Ion Break Scale of Solar Wind Turbulence at High and Low Beta

Understanding how turbulence behaves and is dissipated at kinetic scales in the solar wind is a topic of current interest that remains to be well understood. It has long been known that there is a break in the spectrum of magnetic fluctuations at ion kinetic scales, although the exact scale associated with this break, and therefore its cause, is currently debated, with several recent observational results that have arrived at different conclusions. In particular, it is difficult to distinguish between the ion gyroscale and ion inertial length at 1 AU, since the ion beta β is typically order unity. Here, we take a different approach, and examine many intervals of extremely high and low β, which occur rarely, but with the long dataset of the Wind spacecraft, can be found. The break is seen to occur at the ion gyroradius for β>>1 and the inertial length for β<<1, i.e., whichever is larger. Possible explanations for these results are discussed, including Alfven wave dispersion, damping and current sheets.