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A laboratory model for a meandering zonal jet
  • Kial Douglas Stewart,
  • Fergus Macleod
Kial Douglas Stewart
Australian National University

Corresponding Author:[email protected]

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Fergus Macleod
Australian National University
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Abstract

The meandering jet streams of the Northern Hemisphere influence the weather for more than half of Earth’s population, so it is imperative that we improve our understanding of their behaviour and how they might respond to climate change. Here we describe a novel laboratory model for a meandering zonal jet. This model comprises a large rotating annulus with a series of topographic ridges, and an imposed radial vorticity flux. Flow interactions with the topographic ridges operate to concentrate the zonal transport into a narrow jet, which supports the development and propagation of Rossby waves. We investigate the dynamics of the jet for a range of rotation rates, imposed radial vorticity fluxes, and topographic ridge configurations. The circulations are classified into two distinct regimes: predominantly zonal, or predominantly meandering. The flow regime can be quantified by the ratio of the Ekman dissipation and jet advection timescales, which gives an indication of whether disturbances arising from the flow-topography interaction are dissipated faster than the time taken to circuit the annulus; if not, these disturbances will re-encounter the topography, and thus be reinforced and amplified. For predominantly zonal flows, the radial vorticity flux is mainly performed by transient eddies. For predominantly meandering flows, standing meanders perform 81+/-14% of the radial vorticity flux, with 15+/-16% accommodated by the transient eddies. Our experiments indicate that the Arctic amplification associated with climate change will tend to favour predominantly zonal flow conditions, suggesting a reduced occurrence of atmospheric blocking events caused by the jet streams.