Power Spectral Analysis of Jupiter's Clouds and Kinetic Energy from Cassini

TL;DR

This study analyzes Jupiter's atmospheric dynamics using Cassini data, revealing turbulence-like spectral slopes and emphasizing the importance of full 2D velocity maps for accurate kinetic energy spectra interpretation.

Contribution

It provides the first detailed power spectral analysis of Jupiter's clouds and kinetic energy using full 2D velocity maps from Cassini observations, highlighting turbulence characteristics.

Findings

Power spectra resemble 2D turbulence with slopes near -5/3 and -3.

Full 2D velocity maps are crucial for accurate spectral analysis.

Variations in kinetic energy are linked to features like hotspots and the Great Red Spot.

Abstract

We present suggestive evidence for an inverse energy cascade within Jupiter's atmosphere through a calculation of the power spectrum of its kinetic energy and its cloud patterns. Using Cassini observations, we composed full-longitudinal mosaics of Jupiter's atmosphere at several wavelengths. We also utilized image pairs derived from these observations to generate full-longitudinal maps of wind vectors and atmospheric kinetic energy within Jupiter's troposphere. We computed power spectra of the image mosaics and kinetic energy maps using spherical harmonic analysis. Power spectra of Jupiter's cloud patterns imaged at certain wavelengths resemble theoretical spectra of two-dimensional turbulence, with power-law slopes near -5/3 and -3 at low and high wavenumbers, respectively. The slopes of the kinetic energy power spectrum are also near -5/3 at low wavenumbers. At high wavenumbers, however, the spectral slopes are relatively flatter than the theoretical prediction of -3. Our results also show the importance of calculating spectral slopes from full 2D velocity maps rather than 1D zonal mean velocity profiles, since at large wavenumbers the spectra differ significantly, though at low wavenumbers, the 1D zonal and full 2D kinetic energy spectra are practically indistinguishable. Furthermore, the difference between the image and kinetic energy spectra suggests some caution in the interpretation of power spectrum results solely from image mosaics and its significance for the underlying dynamics. Finally, we also report prominent variations in kinetic energy within the equatorial jet stream that appear to be associated with the 5 {\mu}m hotspots. Other eddies are present within the flow collar of the Great Red Spot, suggesting caution when interpreting snapshots of the flow inside these features as representative of a time-averaged state.