The Role of Temperature Gradients versus Static Stability on the Zonal Wind and Eddy Kinetic Energy Response to Thermal Perturbations

The relative roles of meridional temperature gradients and static stability with regard to the extratropical response to thermal perturbations are explored in a dry primitive equation (PE) GCM. A quasigeostrophic (QG) model is used to separate the relative roles because the static stability in a QG model is externally prescribed and can therefore be altered independently of the meridional temperature gradient. For most experiments, the changes in meridional temperature gradients make the largest contribution to the zonal-mean zonal wind (U) changes, although the static stability changes are also important. In most cases, the mechanism for the static stability response does not directly involve the eddies. Instead, the advection of the static stability perturbation by the zonal-mean vertical velocity accounts for most of the U response to static stability. For increased static stability, advection by the Ferrel cell increases the meridional temperature gradient, which strengthens the jet via thermal wind. The stronger jet then shifts poleward, consistent with various theories in the literature. For eddy kinetic energy (EKE), the direct effect of static stability makes a nonnegligible contribution in most cases; however, the meridional temperature gradient and advection by Ferrel cell effects together are usually more dominant.

Automated summary

The relative roles of meridional temperature gradients and static stability in the extratropical response to thermal perturbations were explored. The changes in meridional temperature gradients had the largest contribution to the zonal-mean zonal wind changes, while the static stability changes were also important. The mechanism for the static stability response did not directly involve the eddies. Instead, the advection of the static stability perturbation accounted for most of the zonal wind response to static stability.