  Observations of Jupiter's deep atmosphere by the Juno spacecraft have
revealed several puzzling facts: The concentration of ammonia is variable down
to pressures of tens of bars, and is strongly dependent on latitude. While most
latitudes exhibit a low abundance, the Equatorial Zone of Jupiter has an
abundance of ammonia that is high and nearly uniform with depth. In parallel,
the Equatorial Zone is peculiar for its absence of lightning, which is
otherwise prevalent most everywhere else on the planet. We show that a model
accounting for the presence of small-scale convection and water storms
originating in Jupiter's deep atmosphere accounts for the observations. Where
strong thunderstorms are observed on the planet, we estimate that the formation
of ammonia-rich hail ('mushballs') and subsequent downdrafts can deplete
efficiency the upper atmosphere of its ammonia and transport it efficiently to
the deeper levels. In the Equatorial Zone, the absence of thunderstorms shows
that this process is not occurring, implying that small-scale convection can
maintain a near-homogeneity of this region. A simple model satisfying mass and
energy balance accounts for the main features of Juno's MWR observations and
successfully reproduces the inverse correlation seen between ammonia abundance
and the lightning rate as function of latitude. We predict that in regions
where ammonia is depleted, water should also be depleted to great depths. The
fact that condensates are not well mixed by convection until far deeper than
their condensation level has consequences for our understanding of Jupiter's
deep interior and of giant-planet atmospheres in general.
