The role of eddies in driving the tropospheric response to stratospheric heating perturbations

In recent years it has become apparent that changes in the stratosphere could have an impact on tropospheric circulation. However, as yet the exact mechanisms involved in the coupling between the stratosphere and troposphere remain uncertain.

Previous modelling results using a simplified general circulation model (sGCM) have shown that heating of the equatorial lower stratosphere can result in a poleward shift of the tropospheric mid-latitude jets whereas heating of the lower stratosphere that is uniform in latitude or localised towards the polar region results in an equatorward shift of the tropospheric jet. Understanding the effect that altered lower stratospheric temperature has on the troposphere is potentially important for many climate forcings such as the 11-year solar cycle, volcanic eruptions, greenhouse gas emissions and ozone depletion/recovery.

Here, further investigation using this sGCM into the mechanisms involved in producing a tropospheric response to stratospheric heating is presented. The results demonstrate the importance of altered eddy momentum fluxes in driving the tropospheric response. Moreover, it is found that the full tropospheric response cannot be produced without a feedback involving changes in tropospheric eddy momentum fluxes. The altered vertical temperature gradient around the tropopause and its latitudinal extent appear to be key to determining the direction of displacement of the tropospheric jet.

The impact of the state of the model troposphere on the response to stratospheric heating is also investigated. Specifically, the impact of introducing topography into the model and the effect of varying tropospheric jet structure is examined.