The interpretation of ionospheric radio drift measurements—II Kinesonde observations of microstructure and vertical motion in sporadic E

Abstract

Dynamic processes in the E-region, resulting mainly in neutral air motions, appear as the direct causes of certain phenomena (e.g. sporadic E) and are also responsible for much of the less obvious variability of the region. Since it is the time variation of the vertical structure which is usually observed, and since the vertical ionization gradients are large, vertical motions are of greatest interest. We show here that the vertical component of motion of the neutral air, although of relatively small magnitude, cannot be neglected in estimating vertical ion motions. It is therefore important that the total motion of the air, and of the ionization, be subject to measurement. We describe a new “kinesonde” radio sounding system with which three-dimensional structure and motions in the ionsphere may be observed at the ground. The kinesonde is a much-elaborated version of the well-known spaced-antenna drift experiment. It obtains digital magnetic tape recordings of the amplitude and RF phase variations of selected echoes on six freely chosen frequencies and on four spaced antennas, simultaneously. The observations are analyzed by a statistically rigorous method in which many of the cross-correlations between pairs of these 48 channels are used to determine a four-dimensional (x, y, z, t) “correloid” in a moving (Vx, Vy, Vz) coordinate system. The velocity V is identified with motions at the ionospheric reflection level and other information describes the random motion, spatial scale, and anisotropic properties of the measurements. In the present paper, we assume that the calculated velocities approximate those of the neutral wind, and infer therefrom the vertical ion motions which these air motions would induce. Measurements performed on sporadic E layers give vertical ion velocities ranging from 1–15 m/s, often upward. In the vicinity of a daytime Es layer, the upward velocity is found to decrease with altitude implying a convergence of ionization toward the sporadic E-layer. Kinesonde measurements are also compared with the time and height variations of several sporadic E-layer sequences obtained by N(h) analysis of ionograms, and are found to account for much of the variation observed.