Propagation characteristics of Pi 2 pulsations observed at high‐ and low‐latitude MAGDAS/CPMN stations: A statistical study

Abstract

The objective of this study is to understand better the propagation of Pi 2 waves in the nighttime region. We examined Pi 2 oscillations that showed high correlation between high‐ and low‐latitude Magnetic Data Acquisition System/Circum Pan‐Pacific Magnetometer Network stations (correlation coefficient: ∣γ∣ ≥ 0.75). For each horizontal component (H and D) we examined the magnetic local time (MLT) dependence of the delay time of high‐latitude Pi 2 oscillations that corresponds to the highest correlation with the low‐latitude Pi 2 oscillation. We found the delay time of the high‐latitude H showed remarkable MLT dependence, especially in the premidnight sector: we found that in the premidnight sector the high‐latitude H oscillation tends to delay from the low‐latitude oscillation (<100 s). On the other hand, the delay time of the high‐latitude D oscillation was not significant (∼±10 s) in the entire nighttime sector. We propose a Pi 2 propagation model to explain the observed delay time of high‐correlation high‐latitude H. The model quantitatively explains the trend of the event distribution. We also examined the spatial distribution of high‐correlation Pi 2 events relative to the center of auroral breakups. It was found that the high‐correlation Pi 2 events tend to occur away from the center of auroral breakups by more than 1.5 MLT. The present result suggests that the high‐correlation H component Pi 2 oscillations at high latitude are a manifestation of forced Alfvén waves excited by fast magnetosonic waves.