By: Boris Galperin, USF CMS Associate Professor
Unraveling the physics of large-scale planetary features takes patience and time. For several years, my colleagues around the globe and I have taken scores of steps forward in developing a theory of hydrodynamic circulation on the gas giants, Jupiter, Saturn, and beyond.
Our research has been theoretical, numerical, and experimental. We summarized the results in the book Zonal Jets, published by Cambridge University Press, which I co-edited with Professor Peter Read of the Oxford University. We’ve been getting there – slowly and steadily – which is why I’m particularly excited about a new publication by French colleagues in the journal Icarus, which is as close to a giant leapfrog advance in the field of turbulence as we could possibly imagine. They performed laboratory experiments that confirmed practically all our major results, both quantitatively and even qualitatively. This is the equivalent of a “mic drop” in physics.
A little background will help.
We have discovered a new flow regime of anisotropic turbulence, which we call “zonostrophic turbulence.” We have shown that this regime is behind the generation and maintenance of zonal jets and, thus, the striped appearance of Jovian and Saturnian disks. Zonal jets, which are east-west bands powered by large-scale, concentrated currents, are also present in the ocean although those are weaker and more chaotic than their gas giants’ counterparts.
It has been a thrilling exercise as a physicist must not only explain zonal jets qualitatively but quantitatively as well. We identified the regime of zonostrophic turbulence in the data collected by the Cassini spacecraft as it was surveying Jupiter. Today, the notion of zonostrophic turbulence has become as important for understanding the circulation on giant planets as geostrophic turbulence is for terrestrial planets. (As a reminder, geostrophic turbulence has been used as a simpler, quasi-two-dimensional model of large-scale planetary and terrestrial circulations.)
While we were able to perform experimental investigation of zonal jets in a laboratory facility of the Sapienza University in Rome, Italy, the device was not large enough to explore a large parameter range. Furthermore, we needed to employ some special techniques to produce strong jets.
And now we can return to the mic drop. A team of scientists at the University of Marseilles led by Dr. Daphne Lemasquerier, now at the University of St. Andrews, has just published the results of their experiments in a rapidly rotating, deep cylindrical tank filled with water. This device was used to perform a series of experiments that examine – in three dimensions – the main tenets of the regime of zonostrophic turbulence. The uniquely designed device was large enough to explore this regime over a broader parameter range. This very detailed independent investigation has confirmed our main results not only qualitatively but also quantitatively. Thus, this paper delivers another piece of convincing evidence in favor of the theory of zonostrophic turbulence and its role in the explanation of the physics of zonal jets and, thus, circulation on giant planets.
Our work continues!