Timescales of Asymmetries in Magnetospheric Dynamics Induced by the IMF <i>By</i> Component

Abstract Recent studies have shown that global geomagnetic activity and particle precipitation are enhanced, when the dawn‐dusk component of the interplanetary magnetic field (IMF) and Earth's magnetic dipole tilt angle have opposite signs. This IMF effect has been demonstrated so far only in statistical studies, which do not reveal its timescales or dynamical evolution. In this paper we study the response of electron precipitation, field‐aligned currents (FACs) and auroral electrojets during events where the IMF rotates from northward or southward orientation to dawn/dusk orientation. The events are collected from years 1995–2022 separately for the winter and summer seasons, resulting into 573–730 events for each dipole tilt and rotation category. Our results show that the IMF ‐effect in the nightside FACs and in the westward electrojet takes 2 hr to develop and 3 hr to maximize, regardless of whether the dusk‐ or dawnward IMF turning occur from a predominantly northward or southward IMF sector. On the dayside, the IMF ‐effect was found to be faster with timescales less than 1 hr, especially in the summer hemisphere. The observed 2–3 hr timescales in the nightside suggests that an asymmetry build‐up in the magnetosphere by convecting open magnetic field lines is required to manifest the IMF ‐effect. We show that the amount of open flux in the magnetosphere responds rapidly to IMF rotations and that the open flux is larger for the opposite signs of the IMF and , suggesting a physical mechanism modulating the dayside reconnection rate.