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  1. Magnetospheric precipitation plays an important role for the coupling of Magnetosphere, Ionosphere, and Thermosphere (M-I-T) systems. Particles from different origins could be energized through various physical mechanisms and in turn disturb the Ionosphere, the ionized region of the Earth’s atmosphere that is important for telecommunication and spacecraft operations. Known to cause aurora, bright displays of light across the night sky, magnetospheric particle precipitation, modifies ionospheric conductance further affecting the plasma convection, field-aligned (FAC) and ionospheric currents, and ionospheric/thermospheric temperature and densities. Therefore, understanding the properties of different sources of magnetospheric precipitation and their relative roles on electrodynamic coupling of M-I across a broad range of spatiotemporal scales is crucial. In this paper, we detail some of the important open questions regarding the origins of magnetospheric particle precipitation and how precipitation affects ionospheric conductance. In a companion paper titled “The Significance of Magnetospheric Precipitation for the Coupling of Magnetosphere-Ionosphere-Thermosphere Systems: Effects on Ionospheric Conductance”, we describe how particle precipitation affects the vertical structure of the ionospheric conductivity and provide recommendations to improve its modelling. 
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  2. Abstract

    We investigate a significant duskside ionospheric density modulation in the Pc5 frequency band and related spatial structures during the storm on 28 May 2017. We take advantage of 3‐D ionospheric observations by the PFISR and simultaneous magnetospheric in situ observations. Inversion of the density suggests that the Pc5 pulsations modulated precipitating electrons over a broad range of energies (~5–500 keV). Such strong electron precipitation likely caused a significant density modulation rate of ~8 and ionospheric Pedersen and Hall conductances to vary rapidly and peaked at ~70–100 S. The reflection coefficient was also substantially modulated between 0.5 and 0.9. Moreover, the observations by the multibeam PFISR and THEMIS E both reveal that the Pc5 pulsations propagated westward in the duskside region. It suggests that quasiperiodic activities in the nightside and subsequent duskward drifts were likely the source of the duskside Pc5 pulsations.

     
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  3. Abstract

    We present observations that show structured diffuse aurora (SDA) correlated with electron precipitation directly from the outer boundary of the outer radiation belt. The SDA maps to the nightside transition region (∼9–12RE) in the magnetic‐equatorial plane during a substorm growth phase. The energy flux of 100‐ to 300‐keV electrons lost from the outer boundary of the radiation belt is ∼0.4 mW/m2, which is comparable to electron dropouts >100 keV during magnetic storms. The latitudinal dispersion of energetic electrons observed in the ionosphere with energetic electrons more equatorward suggests nonadiabatic scattering from a thinning current sheet. The GLobal airglOW (GLOW) model shows significant optical contributions (up to 46%) from electrons >30 keV within the SDA. Ground‐ and space‐based measurements are consistent with the conclusion that the SDA marks the outer radiation belt boundary during substorm growth phase.

     
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