European incoherent scatter VHF radar measurements of vertical velocities were made under polar mesopause summer echo (PMSE) conditions enabling spatial and temporal resolution of 300 m and 2 s and accuracies of 0.1 ms-1 or better. Our observations revealed vertical motions with periods ranging from hours to tens of seconds and vertical wave structure exhibiting both ducted and vertically propagating behavior. Significant correlations were found between the low-pass vertical velocity and velocity uncertainties, velocity variances at high frequencies, radar backscatter power, and radar spectral widths. Specifically, upward motions at lower frequencies correlated with larger uncertainties, high-frequency variances, and radar spectral widths, while downward motions correlated best with larger backscatter power. We show these correlations to lead to biases in the determination of mean vertical motions when data are thresholded by any of the above quantities. We also suggest that these correlations arise from a tendency for turbulence to be associated primarily with the upward phase of wave motions at lower frequencies. A companion paper by Fritts and Hoppe presents a spectral analysis of this same data set. ¿ American Geophysical Union 1995