NSF-RUI: Gravity Waves and the Stratospheric Polar Vortex

This proposal examines the roles of wintertime gravity waves (GWs) in coupling the troposphere to the stratospheric polar vortex. Intense wintertime synoptic disturbances that significantly enhance the Jet Stream curvature and promote suitable flow over topography (like Greenland and Antarctica) can excite strong GWs that readily propagate into the stratosphere. Thermal perturbations induced by GWs can trig- ger the formation of mesoscale polar stratospheric clouds (PSCs) in the lower stratosphere. Gravity wave dissipation can impart strong momentum forcing on the mid/upper polar stratosphere. To this end, the research objectives are (1) to characterize the sources/properties of wintertime GWs in the polar regions and their propagation into the stratosphere, and (2) to assess the interactions between GWs and the polar circulation, in the presence of planetary-scale disturbances over the winter polar region.

Numerical simulations of GW events up to the stratopause will be performed using the University of Oklahoma’s Advanced Regional Prediction System (ARPS), a weather model that has been modified for this study. By comparing simulated wintertime GWs with satellite observations and analyzing GW structures with respect to large-scale flow and topography, wave properties/sources and propagation will be characterized and investigated. By computing momentum flux convergence and identifying extremely cold regions induced by GW perturbations, GW forcings on the polar vortex will be estimated in relation to planetary waves and GW roles in PSC formation will be explored.

To date, the role of wintertime GWs on the polar stratosphere needs investigation. By illuminating GW effects on the polar vortex, new insight on vortex variability can be obtained. As anomalous vortex behaviors have been suggested to bias near-surface climate conditions, such insight can help in better understanding the climate system. While stratospheric influence on tropospheric climate remains controversial, GW effects in the middle atmosphere are extremely important in chemistry-climate models. By examining GW source/characteristics in simulations and observations, this study offers additional constraints on how GW effects can be incorporated into these models, and thereby, improves the models’ effectiveness in assessing climate evolution and ozone variabil- ity. By assessing GWs’ roles in PSC formation, the project can increase present knowledge of ozone changes since PSCs constitute localized regions of chlorine activation and possible ozone destruction.