Radio Jupiter after Voyager: An overview of the Planetary Radio Astronomy observations

Jupiter's low frequency radio emission morphology as observed by the Planetary Radio Astronomy (PRA) instrument onboard the Voyager spacecraft is reviewed. The PRA measurement capabilities and limitations are summarized following over two years of experience with the instrument. As a direct consequence of the PRA spacecraft observations, unprecedented in terms of their sensitivity and frequency coverage, at least three previous unrecognized emission components were discovered: broadband and narrow band kilometric emission and the lesser arc decametric emission. Their properties are reviewed. In addition, the fundamental structure of the decameter and hectometer wavelength emission, which is believed to be almost exclusively in the form of complex but repeating arc structures in the frequency time domain, is described. Dramatic changes in the emission morphology of some components as a function of Sun-Jupiter-spacecraft angle (local time) are described. Finally, the PRA in suit measurements of the Io plasma torus hot to cold electron density and temperature ratios are summarized

Voyager spacecraft radio observations of Jupiter: Initial cruise results

Jupiter's low-frequency radio emission were detected by the planetary radio astronomy instruments onboard the two Voyager spacecraft. The emission is surprisingly similar in morphology but opposite in polarization to the high-frequency Jovian radio noise that were observed with ground-based telescopes for more than two decades. Several possible explanations for the behavior of the low-frequency emission are examined, but none of them is completely satisfactory

Planetary radio astronomy observations from Voyager-2 near Saturn

Voyager-2 planetry radio astronomy measurements obtained near Saturn are discussed. They indicate that Saturnian kilometric radiation is emitted by a strong, dayside source at auroral latitudes in the northern hemisphere and by a weaker (by more than an order of magnitude) source at complementary latitudes in the southern hemisphere. These emissions are variable both due to Saturn's rotation and, on longer time scales, probably due to influences of the solar wind and the satellite Dione. The Saturn electrostatic discharge bursts first discovered by Voyager-1 and attributed to emissions from the B-ring were again observed with the same broadband spectral properties and a 10(h)11(m) + or - 5(m) episodic recurrence period but with an occurrence frequency of only of about 30 percent of that detected with Voyager-1. During the crossing of the ring plane at a distance of 2.88 R sub S, an intense noise event is interpreted to be consequence of the impact/vaporization/ionization of charged micron-size G-ring particles distributed over a total vertical thickness of about 1500 km

Radio Detection of Cosmic Ray Air Showers with Codalema

Studies of the radio detection of Extensive Air Showers is the goal of the demonstrative experiment CODALEMA. Previous analysis have demonstrated that detection around $5.10^{16}$ eV was achieved with this set-up. New results allow for the first time to study the topology of the electric field associated to EAS events on a event by event basis.Comment: 6 pages, 4 figures Proceedings of the Rencontres de Moriond, Very High Energy Phenomena in the Universe, La Thuile, Italy (March 12-19, 2005

Radio Detection of Extensive Air Showers with CODALEMA

The principle and performances of the CODALEMA experimental device, set up to study the possibility of high energy cosmic rays radio detection, are presented. Radio transient signals associated to cosmic rays have been identified, for which arrival directions and shower's electric field topologies have been extracted from the antenna signals. The measured rate, about 1 event per day, corresponds to an energy threshold around 5.10^16 eV. These results allow to determine the perspectives offered by the present experimental design for radiodetection of UHECR at a larger scale.Comment: 4 pages and 3 figures. To appear in the Proceedings of the 29th ICRC, Pune (2005

Radiodetection of Cosmic Ray Extensive Air Showers

We present the characteristics and performance of a demonstration experiment devoted to the observation of ultra high- energy cosmic ray extensive air showers using a radiodetection technique. In a first step, one antenna narrowed band filtered acting as trigger, with a 4 $\sigma$ threshold above sky background-level, was used to tag any radio transient in coincidence on the antenna array. Recently, the addition of 4 particle detectors has allowed us to observe cosmic ray events in coincidence with antennas

Radio Detection of Cosmic Ray Extensive Air Showers: present status of the CODALEMA experiment

Data acquisition and analysis for the CODALEMA experiment, in operation for more than one year, has provided improved knowledge of the characteristics of this new device. At the same time, an important effort has been made to develop processing techniques for extracting transient signals from data containing interference.Comment: september 200

