Heliospheric energetic particle variability over the solar cycle

The energetic particle contents of the heliosphere change from solar maximum to solar minimum. The ultimate responsible for those variations is our changing Sun. Its changes are reflected in the dynamics of the large-scale structure of the heliosphere, the solar output of energetic particles, and definitively, in the origin, intensity, energy and composition of the population of energetic particles observed by spacecraft and earth-based detectors. I will describe the global changes observed over the solar cycle in both the heliospheric energetic particle contents and the large-scale structure of the 3-D heliosphere. The stable and regular pattern of recurrent energetic particle events observed in association with corotating interaction regions (CIRs) during solar minimum is replaced by the irregular and sporadic observation of solar energetic particle (SEP) events associated with the occurrence of fast coronal mass ejections (CMEs). The higher frequency of CMEs and transient events during solar maximum results in a more complex and dynamic heliosphere with important consequences for the propagation of energetic particles. Whereas the heliosphere is relatively undisturbed (CME-free) energetic particles may freely propagate throughout the heliosphere. However, the presence of multiple CMEs causes increases in the heliospheric magnetic field that may result in the confinement of energetic particles and hence the enhancement or attenuation of SEP intensities depending on the location of the observer with respect to the energetic particle confinement. I will review the occurrence frequency of the major SEP events and the effects that they had at different locations of the heliosphere.