Radial Evolution of MHD-Scale Solar Wind Turbulence from 35 Rs to 1 AU

The first two orbits of Parker Solar Probe have provided us with the closest ever in situ measurements to the Sun, enabling solar wind turbulence to be measured down to a heliocentric distance of 35.7 solar radii for the first time. Here, we present measurements of MHD inertial range turbulence at this distance and its radial evolution out to 1 AU. We show how the turbulence spectrum changes with distance, including its spectral index, magnetic compressibility and cross-helicity (imbalance of outward and inward energy fluxes). Power levels at perihelion are several orders of magnitude larger than at 1 AU, and the radial variation of these depends on both scale and the component being considered (inward vs outward). We also show how the large scale end of the inertial range (correlation scale, break scale) changes with distance, moving to smaller scales at smaller radial distances down to 35.7 Rs. These properties are compared to models of Alfvenic turbulence and solar wind evolution to determine both the fundamentals of MHD turbulence, and the role it plays in the generation and evolution of the solar wind.