Vertical winds as a plausible cause for equatorial counter electrojet

Abstract

The signatures of the counter‐electrojet that occurs in the afternoon hours as recorded on the ground and satellite‐borne magnetometers during the magnetically quiet days, clearly indicate reversal of the jet current in a narrow latitude region centered around the dip equator. The latitudinal variation of the vertical (Z) and northward (H) components of the earth's magnetic field reveal that the decrease and reversal of the eastward toroidal current of the jet is maximum around the dip equator.By numerically solving the equations governing the electrojet including the terms due to local winds it is shown that vertically upward winds of 15 ‐ 20 m/s are most effective in producing the counter‐electrojet. The profile of vertical winds adopted in the model calculations was actually measured during twilight hours. It is shown that the latitudinal variations of H and Z observed during the counter‐electrojet can be reproduced satisfactorily by the vertical wind hypothesis. A rocket experiment is suggested to verify the presence of vertical winds during the counter‐electrojet.