Global and Regional Numerical Modeling of Water and Ammonia Cycles on Jupiter

Data analysis of Juno MWR instrument measurements of brightness temperature at six channels showed that ammonia vapor was depleted in the region between ammonia cloud base all the way down to 40-60 bars. The vertical extent of depletion is far greater than previous thought, which assumed that ammonia in the sub-cloud layers were well mixed. We use a state-of-the-art Global Circulation Model (GCM), JupiterMPAS, to investigate the physical and dynamical processes below the water cloud base in hoping to interpret water and ammonia abundances retrieved over a wide range of latitudes. Two mechanisms that may affect ammonia distributions have been examined: “mushball” microphysics and mesoscale circulations. JupiterMPAS model results show that: 1. the mushball microphysics is a viable method to produce ammonia depletion in the region above water cloud base; 2. the treatment of lower boundary conditions in the JupiterMPAS model can impact tracer distribution in the sub-cloud layers; 3. depletion of ammonia via strong mesoscale downdrafts is possible, but its effect on global ammonia distribution is very limited.