Above 100 km altitude, the Earth's atmosphere becomes highly ionized, collisions cease to be important, and dynamics are largely controlled by the terrestrial magnetic field. The terrestrial magnetic field is distorted by the continuous flow of solar wind plasma from the Sun into a cavity known as the magnetosphere, which forms the uppermost region of the Earth's atmosphere. Intense radiation belts of energetic charges form within the magnetosphere, fed from source populations in the ionosphere and the solar wind. Magnetospheric charged particle populations are strongly modified by processes associated with solar activity and solar wind variability, and the varying populations precipitate into the atmosphere causing highly dynamic auroral emissions and chemical changes in the middle atmosphere. The department has a strong research program aimed at understanding how energy carried by the solar wind is transferred into the magnetosphere, dispersed through the system, and eventually deposited in the atmosphere. The program utilizes satellite and ground-based data, together with theoretical analysis and modelling, and involves extensive collaboration with the national and international space science community. There is strong participation in National Science Foundation and NASA programs and the National Space Weather program. The program is enriched by related activities in other UCLA departments.