Monoenergetic drop-off of auroral ion fluxes and their mapping onto the magnetospheric equatorial plane Original Research Article

The Akebono spacecraft has often observed monoenergetic drop-off of auroral ion fluxes in the diffuse auroral region, which we call “Ion Drop-off Band” [Shirai, H., Maezawa, K., Fujimoto, M., Mukai, T., Saito, Y., Kaya, N., 1997. Monoenergetic ion drop-off in the inner magnetosphere. J. Geophys. Res. 102, 19,873]. We showed characteristics of the Ion Drop-off Band and predicted that this structure must be detected near the magnetic equatorial plane. We have found that the Geotail spacecraft near the equatorial plane observed an ion structure that can be identified as the Ion Drop-off Band. Recent observations from the Interball spacecraft also showed ion structures similar to the Ion Drop-off Band near the equatorial plane at <10RE In this study we compare the Akebono observations of the Ion Drop-off Band with Geotail and Interball observations and with the results from ion drift path simulations. We also discuss the possibility of using the Ion Drop-off Bands as tracers for the projection of ionospheric regions onto the equatorial plane. Ion Drop-off Band may provide a definite way to map the ionospheric latitudes to the near-Earth (<10RE) equatorial region.