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The search for lightning on Saturn''s satellite Titan is one scientific target of the Cassini/Huygens mission. Although Voyager 1 did not detect any radio emissions caused by Titan lightning during its flyby in November 1980, one cannot generally rule out their existence, because of low flash rates or ionospheric radiation blockade. Recently, Tokano et al. (Planet. Space Sci. 49 (2001a) 539) have developed a thundercloud model in Titan''s troposphere favoring the existence of Titan lightning due to negatively charged clouds causing temporary electric fields sufficient to initiate cloud-to-ground lightning strokes. In the present investigation we estimate the amount of energy dissipation of such lightning strokes by electrostatic energy considerations similarly to those by Cooray (J. Geophys. Res. 102(D17) (1997) 21,401). The analysis is based on the cloud charge distribution given by Tokano et al. (2001a), which has a monopole structure or a dipole structure depending on the electrification mechanism. It consists of horizontally homogenous charge layers, whose charge densities depend on the altitude above ground. As results we get the typical charge lowered in a possible Titan lightning stroke and the amount of energy dissipation. For a simulated Titan monopolar cloud charged by electron attachment we found that cloud-to-ground strokes lower about 30 C of charge and dissipate energies about 1010 J. For the modelled bipolar clouds charged by collisional charging these values are a few C of lowered charge and about 108–109J of dissipated energy, which are quite similar to typical Earth values. These energies are substantially higher than the energies suggested by Desch and Kaiser (Nature 343 (1990) 442), who concluded from the Voyager data that discharges might be frequent but weak (<106J). We shortly discuss the detection capability of the Cassini/RPWS (Radio and Plasma Wave Science experiment) for possible Titan lightning strokes taking into account the wave attenuation in the frequency range up to 16 MHz during the propagation through Titan''s ionosphere as calculated by Schwingenschuh et al. (Adv. Space Res. 28(10) (2001) 1505). [Copyright &y& Elsevier]

Abstract: The propagation of extremely low frequency (ELF) electromagnetic waves and resonance phenomena in the Earth atmosphere has been extensively studied, in relation with ionospheric dynamics, and thunderstorm and lightning activities. A similar investigation can be performed for any other planet and satellite environment, provided this body is wrapped into an ionosphere. There are, however, important differences between Earth and other bodies, regarding the surface conductivity, the atmospheric electron density, the ionospheric cavity geometry, and the sources of electromagnetic energy. In a first approximation, the size of the cavity defines the range of the resonance frequency; the electron density profile, up to the upper atmospheric boundary, controls the wave attenuation; the nature of the electromagnetic sources influences the field distribution in the cavity; and the body surface conductivity, which gives the reflection and transmission coefficients, indicates to what extent the subsurface can be explored. The knowledge of the frequencies and attenuation rates of the principal eigenmodes provides unique information about the electric properties of the cavity. Instruments capable of monitoring the electromagnetic environment in the ELF range are, therefore, valuable payload elements on balloons, descent probes and landers. We develop models for selected inner planets, gaseous giants and their satellites, and review the propagation process of ELF electromagnetic waves in their atmospheric cavities, with a particular emphasis on the application of the Schumann resonance observation to subsurface studies. The instrumentation suitable for monitoring the electromagnetic environment in geophysical cavities is briefly addressed. [Copyright &y& Elsevier]

Abstract: The propagation of extremely low frequency (ELF) electromagnetic waves in the Earth''s ionospheric cavity and the associated resonance phenomena have been extensively studied, in relation with lightning activity. We perform a similar investigation for Titan, the largest moon of Saturn. There are important differences between Earth and Titan, as far as the cavity geometry, the atmospheric electron density profile, and the surface conductivity are concerned. We present an improved 3D finite element model that provides an estimate of the lowest eigenfrequencies, associated quality factors (Q-factors), and ELF electric field spectra. The data collected by the electric antenna of the Permittivity, Waves, and Altimetry (PWA) instrument reveals the existence of a narrow-band signal at about 36Hz during the entire descent of Huygens upon Titan. We assess the significance of these measurements against the model predictions, with due consideration to the experimental uncertainties. [Copyright &y& Elsevier]

