TYPICAL DISTURBANCES OF THE DAYTIME EQUATORIAL F-REGION OBSERVED WITHA HIGH-RESOLUTION HF RADAR

HF radar measurements were performed near the magnetic equator in Afri ca (Korhogo 9 degrees 24'63''N-5 degrees 37'38''W) during the Internat ional Equatorial Electrojet Year (1993-1994). The HF radar is a high-r esolution 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 du ring 3 days selected as representative of different magnetic condition s, given by magnetometer measurements. Broad Doppler spectra, large ec ho width, and amplitude fluctuations revealed small-scale instability processes up to the F-region peak. The height variations measured at d ifferent 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.