TEMPORAL AND LATITUDINAL VARIATION OF ELECTRON DENSITY DURING THE ASCENDING HALF OF THE SOLAR CYCLE 23 IN THE TOPSIDE F-REGION OF THE INDIAN LOW AND EQUATORIAL LATITUDES.

The effect of solar activity on local time, seasonal and latitudinal variation of electron density Ne measured by the SROSS C2 satellite over the Indian zone during the ascending half of the solar cycle 23 from 1995-2001 at the height of ~500 km is investigated. The SROSS C2 covered the latitude and longitude belts of 31o S - 34o N and 40o- 100o E respectively. Results show that average nighttime (20:00 - 04:00 LT) electron density varies between 0.92?1010 ? 1.62?1012 m-3, decreases to a low value of 0.44?1010 ? 2.65?1011 m-3 before sunrise and after sunrise increases to an average daytime (10:00 ? 14:00 LT) value that varies between 1.03 ?1011 ? 20.19?1012 m-3. There is an evening enhancement in Ne within 18:00 LT to 20:00 LT in the summer solstice. The daytime Ne is highest in the equinoxes with higher value in spring compared to that in autumn. In between the two solstices electron density is higher in winter. Both daytime and nighttime electron density increases with the increase of solar activity in summer, winter and equinoxes. However, annual average electron density appears to follow the ascent of the solar cycle with a time lag of about one year and at the peak of the solar cycle 23 the topside electron density over Indian low and equatorial latitudes exhibits a non-linear relationship with F10.7 cm solar flux. The non-linear relationship between electron density and F10.7 cm solar flux appears to have been caused by non-linear variation of the neutral densities at the bottom and top end of the solar cycle. The variation of the solar ionizing fluxes Lyman α and E10.7 EUV proxy indices have been found to be linear with that of F10.7 and, therefore, appear to have no effect on the observed non-linear variation of electron density with F10.7 cm solar flux.