Remote sensing of the Io torus plasma ribbon using natural radio occultation of the Jovian radio emissions

International audienceWe study the Jovian hectometric (HOM) emissions recorded by the RPWS (Radio and Plasma Wave Science) experiment onboard the Cassini spacecraft during its Jupiter flyby. We analyze the attenuation band associated with the intensity extinction of HOM radiation. This phenomenon is interpreted as a refraction effect of the Jovian hectometric emission inside the Io plasma torus. This attenuation band was regularly observed during periods of more than 5 months, from the beginning of October 2000 to the end of March 2001. We estimate for this period the variation of the electron density versus the central meridian longitude (CML). We find a clear local time dependence. Hence the electron density was not higher than 5.0 × 104 cm−3 during 2 months, when the spacecraft approached the planet on the dayside. In the late afternoon and evening sectors, the electron density increases to 1.5 × 105 cm−3 and reach a higher value at some specific occasions. Additionally, we show that ultraviolet and hectometric wavelength observations have common features related to the morphology of the Io plasma torus. The maxima of enhancements/attenuations of UV/HOM observations occur close to the longitudes of the tip of the magnetic dipole in the southern hemisphere (20° CML) and in the northern hemisphere (200° CML), respectively. This is a significant indication about the importance of the Jovian magnetic field as a physical parameter in the coupling process between Jupiter and the Io satellite

Case studies of SKR planetary rotations

International audienceWe analyze the Saturnian Kilometric Radiation (SKR) recorded by the Radio and Plasma Wave Science experiment (RPWS) onboard the Cassini spacecraft. This radio emission is generated by electron beams carried along by the planetary magnetic field. The regular monitoring of such radiation allowed to derive the planetary rotation rate in the case of Saturn, and the other magnetized planets, like Jupiter and Uranus. Precise investigations of the SKR radiation, recorded by Ulysses and Cassini spacecraft, have shown two different rotation periods in the northern hemisphere and in the southern one. The deviation is of about 13 minutes between both hemispheres. In this work we attempt to characterize the spectral features associated to each hemisphere. Observational parameters are used to describe those features like arc shapes and their orientations (i.e. vertex-early and -late arcs), the symmetric pattern, the time duration and the presence, or not, of a frequency drift rate. We show some cases where the planetary rotation can be 'spectrally' estimated for the northern or southern hemisphere. However a real difficulty appears when we try to follow and track the period, from one rotation to the next. We discuss the spectral complexity of the SKR rotation period particularly when it is compared to the Jovian radio emissions. The concept of the hollow cone is addressed in this context in particular its geometrical symmetry and its axis tangent to the local magnetic field crossing the source region

Analysis of Saturnian planetary rotation following the knowledge on Jovian radio emission

International audienceWe 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

Statistical analysis of Solar Type III radio bursts observed by RPWS experiment in 2004-2017 during the Solar cycles 23-24

International audienceWe report on Solar Type III radio bursts observed by the radio and plasma wave experiment (RPWS) onboard Cassini spacecraft. RPWS instrument measures electric field over a frequency range from few Hz and up to 16 MHz (Rucker et al., 2008). A statistical survey of almost 1000 solar bursts recorded in the time interval from January 2004 to September 2017 is considered in this study. Those solar bursts occurred in the end of the 23 solar cycle (2004-2008) and during the 24 solar cycle (2008-2017). Type III observational parameters are taken into consideration like the emission frequency, the time occurrence, the intensity level, and the heliospheric location (i.e. distance, longitude and latitude) of the spacecraft when the solar burst has been detected. This leads to insist on three main aspects: (a) the occurrence rate of the solar burst, (b) the corresponding electron density derived from heliocentric empirical models and (c) the most plausible source regions at the origin of the Type III bursts. Those characteristics allow us to discuss how Type III bursts are linked to the ecliptic spatial expansion of the Archimedean spiral emerging from the Sun, crossing the Earth’s orbit and reaching the Saturn’s orbits

Statistical analysis of Solar Type III radio bursts observed by RPWS experiment in 2004-2017 during the Solar cycles 23-24

International audienceWe report on Solar Type III radio bursts observed by the radio and plasma wave experiment (RPWS) onboard Cassini spacecraft. RPWS instrument measures electric field over a frequency range from few Hz and up to 16 MHz (Rucker et al., 2008). A statistical survey of almost 1000 solar bursts recorded in the time interval from January 2004 to September 2017 is considered in this study. Those solar bursts occurred in the end of the 23 solar cycle (2004-2008) and during the 24 solar cycle (2008-2017). Type III observational parameters are taken into consideration like the emission frequency, the time occurrence, the intensity level, and the heliospheric location (i.e. distance, longitude and latitude) of the spacecraft when the solar burst has been detected. This leads to insist on three main aspects: (a) the occurrence rate of the solar burst, (b) the corresponding electron density derived from heliocentric empirical models and (c) the most plausible source regions at the origin of the Type III bursts. Those characteristics allow us to discuss how Type III bursts are linked to the ecliptic spatial expansion of the Archimedean spiral emerging from the Sun, crossing the Earth’s orbit and reaching the Saturn’s orbits

