thermosphere in the Indian low latitude sector

Abstract. The ionospheric equivalent slab-thickness is an important parameter which measures the skewness of the electron density profile of the ionosphere. In this paper, the diurnal, seasonal, day-to-day and latitudinal variations of ionospheric parameters namely total electron content (TEC), the peak ionization density of F-layer (NmF2), equivalent slab-thickness (τ) and neutral temperature (Tn) are presented. The simultaneous data of GPS-TEC and NmF2 from Trivan-drum (8.47 ◦ N, 76.91 ◦ E), Waltair (17.7 ◦ N, 83.3 ◦ E) and Delhi (28.58 ◦ N, 77.21 ◦ E) are used to compute the slab-thickness (τ = TEC/NmF2) of the low sunspot period, 2004– 2005. The day-time TEC values at Waltair are found to be greater than those at Trivandrum, while at Delhi the day-time TEC values are much lower compared to those at Trivandrum and Waltair. The trends of variation in the monthly mean di