Modeling Atmospheric Circulation

The Quasi-Biennial Oscillation (QBO) is a cyclic atmospheric process with a period slightly longer than 2 years; it involves reversals of the easterly and westerly phases of equatorial zonal stratospheric winds. The QBO dominates the interannual variability in the tropical stratosphere and causes a secondary circulation with an associated response in the temperature distribution and global effects on trace gas distributions. Thus, general circulation models must simulate the QBO accurately if they are to predict climate more reliably. Giorgetta et al. have developed a model that successfully simulates the QBO by incorporating improved spatial resolution, a realistic simulation of tropical convection, and the effects of gravity waves. With these improvements, their model yields a QBO very similar to the observed one, forced from a broad spectrum of atmospheric waves (as expected from observations) and without the need for specific ad hoc adjustments.—HJS