Space Science Seminar: Galactic Cosmic Rays: Probes for Space Weather and Climate

Doctor Simon Thomas, Space Plasma Group, Mullard Space Science Laboratory

Friday 06 March 2015, 1600-1700
Cavendish Colloquium Room

Galactic cosmic rays are extremely high energy, charged particles that are accelerated at extra-solar sources such as supernovae, active galactic nuclei, quasars, and gamma-ray bursts. They are modulated by enhancements and inhomogenities within the heliospheric magnetic field. Upon arrival at Earth's atmosphere, they produce a shower of secondary particles, some of which result in energetic neutrons which can be detected at ground level. On centennial and millennial time scales, traces of cosmic rays can be found in terrestrial reservoirs, allowing reconstructions of long-term solar variability which have led to the definitions of grand solar maxima and minima.

In this seminar I shall summarise how variations measured in the flux of galactic cosmic rays at Earth can provide information about both long-term evolution of the Sun’s magnetic field and shorter-term enhancements in the heliospheric magnetic field such as coronal mass ejections. In particular I intend to discuss two studies: the cause of the 22-year cycle in cosmic ray flux and how the cycle changes outside of grand solar maximum, and evidence that cosmic ray data can be used to probe the locations of large heliospheric structures, such as large coronal mass ejections, which are the major driver of space weather. The latter of these two studies could result in a means to use ground-based neutron monitors to track large heliospheric structures (effectively in real-time) prior to their arrival at 1 AU.