Paula Wulff - Driving and quenching of zonal flows on gas giants - IPAM at UCLA

Recorded 30 January 2025. Paula Wulff of the University of California, Los Angeles, presents "Driving and quenching of zonal flows on gas giants" at IPAM's Rotating Turbulence: Interplay and Separability of Bulk and Boundary Dynamics Workshop.
Abstract: Both Jupiter and Saturn host fierce east-west winds in their outer convective envelopes, which can be measured at the surface. Gravity measurements from Juno and Cassini have provided constraints on the extent of these jets into the planets’ interiors. 3D (magneto)hydrodynamic simulations can help us to understand both the driving of the zonal winds in gas giant atmospheres as well as the mechanisms that may explain their truncation at depth. We find that the main driving of the jets is associated with upscale transfer directly from the small convective scales to the jets. This transfer is very non-local in spectral space, bypassing large-scale structures. The jet formation is thus not driven by an inverse cascade. Instead, it is due to a direct driving by Reynolds stresses, statistical correlations of velocity components of the small-scale convective flows. Our simulations also indicate the presence of a stably stratified layer at the base of the zonal winds, acting as a lower boundary which is crucial in braking the jets at the depths inferred by the gravity measurements.
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