Our knowledge about the fine structure of lightning processes at Jupiter was substantially limited by the time resolution of previous measurements. Recent observations of the Juno mission revealed ...electromagnetic signals of Jovian rapid whistlers at a cadence of a few lightning discharges per second, comparable to observations of return strokes at Earth. The duration of these discharges was below a few milliseconds and below one millisecond in the case of Jovian dispersed pulses, which were also discovered by Juno. However, it was still uncertain if Jovian lightning processes have the fine structure of steps corresponding to phenomena known from thunderstorms at Earth. Here we show results collected by the Juno Waves instrument during 5 years of measurements at 125-microsecond resolution. We identify radio pulses with typical time separations of one millisecond, which suggest step-like extensions of lightning channels and indicate that Jovian lightning initiation processes are similar to the initiation of intracloud lightning at Earth.
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.
Key Points
We perform direction‐finding analysis for Jupiter's low‐frequency radio emissions
Northern bKOM radio sources are located along high‐latitude auroral magnetic field lines
Four smooth components provide a proxy of the electron density profiles in Jovian inner magnetosphere
Two well‐defined Jovian decametric radio arcs were observed at latitudinal separations of 11°–16° from the Juno spacecraft near Jupiter and the Nançay Decameter Array (NDA) at Earth on 17 May and 25 ...August 2016. These discrete arcs are from the so‐called A source covering both Io‐related and non‐Io‐related emissions. By measuring the wave arrival time at two distant observers with propagation time correction, the remaining delay times are 92.8 ± 1.3 min for the first arc and 116.0 ± 1.2 min for the second arc. This implies that both radio sources are not controlled by the orbital motion of Io but Jupiter's rotation itself. The geometrical information for Juno and NDA and the loss cone‐driven electron cyclotron maser instability theory provide these radio sources that are located at about 173° ± 10° in system III longitude projected onto Jupiter's north surface and imply resonant electron energy ranges from 0.5 to 11 keV.
Key Points
Two decametric (DAM) arcs were observed from widely spaced latitudes by Juno and NDA
Direct evidence of long‐lasting DAM arcs corotating with Jupiter is presented
The loss cone‐driven CMI theory of fundamental X‐mode emission provides a constraint of the concurrent arcs
Synoptic decametric (DAM) radio observations at Jupiter were made in a broad Jovicentric latitudinal range of −21° to +15° by the Juno polar orbiting spacecraft from 21 June to 10 December 2016. We ...investigated the occurrence probability of non‐Io‐related DAM. At 19.5 MHz, as Juno's latitude varies from +15° to −21°, a peak of non‐Io‐B occurrence probability at 175° System III central meridian longitude (CML) gradually shifts in longitude to 140° CML. Also, another peak occurs at 110° CML between −15° and −9°, merging into the bottom edge of the former peak. This J‐shaped feature is similarly seen at 16.5 MHz. Using the Jovian magnetic field models, the fixed hollow cone model can reasonably account for the J‐shaped structure for radio sources traced along active magnetic flux tubes onto Jupiter's surface projected at about 135°–149° System III longitude. Moreover, these non‐Io‐B spectral profiles extend from 13.5 to 23.5 MHz.
Key Points
A J‐shaped occurrence probability within Jovian non‐Io‐related DAM is found extending over a broad latitude range
The fixed hollow cone model can account for the J‐shaped features
Complex structures of non‐Io‐DAM are shown in a wide frequency range of 3.5 to 40.5 MHz
Intense electromagnetic impulses induced by Jupiter's lightning have been recognised to produce both low-frequency dispersed whistler emissions and non-dispersed radio pulses. Here we report the ...discovery of electromagnetic pulses associated with Jovian lightning. Detected by the Juno Waves instrument during its polar perijove passes, the dispersed millisecond pulses called Jupiter dispersed pulses (JDPs) provide evidence of low density holes in Jupiter's ionosphere. 445 of these JDP emissions have been observed in snapshots of electric field waveforms. Assuming that the maximum delay occurs in the vicinity of the free space ordinary mode cutoff frequency, we estimate the characteristic plasma densities (5.1 to 250 cm
) and lengths (0.6 km to 1.3 × 10
km) of plasma irregularities along the line of propagation from lightning to Juno. These irregularities show a direct link to low plasma density holes with ≤250 cm
in the nightside ionosphere.
In this paper, we attempt to clarify the relationship between Jovian hectometric (HOM) and non‐Io‐related decametric (non‐Io‐DAM) radio structure. For that purpose, we extend the analysis by ...including more data and investigating statistical properties of the Jovian DAM and HOM radio emissions based on Cassini and Voyager observations, especially below 16 MHz. We have investigated these emissions observed by the Cassini, Voyager 1, and Voyager 2 spacecraft for specific Jovigraphic latitudes in the range of −3.7°–7.3° and local times in the range of 0.76–21.4 hours. We show a statistical comparison of Cassini, Voyager 1, and Voyager 2 data for occurrence probability in Central Meridian Longitude (CML) versus Io phase and in CML versus Frequency. The main results are as follows: (1) the detailed frequency structures of non‐Io‐related components can be seen for different spacecraft's local time and Jovigraphic latitude, (2) the high frequency of HOM extends up to near 10 MHz, and (3) a new DAM component, named the non‐Io‐D, appears from 40° to 60° CML in the frequency range of 7–11 MHz. On the basis of additional information of different behaviors of non‐Io‐B and non‐Io‐A structures in longitude depending on pre‐ and post‐encounter of Cassini data, we improved the DAM angular beaming model that shows the cone half‐angle of the emitting cone decreases as a function of frequency. We conclude that the changing beaming angle is not affected by Jovigraphic latitude of the spacecraft, but rather due to different local time of the source regions.
