Turbulence Power Spectra in Regions Surrounding Jupiter's South Polar Cyclones From Juno/JIRAM

Abstract

We present a power spectral analysis of two narrow annular regions near Jupiter's South Pole derived from data acquired by the Jovian Infrared Auroral Mapper instrument onboard NASA's Juno mission. In particular, our analysis focuses on the data set acquired by the Jovian Infrared Auroral Mapper M‐band imager (hereafter IMG‐M) that probes Jupiter's thermal emission in a spectral window centered at 4.8 μm. We analyze the power spectral densities of circular paths outside and inside of cyclones on images acquired during six Juno perijoves. The typical spatial resolution is around 55 km pixel−1. We limited our analysis to six acquisitions of the South Pole from February 2017 to May 2018. The power spectral densities both outside and inside the circumpolar ring seem to follow two different power laws. The wave numbers follow average power laws of −0.9 ± 0.2 (inside) and −1.2 ± 0.2 (outside) and of −3.2 ± 0.3 (inside) and −3.4 ± 0.2 (outside), respectively, beneath and above the transition in slope located at ~2 × 10−3 km−1 wave number. This kind of spectral behavior is typical of two‐dimensional turbulence. We interpret the 500 km length scale, corresponding to the transition in slope, as the Rossby deformation radius. It is compatible with the dimensions of a subset of eddy features visible in the regions analyzed, suggesting that a baroclinic instability may exist. If so, it means that the quasi‐geostrophic approximation is valid in this context.

Moist convection drives an upscale energy transfer at Jovian high latitudes

“…3b). This can also be understood with equation (6), in which a small χ-variance corresponds to a small stretching.…”

“…Thus, JIRAM observations are not taken along a constant pressure surface and cannot be directly converted into a potential temperature from which one can infer horizontal motions at the tropopause, as done by ref 17 for the Earth. Consequently, instead of directly using I, we use the optical depth, a proxy of cloud thickness 2,6 . The optical depth is computed as τ a = log(I 0 /I), with I 0 = 0.55946 W.m −2 the maximum brightness measured in the infrared mosaic n02 displayed in Fig.…”

“…The optical depth is computed as τ a = log(I 0 /I), with I 0 = 0.55946 W.m −2 the maximum brightness measured in the infrared mosaic n02 displayed in Fig. 2a, following refs 2,6 . In this study, we define the optical depth anomaly τ as τ = τ a − τ a , with.…”

Turbulence in Large-Scale Two-Dimensional Balanced Hard Sphere Gas Flow

“…The subsequent time-averaging of the modulus of the Fourier transform was computed between t = 24 and t = 72 h. As we can see in Figure 3, Kolmogorov's famous k −5/3 -decay of the kinetic energy spectrum occurs roughly between the wavenumbers 8 and 50; for smaller scales, the k −8/3 -decay is observed. Similar spectra, with two different powers of decay at different ranges of wavenumbers, have been registered in the Jovian atmosphere [33,34]. Despite promising results in simulating turbulent motions of the velocity, our model also has its limitations.…”

Spatial spectrum of temperature fluctuations in buoyancy driven chaotic and turbulent atmosphere

“…The recent papers Refs. [42], [43] reported an analysis of the data obtained with the Jovian Infrared Auroral Mapper (JIRAM) onboard the Juno mission for the Jupiter's South Pole atmosphere. Figure 29 shows an example of the power spectra for the mid-infrared (thermal) emission for Jupiter's south polar atmosphere (the latitudes higher than 82 o S).…”