Irregularities Observed at the Edge of a Mid‐Latitude Ionospheric Depletion Following a Geomagnetic Storm

This manuscript presents the analysis of data from multiple ground- and space-based sensors in North American region before, during, after 12 October 2021 geomagnetic storm. Total electron content (TEC) density show formation equatorward propagation a mid-latitude trough at ∼50°N followed by appearance wider depletion (∼15° latitude) lower latitudes. During recovery phase on 13th, edge this settled around 30° latitude exhibited steep gradient. By 14th, sharp boundary had disappeared. Near small-scale irregularities formed. The impact these was observed within Global Positioning System as elevated rate TEC index (ROTI) presented strong 35 MHz scintillations cosmic radio sources well spread-F ionograms digisonde systems. GPS 35-MHz demonstrated that irregularity narrowly confined (≲5° wide) near region. scintillation also showed were moving relatively slowly ∼7 m s−1, likely toward southeast. Density velocity measurements conditions highly favorable to gradient drift instability (GDI) with one-dimensional growth estimated be ∼0.01 s−1. Since persisted for many hours, more than sufficient GDI considered primary driver case.