The observations from the Juno spacecraft in polar orbit of Jupiter provide for the first time a complete view of Jupiter's radio emissions from all latitudes. Characterizing the latitudinal ...distribution of radio emissions' occurrence and intensity is a useful step for elucidating their origin. Here, we analyze for that purpose the first 3 years of observations from the Waves experiment on the Juno spacecraft (mid‐2016 to mid‐2019). Two prerequisites for the construction of the latitudinal distribution of intensities for each Jovian radio component are (a) to work with absolute flux densities and (b) to be able to associate each radio measurement with a specific radio component. Accordingly, we develop a method to convert the Juno/Waves data in flux densities and then we build a catalog of all Jovian radio components over the first 3 years of Juno's orbital mission. From these, we derive occurrence and intensity distributions versus observer's latitude and frequency for each component; these will be the basis for future detailed studies and interpretations of each component's characteristics and origin.
Key Points
We build a processing pipeline of Juno/Waves data that include conversion to absolute flux densities
We build a catalog of all Jovian radio components over the first 3 years of Juno's orbital mission
We derive occurrence and intensity distributions versus observer's latitude and frequency for each component
By analysing a database of 26 yr of observations of Jupiter with the Nançay Decameter Array, we unambiguously identify the radio emissions caused by the Ganymede–Jupiter interaction. We study the ...energetics of these emissions via the distributions of their intensities, duration, and power, and compare them to the energetics of the Io–Jupiter radio emissions. This allows us to demonstrate that the average emitted radio power is proportional to the Poynting flux from the rotating Jupiter’s magnetosphere intercepted by the obstacle. We then generalize this result to the radio-magnetic scaling law that appears to apply to all plasma interactions between a magnetized flow and an obstacle, magnetized or not. Extrapolating this scaling law to the parameter range corresponding to hot Jupiters, we predict large radio powers emitted by these objects, that should result in detectable radio flux with new-generation radiotelescopes. Comparing the distributions of the durations of Ganymede–Jupiter and Io–Jupiter emission events also suggests that while the latter results from quasi-permanent Alfvén wave excitation by Io, the former likely results from sporadic reconnection between magnetic fields Ganymede and Jupiter, controlled by Jupiter’s magnetic field geometry and modulated by its rotation.
Context. Earth and outer planets are known to produce intense non-thermal radio emissions through a mechanism known as cyclotron maser instability (CMI), requiring the presence of accelerated ...electrons generally arising from magnetospheric current systems. In return, radio emissions are a good probe of these current systems and acceleration processes. The CMI generates highly anisotropic emissions and leads to important visibility effects, which have to be taken into account when interpreting the data. Several studies have shown that modelling the radio source anisotropic beaming pattern can reveal a wealth of physical information about the planetary or exoplanetary magnetospheres that produce these emissions. Aims. We present a numerical tool, called ExPRES (Exoplanetary and Planetary Radio Emission Simulator), which is able to reproduce the occurrence in a time-frequency plane of R−X CMI-generated radio emissions from planetary magnetospheres, exoplanets, or star–planet interacting systems. Special attention is given to the computation of the radio emission beaming at and near its source. Methods. We explain what physical information about the system can be drawn from such radio observations, and how it is obtained. This information may include the location and dynamics of the radio sources, the type of current system leading to electron acceleration and their energy, and, for exoplanetary systems, the orbital period of the emitting body and the strength, rotation period, tilt, and the offset of the planetary magnetic field. Most of these parameters can only be remotely measured via radio observations. Results. The ExPRES code provides the proper framework of analysis and interpretation for past, current, and future observations of planetary radio emissions, as well as for future detection of radio emissions from exoplanetary systems (or magnetic, white dwarf–planet or white dwarf–brown dwarf systems). Our methodology can be easily adapted to simulate specific observations once effective detection is achieved.
