Development of scanning narrow beam riometer

Abstract

A new riometer system of high spatial resolution by means of a scanning narrow beam method is in operation at Syowa Station, Antarctica (69.0°S, 36.6°E, L=6.1) since February 1985. Ionospheric absorption of cosmic radio noise over Syowa Station within 120km in geomagnetic north-south and east-west directions, can be measured with a spatial resolution of 10km and a temporal resolution of 10s. The antenna system has four other fixed-direction beams pointing to the zenith and to the magnetic north, south and west with a zenith angle of 30°. Each signal from these fixed beams, constituting a separate riometer, is used for higher time resolution (0.25s) observation. This riometer system can discriminate a small-scale absorption region of a few tens of kilometers, which cannot be seen by a conventional broad beam riometer. This riometer system can also detect a drift velocity of pulsative absorption with a short wavelength of ∿100km. Comparing simultaneous observations of this riometer and a scanning photometer at Syowa Station, we found a considerable difference in spatial distribution between auroral absorption region and auroral emission region.