The transient response of the troposphere to an imposed stratospheric zonal force

The influence of the stratosphere on the troposphere at timescales of 1-week is examined in an idealised GCM. Model output from two contrasting experiments is compared. The experiments consist of applying a zonally-symmetric force that is meridionally and vertically localised, and is applied either at the top of the atmosphere, or at the surface.

The imposed forces drive the opposite vertical shear, or baroclinic response, but have a similar impact on the vertically-averaged, or barotropic flow. The response of the tropospheric mean flow, and important aspects of the transient eddy behaviour, are remarkably similar in both experiments, and at various timescales.

The results suggest that the influence of meridional shear on Rossby wave propagation may be a crucial aspect of stratosphere-troposphere coupling at short timescales.