Statistical investigation of SKR caterpillar emissions

<p>The radio emissions nicknamed "caterpillars" are believed to be a special form of Saturn kilometric radiation (SKR) at low to very low frequencies. They are coarse spectral structures lasting for several hours mostly below 40 kHz, and their constant central frequency with a typical bandwidth of 10-15 kHz makes them look like caterpillars in a time-frequency spectrogram. We found almost 600 caterpillar emissions with the RPWS (Radio and Plasma Wave Science) instrument throughout Cassini's tour around Saturn. We present a statistical investigation of their occurrence with respect to the position of Cassini, their duration, central frequency, bandwidth, polarization, intensity, and connection to SKR at higher frequencies. We also compare their occurrence with the occurrence of SKR low frequency extensions (LFEs) as many of them are found during so-called long LFEs. We will discuss and investigate the reasons for the loss of total polarization of caterpillars, which could be due to wave reflections at the magnetosheath or due to an incoherent superposition of X-mode with O-mode SKR.</p>