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Abstract Mid‐latitude auroras are conventionally generated during intense magnetic storms. However, mid‐latitude auroras were observed by naked eyes at Beijing China (39°N, 116°E) unusually during a moderate storm event on 1 December 2023 with the minimum Sym‐H index only −120 nT. This study combines conjugative in‐site and ground‐based observations to analyze the auroras and underlying physical processes. Results indicate that both electron and proton auroras appeared at low latitudes. Electron auroras predominantly arise from low‐energy electron precipitation, but proton auroras may be explained by energetic tens of keV proton precipitation. Pc1/EMIC waves are observed at low latitudes in the ionosphere, potentially accounting for mid‐latitude proton auroras. Downward field‐aligned currents (FACs) are also detected at low latitudes, producing significant magnetic perturbations. This study reveals the underlying ionospheric responses to the mid‐latitude auroras to understand potential reasons for observing aurora at such mid‐latitudes during a moderate storm. 

Abstract Within the fully integrated magnetosphere-ionosphere system, many electrodynamic processes interact with each other. We review recent advances in understanding three major meso-scale coupling processes within the system: the transient field-aligned currents (FACs), mid-latitude plasma convection, and auroral particle precipitation. (1) Transient FACs arise due to disturbances from either dayside or nightside magnetosphere. As the interplanetary shocks suddenly compress the dayside magnetosphere, short-lived FACs are induced at high latitudes with their polarity successively changing. Magnetotail dynamics, such as substorm injections, can also disturb the current structures, leading to the formation of substorm current wedges and ring current disruption. (2) The mid-latitude plasma convection is closely associated with electric fields in the system. Recent studies have unraveled some important features and mechanisms of subauroral fast flows. (3) Charged particles, while drifting around the Earth, often experience precipitating loss down to the upper atmosphere, enhancing the auroral conductivity. Recent studies have been devoted to developing more self-consistent geospace circulation models by including a better representation of the auroral conductance. It is expected that including these new advances in geospace circulation models could promisingly strengthen their forecasting capability in space weather applications. The remaining challenges especially in the global modeling of the circulation system are also discussed. 

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.