  We have investigated how the degree of imbalance in solar wind turbulence is
modified by large-scale velocity shears in the solar wind plasma. The balance
between counterpropagating Alfv\'enic fluctuations, which interact nonlinearly
to generate the turbulence, has been quantified by the cross helicity and
Elsasser ratio. Velocity shears at a 30-min timescale were identified, with the
shear amplitude defined in terms of the linear Kelvin-Helmholtz (KH)
instability threshold. The shears were associated with 74 interplanetary
coronal mass ejection (ICME) sheaths observed by the Wind spacecraft at 1 au
between 1997 and 2018. Typically weaker shears upstream of the sheaths and
downstream in the ICME ejecta were also analyzed. In shears below the KH
threshold, imbalance was approximately invariant or weakly rising with shear
amplitude. Above the KH threshold, fluctuations tended toward a balanced state
with increasing shear amplitude. Magnetic compressibility was also found to
increase above the KH threshold. These findings are consistent with velocity
shears being local sources of sunward fluctuations that act to reduce net
imbalances in the antisunward direction, and suggest that the KH instability
plays a role in this process.
