Validation Of the 350 km Effective Height of the Ionosphere for the Low Latitude Region of East Africa

Abstract

The centroid of mass of the ionosphere lies in the region that contains the highest concentration of electrons. The height from the Earth's surface to the point where the centroid is located is called the effective height of the ionosphere. The effective height is useful for aspects such as mapping the Total Electron Content (TEC) Over a given region, calibration Of Global Navigation Satellite System (GNSS) observations, and satellite navigation augmentation among others. Due to the heterogeneous nature of the ionosphere, the effective height varies from one place to another. This variation is particularly pronounced in the low-latitude regions which have high electrodynamic activity. The high electrodynamic activity may render the value Of the effective height used in most models and algorithms unsuitable for the low latitude region, particularly the East African region. In this study, the 350 km effective height of the ionosphere used in many ionospheric algorithms was validated for the East African region. This was determined using data from GNSS receivers and Ionosondes in the region. Another technique that utilizes the GNSS receivers aboard the swarm satellites was introduced to supplement the existing GNSS-TEC methods. The results show that the effective height over the East African region lies in a range of 350 km to 500 km, with a modal value of 400 km. The effective height of the ionosphere exhibit temporal variations, where the day-time values are higher than the night-time values, with the peak appearing between 09:00 UT and 16:00 UT. The seasonal variation showed slightly higher values in the equinox months than in the solstice months. The spatial variation Of the effective height shows an asymmetry between the trough and the crest of the anomaly region, with higher values at the equator during the day-time and vice versa at night. The model predicted values of effective height were validated against the height of the peak electron density (hmF2) obtained from ionosondes for the month of April 2024. The predicted values are in good agreement with the measured values, and performed slightly better than International Reference Ionosphere (IRI) values especially in the day-time ionosphere. The good agreement between the predicted values and observations suggest that, the model may be used to predict the effective height over a place in the East African region where observations are not available. The results showed that while the value of 350 km can still be used for the nighttime ionosphere, the most appropriate value for the East African region is 400 km.