The distribution of MHD turbulence in the heliosphere and the charged particle radiation environment

Magnetohydrodynamic (MHD) turbulence plays an important role in cross scale couplings in the heliospheric system and is central to understanding the distribution and variations of charged particle radiation. The nonlinear turbulent cascade process acts as a conduit connecting large scale fluid-like plasma motions to small scale kinetic motions, and is thus most likely an integral part of heating processes from the coronal base to the outer boundaries of the heliosphere. Turbulence also establishes key parameters that determine the transport (and perhaps also, acceleration) of energetic charged particles. In the inner heliospheric realm of solar energetic particles, turbulence can account for scattering, field line complexity, and topological trapping, and can provide other indirect effects such as turbulent transport affecting CMEs and shocks. To understand the distribution and spectra of galactic cosmic rays, one must know the diffusion tensor and therefore local turbulence properties. Turbulence is transported outward in the supersonic solar wind, while the cosmic rays diffuse and drift inwards from the interstellar medium. Thus to understand how the spectrum of galactic cosmic rays is established at any point in interplanetary space, it is necessary to have knowledge of the turbulence everywhere in the heliosphere. Here we summarize recent progress in this challenging area. Headway has been made by employing a four equation transport model with one point nonlinear modeling of locally homogeneous turbulence. The model follows turbulence energy density, correlation scale, temperature and cross helicity under the influence of specified large scale fields. The turbulence is driven by large scale shear, and in the outer heliosphere, by pickup ions. A few constants must be estimated either from theory or observations -- the MHD Karman-Taylor constants, the shear strength, a turbulence geometry factor ("mixing term"), and the Alfven ratio. The latitudinal dependence of solar wind speed, density and large scale magnetic field are important parameters, while latitude dependence of the boundary conditions must also be established. Using parameters and boundary data that are consistent with observations, the model accounts for radial dependence of the turbulence properties from 1 to 60 AU as observed by Voyager, as well as high latitude Ulysses observations. Cosmic ray modulation models incorporating turbulence modeling also have made substantial progress in providing an "ab initio" description of the distribution of galactic cosmic rays. Support by NASA grants NAG5-11603 and NNG04GA54G, and by NSF grant ATM-0105254 is acknowledged, as are important collaborations with J. W. Bieber, B. Breech, R. A. Burger, P. A. Isenberg, J. Minnie, S. Oughton, S. Parhi, C. W. Smith, and G. P. Zank.