# A High Latitude Model for the E Layer Dominated Ionosphere
## 6 Conclusions  
In this paper, for the first time, we present the empirical Neustrelitz ELDI Event Model (NEEM), which climatologically describes the variation of the E layer dominated ionosphere (ELDI) for the high latitude regions of both hemispheres. NEEM depends on key model drivers. These are the geomagnetic latitude, day of year, local time, solar activity and convection electric field. The model is based on more than two million vertical electron density profiles covering more than one solar cycle from April 2006 to December 2018. The profiles were obtained from ionospheric GPS radio occultation observations on board the COSMIC/FORMOSAT-3 mission. NEEM consists of four submodels. Each submodel is defined by a parametric function equation, which is multiplicatively composed of several terms, one for each driver. The individual submodels NEEM-N, NEEM-H, NEEM-W and NEEM-P describe the peak density, the corresponding height and the width of the vertical E layer electron density profile, as well as the occurrence probability of the ELDI, respectively. The normalized root mean square deviation (NRMS) between the original and the predicted model observables yields similar values across both datasets and both hemispheres. For NEEM-N, we obtain an NRMS varying between 36.1 and 47.1%, and for NEEM-H between 6.1 and 6.3%. In the case of NEEM-W, the NRMS varies between 38.5 and 41.1%, whereas it varies between 56.5 and 60.3% for NEEM-P. In summary, the proposed NEEM represents a promising initial modeling approach for describing the occurrence probability of ELDI events, as well as the associated impact on the E-layer. As such, it paves the way for future prediction of the ELDI and its properties in applications, especially from the fields of terrestrial and space-based telecommunications and navigation. Nevertheless, several possibilities exist to improve NEEM. For example, increasing the size of the modeling dataset could lead to better statistics of the model observables and, thereby, increase the quality of the estimated coefficients. As with other models previously developed in Neustrelitz, the conversion of geographic into geomagnetic coordinates is based on the dipole magnetic field model. An alternative conversion using the IGRF model instead would cause more precise geomagnetic coordinates and, thus, improve the observed dependencies, especially on the geomagnetic latitude. Furthermore, by increasing the number of base functions contained in the individual model terms, the submodels would have more degrees of freedom available to adequately approximate the observed dependencies. Since NEEM is a climatological model that describes the averaged response of the ELDI to the drivers, the reliability to estimate the occurrence of individual ELDI events, often closely related to perturbation induced particle precipitation, is limited. Consequently, the results could certainly be further improved when considering the time delay between the observed solar wind parameters used as model drivers in this study and the magnetospheric-ionospheric-thermospheric response. This is a challenging task that will be addressed in future work. Conceptualization, S.K., N.J. and M.M.H. ; methodology, S.K., N.J. and M.M.H. ; software, S.K. ; formal analysis, S.K., N.J. and M.M.H. ; visualization, S.K. ; writing--original draft preparation, S.K. ; writing--review and editing, S.K., N.J., M.M.H. and J.W. ; supervision, N.J. and M.M.H. ; funding acquisition, M.M.H. All authors have read and agreed to the published version of the manuscript. **Funding:** This research was funded by the German Research Foundation (DFG) under Grant No. HO 6136/1-1. **Acknowledgments:** We thank the international team of the COSMIC/FORMOSAT-3 satellite mission for operating the satellites and the COSMIC Data Analysis and Archive Center for providing the derived observation data.