An experimental investigation of the scintillation of radio stars observed at frequencies of 223 and 456 megacycles per second from a location close to the auroral zone

This paper describes a study of the amplitude and angular scintillations of the Cygnus and Cassiopeia sources at College, Alaska. Phase-switch and phase-sweep interferometers were used at frequencies of 223 and 456 Mc/s for one year centered at about the peak of the recent sunspot cycle. The scintillation effects were found to be of much greater magnitude than at temperate latitudes, and they showed clear evidence of geomagnetic and auroral control. The solar time dependence was considerably less than is observed at temperate latitudes. The zenith-angle dependence of the scintillation amplitude was different for the two sources; for both, the zenith-angle dependence was much less than would be predicted for the case of spherical diffracting irregularities. The relative absence of a zenith-angle effect is attributed to the compensating effect of magnetic field alignment of anisotropic irregularities. The difference between the zenith-angle curves for the two sources, as well as the greater magnitude of the Cygnus scintillations relative to the Cassiopeia scintillations, is attributed to the fact that the Cassiopeia source subtends a larger solid angle than the Cygnus source. The occasional occurrence of long-duration fades on the interferometer records (of periods up to 1 hour) is interpreted in terms of irregularities that on these occasions subtended less than the solid angle of the source and resulted in a diffraction pattern on the ground having autocorrelation distance less than 100 meters.