Beyond the plasmapause, the magnetospheric plasma environment is characterized by high temperatures and low densities. This region usually encompasses the geostationary orbit. The location of the outer boundary of this region, the magnetopause, is controlled by the balance between the ram pressure of the flowing solar wind and the magnetic pressure of the terrestrial magnetic field. See Annex H.3.4 for further discussion of the magnetopause position.
During active periods, large amounts of magnetic energy are injected into the plasma in this region. These are called magnetic storms and substorms and are detectable on the ground as magnetic disturbances at certain latitudes. Hence there is a strong link between hot plasma and high values of the magnetic index Kp.