ON ELLIPTIC POLARIZATION OF THE DECAMETRIC RADIO-EMISSION AND THE LINEAR-MODE COUPLING IN THE JOVIAN MAGNETOSPHERE

We consider the origin of the elliptical polarization of Jupiter's dec ametric emission as a consequence of the moderate linear mode coupling which takes place in the Jovian magnetosphere outside of the source r egion. We recognize conditions of emission propagation along the ray p ath which are necessary for forming of the observed polarization chara cteristic and show that our model explains the main observed propertie s of the polarization (value of ellipticity, independence of polarizat ion on frequency and time, stability of polarization from storm to sto rm). does not need low plasma densities in the emission source and doe s not contradict the modern knowledge on the decametric emission origi n. We show that there is no strong correlation between polarization of the emission at the source and the observed polarization. The observe d degrees of (linear and circular) polarization have to be assumed as limits of possible degrees of the polarization of the emission escapin g the source region. The value of the ellipticity is defined by the le vel of the magnetospheric plasma density n(e), in the ''transitional r egion'', that is in a part of the ray path where the polarization of t he normal waves is essentially elliptical. The plasma density in this region is quite low n(e) < 0.4 cm(-3) and is related to the local elec tron gyrofrequency as n(e) proportional to (f(Be))(nu) where nu simila r or equal to 1 divided by 1.8.