Whilst the instrumentation onboard the ACE and Ulysses spacecraft allows us to study a variety of topics, our primary concern is an ongoing study of the mildly energetic particle output from the Sun. The ACE spacecraft is well placed to observe Earthward particle events such as CMEs and solar flares and also more small scale particle events such as 'coronal flares'. The Ulysses spacecraft can also be used to investigate the more significant particle events and has also provided a wealth of information on Co-rotating Interaction Regions (CIRs), caused when fast and slow solar wind streams interact. One of the more interesting uses of these spacecraft arises from a combination of their quite different perspectives of the interplanetary medium. The Ulysses trajectory is markedly different from ACE's which allows us to study the same event not just from different locations in the ecliptic plane but also as a function of heliographic latitude.

Solar flares are the most energetic explosions in the solar system. Not only do they generate vast quantities of electromagnetic emission, across the spectrum, but they also accelerate particles up to relativistic energies. The specifics of the solar flare mechanism have remained one the most important and elusive questions in the field of solar physics over the past few decades. Of particular interest is understanding how flares impart so much energy to solar particles over such short timescales and also which particles, ions or electrons, are the primary recipient of that energy. 

In general, once solar energetic particles leave the near Sun environment (a few solar radii), we expect them to propagate scatter free in terms of particle-particle collisions however they do experience a certain level of pitch angle scattering from wave-particle interactions with the interplanetary magnetic field (IMF). For a known IMF configuration we can model this propagation with the focused transport equation. Such models provide information on the level of pitch angle scattering in the inner heliosphere and also the source function describing the injection of particles at the Sun. There is also some reason to suspect the transient presence of a 'scattering barrier' behind Earth's orbit. Such a barrier might be the result of an interplanetary CME or from the interaction of fast and slow solar wind streams; application of the focused transport equation will provide us with a better understanding of the effects of such a barrier.

CMEs are of interest not only because of the role they play in driving some geomagnetic disturbances but also because CMEs often drive interplanetary shock fronts. The behaviour of astrophysical shocks is important in heliospheric physics and also in several other astrophysical scenarios e.g. stellar and galactic wind studies. In the context of heliospheric physics, one of the biggest challenges is understanding how magnet-hydro-dynamic (MHD) shocks accelerate particles and also the energetic extent of this behaviour.

CMEs are common candidates for large, long lasting proton events in the inner heliosphere but it is becoming ever more clear that CMEs alone are unlikely to drive the high energy component of these particle events. It may be the case that some combination of flare and CME acceleration occurs. Measurements from the ACE and Ulysses spacecraft may provide us with a more complete understanding of these processes. 

The coronagraphic images of CMEs can often be quite intricate suggesting either a complex CME structure or alternatively, the simultaneous launch of several CMEs; we can certainly see CMEs launched from opposite sides of the Sun at the same time. One possible way to investigate this effect is to take advantage of times where the magnetic connections of the ACE and Ulysses spacecraft are widely separated. Whether neither, one or both of the spacecraft see the effects of a CME, we can place limits upon the spatial extent of a given interplanetary disturbance.

For solar flares, the region of particle acceleration is thought to be relatively small, nevertheless we quite often see energetic particles from the West limb of the Sun which are apparently associated with solar flares from the East limb. The route taken by these particles is not well understood and a greater understanding of the various ways in which energetic solar particles travel heliographically around the Sun would go some way to improving our analysis of interplanetary particle events. In the absence of all other phenomena, the energetic particles should be tied to the IMF and consequently we might trace these particles back to their origin at the Sun. However, the network of coronal magnetic field lines provides ample opportunity for the distribution of energetic particles around the Sun. One further possibility is that interplanetary shocks play some role in redistributing energetic particles around the Sun. The combination of data from the ACE and Ulysses spacecraft have already been used to investigate heliographic transport during an interval of significant solar activity and suggest that one limiting factor is that particles are perhaps not able to cross the heliospheric current sheet. The separation of the spacecraft provides a useful tool for such studies.

At L1, in the mildly relativistic energy range, we might expect to see a variety of different electron populations; coronal electrons, solar flare electrons and electrons released as CMEs leave the Sun. Given the complexity of many solar particle events, the origin of electrons observed by ACE is not always obvious, especially since in many instances we can expect these different populations to be released almost simultaneously.

By studying the context and characteristics of different electron events (such as their anisotropy and spectral behaviour), we are finding new ways to separate these populations at the spacecraft. Not only does this provide a greater opportunity to study these electron populations in isolation but also, by studying how they combine, we might reveal useful information about the chain of physical processes involved in solar particle events.