Sub-hour modulation of L-component of Io-related Jovian decametric emission

Abstract

The variability of Jovian decametric emission (DAM) is studied at time scales from 1 min to 1 h with DAM records of 1991-2007 from the archive of Nancay Radio Observatory. We found that the internal structure of the Io-related radio storms has the dominating periodicity of 23±2 min on average. This estimate practically coincides with the fundamental eigenoscillations of transversal magnetic pulsations in the Io plasma torus. Our autocorrelation analysis confirms the excess of DAM variations with the time scale of the fundamental and first harmonic periods of the Io torus. Moreover, the time scale of arc pattern in DAM dynamic spectra is estimated to be 5.4 min, which corresponds to Io's Alfvén wing diameter or to the 3rd and 4th harmonics of torus proper oscillations. These results could be interpreted in terms of electron acceleration in field-aligned electric fields of standing Alfvén waves trapped in the Io torus. There is an analogous modulation of auroral kilometric radiation of the Earth by magnetic pulsations at field line resonances in the terrestrial magnetosphere (Hanasz et al. 2006, J. Geophys. Res., 111, A03209).

Sub-hour modulation of non-Io Jovian decametric emission

“…These results and histograms ( Fig. 5 and 6) for non-Io emission are approximate to the modulation of Io-related DAM (Arkhypov & Rucker 2008). The simplest interpretation of these agreements is the identity of the modulator.…”

“…This estimate is about the average period of Io-related emission: P = 1403 ± 102 s or 23 ± 2 min (Arkhypov & Rucker 2008). For toroidal (transverse) magnetic oscillations in the Io torus, Glassmeier et al (1989) found theoretically the fundamental period of 1296 s (marked as F0 in Fig.…”

“…We argued in a previous paper (Arkhypov & Rucker 2008) that the Io-related L-burst emission is modulated by the proper oscillations of the Io plasma torus. Such oscillations in the form of a quasi-axisymmetric azimuthal twisting of magnetic-field lines are found in situ (Fig.…”

“…For comparison, we indicate the fundamental period of transverse magnetic oscillations in the Io torus (FO) and the first harmonic (H1) according to Glassmeier et al (1989). The histogram for Io-related DAM is adopted from Arkhypov & Rucker (2008) but recalculated with the other bin set. 1200 s (20 min) are confirmed with Voyager-1 in situ magnetometer measurements (Glassmeier et al 1989).…”

“…In a previous paper (Arkhypov & Rucker 2008), we studied the sub-hour modulation of L-bursts, which are correlated with the orbital position of the Jovian satellite Io. We found that the internal structure of the Io-related radio storms has the dominating periodicity of 23 min on average.…”