The Relationship Between Latitudinal Shifts in the Eddy-driven Jet and the Hadley Cell Edge

Plausible mechanisms have been proposed for latitudinal shifts in the zonal mean Hadley cell and in the eddy-driven jet, but the connection between the two is, thus far, less well understood. We propose that changes in one or the other cannot be completely understood in isolation. We document the relationship between latitudinal shifts in the Hadley cell edge and in the eddy-driven jet in long model simulations, finding, in spite of hints from previous work suggesting a universal ratio between the Hadley cell edge and the eddy-driven jet, that no such universal ratio exists. Rather, the ratio varies by season, hemisphere, and between models. We show that the ratio from year to year scales with the climatological location of the Hadley cell. This suggests that mean conditions in the tropics set the stage for extratropical eddies to modify the Hadley cell. We verify the importance of eddies in setting this ratio by comparing actual Hadley cell edge latitude time series with predicted values. Our results further highlight the importance of a close connection between the Hadley cell and eddy-driven jet.