The Relation Between the Latitudinal Shifts of Midlatitude Diabatic Heating, Eddy Heat Flux, and the Eddy-Driven Jet in CMIP6 Models

The midlatitude storm tracks and eddy-driven jet are predicted to shift poleward in response to anthropogenic climate change. Here the relation between the latitudes of the eddy-driven jet and storm track and their responses to climate change in preindustrial and abrupt 4 x CO2 simulations from the Coupled Model Intercomparison Project Phase 6 (CMIP6) are examined, focusing on the Southern Hemisphere summer. The eddy-driven jet, Ferrel cell, midlatitude diabatic heating, and eddy heat flux all shift poleward in response to climate change, while the eddy-driven jet latitude is positively correlated with the diabatic heating latitude and the Ferrel cell latitude, but is not significantly correlated with the eddy heat flux latitude, and is negatively correlated with the midlatitude diabatic heating strength. The roles of eddy heat flux and diabatic heating in the midlatitude circulation response to climate change are analyzed using the Kuo-Eliassen equation. Each heating term induces a meridional circulation and an associated Coriolis force, which acts to change the vertical shear of the zonal mean zonal wind. It is found that in response to climate change, the heating due to eddy heat flux accelerates the vertical wind shear on the equatorward side of the jet, while the diabatic heating decelerates the vertical wind shear on the poleward side of the jet. The contributions of the heating terms to the momentum budget balance the contributions due to eddy momentum flux and surface friction, which act to shift the vertical shear poleward in response to climate change.