Описание PC индекса
The PC index is an index to monitor the polar cap magnetic activity which is mainly caused by changes in the IMF southward component (BZ) and solar wind velocity. Numerous investigations showed that the IMF southward component drives ionospheric convection over the polae caps, which is sensed by ground magnetometers responding to the two-cell system of currents flowing in the ionosphere. As the Earth rotates under this two-cell current system, a near-pole station is always located under the sun-aligned part of the system (i.e. a transpolar current). This allows derivation of an index from data obtained at a single near-pole station simply calculating a magnetic horizontal component disturbance along the dawn-dusk meridian. Based on an availability of geomagnetic data from near-pole stations Thule (Greenland, 86.5° geomagnetic latitude) and Vostok (Antarctica, -83.4° ), the new magnetic activity index PC was introduced and studied by Troshichev and Andrezen [Planet. Space Sci., 33, 415, 1985], and Troshichev et al. [Planet. Space Sci., 36, 1095, 1988].