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Abstract:
In order to accurately estimate the ionospheric Total Electron Content (TEC) using empirical models, it is crucial to construct the realistic vertical electron density profiles. Inadequate representation of electron density profiles leads to under-/over-estimation of the TEC in model outputs. The NeQuick2 employs semi Epstein type of polynomial to characterize the topside ionospheric structure, wherein, the scale height (H) is the key parameter. Over the equatorial and low latitudes, the NeQuick2 model exhibits large uncertainties, particularly in the topside ionosphere. The NeQuick2 estimates H using empirical formulations, which contains three major parameters namely, Ho– the scale height at the F-layer peak, g – height gradient in H and, r – which controls H at higher altitudes. In this study, a systematic analysis has been carried out, with particular focus on the equatorial and low latitudes, to explore the variability of topside scale height and density profiles on the three empirical parameters using the radio occultation data from COSMIC satellites, over the Indian sector. Model uncertainties in estimating the Ho and consequent impacts on the modelled TEC are investigated. Data assimilation analysis has been carried out to quantitatively understand the effect of deviations in topside scale height, and its latitudinal variations on the uncertainties in accurate estimation of TEC. This study reveals the impact of scale height uncertainties on the TEC estimation errors and demonstrates the need for improvements in empirical formulations for improving accuracies in ionospheric modelling over the equatorial and low latitude sectors.
