Role of zonally asymmetric ozone in modulating downward influence exerted by steady, transient and episodic wave forcing

Decades of observational and modeling research have sought to understand and predict how human-caused and naturally induced changes in stratospheric ozone affect Earth's climate system. As knowledge about ozone has grown over the decades, so too have questions about the role of ozone role as a mediator of climate change between the stratosphere and troposphere. The questions spring largely from an inadequate understanding of the complex and intimate connection that exists between ozone photochemistry, radiative transfer, and the dynamical circulation. Any perturbation imparted to a member of this trinity of physical processes will affect the other two. Indeed, observations show that individual members of the trinity are undergoing changes whose individual and collective effects on the climate of the troposphere-stratosphere coupled system are not well understood.

In this study we focus on the role of ozone as a mediator of troposphere-stratosphere communication. Our emphasis is on downward propagation brought about by the effects of zonal asymmetries in ozone on planetary wave drag and eddy ozone convergences. We employ a mechanistic model of the extratropical atmosphere that couples radiative transfer, ozone transport, ozone photochemistry and the dynamical circulation. Three experimental scenarios are considered: steady wave forcing; transient wave forcing; and a localized momentum pulse that mimics the wave drag exerted by wave breaking. For each scenario we distinguish the relative importance of zonal-mean ozone and zonal asymmetries in ozone (ZAO) in affecting downward signal propagation. Preliminary results show that for certain steady wave forcing, ZAO can cause otherwise steady wind regimes to vacillate. For transient (periodic) wave forcing, ZAO produce vacillating wind regimes that differ markedly in amplitude and period from those that develop when zonal-mean ozone alone is considered. For a localized momentum pulse placed in the lower to mid stratosphere, ZAO weaken downward signal propagation and reduce its temporal persistence. These results are discussed in light of secular changes in stratospheric ozone and increasing greenhouse gas concentrations.