The polarization of escaping terrestrial continuum radiation

Plasma wave measurements from the DE 1 (Dynamics Explorer 1) spacecraft are used to determine the polarization of an escaping terrestrial continuum radiation event that occurred on March 2, 1982. The source of the radiation was determined by direction finding to be located near the magnetic equator on the nightside of the Earth at a radial distance of about 2.8‐3.5 RE. The radiation was emitted in two meridional beams, one north and the other south of the magnetic equator. Polarization measurements using the two orthogonal electric antennas on DE 1 show that the radiation is right‐hand polarized with respect to an outward directed E plane normal in the northern hemisphere and left‐hand polarized in the southern hemisphere. Comparisons with the local magnetic field show that both the northern and southern hemisphere beams are propagating in the L‐O mode at the spacecraft. The mode of propagation has also been confirmed using measurements of the E plane normal angle and ellipse ratio. Because the angle between the magnetic field and the E plane normal rotates through perpendicular as the radiation propagated from the source to the spacecraft, mode coupling effects must be evaluated when considering the mode of propagation in the source. Estimates of the spatial gradients over the ∼ 1‐RE distance between the source and the spacecraft indicate that the radiation has not reached the region of limiting polarization. Therefore the mode of propagation must be the same at the source and at the spacecraft: i.e., the L‐O mode. These observations support the linear conversion model of Jones in which the radiation is produced by coupling from intense upper hybrid resonance emissions near the plasmapause. This conversion mechanism predicts that continuum radiation generated in the vicinity of the plasmapause should be emitted primarily in the L‐O mode. Remote‐sensing analyses based on Jones’ model yield source locations in agreement with those derived by the direction‐finding method.

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