Analysis of elliptical polarization of Saturn kilometric radiation throughout the Cassini mission

Saturn kilometric radiation (SKR) is mostly a fully circularly polarized radio emission from Saturn's auroral region. However, Fischer et al. (2009, doi:10.1029/2009JA014176) found that SKR can show a linear component and be elliptically polarized, and this SKR property is typically found above observational latitudes of about 30 degrees (in both hemispheres). Using all available RPWS (Radio and Plasma Wave Science) data throughout the Cassini mission, we calculated mean polarization properties (linear, circular, total) of SKR for each hour in the frequency range from 100 to 1200 kHz. This revealed transitional latitudes from 20 to 40 degrees in which the linear polarization degree of SKR rises from around 0.1 (which is the usual error for the polarization measurement) up to 0.6. Furthermore, we found that SKR shows a lower total polarization degree at the transitional latitudes. 
We will try to give a reason for this unexpected behavior. We will also show comprehensive meridional plots of SKR circular, linear, and total polarization to understand the polarization properties of this important Saturnian radio emission.