Research Article

An empirical model of ionospheric total electron content (TEC) near the crest of the equatorial ionization anomaly (EIA)

¹ Instituto Nacional de Pesquisas Espaciais (INPE), Av. dos Astronautas, 1758, São José dos Campos, São Paulo 12227-010, Brazil
² National Astronomy and Ionosphere Center, Space and Atmospheric Sciences Department, Arecibo Observatory/SRI International, HC3 Box 53995, Arecibo 00612, PR, USA
³ Department of Physics, Raja Peary Mohan College, Uttarpara, Hooghly 712258, India
⁴ Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive Pasadena, California, Pasadena, CA 91109, USA
⁵ S. K. Mitra Center for Research in Space Environment, University of Calcutta, Calcutta 700009, India

^* Corresponding author: rajkumarhajra@yahoo.co.in

Received: 30 April 2015
Accepted: 12 June 2016

Abstract

We present a geomagnetic quiet time (Dst > −50 nT) empirical model of ionospheric total electron content (TEC) for the northern equatorial ionization anomaly (EIA) crest over Calcutta, India. The model is based on the 1980–1990 TEC measurements from the geostationary Engineering Test Satellite-2 (ETS-2) at the Haringhata (University of Calcutta, India: 22.58° N, 88.38° E geographic; 12.09° N, 160.46° E geomagnetic) ionospheric field station using the technique of Faraday rotation of plane polarized VHF (136.11 MHz) signals. The ground station is situated virtually underneath the northern EIA crest. The monthly mean TEC increases linearly with F_10.7 solar ionizing flux, with a significantly high correlation coefficient (r = 0.89–0.99) between the two. For the same solar flux level, the TEC values are found to be significantly different between the descending and ascending phases of the solar cycle. This ionospheric hysteresis effect depends on the local time as well as on the solar flux level. On an annual scale, TEC exhibits semiannual variations with maximum TEC values occurring during the two equinoxes and minimum at summer solstice. The semiannual variation is strongest during local noon with a summer-to-equinox variability of ~50–100 TEC units. The diurnal pattern of TEC is characterized by a pre-sunrise (0400–0500 LT) minimum and near-noon (1300–1400 LT) maximum. Equatorial electrodynamics is dominated by the equatorial electrojet which in turn controls the daytime TEC variation and its maximum. We combine these long-term analyses to develop an empirical model of monthly mean TEC. The model is validated using both ETS-2 measurements and recent GNSS measurements. It is found that the present model efficiently estimates the TEC values within a 1-σ range from the observed mean values.