Schematic illustration of two possible mechanisms for jet driving. Top row (a): the inverse cascade idea, where eddies merge until the jet scale is reached. The first step in this process illustrates the required anisotropy necessary to prefer either cyclonic or anticyclonic eddies, here illustrated by a sorting of both eddy types. Bottom row (b): the direct driving via Reynolds stresses, where an initial tilt of convective features (second column) yields weak zonal flows that then amplify the tilt until a viscous balance is reached.