Key Points
The detailed frequency structures of non‐Io‐related components are presented
We find a new upper limit of 10 MHz for Jupiter's HOM emission
We find a new DAM component called the non‐Io‐D source
The possibility to apply passive radar sounding techniques to the Jovian icy moons, making use of Jupiter's strong decametric emissions (DAMs), has recently garnered large research interest. In this ...article, we propose a radar sounding simulation approach being able to simulate and compare passive and active acquisitions for a given scenario. The proposed simulator is based on the Stratton-Chu integral used with the linear phase approximation on triangular facets. The external field is modeled with plane waves, the direction, polarization, and amplitude of which can be freely chosen. The time-domain dependence can be either synthetically generated (e.g., Gaussian white noise) or taken from experimental measurements (e.g., waveforms recorded by a radio telescope observing Jupiter). For passive sounding, both autocorrelation and cross-correlation processing are considered. Validation tests were conducted on a series of ideal digital elevation models (DEMs), such as flat surfaces and subsurfaces, or Gaussian rough surfaces, and a good agreement with the existing literature was obtained. To illustrate the capabilities of the proposed simulator, we conducted additional more realistic experiments of radar sounding simulations, where we use both white noise and Jovian waveforms recorded by the LWA1 radio telescope.
Observations of the low frequency part of Jupiter decameter wavelength (DAM) emissions were made using the Cassini radio and plasma wave science (RPWS) instrument. We have analyzed non‐Io‐DAM ...occurrence dependence from 4 MHz to 16 MHz based on the System III central meridian longitude (CML) of the Cassini spacecraft and calculated the occurrence probability for each frequency. As a result of this analysis, the two peaks of non‐Io‐B and non‐Io‐A occurrence probability showed a dramatic change in longitude between 9 MHz and 16 MHz. At 16 MHz two peaks of probability occurred at 160° and 240° CML. As the frequency decreases to 9 MHz, the two peaks converged to become one peak near 205° CML at 9 MHz. This peak gradually disappeared below 9 MHz. Based on Jupiter's magnetic VIP4 model, an angular beaming model was made to explain these observational results by taking into account the decreasing cone half‐angle of the emitting cone from 16 MHz down to 9 MHz. We found the active magnetic flux tubes of non‐Io‐B and non‐Io‐A sources are localized at about 180° ± 10° of System III longitude projected on Jupiter's surface.
Jupiter's ultraviolet (UV) aurorae, the most powerful and intense in the solar system, are caused by energetic electrons precipitating from the magnetosphere into the atmosphere where they excite the ...molecular hydrogen. Previous studies focused on case analyses and/or greater than 30‐keV energy electrons. Here for the first time we provide a comprehensive evaluation of Jovian auroral electron characteristics over the entire relevant range of energies (~100 eV to ~1 MeV). The focus is on the first eight perijoves providing a coarse but complete System III view of the northern and southern auroral regions with corresponding UV observations. The latest magnetic field model JRM09 with a current sheet model is used to map Juno's magnetic foot point onto the UV images and relate the electron measurements to the UV features. We find a recurring pattern where the 3‐ to 30‐keV electron energy flux peaks in a region just equatorward of the main emission. The region corresponds to a minimum of the electron characteristic energy (<10 keV). Its polarward edge corresponds to the equatorward edge of the main oval, which is mapped at M shells of ~51. A refined current sheet model will likely bring this boundary closer to the expected 20–30 RJ. Outside that region, the >100‐keV electrons contribute to most (>~70–80%) of the total downward energy flux and the characteristic energy is usually around 100 keV or higher. We examine the UV brightness per incident energy flux as a function of characteristic energy and compare it to expectations from a model.
Plain Language Summary
Aurorae, also commonly called Northern or Southern Lights, are among the most spectacular displays of nature. They are observed not only at Earth but at other planets too, such as Mars, Jupiter, and Saturn. In fact, Jupiter has the brightest aurora in the solar system. The aurora is created when electrons and/or ions in space precipitate into the atmosphere and excite the ambient gas. At Jupiter, they mostly shine in the ultraviolet which is invisible to our eyes but can be seen with suitable instrumentation. The faster the electrons, the deeper they go into the atmosphere, but also the more energy they carry, which eventually can be converted to create more light. This study is about characterizing the electrons that create Jupiter's aurora using many instruments from the National Aeronautics and Space Administration's Juno Mission. We find that different ultraviolet emissions correspond to different electron characteristics. Knowing the differences will help us to understand the bigger picture to explain the processes that create the aurora.
Key Points
We present a survey of Jovian auroral electrons characteristics from 50 eV to 1000 keV by Juno
We present a metric to identify main oval crossings in electron data using 3‐30 keV electrons energy flux
We estimate the UV brightness per incident electron energy flux as a function of characteristic energy
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