Auroral Kilometric Radiation (AKR) is the strongest terrestrial radio emission, and emanates from the same electron acceleration regions from which particles precipitate into the ionosphere, exciting ...the aurorae and other phenomena. As such, AKR is a barometer for the state of solar wind ‐ magnetosphere ‐ ionosphere coupling. AKR is anisotropically beamed in a hollow cone from a source region generally found at nightside local times, meaning that a single source region cannot be viewed from all local times in the magnetosphere. In radio data such as dynamic spectra, AKR is frequently observed simultaneously to other radio emissions which can have a similar intensity and frequency range, making it difficult to automatically detect. Building on a previously published pipeline to extract AKR emissions from Wind/WAVES data, in this paper a novel automated AKR burst detection technique is presented and applied to Wind/WAVES data. Over a five year interval, about 5000 AKR bursts are detected with median burst length ranging from about 30 to 60 min. During detected burst windows, higher solar wind velocity is observed, and the interplanetary magnetic field clock angle is observed to tend toward BZ < 0, BY < 0, when compared with the entire statistical interval. Additionally, higher geomagnetic activity is observed during burst windows at polar, high and equatorial latitudes.
Plain Language Summary
Auroral Kilometric Radiation (AKR) is a terrestrial radio emission which is excited by the same electrons which enhance the aurorae. Due to a combination of complex beaming, and the statistical position of the source region, an AKR event cannot be observed at all positions in the Earth's magnetosphere. A combination of different radio emissions are simultaneously observed in the radio data, including both AKR and non‐AKR sources. Building on previous work, in this paper individual AKR burst events are automatically detected from Wind/WAVES data over a five year interval. About 5000 events are detected over the interval, during which the observed geomagnetic activity was higher. Higher solar wind velocity and differences in the morphology of the interplanetary magnetic field are also observed during burst windows, both of which are known to excite magnetospheric dynamics.
Key Points
A novel technique has been developed to detect individual Auroral Kilometric Radiation bursts in Wind/WAVES data
When the technique is applied to 2000–2004 data, about 5000 bursts are detected with median duration 30–60 min
During burst windows, higher solar wind velocity, more negative IMF BZ and greater geomagnetic activity is observed
While the terrestrial aurorae are known to be driven primarily by the interaction of the Earth's magnetosphere with the solar wind, there is considerable evidence that auroral emissions on Jupiter ...and Saturn are driven primarily by internal processes, with the main energy source being the planets' rapid rotation. Prior observations have suggested there might be some influence of the solar wind on Jupiter's aurorae and indicated that auroral storms on Saturn can occur at times of solar wind pressure increases. To investigate in detail the dependence of auroral processes on solar wind conditions, a large campaign of observations of these planets has been undertaken using the Hubble Space Telescope, in association with measurements from planetary spacecraft and solar wind conditions both propagated from 1 AU and measured near each planet. The data indicate a brightening of both the auroral emissions and Saturn kilometric radiation at Saturn close in time to the arrival of solar wind shocks and pressure increases, consistent with a direct physical relationship between Saturnian auroral processes and solar wind conditions. At Jupiter the correlation is less strong, with increases in total auroral power seen near the arrival of solar wind forward shocks but little increase observed near reverse shocks. In addition, auroral dawn storms have been observed when there was little change in solar wind conditions. The data are consistent with some solar wind influence on some Jovian auroral processes, while the auroral activity also varies independently of the solar wind. This extensive data set will serve to constrain theoretical models for the interaction of the solar wind with the magnetospheres of Jupiter and Saturn.
Accessing, visualizing and analyzing heterogeneous plasma datasets has always been a tedious task that hindered students and senior researchers as well. Offering user friendly and versatile tools to ...perform basic research tasks is therefore pivotal for data centres including the Centre de Données de la Physique des Plasmas (CDPP http://www.cdpp.eu/) which holds a large variety of plasma data from various Earth, planetary and heliophysics missions and observatories in plasma physics. This clearly helps gaining increased attention, relevant feedback, and enhanced science return on data. These are the key ideas that crystallized at CDPP more than 15 years ago and resulted in the lay-out of the concepts, and then development, of AMDA, the Automated Multi-Dataset Analysis software (http://amda.cdpp.eu/). This paper gives a description of the architecture of AMDA, describes its functionalities, presents some use cases taken from the literature or fruitful collaborations and shows how it offers unique capabilities for educational purposes.
