Low‐latitude zonal and vertical ion drifts seen by DE 2

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Abstract
Horizontal and vertical ion drift data from the DE 2 spacecraft have been used to determine average zonal and vertical plasma flow (electric field) characteristics in the ±26° dip latitude region during a time of high solar activity. The data base consists of over 800 equatorial passes. Horizontal ion drift data were projected along magnetic field lines to the magnetic equator, using a dipole model to yield their apex height dependence. The “average data” local time profile for an apex height bin centered at 400 km indicates westward plasma flow from 0600 to 1900 solar local time (SLT) with a maximum westward velocity of 80 m/s in the early afternoon. There is a sharp change to eastward flow at approximately 1900 hours with an early evening peak of 170 m/s. A secondary nighttime maximum exists at 0430 SLT preceeding the reversal to westward flow. This profile is in good agreement with Jicamarca radar measurements made under similar solar maximum conditions. Harmonic analysis indicates a net superrotation which is strongest at lower apex altitudes. The diurnal term is dominant, but higher order terms through the quatradiurnal are significant. Vertical ion data taken at low (±5°) dip latitudes, while possessing greater scatter, generally agree with Jicamarca values.