THE OCCURRENCE AND CHARACTERISTICS OF RADAR AURORAL ECHOES AT 488 AND 944 MC/S

Abstract

Radar backscatter observations of auroral ionization have been made from Ottawa on two similar systems operating at 488 and 944 Mc/s. These systems, as nearly scaled as was practicable, were operated almost continuously during the period from May 1959 to April 1961, inclusive.Narrow-beam transmitting and receiving antennas were used. They were each fixed in position to intercept the ionosphere at auroral heights in the region where the orthogonality condition for specular reflection is most nearly satisfied. A magnetometer recorded the magnetic disturbance at ground level at a point under the echoing region. Measurements were made of the time, amplitude, range, and frequency spectrum of the auroral echoes on each of the two frequencies, at both the transmitted and orthogonal polarizations.The data obtained indicate a double-peaked night time maximum in the occurrence of auroral echoes. A slight but distinct minimum appears just before local midnight. Equinoctial maxima are observed in the seasonal variation. The probability of occurrence of echoes increases rapidly with increasing magnetic disturbance. The average Doppler frequency shift of the echoes exhibits a systematic diurnal variation. There is a reversal in the direction of apparent motions, coincident with a change in sign of the average magnetic disturbance, and occurring at about the same time as the night time minimum in occurrence. From the two frequency data, echo cross section is found to vary as about the seventh power of the wavelength. There is no distinct evidence of depolarization or rotation of the plane of polarization of the echoes.Observations of the Doppler frequency shifts are interpreted in terms of the motions of auroral ionization. The wavelength dependence of auroral echoes is used to infer certain properties of the scattering medium.