Study of AKR hollow pattern characteristics at sub-auroral regions

International audienceThe 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

Terrestrial kilometric radiation observed on pre-midnight side of the Earth at 1-2 L-Shell

International audienceThe ICE experiment onboard the DEMETER satellite recorded kilometric emissions in the vicinity of the magnetic equatorial plane. Those radiations were observed in the beginning of the year 2010 on the night-side of the Earth and rarely on the day-side. We distinguish two components one appears as a continuum between few kHz and up to 50 kHz and the other one from 50 kHz to 800 kHz. The first component exhibits positive and negative frequency drift rates in the southern and northern hemispheres, at latitudes between 40 • and 20 •. The second component displays multiple spaced frequency bands. Such bands 5 mainly occur near the magnetic equatorial plane with a particular enhancement of the power level when the satellite latitude is close to the magnetic equatorial plane. We show in this study that both components are linked to the terrestrial non-thermal kilometric radiation. Those two components are the trapped and the escaping terrestrial non-thermal kilometric radiation. Above 150 kHz, we have found that the escaping emissions are mainly extended in frequency in the southern hemisphere and in geomagnetic latitude in the opposite hemisphere. DEMETER low altitude orbits lead to describe the frequency and the time 10 evolution of this terrestrial radiation particularly on the evening sector at L-Shell of about 2. We show the dependence of the power intensity on the emission frequency, and provide a hint on the location of the source region and its relation to the Earth's plasmasphere. It is shown that the so-called 'Christmas-tree' pattern associated to the terrestrial kilometric radiation may be associated to the plume and channel generated in the pre-midnight sector of the plasmasphere

Low-altitude frequency-banded equatorial emissions observed below the electron cyclotron frequency

International audienceThe ICE (Instrument Champ Électrique) experiment on board the DEMETER (Detection of ElectroMagnetic Emissions Transmitted from Earthquake Regions) satellite recorded frequency-banded wave emissions below the electron cyclotron frequency, with band spacing frequency low-hybrid resonance, in the vicinity of the magnetic equatorial plane. Those radiations were observed in the beginning of the year 2010 on the night side of Earth and rarely on the day side. We distinguish two components: one appears as frequency bands continuous in time between a few kilohertz and up to 50 kHz, and the other one is from 50 to 800 kHz. The first component exhibits positive and negative frequency drift rates in the Southern Hemisphere and Northern Hemisphere, at latitudes between 40 and 20 •. The second one displays multiple spaced frequency bands. Such bands mainly occur near the magnetic equatorial plane with a particular enhancement of the power level when the satellite latitude is close to the magnetic equatorial plane. We show in this study the similarities and the discrepancies between the non-free-space DEMETER frequency-banded emissions and the well-known free-space terrestrial kilometric radiation. The hollow cones of the DEMETER frequency-banded wave emissions are oriented towards Earth's ionosphere. We suggest that the source region is localized in regions pole-ward of the plasmapause where the ratio of the plasma frequency to gyro-frequency is smaller than one

Reception conditions of low frequency (LF) transmitter signals onboard DEMETER micro-satellite

International audienceWe analyze the flux density variation associated to low frequency (LF) broadcasting transmitters observed by the ICE electric field experiment onboard DEMETER micro-satellite. We select five stations localised around the Mediterranean and the black seas: Tipaza (252 kHz, 02°28'E, 36°33'N, Algeria), Roumoules (216 kHz, 06°08'E, 43°47'N, Monte Carlo), Polatli (180 kHz, 32°25'E, 39°45'N, Turkey), Nador (171 kHz, 02°55'W, 35°02'N, Morocco) and Brasov (153 kHz, 25°36'E,45°40', Romania). The detection of the LF transmitter signals by DEMETER micro-satellite is found to depend on the radiated power, the emitted frequency, and the orbit paths with regard to the location of the stations. This leads us to characterise the reception condition of the LF signals and to define time intervals where the detection probability is high. We firstly discuss the dependence of the reception conditions on the ionospheric disturbances due to the geomagnetic and solar activities, and we secondly attempt to estimate the global electric environment above the Mediterranean and the black seas