At almost any location near the surface of the magnetopause, the Earth's magnetic field provides a sort of natural barrier to the solar wind particles. However, there are two regions, one in each hemisphere, where solar wind particles have a direct access to the Earth's ionosphere. Located above each pole, these regions are known as the polar cusps and are an excellent site for monitoring the coupling between the solar wind and the magnetosphere.
An illustration depiciting the spacecraft formation (in close-up) and the loction of the disturbance in the northern magnetic cusp.
Cluster obtains high resolution measurements in these regions allowing full three-dimensional ion (CIS) and electron (PEACE) distribution functions to be measured. The exterior cusp is also seen as a very turbulent region with vortices in the plasma flow. Cluster measures the flow with high time-resolution and at four locations in space to determine the characteristics of these vortices (see Featured highlight below). The Cluster orbits are devised to ensure that the cusps are crossed as many times as possible in the required spacecraft configuration.
Last Update: 29 November 2010