Modelling the Main Ionospheric Trough in the Eestern European Sector Using EDAM Assimilating GPS Data

The main ionospheric trough is a large-scale spatial depletion in the ionospheric electron density that is several degrees in latitude and is extended in longitude. It exhibits substantial day-to-day variability in both structure and latitude and forms at the interface between the high-latitude and the mid-latitude ionosphere. Observations at mid-latitudes in western Europe show the trough to be a night-time feature, appearing in early evening and progressing equatorward during the course of the night. It retreats rapidly poleward at dawn. Under conditions of increasing geomagnetic activity, the trough moves progressively to lower latitudes. Steep gradients on the trough-walls on either side of the minimum density and their variability can cause problems to radio applications. The Electron Density Assimilative Model (EDAM) provides a method for modelling the ionosphere over a wide geographic area. It assimilates ionospheric observations into a background International Reference Ionosphere (IRI) to provide a full 3D representation of the ionosphere in the geographic regions of interest at specified times and days. This current investigation studies the capability of EDAM to model the ionosphere in the region of the mid-latitude trough under different conditions of seasonal and geomagnetic activity. Measurements from forty GPS stations in Western Europe were assimilated into EDAM to provide a model of the ionosphere in the trough region. Calculations of slant Total Electron Content (sTEC) along satellite-to-receiver ray paths through the resulting modelled ionosphere are then compared with independent, ground-truth, GPS observations. Similar comparisons are also carried out for daytime observations in the absence of the trough for baseline comparisons. Examples of the results are presented and discussed.