A laboratory model for deep-seated jets on the gas giants

Abstract

The strong east-west jet flows on the gas giants, Jupiter Azimuthally directed (that is, zonal, east-west) jet flows are one of the dominant characteristics in the surficial cloud features observed on the gas giants, Jupiter and Saturn. An essential question of planetary dynamics and structure is whether these jet motions exist only within the shallow troposphere or extend through the molecular envelope that exists above the deeper dynamo region 3 . Determining the depth of these atmospheric jets is one of the prime directives of the NASA (National Aeronautics and Space Administration) Juno mission, which entered into low-altitude Jovian orbit in August 2016 4 . Despite the long-lived scientific interest in these flows, dominant multiple jets have been problematic in fully three-dimensional (3D) numerical models of convection. In particular, multiple banded flows are not found in the most recent, high-resolution models that couple the molecular envelope to the deeper dynamo region. In these models, magnetic dissipation damps the higher-latitude deep jets out of existence [5][6][7] . Similarly, dissipation has also proved overly important in laboratory experiments carried out to date. Laboratory approaches were analysed in the framework of the shallow-layer model and strong viscous damping by the container boundaries only allows for the formation of weak zonal jets with tenuous instantaneous signatures [8][9][10][11][12][13][14] . Thus, it has yet to be demonstrated, as proposed for the gas giant planets 15 , that deep zonally dominant jet flows can exist in the presence of boundary dissipation.We have developed a new laboratory experimental device that is capable of generating strong zonal jets despite viscous friction on the boundaries (Fig. 1a). The working fluid is water, contained in a 1.37-m-high by 1-m-diameter cylindrical tank. The depth of the fluid layer is h o = 50 cm at rest, and the tank's rotation rate is Ω = 7.85 rad s −1 (75 revolutions per minute). Once equilibrated at Ω, the water's free surface takes the shape of a paraboloid, with the fluid layer depth ranging from h min 20 cm on the axis of rotation to h max 90 cm at the tank's outer radius. This rotating surface shape is analogous to the large-scale curvature of a deep spherical planetary fluid layer 16,17 . In addition, the rotation provides strong Coriolis forces, as exist in planetary settings. Once solid body rotation is reached, a submersible pump situated at the base of the tank is turned on, and small-scale turbulence is injected at the base of the fluid layer. The pump continuously circulates water through a lattice of 32 outlets (4 mm diameter) and 32 inlets (2 mm diameter) arranged on a flat base plate without any axisymmetric features (see the injection pattern in Supplementary Fig. 1a). Typical root-mean-square (r.m.s.) fluctuating velocities are in the range u r.m.s. 1-5 cm s −1 . This small-scale turbulence is analogous to the convective turbulence that exists in deep planetary interiors 18,19 and constitutes an appropriate s...

Global climate modeling of Saturn's atmosphere. Part III: Global statistical picture of zonostrophic turbulence in high-resolution 3D-turbulent simulations

“…This length scale compares two processes that are competing in the system: the flow capacity to transfer energy uspscale through the value of (which depends on how flow bi-dimensionalization is efficiently set) versus its ability to channel energy in the zonal direction through parameter β (here, the parameter β is estimated at mid-latitude ϕ = 45 • ). In simulations assuming 2D barotropic flows, Sukoriansky et al (2008) and Galperin et al (2010) Galperin et al (2014) and Cabanes et al (2017Cabanes et al ( , 2018 find ≈ 0.75 using observed Jupiter wind fields and laboratory experiments, respectively.…”

Acoustic spectra of a gas-filled rotating spheroid

“…Interested in zonal jets, their formation, geometry, and amplitude in geo-astrophysical flows [13][14][15] , we built a reduced model that obeys the similar force balances. Our apparatus is a rotating oblate spheroid called ZoRo (Zonal flows in Rotating fluids).…”

Multiple zonal jets and convective heat transport barriers in a quasi-geostrophic model of planetary cores

“…Schou et al, 1998;Porco et al, 2003;Livermore et al, 2017) has prompted much effort dedicated to their study, and in particular, their width and amplitude (e.g. Christensen, 2002;Gillet et al, 2007;Read et al, 2015;Cabanes et al, 2017). Although zonal flows (and shear flows in general) do not transport heat outwards, they strongly affect the convection because they can deflect and shear the convective flows, thereby reducing the efficiency of the heat transfer (e.g.…”