[PEM11-P09] A statistical study of Pi2 pulsations observed in the upper ionosphere using Swarm magnetic field data
キーワード：Pi2 pulsations
The properties of Pi2 pulsations observed in the upper ionosphere are studied using magnetic field data acquired by the Swarm-A spacecraft in low Earth orbit (LEO) and at the low-latitude Bohyun ground station (BOH, L = 1,3) for January 2014-Jun 2015. From time intervals when Swarm-A was on the nightside (magnetic local time (MLT) = 1800-0600 hrs) and the BOH station was near midnight (MLT = 2100-0300 hrs), we identified 623 Pi2 events in the horizontal H component of the BOH data. For each event we examine the coherence between the horizontal H component on the ground and the Bx (radial) azimuthal By (azimuthal), or Bz (compressional) components at Swarm-A. Out of 623 events, the Bx-H high coherence (> 0.7) events are ~6%, the By-H high coherence events are ~4%, and the Bz-H high coherence events are ~25%. The ground-satellite high coherence events occurred when the spacecraft was located within a magnetic latitude range of ±50°. Using the ground-satellite high coherence events, we examined the latitudinal structure of the relative amplitude and phase of the ionospheric Pi2 pulsations detected at Swarm-A. Confirming previous observations at LEO, we found that the ionospheric Pi2 pulsations are characterized by symmetric odd mode standing oscillations in the north-south direction, having a node for Bx oscillation and an antinode for Bz oscillation, respectively, at the equator. This indicates that the source of ionospheric Pi2 pulsations is the plasmaspheric resonance.