Study of TEC, slab-thickness and neutral temperature of the thermosphere in the Indian low latitude sector

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 (T n ) 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 slabthickness (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 daytime. 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 (T n ) 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.

Effect of solar cycle on topside ion temperature measured by SROSS C2 and ROCSAT 1 over the Indian equatorial and low latitudes

“…Comparison with the measured T i for corresponding periods indicates that MSISE 90 simulated T n is generally higher than T i during nighttime, while the reverse is true in case of daytime average T i and T n . Venkatesh et al (2011) have found that T n computed from ionospheric slab thickness measurements for the low sunspot years 2004-2005 compare well with MSIS 90 derived temperature over Indian equatorial and low latitudes during daytime hours. A detailed comparative study of the neutral temperature predicted by the MSIS model with ion and electron temperatures measured over the Indian zone will be undertaken and reported in future.…”

“…Higher electron energy results in higher ion temperature in the post sunrise period. This morning peak becomes prominent in the low latitude ionosphere due to the vertical E × B plasma drift, which decreases the electron density followed by an increase in T e (Su et al, 1995(Su et al, , 1996Balan et al, 1997). After sunrise, the ion temperature falls as the electron temperature also falls due to sharing of energy with more electrons.…”

Study of Ionospheric TEC from GPS observations and comparisons with IRI and SPIM model predictions in the low latitude anomaly Indian subcontinental region

“…However, the GPS signals traverse the dispersed ionosphere carrying its signature, hence offer exceptional opportunities for ionospheric research. Ionospheric TEC from ground-based GPS observations have been investigated widely in the past few decades (Mannucci et al, 1998;Liu et al, 2005;McKinnell et al, 2007;Moeketsi et al, 2007;Opperman et al, 2007;Venkatesh et al, 2011). The GPS satellites orbit at about 20,200 km altitude in 6 orbital planes covering almost whole part of the globe.…”

Ionospheric slab thickness at the equatorial anomaly region after the deep solar minimum of cycle 23/24

“…For example, one of the most useful parameters which can be investigated using GNSS data combined with ionosonde data is the ionospheric slab thickness (e.g. Jayachandran et al, 2004;Jin et al, 2007;Stankov and Warnant, 2009;Venkatesh et al, 2011). The ionospheric slab thickness (s) is defined as the ratio of the total electron content (TEC) to the F 2 -layer peak electron density (N m F 2 ), where N m F 2 is proportional to the square of the F 2 -layer critical frequency (f o F 2 ).…”