Linking Hadley Circulation and Storm Tracks in a Conceptual Model of the Atmospheric Energy Balance
Midlatitude storm tracks shift in response to climate change and natural climate variations such as El Niño, but the dynamical mechanisms controlling these shifts are not well established. This paper develops an energy balance model that shows how shifts of the Hadley cell terminus and changes of the meridional energy flux out of the Hadley cell can drive shifts of storm tracks, identified as extrema of the atmospheric meridional eddy energy flux. The distance between the Hadley cell terminus and the storm tracks is primarily controlled by the energy flux out of the Hadley cell. Because tropical forcings alone can modify the Hadley cell terminus, they can also shift extratropical storm tracks, as demonstrated through simulations with an idealized GCM. Additionally, a strengthening of the meridional temperature gradient at the terminus and hence of the energy flux out of the Hadley cell can reduce the distance between the Hadley cell terminus and the storm tracks, enabling storm-track shifts that do not parallel shifts of the Hadley cell terminus. Thus, with the aid of the energy balance model and supporting GCM simulations, a closed theory of storm-track shifts emerges.
© 2018 American Meteorological Society. Manuscript received 31 March 2017, in final form 14 November 2017. Published online: 1 March 2018. We are grateful for the financial support of the National Science Foundation (Grant AGS-1019211). We also thank Xavier Levine for several helpful discussions and for his comments on an early draft of this work.
Published - jas-d-17-0098.1.pdf