Abstract
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 Trivandrum (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 diurnal variation of TEC and NmF2 are similar at Delhi, while they are different at Trivandrum and Waltair during the day-time. The slab-thickness (τ) has shown a pre-sunrise peak around 05:00 LT at all the three stations, except during the summer months over Delhi. A consistent secondary peak in slab-thickness around noon hours has also been observed at Trivandrum and Waltair. During equinox and winter months a large night-time enhancement in the slab-thickness (comparable to the early morning peak in slab-thickness) is observed at Delhi. The latitudinal variation of slab-thickness has shown a decrease from the equatorial station, Trivandrum to the low-mid latitude station, Delhi. The neutral temperatures (Tn) computed from the slab-thickness (τ) has shown a sharp increase around 05:00 LT over Trivandrum and Waltair. Whereas at Delhi, a double peaking around 05:00 and 23:00 LT is observed during winter and equinoctial months. The neutral temperatures computed are compare well with those of the MSIS-90 model derived temperatures.
Highlights
It is known that the equatorial and low latitude ionospheres are more dynamic and play a critical role in the transionospheric communication and navigation systems
With the increasing demand on the transionospheric communication systems used in the navigation of space borne vehicles, such as satellites, aircrafts, as well as surface transportation systems, the measurement of the true value of the total electron content of the ionosphere has become important for making appropriate range corrections, as well as in accounting for errors introduced in the range delays owing to the effects of space weather related events, such as geomagnetic storms and signal scintillations due to ionospheric irregularities
It is readily seen from this figure that the diurnal variation of Total Electron Content (TEC) over Trivandrum typically shows a sharp day minimum of about 5 TECU around 06:00 LT and a broad day maximum with TEC varying from 30 to 50 TECU in all the three different seasons
Summary
It is known that the equatorial and low latitude ionospheres are more dynamic and play a critical role in the transionospheric communication and navigation systems. The ionospheric slab-thickness (τ ) which is the ratio of TEC and F2-layer peak electron density (NmF2) (τ = TEC/NmF2) provides a measure of the skewness of the vertical distribution of the ionization. The diurnal, day-to-day, seasonal and geomagnetic variations of ionospheric slab-thickness in the Indian low and mid latitude regions have been investigated by many researchers (Rastogi et al, 1977; Bhuyan et al, 1986). Since both TEC and NmF2 exhibit a marked latitudinal variation over the equatorial region, it is of interest to examine the latitudinal variation of their ratio, i.e. the slab-thickness (τ ) parameter over the equatorial and low latitude regions. The neutral temperatures from these three stations have been presented and are compared with the MSIS-90 model derived temperatures
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