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Les émissions radio aurorales de Jupiter : observations à distance, in-situ et simulations

Abstract : This thesis focused on the study of Jupiter’s auroral radio emissions, produced close to the local electronic cyclotron frequency by the Maser Cyclotron instability powered by resonant electrons of a few keV, accelerated along high magnetic field lines at high latitude. I first took over, validated and extended the simulation code ExPRES (Exoplanetary and Planetary Radio Emissions Simulator) developed at LESIA, which allows us to pro- duce dynamic spectra of auroral radio emissions visible for a given observer. I performed a parametric study of the simulations of radio emissions induced by Io in order to quantify the role of ExPRES free parameters (distribution function and energy of the electrons, magnetic field model, position of the active magnetic field line and altitude of the ionos- pheric cutoff). This study confirmed that Io emissions are correctly reproduced only when the radiation is oblique to the magnetic field lines, which is simulated by ExPRES through loss cone electronic distribution functions. I have also shown that (a) the parameters that mainly control the shape of the simulated emissions in the time-frequency plane are the magnetic field model and the electron energy, and that (b) the simulations are in excellent agreement with observations, with a time window of uncertainty of ±2 hours. Using this code, I produced long-term simulations of radio emissions induced by Io, and those expected for Europa, Ganymede and Callisto. Comparing these simulations with several years of Jupiter observations recorded with the Voyager / PRA and Cassini / RPWS instruments (punctually supplemented by those of the Nançay decameter array), I proved the existence of radio emissions induced by Europa and Ganymede. The statistical study of these signatures allowed me to measure their average properties (extension in frequency, temporal variability, and occurrence). This result opens a new field of study of planet-satellite interactions other than Io-Jupiter. The comparison of these simulations with the Juno / Waves observations allowed me to unambiguously identify the radio emissions induced by Io, as well as their hemisphere of origin (without knowing their polarization, not measured by Juno / Waves), for an observer close to the equator (case of the Earth) and at higher latitudes. Thanks to these simulations, I have also shown that the emissions are visible only if the opening of the emission angle is greater than 70 ̊± 5 ̊ and if the observer is in the same magnetic hemisphere as the sources. Finally, I began a statistical study of the spatial distribution of auroral radio sources traversed by the Juno probe. I thus mapped the sources of the various components (kilo- meter to HF) of Jovian radio broadcasts. Comparison with recent magnetic field models, as well as UV imagery (Juno / UVS and Hubble / STIS) allowed me to show that they are colocated with the main auroral oval.
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Submitted on : Thursday, December 13, 2018 - 12:56:32 PM
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  • HAL Id : tel-01953894, version 1


Corentin Louis. Les émissions radio aurorales de Jupiter : observations à distance, in-situ et simulations. Astrophysique [astro-ph]. Université Paris Sciences et Lettres; Observatoire de Paris – LESIA, 2018. Français. ⟨tel-01953894⟩



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