Replicating the Hadley cell edge and subtropical jet latitude disconnect in idealized atmospheric models

Abstract

Recent work has shown that variability in the subtropical jet's (STJ) latitude, φSTJ, is not coupled to that of the Hadley cell (HC) edge, φHC, but the robustness of this disconnect has not been examined in detail. Here, we use meteorological reanalysis products, comprehensive climate models, and an idealized atmospheric model to determine the necessary processes for a disconnect between φHC and φSTJ in the Northern Hemisphere's December-January-February season. We find that a decoupling can occur in a dry general circulation model, indicating that large-scale dynamical processes are sufficient to reproduce the metrics' relationship. It is therefore not reliant on explicit variability in the zonal structure, convection, or radiation. Rather, the disconnect requires a sufficiently realistic climatological basic state. Further, we confirm that the robust disconnect between φSTJ and φHC across the model hierarchy reveals their differing sensitivities to midlatitude eddy momentum fluxes; φHC is consistently coupled to the latitude of maximum eddy momentum flux, but φSTJ is not.