The quality control of velocity azimuth display (VAD) winds at the National Centers for Environmental Prediction

This paper describes the operational quality control at the National Centers for Environmental Prediction of the velocity azimuth display (VAD) winds from the WSR 88-D radars. Early use of these data in mid-1995 without quality control showed several problems, and the method described here was developed to characterize those problems and delete from usage data containing the errors.

The errors are characterized as large random errors, large rough (non-random) errors, and errors of large bias. Sources of these errors include large instrument errors, procedural problems, ground clutter, and bird migration. The error diagnosis uses the principals of complex quality control, in which as many independent checks of the data are calculated, in numerical form, before any decisions are made on a datum. This paper describes the checks used and outlines the Decision Making Algorithm in which the data quality is decided.

Results of the error diagnosis are shown. The signal due to the bird migration is especially interesting and observations containing this influence can at some times represent a large percent of all observations. Other types of errors are likewise characterized.