Polarization of Radio Echoes from Auroræ

Abstract

NOTABLE variations in the polarization of radio echoes from aurorae have been observed at Saskatoon (52.1° N., 106.6° W.), using frequencies of 56 and 106.5 Mc./s. Theories of very high-frequency radio propagation predict the maintenance of the transmitted state of polarization under normal ionospheric conditions. An examination by Moore1 of amateur radio transmissions by ‘auroral propagation’ indicated that this was also the case when aurora was present. Observations by Bowles2 confirmed this conclusion, although exceptions occurred when aurora was overhead. More recently, Harang and Landmark3, in reporting on back-scatter echoes during aurora, mentioned that 35 Mc./s. echoes were sometimes completely depolarized and sometimes nearly plane polarized, and that 74 Mc./s. echoes were plane polarized in the same sense as the transmitted signals. The Saskatoon observations are apparently the only ones that have been made so far where it has been possible to verify the auroral origin of the echoes4.