Differences in Stratospheric Radiative-Dynamical Feedbacks in Middle versus Polar Latitudes

Experiments utilizing the GEOS-5 CCM and the AER Rapid Radiative Transfer Model (RRTM) are used to examine how changes in the spatial distribution of stratospheric trace gas abundances under typical climate change scenarios (1960-present) modulate stratospheric wind, potential vorticity, and vertical EP-flux distributions in the middle versus polar latitudes. In particular, GEOS-5 generated distributions of ozone, greenhouse gases, and water vapor are used as inputs in RRTM stratospheric radiative equilibrium (SRE) experiments that isolate the spatial patterns (in the height-latitude plane) of radiative temperature changes due to each individual gas. In turn, the SRE temperature changes allow, via the thermal wind relationship, for an assessment of how the changes in the spatial distribution of each individual gas imparts unique changes to the refractive properties of planetary waves that explain the GEOS-5 simulated decrease in vertical EP-flux in midlatitudes and increase in vertical EP-flux in polar latitudes.

These results highlight how radiative-dynamical feedback processes can be invoked to explain the latitude-dependent differences in vertical EP-fluxes simply by understanding how radiative perturbations modulate the meridional gradient of potential vorticity differently within different portions of the stratospheric polar vortex. We consider how these results provide insight about the mechanisms responsible for trace gas induced changes in the strength of the Brewer-Dobson circulation and stratospheric polar vortex during Northern Hemisphere winter.