ON THE POLARIZATION OF TYPE-I RADIO-BURSTS

Circularly polarized radio radiation maintains its polarization even w here the magnetic held reverses its sign relative to the ray (QT regio n) if the reversal is sufficiently abrupt (strong QT region). Bastian (1995) suggested that coronal turbulence scatters radiation, such as t ype I bursts, sufficiently to make the reversal abrupt where it would otherwise not be. However, the observed directivity of type I bursts s ets an upper limit on the scattering. This limit implies that the turb ulent scattering is not sufficient to maintain the circular polarizati on as in a strong QT region. The conclusion is strengthened by an anal ytical calculation of the polarization. Apparently, the fully polarize d type I bursts, near disk center, encounter no horizontal magnetic fi elds, at least not until high enough in the corona that the QT region is strong anyway.