Abstract
Abstract. A study of dipolarization fronts of the Earth's magnetotail has been performed using seven years (2001–2007) of Cluster data. Events both with and without high-speed earthward flows are included. A superposed epoch analysis of the data shows that the dipolarization is preceeded by a decrease of Bz before the increase. The duration of the dipolarization tends to be decreasing with increasing velocity of the plasma flows. The thickness of the dipolarization front is on average 1.8 plasma inertial lengths, independent of the plasma velocity. We find that the events fall into two categories: Earthward and tailward moving dipolarizations. The dipolarization fronts can be assumed to be tangential discontinuities and the currents on the front have mainly a perpendicular component.
Highlights
Magnetotail dipolarizations are usually associated with substorms (e.g. Baumjohann et al, 1999), after reconnection has taken place on the stretched field lines, the newly connected field lines will move towards the Earth, releasing the magnetic tension
These dipolarizations still leave a lot of questions open, with respect to the details of their structure like: What is the thickness of the dipolarization front, defined as the quick turning from Bx to Bz?; Are there currents flowing on the front, and if so, what is the nature of these currents?; Is the structure of the dipolarization front dependent on its velocity?; Why can Bz decrease to become negative before it starts to increase? In this paper we will try to answer some of these open questions after a short discussion on what has been done before
The important characteristics obtained in these two papers for this present study are: 1. The magnetic field becomes dipolar in the course of the fast earthward flow; 2
Summary
Magnetotail dipolarizations are usually associated with substorms (e.g. Baumjohann et al, 1999), after reconnection has taken place on the stretched field lines, the newly connected field lines will move towards the Earth, releasing the magnetic tension. Zhang et al (2011) studied current carriers observed within thin current sheets ahead of and during the passage of earthward-moving dipolarization fronts in the near-Earth plasma sheet using THEMIS measurements. Contributions by both diamagnetic and polarization currents were found. Nakamura et al (2004) found that 22 % of the fast flows, with |V | > 300 km s−1, observed in their study were tailward From these 219 events 160 events had only positive velocity values and 59 events were categorized as tailward-mixed earthward flow events. In the following we examine these 107 events that took place close to the neutral sheet
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