Diurnal variation anomalies at Tucson

The seasonal changes in diurnal variation at Tucson, Arizona, are of unusual interest because of its location in the transition-belt where the type of diurnal variation changes markedly during the year. Monthly hodograms of the diurnal variation in Earth-current potential-gradient indicate that its changes are generally consistent with the recognized movement of the current systems in the ionosphere northward and southward with the sun. Two definite anomalies, less readily explained, are found to exist. The first is a marked increase in activity in January, which appears as a large increase in amplitude, and the second consists of a decrease and irregularity in the eastward component during March.