Low energy (0.3-25 eV) ion plasma composition and three-dimensional di
fferential velocity distribution measurements have been made from the
Sounding of the Cleft Ion Fountain Energization Region (SCIFER) missio
n. SCIFER traveled poleward into the dayside prenoon cleft region unde
r conditions of low solar activity. Upleg measurements show that the s
ubcleft topside had a rapid density fall-off with altitude (n(e) less
than or equal to 300 cm(-3) at 1400 km altitude), and that the payload
floating potential changed from typical ionospheric negative values o
f about a volt, to zero or positive values consistent with n(e) less t
han or equal to 1000 cm(-3) in sunlight. As the payload moved poleward
and approached apogee, the ion plasma flux abruptly increased. Observ
ations of Langmuir waves at the electron plasma frequency show the pla
sma density increased by a factor of 6 over a scale length of similar
to 1 km. The plasma density boundary coincided with passage into the c
left region, as judged from the appearance of field-perpendicular ion
heating to T-perpendicular to similar to 1 eV, with upward bulk flows
of several km/s for H+, and 1-2 km/s for O+, and warm superthermal tai
ls in the core H+ with characteristic energy similar to 4 eV. An inver
se association was observed between ion temperature and plasma density
, consistent with heating by current-driven waves. The heated cleft pl
asma was H+-dominated in this region, in stark contrast to the O+ domi
nation observed from 3000-6000 km altitude by DE-1 and Akebono near so
lar maximum.