GCRs and SEPs reach the near-Earth space environment from two different “ends” of the heliosphere. GCRs which are predominantly accelerated in the galaxy enter the heliosphere from “outside” and their propagation is often modeled as diffusion through the heliospheric IMF and the heliosheath. SEPs on the other hand, are accelerated at the Sun and then distributed in the heliosphere. This “diffusion” or “distribution” process is called “particle transport” and is a topic of current research. Because of the long life of GCRs of hundreds of thousands of years, the GCR flux is affected only by transport processes. GCRs and SEPs are accelerated by supernova-driven shocks and by solar flares and coronal and CME-driven shocks, respectively. Because we consider the GCRs as a “background” which is modulated by solar activity at all time scales, their acceleration proper is not seen as a prime space weather issue, but understanding their transport is important for long-term predictions and possibly for also for terrestrial climate. On the other hand, SEP acceleration is an important topic for space weather, as the flux of SEPs can vary by many orders of magnitude. The respective roles of solar flares/reconnection and shocks in the deep corona are currently strongly debated, it is well possible that both play a key role in the energization of SEPs.
In order to be accelerated, the speeds of SEPs must exceed the ambient Alfvén speed; the more energetic a particle is, the more energy it gains in most acceleration models. Thus, it appears that SEPs are accelerated out of a “pool” of so-called suprathermal (because they are much faster than the thermal solar wind particles) particles, whose origin is unclear. Remnant solar flare particles, but also suprathermal solar wind particles have been considered for this “pool”. It is these particles which are injected into the acceleration process for SEPs.