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•AMDA (Automated Multi-Dataset Analysis) is an online analysis software and database of in-situ and modeled plasma data in heliophysics and planetary sciences.•AMDA is used in support to science exploitation for a large variety of missions.•AMDA is used by hundreds of students and researchers and facilitated the publication of tens of papers.
The electrodynamic interaction between Io and Jupiter causes electron acceleration in/near the Io flux tube (IFT), which in turn produces intense radio emissions in the hecto‐decameter range, ...displaying arc shapes in the time‐frequency plane. The shapes depend on the hemisphere of origin of the emission and on the Io‐Jupiter‐observer geometry. Assuming radio wave generation by the cyclotron‐maser instability, we simulate t‐f arc shapes as a function of emission beaming, lead angle between the radio emitting field line and the instantaneous Io field line, and electron energy. A good fit of arcs t‐f location and shape is obtained for loss‐cone driven (oblique) emission beamed in a hollow cone of half‐angle ≥80° around the source magnetic field, closing at high frequencies, and of cone thickness ≤1°. The lead angle is found between a few degrees and ∼40° in both hemispheres. Resonant electron energies are about a few keV. Implications on the absence of a plasma cavity at IFT footprints and on Jupiter's internal magnetic field model are discussed.
Aims.
We use multi-spacecraft observations of individual type III radio bursts to calculate the directivity of the radio emission. We compare these data to the results of ray-tracing simulations of ...the radio-wave propagation and probe the plasma properties of the inner heliosphere.
Methods.
We used ray-tracing simulations of radio-wave propagation with anisotropic scattering on density inhomogeneities to study the directivity of radio emissions. Simultaneous observations of type III radio bursts by four widely separated spacecraft were used to calculate the directivity and position of the radio sources. The shape of the directivity pattern deduced for individual events is compared to the directivity pattern resulting from the ray-tracing simulations.
Results.
We show that simultaneous observations of type radio III bursts by four different probes provide an opportunity to estimate the radio source positions and the directivity of the radio emission. The shape of the directivity varies from one event to another and it is consistent with anisotropic scattering of the radio waves.
The reflection‐by‐sheath mechanism of 5 kHz narrowband emissions (NB) at Saturn is confirmed by Cassini observations during several crossings of the magnetopause, which show that the 5 kHz NB can be ...prevented from escaping Saturn's magnetosphere. The L‐O mode 5 kHz NB remained visible in areas of low plasma density but disappeared in regions of high plasma density. In three cases, NB disappeared immediately after the crossings of Saturn's magnetopause. A possible reflected NB event observed near the magnetosheath is discussed. This mechanism can help explain the 5 kHz NB observed at low latitudes outside the Enceladus plasma torus and their upper frequency limit variations. This mechanism significantly improves the current understanding of the 5 kHz NB.
Plain Language Summary
Very low frequency narrowband radio emissions have been observed at about 5 and 20 kHz by the Voyager and Cassini spacecraft at Saturn. Recently, a statistical survey of Saturn narrowband emissions indicated that the 5 kHz narrowband emissions could be reflected by Saturn's magnetosheath due to the high plasma density within. The work presents evidence to confirm the reflection and refraction of 5 kHz narrowband emissions by Saturn's magnetosheath. The observations of narrowband emissions near Saturn's magnetosheath show that sometimes the 5 kHz narrowband emissions cannot pass the magnetosheath when the plasma density is high enough, at other times the polarization reverses near the magnetosheath, which indicates a reflected signal. This survey confirms the reflection‐by‐sheath mechanism, and it is of special importance because this mechanism significantly improves the current understanding of the Saturn narrowband emissions and explains several features of them.
Key Points
The 5‐kHz narrowband emissions (NB) from Saturn can be reflected by density structures in the magnetosheath
Reflection leads to depolarization and trapping of NB inside Saturn's magnetosphere
The upper frequency limit of trapped NB depends on variations in the magnetosheath and the solar wind
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