The auroral zone
The auroral zone is a ring of light emission created by the precipitation of particles in the atmosphere and centred around the magnetic pole. The cusp and boundary layers on the dayside, and the plasma sheet and plasma sheet boundary layer on the nightside are the sources of these precipitations. Transient plasma flows and particle precipitation into the low-altitude cusp are of great interest, as they appear to be produced by phenomena occurring on the magnetopause, such as flux transfer events or solar wind dynamic pressure variations. The spatial scales and time variations of these transients are very important in distinguishing between these two mechanisms. The four Cluster spacecraft cross the low-altitude polar regions at an altitude of a few 100 km at intervals ranging from a few minutes to up to 40 minutes, allowing the time variations of the transient events to be studied.
Auroral oval (in false colour) as seen from space, overlaid on top of a visible image of Earth. The red indicates the brightest aurora and blue the dimmest. The brightest aurora is found at midnight.
The ionosphere is now believed to be an important source of plasma for the magnetosphere and, in particular, for the magnetotail. The polar wind and the nightside auroral zone contribute to the filling of the magnetosphere with plasma. Cluster has enabled measurements of these quantities using its comprehensive plasma physics package.
Last Update: 29 November 2010