Space-Based Investigation of the Topside Ionosphere over Bangladesh Including IRI Predictions

This paper investigates the temporal and latitudinal variation of electron density (Ne) in the topside ionosphere using multi-satellite space-based topside Ne measurements recorded over Bangladesh from 2020 to 2022, considering a portion of low to high solar activity period in the solar cycle 25. For this study, the Swarm satellites provided the topside Ne, and the Constellation Observing System for Meteorology Ionosphere and Climate (COS-MIC) satellites provided radio occultation (RO) measurements of the peak electron density of the F2 layer (NmF2 <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">COSMIC</inf> ). This inspection reveals that, ideally, the Ne is less than the corresponding NmF2COSMIC measurements in most cases. Very few cases were discovered where Ne>NmF2COSMIC, signifying a discrepancy feature of the Ne at Swarm altitude. To delve deeper, corresponding to every Swarm Ne measurement, the International Reference Ionosphere (IRI) model was run to obtain NmF2 <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">IRI</inf> predictions. This investigation further confirms that the topside Ne measured at Swarm altitude is less than IRI-predicted NmF2 <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">IRI</inf> during daytime. The Ne shows a decreasing trend from 00:00-06:00 local time (LT) and an increasing trend from 20:00-24:00 LT. Generally, it is observed that Ne/NmF2 ratio is <1 during 05:00-20:00 LT and > 1 during 20:00-05:00 LT. This investigation also reveals a declining trend in the percentage of instances where Ne/NmF2 <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">IRI</inf> > 1 during low to high solar activity years from 2020 to 2022 in solar cycle 25. The examination of some Swarm passes reveals a traveling ionospheric disturbance (TID) signature and Equatorial Ionospheric Anomaly (EIA) effect.