... The Sun, which is the main source of energy and disturbance propagating through interplanetary space to the Earth, the heliosphere formed by the outflowing solar plasma with the frozen-in interplanetary magnetic field, and the near-Earth space limited by the geomagnetic field are parts of the intricate and highly variable Sun-Earth system. ... Investigation of the Sun-Earth system and related physical processes is the fundamental task of solar-terrestrial physics. ...