Direction‐finding measurements of Jovian low‐frequency radio components by Juno near Perijove 1

Abstract

With the aid of the radio and plasma wave (Waves) instrument on board the Juno spacecraft, the first scientific close encounter to Jupiter (Perijove 1) of Juno led to an opportunity to perform direction‐finding measurements of the intense Jovian broadband kilometric (bKOM) radiation at 10 to 142 kHz, two escaping continuum radiation (ECR) events at 9 to 22 kHz, and two narrowband kilometric (nKOM) radiation events at 45–112 kHz. We conclude that the northern bKOM radio sources are localized on M‐shell = 50–60 field lines where M‐shell is similar to L‐shell for nondipolar fields. The beam cone half‐angle varies from 40° to 55°. By intersecting the wave k vector with the Jovian centrifugal equator, two ECR sources are located inside and outside of 11–12 RJ, and two nKOM sources are found between 11 and 20 RJ. These source frequencies and locations can be used for plasma diagnostics in Jupiter's inner magnetosphere.

Probing Jovian Broadband Kilometric Radio Sources Tied to the Ultraviolet Main Auroral Oval With Juno

“…We presented simultaneous observations of auroras at radio and UV wavelengths as observed from Juno during PJ4 through PJ6 over both hemispheres of Jupiter. Using Jovian radio observations and UV aurora images taken at the same or similar times, we confirmed that bKOM radio sources are tied to the UV main oval, which was originally suggested by the Ulysses radio DF study (Ladreiter et al, ) and the initial Juno radio DF and in situ studies (Imai et al, , ; Kurth, Imai, Hospodarsky, Gurnett, Louarn, et al, ; Kurth, Imai, Hospodarsky, Gurnett, Tetrick, et al, ) but without concurrent UV aurora observations.…”

“…The estimated magnetic M values from the Waves direct and DF methods yield 10 to 12 for the PJ4 north pass, significantly lower than for the PJ5 north event at M = 44–56 and PJ6 north event at M = 22–52 as shown in Table . These M values are within the estimates of the Ulysses bKOM DF study at M = 5–58 (Ladreiter et al, ), but only PJ5 and PJ6 events are in agreement with those of the initial Juno bKOM studies (Imai et al, , ; Kurth, Imai, Hospodarsky, Gurnett, Louarn, et al, ; Kurth, Imai, Hospodarsky, Gurnett, Tetrick, et al, ) at M = 50–60. Another possibility for the PJ4 north event is a response to transient diffusive injections toward the Io plasma torus (e.g., Louarn et al, ).…”

“…The Ulysses direction‐finding (DF) study by Ladreiter et al () first showed that the southern bKOM radiation at 81 and 100 kHz originates from auroral regions. Later, Imai et al () used Juno's DF capability to investigate the northern bKOM radiation from 10 to 142 kHz, finding that M values (e.g., Szalay et al, ) of these radio sources range from 50 to 60, compared to M = 5–58 (Ladreiter et al, ). They also found that the mean cone half‐angle extends from 40° to 55° , consistent with that of 30° to 80° based on the Ulysses study (Ladreiter et al, ).…”

“…The typical range of emission frequencies is between 10 kHz and 1 MHz for bKOM, between 300 kHz and 10 MHz for HOM, and between a few megahertz and 40 MHz for DAM. The sources of these nonthermal emissions are distributed along auroral magnetic field lines at emission frequencies very close to the local electron cyclotron frequency, f ce (Imai et al, 2017a(Imai et al, , 2017bKurth, Imai, Hospodarsky, Gurnett, Louarn, et al, 2017;Kurth, Imai, Hospodarsky, Gurnett, Tetrick, et al, 2017). These sporadic bursts are believed to be the free space right-hand extraordinary (R-X) mode at various temporal scales from minutes down to milliseconds (Carr et al, 1983;Imai et al, 2016;Kurth et al, 2001).…”

A new view of Jupiter's auroral radio spectrum

“…Example VIP4 field lines with a disk current sheet [Connerney et al, 1981] are shown in blue. The low-latitude R-X cutoff incorporates a modified plasma sheet density model [Imai et al, 2017c]. The red dots indicate times when Juno passed through or close to auroral radio sources.…”