Characteristics of flow bursts and dipolarization in the near-Earth magnetotail, including MMS initial results

Abstract:

In the near-Earth's magnetotail, the most dramatic energy conversion process takes place in an explosive manner, involving transient and localized phenomena such as the plasma jets called Bursty bulk flows (BBF), embedding multiple velocity peaks called flow bursts. Multi-point observations from Cluster and THEMIS have established the importance of measuring local gradients of the fields and the plasma to understand the BBF evolution. Among others the magnetic field disturbance forming at the front of BBF/flow bursts, called dipolarization front (DF), has been intensively studied and its importance in understanding the evolution, particularly, interaction of the plasma jets and the Earth’s dipole field, has been established.

With the successful launch of Magnetospheric Multiscale Misssion (MMS), it becomes possible to observe the highly dynamic signatures of these transients with high-time resolution measurements of electromagnetic fields and plasma. The Active Spacecraft Potential Control (ASPOC) neutralizes the spacecraft potential by releasing positive charge produced by indium and thereby controlling the spacecraft potential in order to enable accurate measurements also in sparse plasma environments. During the commissioning phase of MMS, the spacecraft was in a near string-of-pearl configuration.

We present the initial results on the structure of the dipolarization front and its evolution using measurements from the four MMS spacecraft. We also monitor the ambient plasma conditions based on new parameters derived from uncontrolled and controlled spacecraft potential around the dipolarization front using data from ASPOC together with the FIELDS, FPI, and HPCA data.