Magnetosphere–Ionosphere Drivers of Transient‐Large‐Amplitude Geomagnetic Disturbances: Statistical Analysis and Event Study.

We present a comprehensive statistical analysis of high‐frequency transient‐large‐amplitude (TLA) magnetic perturbation events that occurred at 12 high‐latitude ground magnetometer stations throughout Solar Cycle 24 from 2009 to 2019. TLA signatures are defined as one or more second‐timescale dB/dt interval with magnitude ≥6 nT/s within an hour event window. This study characterizes high‐frequency TLA events based on their spatial and temporal behavior, relation to ring current activity, auroral substorms, and nighttime geomagnetic disturbance (GMD) events. We show that TLA events occur primarily at night, solely in the high‐latitude region above 60° geomagnetic latitude, and commonly within 30 min of substorm onsets. The largest TLA events occurred more often in the declining phase of the solar cycle when ring current activity was lower and solar wind velocity was higher, suggesting association to high‐speed streams caused by coronal holes and subsequent corotating interaction regions reaching Earth. TLA perturbations often occurred preceding or within the most extreme nighttime GMD events that have 5–10 min timescales, but the TLA intervals were often even more localized than the ∼300 km effective scale size of GMDs. We provide evidence that shows TLA‐related GMD events are associated with dipolarization fronts in the magnetotail and fast flows toward Earth and are closely temporally associated with poleward boundary intensifications (PBIs) and auroral streamers. The highly localized behavior and connection to the most extreme GMD events suggests that TLA intervals are a ground manifestation of features within rapid and complex ionospheric structures that can drive geomagnetically induced currents. Plain Language Summary: Large changes of the surface geomagnetic field can drive geomagnetically induced currents (GICs) that are a hazardous impact of space weather events. Extreme magnetic field changes with timescales of minutes and hours are the most dangerous because they are the most effective at inducing currents on Earth. Shorter‐period geomagnetic disturbances are less effective at current induction, but we show in this study that they are inherently related to and play an active role in space weather events that are capable of driving GICs. We analyze these high‐frequency events that occurred at stations in the high‐magnetic latitude region throughout Solar Cycle 24 and investigate their association to longer (5–10 min) geomagnetic disturbances that can cause GICs. We show that they are often closely correlated and that the associated events can be driven by bursty flows in the magnetotail and subsequent small‐scale auroral structures. Key Points: Transient‐large‐amplitude (TLA) magnetic field disturbances were most common during the declining phase of Solar Cycle 24A majority of extreme nighttime geomagnetic disturbances (GMDs) from 2015 to 2019 had TLA intervals that preceded or occurred within the GMDTLA‐related GMDs are related to inner magnetosphere dipolarizations, subsequent poleward boundary intensifications, and auroral streamers [ABSTRACT FROM AUTHOR]