At the lowest level of complexity the termination shock is expected to be a fast mode MHD shock which is attempting to propagate Sunwards against the solar wind flow. It is therefore a reverse shock, so that the upstream side is closest to the Sun and the downstream side is further from the Sun. Accordingly, the solar wind plasma should be compressed, heated, deflected, and slowed across the shock, while the magnetic field should increase. In common with other fast mode shocks, a foreshock region is expected upstream, populated by convected solar wind plasma and charged particles reflected and accelerated at the shock (and in the foreshock by Fermi acceleration processes) and by particles leaking from the heliosheath [Macek et al., 1991]. This foreshock is expected to have the usual types of plasma waves and unstable particle distributions found at planetary foreshocks and in front of travelling interplanetary shocks.
The termination shock is believed responsible for the acceleration of the so-called ``anomalous'' cosmic rays. These are (primarily) singly charged hydrogen, helium, argon, nitrogen, oxygen, and carbon nuclei with energies of order 20 - 300 MeV. It is believed that these particles are originally interstellar neutrals that are picked-up by the solar wind, convected outward, and energised at the termination shock. The details of this acceleration process are still being worked on. However this process occurs, the flux of anomalous cosmic rays should peak at the shock and decrease with increasing distance away from it.
At a more complex level, the anomalous and interstellar cosmic rays may have sufficient energy density to modify the termination shock from being a primarily MHD shock to being a cosmic ray-modified shock, as suggested by the pressure of cosmic rays being comparable to the other pressures in the discussion of Eqs (20.2) and (20.3) [Donohue and Zank, 1993; Zank et al., 1994]. . This might affect the detailed shock structure, including the compression ratio of the plasma density on both sides of the shock, and the locations of the shock and heliopause.