Influence of the dawn‐dusk potential drop across the polar cap on the high‐latitude atmospheric vertical current

Approximately 1200 hours of high‐latitude balloon measurements of atmospheric vertical electric fields and conductivity have been used to derive the UT variation of the ionosphere‐to‐ground vertical current. During geomagnetically quiet days the well known UT modulation, with a minimum at 4‐6 UT and a maximum near 19 UT, is observed. During disturbed days, the dawn‐dusk potential drop across the polar cap clearly influences the vertical current, as was predicted by Park and Dejnakarintra (1977)