Electric potential jumps in the Io-Jupiter flux tube

Abstract

The Io flux tube (IFT), along which Io interacts with the Jovian magnetosphere, is the place of plasma acceleration processes resulting in auroral like emissions, in UV, IR and Radio emissions in the decameter range. At Earth, the study of the acceleration processes is mainly made by in situ measurements. Acceleration processes at Jupiter were first deduced from the observation of a particular kind of decameter radio emissions from the IFT: the short (S-)bursts. These radio bursts present a negative drift in the time-frequency domain, which is related to the motion of the energetic electrons which produce them. The measure of their drift thus permits the kinetic energy of the electrons to be obtained, as well as its variations along the IFT which have been interpreted as electric potential jumps. Using an enhanced S-burst detection and drift measurement method, more than 1 h of quasi-continuous decametric emissions recorded at the Kharkov UTR-2 radiotelescope have been analyzed. We observe the evolution of the electron kinetic energy with the longitude of Io with a resolution of $10 s, and detect the presence of acceleration structures with characteristics being consistent with electric potential jumps of few hundred volts, and moving along the IFT in the upward direction (toward Io) at the local sound velocity. r

Non-propagating electric and density structures formed through non-linear interaction of Alfvén waves

“…The diagnostics were made through the analysis of the so-called S-bursts and N-band radio emissions (Hess et al, 2009b;Arkhypov and Rucker, 2011) and a combination of data analysis and numerical simulation (Hess et al, 2007(Hess et al, , 2009a. In a discussion paper, it has been established that the observed quasi-static structures are below the Alfvénic acceleration region, but still in the Alfvénic resonator, in the place where both the incident and the reflected Alfvén waves have a high amplitude (Mottez et al, 2010).…”

A low-noise, high-dynamic-range, digital receiver for radio astronomy applications: an efficient solution for observing radio-bursts from Jupiter, the Sun, pulsars, and other astrophysical plasmas below 30 MHz

“…Those include the observations of the sources that have high occurrence probability for the signal, i.e., are predictable, are of high SNR, and produce timefrequency patterns in spectrograms with various time-frequency scales that require analysis at several values of resolution. A good example of these "predictable" powerful signals is decameter S-burst ("S" = short) emission from Jupiter known to have complex morphology in the time-frequency plane and high occurrence probability under certain conditions defined by the geometric configuration between Earth, Jupiter, and its satellite Io Hess et al 2009). As shown below, the waveform mode can also be used for highly dispersed pulsar observations, since it permits spectral analysis of very fine frequency resolution and/or coherent dedispersion (Lorimer & Kramer 2005).…”

“…A characteristic feature of the patterns seen in the spectrogram is the frequency drift, i.e., a rapid change in the emission peak frequency with time. The value of the frequency drift is of importance for testing various models of the emission generation mechanism, magnetic field of Jupiter, and plasma instabilities in the vicinity of Jupiter (Zarka et al 1996;Hess et al 2009). The data presented in Fig.…”

“…In 2005−2008, the receiver was tested for a frequency bandwidth of 33 MHz at A&A 510, A16 (2010) -Power spectrum -Coherence (Cross-correlation spectrum) Digital frequency down conversion Optional the world's largest decameter radio telescope UTR-2 (Ukraine) (Braude et al 1978;Ryabov et al 2004a;Lecacheux et al 2004). A series of observations were performed that targeted strong as well as comparatively weak (or even yet undetected) sources of radio emission known to exist in the decameter waveband, such as Jupiter Hess et al 2009), Saturn (Griessmeier et al 2008), exoplanets (Zarka et al 2001;Ryabov et al 2004b;Weber et al 2007), radio pulsars, and the Sun (Briand et al 2008;Melnik et al 2008). …”

Magnetic coupling of planets and small bodies with a pulsar wind

“…Neubauer (1980) derived a nonlinear theory of this interaction. The Alfvén wing connecting Io and Jupiter is the only explored case of such a structure in the universe up to now, and it has been the object of recent studies concerning its overall structure (Chust et al 2005;Hess et al 2010), the possibility of particle acceleration (Hess et al 2007b(Hess et al , 2009b, and its consequences on the radio emissions (Queinnec & Zarka 1998;Hess et al 2007aHess et al , 2009a. In the present paper, we develop a theory that generalizes some of Neubauer's results to highly magnetized (B 2 0 μ 0 ρ 0 γ 0 c 2 ) and relativistic plasma flows with Lorentz factors γ 0 1, when a planet immersed in the magnetized pulsar wind acts as a unipolar inductor and generates two stationary Alfvénic structures that emerge from the planet and extend far into the wind.…”