Cosmic noise absorption events at geomagnetically conjugate stations

A two-month program of observations of cosmic radio noise absorption in geomagnetically conjugate areas is described. A closely spaced network of stations in the conjugate area in one hemisphere revealed that the position of maximum correlation changed from event to event and during events. There were, moreover, very rare occasions in which events were exclusively confined to one hemisphere. For the conjugate events, the magnitude of the absorption was greater in the winter hemisphere than in the summer hemisphere, even under similar solar illumination conditions. The conjugate area (defined by the 0.5 correlation coefficient contour) in general appeared to be that of a circle of radius about 700 km, but for individual events the extent was clearly more limited. The movement of the conjugate area is believed to be due to the changing latitude of the point at which exospheric particles are injected into the earth's atmosphere. It is suggested that the greater absorption in the winter hemisphere is possibly the result of the asymmetry of the earth's magnetic field with respect to the earth-sun line.