Abstract:
A study of quarter-hourly ionograms of Kodaikanal (geomag. lat: O'6oN; dip: 3'5°N) showed several instances when the spread-F disappears and subsequently. reappears in two hrs or less during it night. Investigation of such events for a 2-yr period showed that this feature is not associated with systematic opposite changes in layer height and there does not seem to be any particular threshold height for the irregularities below which they cannot sustain.
