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The IONO experiment embarked on INSPIRE-SAT 7 is dedicated to the sounding of the Earth’s ionosphere. INSPIRE-SAT 7 is a French 2U CubeSat, the main purpose of which is the measurement of the Earth’s radiation budget at the top of the atmosphere. It is very similar to the satellite UVSQ-SAT which was launched on 24 January 2021. Its total mass will be 3.0 kg and its averaged power consumption 3 W. It will orbit at a maximum altitude of 600 km on a Sun-synchronous orbit with a descending node at ~0930 LT. The Earth’s ionosphere results from the ionization of the upper atmosphere due to UV radiations and X-rays coming from the Sun. The electron density in the ionosphere depends on the local time, the season, and the solar activity. The propagation of the radio waves is affected by the electron density and also by refraction and reflection phenomena. We consider the following goals for the IONO instrument: improving ionosphere models, in particular the IRI (International Reference Ionosphere); study of the propagation of electromagnetic waves in the ionosphere and the factors which can disturb it (e.g., thunderstorms); analysis of temporal and spatial variability at different scales; study of the coupling between ionosphere and magnetosphere, and the electrical circuit between ionosphere and lithosphere. The observations collected by IONO will be compared to those produced by a VLF-LF antenna network designed for investigating the perturbations of the ionosphere, and the wave propagation, by seismic phenomena.

International audience; We report on electric field measurements recorded by the Electric Field Detector (EFD) and the Instrument Champ Electrique (ICE) onboard, respectively, CSES and DEMETER satellites. We study the variations of Very Low Frequency (VLF) ground-based transmitter signals detected by both satellites during periods of low solar and geomagnetic activities. We consider the variation of VLF power spectra density in the frequency range between few Hertz to 20 kHz. We emphasize on ionospheric disturbances associated to earthquakes occurrences. Such disturbances are linked to waves generated by coupling of neutral particles and electrons related, through the atmosphere, to lithospheric ground displacements. The main peculiarities of seismic ionospheric anomalies are summarized taken into consideration technical complementary of both satellites.

International audience; In this study we investigate ionospheric disturbances over earthquake prone areas with two methods.The satellite based approach - in our case magnetic field measurements from CSES-01 and Swarm mission - shed light on ionospheric F-region plasma variations at low-earth orbit (LEO) altitudes around 500 km. The complemen-tary second technique is based on variations of the so-called Earth-ionosphere waveguide, the cavity between Earth’s surface and the lower ionospheric D/E (day/night) upper boundary at approx. 70-90 km altitude. Electric field ampli-tude and phase perturbations of paths between several narrowband VLF/LF transmitter and a receiver network are continuously recorded.In both cases the lithosphere-atmosphere-ionosphere coupling (LAIC) is a key area and of vital importance in order to establish the propagation char-acteristics from the seismic zone up to high altitudes. Possible mechanisms are discussed in the literature, e.g. [1], [2]. In this presentation we focus on acous-tic waves and atmospheric gravity waves (AGW) as energy-momentum trans-port channel (and filter) to connect the different regions from bottom to top.We examine events form the United States Geological Survey (USGS) earthquake catalog, assign a spatial box of a few degrees in latitude and lon-gitude around the epicenter, investigate measurements from satellite- and/or VLF/LF paths which crosses the box, and report on differences in variations prior and after the events.These findings could point to regular automated procedures in order to disentangle seismic from nonseismic ionospheric pattern and are equally important for upcoming satellite missions and extended ground based networks.

