Large-scale traveling ionospheric disturbances impacting equatorial ionization anomaly development in the local morning hours of the Halloween Superstorms on 29-30 October 2003

This study investigates the development of EIA-like features during the Halloween Superstorms. These features are similar to a well-developed equatorial ionospheric anomaly (EIA) and therefore suggest superfountain effects. We tracked EIA-like features in the early-morning sector of 29-30 October 2003 and at around midday on 30 October. Their plasma environment was studied with field-aligned plasma density, vertical plasma drift, electron temperature, and vertical plasma flow profiles. Coupled thermosphere-ionosphere plasmasphere (CTIP) simulations reproduced storm-generated equatorward wind surges. When these EIA-like features appeared early morning on 29-30 October, there was no forward fountain circulation; only large-scale traveling ionospheric disturbances (TIDs) and strong equatorward winds were present. These provide observational evidence that large-scale TIDs created large plasma depletions over the dip equator and with the aid of equatorward winds some large enhancements at similar to+/-30 degrees N (geomagnetic), resulting in the development of early-morning EIA-like features. We identified TID signatures in the equatorial and midlatitude ionosonde and magnetometer data, and studied EIA-like features at around midday on 30 October utilizing non-field-aligned TOPEX TEC (2000 UT) and published CHAMP TEC (2030 UT; 2200 UT) line plots. According to our analysis, the EIA-like features seen in the TEC data were created by large-scale TIDs at 2000 and 2030 UT and by the combined effects of large-scale TIDs and forward superfountain at 2200 UT. CTIP simulations demonstrate the crucial role of the neutral winds' mechanical or direct effects in the development of high plasma densities at low midlatitudes.