The Dynamic Response of the Winter Stratosphere to an Equable Climate Surface Temperature Gradient

Abstract

Abstract This work investigates the dynamic and thermal response of the winter stratosphere to the presence of a weak meridional surface temperature gradient. Previous work suggested that polar stratospheric clouds could have played a decisive role in maintaining high-latitude warmth, especially over continental interiors, during the polar nights of the late Paleocene and early Eocene epochs; both a chemical source of additional water vapor and a dynamical feedback between the surface climate and stratospheric temperatures have been proposed as mechanisms by which such clouds could form. A principal goal of this work is to investigate the latter problem using a general circulation model with stratospheric resolution that is forced with a very weak surface temperature gradient. It is found that temperatures in the lower stratosphere do not deviate significantly from the control run, which results from a robust flux of wave activity into the winter stratosphere. The strength of the stratosphere’s residual circulation increases slightly in the presence of the weak gradient, as wavenumber 3 begins to propagate to stratospheric altitudes. Changes in the zonal wind field that allow for the altered propagation are in balance with a weakened temperature gradient through the full depth of the troposphere. These simulations also suggest that the tropospheric thermal stratification could be maintained by moist convection at all latitudes in warm climate states with a weak temperature gradient.