Some Measurements of High-Latitude Ionospheric Absorption Using Extraterrestrial Radio Waves

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Abstract
This paper describes the manner im which 30-mc extraterrestrial radio waves have been used to study the radio absorption characteristics of the arctic ionosphere. It opens with a brief discussion of the theory of ionospheric absorption, followed by a description of the basic principles involved in the technique. Two different types of equipment which have been used in these absorption measurements are then discussed and typical records presented. The observations have shown that the regions of anomalous high-latitude absorption typically have lateral dimensions in excess of 100 km, and that marked differences can occur during disturbed periods between stations 800 km apart. Almost all the absorption of the extraterrestrial radio waves occurs below the E region. The absorption correlates well with the local geomagnetic K index, and apparently is associated with the bombardment of the upper atmosphere by the corpuscular streams which produce the aurora. The increase of absorption during daylight hours is thought to be due to a decrease in effective height of the absorbing layer, resulting from a photo detachment of electrons at heights of the order of 60-80 km, rather than to an increase in the strength of the corpuscular bombardment.

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