Abstract
HF radar measurements were performed near the magnetic equator in Africa (Korhogo 9°24'63''Nâ5°37'38''W) during the International Equatorial Electrojet Year (1993â1994). The HF radar is a high-resolution zenithal radar. It gives ionograms, Doppler spectra and echo parameters at several frequencies simultaneously. This paper presents a comparative study of the daytime ionospheric structures observed during 3 days selected as representative of different magnetic conditions, given by magnetometer measurements. Broad Doppler spectra, large echo width, and amplitude fluctuations revealed small-scale instability processes up to the F-region peak. The height variations measured at different altitudes showed gravity waves and larger-scale disturbances related to solar daytime influence and equatorial electric fields. The possibility of retrieving the ionospheric electric fields from these Doppler or height variation measurements in the presence of the other possible equatorial ionospheric disturbances is discussed.
Highlights
Electric ®elds and plasma drifts are essential parameters for understanding the dynamics of the E and F regions of the ionosphere
In this paper we report radar daytime measurements taken during the International Equatorial Electrojet Year (IEEY) in Ivory Coast with the LDG HF radar in the F region
The behavior of the F region has been analyzed at very dierent time- and heightscales using dierent radar parameters and dierent radar frequencies in parallel
Summary
Electric ®elds and plasma drifts are essential parameters for understanding the dynamics of the E and F regions of the ionosphere. Ionospheric drift measurements with coherent HF radar were performed using Doppler spectra or echo height changes with time The latter method is often limited to the evening period (Subbarao and Krishna Murthy, 1994; Jayachandran et al, 1993) when the F-region bottom altitude rises beyond 300 km. This paper presents a new set of HF radar measurements performed during daytime from sunrise to sunset in the F-region at several radar frequencies with high time and height resolution. These measurements have been used for determining the inuence of dierent kind of disturbances on E B plasma drift velocity measurements. Houngninou: Typical disturbances of the daytime equatorial F region observed with a high-resolution HF radar the possibility of using these data for ionospheric electric ®eld measurements and about the inuence of the other equatorial ionospheric disturbances on these measurements
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