| Observations by incoherent-scatter radar have been applied to explore
relationships between the fluxes of incident protons and the resulting
D-region electron densities during a polar-cap radio-absorption event. Using
proton flux data from a GOES geosynchronous satellite, the energy band
having the greatest influence at a selected height is estimated by a process
of trial and error, and empirical relationships are defined. The height
profiles of the effective recombination coefficient are determined for day
and night, and the transition over the evening twilight is investigated for
the height range 60-70 km.
The results show that the day-night change is confined to heights below 80 km,
night-time values at the lower levels being consistent with a balance
between negative ions and electrons controlled by 3-body attachment and
collisional detachment. The daytime results confirm that, contrary to the
prediction of some chemical models, a square-law continuity equation may be
strictly applied. It is confirmed that, as previously reported, the timing
of the sunset change varies with altitude. |