Abstract
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.
Highlights
The nature of ionospheric plasma motions in the F-region at the magnetic equator is such that they are driven by the neutral air wind along the Earth’s magnetic field and by the electric field in the plane perpendicular to it
Measurements of vertical plasma drifts in the equatorial F-region are a valuable means of deriving information on the electric field
Seasonal averages of the vertical component of the equatorial F-region plasma drifts as derived from ionosonde data at Ibadan during January to December 1964, and January to December 1958 under quiet magnetic conditions are plotted in fig
Summary
The nature of ionospheric plasma motions in the F-region at the magnetic equator is such that they are driven by the neutral air wind along the Earth’s magnetic field and by the electric field in the plane perpendicular to it. Measurements of vertical plasma drifts in the equatorial F-region are a valuable means of deriving information on the electric field. The plasma drifts, The quiet time low-latitude plasma drifts are driven by a complex interaction of E- and F-region electrodynamic processes (Richmond, 1995). Oluwafemi models that explain the low-latitude dynamo electric fields and currents are plentiful (Rishbeth, 1971; Heelis et al.,1974; Richmond et al, 1976; Anderson and Mendillo, 1983; Takeda and Maeda, 1983; Farley et al, 1986; Takeda and Yamada, 1987; Kelley, 1989; Haerendel and Eccles, 1992; Eccles, 1998). During geomagnetic active conditions magnetospheric and disturbance dynamo effects can dramatically affect the low-latitude drifts (Fejer and Scherliess, 1997, and references therein; Scherliess and Fejer, 1997; Kelley et al, 2003)
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