5:15 PM - 7:15 PM
[MGI30-P09] Anelastic thermal convection in a rapidly rotating spherical shell and surface banded structures of the Jovian planets
Keywords:Jovian planets, anelastic system, mean zonal flows, banded structure
The banded structures composed of alternating zonal jets observed in the surface atmospheres of Jupiter and Saturn have attracted many researchers in planetary atmospheric sciences. However, a satisfactory physical understanding has not yet been obtained. In this study, we perform massive parallel numerical experiments treating both small-scale convection and planetary-scale flows simultaneously, reveal fine structures of turbulent motions that have not yet been resolved by the previous numerical models, and try to illustrate the dynamical origin of global-scale structures of surface flows of Jovian planets.
We focus on the “deep” model, which explains the zonal wind patterns in the atmospheres of the giant planets. In this “deep” model, the redistribution of angular momentum due to thermal convection inside the rotating gas planet is thought to cause the zonal structure on the surface. It is easy to generate a prograde jet in the equatorial region. However, generating a group of jets that reverses alternately in the middle and high latitude regions is difficult. Recently, it has been shown that even in the “deep” model, by making the thickness of the convection shell as thin as possible compared to the planetary radius, small-scale convective activity can be generated and maintained within the inner spherical shell, and as a result, alternating jets in the middle and high latitudes can be generated (e.g. in Boussinesq fluids, Heimpel and Aurnou 2007, in anelastic fluids, Heimpel et al. 2022).
However, we pointed out that the time integral (1600 rotation time) in past research on the Boussinesq system is short, at most about 0.1 viscous time, and that there is a possibility that the system has not reached equilibrium as a whole and that by performing a long-time integration, we found that multiple zonal jets in the middle and high latitudes, which were seen at a time of around 0.1 viscous time, would merge over time, and that after 16,000 rotation times, there would be a single forward jet, and the banded structure in the middle and high latitudes would disappear (Takehiro et al., 2024).
We expect the same long-time evolution as the Boussinesq system may occur in the anelastic system. In this study, we perform long-time numerical simulations of thermal convection in a thin rotating spherical shell in the whole global domain with the anelastic system by following the setup of Heimpel et al. (2022), which is the most realistic and highest-resolution simulation of Jovian-type atmospheric circulation using the anelastic system. We focus on whether the banded structure disappears after a long time due to merging multiple jets in middle and high latitudes. Our results show the emergence of an intense broad equatorial jet and many narrow jets with alternating directions in the middle and high latitudes in the early stages. However, in a more extended time integration, the narrow alternating jets merged, and at 32,000 rotations, the number of jets was reduced to two prograde jets and one retrograde jet in the middle and high latitudes. Since the kinetic energy is still increasing and has not yet reached a statistical equilibrium, the jets may continue to merge. We will continue to carry out time integration and observe the transitions and properties of the banded structure.
References:
・Heimpel, M. H., Aurnou, J. M., 2007: Turbulent convection in rapidly rotating spherical shells: A model for equatorial and high latitude jets on Jupiter and Saturn. Icarus, 187, 540--557.
・Heimpel, M. H., Yadav, R. K., Featherstone, N. A., Aurnou, J. M., 2022: Polar and mid-latitude vortices and zonal flows on Jupiter and Saturn. Icarus, 379, 114942.
・Takehiro, S., Sasaki, Y., Ishioka, K., Enomoto, T., Nakajima, K., Hayashi, Y.-Y., 2024: Asymptotic profiles of mean zonal flows generated by thermal convetion of Boussinesq fluid in a rapidly rotating thin spherical shell. Icarus, 420, 116154.
We focus on the “deep” model, which explains the zonal wind patterns in the atmospheres of the giant planets. In this “deep” model, the redistribution of angular momentum due to thermal convection inside the rotating gas planet is thought to cause the zonal structure on the surface. It is easy to generate a prograde jet in the equatorial region. However, generating a group of jets that reverses alternately in the middle and high latitude regions is difficult. Recently, it has been shown that even in the “deep” model, by making the thickness of the convection shell as thin as possible compared to the planetary radius, small-scale convective activity can be generated and maintained within the inner spherical shell, and as a result, alternating jets in the middle and high latitudes can be generated (e.g. in Boussinesq fluids, Heimpel and Aurnou 2007, in anelastic fluids, Heimpel et al. 2022).
However, we pointed out that the time integral (1600 rotation time) in past research on the Boussinesq system is short, at most about 0.1 viscous time, and that there is a possibility that the system has not reached equilibrium as a whole and that by performing a long-time integration, we found that multiple zonal jets in the middle and high latitudes, which were seen at a time of around 0.1 viscous time, would merge over time, and that after 16,000 rotation times, there would be a single forward jet, and the banded structure in the middle and high latitudes would disappear (Takehiro et al., 2024).
We expect the same long-time evolution as the Boussinesq system may occur in the anelastic system. In this study, we perform long-time numerical simulations of thermal convection in a thin rotating spherical shell in the whole global domain with the anelastic system by following the setup of Heimpel et al. (2022), which is the most realistic and highest-resolution simulation of Jovian-type atmospheric circulation using the anelastic system. We focus on whether the banded structure disappears after a long time due to merging multiple jets in middle and high latitudes. Our results show the emergence of an intense broad equatorial jet and many narrow jets with alternating directions in the middle and high latitudes in the early stages. However, in a more extended time integration, the narrow alternating jets merged, and at 32,000 rotations, the number of jets was reduced to two prograde jets and one retrograde jet in the middle and high latitudes. Since the kinetic energy is still increasing and has not yet reached a statistical equilibrium, the jets may continue to merge. We will continue to carry out time integration and observe the transitions and properties of the banded structure.
References:
・Heimpel, M. H., Aurnou, J. M., 2007: Turbulent convection in rapidly rotating spherical shells: A model for equatorial and high latitude jets on Jupiter and Saturn. Icarus, 187, 540--557.
・Heimpel, M. H., Yadav, R. K., Featherstone, N. A., Aurnou, J. M., 2022: Polar and mid-latitude vortices and zonal flows on Jupiter and Saturn. Icarus, 379, 114942.
・Takehiro, S., Sasaki, Y., Ishioka, K., Enomoto, T., Nakajima, K., Hayashi, Y.-Y., 2024: Asymptotic profiles of mean zonal flows generated by thermal convetion of Boussinesq fluid in a rapidly rotating thin spherical shell. Icarus, 420, 116154.