SCIFER - Structure of the cleft ion fountain at 1400 km altitude

The SCIFER, sounding rocket intersected the cleft ion fountain (CIF) at an altitude of about 1400 km revealing the structure of upward flows and ion acceleration. This altitude range is intermediate, between lower altitude studies using DE-2 and HILAT data and higher altitude studies using DE-1 and EXOS-D data. Within the observed intense ion heating region the ions are consistent with satellite measurements of the cleft ion fountain of DE-1, or the ''ion wall'' of EXOS-D obtained at much higher altitudes. We conclude from the SCIFER data set that the accelerated ion flux levels at 1400 km altitude are similar to the TAI fluxes measured at higher altitudes. Furthermore the transversely accelerated ions are found within separate ''events'' of 30-40 km latitudinal width and have well-defined boundaries. The ion distribution function within an event indicates transverse-beating up to about 40 eV, occurring a few tens of km below the rocket. The SCIFER data set serves to demonstrate that the cleft ion fountain is composed of discrete structures originating poleward of the electron trapping boundary in regions of depleted ionospheric density.