Electric-field observations from two high-altitude rocket flights in the polar cusp have been combined with satellite observations of ion drifts and energetic particles to infer details of the electric field and convection pattern of the dayside auroral ionosphere. A region of shear flow reversal could be inferred from the electric-field observations on one flight near 1530 magnetic local time 20 min after the Dynamics Explorer 2 (DE-2) satellite crossed through the same region. The drift patterns observed by the two spacecrafts were very similar, although shifted by 0.5°, a shift that is expected from the observed change in the interplanetary magnetic-field (IMF) BZ component during this time. A region of rotational flow reversal was covered by the other flight shortly after magnetic noon, at the same time the DE-2 satellite travelled along roughly the dawn–dusk meridian. By joining points of equal potential, integrated from the two data sets, and assuming the reversal boundary to be an equipotential, we could draw the instantaneous convection pattern showing crescent-shaped convection contours in the dusk cell and more circular-shaped contours in the dawn cell. This pattern has been shown to be in qualitative agreement with the predictions of a geometrical model proposed by Crooker in 1979, when the IMF is oriented towards dawn. The same characteristic patterns but with the dusk and dawn cells reversed, as presented in a recent radar-satellite study for the IMF oriented towards dusk, may serve as additional evidence in favour of this model.
