  The anisotropic nature of solar wind magnetic turbulence fluctuations is
investigated scale-by-scale using high cadence in-situ magnetic field
measurements from the Cluster and ACE spacecraft missions. The data span five
decades in scales from the inertial range to the electron Larmor radius. In
contrast to the inertial range, there is a successive increase towards isotropy
between parallel and transverse power at scales below the ion Larmor radius,
with isotropy being achieved at the electron Larmor radius. In the context of
wave-mediated theories of turbulence, we show that this enhancement in magnetic
fluctuations parallel to the local mean background field is qualitatively
consistent with the magnetic compressibility signature of kinetic Alfven wave
solutions of the linearized Vlasov equation. More generally, we discuss how
these results may arise naturally due to the prominent role of the Hall term at
sub-ion Larmor scales. Furthermore, computing higher-order statistics, we show
that the full statistical signature of the fluctuations at scales below the ion
Larmor radius is that of a single isotropic globally scale-invariant process
distinct from the anisotropic statistics of the inertial range.
