FIGURE 3. Models of the plume onset and disturbance development.

a, b, Wet convective three-dimensional model of the plumes. a, Thermal profiles used to run the simulations and the cloud top level reached by the convective cell assuming a deep water content of 3 times solar abundance and 95% of relative humidity above the condensation level. P, pressure; T, temperature. The continuous line corresponds to the Cassini CIRS thermal profile at the NTB location¹⁹, the dashed line to the Voyager IRIS thermal profile¹⁸ and the dotted line to a synthetic profile with less static stability from 500 to 200 mbar required for the storms to reach the 60 mbar level. The inset shows the wet adiabat extension deep in the atmosphere. b, Convective cell resulting from the model able to fit the observed cloud tops of the plumes and the domain of simulation. c, The plume brightness distribution (inset) results from a two-dimensional model of a round cloud placed in the peak of the jet and evolving as it interacts with the meridional shear of the zonal wind¹⁷ with a spatial resolution of 5 km over a 10,000  5,000 km area. The map (main panel) shows the distribution of Ertel's potential vorticity (PV; greyscale) at 650 mbar after 30 days for a simulation where the jet extends vertically downwards with constant value from the upper cloud layer at altitude 0.6 bar down to at least 5–7 bar (the location of the water clouds and the plume source). Inset and map are at the same scale.