A method to characterize the different extreme waves for islands exposed to various wave regimes: a case study devoted to Reunion Island

This paper outlines a new approach devoted to the analysis of extreme waves in presence of several wave regimes. It entails discriminating the different wave regimes from offshore wave data using classification algorithms, before conducting the extreme wave analysis for each regime separately. The concept is applied to the pilot site of Reunion Island which is affected by three main wave regimes: southern waves, trade-wind waves and cyclonic waves. Several extreme wave scenarios are determined for each regime, based on real historical cases (for cyclonic waves) and extreme value analysis (for non-cyclonic waves). For each scenario, the nearshore wave characteristics are modelled all around Reunion Island and the linear theory equations are used to back calculate the equivalent deep-water wave characteristics for each portion of the coast. The relative exposure of the coastline to the extreme waves of each regime is determined by comparing the equivalent deep-water wave characteristics. <br><br> This method provides a practical framework to perform an analysis of extremes within a complex environment presenting several sources of extreme waves. First, at a particular coastal location, it allows for inter-comparison between various kinds of extreme waves that are generated by different processes and that may occur at different periods of the year. Then, it enables us to analyse the alongshore variability in wave exposition, which is a good indicator of potential runup extreme values. For the case of Reunion Island, cyclonic waves are dominant offshore around the island, with equivalent deep-water wave heights up to 18 m for the northern part. Nevertheless, due to nearshore wave refraction, southern waves may become as energetic as cyclonic waves on the western part of the island and induce similar impacts in terms of runup and submersion. This method can be easily transposed to other case studies and can be adapted, depending on the data availability

Exchange of ejecta between Telesto and Calypso: Tadpoles, horseshoes, and passing orbits

We have numerically integrated the orbits of ejecta from Telesto and Calypso, the two small Trojan companions of Saturn's major satellite Tethys. Ejecta were launched with speeds comparable to or exceeding their parent's escape velocity, consistent with impacts into regolith surfaces. We find that the fates of ejecta fall into several distinct categories, depending on both the speed and direction of launch. The slowest ejecta follow sub-orbital trajectories and re-impact their source moon in less than one day. Slightly faster debris barely escape their parent's Hill sphere and are confined to tadpole orbits, librating about Tethys' triangular Lagrange points L4 (leading, near Telesto) or L5 (trailing, near Calypso) with nearly the same orbital semi-major axis as Tethys, Telesto, and Calypso. These ejecta too eventually re-impact their source moon, but with a median lifetime of a few dozen years. Those which re-impact within the first ten years or so have lifetimes near integer multiples of 348.6 days (half the tadpole period). Still faster debris with azimuthal velocity components >~ 10 m/s enter horseshoe orbits which enclose both L4 and L5 as well as L3, but which avoid Tethys and its Hill sphere. These ejecta impact either Telesto or Calypso at comparable rates, with median lifetimes of several thousand years. However, they cannot reach Tethys itself; only the fastest ejecta, with azimuthal velocities >~ 40 m/s, achieve "passing orbits" which are able to encounter Tethys. Tethys accretes most of these ejecta within several years, but some 1 % of them are scattered either inward to hit Enceladus or outward to strike Dione, over timescales on the order of a few hundred years

The chemical diversity of comets

A fundamental question in cometary science is whether the different dynamical classes of comets have different chemical compositions, which would reflect different initial conditions. From the ground or Earth orbit, radio and infrared spectroscopic observations of a now significant sample of comets indeed reveal deep differences in the relative abundances of cometary ices. However, no obvious correlation with dynamical classes is found. Further results come, or are expected, from space exploration. Such investigations, by nature limited to a small number of objects, are unfortunately focussed on short-period comets (mainly Jupiter-family). But these in situ studies provide "ground truth" for remote sensing. We discuss the chemical differences in comets from our database of spectroscopic radio observations, which has been recently enriched by several Jupiter-family and Halley-type comets.Comment: In press in Earth, Moon and Planets (proceedings of the workshop "Future Ground-based Solar System Research: Synergies with Space Probes and Space Telescopes", Portoferraio, Isola d'Elba, Livorno (Italy), 8-12 September 2008). 6 pages with 2 figure