# A High Latitude Model for the E Layer Dominated Ionosphere
## 1 Introduction  
At middle and low latitudes, where photoionization dominates, the electron density of the F2 layer clearly exceeds that of the E layer, which is closely related to the solar zenith angle at daytime [1]. However, at high latitudes, precipitating energetic particles from the magnetosphere can produce strong enhancements in the electron density of the E layer, as have been occasionally observed using different techniques [2]. E layer electron densities clearly exceeding the peak density of the F2 layer were systematically studied for the firsttime by [PERSON] and [PERSON] [3]. They characterized such events as E layer dominated ionosphere (ELDI), showing the peak electron density at a height range between about 90 and 150 km. ELDI events may occur either due to increased E layer ionization caused by energetic particle precipitation, or due to strong depletion of the F2 layer ionization. Such a depletion may arise, for example, inside the polar hole [4; 5] or inside the mid-latitude trough region [6; 7]. However, previous studies revealed a strong relationship of ELDI events recorded using ionospheric radio occultation (IRO) techniques with the auroral zone and not with the polar cap or the mid-latitude trough region [3; 8; 9]. Therefore, in this work, we interpret ELDI events as occurring due to enhanced particle precipitation, which is capable of producing electron densities in the order of more than \(10^{5}\) cm\({}^{-3}\). The duration of ELDI events can reach up to 5 hours, as [PERSON] et al. [10] found when analyzing ESCAT observations between 2009 and 2011. The ELDI phenomenon is quite different from sporadic E layer events, which are characterized by very thin layers of extremely enhanced electron density occurring preferably at mid-latitudes in summer [11; 12; 13]. By analyzing vertical electron density profiles obtained from IRO observations onboard the COSMIC (Constellation Observing System for Meteorology, Ionosphere and Climate/Formosa Satellite Mission 3) satellite mission [14; 15; 16] and the CHAMP (CHAl-lenging Minisatellite Payload) mission [17], [PERSON] and [PERSON] [3] found that the location of the ELDI events in the Northern Hemisphere can be described by an ellipse having one focal point at the geomagnetic pole. They observed that the semi-major axis of the ellipse and the spread of ELDI events relative to the ellipse increased during enhanced geomagnetic activity, while the number of ELDI events increased for low solar activity and during local night. By evaluating electron density profiles retrieved from incoherent scatter radar observations carried out during low solar activity conditions for the period from 2009 to 2011 at the European Incoherent Scatter Radar (EISCAT) and at the EISCAT Svalbard Radar (ESR), [PERSON] et al. [10] found that at both radar sites, the number of ELDI events increased during winter and spring. Moreover, during both seasons, the number of ELDI events increased around local night at the EISCAT site. [PERSON] et al. [18] analyzed COSMIC IRO electron density profiles at high latitudes during geomagnetic storms that were induced by two high-speed streams in April 2011 and May 2012 and by two coronal mass ejections in July and November 2012. They found that the number of ELDI events increased during the main phases of the storms, whereas their distribution shifted equatorward. [PERSON] et al. [8] investigated ELDI occurrences for the Northern and Southern Hemispheres using CHAMP IRO data from 2001 to 2008 and COSMIC data from 2006 to 2018. They found that in both hemispheres, the ELDI events were distributed along an ellipse located around the geomagnetic pole. Furthermore, they confirmed that more ELDI events occurred during winter and local night as well as during low solar activity and during geomagnetic storms. As a preliminary step for a possible ELDI model, [PERSON] et al. [9] described the elliptical ELDI event distribution by three spatial parameters and one temporal parameter.