Heliospheric magnetic fields, energetic particles, and the solar cycle

The heliosphere is the region filled with magnetized plasma of mainly solar origin. It extends from the solar corona to well beyond the planets, and i s separated from the interstellar medium by the heliopause. The latter is e mbedded in a complex and still unexplored boundary region. The characterist ics of heliospheric plasma, fields, and energetic particles depend on highl y variable internal boundary conditions, and also on quasi-stationary exter nal ones. Both galactic cosmic rays and energetic particles of solar and he liospheric origin are subject to intensity variations over individual solar cycles and also from cycle to cycle. Particle propagation is controlled by spatially and temporally varying interplanetary magnetic fields, frozen in to the solar wind. An overview is presented of the main heliospheric compon ents and processes, and also of the relevant missions and data sets. Partic ular attention is given to flux variations over the last few solar cycles, and to extrapolated effects on the terrestrial environment.