Probabilistic forecasting of scintillation using a physics-based data assimilation model

This paper describes the use of the Advanced Ensemble electron density (Ne) Assimilation System (AENeAS) for forecasting equatorial trans-ionospheric scintillation. AENeAS is a physics-based data assimilation model of the ionosphere/thermosphere. The model assimilates electron density true height profiles from ionosondes and TEC measurements from global navigation satellite system receivers using the local ensemble transform Kalman filter (LETKF). Like any Kalman filter the LETKF requires a background model. AENeAS currently uses the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIE-GCM). The maximum altitude modelled by TIE-GCM is between 500-700km (depending on solar conditions). Therefore, in order to effectively assimilate GNSS measurements and to estimate ionospheric parameters such as the total electron content, an NeQuick topside is fitted above these heights. Anderson and Redmon [2017] have investigated the relationship between the rate of change of h'F (δh'F/δt) at 1930 LT (as measured by a vertical ionosonde) and the occurrence of trans-ionospheric scintillation. The method works since the h'F can be used as a proxy for ExB drift and this is associated with the development of equatorial plasma bubbles. In this paper, the AENeAS ensemble is used to estimate the probability distribution function of δh'F/δt, and thereby provide a probabilistic estimate of the likelihood of scintillation occurring. The skill of the AENeAS model at forecasting scintillation has been calculated using a proper scoring function; the Brier score. The Brier score measures the accuracy of probabilistic predictions for mutually exclusive discrete outcomes (scintillation / no scintillation). Furthermore, the AENeAS Brier score has been compared against existing scintillation forecasting models so its relative skill can be investigated.