Low‐frequency oscillatory flow signatures and high‐speed flows in the Earth's magnetotail

Abstract

AbstractUsing plasma sheet data from Cluster 1 spacecraft from 2001 till 2011, we statistically investigate oscillatory signatures in the plasma bulk flow. These periodic oscillations are compared to high‐speed and quiet flows. Periodic oscillations are observed approximately 8% of the time, while high‐speed flows and quiet flows are observed around 0.5% and 12% of the time, respectively. We remark that periodic oscillations can roughly occur everywhere for xgsm<−10RE and |ygsm|<10RE, while quiet flows mainly occur toward the flanks of this region and toward x =− 10RE. The relation between the geomagnetic and solar activity and the occurrence of periodic oscillations is investigated and reveal that periodic oscillations occur for most Kp values and solar activity, while quiet flows are more common during low magnetospheric and solar activity. We find that the median oscillation frequency of periodic oscillations is 1.7 mHz and the median duration of the oscillation events is 41 min. We also observe that their associated Poynting vectors show a tendency to be earthward (Sx≥0). Finally, the distribution of high‐speed flows and periodic oscillations as a function of the velocity is investigated and reveals that thresholds lower than 200 km/s should not be used to identify high‐speed flows as it could result in misinterpreting a periodic oscillations for a high‐speed flow.