Geodesy and Geodynamics (Sep 2024)
Longitudinal dependence of the forecast accuracy of the ionospheric total electron content in the equatorial zone
Abstract
The longitudinal dependence of the behavior of ionospheric parameters has been the subject of a number of works where significant variations are discovered. This also applies to the prediction of the ionospheric total electron content (TEC), which neural network methods have recently been widely used. However, the results are mainly presented for a limited set of meridians. This paper examines the longitudinal dependence of the TEC forecast accuracy in the equatorial zone. In this case, the methods are used that provided the best accuracy on three meridians: European (30° E), Southeastern (110° E) and American (75° W). Results for the stations considered are analyzed as a function of longitude using the Jet Propulsion Laboratory Global Ionosphere Map (JPL GIM) for 2015. These results are for 2 h ahead and 24 h ahead forecast. It was found that in this case, based on the metric values, three groups of architectures can be distinguished. The first group included long short-term memory (LSTM), gated recurrent unit (GRU), and temporal convolutional networks (TCN) models as a part of unidirectional deep learning models; the second group is based on the recurrent models from the first group, which were supplemented with a bidirectional algorithm, increasing the TEC forecasting accuracy by 2–3 times. The third group, which includes the bidirectional TCN architecture (BiTCN), provided the highest accuracy. For this architecture, according to data obtained for 9 equatorial stations, practical independence of the TEC prediction accuracy from longitude was observed under the following metrics (Mean Absolute Error MAE, Root Mean Square Error RMSE, Mean Absolute Percentage Error MAPE): MAE (2 h) is 0.2 TECU approximately; MAE (24 h) is 0.4 TECU approximately; RMSE (2 h) is less than 0.5 TECU except Niue station (RMSE (2 h) is 1 TECU approximately); RMSE (24 h) is in the range of 1.0–1.7 TECU; MAPE (2 h) < 1% except Darwin station, MAPE (24 h) < 2%. This result was confirmed by data from additional 5 stations that formed latitudinal chains in the equatorial part of the three meridians. The complete correspondence of the observational and predicted TEC values is illustrated using several stations for disturbed conditions on December 19–22, 2015, which included the strongest magnetic storm in the second half of the year (min Dst = −155 nT).
