Diverse Dynamical Response to Orographic Gravity Wave Drag Hotspots-A Zonal Mean Perspective

In the extratropical atmosphere, Rossby waves (RWs) and internal gravity waves (GWs) propagating from the troposphere mediate a coupling with the middle atmosphere by influencing the dynamics therein. In state-of-the-art chemistry-climate models (CCMs), RW effects are well resolved while the majority of GW effects have to be parameterized. Here, we analyze orographic GW (OGW) interaction with resolved dynamics in a comprehensive CCM on daily time scales. For this, we apply a recently developed method of strong OGW drag event composites for three pronounced northern hemisphere OGW hotspots. We show that strong OGW drag events are associated with anomalous resolved wave propagation in the stratosphere. Causal links are inferred from previously published work and are supported by the anomalies in zonal circulation and wave activity tendencies. The nature of these anomalies varies depending on the hotspot region, which underlines the parameterized OGW-resolved dynamics interaction being a two-way process. Plain Language Summary The majority of atmospheric waves are generated near the surface and propagate subsequently upward in the atmosphere. This includes Rossby waves that are resolved in climate models and small-scale gravity waves (GWs) that commonly have to be parameterized. In the middle atmosphere, the waves eventually break, thereby dissipating their momentum and energy, which influences atmospheric dynamics. The interaction of GWs with the large-scale circulation is to date poorly understood. In this study, we associate regionally enhanced GW drag with anomalies in resolved wave propagation in the stratosphere in a comprehensive chemistry-climate model on the time scale of days. For this, we identify strong orographic GW (OGW) events for the three most pronounced northern hemisphere OGW hotspots and construct composites of anomalies of selected variables with respect to the climatological mean. We find that the response of the resolved wavefield strongly depends on the hotspot region, leading to diverse consequences on the large-scale stratospheric circulation. Strong OGW events in the hotspots are in turn determined by the resolved fields from the surface to the level of OGW dissipation, which highlights the two-way coupling between OGWs and resolved flow.

Automated summary

This study investigates the interaction between orographic gravity waves (OGWs) and resolved dynamics in atmospheric models, showing that strong OGW drag events are associated with anomalous wave propagation in the stratosphere. The response of the resolved wavefield to strong OGW events depends on the region, leading to diverse consequences on the large-scale stratospheric circulation. The two-way coupling between OGWs and resolved flow highlights the complexity of atmospheric dynamics.