K.: Day-today variability of equatorial and low latitude F-region ionosphere in the Indian

The F-region variability of the ionosphere during high solar activity period of year, 1970 and 2001, have been studied using different hourly foF2 data from Indian stations, Thiruvananthapuram (8.5°N, 76.8°E), Kodaikanal (10.2 ° N, 77.5°E) near the Dip equator and Delhi (28.6°N, 77.2 ° E) located north of the Equatorial Ionization Anomaly (EIA). During the study three types of changes have been observed viz, single day abnormality, alternate day periodic fluctuations and long-term periodic variations in fof2 values. The day-to-day change in the foF2 values are not always correlated with the corresponding solar and magnetic activity changes. The short as well as the long-term variations in critical frequency of the F layer are found to be mainly controlled by the equatorial electrojet (EEJ) variations. It has been found that the variation in foF2 over Delhi is positively correlated and over equatorial stations the values are negatively correlated with EEJ strength