Abstract
Abstract. Understanding the vertical electron density profile, which is the altitudinal variation of ionospheric electron density distribution is an important aspect for the ionospheric investigations. In this paper, the bottom-side electron density profiles derived from ground based ionosonde data and the ROCSAT-1 in-situ electron density data were used to determine the estimates of the topside electron density profiles using α-Chapman function over an equatorial station Trivandrum (8.47° N, 76.91° E) and a low latitude station Waltair (17.7° N, 83.3° E) in the Indian region. The reconstructed electron density profiles are compared with IRI (2007) model derived vertical electron density profiles which resulted in significant deviations between the two different profiles. Both the reconstructed electron density profiles and the IRI model derived profiles are integrated independently to derive the Total Electron Content (TEC) values which are compared with GPS derived TEC values. TEC values derived from the reconstructed electron density profiles give better estimates with the GPS-TEC compared to those of IRI model derived TEC values. Compared to the GPS-TEC, the IRI model is underestimating the TEC values during day-time and is overestimating during night-time at both the stations. The percentage deviations of IRI derived TEC from GPS-TEC are larger compared to those between reconstructed profile derived TEC and GPS-TEC. F2-layer peak electron density, peak height and electron density at ROCSAT altitudes (≈600 km) are used to derive the effective scale heights (HT) of the topside ionosphere during the period from July 2003 to June 2004. The diurnal and seasonal variations of HT and E×B drift velocities are presented in this paper. The diurnal variation of the effective scale height (HT) shows peak values around noon hours with higher values during day-time and lower values during night-time both at Trivandrum and Waltair. The E×B drift velocities at both the places also have shown a clear diurnal variation with a negative peak around 04:00 LT and maximum during day-time hours. The higher and lower values of HT seem to be associated with positive and negative phases of the E×B drift velocities, respectively.
Highlights
Knowledge on the spatial distribution of electron number densities or concentrations (Ne) in the ionosphere is very important for the estimation and correction of propagation delays in Global Navigation Satellite System (GNSS) during space-weather effects such as ionospheric storm conditions
The integrated Total Electron Content (TEC) values are presented in the respective frames along with the simultaneous GPS observed Total Electron Content values
For the profile derived at 07:00 LT, the IRI model is overestimating the TEC value and in the remaining cases it is underestimating the TEC values when compared with GPS derived TEC
Summary
Knowledge on the spatial distribution of electron number densities or concentrations (Ne) in the ionosphere is very important for the estimation and correction of propagation delays in Global Navigation Satellite System (GNSS) during space-weather effects such as ionospheric storm conditions. Reinisch and Huang (2001) and Huang and Reinisch (2001) introduced a new technique (R-H method) to extrapolate the topside ionosphere based on the information from ground based ionograms They approximated the scale height (Hm) around the F2-layer peak height (hmF2) by an α-Chapman function and assumed that the scale height above the F2-layer peak is constant with height (i.e. Hm(h > hmF2) ≈ Hm(hmF2)). Rama Rao et al (1996) have studied the vertical electron density distribution over an Indian low latitude station, Waltair using ionosonde data assuming the topside effective scale height as HT = 1.6 Hm. the R-H method does not include any additional parameter from the topside ionosphere and likely to cause errors in reproducing the topside plasma distribution, in the equatorial latitudes, due to the assumption of constant scale height above F2-peak height (Reinisch et al, 2004; Tulasi Ram et al, 2009). The diurnal and seasonal variations of the topside effective scale height (HT) have been studied, for the first time, over the Indian equatorial and low latitude region and their dependence on the vertical E × B drift is discussed
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