Intensification and Weakening of Equatorial Plasma Bubble Development Observed by GOLD During Different Phases of a Geomagnetic Storm

Abstract Equatorial plasma bubble (EPB) development during different phases of the geomagnetic storm of 3–4 November 2021 ( SYMH min = −118 nT) was examined using observations and simulations. The initial phase of the storm coincided with postsunset (about 30 min after sunset) at Fortaleza (FZ) and São Luís (SL) with longitudes of ∼38.45°W and ∼44°W respectively on November 3 while the recovery phase of the storm started at 12:45 UT on November 4. GOLD shows the longest (shortest) extension of EPBs on November 3 (4) compared to days before and after November 3 and 4, including quiet days. This indicates an intensification (weakening) of EPBs on November 3 (4). From ionosondes at FZ and SL, a strong (weak) range spread F (SSF (RSF)) was observed on November 3 (4). The postsunset peak F layer height on November 3 reached 450 km and exceeded the preceding and succeeding days by ∼50–100 km at SL indicating the presence of a Prompt Penetration Electric Field (PPEF) which enhanced EPB development via the favorable postsunset vertical E x B and Rayleigh‐Taylor instability (RTI) mechanisms on November 3. The lower‐than‐quiet time F layer height observed on November 4 during Pre‐reversal enhancement (PRE) indicates the presence of a westward‐oriented Disturbance Dynamo Electric Field (DDEF) that undermined RTI growth and led to the weakening of EPB development. Simulation results confirm that the storm‐time electric fields modified the evening‐time ionosphere and influenced the magnitude of vertical E x B drift required for the development of EPBs.