A comparison of ground and satellite observations of F region vertical velocity near the dip equator

Abstract

Nighttime F region vertical electrodynamic drifts were made at the magnetic equatorial stations in Africa, Ibadan (7.4°N, 3.9°E; 6°S dip), and Ouagadougou (12°N, 1.5°W; 5.9°N dip) using ionosondes hmF2 data during 1957/1958 International Geophysical Year (IGY) and 1990 periods, respectively; for high solar flux and geomagnetic quiet time conditions. We compare the seasonal averages of vertical drifts with observations made by Incoherent Scatter Radar (ISR) at Jicamarca (11.95°S, 76.87°W; 2°N dip) and Atmospheric Explorer E (AE‐E) satellite for equatorial F layer vertical drifts reported by Fejer et al. (1995). The results indicate good accord between the three techniques at periods when convection dominates other factors (e.g., around prereversal enhancement) except for June solstice drifts. However, when the drifts are completely downward (negative) between 2000 and 0500 LT sector, the mean discrepancies between ionosondes and ISR drifts are of 8–11 m/s (December solstice), 14–17 m/s (equinoxes) but comparable during June solstice with a value of about 14 m/s. Conversely, the typical values of the differences among ionosondes and AE‐E downward velocities are 7–10 m/s (December solstice), 9–12 m/s (equinoxes), yet again similar in winter with a significantly smaller value of about 3 m/s. The evening reversal times are in excellent agreement, apart from June solstice drifts, which exhibits large fluctuations. The morning reversal times show small variations. Equinoctial prereversal enhancement velocities have amplitudes of approximately 17–35 m/s between the methods. Our data are useful for global ionospheric modeling and for the predictions of development of nighttime equatorial F region irregularities at the African region where there is paucity of data.