Testing Mechanisms of Jet Shift Using Linear Response Function of an Idealized Dry GCM

Many mechanisms have been proposed to explain the poleward shift of the midlatitude jet under global warming. They are based on different aspects of the projected thermodynamic changes, for example, changes in static stability and meridional temperature gradient. Testing different mechanisms proves difficult, because it is not easy to impose one aspect of thermodynamic changes without invoking the others. For example, the increased static stability experiment in Kidston et al. (2011) ended up also increasing the meridional temperature gradient.

Using the linear response function of an idealized dry GCM calculated by Hassanzadeh and Kuang (2016), we can find the forcing needed to achieve a prescribed response. By diagnosing eddies’ response in such simulations, one can then separate influences from different aspects of thermodynamic changes, and evaluate mechanisms based on them. Revised experiment on increased static stability do not show robust increase of eddy wavelength, casting doubt on one of the mechanisms of jet shift in Kidston et al. (2011).