Abstract
The Advanced Ensemble electron density (Ne) Assimilation System (AENeAS) is a new data assimilation model of the ionosphere/thermosphere. The background model is provided by the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIE-GCM) and the assimilation uses the local ensemble transform Kalman filter (LETKF). An outline derivation of the LETKF is provided and the equations are presented in a form analogous to the classic Kalman filter. An enhancement to the efficient LETKF implementation to reduce computational cost is also described. In a 3 day test in June 2017, AENeAS exhibits a total electron content (TEC) RMS error of 2.1 TECU compared with 5.5 TECU for NeQuick and 6.8 for TIE-GCM (with an NeQuick topside).
Highlights
1.1 BackgroundComprehensive, global and timely specifications of the Earth’s upper atmosphere are required to ensure the effective operation, planning and management of both radio frequency (RF) systems and satellites
It is well known that physics-based general circulation models (GCMs) suffer in data assimilation schemes when sporadically forced by data (Baker et al, 1987; Lorenc et al, 1991; Macpherson, 1991; Bloom et al, 1996; Fox-Rabinovitz, 1996)
The changes result in the AENeAS total electron content (TEC) being generally higher than Thermosphere Ionosphere Electrodynamics General Circulation Model (TIE-GCM)+ in the northern hemisphere and lower or unchanged in the south
Summary
Comprehensive, global and timely specifications of the Earth’s upper atmosphere are required to ensure the effective operation, planning and management of both radio frequency (RF) systems and satellites. The atmospheric layers most effected by space weather are the ionosphere and thermosphere. The ionosphere/thermosphere is a coupled system which spans an altitude of approximately 90–2000 km above the Earth’s surface. In this region, radiation from the Sun causes photoionization of neutral molecules (thermosphere) creating a plasma (ions and free electrons, ionosphere). The ionosphere affects all RF systems that operate via or through the ionosphere at frequencies below approximately 2 GHz. the ionosphere affects all RF systems that operate via or through the ionosphere at frequencies below approximately 2 GHz Systems such as global navigation satellite systems (GNSS), high frequency (HF) communications, space-based Earth observation radars and space situational awareness radars can be impaired
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