Kilometric irregularities in the E and F regions of the daytime equatorial ionosphere observed by a high resolution HF radar

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Abstract
During the International Equatorial Electrojet Year, high resolution vertical HF coherent radar experiments were performed in the Ivory Coast (9°24′62″N, 5°37′38″W) at frequencies in the range 1–8 MHz. Kilometric scale irregularities were observed in the E and F regions of the daytime equatorial ionosphere. These irregularities constitute a large sporadic E layer within the altitude range 100 to 150 km, larger than the width of the equatorial electrojet. The higher part of this irregular region is detached in the morning and evening forming an intermediate region at 150–160 km. These 150 km echoes overtakes the E region electrojet echoes at 100–120 km at noon. The echolocation shows that the reflections arise from the vertical direction up to 150 km with a significant contribution of reflections from East West directions above 110 km. The F1 region irregularities are characterized by time and height scales significantly larger than the E region irregularities scales. As in the E region, the F1 region reflections arise from the vertical and from East West directions when the reflection distance increases. The variations of the Doppler frequency versus the observation distance at several sounding frequencies are well explained by a horizontal motion of the irregular plasma flow both in the E and F regions with velocities of 100 m/s and 130 m/s respectively.