Reply to comment by B. Cecconi on "Spectral features of SKR observed by Cassini/RPWS: Frequency bandwidth, flux density and polarization"

International audienceThe main purpose of the paper by Galopeau et al.[2007] was to classify the spectral features of the Saturniankilometric radiation (SKR) starting from three physicalobserved parameters: the frequency bandwidth, the fluxdensity, and the pol arization. We show in the presentresponse that an unsupervised application of arbitrary auto-matic criteria during the data processing (such as a signal-to-noise ratio greater than 23 dB) can totally judge a weaknatural emission as a background noise. As a consequence,such a situation may lead to consideration of only the datapresenting a degree of circular polarization close to 100%and neglect a huge part of the data. Galopeau et al. [2007]considered a phenomenological aspect and gave an estima-tion of the Stokes parameters. This approach leads to firstrecognizing spectral components (flux density and band-width) in the frequency range from 3.5 kHz to 1200 kHz,and then deriving the Stokes parameters for each compo-nent. The Cassini/RPWS instrument provides long-lastingcoverage of radio emissions at Saturn with unprecedentedinstrumental capabilities

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

The Graz seismo-electromagnetic VLF facility

Abstract. In this paper we describe the Graz seismo-electromagnetic very low frequency (VLF) facility, as part of the European VLF receiver network, together with the scientific objectives and results from two years operation. After a brief technical summary of the present system – with heritage from a predecessor facility – i.e. hardware, software, operational modes and environmental influences, we discuss results from statistical data and scientific events related to terrestrial VLF propagation over Europe

A VLF/LF facility network for preseismic electromagnetic investigations

Earthquakes are one of the most frequently occurring natural disasters. Many indications have been collected on the presence of seismo-ionospheric perturbations preceding such tragic phenomena. Radio techniques are the essential tools leading the detection of seismo-electromagnetic emissions by monitoring at very low-frequency (VLF, 3–30 kHz) and low-frequency (LF, 30–300 kHz) sub-ionospheric paths between transmitters and receivers (Hayakawa, 2015). In this brief communication, we present the implementation of a VLF/LF network to search for earthquake electromagnetic precursors. The proposed system is comprised of a monopole antenna including a preamplifier, a GPS receiver and a recording device. This system will deliver a steady stream of real-time amplitude and phase measurements as well as a daily recording VLF/LF data set. The first implementation of the system was done in Graz, Austria. The second one will be in Guyancourt (France), with a third one in Réunion (France) and a fourth one in Moratuwa (Sri Lanka). In the near future, we are planning to expand our network for enhanced monitoring and increased coverage.</p

Case study of radio emission beam associated to very low frequency signal recorded onboard CSES satellite

We report on the variation of electric power density linked to very low frequency (VLF) signal observed during the minimum of solar cycle 25. The detected VLF signal is emitted by the NWC radio station localized in the southern hemisphere, at 21.5∘ S and 114.2∘ E. We attempt in this work to quantify the beam as detected by the Electric Field Detector (EFD) instrument onboard CSES satellite. Geometrical key parameters have been considered to analysis the variation of the power density taking into consideration the distance between the satellite trajectory and the NWC station and its conjugate region. The beam behavior is found to be subject to significant disturbances in the conjugate region with the presence of signal modulations. Above the NWC transmitter station, the beam can be considered as a hollow cone but with irregularity dependence on the electric power density.</p

Ionospheric conductivity effects on electrostatic field penetration into the ionosphere

International audience(Crim., 24 mai 2011, n° 10-85.184, non publié au Bulletin

Beaming Cone of Io-Controlled Jovian Decameter Radiation Derived From the JRMP9 Magnetic Field Model

International audienceWe investigate the angular distribution of the Jovian decameter radiation occurrence probability, relatively to the local magnetic field B and its gradient ∇B in the source region. A previous study based on the O6 magnetic field model of Jupiter revealed that the radio emission is beamed in a hollow cone presenting a flattening in a specific direction. The Jovian decameter radiation, like the other auroral radio emissions of the magnetized planets, is known to be produced by the cyclotron maser instability (CMI). In a plasma with axial symmetry, i.e., where B and ∇B are parallel, the maximum amplification of the waves is obtained for a particular value of the emergence angle relatively to the local magnetic field B. This angle is not constant anymore when B and ∇B are not parallel, so that the emission cone does not have any axial symmetry and then presents a flattening in a privileged direction. In this study, we use the new model of Jupiter's magnetic field based on Juno's first nine orbits, JRMP9, proposed by Connerney et al. [Geophys. Res. Lett., 45, 2590-2596, 2018], in order to analyze the geometry of the emission cone

Evidence of Jovian active longitude: 3. Observational constraints

International audienceThe occurrence probability of the Io-controlled Jovian decameter radio emissions depends on the central meridian longitude and the orbital phase of the satellite Io. Investigations by Galopeau et al. (2004, 2007) have shown that some specific Jovian “active” longitudes favor the radiation. The authors proposed a model which involves the cyclotron maser instability (CMI) as the mechanism at the origin of the Jovian radio emissions produced near the local gyrofrequency, along an active magnetic field line carried away by Io through its revolution around Jupiter. Those studies brought out the existence of an active longitude anchored in Jupiter's magnetic field and directly related to the efficiency of the CMI. In the present analysis, we model the four occurrence regions associated to Io-controlled sources. This approach is in a reverse way of the parametric method developed by Galopeau et al. (2007). The properties of the propagation and polarization of the radio wave, derived from the CMI, are the key ingredients for the study of the beaming cone. It is shown that the lead angle of the active magnetic field line relative to Io has a significant effect on both the selection of the propagation conditions and the limit between the right- and left-hand polarization states. The modeled and observed occurrence regions are found to be similar for a lead angle of about 20°. However, it seems that the behaviors of the southern and northern sources are not alike despite a common generation mechanism