One of the goals of the MAP (Mesoscale Alpine Programme) experiment, conducted in Autumn 1999, was to develop a better understanding of the dynamics of mountain gap flows. In order to create an as-complete-as-possible picture of gap-flow events, a wide range of different measurements (ground-based Doppler Lidar, surface stations, radiosondes, sodar, in situ aircraft measurements including dropsondes and airborne Lidar) were gathered in the Wipp valley in the Austrian Alps. This paper provides a detailed intercomparison of two of the primary instrument platforms used in the gap-wind component of the MAP experiment: the NOAA/ETL scanning Doppler Lidar and in-situ observations collected by the NOAA P3.

A point-by-point comparison between Lidar and aircraft-measured radial winds was performed by identifying those P3 wind observations that were collected within +/- 10 minutes of a Doppler Lidar scan of the same volume within the Wipp Valley. The radial velocities obtained from the eight individual pulses of back-scattered Lidar signal that mostly tightly bounded the volume in which the P3 observations were collected were then tri-linearly interpolated to the point of the P3 wind observation.

The differences between the P3 and Lidar wind measurements were stratified by Lidar backscatter intensity, a synergistic Lidar quality control parameter (SW), the variance among the eight individual Lidar wind returns at the corners of the data volume, and the time offset between the Lidar and P3 observations. The agreement between the P3 and Lidar observations varied significantly among the different gap-flow events. Nevertheless a modest filtering of the Lidar data on the basis of the SW quality control parameter reduced the average rms difference between the Lidar and P3 observations throughout the entire dataset to less than 2 m/s.