AOPP Seminar - Jupiters on Earth

Cyclostrophic rotation in the core region of tropical cyclones imprints a distinct signature upon their turbulence structure. Its intensity is characterized by the radius of maximum wind, Rm, and the azimuthal wind velocity at that radius, Um. The corresponding cyclostrophic Coriolis parameter, 𝑓𝑓̂ = 2 𝑈𝑈𝑚𝑚 𝑅𝑅𝑚𝑚 , far exceeds its planetary counterpart, ƒ, for all storms, and its impact increases with storm intensity. The vortex can be thought of as a system undergoing a superposition of planetary and cyclostrophic rotations represented by the effective Coriolis parameter, 𝑓𝑓̃ = 𝑓𝑓̂ + 𝑓𝑓. On the vortex periphery, 𝑓𝑓̃ merges with ƒ. In the classical Rankine vortex model, the inner region undergoes solid-body rotation rendering 𝑓𝑓̂ constant. In a more realistic representation, 𝑓𝑓̂ is not constant, and the ensuing cyclostrophic β-effect sustains vortex Rossby waves. Horizontal turbulence in such a system can be quantified by a two-dimensional anisotropic spectrum. An alternative description is provided by one-dimensional, longitudinal and transverse spectra computed along the radial direction. For rotating turbulence with vortex Rossby waves, the spectra divulge a coexistence of three ranges: Kolmogorov, peristrophic (spectral amplitudes are proportional to 𝑓𝑓̃2), and zonostrophic (transverse spectrum amplitude is proportional to 𝛽𝛽̂2). A comprehensive database of tropical cyclone winds collected by reconnaissance airplanes reveals that with increasing storm intensity, their cyclostrophic turbulence evolves from purely peristrophic to mixed peristrophic-zonostrophic to predominantly zonostrophic. The latter is akin to the flow regime harboring zonal jets on fast rotating giant planets. The width of the eyewall of tropical cyclones scales with the cyclostrophic Rhines scale, and along with the zonostrophic spectrum within it, this constitutes virtual equivalence between an eyewall and Jovian jets. Hence, Earth’s hurricanes and typhoons can be viewed as Jupiters on Earth.