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Self-Limited Moist Convection and Cloud Formation due to the Weak Planetary Heat Flux on Ice Giants

Presentation #409.03 in the session Uranus and Neptune Systems (Oral Presentation)

Published onOct 23, 2023
Self-Limited Moist Convection and Cloud Formation due to the Weak Planetary Heat Flux on Ice Giants

Storms driven by moist convection and the condensation of CH4 or H2S have been observed countless times on Uranus and Neptune, but their impact on cloud formation, thermal structure, and mixing efficiency at their weather layers remains unclear. We show that moist convection is self-limited by heat transport in ice giants. This effect is regulated by the dominant but previously overlooked heat transport mechanism: latent heat flux. Cloud formation and moist convection, associated with the condensation of cloud-forming species and evaporation of precipitations, can effectively deliver significant heat flow through latent heat. To this means, we first derive an analytical theory and show the upper limit of the cloud density is determined by the planetary heat flux and microphysics of clouds. The eddy diffusivity of CH4 and H2S only depends on the heat fluxes and temperature structure but is independent of the microphysics. We then conduct nonhydrostatic simulations using the SNAP model to validate our analytical theory. The cloud density and cloud-level eddy diffusivity from the numerical solution are consistent with our analytical theory and confirm that these new limits are smaller than the previous results by several orders of magnitude. Our simulations produced three cloud layers that are qualitatively consistent with the recent observations. This work has important implications for the future ice giant mission and observations, including the Uranus Orbiter Probe mission.

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