Origins of perturbations in dayside equatorial ground magnetograms

To determine the cause(s) of perturbations seen in dayside equatorial ground magnetograms, we conducted a systematic survey of simultaneous ground-based and geosynchronous satellite-based observations during the 90-day period from December 1, 2020 to February 28, 2021. We examined Huancayo ground magnetometer observations from 14:00:00 to 20:00:00 UT each day, during which Huancayo passed through local noon. From those data we chose perturbation events selected on the basis of large (>20 nT) event amplitude and classified the selected events as responding primarily to solar wind pressure, or to variations in the north/south component of the interplanetary magnetic field (IMF B_z), or perhaps in part to both. The results show that an equivalent number of events were identified for each model during this 90-day period. Variations in the lagged solar wind dynamic pressure routinely correspond to nearly simultaneous sudden impulses recorded at both geosynchronous orbit and on the ground. Variations in IMF B_z produce erosion signatures at geosynchronous orbit and can correspond to ground events if lag times for reconnection to enhance convection in the magnetosphere are taken into account.