Exploring the Effects of Forcing Quasi-Biennial Oscillations in a Two-Dimensional Model

Phillip A. Politowicz and Matthew H. Hitchman

Department of Atmospheric and Oceanic Sciences, University of Wisconsin-Madison

Analytic forcing of the stratospheric quasi-biennial oscillation (QBO) is introduced into a two-dimensional middle atmosphere model containing interactive radiation, dynamics, photochemistry and climatological aerosols. The "WISCAR" model integrates the temperature equation in time, but diagnoses the meridional stream function and zonal wind. An analytic forcing function for the QBO is derived from zonal wind observations and employed three different ways: (1) as a "thermal nudge" in the temperature equation, or in the diagnostic meridional stream function equation as (2) additional heating or (3) equivalent wave driving. A different amplification factor for each method is required to achieve good agreement with the observed QBO in column ozone. This lends insight into the relationship among thermal perturbations, heating, and vertical motion. The vertical variation of the QBO amplitude leads to a vertical dependence of the phase relationship among vertical motion, temperature, and zonal wind. Equatorial upward motions range from nearly zero to twice the time mean. Feedbacks in the model result in different extratropical responses for the two hemispheres and modulation of the equatorial semiannual oscillation. Chemical feedbacks and phase relationships are explored for the two ozone regimes: photochemical control above 30 km and advective control beneath. Confirming other studies, QBO vertical mostions alter the distribution of odd nitrogen species above 30 km, which, together with the temperature dependence of reaction rates, combine to exert a strong control on ozone perturbations.

Please send questions/comments regarding this website to:jessica@andy.aos.wisc.edu