LXIV. A radio astronomical investigation of drift movements in the upper atmosphere

Summary The metre wavelength emission from the radio stars is diffracted by irregularities in the electron density of the ionosphere, which occur mainly at night at a height of approximately 400 km. Fading records taken with three receiving equipments, triangularly sited, show systematic time displacements, and these are attributed to a steady translational movement of the diffracting screen. The motion is normally of the order of 50—300 m/sec, is generally transverse to the magnetic lines of force and often remains constant over periods of many hours. During the first half of the night the prevailing direction is towards the West, at approximately 01h there is often a reversal, normally effected within a period of 30 minutes, and thereafter the motions are predominantly towards the East. The effective wavelength of the ionospheric irregularities remains appreciably constant over a velocity range of 20 : 1, so that the magnitude of the drift velocity may be estimated from a count of the fading rate. By observing the Cygnus source when it is low on the Northern horizon it is possible to determine the F region drift velocities in the auroral zone ; these are about 400 m/sec, that is, twice as fast as the F region motions at temperate latitudes. Investigation of the drift motions at points separated by 800 km suggests that the drift speeds and directions are the same over wide areas, and experiments made in co-operation with members of the Cavendish Laboratory, Cambridge, over a 200 km base line support this. Observations of F region motions made elsewhere, with different techniques, are in good agreement with the present results.