SCIFER encountered the cleft ion fountain within the cleft ionosphere at 1000 MLT and 1400 km altitude where it was possible to investigate the fine structure of transverse ion acceleration (TIA). Latitudinally narrow (30 km) regions of TIA were found to be closely correlated with broadband low frequency electric fields and reduced ionospheric density. The low frequency electric fields extended up to a few kHz with the largest amplitudes of about 10–20 mV/mp-p occurring below 400 Hz. No spectral features ordered by the ion cyclotron frequencies were observed. Outside regions of TIA the ionospheric density was typically 2 × 10³ cm−3 while inside regions of TIA the density dropped to 5 × 10² cm−3. The correlation between TIA, reduced ionospheric density and broadband low frequency electric fields is so exact, sometimes within a few hundred meters, we interpret the broadband low frequency electric fields as current-driven electrostatic waves, perhaps a mixture of ion cyclotron and ion acoustic waves.