At Jupiter, part of the auroral radio emissions are induced by the Galilean moons Io, Europa and Ganymede. Until now, except for Ganymede, they have been only remotely detected, using ground-based radio-telescopes or electric antennas aboard spacecraft. The polar trajectory of the Juno orbiter allows the spacecraft to cross the range of magnetic flux tubes which sustain the various Jupiter-satellite interactions, and in turn to sample in situ the associated radio emission regions. In this study, we focus on the detection and the characterization of radio sources associated with Io, Europa and Ganymede. Using electric wave measurements or radio observations (Juno/Waves), in situ electron measurements (Juno/JADE-E), and magnetic field measurements (Juno/MAG) we demonstrate that the Cyclotron Maser Instability (CMI) driven by a loss-cone electron distribution function is responsible for the encountered radio sources. We confirmed that radio emissions are associated with Main (MAW) or Reflected Alfvén Wing (RAW), but also show that for Europa and Ganymede, induced radio emissions are associated with Transhemispheric Electron Beam (TEB). For each traversed radio source, we determine the latitudinal extension, the CMI-resonant electron energy, and the bandwidth of the emission. We show that the presence of Alfvén perturbations and downward field aligned currents are necessary for the radio emissions to be amplified.

A document by Brieuc Collet. Click on the document to view its contents.

The MASER (Measuring, Analysing and Simulating Radio Emissions) project provides a comprehensive infrastructure dedicated to low frequency radio emissions (typically < 50 to 100 MHz). The four main radio sources observed in this frequency are the Earth, the Sun, Jupiter and Saturn. They are observed either from ground (down to 10 MHz) or from space (down to a few kHz). Ground observatories are more sensitive than space observatories and capture high resolution data streams (up to a few TB per day for modern instruments). Conversely, space-borne instruments can observe below the ionospheric cut-off (10 MHz) and can be placed closer to the studied object. Several tools have been developed in the last decade for sharing space physcis data. Data visualization tools developed by the CDPP (http://cdpp.eu, Centre de Données de la Physique des Plasmas, in Toulouse, France) and the University of Iowa (Autoplot, http://autoplot.org) are available to display and analyse space physics time series and spectrograms. A planetary radio emission simulation software is developed in LESIA (ExPRES: Exoplanetary and Planetary Radio Emission Simulator). The VESPA (Virtual European Solar and Planetary Access) provides a search interface that allows to discover data of interest for scientific users, and is based on IVOA standards (astronomical International Virtual Observatory Alliance). The University of Iowa also develops Das2server that allows to distribute data with adjustable temporal resolution. MASER is making use of all these tools and standards to distribute datasets from space and ground radio instruments available from the Observatoire de Paris, the Station de Radioastronomie de Nançay and the CDPP deep archive. These datasets include Cassini/RPWS, STEREO/Waves, WIND/Waves, Ulysses/URAP, ISEE3/SBH, Voyager/PRA, Nançay Decameter Array (Routine, NewRoutine, JunoN), RadioJove archive, swedish Viking mission, Interball/POLRAD… MASER also includes a Python software library for reading raw data. This work is supported by CDPP, CNES, PADC and Europlanet-2020-RI. The Europlanet 2020 Research Infrastructure project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 654208.

