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Abstract In this work, it is demonstrated that substorm‐driven penetration electric fields can efficiently enhance the upward plasma transport, favoring the development and structuring of plasma irregularities and the occurrence of scintillation on L‐band signals. While most previous studies focus on investigating penetration electric fields during intense geomagnetic storms, here, the period used (April 01–05, 2020) was under very mild geomagnetic activity (−27 nT SYM‐H 6 nT), so that interplanetary and disturbance dynamo contributions are minimized. This period comprised the same seasonal and solar flux conditions, while undergoing multiple short‐lived substorms, making it well‐suited to evaluate unequivocally: (a) to what extent substorm‐driven penetration electric fields alter electrodynamical processes over low latitudes, and (b) how effective they are in contributing to the structuring of the early nighttime ionosphere and the subsequent occurrence of severe scintillation on L‐band signals. Ground‐based and space‐based multi‐instrument data sets were used. The results show that, even under weak geomagnetic activity, substorm‐driven penetration electric fields—despite being subtle and short‐lived—play a decisive role, enhancing the upward drifts, favoring the development of equatorial plasma bubbles and severe scintillation. The findings indicate that substorms with onsets coinciding with early nighttime are more impactful. This decisive contribution is more likely to be identified during late spring and early fall in the northern hemisphere (or vice versa in the southern hemisphere), when the prereversal vertical drifts are moderate—neither too small nor too large—and may have direct impacts on the day‐to‐day variability of equatorial plasma bubbles. 

Abstract The 14‐panel Advanced Modular Incoherent Scatter Radar (AMISR‐14) system deployed at Jicamarca observed equatorial spread F plumes on two consecutive nights under unfavorable seasonal and solar flux conditions during a period that can be categorized as geomagnetically quiet. The AMISR‐14 capability of observing in multiple pointing directions allowed the characterization of the irregularity zonal drifts revealing that, in addition to their atypical occurrence, the zonal drifts of these plumes/irregularities also presented distinct patterns from one night to another, reversing from east to west on the second night. This work addresses two main subjects: (a) the mechanisms that may have led to the generation of these irregularities, despite the unfavorable conditions, and (b) the mechanisms that possibly led to the reversal (east‐to‐west) in the zonal plasma drift on the second night. To do so a multi‐instrumented and multi‐location investigation was performed. The results indicate the occurrence of simultaneous spread‐F events over the Peruvian and the Brazilian regions, evidencing a non‐local process favoring the development of the irregularities. The results also suggest that, even under very mild geomagnetic perturbation conditions, the recurring penetration of electric fields in the equatorial ionosphere can occur promptly, modifying the equatorial electrodynamics and providing favorable conditions for the plume development. Moreover, the results confirm that the eastward penetration electric fields, combined with the upsurge of Hall conductivity in the nighttime typically associated with the presence of sporadic‐E layers, are likely to be the mechanism leading to the reversal in the irregularity zonal drifts over these regions.