North–South Ionospheric Drifts near the Magnetic Equator

Abstract

WHEN the well known Mitra method, with three aerials spaced at distances of 1–2 wavelengths apart, is used to measure ionospheric drifts close to the magnetic equator, it is difficult to measure the northward component of drift velocity, V_N. This is because the irregularities of the ground diffraction pattern, and also presumably the ionospheric irregularities producing this pattern, are field-aligned and highly elongated in the north–south direction. In consequence the time delays between aerials oriented in this direction are very small; and in the measurements made hitherto at Ibadan, Nigeria (dip 6° S)—for example, by Skinner, Lyon and Wright¹—it has not been possible to obtain significant results for V_N. Some evidence has, however, recently been published2 of significant daytime values of V_N at Thumba, India (dip 0.6° S).