International audience

International audience; Introduction:The 13-year exploration of Saturn with Cassini provided enormous scientific return from the Radio and Plasma Wave Science (RPWS) investigation. While it is not possible to achieve absolute concensus on the most important results fromthis investigation, here we attempt to show the breadth of contributions to the study of the Saturnian system with this instrument. Saturn Kilometric Radiation: Cassini’s RPWS determined that not only does the SKR rotational modulation vary in time, there are typically two different periods in the northern and southern hemispheres. Cassini crossed the SKR source region, confirming that the cyclotron maser instability (CMI) can drive the auroral radio emissions. These are the first in situ observations of a non-terrestrial CMI radio source. In addition, SKR was shown to be generated on field lines threading the UV auroras and diagnositic of magnetospheric dynamics imposed by solar wind compressions and tail reconnection. Enceladus and the E ring:RPWS observations contributed to the mapping of dust from the plumes of Enceladus and the resulting E ring. The discovery of auroral hiss generated by electron beams accelerated from the moon informed our understanding of the electromagnetic interaction of the moon with the magnetosphere. Auroal hiss also provided evidence of this interaction very close to the planet on field linesthreading the moon. Plasma resulting from the ionoization of material coming from Enceladus was modeled through the determination of the electron density in Saturn’s inner magnetosphere. The depletion of the electron density in the plume led to the realization that charged micron-sized dust grains were a major component of a dusty plasma in the vicinity of the moon. Lightning:High frequency radio emissions initiated in lightning strokes enabled RPWS to characterize the occurrence of lightning, hence, convective storms in Saturn’s atmosphere and tracked the development of a Great White Spot storm beginning in late 2010. Coupled with amateur and ISS images, an extensive compilation of thunderstorm activity in Saturn’s atmosphere was possible.Titan’s Ionosphere: The RPWS Langmuir Probe was the first instrument to confirm the existence of a substantial ionosphere at Titan. The Solar EUV dominates the ionization of the upper atmosphere of Titan, although energetic particles in Saturn’s magnetosphere do contribute substantially at all Solar Zenith Angles. Observations over the orbital mission showed the effect of the vaiation of EUV over the solar cycle in the ionospheric density. One of the more intriguing discoveries was the formation of complex negative organic ions and aerosol pre-cursors in the deep ionosphere of Titan, which may have implications for how pre-biotic chemistry occurred on the early Earth. RPWS observations also helped characterize the interaction of Titan with the solar wind and the development of a compound bowshock encompassing both Titan and Saturn’s magnetosphere.Saturn’s Ionosphere:An obvious result of Cassini’s Grand Finale was the first in situ obervations of electron densities and temperatures in Saturn’s topside ionosphere andthe revelation of strong interactions between the rings and the ionosphere.

International audience; In its Grand Finale phase, Cassini traversed a region of the Saturnian system not explored in the preceding 12 years in orbit. These high inclination, highly eccentric orbits took Cassini through the source regions of Saturn kilometric radiation (SKR) on auroral magnetic eld lines, across eld lines that tie the planet to its magnetosphere, the ring system, and through the topside ionosphere near the sub- solar equator just below the ring system. The Radio and Plasma Wave Science (RPWS) instrument studied the conditions in the SKR source region that had only been traversed twice in the entire preceding mission. Near 5 kHz intense narrowband emissions are observed in the Z mode at latitudes above about 10°. Plasma wave phenomena known as VLF saucers were observed on eld lines threading both Enceladus and the ring system, providing evidence of electron beams and quite possibly currents connecting these members of the Saturnian system to the planet. The RPWS found only very small numbers of micronsized dust grains in the region between the rings and the atmosphere. Perhaps some of the most important measurements were of plasma densities and temperatures in Saturn’s equatorial topside ionosphere, providing important information for understanding how the ring system and the ionosphere interact. These observations revealed small- scale structures in the ionospheric densities and large-scale asymmetries associated with ring shadowing. The ionosphere revealed a new plasma wave phenomenon apparently driven by a lower hybrid instability. This paper will summarize evidence of coupling between Saturn, the rings, and the more distant magnetosphere a orded by Cassini’s Grand Finale orbits.

