Sub-hour modulation of non-Io Jovian decametric emission

¹ Institute of Radio Astronomy, National Academy of Sciences of Ukraine, Chervonopraporna 4, 61002 Kharkiv, Ukraine e-mail: alexeyarkhipov@rambler.ru
² Department of Space Radio Physics, Kharkiv V. N. Karazin National University, Svoboda Square 4, 61077 Kharkiv, Ukraine
³ Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, 8042 Graz, Austria e-mail: rucker@oeaw.ac.at

Received: 25 September 2008
Accepted: 8 January 2009

Abstract

The variability of Jovian decametric emission (DAM), which is not controlled by the Io satellite (non-Io), was studied of timescales of between 1 min and 1 h with DAM records of 1991–2007 from the archive of Nançay Radio Observatory. We found that the internal structure of the non-Io radio storms has the dominating periodicity on of average  min . This estimate is in close agreement with the periodicity of Io-related emission and with fundamental eigenoscillations of transversal magnetic pulsations in the Io's plasma torus. The average duration of an arc in non-Io DAM dynamic spectra was estimated to be  min, although the most probable value was  min, which corresponds to Io-related arcs and 3rd and 4th harmonics of torus proper-oscillations. Our results could be interpreted in terms of electron acceleration in parallel electric fields of standing Alfvén waves generated by Io and trapped in the Io torus. This interpretation agrees with previous arguments that the location of some sources of non-Io emission are in the magnetic shell of the Io plasma torus. However, the aurora component of non-Io DAM is not excluded, since the suggested DAM modulation by the fundamental mode of eigenoscillations inherent in aurora magnetic-lines is undetectable in our analysis because of the short duration of non-Io radio storms.