Lidar Observations of Metallic Calcium Ions During 2025 New Year Storm at Mohe (53.5°N, 122.3°E)

Abstract

Storm‐time redistribution of high‐altitude metallic ions provides a sensitive tracer of coupled electrodynamic and neutral‐dynamic processes, but its source–sink balance and triggering pathway remain poorly constrained by direct observations. Here, high‐vertical‐resolution Ca ⁺ resonance‐fluorescence lidar observations at Mohe are combined with Dual‐Channel Optical Interferometer (DCOI) 630 nm thermospheric wind measurements, ionosonde data, and WACCM‐X simulations to investigate an anomalous Ca ⁺ event during the 1 January 2025 geomagnetic storm. The storm reached a minimum Dst of ∼−210 nT and Kp = 8, during which the Ca ⁺ density structure rapidly extended from ∼110 km to 300–350 km between 18:20 and 19:20 UT before descending. The lidar‐derived centroid‐altitude increase rate was 68.7 m/s, representing the apparent evolution of the Ca ⁺ density structure rather than the vertical velocity of individual Ca ⁺ ions. Full‐night column‐density analysis indicates that the high‐altitude enhancement cannot be explained by conservative upward transport of the lower Ca ⁺ layer alone, implying additional transport and source–loss processes. WACCM‐X shows ∼09–15 UT electrodynamic preconditioning, with the electric‐field magnitude increasing from quiet‐day values of ∼1–3 to ∼10.5 mV m ⁻¹ . The rapid Ca ⁺  response occurred later, near the time when DCOI observed abrupt F‐region wind restructuring and a wind‐driven effective drift of ∼80–90 m/s. The event is therefore interpreted as a two‐stage process involving main‐phase electrodynamic preconditioning followed by recovery‐phase wind‐triggered Ca ⁺ redistribution. This study fills an observational gap by linking high‐altitude Ca ⁺ redistribution to both storm‐time electrodynamic forcing and local neutral‐wind restructuring.