The role of downward plasma diffusion in the ionospheric nighttime Weddell Sea Anomaly

Traditionally attributed to prolonged photoionization and ionospheric uplift during summer, the WSA is not reproduced by the latest Thermosphere Ionosphere Electrodynamics General Circulation Model.

We introduce a data‐driven flux approach to incorporate more realistic diffusive flux, significantly improving the model's ability to replicate key WSA features. Simulations show that topside plasma diffusion turns downward in the evening, peaking near midnight, contributing notably to the NmF2 enhancement. Around 22:00 local time, downward plasmaspheric diffusion becomes the dominant plasma source, rivaling or exceeding local photoionization (12.08 vs. 8.50 at 22:30).