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DESCRIPTION:Speaker: Professor Peter Read, University of Oxford.  Title: Baroclinic Turbulence in the Laboratory - A Tale of Two Flow Regimes Abstract: Baroclinic turbulence is a form of geostrophic turbulence in a stably-stratified, rotating fluid that is energised by baroclinic instability. It represents an idealised paradigm for the macroturbulent flow in a planetary atmosphere or ocean on scales from km up to that of the planet itself and is characterised by power law energy spectra and complex dual cascades of energy and (potential) enstrophy. Aspects of the kinetic energy spectra and scale to scale energy transfers, even in the Earth’s atmosphere, are still controversial and challenging to measure reliably, and it is not well understood how these properties of the circulation might differ on other planets, especially on gas giants like Jupiter and Saturn. Here we explore the properties of baroclinic turbulence in well controlled laboratory experiments in rotating cylindrical tanks under a wide range of conditions. Detailed velocity fields are measured by particle image velocimetry, together with temperature profiles via thermistor probes. Depending upon the strength of “planetary vorticity gradients” or the beta-effect (produced topographically in the laboratory), two distinct types of regime are found. With a weak beta effect and moderate rotation, a KE spectrum resembling that in the Earth’s upper troposphere is found, with enstrophy-dominated KE spectra that scale as k-3 at large scales. With a strong beta-effect and fast rotation, however, the KE spectra are anisotropic at large scales with steep (k-5) zonally symmetric KE spectra and shallower (~k-5/3?) residual (non-axisymmetric) spectra, also forming Jupiter-like multiple jets that dominate the KE budget. The experiments also reveal an unexpected dependence of spectra and scale to scale fluxes on the stratification, with possible geophysical and astrophysical implications.   768793
DTSTAMP:20260604T100308
DTSTART:20260610T133000
DTEND:20260610T143000
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SUMMARY;LANGUAGE=en-us:GAFD Seminar: Peter Read (University of Oxford) 
UID:d5ddaf8ed11667c4303d50804054639f@www.exeter.ac.uk
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