Geophysical and Astrophysical Fluid Dynamics

Abstract:

Recent Juno microwave observations have revealed puzzling features of Jupiter’s ammonia distribution, including an ammonia-poor layer extending down to levels of tens of bars outside the equatorial region to at least ±40° [Li et al. 2017]. Guillot et al. [2020] showed that ammonia-rich hail, or “mushballs”, formed during a powerful thunderstorm, can efficiently transport ammonia to the deeper atmosphere and hence could cause the observed ammonia depletion. However, this mechanism has not been tested in numerical simulations in which convective events are self-consistently determined. We have developed a simple parameterization scheme for the mushball process and implemented it into a Jupiter GCM [Young et al. 2019] that includes the following relevant parameterizations: a simple cloud microphysics model for water and ammonia, a water moist convection scheme that transports ammonia as a passive tracer, a dry convection scheme, and a two-stream, semi-grey radiative transfer scheme. In the two-dimensional setup of the aforementioned GCM, we show that mushball precipitation can produce an ammonia depletion qualitatively similar to the Juno observations.We present our preliminary results in three-dimensional simulations, in which a Jupiter-like zonal jet profile emerges spontaneously. We will show the role of different processes, including the mushball process, moist convection and meridional circulation in shaping ammonia distribution. Further, we compare our model output with Juno MWR result, and discuss the implication to future observations.

Abstract:

We measure baroclinic eddy heat transport in a differentially heated rotating annulus laboratory experiment to test mesoscale ocean eddy parameterization frameworks. The differentially heated rotating annulus comprises a fluid placed between two upright coaxial cylinders which are maintained at different temperatures, usually with a cooled inner cylinder and a heated outer.  The annular tank is placed on a rotating table which provides conditions for baroclinic eddies to develop and equilibrate in different flow regimes, depending upon the imposed conditions. As the rotation speed is increased, the equilibrated flow changes from a steady or periodically varying low wavenumber pattern to a more complex, time-varying flow dominated by higher wavenumbers. With a topographic beta effect produced by conically sloping upper boundary, more complex flow regimes are observed combining zonal jets and eddies forming one or more parallel storm tracks. With this possibility to explore varied flow regimes, our experimental approach combines laboratory calorimetry and visualization measurements along with numerical simulations to derive the eddy heat transport properties. In the following, we focus on the visualisation measurement to test related assumptions and parametric dependencies for eddy transport. We first test the assumptions of a down-gradient temperature flux-gradient relationship, determining coefficients of the eddy transport tensor, and exploring scaling relations for the eddy coefficients. A clear statistical scaling is found between eddy heat fluxes and physical variables such as eddy energy, the beta effect, and the temperature contrast.

Abstract:

Recent Juno microwave observations revealed some puzzling features of the ammonia distribution. In particular, an ammonia-poor layer extends down to levels of tens of bars in Jupiter outside the equatorial region to at least ±40^° [Li et al. 2017]. Such a depletion has not yet emerged in general circulation models (GCMs). Guillot et al. [2020] showed that ammonia vapour can dissolve in water ice within violent storms, forming ammonia-rich hail, or "mushballs", that leads to an efficient transport of ammonia to the deeper atmosphere and hence its observed depletion. However, this mechanism has not been tested in numerical simulations in which convective events are self-consistently determined. 

We present a simple parameterization scheme for the mushball process. Our scheme determines the mushball concentration using the water-ammonia equilibrium phase diagram, and considers the transport of water and ammonia due to its associated downdraft. We implemented this scheme to a GCM based on the MITgcm [Young et al. 2019] that includes the following key parameterizations: a water moist convection scheme, a simple cloud microphysics model for water and ammonia, a dry convection scheme, and a two-stream radiative transfer scheme. We present our preliminary results using water and ammonia abundance according to Juno observations. Further, we discuss the ability of the "mushball" scheme to reproduce the Juno observations and explore which parameters are the most important to understand the ammonia distribution in the deep layers of Jupiter.