Jovian Auroral Radio Sources Detected In Situ by Juno/Waves: Comparisons With Model Auroral Ovals and Simultaneous HST FUV Images

Abstract

Since the discovery of Jovian auroral radio emissions, the question arises of the source positions of the different components (broadband kilometric, hectometric, and decametric) and their association with far ultraviolet (FUV) auroral emissions. We surveyed Juno's first 15 perijoves to track local radio sources from in situ Juno/Waves measurements (50 Hz to 40 MHz). This allowed us to study the 3‐D spatial distribution of the broadband kilometric, hectometric, and decametric radio sources. These sources are carried by the same magnetic field lines, with the bulk of them at apex M ranging from 15 to 60 (distance measured in RJ at the magnetic equator). Finally, comparisons with images of the Jovian FUV aurorae simultaneously acquired by the Hubble Space Telescope (HST) reveal a partial spatial colocation of the FUV main oval emission with the identified local radio sources.

Ganymede‐Induced Decametric Radio Emission: In Situ Observations and Measurements by Juno

“…The loss cone-driven CMI then seems to be a common way to amplify waves and produce radio emissions, sustained by an Alfvénic acceleration process in the case of auroral radio emissions (Louarn et al, 2017(Louarn et al, , 2018 as in the case of moon-induced radio emissions (present study). The next step should be to study the more numerous radio source crossings of Io's tail (Louis et al, 2019;Szalay et al, 2018Szalay et al, , 2020b, in order to explain (i) how radio emission can be produced tens of degrees away from the MAW spot, (ii) why these radio emissions are not observed from a distant point of view, and (iii) how the electron distribution function and the radio emission intensity evolve with distance from the MAW spot.…”

“…In particular, the instruments Waves (radio and plasma waves, Kurth et al, 2017), JADE‐E (Jovian Auroral Distributions Experiment‐Electrons, McComas et al, 2017), and MAG (Magnetometer, Connerney et al, 2017) offer a unique opportunity to investigate in situ the Jovian radio emissions produced in these polar regions. These instruments enable constraints on the position of the sources (Imai et al, 2017, 2019; Louis et al, 2019) and the mechanism producing these emissions (Louarn et al, 2017, 2018), the cyclotron maser instability (CMI), which is also responsible for the production of the auroral kilometric radiation at Earth and Saturn (Le Queau et al, 1984a, 1984b; Pritchett, 1986a; Treumann, 2006; Wu, 1985; Wu & Lee, 1979).…”

A New Framework to Explain Changes in Io's Footprint Tail Electron Fluxes

“…Of these features, Io's auroral signature is one of the most persistent and identifiable auroras, with a rich observational history spanning decades. Remote measurements of Io's interaction with Jupiter have covered a variety of wavelengths: radio (e.g., Bigg, 1964; Dulk, 1965; Hess et al, 2009; Louis et al, 2017, 2019; Warwick et al, 1979; Zarka, 1998, 2007; Zarka et al, 2018), ultraviolet (e.g., Bonfond, Grodent, et al, 2017; Bonfond, Saur, et al, 2017; Bonfond et al, 2008, 2009, 2013; Clarke et al, 1996), infrared (e.g., Connerney et al, 1993; Mura et al, 2018; Radioti et al, 2013), and visible (e.g., Ingersoll et al, 1998).…”

Ganymede--induced decametric radio emission: in-situ observations and measurements by Juno

“…The loss-cone-driven CMI then seems to be a common way to amplify waves and produce radio emissions, sustained by an Alfvénic acceleration process in the case of auroral radio emissions (Louarn et al, 2017(Louarn et al, , 2018 as in the case of moon-induced radio emissions (present study). The next step should be to study the more numerous radio source crossings of Io's tail (Szalay et al, 2018;Louis et al, 2019;Szalay et al, 2020b), in order to explain (i) how radio emission can be produced 10s of degrees away from the main Alfvén Wing spot, (ii) why these radio emissions are not observed from a distant point of view and (iii) how the electron distribution function and the radio emission intensity evolve with distance from the Main Alfvén Wing spot.…”

“…In particular the instruments Waves (radio and plasma waves, Kurth et al, 2017), JADE-E (Jovian Auroral Distributions Experiment -Electrons, McComas et al, 2017) and MAG (Magnetometer , Connerney et al, 2017) offer a unique opportunity to investigate in-situ the Jovian radio emissions produced in these polar regions. These instruments enable constraints on the position of the sources (Louis et al, 2019;Imai et al, 2017Imai et al, , 2019 and the mechanism producing these emissions (Louarn et al, 2017(Louarn et al, , 2018, the Cyclotron Maser Instability (CMI), which is also responsible for the production of the auroral kilometric radiation at Earth and Saturn (Treumann, 2006;Wu, 1985;Wu & Lee, 1979;Le Queau et al, 1984b, 1984aPritchett, 1986a). This instability produces emissions very close to the electron cyclotron frequency f ce , and requires two primary conditions: (i) a magnetized plasma, where the electron plasma frequency f pe (proportional to the square root of the electron plasma density n e ) is much lower than the electron cyclotron frequency f ce (proportional to the magnetic field amplitude B); and (ii) a weakly relativistic electron population previously accelerated along high-latitude magnetic field lines at typical energies of a few keV.…”