EVOLUTION OF TURBULENT MAGNETIC FLUCTUATION POWER WITH HELIOSPHERIC DISTANCE

On the basis of transport theories appropriate to a radially expanding solar wind, new results for the evolution of the energy density in so lar wind fluctuations at MHD scales are derived. The models, which rep resent a departure from the well-known WKB description, include the ef fects of ''mixing'', driving by stream-stream interactions (compressio n and shear) and interstellar pick-up ions as well as non-isotropic MH D turbulence. Magnetometer data from Voyager 1 and 2 and Pioneer 11 ar e compared to the turbulence-based models and close agreement is found between theory and data for a reasonable choice of parameters.