Abstract: During the descent of the Huygens probe through the atmosphere of Titan, on January 14th, 2005, the permittivity, waves and altimetry (PWA) subsystem, a component of the Huygens atmospheric structure instrument (HASI), detected an ionized layer at altitudes around 63km with two different instruments, the relaxation probe (RP) and the mutual impedance probe (MIP). A very detailed analysis of both data sets is required, in order to correct for environmental effects and compare the two independent estimates of the electrical conductivity. The present work is dedicated to the MIP data analysis. New laboratory tests have been performed to validate or improve the available calibration results. Temperature effects have been included and numerical models of the MIP sensors and electric circuitry have been developed to take into account the proximity of the Huygens probe body. The effect of the vertical motion of the vessel in the ionized atmosphere is estimated in both analytical and numerical ways. The peculiar performance of the instrument in the altitude range 100–140km is scrutinized. The existence of a prominent ionized layer, and of enhancements in the conductivity and electron density profiles at 63km, are discussed in the light of previous theoretical predictions. [Copyright &y& Elsevier]

Abstract: The low-frequency data collected with the antenna of the Permittivity, Wave and Altimetry experiment on board the Huygens Probe that landed on Titan on 14 January 2005 have been thoroughly analyzed considering different possible natural and artificial effects. Although a definite conclusion is still subject to the outcome of complementary inquiries, it results from our analysis that the observations can be explained, for the most part, in term of natural phenomena rather than being artifacts. Extremely-low frequency waves generated in the ionosphere of Titan, driven by the corotating Saturn''s frozen plasma flow, are assumed to be the most likely source for the observation of the second eigenmode of a Schumann-like resonance at around 36 Hz in the moon-ionosphere cavity. This particular mode is thought to be enhanced with respect to other harmonics because of the particular location of the landing site with respect to that of the supposed sources. The power budget of the observed wave amplitude seems to be consistent with a rough model of the global current of the wake-ionosphere circuit. Broadband low-frequency noise events which are observed sporadically during the descent are probably due to shot noise on the antenna when the Probe is crossing aerosol clouds, an interpretation supported by post-flight ground tests. Contrary to the situation encountered on Earth, atmospheric lightning does not appear to be the source of a conventional Schumann resonance on Titan. [Copyright &y& Elsevier]

Abstract: The permittivity, waves and altimetry (PWA) instrument was designed for the investigation of the electric properties and other related physical characteristics of the atmosphere of Titan, from an altitude around 140km down to the surface. PWA carried sensors to measure the atmospheric conductivity, and record electromagnetic and acoustic waves up to frequencies of 11.5 and 6.7kHz, respectively. PWA also measured the relief roughness during the descent and the permittivity of the surface after touchdown. The measurements and the results of the preliminary analysis are presented. An ionized layer is detected at altitudes above 50km, using two independent techniques, and the presence of free electrons in the upper atmosphere is confirmed. An electric signal at around 36Hz is observed throughout the descent, but it is not yet confirmed that this emission is unambiguously related to a resonance of the ionospheric cavity. The relative dielectric constant of Titan''s surface material is nearly 2 and the electric conductivity 4×10−10 Sm−1. The electric properties of the surface seem to evolve after touch-down, possibly due to a local warming of the landing site by the Huygens Probe body. [Copyright &y& Elsevier]

Electrocardiographic changes were evaluated retrospectively in five patients without previous episodes of syncope or ventricular fibrillation who developed abnormal ST segment elevation mimicking the Brugada syndrome in leads V1-V3 after the administration of class Ic antiarrhythmic drugs. Pilsicainide (four patients) or flecainide (one patient) were administered orally for the treatment of symptomatic paroxysmal atrial fibrillation or premature atrial contractions. The QRS duration, QTc, and JT intervals on 12 lead surface ECG before administration of these drugs were all within normal range. After administration of the drugs, coved-type ST segment elevation in the right precordial leads was observed with mild QRS prolongation, but there were no apparent changes in JT intervals. No serious arrhythmias were observed during the follow up periods. Since ST segment elevation with mild QRS prolongation was observed with both pilsicainide and flecainide, strong sodium channel blocking effects in the depolarisation may have been the main factors responsible for the ECG changes. As the relation between ST segment elevation and the incidence of serious arrhythmias has not yet been sufficiently clarified, electrocardiographic changes should be closely monitored whenever class Ic drugs are given. [ABSTRACT FROM AUTHOR]