The Role of Large-scale, Merging Solar Wind Fluctuations in the Time-dependent Modulation of Cosmic Rays in the Heliosphere

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A new axisymmetric magnetohydrodynamic (MHD) code will be developed for determining the evolution of the solar wind as a function of both heliocentric distance and helioaltitude. It will include the effects of the solar wind termination shock, and the interstellar pick up ions. Stream and transient structures will be imposed at the inner boundary using single-point spacecraft measurements combined with an helioaltitude extrapolation scheme inferred from Ulysses and SOHO observations. This MHD code will be combined with an existing axisymmetric cosmic ray transport code which accounts for particle drifts and allows the prescription of a very general diffusion tensor. The resulting compound code will greatly enhance our capability to understand the primary causes of galactic cosmic ray modulation throughout the solar cycle.