  It is widely reported that the power spectra of magnetic field and velocity
fluctuations in the solar wind have power law scalings with inertial-range
spectral indices of -5/3 and -3/2 respectively. Studies of solar wind
turbulence have repeatedly demonstrated the impact of discontinuities and
coherent structures on the measured spectral index. Whether or not such
discontinuities are self-generated by the turbulence or simply observations of
advected structures from the inner heliosphere has been a matter of
considerable debate. This work presents a statistical study of magnetic field
and velocity spectral indices over 10 years of solar-wind observations; we find
that anomalously steep magnetic spectra occur in magnetically dominated
intervals with negative residual energy. However, this increase in negative
residual energy has no noticeable impact on the spectral index of the velocity
fluctuations, suggesting that these intervals with negative residual energy
correspond to intermittent magnetic structures. We show statistically that the
difference between magnetic and velocity spectral indices is a monotonic
function of residual energy, consistent with previous work which suggests that
intermittency in fluctuations causes spectral steepening. Additionally, a
statistical analysis of cross helicity demonstrates that when the turbulence is
balanced (low cross-helicity), the magnetic and velocity spectral indices are
not equal, which suggests that our observations of negative residual energy and
intermittent structures are related to non-linear turbulent interactions rather
than the presence of advected pre-existing flux-tube structures.
