New periodicity in Jovian decametric radio emission

Abstract

We report on the finding of a new periodicity in the Jovian decametric radio emission (DAM). Periodic bursts of non‐Io component of DAM which recur with a period 1.5% longer than the Jupiter rotation (System III) have been found in the dynamic radio spectra acquired by STEREO/WAVES, Wind/WAVES and Cassini/RPWS during the years 2002–2008. Typically, the bursts appear very periodically over several Jovian days with a decreasing intensity and they display a negative frequency drift. All the bursts were detected within the same sector of Jovian Central Meridian Longitude (III), between 300° and 60° (via 360°) of CML (III), close to the region of the non‐Io‐C source. No correlation has been found with the position of Io. Considering the simultaneous stereoscopic observations onboard STEREO‐A and STEREO‐B, as well as Wind and Cassini we can conclude that the sources of the periodic bursts most probably sub‐corotate with Jupiter.

Periodic bursts of Jovian non-Io decametric radio emission

“…Using the fact that Jovian radio emission is emitted in a hollow cone attached to the Jovian magnetic field or to the Io flux tube and the known rotation rate of Jovian magnetosphere (9.925 h) or Io's orbital period (42.46 h) as well as distances between Jupiter and each of the spacecraft the DAM emission can be identified by means of the time difference between sequential detection of the radio emission from the same radio source by the two spacecraft separated in space. In particular, this time delay consists of the light travel time difference between a radio source and an observer and the time interval which is necessary to rotate the radio beam by the angular separation (as seen from Jupiter) between the two spacecraft (see Panchenko et al, 2010). Therefore, the stereoscopic observations allow to (1) separate Jovian arc-like radio emission from the solar radio bursts and (2) unambiguously distinguish between Io and non-Io controlled component of DAM.…”

“…Generally, non-Io DAM is a highly variable and sporadic radio emission which appears in a form of arcs in time–frequency coordinates and modulated by the rotation of the Jovian magnetosphere. Recently, Panchenko et al (2010) and Panchenko and Rucker (2011) have reported findings of the new type of Io independent radio bursts of DAM—periodic non-Io DAM burst. This emission is observed in the decametric frequency range (typically 5–12 MHz) in the form of arc-like radio bursts.…”

Planetary radio astronomy: Earth, giant planets, and beyond

“…These latitudinal extended fingers may be a plasma source which supplies the cyclotron maser in the auroral region. Therefore, it has been suggested that the interchange instability in the Io torus, triggered by the solar wind pulses, may be a possible generation mechanism of the periodic non-Io DAM bursts (Panchenko et al, 2013). Besides the main group of periodic bursts, two other groups of periodic features, rarely observed in the radio spectra, were found.…”

“…The non-Io component of the DAM is a highly variable and sporadic radio emission, generally modulated by the rotation of the Jovian magnetosphere. Recently, Panchenko et al (2010Panchenko et al ( , 2013 and Panchenko and Rucker (2011) reported on the finding of new types of intense non-Io DAM bursts recorded by STEREO/WAVES, Wind/Waves and Cassini/RPWS space borne radio instruments in a frequency range from 5 MHz to 12-16 MHz, which are rarely observable on the Earth due to ionospheric cut-off below 10 MHz. The examples of these bursts are presented in Fig.…”

“…Additionally, the Lomb-Scargle spectral analysis has shown that the periodic bursts exhibit a tendency to occur in groups every ∼25 days, i.e. the synoptic solar rotation period as viewed from Jupiter (Panchenko et al, 2013). The recent simultaneous observations of the periodic non-Io DAM using the radio experiment onboard the two STEREO spacecraft and the ground-based radio telescope URAN-2 (Poltava, Ukraine) have shown that the periodic bursts are observed as right and left hand polarized radio emission associated with the Northern and Southern magnetic hemispheres of Jupiter, respectively.…”