What Drives the Brewer–Dobson Circulation?

Abstract

Recent studies have revealed strong interactions between resolved Rossby wave and parameterized gravity wave driving in stratosphere-resolving atmospheric models. Perturbations to the parameterized wave driving are often compensated by opposite changes in the resolved wave driving, leading to ambiguity in the relative roles of these waves in driving the Brewer–Dobson circulation. Building on previous work, this study identifies three mechanisms for these interactions and explores them in an idealized atmospheric model. The three mechanisms are associated with a stability constraint, a potential vorticity mixing constraint, and a nonlocal interaction driven by modifications to the refractive index of planetary wave propagation. While the first mechanism is likely for strong-amplitude and meridionally narrow parameterized torques, the second is most likely for parameterized torques applied inside the winter-hemisphere surf-zone region, a key breaking region for planetary waves. The third mechanism, on the other hand, is most relevant for parameterized torques just outside the surf zone. It is likely for multiple mechanisms to act in concert, and it is largely a matter of the torques' location and the interaction time scale that determines the dominant mechanism. In light of these interactions, the conventional paradigm for separating the relative roles of Rossby and gravity wave driving by downward control is critiqued. A modified approach is suggested, one that explicitly considers the impact of wave driving on the potential vorticity of the stratosphere. While this approach blurs the roles of Rossby and gravity waves, it provides more intuition into how perturbations to each component impact the circulation as a whole.

Simulating influences of QBO phases and orographic gravity wave forcing on planetary waves in the middle atmosphere

“…Recently, some studies revealed possible compensation of PW drag of the middle atmospheric circulation by parameterized OGWs in general circulation models (McLandress and McFarlane 1993;Cohen et al 2013Cohen et al , 2014Sigmond and Shepherd 2014;Watson and Gray 2015). Our results show that taking account of OGW parameterization can both decrease or increase wave amplitudes, EP-fluxes, and wave drag of the mean flow depending on the considered PW modes.…”

A New Gravity Wave Parameterization Including Three-Dimensional Propagation

“…The large negative difference observed in the zonal GWF in the mesosphere above the polar night jet (i.e., 0.5-0.05 hPa at 60-80°S and 0.1-0.01 hPa at approximately 50°S) is largely compensated by a positive difference in ∇⋅ F of the same order of magnitude. This may be due to a compensation mechanism between parameterized and resolved waves, as suggested by recent studies (McLandress et al 2012;Cohen et al 2013Cohen et al , 2014Scheffler and Pulido 2015).…”

Characteristics of Gravity Waves from Convection and Implications for Their Parameterization in Global Circulation Models

“…The uncertainty is particularly large for nonorographic GWs. Furthermore, an acceleration of the BDC of 2.0%-3.2% (decade) 21 is seen across models, but there again exists no consensus on the contributions from different wave types in driving this trend (Butchart et al 2006(Butchart et al , 2010Cohen et al 2014;Abalos et al 2015). The differences in resolved versus gravity wave contributions reflect our poor ability to simulate gravity waves.…”