International audience; A dipole model ("birotor dipole") was proposed for Saturn's inner magnetic field: this dipole presents the particularity to have North and South poles rotating around Saturn's axis at two different angular velocities; this dipole is tilted and not centered. The spin rates and the associated rotation phases are derived from a continuous wavelet transform analysis of the intensity of the Saturnian kilometric radiation (SKR) signal received at 290 kHz between July 2004 and June 2012 by the radio and plasma wave science (RPWS) experiment on board Cassini. 57 revolutions of the spacecraft, the periapsis of which is less than 5 Saturnian radii, have been selected for this study. For each of these chosen orbits, it is possible to fit with high precision the measurements of the MAG data experiment given by the magnetometer embarked on board Cassini. A nonrotating external magnetic field completes the model. This study suggests that Saturn's inner magnetic field is neither stationary nor fully axisymmetric. These results can be used as a boundary condition for modelling and constraining the planetary dynamo and they can be a starting point for the study of Saturn's inner structure and the comparison with the interior of Jupiter. An average of the birotor dipole magnetic potential is performed on the azimuthal angle revealing an average axisymmetrical component which can be compared with the published zonal models proposed for Saturn's magnetic field. The presence of a "birotor quadrupole" is required in the present model to improve the agreement for the third order Gauss coefficient.

International audience; Cassini ends its 13-year exploration of the Saturnian system in 22 high inclination Grand Finale orbits with perikrones falling between the inner edge of the D ring and the upper limits of Saturn's atmosphere. The Cassini Radio and Plasma Wave Science (RPWS) instrument makes a variety of observations in these unique orbits including Saturn kilometric radiation, plasma waves such as auroral hiss associated with Saturn's auroras, dust via impacts with Cassini, and the upper reaches of Saturn's ionosphere. This paper will provide an overview of the RPWS results from this final phase of the Cassini mission with the unique opportunities afforded by the orbit. Based on early Grand Finale orbits, we can already say that the spacecraft has passed through cyclotron maser source regions of the Saturn kilometric radiation a number of times, found only small amounts of micron-sized dust in the equatorial region, and observed highly variable densities of cold plasma of order 1000 cm-3 in the ionosphere at altitudes of a few thousand km.

International audience; Since the insertion of Cassini in the Saturnian system in July 2004, the radio and plasma wave science (RPWS) experiment on board the spacecraft revealed the presence of two distinct and variable rotation periods in the Saturnian kilometric radiation (SKR) which were attributed to the northern and southern hemispheres respectively. The present study is based on the hypothesis that the periodic time modulations present in the SKR are mainly due to the rotation of Saturn's inner magnetic field. The existence of a double period implies that the inner field is not only limited to a simple rotation dipole but displays more complex structures having the same time periodicities than the radio emission. In order to build a model of this complex magnetic field, it is absolutely necessary to know the accurate phases of rotation linked with the two periods. The radio observations from the RPWS experiment allow a continuous and accurate follow-up of these rotation phases, since the SKR emission is permanently observable and produced very close to the planetary surface. A continuous wavelet transform analysis of the intensity of the SKR signal received at 290 kHz between July 2004 and June 2012 was performed in order to calculate in the same time the different periodicities and phases. The rotation phases associated to the main two periods allow us to define a North and South longitude system essential for such a study. In this context, a dipole model ("birotor dipole") was proposed for Saturn's inner magnetic field: this dipole presents the particularity to have North and South poles rotating around Saturn's axis at two different angular velocities; this dipole is tilted and not centered. 57 Cassini's revolutions, the periapsis of which is less than 5 Saturnian radii, have been selected for this study. For each of these chosen orbits, it is possible to fit with high precision the measurements of the MAG data experiment given by the magnetometers embarked on board Cassini. A nonrotating external magnetic field completes the model. This study suggests that Saturn's inner magnetic field is neither stationary nor fully axisymmetric. These results can be used as a boundary condition for modelling and constraining the planetary dynamo and they can be a starting point for the study of Saturn's inner structure and the comparison with the interior of Jupiter.

