A new type of periodic burst
By analyzing the dynamic radio spectra recorded by the STEREO/WAVES, Wind/WAVES and Cassini/ RPWS instruments during 2000-2010 we have discovered, for the first time, a new type of radio burst in the Jovian decametric emission (DAM). These bursts, which have been identified as not controlled by Io (non-Io DAM), are observed in a decametric frequency range from ~4 MHz up to ~ 16 MHz (Fig. 1) and recur very regularly over several Jovian days with an average period of ~10.07 hours. This new period is surprisingly ~1.5% longer than the Jupiter rotation (~09:55). All bursts were detected within the same range of Jovian Central Meridian Longitude, between 300° and 60°, close to the region of non-Io-C source. This suggests the existence of ”active longitudes” or preferable source locations where the generation of the periodic bursts is more efficient.
Stereoscopic observations performed by STEREO/WAVES as well as Wind/WAVES and Cassini/RPWS have shown that the sources of the periodic bursts sub-corotate with Jupiter and remain active during longer periods of time (maximum 11 Jupiter’s rotations). Therefore we are probably dealing with a rotating emission beam rather than with a clock-like (stroboscopic) emission.
 - Fig. 2
Additionally, the emission hollow cone pattern of the periodic bursts has a strong anisotropy (i.e. the intensity of the radiation depends on an angle with respect to the symmetry axis), because generally, only one burst per Jupiter rotation is observed.
Our recent analysis of the solar wind activity (web link to … ) around Jupiter has revealed a strong correlation between the occurrence of periodic bursts and significant enhancement of the solar wind ram pressure (Fig. 2). Additionally, most of the detctions of periodic radio bursts occurred after strong intensification of the ’typical’ non-Io DAM emission (strong storms of non-Io DAM) which is known to be significantly affected by the solar wind.
We suggest that these new periodic bursts of Jovian non-Io DAM are deeply connected with the complex interaction between the Jovian magnetosphere and the sub-corotating, highly structured, plasma environment. Besides the general scientific value of these findings, a full understanding of the nature of this phenomenon may shed light on the physics of the global plasma dynamics in the Jovian magnetosphere and its interaction with the solar wind.
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