Abstract
Using models of a line current and a band current with a parabolic intensity distribution across the width, techniques to deduce the speed, the direction of motion and the zenith crossing time of the electrojet from observations of surface magnetic perturbations are studied. From the current motions deduced by these techniques and the observed traces of the Auroral Infrasonic Waves (AIW), the following four facts are established. 1. (1) The time between the zenith crossing of the current and the arrival of AIW at the ground is reasonable. 2. (2) The direction of travel of AIW is considered to be parallel to the current drift or parallel to the current flow. 3. (3) The trace velocity of AIW is equal to the calculated drift velocity of the current. 4. (4) AIW can be produced only by a line (or a narrow band) current. Several minutes before the AIW arrive at the ground, the existence of certain motions of westward current which satisfy the AIW emission conditions proposed by Wilson (1972) have been confirmed. However there are several cases in which a succession of two equatorward supersonic zenith crossings of westward current have induced only one AIW.
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