The role of tropospheric synoptic eddies in stratosphere—troposphere coupling

The presence of a tropospheric eddy feedback as a response to strong stratospheric variability such as sudden stratospheric warmings is well documented. It is however not clear to what extent synoptic-scale eddies are responsible for the downward propagation of the stratospheric annular mode signal into the troposphere.

The effect of tropospheric synoptic eddies on the downward influence of stratospheric signals is investigated in a spectral dynamical core model. The stratosphere is perturbed by a tropospheric topographic forcing, which initiates stratospheric sudden warmings. Two model runs are compared, one with a full spectrum of fully interactive eddies, while another run was performed, where synoptic eddies are excluded, but with the synoptic eddy-forcing added back non-interactively. The eddies are therefore not able to influence the response to the stratospheric signal, while the eddy forcing establishes a comparable tropospheric mean state.

Initial results indicate an important role of the tropospheric synoptic eddies, and additional findings from these runs are explored and documented in order to contribute to advancing our understanding of stratosphere – troposphere coupling.