Eddy-Driven Jet Sensitivity to Diabatic Heating in an Idealized GCM

The eddy-driven jet is studied using a dry idealized model to determine its sensitivity to thermal forcings. The jet latitude, speed and variability is investigated under a series of Gaussian patch thermal forcing simulations applied systematically on a latitude-sigma grid in the troposphere. This work builds on previous studies by isolating the responses of the jet speed and latitude as opposed to combining them into a single annular mode index. It also explores the sensitivity of the jet to much smaller spatial heatings rather than applying forcing patterns to simulate anthropogenic climate change, as the size and magnitude of the forcings due to anthropogenic climate change are uncertain. This study explores the jet speed and latitude sensitivities to locally applied forcings in summer and winter conditions. The jet speed and latitude are found to have different sensitivity distributions from each other, which also vary between summer and winter. A simple mechanistic understanding of these sensitivities is presented by considering how the individual thermal forcings modify mean isentropic surfaces. In the cases analysed, the jet response to forcing scales approximately linearly with the strength of the forcing, and when the forcings are applied in combination. The findings show a rich latitude-pressure distribution of jet responses to thermal forcings, which will aid interpretation of jet responses in a changing climate. Furthermore, they highlight the areas where uncertainty needs to be reduced in the size and position of expected anthropogenic forcings, in order that the uncertainty in changes of the eddy-driven jet is reduced.