The heliosphere: Its origin and exploration

The heliosphere exists because of the presence of the solar wind, the expanding hot upper atmosphere (the corona) of the Sun, which excludes the local interstellar medium (LISM) from the vicinity of the Sun and planets. The size and boundaries of the heliosphere are determined through the interaction between the solar wind and the LISM. The internal properties, structure, and dynamics of the heliospheric medium are defined by spatial and temporal variability of the regions of origin of the solar wind in the solar corona. The variability of the solar wind leads to evolving, dynamic phenomena throughout the heliosphere on all spatial and temporal scales. The most important timescale is imposed by the approximately 11-year solar activity cycle and the approximately 22-year solar magnetic cycle (the Hale cycle). Regions of the origin and of the properties of the solar wind undergo considerable change on this 11-year timescale, the dominant parameter in the description of the global heliosphere. Due to the rotation of the Sun and the interaction of this rotation with the generation of the internal and external magnetic fields of the Sun, the 11-year periodicity is most significant in the heliosphere in the solar meridian, and thus as a function of heliolatitude.