NASA Goddard Space Flight Center
Origin and Consequences of Large Solar Energetic Particle Events
Solar energetic particle (SEP) events were first detected some seven decades ago, but their impact on human tehnology became evident only recently. The demise of some recent space missions indicate that SEPs have wide-spread consequences for space exploration. They can alter the Van Allen radiation belts and pose danger to the crew and passengers on board air planes in polar routes. They can modify the properties of ionosphere and hence affect radio communications. They can even cause ozone depletion in our atmosphere by producing radicals that interact with ozone. How the Sun accelerates the coronal particles to nonthermal energies has been a mystery. The extensive coronagraph observations that became available in the mid-1990s from the Solar and Heliospheric Observatory mission finally helped us make progress in establishing the close connection between SEPs and coronal mass ejections (CMEs). It is generally accepted that CMEs and solar flares are the two main sources of SEPs, although the ones reaching the interplanetary space seem mainly accelerated at the shocks driven by CMEs. This point will be illustrated using the relation between CME kinematics and spectral properties of SEP events. This lecture aims at providing a summary of our current understanding of the SEP phenomenon.