Observation of Turbulent Magnetohydrodynamic Cascade in the Jovian Magnetosheath

Abstract

We present the first estimation of the energy cascade rate in Jupiter’s magnetosheath (MS). We use in situ observations from the Jovian Auroral Distributions Experiment and the magnetometer investigation instruments on board the Juno spacecraft, in concert with two recent compressible models, to investigate the cascade rate in the magnetohydrodynamic (MHD) scales. While a high level of compressible density fluctuations is observed in the Jovian MS, a constant energy flux exists in the MHD inertial range. The compressible isothermal and polytropic energy cascade rates increase in the MHD range when density fluctuations are present. We find that the energy cascade rate in Jupiter’s magnetosheath is at least 2 orders of magnitude (100 times) smaller than the corresponding typical value in the Earth’s magnetosheath.

Jovian Magnetosheath Turbulence Driven by Whistler

“…The spectrum further reveals an inertial range with a spectral slope of −1.4 and a spectral knee at around ion gyroradius ρ i , followed by a relatively steeper spectrum with a spectral index of k −2.6 at smaller scales. Similar behavior is reported in the spectrum observed by Bandyopadhyay et al (2021) and Andrés et al (2023) [47,48]. Both studies reported the presence of Kolmogorov-type turbulence; however, the spectral break was only observed by Andrés et al (2023) [47].…”

“…Similar behavior is reported in the spectrum observed by Bandyopadhyay et al (2021) and Andrés et al (2023) [47,48]. Both studies reported the presence of Kolmogorov-type turbulence; however, the spectral break was only observed by Andrés et al (2023) [47]. In addition, they observed steepening in the magnetic field spectrum near ion gyroradius ρ i , indicating the presence of dissipative processes.…”

“…It is important to note that figure 3 is merely a drawing with arbitrary tick labels created for qualitative description and interpretation of the results. One can notice that the theoretical magnetic field spectrum quite confirms the presence of spectral knee, which is also observed by Juno spacecraft [47]. However, it is evident that after the spectral knee in the theoretical spectrum, the spectrum gets steeper with the spectral slope −4.2.…”

“…The spectral slope at the larger scale is −1.4 and the spectral slope value at the smaller scale is equal to −2.6. The corresponding spectral slope values estimated theoretically in the frequency domain i.e., −1.8 and −4.2 are much steeper than what has been found in the observation [47,48], respectively at low and high frequencies. In figure 3, we present a comparative sketch between an observational broadband spectrum, and a predicted turbulence spectrum of the whistler wave in the frequency domain to highlight the main observations.…”

“…The role of whistler waves in the turbulent cascade is very crucial in various regions in space [39,[44][45][46]. In a recent study, Andrés et al (2023) [47] investigated the energy cascade rate in the magnetohydrodynamic (MHD) scales in Jupiter's magnetosheath using in situ observations from the Juno mission in Jupiterʼs magnetosphere and compressible exact relations. Bandyopadhyay et al (2021) [48] examined the fluid-scale turbulence in the Jupiter's magnetosheath using in situ measurements from the Jovian Auroral Distributions Experiments (JADE) instrument onboard Juno spacecraft.…”