Abstract. In recent years the variability of the cosmic ray flux has become one of the main issues interpreting cosmogenic elements and especially their connection with climate. In this review, an interdisciplinary team of scientists brings together our knowledge of the evolution and modulation of the cosmic ray flux from its origin in the Milky Way, during its propagation through the heliosphere, up to its interaction with the Earth's magnetosphere, resulting, finally, in the production of cosmogenic isotopes in the Earth' atmosphere. The interpretation of the cosmogenic isotopes and the cosmic ray -cloud connection are also intensively discussed. Finally, we discuss some open questions.

[1] Two termination shock acceleration modulation models are used to study the modulation of anomalous protons, in particular the effects of different scenarios for global solar wind speed (V) variations in the heliosheath. The first numerical model simulates a symmetric heliosphere and the second simulates an asymmetric heliosphere with respect to the Sun. The modulation differences between these models are illustrated and discussed. The geometry of the heliosphere in the latter model is deduced from a time-dependent three-dimensional hydrodynamic model of the heliosphere which provides the different scenarios for the V-profiles in the heliosheath. The modulation models include the solar wind termination shock, global drifts, adiabatic energy changes, diffusion, convection, and a heliosheath. The anomalous protons are kinetically described using the Parker transport equation. A solar wind speed decreasing stronger than the generally assumed V / 1/r 2 dependence, with r the radial distance from the Sun, is studied as well as an extreme scenario with V / r 2 . The stronger decrease produces a compressive flow in the heliosheath which results in additional acceleration of anomalous protons in the heliosheath. The solutions are shown for solar minimum and moderate maximum modulation conditions for both heliospheric magnetic field polarity cycles. Significant modulation differences are found to occur between these different scenarios for V in the heliosheath. If the stronger than V / 1/r 2 scenarios in the heliosheath are real, the anomalous intensities should increase beyond the TS, which should be measurable by the Voyager 1 spacecraft in the near future.

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An asymmetric solar wind termination shock ( TS) model is used to study the effects on the modulation of cosmicray protons for different scenarios of the solar wind speed (V ) in the heliosheath. This two-dimensional model is applied using predictions for V in the heliosheath that were calculated with a time-dependent three-dimensional hydrodynamic model. Decreases stronger than the generally assumed V / 1/r 2 in the heliosheath are studied, as well as an extreme case, V / r 2 , where r is the radial distance.The effect of the TS is enhanced under certain circumstances, and ''barrier''-type modulation in the heliosheath also depends on the chosen V-profiles. Significant changes occur mostly for the A < 0 solar magnetic polarity cycle, at all distances in the equatorial plane, when the V is changed from an incompressible fluid (V / 1/r 2 , : = V ¼ 0) in the heliosheath, to V / 1/r 8 , in a symmetrical model. For the asymmetrical case the TS is predicted to be more effective in the heliospheric nose than in the tail, especially for the A < 0 cycle during solar minimum conditions. The different profiles for V do not have a significant effect on the intensities inside the TS, but in the heliosheath the difference can be quite significant. It is found that V / 1/r 2 in the heliosheath is an oversimplification. The consequent effects of having : = V 6 ¼ 0 in the heliosheath prove to be relevant for cosmic-ray modulation and acceleration, especially now that the Voyager 1 spacecraft encountered the TS and entered the heliosheath. Subject headingg s: cosmic rays -solar wind -Sun: particle emission

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