Events / Jovian weather at depth: from dark to dawn

Cheng Li

Abstract: Jupiter represents a class of planets whose major composition is hydrogen and helium, with a few condensable species forming visible clouds high up. Jovian atmospheres typically feature multiple zonal jets at the speed of hundreds of meters per second, and incessant popping of small-scale storms and vortices. By employing an Earth-like general circulation model, multiple authors have declared success in modeling the Jovian atmosphere by producing zonal jets in the low latitudes and vortices in the high latitudes. However, the most recent observation of Jupiter’s atmosphere at depth by the Juno spacecraft contradicts what one would infer from the standard picture, that chemically inert tracers shall mix through the troposphere. Juno observed that ammonia gas is significantly depleted down to several tens of bars, well below its condensation level. The observation casts doubts on whether we really understand the most basic principle of the general circulation of Jovian atmospheres. Answers to questions like “How does the internal heat transfer through the atmosphere?”, “What is the entropy of Jupiter’s interior” become more obscure than before. Here I demonstrate that primordial heat inside Jupiter should be transported by gravity waves rather than convection to the tropopause where energy can radiate out. As a result, Jupiter’s weather layer is stably stratified as opposed to neutrally stratified, probably down to hundreds of bars. This affects the value of the isentrope chosen to model Jupiter’s interior when using the temperature measured at 1 bar pressure level.