International audience; We report on the Saturnian Radio Emission (SRE) recorded at Saturn by the Cassini Radio and Plasma Wave Science experiment (RPWS). We attempt to estimate the planetary rotation by applying the spectral method previously considered for the Jupiter radio emissions. This technique consists to distinguish between the spectral patterns occurring during one full Jovian rotation. Hence symmetrical features act around the axis of the planetary magnetic field due to the hollow cone beam. Therefore arc shapes appear with different orientations, i.e. vertex-early and -late arcs. This spectral 'symmetry' is fortified by the inclination between the geographical and the magnetic axes. The Saturnian radio emissions exhibit more spectral complexity because both axes (.i.e. magnetic and geographic) are quasi-aligned. Arc shapes are not frequently observed as in the case of Jupiter. We illustrate in our analysis that there is possibility to separate between Saturnian planetary rotations. Their occurrences are compared to the classic technique based on the variation of the Saturnian Kilometric Radiation (SKR) versus the sub-solar phase and the observation time (Kurth et al., JGR, 113, 2008). We discuss and we show that in several cases the planetary rotation accuracy is less than few minutes when combining both methods. We emphasize on spectral features by showing that the SRE and the SKR exhibit similar planetary rotation despite a difference in the emission frequency range.

International audience; We study the Type III solar bursts simultaneously recorded by radio experiments onboard Cassini, Ulysses and Wind. Those radio bursts cover a large frequency range from about 14 MHz to a few kHz. The corresponding source locations are mainly in the solar corona and the interplanetary medium. The empirical electron density models provide different distances depending on the emission mode, fundamental or harmonic. A real trouble arises due to the distance discrepancies, as inferred from the models. Also the Archimedean spiral trajectories of the electrons, at the origin of the Type III bursts, are another difficulty to correctly estimate the source locations. We show in our analysis that the stereoscopic observations are essential to reduce the source location inaccuracy. We finally discuss the relationship between the Type III beams, the emission modes and the source locations.

International audience; The radio and plasma wave science (RPWS) experiment on board the Cassini spacecraft, orbiting around Saturn since July 2004, revealed the presence of two distinct and variable rotation periods in the Saturnian kilometric radiation (SKR). These two periods were attributed to the northern and southern hemispheres respectively. We suppose that the periodic time modulations present in the SKR are mainly due to the rotation of Saturn's inner magnetic field. The existence of a double period implies that the inner field is not only limited to a simple rotation dipole but displays more complex structures having the same time periodicities than the radio emission. In order to build a model of this complex magnetic field, it is absolutely necessary to know the accurate phases of rotation linked with the two periods. The radio observations from the RPWS experiment allow a continuous and accurate follow-up of these rotation phases, since the SKR emission is permanently observable and produced very close to the planetary surface. A continuous wavelet transform analysis of the intensity of the SKR signal received at 290 kHz between July 2004 and June 2012 was performed in order to calculate in the same time the different periodicities and phases. A dipole model was proposed for Saturn's inner magnetic field: this dipole presents the particularity to have North and South poles rotating around Saturn's axis at two different angular velocities; this dipole is tilted and not centered. 57 Cassini's revolutions, the periapsis of which is less than 5 Saturnian radii, have been selected for this study. For each of these chosen orbits, it is possible to fit with high precision the measurements of the MAG data experiment given by the magnetometers embarked on board Cassini. A nonrotating external magnetic field completes the model. This study suggests that Saturn's inner magnetic field is neither stationary nor fully axisymmetric. These results can be used as a boundary condition for modelling and constraining the planetary dynamo and they can be a starting point for the study of Saturn's inner structure and the comparison with the interior of Jupiter.

International audience; The radio and plasma wave science (RPWS) experiment on board the Cassini spacecraft, orbiting around Saturn since July 2004, revealed the presence of two distinct and variable rotation periods in the Saturnian kilometric radiation (SKR). These two periods were attributed to the northern and southern hemispheres respectively. The existence of a double period makes the study of the planetary magnetic field much more complicated and the building of a field model, based on the direct measurements of the MAG experiment from the magnetometers embarked on board Cassini, turns out to be uncertain. The first reason is the difficulty for defining a longitude system linked to the variable period, because the internal magnetic field measurements from MAG are not continuous. The second reason is the existence itself of two distinct periods which could imply the existence of a double rotation magnetic structure generated by Saturn's dynamo. However, the radio observations from the RPWS experiment allow a continuous and accurate follow-up of the rotation phase of the variable two periods, since the SKR emission is permanently observable and produced very close to the planetary surface. A wavelet transform analysis of the intensity of the SKR signal received at 290 kHz was performed in order to calculate the rotation phase of each Saturnian hemisphere. A dipole model was proposed for Saturn's inner magnetic field: this dipole presents the particularity to rotate around Saturn's axis at two different angular velocities; it is tilted and not centered. Then it is possible to fit the MAG data for each Cassini's revolution around the planet the periapsis of which is less than 5 Saturnian radii. This study suggests that Saturn's inner magnetic field is neither stationary nor fully axisymmetric. Such a result can be used as a boundary condition for modelling and constraining the planetary dynamo.

