Quality Assessment of Weather Radar Wind Profiles during Bird Migration

Wind profiles from an operational C-band Doppler radar have been combined with data from a bird tracking radar in order to assess the wind profile quality during bird migration. The weather radar wind profiles (WRWP) are retrieved using the well-known Volume Velocity Processing (VVP) technique. The X-band bird radar performed range-height scans perpendicular to the main migration direction and bird densities were deduced by counting and normalizing the observed echoes. It is found that the radial velocity standard deviation (sigma_r) obtained from the VVP retrieval is a skillful indicator of bird migration. Using a threshold of 2 m/s on sigma_r, more than 93% of the bird-contaminated wind vectors are rejected while over 70% of the true wind vectors are accepted correctly. The raw weather radar wind vectors have a positive speed bias of maximum 8.6+/-3.8 m/s against the HIRLAM numerical weather prediction model, while the quality-controlled wind vectors have a negligible speed bias. From the statistics against the HIRLAM background, it is concluded that all (significant) bird contamination is removed and that high-quality weather radar wind profiles can be obtained, even during the bird migration season.