Morphology of F-region vertical E×B drifts in the African sector using ionosonde measurements

O. S. Oyekola, C. C. Oluwafemi


F-region vertical velocities are derived from the ground-based ionosonde data for Ibadan (7.4°N, 3.9°E; dip 6°S:
an equatorial station in the African zone), to study the general characteristics of electrodynamics of equatorial
ionosphere, such as their variation with season, solar cycle, and magnetic activity at different local time sectors.
The results show profound seasonal and geomagnetic effects. Except for equinoctial period, there is an excellent
consistency in the magnitudes (nearly 20 m/s) and patterns of upward daytime F-region drifts at low and high
solar activity periods. Evening F-region exhibits strong motion with absolute mean value for quiet-time (15 m/s)
greater than on disturbed-time (10 m/s). The average downward quiet midnight-early morning hours sector value
is well below than 10 m/s. The evening reversal time is earliest and latest during solstitial periods. Prereversal
peak is season dependent and varies strongly with magnetic activity. We show that prereversal peak, daytime,
and nighttime maximum drifts saturate at particular values of F10.7 cm solar radio flux index, effects not noticed
with corresponding sunspot number. Our observations confirm several previous results from other equatorial
sites utilizing different experimental techniques.


equatorial F-region;ionospheric variability;ionospheric modelling;ionosonde observations;ionospheric dynamics

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Published by INGV, Istituto Nazionale di Geofisica e Vulcanologia - ISSN: 2037-416X