International audience; Two distinct and variable rotation periods in Saturn’s radio emissions were revealed by observations performed by the radio and plasma wave science (RPWS) experiment on board the Cassini spacecraft. These two periods, first measured at 10.6 hours and 10.8 hours, were quickly attributed to SKR produced in the northern and southern hemispheres respectively. Later observations showed that these two periods varied and became equal after the time of Saturn’s equinox. Most of magnetospheric phenomena in Saturn’s environment are affected by the planet spin despite the apparent steep axisymmetry of the internal magnetic field. The existence of a double period makes the study of the planetary magnetic field much more complicated and the building of a field model, based on the direct measurements of the MAG experiment from the magnetometers embarked on board Cassini, turns out to be uncertain. The first reason is the difficulty for defining a longitude system linked to the variable period, because the internal magnetic field measurements from MAG are not continuous. The second reason is the existence itself of two distinct periods which could imply the existence of a double rotation magnetic structure generated by Saturn’s dynamo. However, the radio observations from the RPWS experiment allow a continuous and accurate follow-up of the rotation phase of the variable two periods, since the SKR emission is permanently observable and produced very close to the planetary surface. A wavelet transform analysis of the intensity of the SKR signal received at 290 kHz was performed in order to calculate the rotation phase of each Saturnian hemisphere. A dipole model was proposed for Saturn’s inner magnetic field: this dipole presents the particularity to rotate around Saturn’s axis at two different angular velocities; it is tilted and not centered. Then it is possible to fit the MAG data for each Cassini’s revolution around the planet the periapsis of which is less than 5 Saturnian radii. This study suggests that Saturn’s inner magnetic field is neither stationary nor fully axisymmetric.

International audience; A recent study of the Io-controlled Jovian decameter radiation revealed that the radio emission is beamed in a hollow cone which presents a flattening in a spe- cific direction linked to the local magnetic field in the source. We investigate some reasons for the existence of such a flattening. The Jovian decameter radiation, like the other auroral radio emissions emanating from the magnetized planets in the solar system, is known to be produced by the cyclotron maser instability (CMI). This mechanism allows the direct amplification of the waves through a resonant coupling between the elec- tron population of the plasma and the electromagneticwaves with right circular polarization of the X mode. In a medium with axial symmetry, i.e., where B and ∇B are parallel, this amplification is maximum for a particular value of the emergence angle relatively to the local magnetic field B. We suppose that the plasma is constituted of a cold component which supports the wave propagation and an energetic component which takes part in the growth of the waves by supplying the CMI with free energy. When B and ∇B are not parallel, the angle corresponding to the maximum am- plification is not constant anymore, so that the emis- sion cone does not have any axial symmetry and then presents a flattening; it is the case of the Io-controlled Jovian decameter radiation.

International audience; The results we have recently obtained about the beaming of the Io-controlled decameter Jovian radio emission allow us to conclude that this radiation is emitted in a hollow cone flattened in a particular direction linked to the local magnetic field. The existence of such an emission cone leads us to understand the location of the Io-controlled sources (Io-A, Io-B, Io-C, and Io-D) in the CML-Io phase diagram and to interpret their dependence on the longitude as the manifestation of a Jovian active longitude sector, where the emission mechanism is the most efficient. We study the origin of the flattening of the emission cone in the framework of a radio emission produced by the cyclotron maser instability in an inhomogeneous medium where the local magnetic field B and the gradient of its modulus ∇B are not parallel, i.e., in a geometry without axial symmetry. We consider that the radiation propagates in the source region in the X-mode near its cutoff frequency.

