The Role of Ozone in the Secondary Circulation of the QBO: Linear Theory

Abstract The secondary circulation is central to understanding how changes in ozone (or other radiatively active species) might affect the dynamics of the quasibiennial oscillation (QBO). We develop here a linearized scaling theory to quantify the potential role of ozone in determining the secondary circulation, and validate it against a radiative/photochemical/convective equilibrium column model that reproduces the observed temperature and ozone anomalies of the QBO. Although the potential for radiative heating due to ozone to affect the secondary circulation is generally appreciated, theoretical discussions of the secondary circulation have not included an explicit representation of the ozone budget. For realistic parameter values, ozone heating can play a dominant role in determining the strength and structure of the secondary circulation. In particular, the photochemical sink in the lower stratosphere where ozone is conventionally thought to be determined by transport is key to obtaining a realistic circulation: in its absence the theory predicts a much weaker circulation in which vertical motion is aligned with the core of the jets rather than the shear zones. The photochemical sink (and thus the secondary circulation) depends nonlocally on the ozone column above. We further apply this theory to estimate the component of the secondary circulation that is due to ozone heating, confirming a previously inferred over‐estimate of the secondary circulation in ERA 5. These results have implications for understanding the role of interactive ozone in model‐generated QBOs.