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The first statistical results on the occurrence of abnormal subauroral iondrifts (ASAID) are presented based on electric and magnetic fieldmeasurements from the low-altitude Astrid-2 satellite. ASAID are narrowregions of rapid eastward ion drifts observed in the subauroral ionosphere.They correspond to equatorward-directed electric fields with peak amplitudesseen to vary between 45 mV/m and 185 mV/m, and with latitudinal extensionsbetween 0.2° and 1.2° Corrected Geomagnetic Latitude (CGLat),reaching in some cases up to 3.0° CGLat.  Opposite to subauroral ion drifts (SAID) that are known to besubstorm-related, ASAID are seen to occur predominantly during extendedperiods of low substorm activity. Our results show that ASAID are located inthe vicinity of the equatorward edge of the auroral oval, mainly in thepostmidnight sector between 23:00 and 03:00 magnetic local time. They areassociated with a local current system with the same scale-size as thecorresponding ASAID, composed by a region of downward field-aligned currents(FACs) flowing in the ASAID poleward side, and a region of upward flowingFACs in the equatorward side. The FACs have densities between 0.5 and 2.0 μA/m<sup>2</sup>.The data suggest that ASAID do not contribute significantly tothe reduction of the ionospheric conductivity. ASAID are seen to have lifetimes of at least 3.5 h.  A discussion on possible mechanisms for the generation of ASAID is presented.We speculate that the proximity of the electron to the ion plasma sheet innerboundaries and of the plasmapause to the ring current outer edge, duringextended quiet times, is an important key for the understanding of thegeneration of ASAID electric fields

Statistical study on the occurrence of ASAID electric fields