International audience; We report on electric field measurements recorded by DEMETER/ICE experiment above very low frequency (VLF) transmitter stations. The sun-synchronous orbits of the DEMETER satellite lead us to cover an invariant latitude range between-65 • and +65 • in a time interval of about 40 minutes. We select three ground-based transmitter stations localised in Australia (NWC, 19.8 kHz), in Germany (DFY, 16.58 kHz) and in Japan (JP, 17.8 kHz). We analyse the complete set of data recorded from August 2004 to December 2010. We distinguish between the VLF signals observed when the satellite was on day-or night-sides of the Earth at about 22 LT and 10 LT, respectively. We characterize the reception condition of the VLF signal taking into consideration the satellite position above the transmitter stations. We find that the signal amplitude is increasing (up to a maximum) and decreasing (down to a minimum) in a time interval of about 12 days. This 'regular' reception of the VLF signal is a signature of quiet ionosphere behaviour above the transmitter stations. We discuss in our contribution about the time intervals where the VLF signals were almost not detected. The origins of the signal attenuation seem to be linked to the ionospheric perturbations due to the solar activity, the earthquake occurrences and the geomagnetic activity.

International audience; Four zones of enhanced probability are found in the CML-Io phase diagram, where the occurrence of the Jovian decameter radio emissions is plotted versus the central meridian longitude (CML) and the orbital phase of Io. These zones are the so-called Io-controlled sources Io-A, Io-B (emitted from the northern hemisphere), and Io-C, Io-D (emitted from the south). In a recent work, we have studied the occurrence probability in a polar diagram linked to the local magnetic field, making the assumption that the magnetic field intensity gradient plays the role of an optical axis for the wave propagation. For a given Jovian magnetic field model, the four sources Io-A, Io-B, Io-C and Io-D are plotted as a function of the colatitude angle θ relative to the gradient of the magnetic field (radial coordinate) and an azimuth angle ψ linked to the direction of magnetic field vector. Our previous results revealed that the angle θ is not constant and that the Jovian decameter emission controlled by Io is radiated in a hollow cone which is not axi-symmetrical around the magnetic field gradient but flattened in the direction of the magnetic field vector. The relative directions of the magnetic field and its gradient within the radio source seem to play a crucial role in the angular distribution of the occurrence probability. Thus we analyze the effect of the choice of the magnetic field model (in particular the O6, VIP4, VIT4 and VIPAL models) on this distribution and the consequences for the emission cone. The use of elliptic coordinates in a frame linked to the local magnetic field is very relevant for such a study.

International audience; We study the properties of solar Type III radio bursts that were simultaneously observed by RPWS/Cassini, URAP/Ulysses and WAVES/Wind experiments. The observations covered a time interval of about one year during which the spacecraft trajectories where localized in the ecliptic plane for Wind and Cassini, and at high heliographic latitudes (of about -75°) for Ulysses spacecraft. The data set consists of the flux density and the arrival time as a function of frequency in the range of a few kHz to 16 MHz. This leads us to determine the time profiles associated to the electron beam evolution along the interplanetary magnetic field where the trajectory is supposed to be an Archimedean spiral. We assume that the trajectories are contained in the plane of the ecliptic and the velocity of the solar wind is constant and equal to 400 km/s. Several empirical models of electron density are considered in the estimation of the electron beam evolution. We show that some of these models may be used to outline the real Type III burst trajectory, and others not. We discuss the particularity of each model and we attempt to classify them taking into consideration the different regions where the radio was propagating, i.e. the solar corona (few solar radii) and the interplanetary medium up to the orbit of the Earth (~ 1 AU) and Jupiter (~ 5 AU).

