Heliophysics: The Science Behind Space Weather and Climate

Heliophysics encompasses the science of the Sun and its manifold interactions with the diverse range of bodies which surround it: the Moon, the Earth, the planets, comets, asteroids, the interplanetary medium and the local arm of our Galaxy. Solar-terrestrial interactions which include both the day-to-day variations in space weather and the long term solar influences on climate, have long occupied our attentions for the obvious reasons that our society and civilization are directly impacted. However, spurred by our far reaching explorations of the entire breadth of the heliosphere over the last 50 years, the traditional disciplines of space science and solar-terrestrial physics have blossomed and merged into a richer field of study, predicated on comparative studies and integrated systems perspectives, which is now called heliophysics. Like meteorology, heliophysics is formulated in terms of the pillars of classical physics: radiative transfer, fluid dynamics, thermodynamics and kinetic theory. But there is an interesting twist: classical electromagnetism is also an essential element of the science due to the much lower densities and higher temperatures that prevail beyond the Earth's dense and relatively cool atmosphere. Consequently, in making the transition from meteorology to heliophysics, the basic physical parameters must be augmented by the (divergence free) vector magnetic field. It is this wily magnetic field that ultimately shapes the unique character of heliophysics and leads to its diverse range of explosive and intermittent phenomena.