EXPLORING THE EFFECTS OF FORCING QUASI-BIENNIAL OSCILLATIONS IN A 2-DIMENSIONAL MODEL

Analytic forcing of the stratospheric quasi-biennial oscillation (QBO) is intro duced into a two-dimensional middle atmosphere model contain ing 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 obse rvations and employed in three different ways: (1) as a ''thermal nudg e'' in the temperature equation, or in the diagnostic meridional strea m function equation as (2) additional heating or (3) equivalent wave d riving. A different amplification factor for each method is required t o achieve good agreement with the observed QBO in column ozone. This l ends insight into the relationship among thermal perturbations, heatin g, and vertical motion. The vertical variation of QBO amplitude leads to a vertical dependence of the phase relationship among vertical moti on, temperature, and zonal wind. Equatorial upward motions range from nearly zero to twice the time mean. Feedbacks in the model result in d ifferent extratropical responses for the two hemispheres and modulatio n of the equatorial semiannual oscillation. Chemical feedbacks and pha se relationships are explored for the two ozone regimes: photochemical control above 30 km and advective control beneath. Confirming other s tudies, QBO vertical motions alter the distribution of odd nitrogen sp ecies above 30 km, which, together with the temperature dependence of reaction rates, combine to exert a strong control on ozone perturbatio ns.