Abstract

Low Earth orbit satellites frequently encounter Pc1 pulsations, but most have been observed with limited latitudinal extent or short lifetime. In this study we analyze two large‐scale Pc1 pulsations (both latitudinally wide and long‐lasting) generated by ionospheric ducting effect using Swarm and ground magnetometers on 25 June and 3 September 2015. Swarm observed the 25 June pulsations on both dayside and nightside during the storm time substorm (a strong geomagnetic storm on 23 June with \(D_{st} = − 204~nT\)). We found the Pc1 pulsations were pervasive in both magnetic local time sectors of dayside and nightside for at least 2 hr. Another large Pc1 pulsation on 3 September was observed during a nonstorm substorm period. We conclude that (1) ionospheric ducting can transmit Pc1 waves to a wide range of L shells, (2) geomagnetic storm is not a prerequisite for such large‐scale ducting, and (3) wave intensity can abruptly decrease across sharp gradients in the ionospheric plasma density.