COSMIC-RAY MODULATION STUDIES IN THE OUTER HELIOSPHERE

During the last decade, the Pioneer 10 and 11, and Voyager 1 and 2 missions have greatly expanded our understanding of the structure and extent of the outer heliosphere. In particular, studies of the solar modulation of galactic cosmic rays in this heliosphere have benefited enormously from these missions. Our current understanding of this modulation mechanism, mainly in terms of numerical solutions of the Parker transport equation, is briefly reviewed in this paper. The first crossing by one of these four spacecraft of the termination shock of the heliosphere is eagerly awaited, and much of the present work is done in anticipation of this event.