A morphological study of vertical ionospheric flows in the high‐latitude F region

Abstract

We have studied the vertical bulk ion drift data recorded by the DE 2 satellite between 200 and 1000km altitudes. For this data set we have found that field‐aligned ion flows between 100ms−1 and 3km s−1 are a common occurrence in the high‐latitude F region. The flows are predominantly upward near the cusp region and throughout the auroral zone. Strong downward flows of somewhat smaller magnitude are also recorded but mostly over the polar cap. These statements are true for all drift speeds in excess of 50ms−1 and for all altitudes and magnetic activity levels sampled. The morphology of low‐altitude upward flowing ions agrees well with the morphology of outflowing ions, ion beams, and ion conics observed at much higher altitudes, but the low‐altitude fluxes are often considerably greater. This suggests that a large fraction of the upflowing ions actually returns to the ionosphere, to be observed as large downward ion fluxes. We propose that upflowing ion events are generated by sudden large changes in the ion temperature below the neutral exobase, where ion frictional heating dominates the ion energy balance. The sudden changes in temperature occur when the horizontal velocity of a convecting field tube increases rapidly in regions like the cusp.