Propagation effects influencing the observed polarization of the Jovian decametric emission

Jovian decametric emission is known to exhibit 100% elliptical polarization at all frequencies in the measured range from 10 to 38 MHz. The ellipticity of polarization is approximately constant as a function of frequency and time but differs for different sources. We suppose that the elliptical polarization of the observed emission is a consequence of propagation effects along the wave path from the source to the observer. We believe that outside of the source in the Jovian magnetosphere, there exists a region of moderate linear mode coupling which causes the ellipticity of the observed emission. We evidence conditions of the emission propagation along ray paths which are necessary for self-consistent explanation of the observed polarization and show that the observed features of the polarization are determined by the distribution of the magnetospheric plasma within the inner Jovian magnetosphere. The relatively small change of the ellipticity from storm to storm is a consequence of a relative variation of the magnetospheric background plasma in time. The value of the ellipticity is determined by the level of the magnetospheric plasma density n(e) in the so-called "transitional region". This plasma density is quite low n(e) < 0.4 cm(-4) and is related with the local electron gyrofrequency as n(e) proportional to (f(Be))(v) where v similar or equal to 1 divided by 1.8.