The influence of deep jets on Jupiter's weather layer in a 1.5-layer shallow-water model

Abstract

The depth of the jet streams seen in Jupiter’s outer weather layer has long been debated, with alternative suggestions of confinement to the weather layer, and extensions deep into the planet being considered. Interpretation of measurements from NASA’s Juno probe have suggested that the weather-layer jets do extend deep into the planet down to depths of O(3,000k m). However this relies on the assumption that the jet profile does not change its spatial structure with depth, which may not be the case. In this work we consider a simple 1.5-layer shallow-water model of Jupiter-like jet streams, with prescribed deep jets in the lower layer, and look at the parameters affecting the strength of the coupling between the layers. We find the value of the Rossby deformation scale, LD to be particularly important, not just in setting the magnitude of variations in layer depth, but also in dictating the effectiveness of radiative damping. We also find the radiative damping timescales, the energy injection rate, and the spacing of the deep jets to be important. We combine these findings into our best-guess simulations of the real-Jupiter and find that the low atitudes are relatively uncoupled between the layers, with the high latitudes being more tightly coupled. These effects can be tied to the smallness of Jupiter’s LD and the effectiveness of radiative damping as a coupling mechanism. These simulations do, however, produce equatorial subrotation, and eddy-momentum fluxes unlike those on the real planet. It may be, therefore, that spatially-varying forcing, and very long radiative damping timescales are required for this model to be more Jupiter-like.