Helios-1 Faraday rotation experiment: results and interpretations of the Solar occultations in 1975

Abstract

The polarization angle of the HELIOS-1 downlink signal has been monitored during two solar occultations in 1975 at two widely separated ground stations. Significant Faraday rotation of the signal occurs whenever the signal ray path passes through the solar corona near superior conjunction. Large-scale variations in the data arise both from rotation of the solar corona and from the slowly changing solar offset (point of smallest heliocentric distance along ray path). A simplified model of the solar corona has been developed to simulate the results of the Faraday rotation measurements. In this model the known polarity of the large-scale interplanetary magnetic field is employed as an aid in determination of the product N · B (electron density x magnetic field) as a function of heliographic longitude and heliocentric distance r within 2-10 R_☉ . In this distance range N · B is proportional to r^-5.5. If the magnetic field can be assumed to follow an inverse square law over this range, the electron density is found to be decreasing as r^-3.5, in good agreement with previous results. The derived longitudinal structure for the corona during both occultations is consistent with synoptic coronal white light observations.

          ARK: https://n2t.net/ark:/88439/y065590

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