Convective heat transfer and the pattern of thermal emission on the gas giants

Abstract

S U M M A R YJupiter and Saturn emit nearly twice the thermal energy they receive from the Sun. Although insolation decreases toward the poles, the large-scale outward heat flux is nearly uniform, with smaller-scale latitudinal undulations that correlate with the zonal jet streams. Here we present numerical models of rapidly rotating, turbulent 3-D convection in geometrically thin, uniformly forced layers of Boussinesq fluid that approximate the deep convection zones of Jupiter and Saturn. In previous studies we have demonstrated that such models generate zonal flows comparable to those observed on the gas giants. By analysing the simulated patterns of convective heat transfer, we show here that deep convection in the gas giants can explain the anomalously uniform large-scale thermal emissions as well as the jet-scale variations. In particular, we find that convective heat transfer by quasi-geostrophic thermal plumes in relatively thin spherical shell geometry generates an outward heat flow pattern with a broad equatorial minimum and peaks at the poles. The results suggest an alternative to the hypothesis that insolation controls the large-scale patterns of heat flux and zonal flow on the gas giants. Instead, we propose that the large-scale thermal and zonal flow fields originate deep within the planets' molecular envelopes.

Dynamo Models for Planets Other Than Earth

“…A recent model by Stanley (2008) employs an outer thermal boundary condition on the dynamo model to mimic the effect of laterally varying solar insolation, or alternatively, the thermal perturbations naturally produced by convection in Saturn's non-metallic outer layers (Aurnou et al 2008). They find that the surface magnetic fields can be axisymmetrized through these zonal flows, but only when the boundary thermal perturbations result in thermal winds matching the sign and morphology of those already occurring in the deeper interior.…”

Implications of the ammonia distribution on Jupiter from 1 to 100 bars as measured by the Juno microwave radiometer

“…The above discussion uses the primitive equations, which are valid for thin atmospheric layers. There are also published models of fully 3-D thermal convection between rotating spherical shells whose spacing is a significant fraction of the planetary radius [e.g., Roberts, 1968;Busse, 1970;Glatzmaier et al, 2009;Christensen, 2002;Aurnou et al, 2008;Kaspi et al, 2009;Heimpel et al, 2016]. The 3-D models have positive u 0 w 0 below the surface at the equator and are successful in producing an eastward zonal jet there.…”

Convective heat transfer in planetary dynamo models

“…Such flows are not typically observed in plane layer convection. Strong shearing in these zonal flows can influence heat transfer from inner to outer boundary [ Aurnou et al , 2008]. Despite these possible complications, a meta‐analysis by Aurnou [2007] shows that heat transfer scaling behavior may not strongly differ between the plane layer and spherical shell geometries.…”