Polar Vortex Formation in Giant Planet Atmospheres Under Moist Convection

A strong cyclonic vortex has been observed on each of Saturn’s poles, coincident with a local maximum in observed tropospheric temperature1,2,3 . Neptune also exhibits a hot, though much more transient4 , region on the South Pole. The creation and maintenance of Saturn’s polar vortices, and their presence or absence on the other giant planets, are not understood. Additionally, highly energetic, small-scale storm-like features have been observed on each of the giant planets, originating from the water cloud level or perhaps lower. Previous studies suggest that these small storms are moist convective and play a significant role in global heat transfer from the hot interior to space5,6 . Here we show that simple ‘storm’ forcing, motivated by moist convection, can create a strong polar cyclone through the depth of the troposphere. Using a shallow water model, we find that shallow polar flows on giant planets may be qualitatively expressed by two parameters: a scaled planetary size and a scaled energy density of the atmosphere. We also suggest that the observed difference in a typical eddy length scale between Saturn and Jupiter may preclude a Jovian polar cyclone, a question that will be resolved by the Juno mission in 2016.