Auroral ionization and the absorption and scintillation of radio stars

Abstract

The absorption of the radiation from extra-terrestrial radio sources, when observed at low elevations to the north of Jodrell Bank (Geomagnetic latitude 56°), is discussed. At lower culmination the Cygnus radio source is at an elevation of only 4°, and the line of sight to the source then passes through the ionosphere near the zone of maximum auroral activity. Combined observations of the source intensity at 36 Mc/s and 100 Mc/s, and of radar back-scatter echoes at 36 Mc/s, have been made using the 250 ft steerable telescope. The absorption and certain back-scatter echoes can be related to an ionized layer at a height of the order of 100 km, associated with auroral activity. It is shown that with a high sensitivity radar equipment at 36 Mc/s, weak auroral-type echoes from irregularities in the E-region aligned along the earth's field occur on about 40 per cent of all days at quite low geomagnetic latitudes. The suggestion is made that the scintillation of radio stars observed from latitudes similar to that of Jodrell Bank is not due entirely to irregularities in the F-region, but that there is a large contribution from these aligned irregularities at E-region heights.