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East-west ion drifts at mid-latitudes observed by Dynamics Explorer 2


  • R. A. Heelis,

  • W. R. Coley


Zonal ion drifts measured from the the polar orbiting DE 2 spacecraft are examined to determine the effects of dynamo electric fields and penetration of high latitude electric fields at middle latitudes. Construction of a local time distribution from satellite data results in a mixture of local time and season as well as a range of magnetic activity encompassing Kp ≤ 2 and Kp ≥3. Thus some combination of magnetospheric effects, expected to dominate during disturbed times, are seen during both quiet and disturbed times and solar tidal influences are most easily observed during quiet times. During quiet times, at invariant latitudes near 25°, the solar diurnal tide dominates the local time distribution of the ion drift. At latitudes above 50° a diurnal component of comparable magnitude is also present, but its magnetospheric origin produces a shift in phase of almost 180° from the lower latitude diurnal tide. In the intervening region, between 20° and 50° invariant latitude, semidiurnal and terdiurnal components in the local time distribution of the drift velocity are also seen. These components are generally larger than those seen by ground based radars during quiet times and may be attributable in part to a difference in solar activity and in part to a combination of the solar tides and magnetospheric penetration fields.

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