Cluster at the magnetospheric cusps

The existence of the Earth's magnetospheric cusp, defined as the singular field line, a separatrix, which spreads over the whole magnetopause, is discussed. The real cusp is much more complex and its properties are determined by the nature of the interaction of the solar wind and the interplanetary magnetic field (IMF) with the magnetosphere. The cusps plays a important role since it is the reversal of the terrestrial magnetic field with respect to the IMF around the cusp that permits both southward and northward IMF to reconnect. The cusp has proved to be an excellent laboratory for studying plasma turbulence and wave-particle interactions.