Reply to Comments on “A turning point in auroral physics”

Haerendel's conviction (An Apparent Controversy in Auroral Physics, Eos, this issue) that a potential difference is responsible for the downward acceleration of auroral electrons is based on there being an upward acceleration of positive ions, caused apparently by a corresponding electric field. However, even if one accepts on face value this indication of an upward directed quasi‐static electric field, the inevitable presence of a downward directed field farther along the line, where the equipotentials must close and the ions are slowed down again, prevents the negative potential well having any net effect on the energy of either ions or electrons traversing it. The conviction is therefore unfounded. Stern (Origin of Auroral Arcs, Eos, this issue) is swayed to the same conclusion by the fact that in order to deliver the necessary power, electrons need to be forced through the magnetic mirror field. Again, though, even setting aside the fact that static fields cannot produce net acceleration, the conclusion overlooks the fact that any process leading to downward acceleration will accomplish the same feat. Similarly, his claim that a voltage drop has been shown to exist is false. The measurements in question were of electrons, not electric fields. They demonstrate that downward acceleration occurs but do not reveal the process responsible.