ESA Science & Technology11-Jul-2005 09:56:42

Plasma Regions

Polar Cusps

Almost anywhere near the surface of the magnetopause, the Earth's magnetic field is tangential to the magnetopause, making a sort of natural barrier to the solar wind particles. There are only two regions, one in each hemisphere, where the magnetic field is approximately perpendicular to the magnetopause, allowing a more direct entry of solar wind particles into the magnetic field with the geomagnetic field appears to occur around these regions, southward of the cusp in the entry layer and northward of it on the magnetic lobes. Only a few examples have so far been found and with only limited resolution measurements.

Cluster  II will make much higher resolution measurements, in particular in burst mode (107  kbit/s), allowing full three-dimensional ion (CIS) and electron (PEACE) distribution functions to be measured every spin (4  s). The exterior cusp is also seen as a very turbulent region with vortices in the plasma flow. Cluster  II will measure the flow with high resolution in time and at four locations in space to determine the characteristics of these vortices. The Cluster  II orbits aim to ensure that the cusps are crossed as many times as possible in the required spacecraft configuration.

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