospheric Sciences
https://doi.org/10.2151/jmsj.2015-054

The combined influences of westerly phase of the QBO (QBO-W) and solar maximum (S_max) conditions on the Northern Hemisphere extratropical winter circulation are investigated using reanalysis data and CCSR/NIES Chemistry Climate Model (CCM) simulations.
The composite analysis indicates strengthened polar vortex in December followed by weakened polar vortex in February–March for QBO-W during S_max (QBO-W/S_max) conditions (Fig. 1).
In December, the dynamical processes related to the QBO-W and S_max may work in concert to maintain the stronger vortex during QBO-W/S_max.
The amplification of tropospheric wavenumber 1 (WN1) wave in January during QBO-W/S_max results in the enhancement of upward WN1 propagation from troposphere into stratosphere, leading to the weakened polar vortex in February–March. Although wavenumber 2 (WN2) waves do not play a direct role in forcing the stratospheric vortex evolution, their tropospheric response to QBO-W/S_max conditions appears to be related to the maintenance of westerly wind anomaly in the high-latitude troposphere in January (Fig. 2).