Measurements of radio star and satellite scintillations at a subauroral latitude

Abstract

Observations of two radio stars, Cygnus A and Cassiopeia A, and of two satellites, Cosmos I and Transit 4A, have yielded data on lower and upper atmospheric irregularities. The frequencies studied have included 20 Mc, 40 Mc and 54 Mc for satellite transmissions, and 30 Mc to 3000 Mc for radio star signals. The antennas used have ranged from a dipole to a 150-foot parabola. The irregularities in refractive index in the lower atmosphere produce amplitude fluctuations up to several times average with a fading rate of 3 to 0.5 per minute while ionospheric amplitude fluctuations can increase several decibels, with rates from 1 to 60 per minute. Lower atmosphere scintillation rates increase as the elevation angle increases and generally disappear above <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5\deg</tex> of elevation. During intense magnetic storms, the ionospheric scintillation rate is a function of wavelength in the UHF range. Ionospheric scintillations are functions of both magnetic conditions and of the subionospheric latitudes of the irregularities; they are observed at zenith at the geomagnetic latitude of the Sagamore Hill Radio Observatory ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">54\deg</tex> ). Using spaced receivers, heights of single irregularities have ranged from about 100 to 600 km and representative sizes from about 0.1 to 4 km. Irregularities constitute the prime factor affecting the level, phase and angle of arrival of signals propagated through the auroral regions.