An additional layer in the low-latitude ionosphere in Indian longitudes: total electron content observations and modeling

Abstract

The paper presents the observations and modeling of an additional layer in the low-latitude ionosphere in Indian longitudes. The signatures of the additional layer are observed as ledges or humps between the equatorial ionization anomaly trough and crest (EIA) in the latitudinal profiles of total electron content (TEC), measured using a single ground-based beacon receiver located at Trivandrum (8.5° N, 77° E, dip 0.5° N) in India. The ground-based ionograms also show the presence of the so-called F₃ layer for a short duration corresponding to these signatures, and the layer is found to drift upward to the topside ionosphere. The study provides first observational evidence that the so-called "humps" in the latitudinal variation of TEC are nothing but the upward propagating F₃layer. This conclusion is supported by theoretical modeling using the Sheffield University Plasmasphere Ionosphere Model. It is shown that upward E× B drift and strong equatorward neutral wind (perturbed by atmospheric waves) can produce the humps in the latitudinal variation of TEC through the reduction in the downward diffusion of ionization along geomagnetic field lines. The model results also show that the F₃ layer drifts to the topside and forms topside ledges.