International audience; The Earth's auroral kilometric radiation (AKR) is expected to exhibit a hollow pattern similar to that reported for the comparable emissions from Jupiter (e.g. Jovian decametric emissions - DAM). The hollow pattern is a hollow cone beam with apex at the point of AKR emission, axis tangent to the magnetic field direction, and an opening angle of the order of 80°. The properties of the hollow cone can be derived from the so-called dynamic spectrum which displays the radiation versus the observation time and the frequency. We analyze the auroral kilometric radiation recorded by the electric field experiment (ICE) onboard DEMETER micro-satellite. The dynamic spectra lead us to study the occurrence of the AKR recorded in the sub-auroral regions when the micro-satellite was at altitudes of about 700 km. We address in this contribution issues concerning the characteristics (occurrence, latitude and longitude) of the AKR hollow beam and their relations to the seasonal and solar activity variations.

Observations performed by the radio and plasma wave science (RPWS) experiment on board the Cassini spacecraft revealed two distinct and variable rotation periods in Saturn's radio emissions. These two periods, first measured at 10.6 hours and 10.8 hours, were quickly attributed to SKR produced in the northern and southern hemispheres respectively. Later observations showed that these two periods varied and became equal after the time of Saturn's equinox. Most of magnetospheric phenomena in Saturn's environment are affected by the planet spin despite the apparent steep axisymmetry of the internal magnetic field. The existence of a double period makes the study of the planetary magnetic field much more complicated and the building of a field model, based on the direct measurements of the MAG experiment from the magnetometers embarked on board Cassini, turns out to be uncertain. The first reason is the difficulty for defining a longitude system linked to the variable period, because the internal magnetic field measurements from MAG are not continuous. The second reason is the existence itself of two distinct periods which could imply the existence of a double rotation magnetic structure generated by Saturn's dynamo. However, the radio observations from the RPWS experiment allow a continuous and accurate follow-up of the rotation phase of the variable two periods, since the SKR emission is permanently observable and produced very close to the planetary surface. We have performed a wavelet transform analysis of the intensity of the SKR signal received at 290 kHz in order to calculate the rotation phase of each Saturnian hemisphere. Then the inner magnetic field is expanded in series of spherical harmonics for each Cassini's revolution around the planet the periapsis of which is less than 5 Saturnian radii.

Four zones of enhanced probability are revealed in the CML-Io phase diagram, where the occurrence of the Jovian decameter radiation is plotted versus the central meridian longitude (CML) and the phase of the satellite Io. These zones are usually named Io-controlled sources Io-A, Io-B (emitted from the northern hemisphere), and Io-C, Io-D (emitted from the south). Supposing that the radio emission is generated near the local gyro-frequency (by the cyclotron maser instability) along a magnetic field line carried away by Io during its revolution around Jupiter (with a lead angle δ), we examine the occurrence probability of the radiation in a polar diagram defined by the local magnetic field. The location of the four Io-controlled sources (Io-A, Io-B, Io-C and Io-D) are plotted as a function of the colatitude angle θ relative to the gradient of the magnetic field (playing the role of an optical axis for the wave propagation) and an azimuth angle ψ linked to the direction of magnetic field vector. The angular distribution of the sources clearly shows that the angle θ is not constant, so that the Jovian decameter emission controlled by Io is radiated in a hollow cone which is not axi-symmetrical around the magnetic field gradient but flattened in the direction of the magnetic field vector. A precise oblate beaming cone has been computed for each Jovian hemisphere using elliptic coordinates. Our result is compatible with the existence of a sector of active longitude favouring the radiation in regions of the CML-Io phase diagram that are in good agreement with the observations.

Long-term observations of Jupiter's decametric (DAM) radiation have shown that a large part of emission is modulated by two dominant factors: the planetary rotation and the orbital phase of Io. The first one indicates that the occurrence probability of the radiation depends on the observer's longitude, while the second factor points to a control of part of the radio emission by Io. Spectropolarimeter measurements showed that the radiation emitted from the northern and southern hemispheres are right-hand and left-hand circular polarized, respectively. Here we compare the Jovian decametric polarization observations to those derived from the active longitude model proposed by Galopeau et al. (JGR, 109, 2004). This model gives evidence of the presence of a longitude range in the northern and southern hemispheres favoring the radio decametric emission and leading to a higher occurrence probability. We discuss the common polarization features between the model and the observations, and we show that the behaviors of the southern and northern sources are not alike despite a same generation mechanism.