A theoretical study of parcel stability and cloud distribution in a Jovian hot spot

The Galileo probe penetrated Jupiter’s atmosphere at a hot spot, a region of unusual clarity and dryness centered at 7°N. The measured abundances of condensable species were puzzling since strong depletion of volatiles was found from 0.4 to 12 bar, far below the condensation levels. In this paper we explore in detail thermally driven dry downdraft scenarios to simulate hot spot conditions. We compare the hot spot temperature profile with that of surrounding areas to evaluate their relative buoyancy and the parcel level of descent. For the hot spot we use the vertical thermal profile and composition measured in situ by the Galileo probe, as well as the distribution of condensable species inferred by the NIMS experiment on board of the Galileo orbiter. The environment is characterized by the thermal profile measured by the Voyager 1 radio probe experiment down to 1 bar. Downward, the profile is extended adiabatically using different values for the ortho–para distribution of H2. Different concentrations of the condensables (relative humidity from 1 to 100%) were tested for the environment using a deep value (P>8 bar) of 1 to 4 times the solar abundance of NH3 and 1 to 2 times for H2O. Under these conditions, dry downdrafts can sink in Jupiter’s atmosphere to the ∼5 to 15 bar level depending on the particular values used. Conversely, in a second numerical experiment, we simulate the hot spot’s composition and temperature profiles measured by the Galileo probe using a downward dry jet entraining model. Qualitative agreement is found for different parameterizations of the entrainment rates. Furthermore, a thermochemical model predicts at the hot spot, the existence of a NH3 cloud with a base at ∼550 mbar and an NH4SH cloud with a base at ∼1.6 bar. Finally, the number of hot spots presented in a latitude circle could be related to the depth of the hot spot motions through the Rossby deformation radius.