  The giant planet atmospheres exhibit alternating prograde (eastward) and
retrograde (westward) jets of different speeds and widths, with an equatorial
jet that is prograde on Jupiter and Saturn and retrograde on Uranus and
Neptune. The jets are variously thought to be driven by differential radiative
heating of the upper atmosphere or by intrinsic heat fluxes emanating from the
deep interior. But existing models cannot account for the different flow
configurations on the giant planets in an energetically consistent manner. Here
a three-dimensional general circulation model is used to show that the
different flow configurations can be reproduced by mechanisms universal across
the giant planets if differences in their radiative heating and intrinsic heat
fluxes are taken into account. Whether the equatorial jet is prograde or
retrograde depends on whether the deep intrinsic heat fluxes are strong enough
that convection penetrates into the upper troposphere and generates strong
equatorial Rossby waves there. Prograde equatorial jets result if convective
Rossby wave generation is strong and low-latitude angular momentum flux
divergence owing to baroclinic eddies generated off the equator is sufficiently
weak (Jupiter and Saturn). Retrograde equatorial jets result if either
convective Rossby wave generation is weak or absent (Uranus) or low-latitude
angular momentum flux divergence owing to baroclinic eddies is sufficiently
strong (Neptune). The different speeds and widths of the off-equatorial jets
depend, among other factors, on the differential radiative heating of the
atmosphere and the altitude of the jets, which are vertically sheared. The
simulations have closed energy and angular momentum balances that are
consistent with observations of the giant planets.
