Sporadic E at VHF in the USA

Abstract

An analysis is made of sporadic-E propagation observed on the Cedar Rapids to Sterling path during the four years, 1952-1955. VHF transmissions over this path at frequencies of 27.775 mc and 49.8 mc provided the Es data. At this latitude, the summer months receive the preponderance of sporadic E. Diurnally, sporadic-E occurrence tends to favor the day-time and evening hours with peaks of incidence about 1000 and 1800. No variation with sunspot number has been discerned. As a rule, higher Es signal intensities are recorded at 28 than at 50 mc. Cumulative distributions of signal intensity are presented for the two frequencies. A relationship is found between the frequency dependence of Es signal intensities ≥-70 db, relative to inverse distance, and the distribution of fEs values at Washington, D.C. The relationship promises to be useful in the prediction of Es signal intensities on a worldwide basis. An inverse correspondence is shown between sporadic-E occurrence and geomagnetic activity. The correspondence holds only over selected time intervals. The frequency dependence of received power under sporadic-E conditions is different from that during normal scatter. The median frequency exponent is two or more times as large for sporadic E, and the exponents cover a much wider range of values. This is tentatively explained by considering the Es region to be composed of patches of intense nonuniform ionization, an hypothesis previously used to explain vertical-incidence data.