Detection of meridional currents in the equatorial ionosphere
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Theoretical investigations predict meridional currents in the dynamo region of the ionosphere a few degrees north and south of the magnetic equator as a consequence of the equatorial electrojet. The magnetic fields of these currents are perpendicular to the permanent magnetic field of the Earth and cause a height variation of the magnetic declination. It was the aim of six rocket launches performed in 1970 near noon at Natal, Brazil, to detect these currents. To reach this objective, identical payloads each consisting of two flux-gate magnetometers, a solar aspect sensor, an experiment to measure the angle between the magnetic field and the direction to the Sun, and an impedance probe to determine the electron density were launched under different magnetic conditions. The predicted variation of the declination has been observed but with considerably higher amplitude than was expected. On the other hand, the measured height integrated current density in the west-east direction was smaller than deduced from ground based magnetic H-variations. These discrepancies can be explained by currents flowing at 5 degrees off the magnetic equator, on both sides, with intensities of about 0.3 of the electrojet intensity at the same height but in reversed direction. Such reversed currents have recently been observed from ground based magnetic observations by others and have also been interpreted theoretically by ionospheric wind effects.
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