E Layer Dominated Ionosphere Occurrences as a Function of Geophysical and Space Weather Conditions

Abstract

At some locations, especially in the auroral regions, the ionization of the E layer can dominate over that of the F2 layer, which is called the E layer dominated ionosphere (ELDI). In the present work we investigate the spatiotemporal variation of the ELDI depending on the season, solar activity, geomagnetic activity, interplanetary magnetic field, convection electric field, and solar wind energy. We specify each distribution of ELDI events by the values of four parameters. In this regard, we compute the height, full width at half maximum, and position of a Gaussian function relative to a precomputed reference ellipse as parameters to describe the spatial distribution of ELDI events in geocentric latitude/longitude coordinates. To study the temporal variation of the ELDI events, we estimate the weighted mean local time of the distribution as the fourth parameter. The database used for our investigations contains more than 3.5 million vertical electron density profiles derived from ionospheric GPS radio occultation observations on board the COSMIC/FORMOSAT-3 (Constellation Observing System for Meteorology, Ionosphere, and Climate/Formosa Satellite Mission 3) mission, covering a period of almost 13 years. The analysis of observations representing changing geophysical conditions results in clear trends for all ELDI parameters. In this context, the mean local time varies mostly between 01:00 and 02:00 local time, while the probability of ELDI occurrence is increased in local winter and in the case of low solar activity. Likewise, an increase in the solar wind parameters increases the number of ELDI events and leads to an equatorward shift of their position. The relationships found in our investigations can serve as a basis for future modeling studies addressing ELDI occurrences as a function of selected geophysical quantities.