IT is well established1–3 that the spread-F phenomenon, which is observed as diffuse echoes on the ionograms is a common feature during night time between the dip latitudes 20°N and 20°S. Based on the study of ionograms and published monthly f0F2 bulletins, morphological features of spread F have been reported for several equatorial stations1,4–10. Equatorial spread F as seen on the ionograms generally starts around the time of reversal of the F-region vertical motion in the evening and continues to grow in intensity during the downward motion of the F region11. Usually spread F persists only for few hours and on some occasions continues throughout the night. Sometimes, after the disappearance in the pre-midnight period, spread F reappears in the post-midnight period.