Connecting the energy and momentum flux response to climate change using the Eliassen-Palm relation

Coupled climate models project that extratropical storm tracks and eddy-driven jets generally shift poleward in response to increased CO₂ concentration. Here the connection between the storm-track and jet responses to climate change is examined using the Eliassen-Palm (EP) relation. The EP relation states that the eddy potential energy flux is equal to the eddy momentumflux times the Doppler-shifted phase speed. The EP relation can be used to connect the storm-track and eddy-driven jet responses to climate change assuming 1) the storm-track and eddy potential energy flux responses are consistent and 2) the response of the Dopplershifted phase speed is negligible. Weexamine the extent to which the EP relation connects the eddy-driven jet (eddy momentum flux convergence) response to climate change with the storm-track (eddy potential energy flux) response in two idealized aquaplanet model experiments. The two experiments, which differ in their radiation schemes, both show a poleward shift of the storm track in response to climate change. However, the eddy-driven jet shifts poleward using the sophisticated radiation scheme but equatorward using the gray radiation scheme. The EP relation gives a good approximation of the momentum flux response and the eddydriven jet shift, given the eddy potential energy flux response, because the Doppler-shifted phase speed response is negligible. According to the EP relation, the opposite shift of the eddy-driven jet for the different radiation schemes is associated with dividing the eddy potential energy flux response by the climatological Doppler-shifted phase speed, which is dominated by the zonal-mean zonal wind.