A new view of Jupiter's auroral radio spectrum

Abstract

Juno's first perijove science observations were carried out on 27 August 2016. The 90° orbit inclination and 4163 km periapsis altitude provide the first opportunity to explore Jupiter's polar magnetosphere. A radio and plasma wave instrument on Juno called Waves provided a new view of Jupiter's auroral radio emissions from near 10 kHz to ~30 MHz. This frequency range covers the classically named decametric, hectometric, and broadband kilometric radio emissions, and Juno observations showed much of this entire spectrum to consist of V‐shaped emissions in frequency‐time space with intensified vertices located very close to the electron cyclotron frequency. The proximity of the radio emissions to the cyclotron frequency along with loss cone features in the energetic electron distribution strongly suggests that Juno passed very close to, if not through, one or more of the cyclotron maser instability sources thought to be responsible for Jupiter's auroral radio emissions.

Generation of the Jovian hectometric radiation: First lessons from Juno

“…The observations made in the northern hemisphere during the first crossing of the HOM source (source “B” in Kurth et al . []) are very similar. They show no clear trace of particle acceleration and support the case for loss cone distributions being the driver of the CMI process.…”

“…The region corresponds to the source labeled C in Figure 4 of Kurth et al . []. This time period is also discussed in Szalay et al .…”

“…From Figure , one can deduce that large amplifications (defined by amplification rates above 80% of the maximum growth) are obtained at propagation angles varying from 85° to 82°at 13:28:17 and 85° to 79° at 13:28:49, over the frequency bandwidth Δ ω ~ 3–7 × 10 −3 and Δ ω ~ 3–14 × 10 −3 , respectively. This corresponds to Δ f ~50 kHz, which is consistent with the high spectral resolution measurements performed in the source [ Kurth et al ., , Figure 4]. The typical spectral width of amplification is ~0.5–1 × 10 −2 .…”

“…The present investigation also relies on Kurth et al . [] which presents an overview of the first Juno radio observations, with descriptions of several close approaches or crossings of radio sources regions.…”

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

“…Juno/Waves data from Perijoves 1 to 15 were visually inspected to identify radio sources encountered along the probe trajectory (Kurth et al, ). For the sake of simplicity, we used a single selection criterion, namely, emissions observed at frequencies lower than 1.01× f ce , based on Louarn et al (), who measured CMI‐driven radio emissions at a frequency up to 1% above f ce .…”