Modelling of mid-latitude ionospheric trough location and dynamics using multi-frequency radio sounding and in-situ observations

Abstract

The Earth’s ionosphere is characterized by seasonal and diurnal variations due to Solar influences. Extreme ultraviolet (EUV) radiation, X-rays, Lyman-alpha are the main factors affecting the electron density distribution of the ionosphere. In addition, the ionosphere is not homogeneous and has several large-scale features. One of these is the mid-latitude ionospheric trough, which is the main focus of this research. The mid-latitude ionospheric trough (MIT) is the phenomenon of electron density depletion in the nocturnal F region located at subauroral latitudes. This phenomenon, characterized by sharp electron density gradients, and so may poses challenges to trans-ionospheric radio systems, including Global Navigation Satellite Systems (GNSS), by possibility of causing signal delays and scintillation. This research aims to enhance our understanding of the MIT by analyzing long-term in-situ electron density data from the GRACE (2002–2015) and Swarm (2013–2019) satellites, alongside ground-based total electron content (TEC) data from IGS Global Ionosphere Maps (1998–2023). The study examines MIT characteristics such as position, width, depth, and occurrence probability across both hemispheres, considering factors like magnetic local time, seasons, solar activity, and geomagnetic conditions. A statistical MIT model was developed, validated against ESA’s PRISM product, and demonstrated compatibility with storm-time dynamics during 356 geomagnetic storms (2002–2019). The model was evaluated during extreme geomagnetic event, namely the Mother’s Day storm in May 2024, showing its capacity to reproduce smoothed trough behavior.