Origins of perturbations in dayside equatorial ground magnetograms

Abstract

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 Bz), 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 Bz 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.

Keywords

• dayside magnetosphere
• dayside equatorial ionosphere
• geosynchronous magnetic field