Atmospheric Dynamics and Vertical Structure of Uranus and Neptune's Weather Layers

The Icy Giants Uranus and Neptune have similar rotation periods, large orbital inclinations and intense zonal winds at the visible cloud level. The winds are organized into three broad jets: a zonal jet that flows to the West at low latitudes and single jets that flow to the East in each hemisphere at mid and high-latitudes. The intensity of the winds observed at the cloud level remains a mystery considering the small energy available at the distance of the planets to the Sun. Both planets have zonal bands with low contrast that do not correlate with the structure of the winds. They also have dark anticyclones and bright cloud systems but present striking differences in the abundance of these features and their size and latitudinal distribution. The bands and major meteorological systems are observed at altitudes compatible with methane clouds and observational evidence suggests the presence of a deeper cloud of hydrogen sulfide and a latitudinal variation of hydrogen sulfide and methane with depletion of methane at high latitudes and more detectable hydrogen sulfide near the poles. Other chemical species like ammonia hydrosulfide and water should condense forming deep clouds at pressures of tens to hundreds of bars. A small number of bright features in both planets are good candidates for moist convective storms possibly powered by methane condensation. The expected deep abundances of volatiles in these cold atmospheres are at least 10 times larger than those on Jupiter and Saturn making the global distribution of volatiles a key feature to determine the stability of the atmosphere, influencing also the vertical wind shear and inhibiting the development of large moist convective storms. The combination of deep massive clouds, weak solar and internal heat forcing, extremely long seasons and potential effects in favor and against moist convection place these planets in a dynamic regime unlike any other in Solar System planets. Here we explore the observed meteorology at cloud level and the deep "weather layers" of these planets. We show that a combination of orbital and in situ data will probably be required to answer satisfactorily outstanding questions in the behavior of these atmospheres.