Auroral Kilometric Radiation (AKR) is radio emission that originates in particle acceleration regions along magnetic field lines, coinciding with discrete auroral arcs. Found in both hemispheres, an increase in the amplitude of a particular AKR source denotes the strengthening of parallel electric fields in the auroral zone, while the emission frequency gives insight into source region morphology. AKR viewing geometry is complex due to the confinement of the source regions to nightside local times and the anisotropy of the beaming pattern, so observations are highly dependent on spacecraft viewing position. We present a novel, empirical technique that selects AKR emission from remote radio observations made with the spin-axis aligned antenna of the Wind/WAVES instrument, based on the rapidly varying amplitude of AKR across spacecraft spin timescales. This selection is applied to 30 days of data in 1999, during which the Cassini spacecraft flew close to Earth and recorded AKR for the majority of the period, while the Wind spacecraft completed close to two, precessing petal orbits. We examine the flux density and integrated power, which gives an occurrence distribution with spacecraft local time that is typical of AKR, with an increase in power of around $10^{3}$ Wsr$^{-1}$ between dayside and nightside observations. We also find a statistically significant ($p < 10^{-5}$), previously observed diurnal modulation of the AKR integrated power for the period, further verifying the empirical selection of AKR and showing the promise of its application to larger subsets of Wind/WAVES observations.

On October 28th 2021 the Sun released a large Coronal Mass Ejection (CME) in Earth’s direction. An X1.0 class solar flare and a rare ground level enhancement (GLE) were observed, along with bright solar radio bursts. Here we examine data from the near-Earth environment to investigate the terrestrial response to this solar event, as a typical example of Sun-Earth interactions. The CME arrival is tracked at $\sim$1 AU from Wind radio observations and the interplanetary magnetic field (IMF) and solar wind dynamic pressure by \textit{in-situ} measurements of OMNI spacecraft. Geomagnetic activity is studied with indices including SYM-H while the auroral response is monitored by remote Wind radio measurements of Auroral Kilometric Radiation (AKR) and SSUSI UV observations. We quantify the timeline for solar wind-magnetosphere coupling via exploration of the dayside reconnection rate and polar cap voltages and address the visibility of AKR sources for a dayside radio observatory.

Reanalyzing Cassini radio observations performed during Jupiter’s flyby of 2000-2001, we study the internal (rotational) versus external (solar wind) control of Jupiter’s radio emissions, from kilometer to decameter wavelengths, and the relations between the different auroral radio components. For that purpose, we build a database of the occurrence of Jovian auroral radio components bKOM, HOM and DAM observed by Cassini, and then frequency-longitude stacked plots of the polarized intensity of these radio components. Comparing the results obtained inbound and outbound, as a function of the Observer’s or Sun’s longitude, we find that HOM & DAM are dominantly rotation-modulated (i.e. emitted from searchlight-like sources fixed in Jovian longitude), whereas bKOM is modulated more strongly by the solar wind than by the rotation (i.e. emitted from sources more active within a given Local Time sector). We propose a simple analytical description of these internal and external modulations and evaluate its main parameters (the amplitude of each control) for HOM+DAM and bKOM. Comparing Cassini and Nançay Decameter Array data, we find that HOM is primarily connected to the decameter emissions originating from the dusk sector of the Jovian magnetosphere. HOM and DAM components form a complex but stable pattern in the frequency-longitude plane, that remains to be modelled. HOM also seems to be related to the so-called ‘lesser arcs’ identified by Voyager. bKOM consists of a main part above ∼40 kHz in antiphase with HOM occurrence, and detached patches below ∼80 kHz in phase with HOM occurrence.

We study 10 years (1995-2004 inclusive) of auroral kilometric radiation (AKR) radio emission data from the Wind spacecraft to examine the link between AKR and terrestrial substorms. We use substorm lists based on parameters including ground magnetometer signatures and geosynchronous particle injections as a basis for superposed epoch analyses of the AKR data. The results for each list show a similar, clear response of the AKR power around substorm onset. For nearly all event lists, the average response shows that the AKR power begins to increase around 20 minutes prior to expansion phase onset, as defined by the respective lists. The analysis of the spectral parameters of AKR bursts show that this increase in power is due to an extension of the source region to higher altitudes, which also precedes expansion phase onset by 20 minutes. Our observations show that the minimum frequency channel that observes AKR at this time, on average, is 60 kHz. AKR visibility is highly sensitive to observing spacecraft location, and the biggest radio response to substorm onset is seen in the 2100 - 0300 hr LT sector.