Medium Frequency Conjugate Echoes Observed on Topside-Sounder Data

The results of a statistical study of conjugate echoes observed on Alouette II topside-sounder data are presented and compared, where possible, with Alouette I and Explorer XX results. The percentage occurrence of conjugate echoes is either independent of K p or decreases slightly as K p increases from 0 to 6. Most of the data show a nighttime maximum in the occurrence of conjugate echoes; however, the occurrence of higher-frequency echoes tends to peak near 07 hours local time, which agrees with the Explorer XX results. The occurrence of conjugate echoes increases as the L value decreases from 4 to about 1.35. There is an oscillation in the occurrence of conjugate echoes with either local time or calendar date (day of the year); because of the characteristics of the satellite orbit, it is difficult to distinguish between these two possibilities at the present time.