A Possible Mechanism to Explain the Prograde Equatorial Jet of a Jupiter-like Gaseous Giant

Abstract

Gaseous giants are characterized by their deep atmospheres, which lack clear boundaries with their interiors; therefore, their internal states could directly influence atmospheric dynamics. So far, most modeling studies have considered deep convection as the primary mechanism by which the interior influences atmospheric dynamics. In this work, we propose another possible mechanism that might crucially determine the appearance of gaseous giants' atmospheric cloud-top jet winds, tracing them to a typical hydromagnetic wave (the so-called equatorial Magnetic-Archimedes-Coriolis wave) generated within the stably stratified, strongly magnetized helium rain layer. The associated thermal perturbations can propagate upward through the convective molecular hydrogen envelope, eventually affecting the atmospheric thermal structure - the zonal inhomogeneities that are conducive to the formation of the eastward atmospheric equatorial jet (super-rotation). Our results have important implications for understanding the equatorial dynamics of gaseous giants. This mechanism could also help explain the equatorial westward jets (sub-rotation) observed on Uranus and Neptune, which lack the helium rain layers.

Figures (6)

• Figure 1: The Jupiter-like gaseous giant reference states considered in our study. (a) Gravity $g$gastine-wicht-2021, (b) Electrical conductivity $\sigma$french-etal-2012, (c) Pressure $p_0$mil-2016, (d) Density $\rho_0$helled-2018, (e) Buoyancy frequency $N$, and (f) Equatorial magnetic field strength $B_0$connerneyzaghoo as a function of the fraction of radius. The shaded area is HRL.
• Figure 2: Equatorial confinement of eMAC waves. (a) Latitudinal distribution of eMAC waves in Eqn. \ref{['eqn:m1']} ($\tilde{\alpha}$ is set to be the real numbers). (b) Sketch of the normalized eMAC waves on the longitude-latitude plane with a stable-layer thickness of 3500 km and $m=1$.
• Figure 3: Zonal wind structure with a stable-layer thickness of 3500 km. (a) A snapshot of zonal-mean zonal wind on the latitude-pressure diagram at year 15 of the model run. Eastward winds are represented by positive values, while westward winds are represented by negative values. (b) A time-pressure diagram at the equator, showing the equatorial jet evolution. The quasi-periodic oscillation is located in the stratosphere, with a stable eastward jet in the troposphere.
• Figure 4: A sample of four generated zonal wind profiles at 0.3 bar in our simulations (colored line) with different thicknesses $H$ of stable layers. The pink dot-dashed line shows the simulation result without stable layers and eMAC wave forcing. The observed Jupiter's cloud-level wind is shown in black johnson.
• Figure 5: Vertical velocity in the equatorial region at 1 bar. The Chevron pattern exhibits a northwest-southeast tilt in the northern hemisphere.