The Alouette 2 topside sounder data have been used extensively to study the field‐aligned propagation of HF radio waves. We present information about the physical characteristics of magnetospheric ducts with reference to their scale sizes and peak fractional deviations of electron density. The results are in general agreement with previously published results of Muldrew (1963) with Alouette 1 data and Loftus et al. (1966) with Explorer 20 data. In our study of the conjugate ducting phenomenon we analyzed more than 400,000 Alouette 2 ionograms. A select sample of data (2100 ionograms) is used to decipher the duct characteristics.
This paper reports the high rate of occurrence of conjugate echoes observed by the Alouette 2 topside‐sounder at the longitudes of Singapore during the year 1966. The ionograms containing conjugate echoes observed at Singapore and other equatorial and midlatitude stations are mostly in the form of sequences. Some sequences last as long as the corresponding soundings. Occurrence of such sequences may be attributed to the presence of field‐aligned irregularities over a wide range of L values in the magnetosphere. However, the sounding times are, quite often, not long enough to observe fully the extent of the magnetosphere over which the field‐aligned irregularities exist. No obvious correlation between the occurrence rate of conjugate echoes and the magnetic Kp index was found.
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