On the character and distribution of lower-frequency radio emissionsat Saturn and their relationship to substorm-like events

摘要

With the arrival of the Cassini spacecraft at Saturn in July 2004, there have beenquasi-continuous observations of Saturn kilometric radiation (SKR) emissions.Exploration of the nightside magnetosphere has revealed evidence of plasmoid-likemagnetic structures and other phenomena indicative of the Kronian equivalent ofterrestrial substorms. In general, there is a good correlation between the timing ofreconnection events and enhancements in the auroral SKR emission. Eight of ninereconnection events studied occur at SKR phases where the SKR power would beexpected to be rising with time. Thus, while the recurrence rate of substorm-like events atSaturn is likely much longer than the planetary rotation timescale, the events are favored tooccur at a particular phase of the rotation. We show three examples in each of which theSKR spectrum extends to lower frequencies than usual. This can be interpreted as anexpansion of the auroral particle acceleration region to higher altitudes along magneticfield, lines as a direct consequence of an increase in the magnetosphere-ionosphere currentdensity driven by substorm-like events. We then conduct a survey of such low-frequencyextensions during the equatorial orbits of 2005-2006 and place some constraints onvisibility of these radio emissions.